Adrenal/Suprarenal Gland

Adrenal/Suprarenal Gland

Pyramid shape pair of glands that sit on top of kidneys (suprarenal), about 3cm by 5cm
Adrenal medulla – inner part composed mostly of nervous tissue (part of sympathetic nervous system)
Adrenal cortex – outer part surrounded adrenal medulla; secretes many hormones, collectively known as corticosteroids; 3 layers – zona glomerulosa (outer); zona fasciculata (middle; thicker); zona reticularis (inner)

Adrenocorticol hormones:
Mineralocorticoids:
• function is to regulate electrolyte concentrations

Aldosterone:
• accounts for 95% of mineralocorticoids
• decreased secretion of sodium by acting on distal parts of kidney tubules  stimulates resorption of sodium ions
• also enhances sodium ion resorption from sweat, salvia and gastric juice
• secretion is stimulated by increasing levels of potassium, low levels of sodium, decreasing blood volume, decreasing blood pressure
• renin-angiotensin system is a major regulator of aldosterone release

Glucocorticoids:
• influence metabolism of most cells by increasing availability of glucose
• cortisol is the main glucocorticoid
• physiologic effects occur as low levels, whereas pharmacological effects occur at very high levels

Cortisol:
• stimulated by ACTH
• levels raise dramatically during stress – purpose is to protect certain metabolic functions at the expense of others
• promotes gluconeogenesis and reduced peripheral utilisation of glucose  hyperglycaemia; mobilise fats (lipolysis) to be used for energy metabolism; stimulate protein catabolism (provides amino acids for glucose synthesis); depresses inflammatory and immune responses
• in serum, 95% is bound to protein

Gonadocorticoids:
• mostly androgens (eg testosterone)
• stimulated by ACTH

Adrenal medullary hormones:
Catecholamines:
• epinephrine/adrenaline and norepinephrine/noradrenaline
• stimulated by preganglionic fibres of sympathetic nervous system
• increase heart and metabolic rates; increase blood pressure; vasoconstriction

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