Free Human physiology multiple-choice practice questions with hints and explanations, at three levels: key terms and facts, applying the concepts, cases and analysis.
Which hormones are the main regulators of the body's basal metabolic rate?
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Before this: Human anatomy
Physiology is the study of how the body works. Anatomy tells you where the heart is; physiology tells you how it pumps and how the pumping is controlled.
One idea runs through the whole subject: homeostasis. The body keeps its internal conditions, such as temperature, blood pressure, blood glucose and pH, within a narrow range.
Most of this control works by negative feedback. A change is detected and the body responds in the opposite direction, so the change becomes smaller. A feedback loop has three parts:
Positive feedback is rare. It makes a change bigger until an event is finished. Examples are contractions during childbirth (oxytocin), blood clotting and the LH surge that triggers ovulation.
Answer: Negative feedback. The response (insulin) opposes the change (high glucose), so it is negative feedback. Positive feedback would push glucose even higher. Hormones can carry feedback without nerves.
Many questions start from a number. Learn these resting values for a healthy adult:
Two formulas link the heart and the vessels:
CO is cardiac output, HR heart rate and SV stroke volume, the blood pumped per beat. Example: 70 beats/min × 70 mL = 4900 mL/min, about 4.9 L/min.
MAP is the mean arterial pressure and TPR the total peripheral resistance of the vessels. At 120/80 mmHg, MAP ≈ 80 + 40/3 ≈ 93 mmHg.
Gases move by diffusion, from high to low partial pressure. Oxygen moves from the alveoli into the blood; carbon dioxide moves from the blood into the alveoli. Most CO₂ travels in the blood as bicarbonate.
Answer: 4.8 L/min. CO = HR × SV = 80 × 60 = 4800 mL/min = 4.8 L/min. Adding the numbers (140) or dividing them (1.33) is the wrong operation; 48 L/min is a slip when converting mL to L.
Heart rhythm. Each beat starts in the sinoatrial (SA) node in the right atrium, the natural pacemaker. The signal spreads over the atria, then is delayed in the atrioventricular (AV) node, so the atria finish emptying before the ventricles contract.
On an ECG, the P wave is atrial depolarisation, the QRS complex is ventricular depolarisation and the T wave is ventricular repolarisation.
Nerves. In an action potential, sodium ions (Na⁺) flow into the cell and cause depolarisation. Potassium ions (K⁺) then flow out and cause repolarisation.
Kidney. The functional unit is the nephron. Blood is filtered in the glomerulus, and the proximal tubule reabsorbs most of the filtered water and sodium.
Glucose. Insulin lowers blood glucose by moving glucose into cells. Glucagon raises it by breaking down glycogen in the liver and making new glucose.
Acid–base. CO₂ acts as an acid. Too much CO₂ (slow breathing) causes respiratory acidosis; too little (fast breathing) causes respiratory alkalosis. Changes in bicarbonate cause metabolic acidosis or alkalosis.
Answer: So the atria finish contracting before the ventricles contract. The short delay lets the atria push their blood into the ventricles first. Repolarisation of the ventricles is the T wave and has nothing to do with this delay.
Most physiology questions describe a change and ask what happens next. Work through it like a chain:
Write small arrows as you go: “volume ↓ ⇒ SV ↓ ⇒ CO ↓ ⇒ MAP ↓”. This keeps the direction of every change clear.
Follow the chain one link at a time. Try to predict the next link before you open it.
A healthy adult loses about 1 L of blood. Before the bleed, HR was 70 beats/min and SV was 70 mL. What does the body do in the first minutes, and what signs do you expect?
Blood volume falls, so less blood returns to the heart. The ventricles fill less and the stroke volume falls, say from 70 mL to 50 mL.
At the old heart rate, CO = 70 × 50 mL = 3500 mL/min instead of 4900 mL/min. With a lower cardiac output, MAP = CO × TPR starts to fall.
Baroreceptors in the carotid sinus and the aortic arch sense the lower pressure and send fewer signals to the medulla.
The medulla increases sympathetic activity and reduces vagal activity. The heart beats faster and vessels in the skin and gut constrict, which raises TPR.
To bring CO back to 4900 mL/min with SV = 50 mL, the heart rate must rise to 4900 / 50 = 98 beats/min.
Less blood reaches the kidneys, renin rises, and angiotensin II, aldosterone and ADH increase. The kidney keeps sodium and water, so less urine is produced.
Every response opposes the fall in pressure, as negative feedback should. So blood pressure can stay near normal at first, while the heart rate rises.
Tachycardia (about 98/min), cool pale skin from vasoconstriction and a low urine output; blood pressure is at first held near normal.
Answer: Low CO₂ and high pH (respiratory alkalosis). Fast breathing removes CO₂, and less CO₂ means less acid, so the pH rises. Choosing respiratory acidosis is the reversed direction: that happens with slow, shallow breathing.
For hard questions, draw the arrow chain. Start from the first change and let negative feedback tell you the direction of each response.
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Which type of white blood cell is the most numerous in healthy adult blood?
Neutrophils make up roughly half or more of circulating white cells. They are phagocytes that respond quickly to bacterial infection.
Which protein forms the mesh that stabilises a blood clot?
Thrombin converts soluble fibrinogen into insoluble fibrin strands, which bind the platelet plug and trap red cells to form a stable clot.
In Graves' disease, what thyroid function results are expected and why?
TSH-receptor antibodies stimulate the thyroid independently of TSH. The resulting high T4 and T3 suppress pituitary TSH by negative feedback.
One idea runs through the whole subject: homeostasis. The body keeps its internal conditions, such as temperature, blood pressure, blood glucose and pH, within a narrow range.
Most of this control works by negative feedback. A change is detected and the body responds in the opposite direction, so the change becomes smaller. A feedback loop has three parts:
Every question has four options, and only one is right. Stuck? Open a small hint first, and the full explanation only when you need it.