The Adrenal Gland Flashcards
Where are the adrenal glands found?
Superior pole of the kidney in the retroperitoneal space - each weighing 4g
What does the adrenal gland consist of?
Two separate endocrine glands:
• Adrenal medulla
• Adrenal cortex
Both play a role in body’s response to stress
What is the adrenal medulla and its function?
It is a modified sympathetic ganglion derived from neural crest tissue.
Secretes catecholamines:
• Mainly epinephrine (adrenaline)
• Norepinephrine
• Dopamine
What is the adrenal cortex and its function?
True endocrine gland derived from mesoderm and secretes three classes of steroid hormones:
• Mineralocorticoids i.e. aldosterone
• Glucocorticoids i.e. cortisol
• Sex steroids i.e. testosterone
What is the function of mineralocorticoids (i.e. aldosterone)?
Regulation of Na and K
What is the function of glucocorticoids (i.e. cortisol)?
Maintaining plasma glucose
Describe the structure of the adrenal gland
- Cortex on the outside arranged in three concentric zones which produce different hormones
- Medulla on the inside
What are the three concentric zones of the cortex?
Outside in:
• Zona glomerulosa –> Aldosterone
• Zona fasciculata –> Glucocorticoids
• Zona reticularis –> Sex hormones
Why do different layers of the adrenal cortex produce different hormones?
All steroid hormones are derived from cholesterol, but different enzymes are found in different adrenal zones, resulting in different end products e.g. enzymes needed to make aldosterone are found only in the zona glomerulosa
What hormone does the zona glomerulosa produce?
Aldosterone
What hormone does the zona fasciculata produce?
Glucocorticoids
What hormone does the zona reticularis produce?
Sex hormone
What is the intermediate hormone formed in the ZG when producing aldosterone?
Progesterone (+ 21-hydroxylase) –> corticosterone –> aldosterone
What enzyme catalyses the reaction that forms cortisol in the ZF?
21-hydroxylase
What is the precursor of estrone and what enzyme catalyses it’s conversion in the ZR?
Androstenedione (from progesterone) (+aromatase) –> estrone
What is the precursor of estradiol and what enzyme catalyses it’s conversion in the ZR?
Testosterone (from androstenedione) (+aromatase) –> estradiol
What does dihydrotestosterone (DHT) form from?
Testosterone
What can DHEA form?
Androstenedione (in the ZR) which will form sex hormones
Name a condition caused by defects in 21-hydroxylase?
Congenital adrenal hyperplasia
Describe congenital adrenal hyperplasia
Deficiency of aldosterone and cortisol and associated disruption of salt and glucose balance.
Androgen biosynthesis is unaffected so accumulating steroid precursors are channelled into excessive adrenal androgen production.
Why is malformed and ambiguous genitalia a clinical features of congenital adrenal hyperplasia?
Due to excess production of androgen, as no progesterone is catalysed by 21-hydroxylase.
This causes excess oestrogen, progesterone and testosterone
Name the steps in the hypothalamic-pituitary-adrenal pathway
Hypothalamus
- > CRH
- > Anterior pituitary
- > ACTH (short loops neg. feedback on CRH)
- > Adrenal cortex
- > Cortisol (short NF on ACTH and long NF on CRH)
- > Target tissue for response