Endocrine System

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1.14   Biological Clocks – Biological clocks are systems built within the human body. The body machine follows a 24-hour cycle, coinciding with the rising and setting of the sun. Heartbeat, blood pressure and temperature, which are under the influence of hormones, are regulated by the daily cycles of the biological clocks. The most obvious daily cycle is sleep, during which the heart rate, blood pressure and temperature fall.

The Thymus

1.15   The thymus is a flat, pinkish-grey organ that plays an important part in the immune system of the body. It is located high in the upper chest cavity behind the breastbone and extends into the lower neck below the thyroid gland. When a person is born, the thymus is just about 15 grams. By the age of 12 it grows to about twice its original size, but by adulthood, the organ shrinks so much that it may be hard to distinguish it from the fatty tissue that surrounds it. The thymus helps in the development of white blood cells in the bone marrow. White blood cells help the body to fight/defend infection and disease. White blood cells are involved in the production of antibodies, in recognising and destroying specific types of cells and also in remembering a specific pathogen (a disease causing microorganism) in case it is encountered again.

1.16   Some of the white blood cells are changed into T-cells in the thymus to inhabit the blood, lymph nodes and spleen. These T-cells attack bacteria, viruses, cancer cells and various other harmful microorganisms. T-cells are sometimes called “killer cells” because of their ability to find and destroy such organisms.

 The Parathyroid Gland

1.17   The parathyroid gland consists of four tiny glands that function as one gland. These glands lie in the front of the neck, close to the thyroid gland. The hormone produced by the parathyroid gland raises the amount of calcium in the blood when it becomes low. It also helps in absorbing more calcium from the digestive tract. Calcium is necessary for a number of body functions including bone growth and muscle and nerve functions.

 The Reproductive Organs

1.18   The “testes” in males and “ovaries” in females produce hormones that regulate the development of sex characteristics and initiate the production of reproductive cells.