Physiology 6 - Adrenal Flashcards
Where are the adrenal glands found?
On the superior pole of the kidneys at roughly T12.
How are the adrenal glands peritonised?
Retroperitoneal just like the kidneys
Describe the arterial blood supply of the adrenal gland?
Aorta:
- > Inf Phrenic Art -> Sup suprarenal Art
- > Middle Suprarenal Art
- > Renal Artery -> Inf Suprarenal Art
DEscribe the venous drainage of the adrenal gland?
Different on each side
Left adrenal veins –> Left renal vein
Right Adrenal veins –> IVC
Describe the structure of the adrenal gland?
Adrenal Cortex: (Steroid hormones)
Zona Glomerulosa
Zona Fasciculata
Zona Reticularis
Then the adrenal medulla in the middle
The whole thing is surrounded by a fibrous capsule
What kind of tissue makes up the adrenal cortex vs medulla?
Adrenal cortex is a true endocrine gland derived from mesoderm
Adrenal Medulla is a modified symp. ganglion made of neural crest tissue
What is secreted the zona glomerulosa?
Outer section of Adrenal cortex secreates Mineralocorticoids e.g. Aldosterone
What is secreted by the zona fasciculata?
Middle section of adrenal cortex secretes glucocorticoids e.g. Cortisol
What does the Zona reticularis do?
Inner layer of adrenal cortex secretes sex steroids e.g. testosterone
(most sex steroids are produced in the gonads)
What is produced in the adrenal medulla?
Catecholamines (tyrosine derived, water soluble amines)
E.g. Epinephrine, Norepinephrine and dopamine
The adrenal medulla has an unusual autonomic nerve supply, how so?
Pre-ganglionic fibres synapse to cells in the adrenal medulla.
Instead of having post-synaptic fibres, the medulla secretes its neurohormones directly into the blood
Briefly describe the pathway of steroid synthesis in the adrenal cortex?
All start with cholesterol.
Different enzymes are found in each layer, sending them down different branches and so producing the different hormones.
The most important is 21-hydroxylase, found in the pathway for producing aldosterone and cortisol.
remind yourself of the HPA axis (Specifically for glucocorticoids) and the hormones involved?
Hypothalamus = Corticotrophin Releasing Hormone (CRH)
Ant Pituitary = Adrenocorticotrophic Hormone (ACTH)
Zona Fasciculata = Cortisol
As a steroid hormone, describe how Cortisol travels the blood?
95% of cortisol is bound to Cortisol Binding Globulin
Describe the -ve feedback control of Cortisol
Cortisol has a -ve feedback on CRH & ACTH
ACTH has a -ve feedback on CRH
How does cortisol work?
It bind to cytoplasmic glucorticoid receptors (found in all nucleated cells)
- > Hormone-receptor complex migrates to nucleus
- > Binds to DNA
- > Alters gene expression, transcription & translation
Does cortisol secretion follow any pattern or rhythm?
Yes a Marked Circadian rhythm!
Cortisol peaks at 6-9am and has its nadir at 12pm
Preceded by a similar ACTH rhythm
Smaller fluctuations occur throughout the day due to stress stimuli
What are cortisols affects on glucose?
- Permissive to GLucagon
- Increased Gluconeogenesis (stimulates gluconeogenic enzyme formation)
- Increased Proteolysis
- Increased Lipolysis
- Decreases Insulin sensitivity
What are cortisols affect on calcium?
- Decreases gut absorption
- Increases Kidney excretion
- Increases bone resorption
What are cortisols affects on the brain?
Excess cortisol linked to depression and impaired cognitive function
What are cortisols affect on norepinephrine?
Permissive to norepinephrine
Specifically in regards to vasoconstriction
What are cortisols effects on immunity?
Depresses immunity by:
- Reducing lymphocyte count
- Reducing Antibody formation
- Reducing inflammatory response
Summary of cortisols affects?
- Increases plasma glucose
- Decreases plasma Calcium
- Increases bone resorption
- Permissive to vasoconstrictive action of norepinephrine
- Supresses Immunity
In what way is cortisol particularly essential for life?
Its permissive effect on glucagon is most important.
Without cortisol glucagon can’t sufficiently respond to hypoglycaemia and your brain would die.
How is cortisol related to diabetes?
Cortisol is glucose counter-regulatory, meaning it raises blood glucose.
Therefore excess cortisol is considered diabetogenic
What does it mean to be a mineralocorticoid?
A hormones that effects resorption/excretion of minerals
What are the effects of aldosterone?
Increases Na+ resorption
Incerases K+ Excretion
What triggers secretion of aldosterone?
The Renin-angiotensin-Aldosterone system (RAAS)
Part of the long term control of blood pressure
What would happen with excess or insufficient aldosterone?
Excess aldosterone –> Excess Na+ –> Increased blood volume & hypertension
Insufficient aldosterone –> Insufficient Na+ –> DIminished blood volume and hypotension
