Human Physiology (Digestion, Circulation, Respiration, Excretion, Locomotion, Neural and Endocrine Control)
Human Physiology integrates digestion, circulation, respiration, excretion, locomotion, neural control and endocrine regulation.
Core rules
- Pepsinogen is activated to pepsin by HCl; bile emulsifies fats; most nutrient absorption occurs in the small intestine.
- The SA node sets heart rhythm; cardiac output = heart rate x stroke volume.
- Haemoglobin carries oxygen; CO2 is mainly transported as bicarbonate.
- The nephron filters, reabsorbs and secretes; ADH increases water reabsorption; aldosterone promotes sodium reabsorption.
- Muscle contraction follows the sliding filament model: actin slides over myosin and the sarcomere shortens.
- Neurons maintain resting potential by Na+/K+ pumps and ion channels; endocrine glands release hormones into blood.
Worked example
A person has heart rate 72 beats per minute and stroke volume 70 mL. Cardiac output = 72 x 70 = 5,040 mL per minute, about 5 L/min. The reasoning uses the product of rate and volume, not the number of chambers. During exercise, both heart rate and stroke volume can rise, increasing output.
Traps
- Pepsinogen is inactive until HCl activates it.
- ADH increases water reabsorption, not urine volume.
- In the sliding filament model, filaments slide; they do not shorten.
- Insulin lowers blood glucose; glucagon raises it.