Endocrine System is defined as a system of ductless glands that regulates bodily functions via hormones secreted into the bloodstream.
Endocrine Disorders : The endocrine system includes the hypothalamus, pituitary gland, pineal body, thyroid, adrenal glands, and gonads (ovaries and testes). An endocrine disorder is said to occur when there is oversecterin or undersecretion of any of these hormones. The endocrine and the nervous systems regulate body activities.
Tag words: Hormones, Steroids, Anabolic steroids, pituitary gland, pineal body, hormones, steroids, adrogens, Adrenocorticotropic hormone, Antidiurtetic hormone, Oxytocin, insulin, glucagon, epinephrine, norepinephrine
CNS : Acts through electrical impulses and neurotransmitters which cause muscle contraction and glandular secretion. The effect is of short duration, measured in seconds, and localized.
Endocrine system produces chemical messengers (hormones) that influence growth, development, and metabolic activities. There are two major categories of glands in the body - exocrine and endocrine .
Exocrine Glands: Produce secretions which are released to the outside; the sweat, salivary mammary, and digestive gland systems are examples of exocrine glands.
Endocrine Glands: Ductless glands. Greek term "endo," means within, and "krine," means secrete. The hormones are secreted directly into the blood and are carried throughout the body where they influence the appropriate receptor sites for that hormone.
Mixed Glands (Exocrine and Endocrine) Some glands have non-endocrine regions that have functions other than hormone secretion. For example, the pancreas has a major exocrine portion that secretes digestive enzymes and an endocrine portion that secretes hormones.
The ovaries and testes secrete hormones and also produce the ova and sperm.
Some organs, such as the stomach, t he intestines, and heart, produce hormones, but their primary function is not hormone secretion.
Male: Pituitary gland
Female: Pineal body
Thyroid Gland M&F
Thymus M&F
Adrenal Gland: M&F
Pancreas M&F
Ovary (female)
Testis (Male)
Diagram showing the major Endocrine Glands of the Human body.
1. Pituitary Gland (hypophysis) is 1 cm in diameter, pea sized. It is surrounded by bone and it rests in the sella turcica, a cavity in the sphenoid bone, connected to the hypothalamus of the brain by a slender stalk - the infundibulum.
2 distinct regions: The anterior lobe adenohypophysis, activity controlled by hypothalamus's hormones. The posterior lobe : neurohypophysis, controlled by nerve stimulation.
Hormones of the Anterior Lobe (Adenohypophysis)
1. Growth hormones: stimulate growth of bones, and muscles through increased protein synthesis. It affects appearance & height. If there is too little growth hormone in a child: pituitary dwarf of normal proportions but small stature. Excess of the hormone: Giant .
2. TSH or thyrotropin. Produced by glandular cells of the thyroid gland. Hypersecretion of thyroid-stimulating hormone > the thyroid gland enlarges and secretes too much thyroxine. If there is too much thyroxine the condition is hyperthyroidism , if too little, the patient is said to be myxoedemic.
3. Adrenocorticotropic hormone reacts with receptor sites in the cortex of the adrenal gland to stimulate the secretion of cortical hormones, particularly cortisol.
4. Gonadotropic hormones react with receptor sites in the gonads, or ovaries and testes, to regulate the development, growth, and function of these organs.
5. Prolactin hormone facilitates development of glandular tissue in the female breast.
Hormones of the Posterior Lobe (Neurohypophysis)
1. Antidiuretic: facilitates reabsorption of water in the kidney tubules. Insufficient amounts of antidiuretic hormone cause excessive water loss in the urine.
2. Oxytocin causes contraction of the smooth muscle of the uterus & brings about the ejection of milk during lactation.
2. Pineal Gland:
Pineal body / epiphysis cerebri, is cone-
shaped in structure and protrudes from
the third ventricle of the brain. The pineal
gland consists of neurons, neuroglial
cells, and specialized secretory cells
called pinealocytes. The pinealocytes
synthesize the hormone melatonin which
is secreted directly into the cerebrospinal
fluid. From the CSF it is absorbed by the
blood. Melatonin affects reproductive
development and daily physiologic
cycles of both humans and mammals.
Diagram of the Pituitary / Pineal Glands. 3. Thyroid Gland
The Thyroid gland is located in the neck and it is richly supplied with blood, it has two lobes, one on each side of the trachea, just below the larynx (voice box). An isthmus connects the right and left sides. The thyroid gland consists of follicles which produce the hormones: thyroxin and triidothyroxine . Both these hormones are rich in iodine.
95 % of thyroid hormone is thyroxine. 5 % is triiodothyronine. Iodine is required for the manufacture of both of these hormones. Thyroid hormone secretion is regulated by a negative feedback mechanism that involves the amount of circulating hormone, hypothalamus, and adenohypophysis.
Iodine deficiency will lead to thyroid hormone deficiency. This stimulates the anterior pituitary to secrete thyroid-stimulating hormone, which causes the thyroid gland to increase in size in a vain attempt to produce more hormones. But it cannot produce more hormones because it does not have the necessary raw material, iodine. This type of thyroid enlargement is called simple goiter or iodine deficiency goiter.
