General Science Quiz: Human Body: Important Facts

The stapes, shaped like a stirrup, is the innermost of the three ossicles of the middle ear and is the smallest bone in the human body, measuring only a few millimetres; the smallest muscle of the body, the stapedius, is attached to it.

The adult human skeleton has 206 bones, of which 80 belong to the axial skeleton, that is the skull, vertebral column and chest, and 126 to the appendicular skeleton of the limbs and girdles.

The liver weighs about one and a half kilograms and is both the largest gland and the largest internal organ of the body; it secretes bile, stores glycogen, iron and vitamin A, converts ammonia into urea and detoxifies drugs and poisons.

The sino-atrial node is a small patch of specialised muscle tissue in the wall of the right atrium near the opening of the superior vena cava, and it generates the impulse that sets the rate of each heartbeat without any outside stimulus, which is why it is called the pacemaker.

Red blood cells are produced in the red bone marrow, lose their nucleus on maturing and survive roughly four months, after which they are broken down in the spleen, which is accordingly called the graveyard of red blood cells; the iron released from their haemoglobin is used again.

The Austrian scientist Karl Landsteiner discovered the A, B and O blood groups in 1901 and received the Nobel Prize for Physiology or Medicine in 1930 for the work; he was also associated with the discovery of the Rh factor, named after the rhesus monkey.

The cerebellum lies behind and below the cerebrum and coordinates voluntary muscular activity, so it keeps the body balanced and the posture steady; damage to it causes a staggering walk even though the muscles are strong.

The islets of Langerhans are patches of endocrine tissue in the pancreas, and their beta cells secrete insulin, which lowers the level of glucose in the blood by helping cells take it up and by storing the surplus as glycogen; a lack of insulin causes diabetes mellitus.

Each kidney contains about a million nephrons, and each nephron consists of a Bowman's capsule enclosing a knot of capillaries called the glomerulus, followed by a tubule in which useful substances are reabsorbed; together they filter the blood and form urine.

The thyroid is a butterfly-shaped gland in the neck, in front of the windpipe, and is the largest of the ductless or endocrine glands; it secretes thyroxine, for which iodine is essential, and the hormone controls the rate of metabolism, growth and development.

The hyoid is a U-shaped or horseshoe-shaped bone lying in the front of the neck below the lower jaw; it is held in place only by muscles and ligaments and forms no joint with any other bone, which is why it supports the tongue and helps in speech and swallowing.

Twelve pairs of cranial nerves arise from the brain and serve the head and neck, among them the optic nerve of sight, the auditory nerve of hearing and the vagus, the longest cranial nerve, which reaches the heart and the abdomen; thirty-one pairs of spinal nerves arise from the spinal…