Urinary

The anti-diuretic hormone (ADH) helps to regulate fluid balance in the body.

Revision summary of the endocrine system 251

Key words associated with the endocrine system

ductless glands

dwarfism

pancreas

\

hormone

diabetes insipidus

insulin

pituitary

melanocyte-stimulating

hypoglycaemia

thyroid

hormone (MSH)

diabetes mellitus

parathyroids

pineal gland

testosterone

adrenals

melatonin

oestrogen

islets of Langerhans

triodothyronine (T3)

progesterone

ovaries

thyroxine (T4)

virilism

testes

calcitonin

hirsutism

growth hormone

thyrotoxicosis/Graves'

amenorrhea

thyroid-stimulating hormone

disease

gynaecomastia

(TSH)

cretinism

polycystic ovary syndrome

adrenocorticotrophic

myxoedema

puberty

h ormon e (ACTH )

tetany

menstrual cycle

gonadotrophic hormones

glucocorticoids

ovarian follicles

(FSH and LH)

mineral corticoids

ovum

prolactin

sex corticoids

fallopian tubes

antidiuretic hormone (ADH)

Cushing's syndrome

fertilisation

oxytocin

Addison's disease

pregnancy

gigantism

adrenaline

trimester

-

noradrenaline

menopause

Revision summary of the endocrine system

• The endocrine system consists of ductless glands that secrete hormones into the bloodstream.

• Endocrine glands are concerned with the regulation of metabolic processes.

• A hormone is a chemical regulator secreted by an endocrine gland into the bloodstream and has the power to influence the activity of other organs.

• The main endocrine glands are the pituitary (attached to base of brain), thyroid (neck), parathyroids (posterior to the thyroid glands), adrenals (top of kidneys), islets of Langerhans (in the pancreas), ovaries (in the female) and testes (in the male).

• The principal hormones secreted by the anterior lobe of the pituitary include the growth hormone, thyroid-stimulating hormone (TSH), adrenocorticotrophic hormone (ACTH), gonadotrophic hormones (FSH and LH), prolactin and melanocyte-stimulating hormone (MSH).

• The growth hormone controls the growth of long bone and muscle.

• Thyroid-stimulating hormone (TSH) controls the growth and activity of the thyroid gland.

• Adrenocorticotrophic hormone (ACTH) controls the growth and hormonal output of the adrenal cortex.

• Gonadotrophic hormones (FSH and LH) control the development and growth of the ovaries and testes.

• Prolactin stimulates the secretion of milk from the breasts following birth.

• Melanocyte-stimulating hormone (MSH) stimulates the production of melanin in the basal cell layer of the skin.

• Hypersecretion of the growth hormone from the pituitary gland can lead to gigantism in childhood and acromegaly in adulthood.

• Hyposecretion of the growth hormone from the pituitary gland during childhood leads to dwarfism.

• The posterior lobe of the pituitary secretes antidiuretic hormone (ADH) and oxytocin.

• Hyposecretion of the anti-diuretic hormone (ADH) by the posterior lobe of the pituitary can lead to diabetes insipidus.

• The pineal gland is attached by a stalk in the central part of the brain and secretes a hormone called melatonin which is thought to regulate circadian rhythms and influence mood.

• The thyroid gland's principal secretions are triodothyronine (T3) and thyroxine (T4) which regulate metabolism and influence growth and development.

• The thyroid gland also secretes calcitonin which controls the levels of calcium in the blood.

• Hypersecretion of the thyroid hormones leads to a condition called thryrotoxicosis or Graves' disease.

• Hyposecretion of the thyroid hormones leads to cretinism in childhood and myxoedema in adulthood.

• The parathyroid glands help regulate calcium metabolism.

• Hypersecretion of parathormone can lead to renal stones, kidney failure, softening of the bones, and tumours.

• Hyposecretion of parathormone can lead to a condition called tetany.

• The adrenal glands have two parts — an outer cortex and an inner medulla.

• The principal hormones secreted by the adrenal cortex include glucocorticoids, mineral corticoids and sex corticoids.

• Glucocorticoids influence the metabolism of protein, carbohydrates and utilisation of fats.

• Mineral corticoids are concerned with maintaining water and electrolyte balance.

• Sex corticoids control the development of the secondary sex characteristics and the function of the reproductive organs.

• Hypersecretion of the mineral corticoids can lead to kidney failure, high blood pressure and an excess of potassium in the blood.

• Hypersecretion of the gluco corticoids can lead to a condition called Cushing's syndrome.

• Hypersecretion of the sex corticoids can lead to hirsutism and amenorrhea in the female and muscle atrophy and development of breasts in the male.

• Hyposecretion of the corticosteroid hormones can lead to a condition called Addison's disease.

• The principal hormones secreted by the adrenal medulla include adrenaline and noradrenaline.

• Adrenaline and noradrenaline are under the control of the sympathetic nervous system and are released at times of stress.

• The pancreas is a dual organ as it has dual function — exocrine and endocrine.

• The exocrine function is the secretion of pancreatic juice to assist with digestion.

• The endocrine function is the secretion of insulin from the islets of Langerhans cells which helps regulate blood sugar levels.

• Hypersecretion can lead to hypoglycaemia.

• Hyposecretion can lead to a condition called diabetes mellitus.

• The testes (in the male) have two functions — the secretion of testosterone and the production of sperm.

• The ovaries (in the female) have two functions — the production of ova and production of the hormones oestrogen and progesterone.

• Hypersecretion of the hormone testosterone in women can lead to virilism, hirsutism and amenorrhea.

• Hypersecretion of oestrogen and progesterone in the male can lead to gynaecomastia.

• Hyposecretion of oestrogen and progesterone in the female can lead to polycystic ovary syndrome.

• Puberty is a natural glandular change due to stimulation of the ovaries and testes by the pituitary gonadotrophic hormones.

• Starting at puberty, the female reproductive system undergoes a regular sequence of monthly events, known as the menstrual cycle.

• The ovaries undergo cyclical changes, in which a certain number of ovarian follicles develop. When one ovum completes the development process, it is released into one of the fallopian tubes. If fertilisation does not occur, the developed ovum disintegrates and a new cycle begins.

• The menstrual cycle lasts approximately 28 days, although it can be longer or shorter than this.

• Pregnancy takes approximately nine calendar months and is divided into three trimesters.

• During the first trimester all of the body systems develop.

• The second trimester consists of rapid foetal growth and the completion of systemic development.

• The third trimester is mostly a weight-gaining and maturing process, preparing the baby for life outside of the womb.

• In the menopause, the ovaries cease responding to the follicle-stimulating hormone (FSH), resulting in lower levels of oestrogen and progesterone secretion.

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