For life to continue, precise internal body conditions must be maintained regardless of external conditions The principle function of regulatory systems is to maintain homeostasis Homeostasis: The process of maintaining a relatively stable internal environment Claude Bernard
Walter Cannon
(1813 – 1878)
(1871 – 1945)
• Not a static process (dynamic equilibrium) • Requires energy (unlike a true equilibrium state)
Pathophysiology: The study of homeostatic imbalance (i.e., disease) (moderate imbalance = illness; extreme imbalance = death)
Course Introduction
Example: Temperature regulation
Regulatory Systems:
Homeostatic conditions are maintained via feedback systems autoregulation vs. extrinsic regulation
Body temp = 96.5º Input
Information
Control center
(Hypothalamus)
(set point)
(98.6º)
(-) Receptor
Output
Feedback
(transducer)
Effector
(Muscles)
(body heats up) (change in system)
Negative Feedback: Drives system toward set point (promotes stability)
Effect (Shivering)
Most common type of feedback system found in the human body
Page 6 6
Course Introduction
Example: Delivery of fetus
Regulatory Systems:
Homeostatic conditions are maintained via feedback systems autoregulation vs. extrinsic regulation
Cervix stretches Input
Information
Control center
(Hypothalamus)
(set point)
(no stretch)
(+) Receptor
Output
Feedback
(transducer)
Effector
(Uterus)
(cervix stretches) (change in system)
Effect
Positive Feedback: Drives system away from set point
(Uterus contracts)
Rare type of feedback system found in the human body
(promotes instability)
Course Introduction
Pathophysiology: The initiation of abnormal positive feedback systems often associated with disease / trauma
(set point = 120 / 80 mm Hg)
Input BP
Example: Blood loss due to trauma
Vasomotor center
Feedback
(-) (+)
Baroreceptor (e.g., aortic arch) decrease (increase in blood pressure)
Output Heart Blood Vessels Not enough blood
Effect Heart rate; Vasoconstriction
Heart weakens (no nutrients…)
Guyton & Hall (Textbook of Medical Physiology, 12th ed.) – Figure 1.3