The Adrenal Gland Flashcards
Where are the adrenal glands located?
On the superior pole of the kidney in the retroperitoneal space
What are the characteristics of the adrenal medulla?
The adrenal medulla is a modified sympathetic ganglion derived from neural crest tissue
What does the adrenal medulla secrete?
Catecholamines
Mainly epinephrine, norepinephrine and dopamine
What are the characteristics of the adrenal cortex?
Adrenal cortex is a true endocrine gland derived from mesoderm
What does the adrenal cortex secrete?
The adrenal cortex secretes three classes of steroid hormones:
Mineralocorticoids- involved in regulation of sodium and potassium
Glucocorticoids- involved in regulation of plasma glucose
Sex steroids
What are the three layers of the adrenal cortex, from superficial to deep?
Zona glomerulosa
Zona fasciculata
Zona reticularis
What does the zona glomerulosa secrete?
Aldosterone
What does the zona fasciculata secrete?
Glucocorticoids
What does the zona reticularis secrete?
Sex hormones
Briefly describe the synthetic pathways of the adrenal cortex
All steroid hormones are derived from cholesterol but different enzymes are found in different adrenal zones so different end products are formed
How does a deficit in 21-hydroxylase cause adrenal hyperplasia?
Lack of 21-hydroxylase inhibits synthesis of cortisol
This removes the negative feedback on ACTH and CRH release
Increased ACTH secretion is responsible for enlargement of adrenal glands
What kind of hormone is cortisol?
Glucocorticoid hormone
How do cortisol receptors react to cortisol?
Hormone receptor complex migrates to the nucleus, binding to DNA via a hormone-response element to alter gene expression, transcription and translation
Describe how plasma levels of cortisol fluctuate
Plasma levels of cortisol show a characteristic pattern with a marked circadian rhythm, preceded by a similar pattern of ACTH. Cortisol bursts last longer as half-life is much longer. Peak is ~6-9am, lowest level is ~midnight
Other fluctuations occur throughout the day due to effects of other stimuli related to stress
How does cortisol act on glucose metabolism?
Gluconeogenesis- cortisol stimulates formation of gluconeogenic enzymes in the liver
Proteolysis- cortisol stimulates the breakdown of muscle protein to provide gluconeogenic substrates for the liver
Lipolysis- cortisol stimulates lipolysis in adipose tissue which increases free fatty acids in the plasma and so creates an alternative fuel supply that allows blood glucose to be protected while also creating a substrate (glycerol) for gluconeogenesis
Decreases insulin sensitivity of muscles and adipose tissue
What are the non-glucocorticoid actions of cortisol?
Negative effect on calcium balance- decrease absorption from the gut, increases excretion at kidney resulting in net calcium loss
Impairment of mood and cognition- depression and impaired cognitive function linked to hypercortisolaemia
Permissive effects on norepinephrine- particularly in vascular smooth muscle
Suppression of the immune system- cortisol reduces circulating lymphocyte count, reduces antibody formation and inhibits the inflammatory response
What are the side effects of glucocorticoid therapy?
Increased severity and frequency of infection
Loss of percutaneous fat stores gives appearance of thinning skin and makes it more fragile
What kind of hormone is aldosterone?
Mineralocorticoid
What is the function of aldosterone?
Aldosterone acts on the distal tubule of the kidney to determine the levels of minerals reabsorbed/secreted.
Aldosterone increases the reabsorption of sodium ions and promotes the excretion of potassium ions
What are the effects of aldosterone secretion?
Increased aldosterone release stimulates sodium and water retention and potassium depletion, resulting in increased blood volume and pressure
The opposite is true of decreased aldosterone
What type of tissue is the adrenal medulla?
Modified sympathetic ganglia rather than true endocrine tissue. Preganglionic sympathetic fibres terminate on specialised postganglionic cells in the adrenal medulla, which do not have axons and instead release their neurohormones directly into the blood
