The endocrine system controls growth and development during childhood, regulation of bodily functions in adulthood, and the reproductive process.
The endocrine system is important for the control and regulation of all the major functions and processes of the body:
Hormones interact to maintain the above functions and help to regulate our responses to disease, our ability to reproduce and even influence our relationships and behaviour (such as mother:child bonding).
As can be seen, many of the hormones act on tissues and organs at several sites throughout the body. The target cells in these tissues or organs contain specialised structures (receptors) to which only a specific hormone can bind. The response that occurs in the cell will depend on the receptor and cell type, and the effects of other hormones to which that cell may also be exposed. Also, a hormone that stimulates the activity of one cell type may suppress that of a different cell type.
A similar, but not identical, endocrine system to that of humans is found in nearly all vertebrates including other mammals, fish, amphibians, reptiles and birds, although the precise structures and roles of the various organs and hormones differ between different groups, particularly in relation to the different life cycle and development stages in different species. Invertebrates such as molluscs, crustacea and insects also have endocrine systems that control a similar range of body functions although these have evolved along markedly different lines to those of vertebrates.
The main glands and hormones of mammals are:
|Gland||Hormones||Target organs||Main actions|
|Hypothalamus (specialised region of the brain)||Releasing or inhibiting hormones (e.g. growth hormone releasing hormone (GHRH), somatostatin, corticotropin releasing hormone (CRH), arginine vasopressin (AVP), gonadotropin releasing hormone (GnRH) & thyrotropin releasing hormone (TRH)||Anterior pituitary||Controls production/release of other hormones|
|Antidiuretic hormone (ADH)||Kidney||Controls water loss|
|Oxytocin (OT) -released via the posterior pituitary (neurohypothysis)||Uterus, Mammary glands|
|Anterior pituitary [adenohypophysis]||Luteinizing hormone (LH)||Gonads||Control of ovarian oestrus cycle & Leydig cells in testis Control of ovarian oestrus cycle & Sertoli cells in testis Promotes milk production|
|Follicle stimulating hormone (FSH)||Gonads|
|Thyroid stimulating hormone (TSH)||Thyroid glands||Stimulates T4 production/release Affects growth and metabolism|
|Growth hormone (GH)||Generalised|
|Adrenocorticotropic hormone (ACTH)||Adrenal glands||Stimulates adrenal cortex|
|Thyroid||Thyroxine (T4) [active form is tri-iodothyronine T3]||Many tissues||Control of general metabolic rate, also important for development and reproductive functions|
|Adrenal [suprarenal] cortex||Glucocorticoids (e.g. cortisol & corticosterone||Many tissues||Diverse effects on inflammation and protein synthesis|
|Mineralocorticoids (e.g. aldosterone)||Many tissues||Salt balance|
|Adrenal [suprarenal] medulla||Adrenaline (Epinephrine)||Many tissues||Glycogenolysis, lipid mobilisation, smooth muscle contraction, cardiac function|
|Noradrenaline (Norepinephrine)||Many tissues||Lipid mobilisation, arteriole contraction|
|Pancreas||Insulin||Many tissues including liver, adipose tissue & muscle||Facilitates utilisation of glucose by cells & prevents excessive glycogen breakdown in liver & muscle|
|Glucagon||Many tissues including liver, adipose tissue & muscle||Prevents hypoglycaemia through action on carbohydrate, fat & protein metabolism|
|Gonads||Sex steroids (e.g. oestradiol, testosterone, progesterone)||Brain, gonads, accessory sex organs||Sexual development & maintainance of reproductive function and behaviour|