Human Anatomy and Physiology MCQs with Explanations

The adult human skeleton has 206 bones. A newborn has roughly 300, because bones of the skull, spine and pelvis fuse during growth, so 300 is the infant figure and not the adult one.

Humans normally have 12 pairs of ribs, 24 in all. The first seven pairs attach directly to the sternum (true ribs), pairs eight to ten join it indirectly through costal cartilage, and the last two pairs are floating ribs with no anterior attachment.

Group O red blood cells carry neither the A nor the B antigen, so they can be given to a recipient of any other group in an emergency, with O negative being the classic universal donor. Group AB is the opposite case, the universal recipient, because its plasma contains no anti-A or anti-B antibodies.

120 mmHg is the systolic pressure, recorded while the ventricles contract and eject blood into the arteries; 80 mmHg is the diastolic pressure recorded while the heart relaxes and refills. Venous pressure is far lower than either figure.

Human body cells are diploid and contain 23 pairs, that is 46 chromosomes: 22 pairs of autosomes plus one pair of sex chromosomes. Gametes, the sperm and the ovum, are haploid and carry 23 chromosomes.

Each kidney contains about a million nephrons, which filter blood, reabsorb the substances the body needs and pass the rest out as urine. Alveoli are the air sacs of the lung, villi line the small intestine and neurons are nerve cells.

The liver is the largest gland and also the largest internal organ, weighing roughly 1.4 to 1.5 kg in an adult; it secretes bile and carries out the metabolism of proteins, carbohydrates, fats and drugs. The skin is the largest organ of the body overall, but it is not a gland.

The cerebellum co-ordinates and fine-tunes voluntary muscle activity and keeps posture and balance steady, so injury to it makes movements jerky and unsteady. The cerebrum carries out conscious thought and initiates voluntary action, while the hypothalamus regulates temperature, hunger and hormone release.

Insulin is made by the beta cells of the islets of Langerhans in the pancreas, and too little of it, or insensitivity to it, produces diabetes mellitus. The thyroid follicles secrete thyroxine, the adrenal cortex secretes cortisol and the posterior pituitary releases ADH and oxytocin.

Scurvy results from a shortage of vitamin C (ascorbic acid), which is needed to build collagen; it classically struck sailors without fresh fruit or vegetables and is relieved by citrus juice. Vitamin B1 deficiency causes beriberi, vitamin A causes night blindness and vitamin D causes rickets.

Ultraviolet radiation converts a cholesterol derivative in the skin into vitamin D, which is then activated by the liver and the kidney; the vitamin is required for the absorption of calcium and phosphate and so for healthy bone. Vitamin K is also made inside the body, but by bacteria living in the intestine rather than by sunlight.

Only the female Anopheles mosquito spreads Plasmodium, which multiplies in the liver and then bursts red blood cells, producing the repeated attacks of fever and rigour. Aedes transmits dengue and yellow fever, Culex transmits filariasis and the sandfly transmits kala-azar.

Tuberculosis is caused by the bacterium Mycobacterium tuberculosis, which chiefly attacks the lungs and can be treated with antibiotics. Influenza, measles and dengue are viral diseases, so antibiotics have no effect on them.

The small intestine is lined with villi and microvilli that multiply its surface area, making it the chief site for absorption of the end products of digestion. The stomach mainly churns food and begins protein digestion, while the large intestine reabsorbs water and salts.