Major endocrine glands, their hormones and functions
Introduction
- The glands which do not have any duct are called ductless glands or endocrine glands.
- Literally, the term ‘endocrine’ means internally secreting.
- Their secretions are called internal secretions or hormones.
- These are released directly into the blood, which carries them to different parts of the body, and where they coordinate their metabolic activities.
- They are usually located far away from the site of their action.
- The study of those glands and the hormones they produce is called endocrinology.
- Some glands of the body, such as pancreas and gonads, are dual in nature, having both exocrine and endocrine functions.
- Such glands are called heterocrine glands or mixed glands.
- They have following main functions:
- Helps in maintaining homeostasis by regulating activities such as concentration of chemicals in body fluids and the metabolism of proteins, carbohydrates and lipids.
- Their secretions act in concert with the nervous system to help the body react to stress properly.
- They are major regulator of growth and development, including sexual development and reproduction.
- They are of various types. They are as follows.
1) Posterior pituitary (neurohypophysis)
| Hormones | Function of hormones | Means of control |
| Antidiuretic hormones (ADH, Vasopressin) | Increases water absorption from kidney tubules.
Raises blood pressure. |
Synthesized in hypothalamus, released from neurohypophysis.
|
| Oxytoxin | Stimulates contraction of pregnant uterus.
Milk ejection from breasts after childbirth. |
Synthesized in hypothalamus released from neurohypophysis. |
2) Anterior pituitary (Adenohypophysis)
| Growth hormone (GH, somatotropic hormone, STH) | Stimulates growth of bone, muscles.
Promotes protein synthesis, fat mobilization.
Slows carbohydrate metabolism.
|
Hypothalamic growth hormone releasing hormone (GHRH), growth hormone inhibiting hormone (GHIH). |
| Prolactin | Promotes breast development during pregnancy.
Milk production after child birth. |
Hypothalamic prolactin inhibiting hormone (PIH), prolactin releasing hormone (PRH). |
| Thyroid stimulating hormone (TSH) | Stimulates production and secretion of thyroid hormones. | Hypothalamic thyrotropin releasing hormone (TRH). |
| Adrenocorticotropic hormone (ACTH) | Stimulates production and secretion of adrenal cortex steroids. | Hypothalamic corticotropic releasing hormone (CRH). |
| Luteinizing hormone (LH) | In female, stimulates development of corpus luteum, release of oocyte, production of progesterone and oestrogen.
In male, stimulates secretion of testosterone, development of interstitial tissues of testis. |
Hypothalamic gonadotropin releasing hormone (GnRH). |
| Follicle stimulating hormone (FSH) | In female, stimulates growth of ovarian follicle, ovulation.
In male, stimulates sperm production. |
Hypothalamic gonadotropin releasing hormone (GnRH). |
| Melanocyte stimulating hormone (MSH) | Apparently involved with skin color (melanocytes) in combination with ACTH, role uncertain. | Uncertain. |
3) Thyroid gland
| Follicular cells | ||
| Thyroid hormones, thyroxin (T4), triiodothyronine (T3) | Increase metabolic rate, sensitivity of cardiovascular system to sympathetic nervous activity.
Affect maturation, homeostasis of skeletal muscles. |
Thyroid stimulating hormone (TSH) from adenohypophysis.
TSH regulated by thyrotropin releasing hormone (TRH) from brain. |
| Parafollicular cells | ||
| Calcitonin | Lowers blood calcium and phosphate levels.
Acts on bone, kidney and other cells. |
Blood calcium concentration. |
4) Parathyroid glands
| Parathormone (PTH, parathyroid hormone) | Increases blood calcium and decreases blood phosphate level.
Acts on bone, intestine, kidney and other cells.
|
Blood calcium concentration. |
5) Adrenal medulla
| Epinephrine (adrenaline) | Increase heart rate, blood pressure.
Regulates diameter of arterioles.
Stimulates contraction of smooth muscles.
Increases blood glucose concentration. |
Sympathetic nerous system. |
| Norepinephrine (noradrenaline) | Constricts arterioles.
Increases metabolic rate. |
Sympathetic nervous system |
6) Adrenal cortex
| Glucocorticoids, mainly cortisol, corticosterone, 11- deoxycorticosterone. | Affect metabolism of all nutrients.
Regulates blood glucose concentration.
Anti-inflammatories, affect growth.
Decrease effects of stress, ACTH secretion. |
Corticotropin releasing hormone (CRH) from hypothalamus
ACTH from adenohypophysis. |
| Mineralocorticoids, mainly aldosterone | Control sodium retention and potassium loss in kidney tubules. | Angiotensin II
Blood potassium concentration. |
| Gonadocorticoids (adrenal sex hormones, androgens) | Slight effect on ovaries and testes. | ACTH |
7) Pancreas
| Beta-cells in pancreatic islets | ||
| Insulin | Lowers blood glucose by facilitating glucose transport across plasma membranes.
Increasing glycogen storage.
Affects muscles, liver and adipose tissues. |
Blood glucose concentration. |
| Alpha cells in pancreatic islets | ||
| Glucagon | Increases blood glucose concentration. | Blood glucose concentration. |
8)Gonads
| Ovaries (follicle) | ||
| Estrogens | Affects development of sex organs and female characteristics.
Initiates development of ovarian follicle. |
Follicle stimulating hormone (FSH). |
| Ovaries (corpus luteum) | ||
| Progesterone , estrogens | Influence menstrual cycle.
Stimulates growth of uterine wall, maintains pregnancy. |
Luteinizing hormone (LH). |
| Placenta | ||
| Estrogens, progesterone, human chorionic gonadotropin (HCG) | Maintains pregnancy. | Uncertain. |
| Testes | ||
| Androgens, mainly testosterone | Affects development of sex organs and male characteristics.
Aids sperm production. |
Luteinizing hormone.
|
9) Thymus
| Thymosin alpha, thymosin B1 to B5, thymopoietin I and II, thymic humoral factor (THF), factor thymic serum (FTS), thymostimulin | Help develop T-cell in thymus.
Maintain T-cells in other lymphoid tissues.
Involved in development of some B- into antibody producing plasma cells. |
Uncertain. |
10)Digestive system
| Secretin | Stimulates release of pancreatic juice to neutralize stomach acid. | Acid in small intestine. |
| Gastrin | Produces digestive enzymes and hydrochloric acid in stomach. | Food entering stomach. |
| Cholecystokinin (CCK) | Stimulates release of pancreatic enzymes.
Gall bladder contraction. |
Food in duodenum. |
11) Heart
| Atriopeptin (atrial natriuretic factor, ANF). | Helps maintain balance of fluids, electrolytes.
Decreases blood pressure and volume. |
Salt concentration, blood pressure and blood volume. |
12) Kidney
| Renin | Acts upon plasma protein angiotensinogen. | Decrease blood pressure |
13) Pineal body
| Melatonin | Regulates developments of gonads.
Slows menstrual cycle in females. |
Uncertain. |
References:
i) https://www.webmd.com/diabetes/endocrine-system-facts
ii) https://training.seer.cancer.gov/anatomy/endocrine/glands/
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Shailesh Koirala
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