5. THE MECHANISM OF THE ENDOCRINE
The Endocrine System
Two types of glands in our body are as follows:
1. Exocrine glands produce chemical substances which are sent to activate other organs via their own ducts. Examples of exocrine glands are the salivary glands, gastro-intestinal glands, lacrimal glands, sweat glands or sudoriparous gland.
2. Endocrine glands produce chemical substances which are sent to activate other organs through the bloodstream since they do not have their own ducts. These chemical substances are called hormones and are steroid amino acids. Endocrine glands can be found all over our body. They produce many types of hormones each for different tasks. These hormone control specific organs for body growth and may hormones stimulate or restrain organs.
Seven significant endocrine glands are:
2.1 Pituitary Gland.
Pituitary gland is in the mid-lower part of the hypothalamus. This gland produces mucus like substance, so it is called pituitary gland. The pituitary gland is composed of cells with different shapes.
Size and general Characteristics of the Pituitary gland. The weight of the pituitary gland in males is about 0.5 – 0.6 gram while it is slightly heavier in females at 0.6 -0.7 gram.
The pituitary gland can be divided into 3 parts. They are the anterior pituitary, the intermediate pituitary, and the posterior pituitary. Each part has its own structure and way of producing hormones.
The hormone produced by the pituitary control the body growth, the function of the thyroid gland, the adrenal gland, kidneys, and the reproduction system.
2.2 The Thyroid Gland
The thyroid gland has 2 lobes to both sides of the larynx which are connected by thin tissue. The thyroid gland is the largest endocrine gland in our body. A lot of blood vessels feed this 15-20-gram heavy gland. Significant hormones produced by the thyroid gland are as follows:
1) Thyroxin Hormone controls the metabolism of food, stimulating the changing of the glycogen to glucose and bringing the glucose into cell membranes of the digestive tract. Hence, it helps increase glucose level in blood.
Abnormalities in Thyroxin Hormone Levels
(1) Simple goiter is the enlargement of the thyroid gland because the anterior lobe produces the thyroid–stimulating hormone (TSH stimulates the thyroid glands to produce hormone under normal condition). This stimulates the thyroid gland too much until it is not able to produce thyroxin to restrain the flow of the TSH from the pituitary gland.
(2) Toxic goiter happens when the thyroid gland produces too much hormone because of thyroid cancer.
(3) Graves' disease or exophthalmic goiter is caused by the thyroid gland producing too much hormone because it is over stimulated by TSH. A patient will have a high metabolism of food. A patient becomes exhausted, loses weight despite eating a lot, being out of breath, and reacts fast to stimulation. This may cause Graves' ophthalmopathy or exophthalmos due to increase of water and tissue at the back of the eyeball. This condition is more common in females than in males.
(4) Cretinism is a condition of stunted physical and mental growth caused by the malfunction of the thyroid gland before or after childbirth. It reduces the growth of bones and the body will stay undersized. Other effects are mental deficiency, retardation, rough and dry skin, and bald head.
(5) Myxedema occurs in adults because the thyroid gland does not produce enough thyroid hormone. Significant symptoms are slow development of body and mind, convulsions, rough and pale-dry skin, low effectiveness of heart and the kidney, inactivity, depression, weakened memory, too much fat, body weakness, and easily infection by disease. This illness is more common in women than in men.
2) Calcitonin is a hormone from the thyroid gland and functions as a regulator for the calcium level in blood. Excess calcium pulled from the blood and deposited into the bones; the calcium level in the blood controls the flow of the hormone. This hormone functions together with the hormone from the parathyroid gland and vitamin D.
2.3 Parathyroid Gland
The parathyroid glands are very light endocrine glands attached to the back of thyroid tissue. Humans have 2 glands on each side of the thyroid glands. They are shaped like small brown-red or brown-yellow eggs with a total weight of just 0.03 -0.05 gram
The significant hormone produced from these glands is the parathyroid hormone. The function of this hormone is to maintain the balance of calcium and phosphorus in our body. It works closely together with calcitonin. Since the level of calcium in the blood is essential for the functionality of muscles, nerves and the heartbeat, the parathyroid hormone is an indispensable endocrine for life.
2.4 Adrenal gland
The Adrenal glands sit on top of the two kidneys. The right gland looks like a triangle and the left gland is shaped like a half-moon. Each gland has two distinct structures, the outer adrenal cortex and the inner medulla, both of which produce many types of hormones.
1) Adrenal cortex. The adrenal cortex is one of the endocrine glands which can produce more than 50 hormones. The hormones produced by this gland can be divided into 3 groups:
(1) Glucocorticoids. This hormone plays a major role in the regulation of the metabolism of glucose. It also regulates the metabolism of proteins and fats including the balancing of minerals. If we have too much glucocorticoid hormone, we might develop Cushing’s syndrome. A common sign of Cushing’s syndrome is the growth of fat pads along the collar bone and on the back of the neck (buffalo hump) and a round face often referred to as a "moon face". This syndrome is associated with prolonged exposure to inappropriately high levels of the hormone cortisol.
(2) Mineralocorticoid hormones. These hormones are involved with the retention of sodium, a mineral, in our body. Aldosterone is a significant hormone which controls the function of the kidney when reabsorbing water and sodium back into the blood vessels. It also controls the secretion of potassium in our body to regulate blood pressure.
(3) Androgenic hormone or testoid is a common name for many hormones such as testosterone, androstenedione, and androsterone.
2) The Adrenal Medulla produces two significant hormones, adrenalin or epinephrine and noradrenalin or norepinephrine. The adrenal medulla produces about 70% adrenalin and 30% noradrenalin. Both hormones can be found in adults but only noradrenalin is found in children.
(1) Adrenalin or epinephrine. Adrenalin is the hormone which increases blood sugar, blood pressure and heartbeat. It also stimulates the small arteries in organs to enlarge but the small arteries in the skin and the abdominal cavity to contract.
(2) Noradrenalin or norepinephrine. The noradrenalin hormone has a similar effect on our body to the effects of adrenalin. However, adrenaline causes the better effects. This hormone will also flow from the sympathetic nerve endings and increases the blood pressure by constricting the arteries to the organs.
2.5 Pancreas
Within the pancreas tissue are about 2,500,000 small glands called Islets of Langerhans which accounts for only one percent of the whole pancreas. 2 types of hormones are produced by the Islets of Langerhans which are:
(1) Insulin which is released from beta (β) cells at the center of the islets of Langerhans. The significant function of this hormone is to normalize the sugar level in the blood. When our body has a high level of blood sugar, the insulin will stimulate the liver cells and the muscle cells to bring more glucose into the cells and change the glucose to glycogen which can be stored there. Moreover, insulin increases the rate of glucose uptake in the cells and normalizes the blood sugar level. If the cell group which produces the insulin is destroyed, the blood sugar level will be higher than normal and will cause diabetes.
(2) Glucagon is the hormone produced from the Alfa (α) cells which are a type of cells in the Islets of Langerhans. The glucagon will stimulate the release of glucose from the liver and muscles into the blood so that the blood sugar level rises.
2.6 Ovaries are part of the female reproductive system.
The significant hormones produced by the ovaries are estrogen and progesterone.
The estrogen controls the feminine appearance such as, high-pitched sound, full hips, reproductive organs, breasts, pubic hair and armpit hair. It also takes part in promoting the menstrual changes at the ovaries and the endometrium.
Progesterone is produced by the corpus luteum inside the ovaries, during pregnancy some of it is produced in the placenta. A small amount is also produced in the adrenal glands. This hormone is the most significant hormone in preparation for pregnancy and during pregnancy. This hormone influences directly the changes to the endometrium, the ovaries and the uterus. Progesterone is controlled by the luteinizing hormone (LH) produced in the anterior pituitary gland.
2.7 Testes
The testes are part of the male reproductive system. The most significant hormone produced by this gland is testosterone which is produced since young age. Secretion of the interstitial cell stimulating hormone or ICSH will be stimulated by the hormone from the anterior pituitary gland (LH or ICSH). Other than producing testosterone, the testes also produce minute amounts of estrogen which is the female hormone.
Testosterone controls the development of male reproductive tissues (testes and prostate) and the development of secondary sexual characteristics such as cracked voice, pointed Adam’s apple, mustache at lips, hair at legs, arm pits and pubic hair, and increased bone and muscle mass at the shoulders, arms and legs which are much stronger than those of the opposite sex.
Abnormal levels of testosterone may result in:
(1) If the testes are physically injured it may result in castration and sterility. The following absence of testosterone affects sexual appearance and body growth.
(2) A high level of testosterone or premature production during young age, maybe because of a tumor in the testis, might trigger a precocious puberty and premature development of both the secondary sexual characteristics and the reproductive organs.
Significant Endocrine Glands Their Names, Hormones and Functions
