Adrenal Glands

adrenal gland location

• sit on top of kidneys.

Blood supply to the adrenals

• Superior adrenal arterty

• middle adrenal artery

• inferior adrenal artery

Layers of the adrenal gland

• capsule on the outside

• Adrenal cortex ‘looks like thick skin’

• Adrenal Medulla in the centre.

Layers of the adrenal cortex

• zona glomerulosa

• zona faschiculata

• zona reticularis

Zona glomerulosa function

• secretes aldosterone

• Mineral corticoid → causes uptake of sodium in the kidney

• water follows the minerals → when there is more sodium in the blood stream, there will also be more water, meaning higher blood pressure.

Angiotensin II, aldosterone and filtration

1. Stimulus: low blood pessure or low blood volume. When blood pressure drops, kidneys respond.

2. renin release: kidneys release renin into the bloodstream → renin converts angiotensinogen (from the liver) into angiotensin I.

3. Angintensin I to angiotensin II: Angiotensin I travels to the lungs, where ACE( angiotensin converging enzyme) converts it into angiotensin II → the active form.

4. Effects of angiotensin II: vasoconstriction → narrowing of blood vessels → increase in blood pressure. Stimulates aldosterone release.

5. Aldosterone action: Acts on the kidneys to increase reabsorbtion of sodium and chloride since water follows sodium by osmosis.

6. result → increase in blood volume, therefore, increase in blood pressure.

overall → feedback loop that maintains blood pressure and fluid balance by constricting blood vessels and retaining salt and water in the kidneys.

Zona fasiculata

• secretes cortisol → glucocorticoid (changes glucose concentration and is a cortical steroid).

• Causes glucogemesis from lipolysis and protein catabolism so blood glucose increase and the immume system is inhibited.

• 90% of the hormones produced by the adrenal cortex is cortisol.

Control of corticosterioids

• corticotropin releasing hormone causes adrenal corticotropic hormone (ACTH or corticotropin, a tropic hormone) to be secreted which then causes cortisol production in the adrenal cortex.

• This causes:

  • Glucogenesis from protein and fat catabolism, heatic glucose secretion and immuno suppression.

  • These act as a negative feedback loop to downregulate cortocotripin releasing hormone.

Zona reticularis

• secretes androgens → main products are the androgen androstenedione and the androgen precursos (DHEA)

• Androstendione promotes growth and development

• DHEA is converted into other androgens (male sex steroids).

Disease of the adrenal cortex

• all due to over / underproduction of adrenal hormones

• Good to know image →

Hypercortisolemia (cushings syndrome)

• cortisol and its synthetic analogs have a wide range of effects that lead to a cushoing syndrome.

  • Cortical steroids increase the rate of

    • glucogenesis

    • glucose secretion by the liver

    • breakdown of fat and protain

      • this is to supply material for glucogenesis.

    • decreased glucose uptake and use by peripheral tissues:

      • With extremely high amounts of cortisol, or a synthetic cortical steroid, lack of tissue repair can lead to striae.

    • Large doses of cortical steroids cause hyperglycemia and the breakdown of muscle.

    • Fat gets redistributed

      • Abdomen, posterior nck

Cushings disease

• due to an adenoma that produces ACTH, leading to an ectremely high cortisol.

Congenital adrenal hypoplasia (CAH)

• inability to produce cortisol / aldosterone, leading to an overproduction of androgens in the fetus.

  • Lack of negative feedback from cortisol means precursoes are made in huge amounts and make more andrpgens.

  • overproduction of androgens causes virilxation of the XY fetus, causing them to be intersex.

Addison disease

• addison disease (primary adrenal insufficiency) occurs due to an autoimmune attack on the adrenal cortex, so that cortisol cannot be made.

  • aldosterone and androgen production would also be decreased.

  • with the destruction of so many cortical steroids, you get the following symptomr:

    • weight loss, dehydration, hypotensionl, hyponateamia, hyperkalemia, hypoglycemia as a result.

Adrenal medulla

• secretes chatecholamines

• epinepherine and norepinepherine → made by chromaffin cells.

• epinepherine and norepinepherine stimulate the sympathetic nervous system (fight, flight, fight).

innervation of the adrenal medulla

• stictly from sympsathetic branch

• when SNS nerves synapse on the chromaffin cells which release E and NE.

• The adrenal medulla is a modified sympathetic ganglion.

Stress and the adrenal

• sympathetic neural stimulus → epinepherine and norepinepherine are released by the adrenal medulla.

• Stimulation by ACTH causes cortisol and other cortical hormones to be released from the adrenal cortex.