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Anatomy & Physiology - Body Systems

The Endocrine System

The branches of science that will help you understand the body parts and functions are anatomy and physiology. Anatomy deals with studying the human body (the components, structure and position), and physiology is the study of how the body functions.

Body Systems

The body comprises several systems: The Cardiovascular system, Digestive system, Endocrine system, Muscular system, Neurological system, Respiratory system and Skeletal system.

The Endocrine System

The endocrine system affects bodily activities by releasing chemical messages, called hormones, into the bloodstream from the exocrine and endocrine glands. The function of hormones is to:

  • Control the internal environment by regulating its chemical composition and volume
  • Respond to environmental changes to help the body cope with emergencies - infection, stress etc
  • Help regulate organic metabolism and energy balance
  • Contribute to the management of growth and development

Hormones are chemicals that cause specific changes in particular parts of the body. Their effects are slower and more general than nerve action. T They can control long-term changes such as growth rate, activity, and sexual maturity.

The endocrine or ductless glands secrete their hormones directly into the bloodstream. The hormones circulate throughout the body and reach their target organ via the bloodstream. When hormones pass through the liver, they are converted by the kidneys. Tests on such hormonal products in urine can be used to detect pregnancy.

The endocrine system comprises a series of glands that secrete hormones; they are found throughout the body and include the pituitary, thyroid, parathyroids, thymus, supra-renal or adrenal glands, part of the pancreas and parts of the ovaries and testes. Although these glands are separate, certainly, they are functionally closely related because the health of the body is dependent upon the correctly balanced output from the various glands that form this system.

The Pituitary Gland (Hypophysis)

This gland has been described as the leader of the endocrine orchestra. It consists of two lobes, anterior and posterior. The anterior lobe secretes many hormones, including the growth-promoting somatotropic hormone, which controls the bones and muscles and, in this way, determines the overall size of the individual. Over secretion of the hormone in children produces gigantism and under secretion has dwarfism. The anterior lobe also produces gonadotropic hormones for both male and female gonad activity. Thyrotropic hormones regulate the thyroid, and adrenocorticotropic hormones regulate the adrenal cortex. It also produces metabolic hormones.

The posterior lobe produces two hormones - oxytocin and vasopressin. Oxytocin causes the uterine muscles to contract; it also causes the ducts of the mammary glands to contract and, in this way, helps to express the milk that the gland has secreted into the ducts. Vasopressin is an antidiuretic hormone that directly affects the kidneys' tubules and increases the amount of fluid they absorb so that less urine is excreted. It also contracts blood vessels in the heart and lungs, raising blood pressure. It is not sure whether these two hormones are manufactured in the posterior lobe or whether they are produced in the hypothalamus and passed down the stalk of the pituitary gland to be stored in the posterior lobe and liberated from there into circulation.

The Thyroid

This gland's right and left lobes lie on either side of the trachea, united by the isthmus. The average size of each lobe is 4cm long and 2cm across, but these sizes may vary considerably. The secretion of this gland is thyroxine and tri-iodothyronine. Thyroxine controls metabolism. Both hormones contain iodine, but thyronine is more active than thyroxin. Under-secretion of this hormone in children produces cretinism; the children show stunted growth (dwarfism) and fail to develop mentally. Under secretion in adults results in a low metabolic rate. Over secretion in adults gives rise to exophthalmic goitre, and the metabolic rate is higher than usual. Such persons may eat well but burn up so much fuel that they remain thin. A rapid pulse rate usually accompanies this. This gland, therefore, has a profound influence on both mental and physical activity.

The Parathyroid Glands

Four of these glands, two on either side, lie behind the thyroid. Their secretion is parathormone - the function of which is to raise the blood calcium and maintain the balance of calcium and phosphorus in the blood and bone structures. Under secretion gives rise to a condition known as tetany in which the muscles go into spasm, and over-secretion causes calcium to be lost to the blood from the bones giving rise to softened bones, raised blood calcium and marked depression of the nervous system.

The Thymus Gland

This gland lies in the lower part of the neck and attains a maximum length of about 6cm. After puberty, the thymus begins to atrophy, so adult-only fibrous remnants are found. Its secretion is thought to act as a brake on the development of sex organs so that as the thymus atrophies, the sex organs develop. Recent research into the activity of this gland reveals that it plays an important part in the body's immune system by producing T lymphocy - the T standing for thymus derived.

The Suprarenal or Adrenal Glands

These are two in number, triangular and yellow. They lay one over each kidney. They are divided like the kidney into two parts, the cortex and the medulla. The cortex is the outer part of the gland and produces several hormones called corticosteroids. Their function is to control sodium and potassium balance, stimulate glucose storage, and affect or supplement the production of sex hormones. The medulla or inner layer produces adrenaline, a potent vasoconstrictor. Adrenaline raises vessels and raises blood sugar by increasing the output of sugar from the liver. The amount of adrenaline secreted is increased considerably by excitement, fear, or anger, which has caused the adrenals sometimes to be referred to as the glands of fright and fight.

The Gonads or Sex Glands

These glands are naturally different in men and women because they serve other complementary functions in many respects. In the female, the gonads are the ovaries, and in the male, the testes. Female sex hormones are oestrogen and progesterone. The male sex hormone is testosterone, though each sex produces a small quantity of the opposite hormone. The female hormones are responsible for developing the rounded, feminine figure, breast growth, pubic and auxiliary hair and all the usual manifestations of femininity and reproduction. Male hormone is accountable for voice changes, increased muscle mass, hair development on the body and face and the normal development of manliness.


The endocrine part of the pancreas consists of clumps of cells called islets of Langerhans that secrete insulin. Insulin regulates the sugar level in the blood and converts sugar into heat and energy. Too little insulin results in a disease known as diabetes mellitus. This disease is divided into one form, juvenile-onset, which occurs before the age of 25, and another form that begins in maturity. It is a prevalent disease. It is known that some half a million people in the United Kingdom suffer from it sufficiently badly to need treatment. Still, it has been estimated that there are many more people in whom the disease exists at a sub-treatment level.

Page Reference

If you quote information from this page in your work, then the reference for this page is:

  • MACKENZIE, B. (2001) Physiology - Endocrine System [WWW] Available from: [Accessed