Endocrine gland
 | This article needs additional citations for verification. (January 2010) |
| Endocrine glands | |
|---|---|
 The major endocrine glands:
1 Pineal gland 2 Pituitary gland 3 Thyroid gland 4 Thymus 5 Adrenal gland 6 Pancreas 7 Ovary 8 Testicle | |
| Details | |
| System | Endocrine system |
| Identifiers | |
| Latin | glandulae endocrine |
| MeSH | D004702 |
| TA98 | A11.0.00.000 |
| TA2 | 3852 |
| TH | H2.00.02.0.03072 |
| FMA | 9602 |
| Anatomical terminology | |
Endocrine glands are ductless
Pituitary gland
The pituitary gland hangs from the base of the brain by the pituitary stalk, and is enclosed by bone. It consists of a hormone-producing glandular portion of the anterior pituitary and a neural portion of the posterior pituitary, which is an extension of the hypothalamus. The hypothalamus regulates the hormonal output of the anterior pituitary and creates two hormones that it exports to the posterior pituitary for storage and later release.
Four of the six anterior pituitary hormones are tropic hormones that regulate the function of other endocrine organs. Most anterior pituitary hormones exhibit a diurnal rhythm of release, which is subject to modification by stimuli influencing the hypothalamus.
Somatotropic hormone or
The
The intermediate lobe of the pituitary gland secretes only one enzyme that is
The neurohypophysis stores and releases two hypothalamic hormones:
- Oxytocin stimulates powerful uterine contractions, which trigger labour and delivery of an infant, and milk ejection in nursing women. Its release is mediated reflexively by the hypothalamus and represents a positive feedback mechanism.
- Antidiuretic hormone stimulates the kidney tubules to reabsorb and conserve water, resulting in small volumes of highly concentrated urine and decreased plasma osmolality. Antidiuretic hormone is released in response to high solute concentrations in the blood and inhibited by low solute concentrations in the blood. Hyposecretion results in diabetes insipidus.
Thyroid gland
The thyroid gland is located in the front of the neck, in front of the thyroid cartilage, and is shaped like a butterfly, with two wings connected by a central isthmus. Thyroid tissue consists of follicles with a stored protein called colloid, containing[thyroglobulin], a precursor to other thyroid hormones, which are manufactured within the colloid.
The
Calcitonin, produced by the parafollicular cells (C cells) of the thyroid gland in response to rising blood calcium levels, depresses blood calcium levels by inhibiting bone matrix resorption and enhancing calcium deposit in bones. Excessive secretion cause hyperthyroidism and deficiency cause hypothyroidism.
Parathyroid glands
The parathyroid glands, of which there are 4–6, are found on the back of the thyroid glands, and secrete parathyroid hormone,[2] This causes an increase in blood calcium levels by targeting bone, the intestine, and the kidneys. The parathyroid hormone is the antagonist of calcitonin. Parathyroid hormone release is triggered by falling blood calcium levels and is inhibited by rising blood calcium levels.
Adrenal glands
The adrenal glands are located above the kidneys in humans and in front of the kidneys in other animals. The adrenal glands produce a variety of hormones including adrenaline and the steroids aldosterone cortisol and Dehydroepiandrosterone sulfate (DHEA).[3] Adrenaline increases blood pressure, heart rate, and metabolism in reaction to stress, the aldosterone controls the body’s salt and water balance , the cortisol plays a role in stress response and the dehydroepiandrosterone sulfate (DHEA) produces aids in production of body odor and growth of body hair during puberty.
Pancreas
The pancreas, located in the abdomen, below and behind the stomach, is both an exocrine and an endocrine gland. The alpha and beta cells are the endocrine cells in the pancreatic islets that release insulin and glucagon and smaller amounts of other hormones into the blood. Insulin and glucagon influence blood sugar levels. Glucagon is released when the blood glucose level is low and stimulates the liver to release glucose into the blood. Insulin increases the rate of glucose uptake and metabolism by most body cells.
Somatostatin is released by delta cells and acts as an inhibitor of GH, insulin, and glucagon.
Gonads
The ovaries of the female, located in the pelvic cavity, release two main hormones. Secretion of estrogens by the ovarian follicles begins at puberty under the influence of follicle-stimulating hormone. Estrogens stimulate the maturation of the female reproductive system and the development of secondary sexual characteristics. Progesterone is released in response to high blood levels of luteinizing hormone. It works with estrogens in establishing the menstrual cycle.
The testes of the male begin to produce testosterone at puberty in response to luteinizing hormone. Testosterone promotes maturation of the male reproductive organs, development of secondary sex characteristics such as increased muscle and bone mass, and the growth of body hair.
Pineal gland
The pineal gland is located in the
Other hormone-producing structures
Many body organs not normally considered endocrine organs contain isolated cell clusters that secrete hormones. Examples include the heart (atrial natriuretic peptide); gastrointestinal tract organs (gastrin, secretin, and others); the placenta (hormones of pregnancy—estrogen, progesterone, and others); the kidneys (erythropoietin and renin); the thymus; skin (cholecalciferol); and adipose tissue (leptin and resistin).
Development
Endocrine glands derive from all three germ layers.[citation needed]
The natural decrease in function of the female's ovaries during late middle age results in
Functions
Hormones
Local chemical messengers, not generally considered part of the endocrine system, include
The ability of a target cell to respond to a hormone depends on the presence of receptors, within the cell or on its plasma membrane, to which the hormone can bind.
Hormone receptors are dynamic structures. Changes in the number and sensitivity of hormone receptors may occur in response to high or low levels of stimulating hormones.
Blood levels of hormones reflect a balance between secretion and degradation/excretion. The liver and kidneys are the major organs that degrade hormones; breakdown products are excreted in urine and faeces.
Hormone half-life and duration of activity are limited and vary from hormone to hormone.
Interaction of hormones at target cells Permissiveness is the situation in which a hormone cannot exert its full effects without the presence of another hormone.
Synergism occurs when two or more hormones produce the same effects in a target cell and their results are amplified.
Antagonism occurs when a hormone opposes or reverses the effect of another hormone.
Control
The endocrine glands belong to the body's control system. The hormones which they produce help to regulate the functions of cells and tissues throughout the body. Endocrine organs are activated to release their hormones by humoral, neural, or hormonal stimuli. Negative feedback is important in regulating hormone levels in the blood.
The nervous system, acting through hypothalamic controls, can in certain cases override or modulate hormonal effects.
Clinical significance
Disease
Endocrine disease is characterized by irregulated hormone release (a productive
Endocrinopathies are classified as primary, secondary, or tertiary. Primary endocrine disease inhibits the action of downstream glands. Secondary endocrine disease is indicative of a problem with the pituitary gland. Tertiary endocrine disease is associated with dysfunction of the hypothalamus and its releasing hormones.[citation needed]
As the
Other common diseases that result from endocrine dysfunction include Addison's disease, Cushing's disease and Grave's disease. Cushing's disease and Addison's disease are pathologies involving the dysfunction of the adrenal gland. Dysfunction in the adrenal gland could be due to primary or secondary factors and can result in hypercortisolism or hypocortisolism. Cushing's disease is characterized by the hypersecretion of the adrenocorticotropic hormone due to a pituitary adenoma that ultimately causes endogenous hypercortisolism by stimulating the adrenal glands.[7] Some clinical signs of Cushing's disease include obesity, moon face, and hirsutism.[8] Addison's disease is an endocrine disease that results from hypocortisolism caused by adrenal gland insufficiency. Adrenal insufficiency is significant because it is correlated with decreased ability to maintain blood pressure and blood sugar, a defect that can prove to be fatal.[9]
Graves' disease involves the hyperactivity of the thyroid gland which produces the T3 and T4 hormones.[8] Graves' disease effects range from excess sweating, fatigue, heat intolerance and high blood pressure to swelling of the eyes that causes redness, puffiness and in rare cases reduced or double vision.[citation needed]
References
- PMID 25589270.
- University of Nebraska at Omaha.
- ^ "Adrenal gland". Medline Plus/Merriam-Webster Dictionary. Retrieved 11 February 2015.
- ^ "Mortality and Burden of Disease Estimates for WHO Member States in 2002" (xls). World Health Organization. 2002.
- ISBN 978-0-07-139140-5.
- S2CID 1703215.
- ^ Buliman A, Tataranu LG, Paun DL, Mirica A, Dumitrache C (2016). "Cushing's disease: a multidisciplinary overview of the clinical features, diagnosis, and treatment". Journal of Medicine & Life. 9 (1): 12–18.
- ^ a b Vander, Arthur (2008). Vander's Human Physiology: the mechanisms of body function. Boston: McGraw-Hill Higher Education. pp. 345-347
- S2CID 13552007.
