Hormones are chemical substances produced by specialized cells of the body. Because they travel in the blood, hormones reach all body tissues. However, only target organs contain receptors that recognize a particular hormone. The receptors maintain the tissue’s responsiveness to hormonal stimulation.
Review Figure Hormones secreted by the anterior and posterior pituitary gland and their target organs, which illustrates hormones of the pituitary gland and their target organs. The organs shown in Figure Hormones secreted by the anterior and posterior pituitary gland and their target organs are directly affected by the amounts of hormones released into the bloodstream by the pituitary gland. For example, underproduction of growth hormone (GH) in children results in dwarfism.
Hormones secreted by the anterior and posterior pituitary gland and their target organs.
Hormone secretion to a target organ is determined by the body’s need for the hormone at any given time and is regulated so that there is no overproduction (hyper/secretion) or underproduction (hypo/ secretion). There are times when the body’s regulating mechanism does not operate properly, and hormonal levels become excessive or deficient, causing various disorders.
Although all major hormones circulate to virtually all tissues, each hormone exerts specific effects on its target organ. If a hormone has a specific effect on the stomach, that hormone’s target organ is the stomach.If the hormone has a specific effect on the heart, the target organ is the heart
Hormones have four key characteristics. They are:
Endo/crine gland dysfunction may result in hypo/secretion or hyper/secretion of its hormones. The prefix hyper- means excessive, above normal. The prefix hypo- means under, below, deficient.
The (1) pituitary gland is one of the most important endocrine glands. Its hormone secretions influence the functions of many organs in the body, as illustrated in Figure Hormones secreted by the anterior and posterior pituitary gland and their target organs Located below the brain, it is no larger than a pea.
Locations of major endocrine glands.
The pituitary gland consists of two distinct portions: an anter/ior lobe and a poster/ior lobe.
The anter/ior lobe (aden/o/hypophysis) develops from an upgrowth of the pharynx and is glandular in nature; the poster/ior lobe (neur/o/hypophysis) develops from a down growth from the base of the brain and consists of nervous tissue. Although both lobes secrete various hormones that regulate body functions, two hormones secreted by the neur/o/hypophysis are produced in the hypothalamus. The neur/o/hypophysis merely acts as a storage site until the hormones are released.(See Figure Hormones secreted by the anterior and posterior pituitary gland and their target organs.)
Overproduction of GH in children produces an exceptionally large person, a condition known as gigant/ism. Underproduction of GH in children is likely to produce an exceptionally small person, a condition called dwarf/ism.
The CF acr/o means extremity. Acr/o/megaly, a chronic metabolic condition, is characterized by a gradual, marked enlargement and thickening of the bones of the face and jaw. This condition, which affl icts middleaged and older persons, is caused by overproduction of growth hormone and is treated by radiation, pharmacologic agents, or surgery, commonly involving partial resection of the pituitary gland.
The (2) thyroid gland is located on the front and sides of the trachea just below the larynx. Its two lobes are separated by a strip of tissue called the isthmus. Label the thyroid gland in Figure Locations of major endocrine glands.
This table identifies pituitary hormones, their target organs and functions, and associated disorders.
Hyper/thyroid/ism is caused by excessive secretion of the thyroid gland. The gland increases the body’s metabolism and intensifies the demand for food.
Exophthalmos caused by Graves disease.
Hyper/thyroid/ism involves enlargement of the thyroid gland associated with hypersecretion of thyroxine. It is characterized by exophthalmos (bulging of the eyes), which develops because of edema in the tissues of the eye sockets and swelling of the extrinsic eye muscles. Hyper/ thyroid/ism also is called Graves disease, ex/ophthalm/ic goiter, thyr/o/toxic/osis, and tox/ic goiter. (See Figure Enlargement of the thyroid gland in goiter.)
Enlargement of the thyroid gland in goiter.
Calc/emia indicates an abnormal presence of calcium in the blood.
The (3) parathyroid glands are located on the posterior surface of the thyroid gland. The parathyroid glands are so called because they are located around the thyroid gland. Label the parathyroid glands in Figure Locations of major endocrine glands.
Usually there are two pairs of para/thyr/oid glands associated with each of the thyroid’s lobes, but the exact number varies. Nevertheless, as many as eight glands have been reported. The para/thyr/oid glands were detected accidentally. Surgeons observed that most patients who had either a partial or total thyroid/ectomy recovered uneventfully, whereas some experienced uncontrolled muscle spasms and severe pain and subsequently died.
It was only after several such unexpected deaths that the parathyroid glands were discovered and their hormonal function, quite different from that of the thyroid gland hormones, became obvious. The parathyroid glands are responsible for controlling calcium levels in the blood.
Oste/ itis fibrosa cystica is an inflammatory degenerative condition in which normal bone is replaced by cysts and fibrous tissue. It is usually associated with hyper/ para/ thyroid/ ism.
The (4) adrenal glands, also known as the supra/ren/al glands, are paired structures located super/ior to the kidneys.
Each adrenal gland is structurally and functionally differentiated into two sections: the outer adrenal cortex, which comprises the bulk of the gland, and the inner portion, the adrenal medulla. The hormones produced by each part have different functions.
This table identifies parathyroid hormone along with its target organs and functions and associated disorders.
Pancreas (Islets of Langerhans)
The (5) pancreas is located posterior to the stomach. Hormone producing cells of the pancreas are called islets of Langerhans. The islets produce two distinct hormones: alpha cells, which produce glucagons, and beta cells, which produce insulin. Both hormones play an important role in the proper metabolism of sugars and starches in the body. Label the pancreas in Figure Locations of major endocrine glands.
Gluc/ose is the chief source of energy for living organisms.
A gluc/o/meter is used to calculate blood glucose from one drop of blood. An instrument used by patients with diabetes to monitor their blood glucose levels is known as agluc/o/meter
Hyper/glyc/emia is an excessive amount of glucose or sugar in the blood. Deficiency of glucose (sugar) in the blood is hypo/glyc/emia.
A less than normal amount of gluc/ose in the blood, usually caused by excessive secretion of insulin by the pancreas, administration of too much insulin, or dietary deficiency, is called hypo/glyc/emia. Treatment is administration of gluc/ose by mouth if the person is conscious or an IV solution if the person is unconscious.
Insulin, an essential hormone for conversion of sugar, starches, and other food into energy, is required for normal daily living. Diabetes commonly results in hyper/glyc/emia. It occurs if the pancreas does not produce sufficient amounts of insulin or if the cells of the body become resistant to insulin and do not utilize insulin properly.
If hyper/glyc/emia occurs, the diabetic person can reduce the amount of gluc/ose in the blood by injecting himself or herself with the hormone called insulin.
Diabetes is a general term that, when used alone, refers to diabetes mellitus (DM), a disease that occurs in two primary forms: type 1 diabetes and type 2 diabetes. When insulin is lacking, glucose does not enter cells but returns to the bloodstream with a subsequent rise in its concentration in the blood, a condition known as hyper/glyc/emia. Low blood glucose levels cause the opposite condition (hypo/glyc/emia).
Diabetic patients whose bodies use excessive insulin have abnormally low glucose levels.
When a person drinks too much water, he or she may experience a condition of excessive urine production (urination). The medical term for this condition is poly/uria
TABLE: PANCREATIC HORMONES
Pineal and Thymus Glands
The (6) pineal gland and (7) thymus gland are classified as endocrine glands, but little is known about their endocrine function. Label these structures in Figure Locations of major endocrine glands.
Ovaries and Testes
The (8) ovaries are a pair of small, almond-shaped glands positioned in the upper pelvic cavity, one on each side of the uterus. The (9) testes are paired oval glands surrounded by the scrotal sac.
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