Mohammad Rashad Fath El-Bab
Fundamentals of the
HISTOLOGY OF BIRDS PART I
HISTOLOGY OF POULTRY An Introductory Text for Veterinary Students
-1-
SECOND EDITION
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Mohammad Rashad Fath El-Bab
Fundamentals of the
HISTOLOGY OF BIRDS PART I
HISTOLOGY OF POULTRY
An Introductory Text for Veterinary Students
SECOND EDITION -3-
-4-
Mohammad Rashad Fath El-Bab Professor of Histology Department of Anatomy and Histology Faculty of Veterinary Medicine Assiut University ASSIUT – EGYPT Alexander von Humboldt Fellow 1980 – 1982 Home Page: http://www.geocities.com/mohamed_fath_el_bab2000 E/mail:
[email protected] [email protected]
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CONTENTS CHAPTER
PAGE
1
Blood
1
2
The lymphatic system
8
3
The ultimobranchial body
24
4
The respiratory system
29
5
The digestive system
48
6
The urinary system
77
7
The male reproductive system
84
8
The female reproductive system
92
9
The skin
109
10
The sense organs
117
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PREFACE This book is written primarily for veterinary medical students. The micromorphological structure of the tissues and organs of domestic fowl is described. The illustrations are of the kind that seen to be the most helpful to students when actually examining specimens, namely, photomicrographs to show the general structure under the low magnification and diagrammatic drawings which are found more useful for the veterinary students and others in the farm sciences. My thanks are due to my colleague, Prof. Dr. M.N.K. Mustafa who has generously allowed me to use original illustrations. Finally I am indebted to all my colleagues at the Department of Anatomy and Histology, Faculty of Veterinary Medicine, Assiut University for help and encouragement that I have received form them.
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Birds have elliptical nucleated erythrocytes, which are large (12.2 ± 7.3 micron) and biconvex. The mean number of erythrocytes is 3 - 4.5 millions per cubic mm of blood. When supravitally stained with brilliant cresyl blue, some erythrocytes show granules or a network of fibrils. Such cells are called reticulocytes. They occur most often and are considered to be immature erythrocytes and have considerable significance in anemia. 1- Leukocytes: The total leukocyte count is higher in the young than in the old birds. The mean number of leukocytes is 20 - 30 thousands per cubic mm of blood. A-Granulocytes: a- Neutrophils: In chicken, the cells that correspond to neutrophils are called heterophils. They are not the commonest leukocytes in the blood, reaching 20 - 50 %. The heterophils present cytoplasmic granules that stain red but are not the same as those of the eosinophil granulocytes. In the chicken the heterophil granules are large, elongated, and bright red,
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whereas the eosinophil granules are round and brick red. They contain an irregularly lobulated polymorphic nucleus. b- Eosinophils: They reach a 2 - 8 % of the total leukocyte count of the blood. The cytoplasm contains small, rounded and brick red granules. The nucleus is coarser than that of a heterophil and has only 2 - 3 lobes when mature. c- Basophils: Contrary to those of mammals, the basophils in chicken are not rare. They make up about 1 - 5 % of the total leukocytic count. They have a coarse polymorphic nucleus and rather sparse, coarse, basophilic granules in the cytoplasm. B- Agranulocytes: a- Lymphocytes: They are the commonest leukocytes in the blood, reaching 60 - 65 % of the total leukocyte count. They are characterized by a relatively large nucleus, which is rich in chromatin. The nucleus is surrounded by a thin layer of basophilic cytoplasm.
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b- Monocytes: They reach a 1 - 4 % of the total leukocyte count. They have abundant, weakly basophilic, gray-blue cytoplasm, which often shows pseudopodia. The large nucleus is usually indented on one side. C- Blood platelets: (Thrmobocytes) The birds have true, nucleated thrombocytes, which resemble the erythrocytes but are shorter and have a large rounded nucleus, a slightly basophilic cytoplasm with 1 - 2 dark granules, and occasionally vacuoles. They number about 30 - 75 thousands per cubic mm.
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ERYTHROCYTES a- Avian erythrocyte ( surface view ). b- Avian erythrocyte (profile ). c- Mammalian erythrocyte ( surface view ). d- Mammalian erythrocyte (profile ).
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1- Erythrocyte. 2- Small lymphocyte. 3- Large lymphocyte. 4- Monocyte. 5- Thrombocyte. 6- Heterophil. 7- Eosinophil. 8- Basophil.
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AVIAN BLOOD CELLS 1. Erythrocyte.
5. Monocyte.
2. Heterophil.
6. Lymphocyte.
3. Thrombocyte.
7. Basophil.
4. Eosinophil.
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CHAPTER 2
THE LYMPHATIC SYSTEM The lymphatic system in birds consists of: I- Lymphatic vessels. II- Lymphoid tissue.
I- LYMPHATIC VESSELS Lymphatic vessels collect lymph from most parts of the body, as fine networks of lymphatic capillaries draining into large collecting trunks, which eventually open into the venous system. Within the trunk the lymphatic vessels usually accompany the arteries whereas outside the trunk they follow the veins.
Structure: The wall of the lymphatic vessel consists of: a- Endothelium. b- Sheath of collagenous fibers, elastic fibers and smooth muscle fibers. The lymphatic vessels of birds possess valves.
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Lymphatic Hearts: The lymphatic hearts are muscular dilatations of the lymphatic vessels. Structure: The wall of the lymphatic heart consists of three layers: a- Endothelium. b- Muscular layer. c- Fibrous layer. Function of lymphatic vessels: 1- They return the leaked fluid from the blood capillaries back to the blood stream, thus maintaining osmotic and colloid balance. 2- They are essential for migration of lymphocytes. 3- They transport large molecular complex e.g. Hormones enzymes. 4- Lymph is responsible for tumescence of phallus, besides it comprises the main part of the seminal fluid.
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LYMPHOCYTES They are primary cells involved in all immunological reactions. Types: A- Thymus - dependent lymphocytes (T lymphocytes). B- Bursa - dependent lymphocytes (B lymphocytes). - They are morphologically similar but have different functions and properties. - T and B lymphocytes are distinguished mainly by their surface properties. (The surface of B lymphocytes has a high concentration of immunoglobulin). - T and B lymphocytes may also be distinguished by their density and electrophoretic mobility. Function of lymphocytes: 1 - T lymphocytes: a - Play the main role in cell-mediated immune responses. b - They have cytotoxic activities. c- They co-operate with B lymphocytes in antibody production.
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2 - B lymphocytes: They transform into plasma cells, which synthesize and secrete antibodies. Lymphocyte migration and recirculation: * Lymphocytes migrate via the blood and lymphatic circulation along TWO pathways: a- Movement to and from the primary lymphoid tissue (thymus & bursa). b- Movement within secondary lymphoid tissue. B lymphocytes become localized in: * Germinal centers. * Peripheral zone of lymph node. * Periellipsoidal areas of the spleen. T lymphocytes become localized in: * Bone marrow. * Central zone of lymph nodes. * Periarteriolar sheath of the spleen.
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II- LYMPHOID TISSUE Divided into: I- Primary lymphoid tissue: Into the primary lymphoid tissue, the incoming stem cells differentiate and proliferate into T and B lymphocytes which are then transferred to the secondary lymphoid tissue. It consists of: a- Thymus. b- Cloacal bursa. c- Bone marrow. II- Secondary lymphoid tissue: The
secondary
lymphoid
tissue
completes
the
differentiation (and prolipheration) of T and B lymphocytes, derived from the primary lymphoid tissue into the respective effector cells. It consists of: a- Spleen. b- Bone marrow. c- Mural lymphoid nodules. d- Lymph nodes. e- Solitary and aggregated lymphoid nodules.
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I- Primary Lymphoid Tissue: 1) Thymus: 0.5 % of the body weight at 4 - 17 week. Regresses at sexual maturity. Thymus may restore its activity following annual breeding cycle, during molting, and anemia. Structure: (A) Framework: a- Capsule. b- Septa. (B) Parenchyma: = Thymus lobules. a - Cortex: 1- T lymphocytes: densely packed. 2- Epithelial reticular cells: (few) Cortex decreases with age (Absent at 8th month). b- Medulla: 1- Epithelial reticular cells: (numerous). 2- Macrophages + Plasma cells + Mast cells + RBC + Granulocytes + Myoid cells. 3- Hassal's corpuscles.
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Origin of thymus: Epithelial cells derived from the third and fourth pharyngeal pouches. Origin of T lymphocytes: From stem cells produced in the yolk sac. These cells migrate into the thymus (via blood stream) at about 7 days of incubation. Function of the thymus: 1- The thymus is a maturation center in which stem cells are differentiated into T lymphocytes. (Through the effect of thymosin hormone). 2- The thymus plays a role in the maturation of B Lymphocytes. 3- Some cells of the thymus produce antibodies. Thymus may function as secondary lymphoid tissue. 4- Thymus acts as erythropoietic tissue. 2) Cloacal bursa: - Transient organ. - Reaches the greatest size at the 6th week. - Involutes at sexual maturity. Structure: The wall is composed of three layers:
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A)- Mucosa: (Folded) Each fold contains numerous lymphatic follicles: (800012000). Each lymphatic follicle consists of: a - Cortex: (Dark) Contains numerous B lymphocytes and blood capillaries. b- Medulla: (Light) Contains numerous epithelial reticular cells and few B lymphocytes. N.B. A basement membrane separates the cortex from the medulla. B)- Muscularis: Smooth muscle coat. C)- Serosa. Origin of cloacal bursa: Endoderm or ectoderm or both endo - and ectoderm. At the 5th day of incubation. Origin of B lymphocytes: From stem cells produced in the yolk sac. These cells migrate to the cloacal bursa via blood stream. Function of the cloacal bursa: - Differentiation of the stem cells into B lymphocytes. - Maturation of B lymphocytes into plasma cells. - 22 -
* During and after involution of the cloacal bursa, differentiation of B lymphocytes may occur in the bone marrow. II- Secondary Lymphoid Tissue: 1) Spleen: Structure: 1- Framework: a- Capsule b- Septa: not clear. 2- Parenchyma: A- White pulp: Collection of lymphocytes surrounding a central artery. The latter gives penicillar arterioles - sheathed capillaries (ellipsoids) - terminal arterioles. The periellipsoidal lymphocytes = B lymphocytes. The periarteriolar lymphocytes = T lymphocytes. The germinal centers = B lymphocytes. B- Red pulp: a-Cords of lymphoid tissue: - Reticular cells.
– Macrophages.
- Granulocytes.
- Plasma cells.
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b- Sinusoids. Function of the spleen: 1- The spleen is an important site of antibody production. 2- It disposes the dead RBCs. 2) Bone Marrow: Function: 1-Acts as a source of undifferentiated B lymphocytes 2- It's cells are capable to produce antibodies. The bone marrow functions as secondary lymphoid tissue. 3) Mural lymphoid nodules: They are found either within or very closely applied to the lymphatic vessels. Structure: Either small diffuse infiltrations of small lymphocytes. Or large aggregations of lymphoid tissue containing up to four germinal centers. - No capsule. - They contain: B lymphocytes 53 % T lymphocytes 38 % 4)- Lymph nodes: Structure: It is surrounded by a capsule.
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It consists of: 1- Central sinus: (Subcapsular sinus) At the center of the node. Continues with the afferent vessels. Open into the peripheral zone. Towards the distal end of the node, it subdivides into many smaller sinuses, which drain into the efferent vessel. 2- Central zone: (Cortex) Dense lymphoid tissue. Surrounds the central sinus. Contains T lymphocytes. 2- Peripheral zone: (Medulla) Loose lymphoid tissue. Contains B lymphocytes. 4- Germinal centers: Found mainly into the central zone. Contains B lymphocytes. 5) Solitary and aggregated lymphoid nodules: a- Lymphoid tissue in the digestive tract: 1- Aggregated lymphoid nodules of the oral cavity and pharynx. 2- Aggregated lymphoid nodules of the oesophagus.
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3- Aggregated lymphoid nodules of the small intestine (ileum). 4- Aggregated lymphoid nodules of the caeca. The aforementioned lymphoid tissue consists of both T and B lymphocytes. b- Lymphoid tissue in the oculonasal region: - Includes both solitary and aggregated lymphoid nodules. - Occurs into: Glands of nictitating membrane. Lachrymal gland. Salt gland (nasal gland). The majority of the aforementioned lymphoid tissue consists of B lymphocytes. c- Lymphoid tissue in other organs and tissues: In: Liver - gall bladder - pancreas - kidneys - lungs - endocrines gonads - nerves - skin. The structure of this lymphoid tissue simulates that of lymphoid tissue elsewhere.
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The avian bursa of Fabricius. Lymphatic nodules are aggregated in such a way as to impart the architectural characteristics of the thymus gland.
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Germinal center
MURAL LYMPHOID NODULE LV: Lymph vessel.
- 28 -
رسمة بالعرض
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Diagram to show the white pulp and its blood supply in the spleen of Gallus.
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CHAPTER 3
THE ULTIMOBRANCHIAL BODIES (The ultimobranchial glands) Anatomy: - Two diffuse structures. - Lie on either side of the anterior thorax, posterior to the parathyroid IV. - Lenticular or ovoid in shape. - 2 - 3 mm in length. Histology: The ultimobranchial body consists of: 1- Framework. 2- Epithelial component. 3- Lymphoid component. 4- Eosinophilic component. 5- Blood vessels. 6- Nerves. 1- Framework: a- Capsule: Not clear. b- Stroma: Fine elastic fibers.
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2- Epithelial component: A) C - cells: - Calcitonin - producing cells. - Numerous (major proportion). - Arranged into strands or cords or singly distributed. - Rounded, oval, or polygonal in shape. - Granular cytoplasm. - Large, vesicular, eccentric nucleus. - There are numerous blood vessels beside these cells. B) Parathyroid nodules: - 3 nodules. - Parathyroid cells. - Each nodule is surrounded by a capsule. C) Vesicular structures: - Various amounts. - Very diverse in shape: Few large vesicles. Numerous small vesicles. - Lined by: a- Low columnar epithelium (simple or stratified). b- Cuboidal epithelium.
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The cells of these both types present numerous cytoplasmic granules (mucus - secreting cells). The apex of the cells is furnished with short, irregular microvilli. c- Squamous epithelium: The cells of this type present poorly granular cytoplasm. - The nucleus is rounded or oval in shape presenting fine chromatin and 1 - 2 nucleoli. - The lumen contains: a- Colloidal material = homogenous. b- Cellular material = desquamation. c- Granular material = basophilic granules. The large vesicles (cystic vesicles) are lined by stratified squamous epithelium with ovoid nuclei. The cells show no secretory activity. 3- Lymphoid component: - Areas of lymphoid cells (small lymphocytes). - They are found at any point within the gland. 4- Eosinophilic component: - Eosinophil leukocytes. - Decrease by age.
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5- Blood vessels: Arterioles - capillaries – venules 6- Nerves: Vagus. Recurrent. Sympathetic nerve (adrenergic nerve).
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ULTIMOBRANCHIAL BODY Cp: Capsule
V: Large vesicles
P: Parathyroid
L: Lymphoid foci
C: C-cells
- 35 -
v: Small vesicles
CHAPTER 4
THE RESPIRATORY SYSTEM THE NASAL CAVITY The nasal cavity consists of: A) The nasal vestibule: The nostrils are covered by skin, which changes to keratinized stratified squamous epithelium lining the vestibule. B) The respiratory region: a- Lamina epithelialis: Pseudostratified
ciliated
columnar
epithelium
with
numerous goblet cells, arranged into crypts (intraepithelial glands). b- Lamina propria: - Collagenous and elastic fibers. - Numerous lymphocytes. - Blood vessels and lymphatics. The nasal cavity opens into the oral cavity by way of the choana, a median slit in the roof of the mouth. The epithelium of the respiratory region changes abruptly on the nasal side of the choanal margin into the stratified squamous epithelium of the oral cavity.
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C) The olfactory region: a) Lamina epithelialis: 1- Supporting cells. 2- Olfactory cells. 3- Basal cells. b) Lamina propria: - Collagenous and elastic fibers. - Mucous glands (Bowman's glands). - Blood vessels and nerves. The Nasal Glands: In most birds the nasal gland consists of a lateral and a medial lobe, each with its own duct and ostium in the vestibular region of the nasal cavity. The gland is surrounded by a thick c.t. capsule. In chicken, a median lobe is only present. The gland produces a non-serous, non-mucoidal secretion. In marine birds the gland secrets a hypertonic 5% solution of sodium chloride (so it is called salt glands), thus enabling these birds to drink sea water. The gland has an osmioregulatory function in some desert species.
- 37 -
The gland is crescentic-shaped. lies on the lateral nasal cavity under the dorsal rim of the orbit. Structure: The gland is surrounded by a thick capsule. The capsule gives rise to septa that divide the gland into separate lobules- (not clear in fowl). The parenchyma is consisted of: 1- The duct: Arises from the lateral end of the gland and ends on the nasal septum at the vestibular region. It is lined by simple columnar epithelium. 2- The primary tubules (2 - 3): They are lined by pseudostratified columnar epithelium. 3- The secondary tubules: They are lined by short pseudostratified columnar epithelium. 3- The tertiary tubules: They are lined by simple cuboidal epithelium. All of the aforementioned cell types are very rich with mitochondria.
- 38 -
THE LARYNX The wall of the larynx consists of: 1- Mucosa: a- Lamina epithelialis: Pseudostratified ciliated columnar epithelium with goblet cells (intraepithelial glands). b- Lamina propria: C.t layer rich in elastic fibers. 2- Laryngeal cartilage: The laryngeal skeleton consists of four cartilages which become partly ossified, namely cricoid, procricoid and two arytenoid cartilages. No thyroid cartilage. No epiglottic cartilage. 3- Laryngeal muscle: Skeletal muscle fibers. 4- Adventitia.
THE TRACHEA The wall of the trachea consists of:
A)
Mucosa:
a- Lamina epithelialis: - 39 -
Pseudostratified
ciliated
columnar
epithelium
with
numerous goblet cells. The latter are oriented into crypts (intraepithelial glands). b- Lamina propria: Dense irregular c.t. presenting abundant lymphocytes.
B) Submucosa: Loose c.t. containing numerous elastic fibers. Mucosal and submucosal glands are of variable occurrence. C) Tracheal cartilage: - Complete cartilagenous rings. - Hyaline cartilage (tend to ossify in aquatic birds e.g. Goose and duck). D) Adventitia: Loose c.t. There are two longitudinally - arranged striated muscles associated with the trachea, namely the sternotracheo-laryngeus medialis and the sternotracheo-laryngeus lateralis.
THE SYRINX The syrinx is located at the junction of the trachea and bronchi. The syrinx is the organ of voice production, it is formed of:
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A) Cartilagenous skeleton: (variably ossified) a- Tympanic cartilages (four). b- Pessulus. c- Caudal syringeal cartilages (4 + 3 = 7). B) Medial tympanic membranes. C) Lateral tympanic membranes: 1- Mucosa: (1) Lamina epithelialis: Simple cuboidal epithelium with goblet cells. (2) Lamina propria: C.t. layer rich in elastic fibers. 2- Muscle layer: Few smooth muscle fibers. 3- Serosa: Simple squamous epithelium.
- 41 -
THE LUNGS The lungs of birds are very different from the lungs of mammals. Compared to the size of the thoracic cavity, the lungs are extremely small. Moreover they do not change volume during inhalation and exhalation. The structures that do change volume are the air sacs, which are continuous with the duct system of the lung. The duct system bears no similarity to that in mammals. The primary bronchi enter the lung and expand as the vestibulum. The latter continues through the lung as the mesobronchus and is connected to the abdominal air sac. The secondary bronchi are described as dorsal bronchi, ventral bronchi or lateral bronchi on the bases of their gross orientation. Secondary
bronchi
give
rise
to
tertiary
bronchi
(parabronchi). The parabronchi are analogous to the alveolar duct of mammals. Atria project radially from the parabronchi. These atria are continuous with the air capillaries. The air capillaries are responsible for the actual exchange of gases with the closely associated vascular capillaries.
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The air sacs associated with the avian lung aid in the movement of air through the lung. They are membranous structures, which do not contribute to the exchange of gases. Most birds have nine air sacs: single (unpaired) cervical, paired claviculars, paired cranial thoracics, paired caudal thoracics, paired abdominals. The air sacs occur free in the body cavities and send diverticula into the bones with which they are associated. Recurrent bronchi extend from the air sacs and attach to the parabronchi. Recurrent bronchi are involved in the return of the air from the air sacs to the lung proper. Structure:
1- The primary bronchi: (2) They are extensions of the bifurcated trachea and are similar in structure to their extrapulmonary portion. A) Mucosa: a- Lamina epithelialis: Pseudostratified ciliated columnar epithelium with goblet cells and intraepithelial mucous glands. b- Lamina propria : Loose c.t. presenting numerous lymphocytes.
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B) Muscular layer: Circularly or spirally oriented smooth muscle fibers. C) Cartilagenous layer: Cartilagenous rings (Hyaline) are present in the initial portions of the primary bronchi. They are replaced by plaques of cartilage within the intra pulmonary portion of the primary bronchi. The cartilagenous plaques are lost within the vestibulum. D) Adventitia. 2- The vestibulum: (2) The
vestibulum
is
an
enlarged
portion
of
the
intrapulmonary primary bronchus, which continued caudally by the mesobronchus. The structure of the vestibulum is similar to the intrapulmonary portion of the primary bronchus, but it lacks cartilage. 3- Secondary bronchi: (3) A)
Mucosa:
a- Lamina epithelialis: Simple columnar (ciliated) or simple cuboidal cells. No goblet cells.
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b- Lamina propria: Is thin and contains many elastic fibers and is usually devoid of lymphatic tissue. B) Muscular layer: Consists of interrupted and multidirectionally oriented smooth muscle fibers. The secondary bronchi contain no cartilage. C) Adventitia: Peribronchial c.t.
4- Tertiary bronchi: (Parabronchi) The tertiary bronchus and its surrounding tissues is considered as the respiratory portion of the lung. It is formed of:
A) Mucosa: a- Simple cuboidal or squamous epithelium. b- Lamina propria Thin layer of fine c.t. B) Muscular layer: It consists of 3 - 5 layers of smooth muscle fibers.
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5- Atria (air vesicles): The atria are lined by simple squamous epithelium supported by fine interstitial c.t. 6- Air capillaries: The wall of the air capillaries is composed of single layer of squamous epithelium. Blood - air barrier: Consists of: 1- The squamous epithelial cells lining the air capillary. 2- The basal lamina. 3- The c.t. layer. 4- The basal lamina. 5- The endothelial cells lining the blood capillary.
AIR SACS The air sacs are lined by simple cuboidal or simple squamous epithelium.
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NASAL CAVITY 1-Nostrils.
7-Oral cavity.
2-Nasal vestibule.
8-Tongue.
3-Respiratory region.
9-Pharynx.
4-Olfactory region.
10-Oesophagus.
5-Nasal conchae.
11-Trachea.
6-Beak.
12- Brain.
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THE RESPIRATORY REGION A- Lamina epithelialis: 1-Pseudostratified ciliated columnar epithelium. 2-Intraepithelial glands ( mucus-secreting cells ). B- Lamina propria : C: Cartilage.
- 48 -
THE TRACHEA 1- Epithelium. 2- Mucous glands 3- Bone. 4- Cartilage. 5-SkeIetal muscle
- 49 -
CROSS SECTION THROUGH THE TRACHEA OF THE CHICKEN a, ciliated columnar epithelium. b, mucous glands. c, propria containing lymphocytes. d, cartilage.
- 50 -
A HORIZONTAL SECTION THROUGH THE SYRINX OF THE DOMESTIC FOWL. T : Trachea. 1- Tympanic cartilage forming tympanum. 2- First caudal cartilages. 3- Last caudal cartilages. 4- Pessulus. 5- Lateral tympaniform membrane. 6- Medial tympaniform membrane. - 51 -
THE LUNG OF THE FOWL
- 52 -
LUNG LOBULE
- 53 -
AIR-BLOOD BARRIER - 54 -
CHAPTER 5
THE DIGESTIVE SYSTEM THE ORAL CAVITY The oral cavity is surrounded by the beak which consists of: 1- Epidermis: Consists of: a- Stratum basale. b- Stratum spinosum. c- Stratum corneum (thick). Both stratum granulosum and stratum lucidum are not clear. 2- Dermis: C.t. layer. 3- Bone (upper and lower jaw bones).
The oral cavity is lined by: A) Mucosa: a- Lamina epithelialis: Cornified stratified squamous epithelium. (Cutaneous mucous membrane). b- Lamina propria: Dense c.t.
- 55 -
B) Submucosa: Loose c.t. containing mucous salivary glands, and lymphoreticular tissue. The tongue: The tongue is narrow, elongated and pointed. It consists of: [A] Mucosa: a- Lamina epithelialis: Cornified stratified squamous epithelium, which continued over the apex of the tongue and its lower surface. Macroscopic, caudally directed, cornified papillae occur in a transverse row on the root of the tongue and in several rows across the roof of the mouth. The last of these, the palatine row marks the border between the mouth and the pharynx. The tongue is devoid of taste buds. A taste bud (large) can be seen closely associated with the duct of a salivary glands. They are seen mainly in the mucosa of the pharynx and on the base of the tongue, and extend as far as the entrance to the oesophagus.
- 56 -
b- Lamina propria: Dense c.t. [B] Submucosa: The submucosa is formed posteriorly and consists of loose c.t. containing, a- Numerous mucous salivary glands. b- Skeletal muscle. c- Bone. The skeleton of the tongue consists of: a- Anteriorly: cartilage. b- Posteriorly: bone (entoglossal bone).
THE PHARYNX The lining of the pharynx is similar to that of the oral cavity.
- 57 -
THE OESOPHAGUS The wall of the oesophagus consists of: A) Mucosa: (Longitudinally folded) a- Lamina epithelialis: Cornified thick stratified squamous epithelium.
b- Lamina propria: Loose c. t. layer containing diffuse lymphocytic infiltration and lymph nodules (forming the oesophageal tonsils near the stomach). Numerous, large, sac - lick mucous glands demonstrate themselves within the lamina propria. c- Muscularis mucosa: Thick (as thick as the outer longitudinal muscle layer of the muscularis) layer of longitudinally oriented smooth muscle layer which follows the folds (undulating). B) Submucosa: Thin layer of loose c. t. C) Muscularis: a- Thick inner circular smooth muscle layer. b-Thin outer longitudinal smooth muscle layer.
- 58 -
D) Adventitia: Loose c. t. layer with blood vessels and nerves.
THE CROP The crop (ingluvies) is an oesophageal diverticulum. The structure of the crop resembles that of the oesophagus. Mucous glands are mostly absent in galliform and columbiform birds (they are regularly present in ducks and geese). In columbiform birds, the superficial cells of the lamina epithelialis undergo fatty change to a substance called crop milk, which serves as nourishment for the youngs (the nestlings).
THE STOMACH A) The proventriculus: The wall of the proventriculus (glandular stomach) consists of: 1- Mucosa: (extensively folded) Elevations into the tunica mucosa (papillae) contain the openings of the excretory ducts of the proventricular glands. a- Lamina epithelialis: Simple columnar epithelium (mucus - secreting cells).
- 59 -
b- Lamina propria: It is a c.t. layer containing numerous accumulations of diffuse and nodular lymphatic tissue. It
contains
the
proventricular
glands.
The
proventricular glands are compound tubular glands. The tubular adenomeres radiate 360° around a central collecting sinus. The latter leads to tertiary ducts, which join to form secondary ducts, which join to form primary duct which passes to the mucosal papilla and opens into the lumen. The glandular epithelium of the tubular adenomeres is
of
the
cuboidal
or
low
columnar
variety
(oxynticopeptic cells). The primary, secondary, tertiary ducts are lined by columnar epithelium. c- Muscularis mucosa: Longitudinally oriented smooth muscle fibers, oriented into two layers; internal and external to the proventricular glands. 2- Submucosa: Thin layer of c.t.
- 60 -
2- Muscularis: Smooth muscle fibers. a- Thick inner circular layer. b-Thin outer longitudinal layer. 4- Serosa. B) Ventriculus: (Gizzard) The wall of the ventriculus (muscular stomach) is composed of: 1- Mucosa: a- Lamina epithelialis: Single layer of low columnar cells with rounded basally located nuclei. The lining epithelium is covered by a compact mass arranged in vertical columns formed of the secretion of the gizzard glands (chief cells) and is composed of carbohydrates and proteins. These columns are held by matrix substance derived from the surface cells. This compact mass acts as a rough grinding surface. b- Lamina propria: Is a c.t. layer containing the gizzard glands. The gizzard glands are composed of: I- Basal cells: cuboidal. II- Chief cells: cuboidal or low columnar.
- 61 -
III- Surface cells: tall columnar. c- Muscularis mucosa: is absent. 2- Submucosa: Thin layer of c.t. rich in elastic fibers. 3- Muscularis: (very thick) Smooth muscle fibers oriented into three layers: I- Inner oblique layer. II- Middle circular layer (thick). III- Outer longitudinal layer. 4- Serosa.
THE INTESTINE A) The small intestine: The wall of the small intestine is composed of: 1- Mucosa: The mucosa is thrown into regularly arranged villi, which are very long into the duodenum and gradually become shorter and thicker distally. a- Lamina epithelialis: - Simple columnar epithelium with goblet cells. - Enterochromaffin cells.
- 62 -
b- Lamina propria: It is a c.t. layer containing reticular fibers, smooth muscle fibers, numerous lymphocytes, central lacteal and lymphatic vessels. The lamina propria contains the crypts of Lieberkühn: - Short, simple tubular gland. - Lined by: Simple
columnar epithelium.
Goblet cells.
Enterochromaffin
cells.
c- Muscularis mucosa: ill - developed layer of smooth muscle fibers. 2- Submucosa: Very thin layer of c.t. containing many elastic fibers and numerous lymphocytes. Duodenal glands are absent. 3- Muscularis: Smooth muscle layer. a- Thick inner circular layer. b-Thin outer longitudinal layer. 4- Serosa.
- 63 -
B) The large intestine: (caeca and colo-rectum) The structure of the large intestine resembles that of the small intestine expect: 1- The mucosa present relatively shorter villi, which decrease in height caudally. 2- The lamina propria is filled with lymphoid cells and lymph nodules (caecal tonsils). 3- The goblet cells increase in amount caudally.
THE CLOACA The cloaca is the common orifice for the digestive, excretory and reproductive organs. It is lined by simple columnar epithelium with goblet cells. The tunica mucosa is extensively folded and accounts for the compartmentalization of the cloaca into: 1- Coprodeum: (continuous with the large intestine) with low villi and very short crypts of Lieberkühn. 2- Urodeum: (receives the ureters and the genital tracts) with folds and furrows. 3- Proctodeum: (opens into the anus) lined with simple columnar epithelium. The lamina propria contains numerous lymphoid tissues.
- 64 -
The importance of the cloaca as a site of water reabsorption was overestimated at one time. The explanation for this lay in the fact that the amount of urine passed into the cloaca was erroneously estimated at between one and two liters per day for the fowl and goose respectively. In fact, only about 150 ml of secondary urine are voided into the cloaca. Some of the water from this already-small amount of urine is withdrawn in the cloaca. The rest of the urine is mixed with the faeces in such concentrated form that the uric acid crystallizes out.
THE ANUS 1- Mucosa: (highly folded) a- Lamina epithelialis: Cornified stratified squamous epithelium. b- Lamina propria : c.t. layer showing abundant lymphatic tissue. The muscularis mucosa is absent. 2- Muscularis: Skeletal muscle fibers forming the anal sphincter.
- 65 -
ASSOCIATED GLANDS A) The salivary glands: Definitive salivary glands are not present. Instead, the mucosal-submucosal c.t. of the oral cavity is well-endowed with simple branched tubular mucous glands. These glands are lined by tall columnar cells, with basophilic foamy cytoplasm and flat basal nuclei. They are distributed into the mucous membrane of the palate as: 1- The maxillary glands. 2- The lateral palatine glands. 3- The medial palatine glands. 4- The pterygoid and tuberal glands. 5- The anterior mandibular glands. 6- The posterior mandibular glands. 7- The angular glands. B) The pancreas: 1- Framework: a- Capsule: The pancreas is surrounded by a delicate c.t. capsule.
- 66 -
b- Interlobular c. t. : The interlobular c. t. is indistinct, so there is no pronounced lobulation. 2- Parenchyma: The pancreas is a compound tubuloacinar gland. a- Exocrine portion: (pancreatic acini) 1- Pancreatic acini: Lined by low columnar epithelium with large, rounded basal nucleus. 2- Ducts: 1) Centro-acinar cells (flat) can occasionally be seen. 2) Intralobular ducts are very short (flat epithelium). 3) Intermediate tubules are slender (flat epithelium). 4) Large ducts (cuboidal epithelium). 5) Main ducts (columnar epithelium). b- Endocrine portion: (Islets of Langerhans) - Numerous. - Two types: I- Alpha islets: (large) Containing columnar alpha cells and few D cells. II- Beta islets: (small) Containing polygonal beta cells
- 67 -
C) The liver: 1- Framework: a- Capsule: The liver is surrounded by a thin capsula fibrosa. b- Interlobular c. t.: The interlobular c. t. is scarce so the hepatic lobules are not clear. 2- Parenchyma: The parenchyma is composed of several hepatic plates orienting radially around the central vein. Each hepatic plate is composed of two rows of hepatic cells. The hepatic cells are hexagonal. Each contains a large, central,
rounded
nucleus.
The
cytoplasm
contains
mitochondria, Golgi apparatus, sER, rER, glycogen and lipid droplets. The hepatic plates are separated by hepatic sinusoids, which drain into the central vein. The hepatic lobules are separated by several portal areas.
- 68 -
رسمة بالعرض
- 69 -
THE TONGUE ( T. S. ) 1- Mucosa : a. Lamina epithelialis : Comified stratified squamous epithelium b. Lamina propria. 2-Submucosa : a. Mucous glands. b. Cartilage ( anteriorly )- Bone (posteriorly ) c. Muscle.
- 70 -
THE OESOPHAGUS 1- Mucosa: a. Lamina epithelialis. b. Lamina propria. c. Muscularis mucosa. 2- Submucosa. 3-Muscularis. a. Thick inner circular layer. b. Thin outer longitudinal layer. 4- Adventitia. - 71 -
THE OESOPHAGUS 1-Mucosa: a. Lamina epithelialis. b. Lamina propria. c. Muscularis mucosa. 2- Submucosa. 3-MuscuIaris. a. Thick inner circular layer. b. Thin outer longitudinal layer. 4- Adventitia. - 72 -
The mucosa of the esophagus of birds L: Lamina epithelialis M: Mucous glands.
- 73 -
THE PROVENTRICULUS 1 - Mucosa: a. Lamina epithelialis. b. Lamina propria. c. Muscularis mucosa. 2 - Submucosa. 3 -Muscularis : a. Thick inner circular layer. b. Thin outer longitudinal layer, 4 - Serosa.
- 74 -
PROVENTRICULUS 1- Surface epithelium. 2- Muscularis mucosa. 3- Proventricular gland 4- Muscularis. 5- Serosa .
Transverse Section of a Tubular Gland of the Stomach.
- 75 -
THE VENTRICULUS ( THE GIZZARD ) 1 - Mucosa : a. Lamina epithelialis. b. Lamina propria. 2 - Submucosa. 3 - Muscularis: a. Inner oblique layer. b. Middle circular layer. c. Outer longitudinal layer. 4 - Serosa. - 76 -
THE VENTRICULUS ( THE GIZZARD ) 1 - Mucosa : a. Lamina epithelialis. b. Lamina propria. 2 - Submucosa. 3 - Muscularis: . Inner oblique layer. . Middle circular layer. . Outer longitudinal layer. 4 - Serosa.
- 77 -
THE SMALL INTESTINE 1 - Mucosa: a. Lamina epithelialis. b. Lamina propria. c. Muscularis mucosa. 2- Submucosa. 3 - Muscularis : a. Thick inner circular layer. b. Thin outer longitudinal layer 4 - Serosa.
- 78 -
THE SMALL INTESTINE 1 - Mucosa: a. Lamina epithelialis. b. Lamina propria. c. Muscularis mucosa. 2 - Submucosa. 3 - Muscularis : a. Thick inner circular layer. b. Thin outer longitudinal layer 4 - Serosa.
- 79 -
THE INTESTINE
SMALL INTESTINE. x50 1. Villus. 2. Columnar epithelium. 3. Intestinal glands.
CAECAL APEX. X 110 1. Lymphoid tissue. 2. Goblet cells. 3. Intestinal glands.
RECTUM. x 30 1. Epithelium. 2. Glands. 3. Muscle.
- 80 -
The Pancreas
The liver 1. Capsule. 2. Portal tract. 3. Sinusoid. 4. Liver cells
- 81 -
SECTION FROM THE LIVER OF A CHICKEN. a, cells of the liver lobule. b, sinusoids. c, branch of the portal vein. d, artery. e, bile duct. f, lymphocytes.
- 82 -
DIAGRAMATIC REPRESENTATION OF A LONGITUDINAL SECTION OF THE CLOACA a colon; b coprodeum; c urodeum; d proctodeum; e anus; f m. sphincter ani; g bursa of Fabricius; h orifice of the ureter; i orifice of the ductus deferens or oviduct.
- 83 -
CHAPTER 6
THE URINARY SYSTEM THE KIDNEY The kidney consists of lobules. Each lobule is composed of an outer cortical and inner medullary tissue. The cortical substance extends into the depth of the kidney between and around the medullary substance (cones), therefore no clear delineation of cortical and medullary layers could be seen. The medullary substance is formed from a number of medullary cones, each of which drains into a single primary branch of the ureter. There is no renal pelvis. There is no area cribrosa. The kidney consists of individual lobules, which are richly supplied with blood carried in the glomerulus-bearing arteries and in afferent and efferent veins, connected by capillaries. On the basis of their different vascular architecture, three types of lobules are recognized, which together give the surface of the kidney an appearance reminiscent of cerebral gyri. The basic uriniferous structures of the kidney lobules are the nephrons which, compared with those of mammals, are very
- 84 -
numerous; the fowl, for instance, is said to have 200,000 nephrons. Each of these nephrons consists of a corpusculum renis and a tubule which latter can be differentiated into different segments by their course and epithelial structure. The renal corpuscles are smaller than in the mammal, measuring, in the fowl, between 35 and 90 m. The smaller variety is situated near the surface, the larger ones towards the base of the lobules. The renal corpuscle consists of a vascular tuft, the glomerulus, which is interposed in the arterial blood stream through a vas afferents and a vas efferent, and a double walled capsula glomeruli, which surrounds the glomerulus. The outer layer of the capsule is formed of flat, single-layered epithelium whereas the internal layer has peculiarly formed cells, the epicytes, which lie closely against the capillary loops of the glomerulus. Between the outer and inner layer of the glomerular capsule there is a space into which the primary urine, a protein-free ultra filtrate, is passed. From there the urine passes into the tubules of the nephron, which leave the capsule at the so-called urinary pole, and then passes into the proximal convoluted tubule (tubulus contortus of the first order). Next follows the hairpin-shaped loop of Henle with a descending thick and an ascending thin limb. The latter
- 85 -
continues into the distal convoluted tubule (tubulus contortus of the second order) and finally terminates in the straight tubule. The diameter of the latter is at first small but increases as it is joined by other tubules to form the tubuli collectivi, which carry the urine into the ureter. The tubules described above belong to the larger renal corpuscles and are therefore found in the basal part of the lobule. Another type of kidney tubule, which is devoid of loops of Henle, is confined to the cortical region of the lobule. In the birds kidney there are neither renal calyces nor a renal pelvis, instead a series of collecting ducts leave the kidney at its medial border to terminate directly in the ureter. The ureter begins at the cranial lobe of the kidney and runs caudally along its ventromedial border. In the male it crosses the ductus deferens. After transversing the a. ischiadica, it crosses the caudal border of the kidney and, running along the dorsal wall of the abdomen, it reaches the cloaca to terminate in the middle compartment, the urodeum. In the male and female the ureter opening is situated medial to that of the vas deferens and the slitlike opening of the oviduct respectively. The function of the nephron in the process of urine formation is filtration, reabsorption and secretion. Filtration occurs in the renal corpuscles. During this process the end
- 86 -
products of protein metabolism, which in birds are mainly uric acid and small amounts of other nitrogenous breakdown products as well as glucose and electrolytes, are filtered from the blood along with large amounts of water. It has been calculated that in 24 hours the fowl will filter some 6 liters of fluid. But since only 150 ml of urine will reach the cloaca in the same period, more than 90 % of the water must be reabsorbed during the passage through the tubular apparatus. Both absorptive and secretory functions of the tubular epithelium are involved and so-called threshold substances, such as glucose and electrolytes, which are normal constituents of the plasma, are returned to the blood. Part of the active function of the renal epithelium is the synthesis of uric acid, which is also produced in the liver in amounts that vary from species to species. Three types of NEPHRONS could be distinguished: A) Cortical nephrons: - Majority. - Found into the cortex only. - Have small glomerulus. - The proximal and distal convoluted tubules are connected by short, narrow cortical intermediate tubule.
- 87 -
B) Medullary nephrons: - Minority. - Found partly into the medulla. - Have large glomerulus. - The proximal and distal convoluted tubules are connected by long, medullary loop. C) Intermediate nephrons: - Rare. - Intermediate in structure between A and B. - The proximal and distal convoluted tubules are connected by short medullary loop. - In the distal convoluted tubules the cell apex forms a projecting bleb of relatively clear cytoplasm that occupies a large part of the lumen. The connecting and collecting tubules secrete mucin, so their cells contain mucopolysaccharides within its supranuclear portions.
- 88 -
THE URINARY PASSAGES THE URETER A) Mucosa: a- Lamina epithelialis: Pseudostratified columnar epithelium. b- Lamina propria-submucosa: Loose c. t. layer with diffuse lymphocytic tissue. B) Muscularis: Smooth muscle fibers a- Outer longitudinal layer. b- Middle circular layer. c- Longitudinal layer at the urodeum. C) Adventitia. THE URODEUM It is lined with simple columnar epithelium. The lamina propria is rich in lymph nodules.
- 89 -
THE KIDNEY
Section of the Cortical Substance of the Kidney. 1. Renal corpuscle. 2. Convoluted tubules.
Section of the Cortical Substance of the Kidney. gl. Glomerulus; c.t., convoluted tubules.
Transverse Section of Straight Tubules of the Kidney. c., capillary blood-vessel.
- 90 -
CHAPTER 7
THE MALE REPRODUCTIVE SYSTEM THE TESTIS The testis is yellowish to grayish-white during the resting stage and almost pure white during the stage of activity. It is enclosed in the fibrous tunica albuginea and external to this it is covered by peritoneum. Delicate tracts of connective tissue radiate from the tunica into the organ but true septa are not formed. Pigment cells are not infrequently found in fairly large numbers in the connective tissue capsule and the interstitium of the testes in both the cockerel and turkey stag. The very twisted seminiferous tubules (tubuli seminiferi contorti) are embedded in the vascular interstitial connective tissue, which also contains the hormone-forming Leydig cells. These seminiferous tubules, which measure 150 - 200 m in diameter, are enclosed by a thin tunica propria, which consists of collagen fibers. Internal to this is the basal membrane on which lies the germinal epithelium made up of two functionally different cell types. These are the supporting Sertoli cells and the germinal cells. The Sertoli cells have an oval nucleus, poor in chromatin. Their broad base lies against the basal membrane and the slim part of their cytoplasm - 91 -
projects into the lumen of the tubules, spreading out in finger-like processes. Between these Sertoli cells all the different developmental stages of the germ cells may be seen extending up to the lumen. The seminiferous tubules collect into the rete testis. Arising from this are the ductuli efferentes and, subsequently, the ductus epididymidis. Spermatogenesis: Immediately on the basal membrane of the seminiferous tubule are situated the spermatogonia which arose from the primordial germ cell and have a spherical, chromatin-rich nucleus. These divided equatorially giving rise to two unequal cells. One of these cells remains a spermatogonium while the other develops into a primary spermatocyte. This bivalent
multiplication
ensures
the
persistence
of
the
spermatogonia and therefore the continuing formation of further primary spermatocytes. The primary spermatocytes grow into large cells with loosely structured nuclei; there is pairing or conjugation of homologous chromosomes allowing the exchange of genes. In the first maturation division the primary spermatocytes divide by reduction division or meiosis, without preceding longitudinal cleavage of their chromosomes, into two daughter cells the secondary spermatocytes, which have haploid
- 92 -
chromosome
complement.
Two
haploid
spermatids,
the
precursors of the spermatozoa, result from the second maturation division, which is a normal mitotic division, of the secondary spermatocytes. Thus from one primary spermatocyte four haploid spermatids have developed. These are strikingly small cells, the apical ends of which are in close contract with the Sertoli cells, thus facilitating the exchange of nutrients. The spermatids now undergo the process known as spermiogenesis, which means the transformation of spermatids into spermatozoa. After completion of this transformation process, the spermatozoa consist of a head, neck, mid-piece and tail. In the chicken, the head of the spermatozoon is awl-like tapering to a fine point, and the middle piece is absent. Although from the point of view of volume the sperms are among the smallest cells of the body, they are of considerable length. For example, the sperms of the fowl measure 90 - 100 m, while those of the pigeon are 180 m in length. The longest part is the tail. The sperms, which at this first stage are still immobile, are carried by the stream of secretion from the seminiferous tubules to the rete testes, thence to the ductuli efferentes and finally through the ductus epididymidis into the ductus deferens, where they complete their maturation.
- 93 -
THE EPIDIDYMIS The ductus epididymidis is composed of an inner lining epithelium of the pseudostratified columnar variety and an outer connective tissue layer.
THE DUCTUS DEFERENS The ductus deferens arises, without any clear line of differentiation from the epididymis. It accompanies the ureter beneath which it crosses from medial to lateral at the level of the caudal lobe of the kidney, to terminate in a small papilla in the urodeum, the middle compartment of the cloaca. During the mating period the ductus deferens increases considerably both in length and thickness and becomes folded into numerous meandering convolutions. At that time it acts as a sperm reservoir and is recognizable by its white colour. The epithelium of the epididymal canals produces a secretion, but such function has not been demonstrated in the epithelium of the ductus deferens. The male bird has no accessory sex glands. The semen or ejaculate consists of the spermatozoa and the epididymal secretion. In the fowl the ejaculate has a volume of between 0.8 and 1.0, ml and the number of sperms lies between 50,000 and 6,000,000 per cmm. The concentration of the semen
- 94 -
decreases with the number of copulations. A cockerel can copulate, or tread, up to 50 times per day. Once the sperms have been introduced into the female genital tract, they remain fertile for 10 - 21 days in the fowl and 8 - 10 days in the duck and goose. The wall of the ductus deferens consists of: A) Mucosa: 1- Pseudostratified columnar epithelium with secretory activity. 2- Thin c.t. layer. B) Muscular layer: Smooth muscle fibers. C) Adventitia: Fibrous layer.
THE MALE COPULATORY ORGAN (PENIS) The copulatory organ, or penis, is rudimentary in the cockerel and absent in the pigeon. In both species the everted proctodeum accomplishes the transfer of semen into the cloaca of the female, which is also everted during mating. In contrast, the gander and dark both have a copulatory organ which, in the erect - 95 -
state, measures about 6 - 8 cm in the dark and 7 - 9 cm in the gander. The penis arises at the transition between urodeum and proctodeum on the ventral surface of the cloaca. It consists of a short, connective tissue body and a free tube, reaching to the tip of the penis. The organ is covered with mucous membrane and it forms a seminal groove in spiral coils. At the edges of the groove the mucous membrane is raised by the presence of erectile tissue. During copulation this groove is closed forming a tube which transfers the semen into the cloaca or the terminal part of the oviduct (vagina) of the female. The penis is protruded from and retracted into the male's cloaca by muscular action. Erection of the organ is achieved by the influx of lymph into the interior of the blind tube. This fluid is supplied by a pair of lymphproducing cavities situated at the base of the penis, which, in their turn, are in functional relation to the so-called vascular bodies from which the lymph permeates. In newly hatched male chicks a rudimentary copulatory organ is present on the ventral wall of the cloaca. It consists of a basal part and a tight, shiny upper part, which is pointed or convex. With appropriate dexterity, this small raised structure can be everted from the cloaca and the sex of the day-old chick thus determined with a high degree of reliability.
- 96 -
The ejaculatory duct is lined by pseudostratified columnar epithelium, and covered by low columnar epithelium containing mucin-secreting cells. The ejaculatory duct is associated with a ring of erectile vascular bodies; the white body, the round folds and the lymph folds. The white body and the round folds are called phallus and are bounded by stratified squamous epithelium. The paracloacal bodies are vascularized bodies covered by pseudostratified columnar epithelium, which contains goblet cells and some glands extending into the submucosa.
- 97 -
THE TESTIS
Section of the Testis. f.c., fibrous covering ; s.t., seminiferous tubule ; a., small artery.
Diagrammatic representation of the Cells of a Seminiferous Tubule. s.g., spermatogonia; sc., spermatocytes ; st., spermatids ; sz., spermatozoa ; i., interstitial cells.
Testis 1. Seminiferous tubules, showing spermatogenesis.
Seminiferous tubule 1. Spermatozoa. 2. Spermatogenesis.
- 98 -
CHAPTER 8
THE FEMALE REPRODUCTIVE SYSTEM THE OVARY The functional gonad of the hen is the left ovary. The ovary of birds is not as compact as those in mammals. Rather, the ovary consists of finger-like projections, which are suspended pendulously from the abdominal wall by the mesovarium. The ovary consists of: A) Cortex (zona parenchymatosa). B) Medulla (zona vasculosa). (A) and (B) are distinctly separated in young chicks. A) The cortex: a) Ovarian surface epithelium: - Cuboidal cells or flattened cells. - Tunica albuginea. b) Stroma: Network of numerous collagenous fibers and several types of cells: 1) Eosinophils. 2) Interstitial cells (medullary and cortical). 3) Vascular cells (fat - laden cells). - 99 -
4) Pigments (haemocidrin). c) Ova: 1- Primary oocytes: - 30 - 400 microns. - Central nucleus. - Granular cytoplasm. - Balbiani body (yolk spheres, mitochondria, Golgi complex). II - Maturing ova: The ova are found within follicles, which project from the surface of the ovary. The term follicle is misnomer because an antrum does not develop. The wall of the mature ovum consists of: 1 - Zona radiata : - It is a part of the oocytes. - Appears as processes from the oocyte. - Covered by the vitelline. 2- Perivitelline membrane: - Non cellular layer. - Formed by the follicular epithelium. - Formed of 2 layers:
- 100 -
a- Inner. b- Outer: develops after ovulation. 3- Follicular epithelium: (membrana granulosa): - Immediately adjacent to the ovum. - Simple cuboidal (in the small oocytes). - Pseudostratified columnar (in the large oocytes). - They are the yolk forming cells. 4- Basement membrane. 5- Theca interna: - Spindle cells (fibroblasts). - Fine collagenous fibers. - Islets of luteal cells (thecal gland cells). 6- Theca externa: - Collagenous fibers. - Fibroblasts. - Few elastic fibers. - Smooth muscle fibers. 7- Stigma: (Avascular spot). THE THECAL GLANDS: Islets of epithelial cells (spherical, oval, elongated). Scattered around the follicle within the theca interna (or externa in large follicles).
- 101 -
Consist of: a) Steroid-producing cells: - Irregular in shape - Oval or rounded nucleus. - With lipid droplets - sER - Golgi apparatus. b- Enclosing cells: Flat in shape - peripherally situated elongated nucleus cytoplasm contains fibrils. In birds the female has a chromosome complement of 2n + xy and the male 2n + xx, so that the female is heterozygote
and
the
male
homozygote.
The
chromosome formula for the mature egg is therefore either n +x (male ovum) or n + y (female ovum) while all the sperms have a chromosome complement of n+x. The sex of the individual is thus determined by the sperm in mammals and by the ovum in birds. The number of follicles initially present in the fully developed ovary far exceeds the number of eggs produced during the several years of laying activity. The fact that in old birds the ovary is completely devoid of follicles is due to a process described as follicular atresia. This is a degeneration of follicles of all sizes and in all functional stages of the ovary. The process is
- 102 -
initiated by multiplication of the blood vessels of the theca folliculi and atrophy of the follicular epithelium with simultaneous absorption of the content of the follicles. Nests of epithelioid cells remain in the ovary as the remnants of such atrophic follicles; they are enclosed by fibrous tissue. The larger follicles sometimes empty their contents into the surrounding connective tissue, where they are absorbed. Numerous investigations have been concerned with the question as to whether the follicular capsules, the calyces, proliferate after ovulation and form structures, which produce progesterone. If this occurs they would be comparable to the corpus luteum of mammals. Some authors believe this to be so, but more recent investigations have shown that there is no corpus luteum in birds. It has been demonstrated that degenerative processes take place in the follicular capsule after ovulation leading to complete dissolution within a few days. B) The medulla (zona vasculosa): - Numerous blood vessels, blood sinuses, and lymph vessels. - Nerve bundles.
- 103 -
- Smooth muscle bundles.
THE OVIDUCT Consisted of: 1 - The infundibulum: - Subdivided into: A] The funnel. B] The neck.
A] The funnel wall consists of: 1- Lining epithelium : Simple columnar ciliated epithelium - and shows longitudinally oriented ridges. 2- Smooth muscles bundles (scattered). 3- C. t. layer. 4- Peritoneum (serosa). B] The neck wall consists of the same layers however, a- There are four types of epithelial cells: 1 - Ciliated cells: - Non glandular. - Columnar cells. - Basal oval nucleus. - Tuft of cilia.
- 104 -
2- Goblet cells. 3- Cuboidal cells (Granular cells): - Secretory. - Found at the bases of the ridges. - Large basal nucleus. - With PAS + ve granules. 4- Tubular gland cells: - At the caudal portion of the infundibulum. - Low pyramidal. - Few or moderate eosinophilic granules. - Spherical nucleus. b- The longitudinal epithelial ridges increase in depth and bears small secondary folds. c- The muscle bundles are arranged into ill-defined longitudinal and circular layers. II- The magnum: (Long) A) Mucosa: (numerous high folds). a- Lamina epithelialis: Simple columnar ciliated epithelium with goblet cells. b- Lamina propria: Thick - contains numerous branched tubular glands. The glandular cells are pyramidal with basal nuclei.
- 105 -
B) Muscular layer: (Thick) Smooth muscle fibers: a) Inner circular layer. b) Outer longitudinal layer. C) Serosa. III - The isthmus: (Short) Similar to magnum but: - Surface epithelium is tall. - Tubular glands are not well developed. - Muscular layer is thick. IV- The uterus (the shell gland): A) Mucosa: Leaf shaped folds. a- Lamina epithelialis: Single layer of columnar cells with alternating apical and basal cells. b- Lamina propria: - Contains coiled tubular gland closely packed together. - The glandular cells appear vacuolated and present large basal nucleus.
- 106 -
B) Muscular layer: (well developed) a) Inner circular layer. b) Outer longitudinal layer. C) Serosa. V- The vagina: (Short) - Narrow duct. A) Mucosa: - Long, slender folds with numerous small secondary folds. - No tubular glands within the corium of these folds. - Lamina epithelialis is composed of tall: a- Ciliated cells. b- Non-ciliated glandular cells. B) Muscularis: The muscular layer consisted of: a- Thick inner circular layer. b- Thin outer longitudinal layer. C) Serosa.
- 107 -
THE AVIAN EGG The egg of birds consists of: 1) The fertilized or unfertilized egg cell or sphere of yolk, which is produced by the ovary and already has a thin covering yolk membrane. 2) The sphere of yolk is surrounded by three layers of egg white or albumen; these are of varying viscosity, the outer and inner layers being less viscous than the middle layer, which latter is of much greater volume. 1) The chalazae are spirally twisted, cord-like structures, which are suspended in the albumen and tightly attached to the yolk membrane. 2) The double-layered shell membrane between which lies the air chamber at the blunt pole of the egg. 3) The calcium shell and on the outside the cuticula which can be compared to a covering of varnish.
- 108 -
صورة بالعرض
- 109 -
- 110 -
- 111 -
OVIDUCT OF BIRDS 1- Infundibulum. 2- Magnum. 3- Isthmus. 4- Uterus. 5- Vagina. O: Ovary. R: Rectum. C: Cloaca.
- 112 -
The oviduct of the chicken (magnum) 1- Mucosa: a. Lamina epithelialis: simple columnar epithelium. b. Lamina propria : contains tubular glands. 2- Muscularis: a. Inner circular layer. b. Outer longitudinal layer. 3- Serosa.
- 113 -
THE OVIDUCT
INFUNDIBULUM. x 60
1. Epithelium. 2. Corium. 3. Muscle.
ISTHMUS x 80 1.Epithelium. 2.Lamina propria. 3.Glands. 4. Muscle.
UTERUS. x 35 1. Leaf-like folds. 2. Epithelium. 3. Glands. 4. Corium.
VAGINA. x 25 1. Longitudinal ridges with secondary folds. 2. Epithelium. 3. Corium.
- 114 -
THE EGG
- 115 -
CHAPTER 9
THE SKIN A) The epidermis: Thin - loose - dry. Three strata could be recognized. a) Stratum basale. b) Stratum spinosum. c) Stratum corneum B) The dermis: Composed of collagenous fibers. The papillary layer is not defined. No glands. Numerous lymphatic tissues. Feathers. Subcutis: A layer of dense c. t. Feathers: They are of epidermal origin. They develop within a follicle. Consists of two parts: 1) Quill (calamus).
- 116 -
2) Vane (vexillum): a) A Rachis: It is the continuation of the quill above the skin surface. b) Barbs: They project laterally from the rachis in an oblique and parallel manner. They possess proximal and distal barbules that are oriented at right angles to the barbs parallel to the rachis. Down feathers: Have small and thin raches. The barbs are devoid of barbules, thus these feathers are loose and fluffy; they serve as good insulation. Filoplums: Are feathers with a hair-like structure. They are scattered over the body but are especially predominant structures on the head and neck.
- 117 -
THE UROPYGIAL GLAND Or oil gland Or preen gland. Is the only cutaneous gland of poultry. It is a paired organ, which unites to form one pearshaped structure of the size of a hazelnut. It rests on the last coccygeal vertebrae just under the skin. The uropygial gland is a branched, alveolar holocrine gland, resembling the sebaceous glands. The secretion is utilized in oiling the feathers. It is highly developed in aquatic birds. I - Framework: A) Capsule: A tough collagenous capsule surrounds each half of the gland. B) Trabeculae: Divide the peripheral part of the gland sinus into niches. II - Parenchyma: Branched alveolar holocrine gland.
- 118 -
The alveoli are lined by many-layered glandular epithelium. They marginal calls are low, but the more central ones are polygonal. Fat globules appear within the cytoplasm. The nuclei undergo shrinkage, followed by disintegration of the cells, which form fatlike spheroid droplets. The excretory ducts end at the apex of a common papilla. The papilla contains smooth muscle fibers that extend around the excretory duct. They run circularly around the excretory ducts or follow a longitudinal course.
- 119 -
THE SKIN OF BIRDS 1. Epidermis (Thin). 2. Dermis.
- 120 -
Section through the uropygial gland of the chicken. I, a, secretory tissue; b, excretory duct; c, feather papilla in oblique section;
d, circular smooth muscle fibers;
longitudinal muscle fibers; f, adipose tissue (plurivacuolar); II, marginal portion of the secretory tissue.
- 121 -
e,
THE UROPYGIAL GLAND Notice the numerous sebaceous alveolar adenomeres.
- 122 -
C. S. into the uropygial gland Notice, the holocrine secretory activity of the alveolar adenomeres
- 123 -
CHAPTER 10
THE SENSE ORGANS THE EYE In shape the eyeball of the fowl may be said to consist of the segments of two spheres of different curvature, connected by a
conical
intermediate
portion.
The
posterior
segment
corresponds to the greater part of the sclera, the anterior segment is formed by the cornea, and the conical connection consists of that part of the sclera in which the bony scleral ring is developed. 1) The cornea: The cornea is of a horny consistence and is transparent, and thus offers no obstacle to the passage of light into the interior of the eyeball. It is composed anteriorly of a layer of stratified squamous epithelium, about four cells in depth. The deep cells are cuboidal, and have small dense spherical nuclei, with deeply eosinophilic cytoplasm. The anterior homogenous membrane-Bowman's membrane- is not easy to detect. The proper corneal membrane, constituting the bulk of the cornea, is composed of dense transparent connective tissue,
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between the fibers of which are a few irregularly scattered elongated nuclei and a homogeneous interfibrous substance. The posterior limiting membrane-Descemet's membraneis a delicate hyaline membrane at the back of the cornea, on which stand regularly spaced flattered cells, the corneal endothelium. 2) The sclero-corneal junction: At the sclero-corneal junction several interesting features are present. The scleral ossicls form an equatorial osseous ring. This bony substance merges with the cartilage of the sclera. 3) The canal of Schlemm: The canal of Schlemm is formed by the fusion of a number of endothelial-lined irregular spaces, which encircle the eye at the junction. The striated ciliary muscles also radiate from this region. 4) The sclera: The sclera is dense and white, and consists of an internal layer of hyaline cartilage with a superimposed layer of fibrous tissue. Within the sclera is a vascular and pigmented tunic divisible into choroid, ciliary body, and iris.
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5) The choroid: The choroid is a thin, dark-colored and richly vascular membrane lining the posterior part of the eyeball. No tapetum is present. 6) The ciliary body: The ciliary body is the thickened and radially folded anterior part of the choroid. Associated with it is the striated ciliary muscle, upon which depends the rapidly effected accommodation of the eye for near or distant objects. The third cerebral nerve causes contraction and the sympathetic nerve relaxation of the ciliary muscle. 7) The pecten: A remarkable structure, known as the pecten, projects from the interior of the eyeball from the region of the entrance of the optic nerve. It is a very vascular-pigmented membranous organ arising from the retina. It is made up of a lamina, folded fanwise, and therefore showing a zigzag formation upon transverse section. There are usually fifteen folds, and the free extremity is thickened to form a bridge. Histologically it is seen to be composed of tortuous capillaries, with numerous pigmented cells, melanophores,
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containing spherical brown granules scattered between the vessels. The function of the pecten is not known. Many functions have been tentatively ascribed to it, including nutritive, excretory, protective and accommodatory. Nerve fibers derived from the optic nerve have been described within it. 8) Iris: Continuous with the choroid is the iris, a pigmented diaphragm pierced by a round pupil. The yellow colour of the iris of the fowl is probably dependent upon the presence of fat globules contained within the cells. Dilatation and contraction of the pupil is effected by the action of the sphincter and dilator muscle fibers embedded in the substance of the iris. The dilator muscle is stimulated by sympathetic fibers from the cranial cervical ganglion and the sphincter muscle receives nerve innervations from the third cranial nerve from the ciliary ganglion. From infront to behind the following tissues may be easily recognized: a thin, flattened endothelium, followed by the muscle fibers, thin connective tissue and vessels, and finally a layer of deeply pigmented epithelium.
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9) The retina: Within the choroid is the retina, consisting of nerve cells and fibers directly or indirectly continuous with the optic nerve and arranged in layers as in the mammalian eye. The avian retina is thick, and each layer is prominently marked. There are two foveae, a central fovea, which is the more sensitive, consisting mainly of cones, and a temporal fovea, consisting also mostly of cones. It is thought that the central fovea is used for monocular vision and the temporal fovea for binocular vision. The rods are extremely sensitive to light, by virtue of the rhodopsin content, and are contractile in birds. The cones contain yellow oil droplets, believed to serve as a colour filter. The layers of the retina are: (1) a thick layer of pigmented epithelium; (2) the layer of rods and cones; (3) an outer limiting membrane; (4) the outer nuclear layer; (5) the outer plexiform layer; (6) the inner nuclear layer; (7) the inner plexiform layer; (8) the ganglionic cellular layer; (9) optic nerve fibers;
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(10) the inner limiting membrane. 10) The lens: Around the equator of the lens is an annular pad formed of long narrow radial cells. On the back of the lens they are succeeded by the lens fibers. Between the lens pad and the nucleus formed by the lens fibers there is a cleft, the lens chamber.
Eyelids The upper eyelid is short and thick, and its free margin splits into two sheets. On the superior conjunctiva the epithelium is two-layered cuboidal, while the inferior conjunctiva is lined by columnar epithelium. The lamina propria contains an abundance of lymphocytes. The third eyelid lacks cartilagenous support. It may be drawn completely over the eyeball by means of two smooth muscles. Its bulbar surface bears the so-called feathered epithelium, composed of cells with many fine cytoplasmic processes. It supposed to keep the cornea polished. The gland of the third eyelid is often larger than the lachrymal gland. It is extensively branching alveolar gland with columnar cells, which are filled with acidophilic granules.
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THE EAR The ear has no external appendage to the head in birds. An opening, the external auditory meatus, leads into a canal, which is closed by the ear drum, the tympanic membrane. This membrane is thin and forms a complete partition between the outer ear and the middle ear. The middle ear comprises the tympanum, an irregular cavity in the temporal bone, which is in communication with the pharynx (throat) by the auditive tube. The right and left tubes meet in the mid-line, and unite to form a membranous duct opening into the roof of the mouth. This arrangement is quite different from that in mammals. However, in both groups of animals the function is the same, to equilibrate the air pressure with the environment. The air within the tympanic cavity is also in communication by small openings with the bone spaces or diploë of bones of the cranium. The columella is a cartilagenous rod, partly ossified and jointed, stretches across the tympanic cavity. The outer end of the rod has three cartilaginous processes, one attached to the tympanic membrane, a second to the wall of the cavity near the tympanic membrane, and the third runs downward between the pterygoid and quadrate bone. The other end, somewhat expanded and disc-like, fits into
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the oval opening, the fenestra vestibuli, in the inner wall of the cavity. Transmission of vibration from the tympanum to the inner ear is effected by the columella. The inner ear, containing the essential parts of the organ of hearing, is embedded in the temporal bone medial to the tympanum and consists of a bony and membranous labyrinth. The bony labyrinth is a complete system of cavities and tunnels which is formed of the central cavity or vistibule, three semicircular canals and a cochlea. The cochlea differs from the corresponding tube of mammals in being short and only slightly curved instead of spirally coiled. The membranous labyrinth is divisible into two parts. The superior part consists of a utricle and two sinuses (posterior and superior) and three semicircular ducts, each with an ampulla. The semicircular ducts are superior, posterior and lateral, and are arranged along different planes of the head. The superior duct is in a vertical and longitudinal plane: the posterior duct lies in a transverse and vertical plane: the lateral duct is practically horizontal. The sensory impulses are received by the vestibular part of the auditory nerve, the nerve endings are in association with hair cells on the ampullae (maculae). The ducts are filled with endolymph, which is contained within the membranous labyrinth. The semicircular
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ducts are concerned with the mechanism, which controls balance. The inferior part of the membranous labyrinth consists of a cochlear duct and a saccule from which an endolymphatic duct extends to end in a small sac under the dura mater in the cranium. The saccule may be considered as an appendage to the utricle. The cochlear duct is only slightly twisted. In mammals it usually has several coils or twists. Within the cochlear duct, bathed in endolymph, lies the complex organ of hearing, the Organ of Corti, which occupies a transverse position in the greater part of the duct. The blind end of the duct carries the lagena, also a specialized part of the duct, which responds to the lower notes leaving the higher frequencies to the basilar membrane. Both the Organ of Corti and the lagena have numerous hair cells. Above the ciliated cells of the Organ of Corti is a tectorial membrane and below is the basilar membrane on which the hair cells stand. It has been estimated that the number of hair cells is in the region of three thousand, a comparatively small figure.
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Diagram of a section through the Eyeball. c., cornea; c.I., crystalline lens; i., iris; s.r., scleral ring; c.b., cilliary body; v.b., vitreous body; s., sclera; ch., choroid ; r., retina; p., pecten; o.n., optic nerve.
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SECTION THROUGH THE RETINA, CHOROID AND SCLERA. 1. Sclera.
2. Choroid.
3. Retina.
TRANSVERSE SECTION OF THE PECTEN. 1. Pecten. 2. Retina.
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DIAGRAM OF THE MEMBRANOUS LABYRINTH OF THE INTERNAL EAR.
DIAGRAM OF TYMPANIC CAVITY AND COCHLEAR DUCT.
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REFERENCES
Bradley, O.C. (1960): The structure of the fowl. Fourth edition. Oliver and body. Edinburgh and London. Hodges, R.D. (1974): The histology of the fowl. Academic press, London and New York. King, A.S. and J. Mclelland (1975): Outlines of avian anatomy. Bailliere Tindall. London. Nickel, R., A. Schummer and E. Seiferle (1977): Anatomy of the domestic birds. Verlag Paul Parey. Berlin-Hamburg. Sturkie, P.D. (1976): Avian physiology. 3rd edition. SpringerVerlage - New York.
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رقم اإليداع بدار الكتب المصرية 4332/0993
CHAPTER 1
BLOOD 5- Erythrocytes:
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