Human Physiology and Homeostasis
Core concepts
Understand negative feedback as the organizing principle of homeostasis (thermoregulation, blood glucose, water/salt balance, blood pH). Know the composition and functions of blood, the cardiac cycle, blood pressure regulation, gas exchange in alveoli, and the nephron's role in filtration, reabsorption, and secretion. Be able to explain digestion and absorption of the major nutrients and the role of the liver. Distinguish negative from positive feedback (e.g., oxytocin in childbirth, blood clotting).
Traps in questions
- Homeostasis restores a set point; it does not eliminate the stimulus entirely.
- In the nephron, most reabsorption occurs in the proximal convoluted tubule; the loop of Henle builds the medullary gradient.
- ADH increases water reabsorption (concentrated urine); aldosterone increases Na⁺ reabsorption.
- Insulin lowers blood glucose; glucagon raises it - do not reverse.
- Gas exchange is by diffusion; breathing movements only create the gradient.
Worked example / rule of thumb
Dehydration scenario: plasma osmolarity rises → osmoreceptors in the hypothalamus → ADH release → increased water reabsorption in collecting ducts → small volume of concentrated urine. Rule of thumb: stimulus → sensor → control center → effector → response that opposes the stimulus. Always state which variable is being regulated (osmolarity, glucose, temperature, pH) and identify the effector organ.