Human Nutrition, Respiration and Body Fluids and Circulation
What the exam tests
This section covers human nutrition, respiration, body fluids, and circulation. Questions test digestive enzymes, absorption, gas transport, blood composition, blood groups, cardiac cycle, and ECG.
Core rules
- Digestion: carbohydrates begin in the mouth with salivary amylase; proteins begin in the stomach with pepsin; fats are emulsified by bile and digested by pancreatic lipase. Absorption occurs mainly in the small intestine (villi, microvilli).
- Respiration: gas exchange occurs in alveoli. Oxygen binds hemoglobin; CO2 is transported as bicarbonate, dissolved in plasma, and bound to hemoglobin. The Bohr effect shifts the oxygen dissociation curve right when CO2/H+ increases.
- Blood: plasma, RBCs, WBCs, platelets. ABO blood groups have A and B antigens; antibodies are anti-A and anti-B. Clotting involves platelets, fibrin, and clotting factors.
- Circulation: the heart has four chambers; the SA node is the pacemaker; the cardiac cycle includes systole and diastole. Cardiac output = stroke volume × heart rate.
Worked example
A person has a stroke volume of 70 mL and a heart rate of 75 beats/min. Cardiac output = 70 × 75 = 5250 mL/min, or 5.25 L/min. During exercise, both stroke volume and heart rate increase, so cardiac output rises. Reasoning: cardiac output is the volume of blood pumped by one ventricle per minute, not the total blood volume.
Traps
Do not say all digestion occurs in the stomach; most absorption is in the small intestine. Oxygen is mostly carried by hemoglobin, while CO2 is mostly carried as bicarbonate. Anti-A antibodies are present in blood group B, not group A. The SA node initiates the heartbeat; the AV node delays the impulse.