Human Anatomy and Physiology, Homeostasis and Hygiene
What you must understand
Organ systems: skeletal (support, protection, mineral store, blood cell formation in marrow), muscular (movement, heat), digestive (mechanical and chemical breakdown, absorption in the small intestine, water reabsorption in the large intestine), respiratory (gas exchange in alveoli), circulatory (heart, vessels, blood; systemic and pulmonary circuits), excretory (nephrons filter, reabsorb, secrete; urine formation), nervous (central and peripheral, reflex arc), endocrine (hormones, feedback), immune and reproductive.
Homeostasis keeps internal conditions stable through negative feedback: a deviation triggers a response that reverses it. Examples: blood glucose regulated by insulin and glucagon, body temperature by heat loss and production, osmotic balance by kidneys.
Higher nervous activity involves conditioned and unconditioned reflexes, excitation and inhibition, and signaling systems. Hygiene covers diet, exercise, sleep, vaccination, and avoiding risk factors such as smoking.
Traps
- Absorption of nutrients occurs mainly in the small intestine, not the stomach.
- Insulin lowers glucose; glucagon raises it - do not reverse.
- The pulmonary circuit carries deoxygenated blood to the lungs; the systemic circuit carries oxygenated blood to tissues.
- Unconditioned reflexes are innate; conditioned reflexes are acquired and can fade.
Rule of thumb
Every homeostasis question asks: what is the sensor, what is the response, and does the response oppose the deviation?
Worked example: After a sugary meal blood glucose rises; the pancreas releases insulin; cells take up glucose and the liver stores glycogen; glucose falls - negative feedback restores the set point.