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Endocrine > Adrenal gland > Flashcards

Adrenal gland Flashcards

1
Q

stress definition

A

A change that disturbs or threatens to disturb homeostasis- for example physical trauma, infection, intense heat or cold, starvation, surgery, severe blood loss, pain and dehydration, anxiety and depression

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2
Q

How does optimal performance vary with stress?

A

low stress, an individual is often inactive and laidback

medium stress- peak, best optimal performance

between medium and high appears the stress zone- an individual is anxious

high stress- panic, anger and violence- overload

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3
Q

Adrenal gland definition

A

Suprarenal endocrine gland that produce a variety of hormones, including adrenaline and steroids aldosterone and cortisol

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4
Q

Location of adrenal glands

A

Two, each found above the kidneys

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5
Q

vasculature of adrenal glands

A

adrenal arteries branch from the renal and inferior phrenic arteries

left adrenal vein drains to renal vein

right adrenal vein drains into inferior vena cava

small arterioles from an arterial plexus beneath the capsule surrounding the adrenal gland and then enter a sinusoidal system that penetrates the cortex and the medulla, draining into a single central adrenal vein in each gland

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6
Q

Two components of the adrenal glands + brief function

A

inner medulla- secretes catecholamines noradrenaline and adrenaline

outer cortex- secretes steroid hormones

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7
Q

Explain the embryology of the adrenal glands

A

adrenal cortex and adrenal medulla develop from different origins

cortex- develops from mesoderm close to the mesonephros

medulla- develops from neural crest tissue

adrenal gland is identifiable as a separate organ at 2 months gestation and is composed of a fetal zone and definitive zone

‘fetal zone’ is prominent in the fetus but regresses after birth

The fetal zone produces androgens which the placenta aromatises to oestrogens

the definitive zone is similar to the adult adrenal cortex

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8
Q

structure of adrenal gland

A

inner adrenal medulla formed of groups of chromaffin cells packed with catecholamine granules which store large quantities of adrenaline and noradrenaline

adrenal cortex is formed of sheets of cells surrounded by capillaries and arranged in three zones

zona glomerulosa: outer that produces aldosterone

zona fasciculata: middle that makes cortistol

zona reticularis- inner that makes small amounts of androgens

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9
Q

innervation of kidney

A

principally to the medulla- innervated by thoracic preganglionic sympathetic nerves which release ACh that act upon nicotinic receptors

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10
Q

Length of time of adrenaline release during stress

A

seconds

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11
Q

Length of time of adrenaline half life during stress

A

10 seconds

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12
Q

Length of time of adrenaline action during stress

A

seconds

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13
Q

How much adrenaline is depleted?

A

only a small fraction

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14
Q

synthesis of adrenaline

A

In the cytoplasm of chromaffiin cells tyrosine is converted into L DOPA by tyrosine hydroxylase

DOPA to dopamine by DOPA carboxylase

dopamine is then pumped into granules and is converted into noradrenaline by dopamine beta hydroxylase

noradrenaline is then stored or pumped out of the granule for conversion into adrenaline by phenyl-N-methyl transferase in the cytoplasm

adrenaline is then pumped into granules for storage and release

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15
Q

In a broad way, increased adrenaline secretion causes what changes

A

increase the circulation

increase the availability of energy substrates

decreases non essential activities

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16
Q

disorders of adrenal medulla function

A

phaeochromocytoma- tumour arising from chromaffin cells which leads to the uncontrolled secretion of adrenaline and noadrenaline

symptoms- hypertension and tachycardia

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17
Q

How much adrenaline is secreted relative to noradrenaline?

A

adrenaline 80%

noradrenaline 20%

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18
Q

3 main hormones the cortex produces and

A

cortisol- glucocorticoid

aldosterone- mineralcorticoid

androgens from cholesterol

19
Q

synthesis of adrenal steroid hormone

A
  1. cholesterol is stored in lipid droplets as cholesterol ester in adrenal cortex cells and is mobilised by adrenocorticotropic hormone
  2. the rate limiting step is the cleavage of the side chain of cholesterol by cytochrome P450 side chain cleave enzyme to yield pregnenolone
  3. enzymes which convert pregnenolone to glucocorticoids and mineralcorticoids via intermediates are found in the mitochondria and smooth endoplasmic reticulum, therefore these organelles are prominent in the cortex cells
20
Q

plasma transport of cortisol

A

binds to cortisol-binding globulin in plasma with high affinity and to albumin with low affinity

21
Q

plasma transport of aldosterone

A

no high affinity binding protein is present in plasma, so weakling binds to albumin and has a shorter half life than cortisol as a result

22
Q

corticosteroid definition

A

class of steroid hormones that are produced in the adrenal cortex of vertebrates

23
Q

glucocorticoid definition

A

class of corticosteroids that are involved in the regulation of glucose metabolism, hence the name

24
Q

mineralocorticoid definition

A

class of corticosteroid that are involved in the retention of sodium, a mineral, hence the name

25
Q

cortisol receptors

A

glucocorticoid receptors that are present in almost all cells

located in the cytoplasm of cells and migrate to the nucleus to regulate gene transcription when cortisol binds

26
Q

metabolism of cortisol explained

A

cortisol is converted in the liver to the relatively inactive metabolite, cortisone by 11B-hydroxysteroid dehydrogenase

27
Q

control of cortisol output explained

A
  1. hypothalamus releases corticotrophin releasing factor in response to stress
  2. CRF acts on the anterior pituitary corticotrophis to stimulate adrenocorticotrophic hormone production and release
  3. ACTH is cleaved from the prohormone POMC and stimulates the zona fasciculata cells via cyclic AMP to stimulate cortisol production
28
Q

actions of cortisol

A

provides protection of the body in prolonged stress- primarily to preserve glucose for the brain

exerts widespread actions on many tissues

cortisol stimulates the metabolism of:

  • carbohydrates- stimulates glucose production- opposite effect to insulin
  • lipids- stimulates lipolysis and ketogenesis- results in redistribution of fat to trunk if fatty acids are in excess
  • proteins- stimulates gluconeogenesis

cardiovascular effects

  • maintains the circulation via increased myocardial contraction, increases vascular tone
  • maintains plasma volume by preventing increased vascular permeability

ion control
- promotes sodium retension and potassium excretion

haemopoiesis stimulation

immune system

  • immunosuppressive actions
  • inhibits leukocyte translocation from blood to sites of tissue damage or infection
  • stimulates lymphocyte destruction
  • glucocorticoid selective drugs used therapeutically to treat inflammatory diseases such as asthma and eczema
29
Q

Addison’s disease explained

A

cortisol insufficiency where the adrenal glands do not produce enough steroid hormones

darkening of the skin may occur due to high levels of circulating melanocyte stimulating hormone

most often autoimmune

secondary adrenal insufficiency is caused by not enough ACTH produced by the anterior pituitary

30
Q

Cushing’s disease explained

A

coritsol excess

characterised by the increased secretion of ACTH from the anterior pituitary

often due to a functioning pituitary adenoma

glaucoma often happens- tumour presses on optic nerve

weight gain, hypotension, poor memory loss, irritability, moon face and red stretch marks

31
Q

aldosterone receptors explained

A

mineralcorticoid receptors are present in the nuclei of only a few cell types:

kidney collecting tubule epithelia, salivary and sweat glands

cortisol also binds to the mineralcorticoid receptors therefore in aldosterone targets, cortisol is deactivated to prevent unwanted cortisol activation

32
Q

actions of aldosterone

A

in kidney
regulates ion transport in the collecting tubules in order to stimulate reabsorption of sodium in exchange for secretion of potassium, hydrogen and ammonium ions

in salivary and sweat glands, aldosterone regulates ion transport to retain sodium

33
Q

why is there a 2h lag in response to aldosterone?

A

MR effects are via stimulating transcription of the Na/K ATPase protein

34
Q

control of aldosterone output

A

stimulated by the renin-angiotensin system, which in turn is stimulated by low plasma sodium or low renal blood pressure

low plasma sodium and low blood pressure stimulates renin release which acts in the lungs to stimulate the conversion of angiotensin I to angiotensin II by activating angiotensin converting enzyme ACE.

AII stimulates output of aldosterone from the zona glomerulosa of the adrenal cortex

35
Q

angiotensin II function

A

causes arteriolar constriction and drinking in response to thirst

36
Q

examples of abnormal plasma concentrations of aldosterone

A

hypoaldosteronism- in adrenal failure, leads to sodium loss, low blood volume and low blood pressure

hyperaldosteronism- Conn’s syndrome, results in excess sodium retention, water retention and an increase in blood pressure

37
Q

treatment for hyperaldosteronism

A

spironolactone - an aldosterone antagonist used as an antihypertensive

38
Q

example of a weak androgen

A

DHEA- dehydroepiandrosterone

39
Q

DHEA action

A

stimulates axillary/pubic hair development at puberty and libido

40
Q

What is DHEA release stimulated by?

A

Adrenocorticotropic hormone

41
Q

How much DHEA is released?

A

very little

42
Q

disease associated with androgens

A

congenital adrenal hyperplasia

inability to produce adrenal steroids

an inherited disorder arising from mutations in enzymes or steroid synthesis, such as 21-hydroxylase

leads to masculination of females and precocious puberty

43
Q

What is Nelson’s syndrome?

A

Addison’s disease, due to the surgical removal of the adrenals

44
Q

what clears the corticosteroids?

A

kidney filters free steroid hormones but reabsorbs 90%

liver converts steroid hormones to hydrophilic metabolites by hydroxylation and conjugation reactions- can cause liver damage such as cirrhosis in alcoholics causing cortisol build up.

Endocrine (5 decks)

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