Adrenal gland (plus some extra hormones)

Where are the adrenal glands?

They are paired, lying craniomedial to the kidneys. They are beneath the peritoneum

What are the two areas of the adrenal gland?

The medulla and the cortex

What is produced by the adrenal medulla?

Catecholamines (adrenaline, noradrenaline and dopamine)

What are the three layers of the adrenal cortex?

- Zona reticularis (innermost)

- Zona fasciculata

- Zona glomerulosa (outermost)

What does the zona reticularis produce?

Androgens (e.g. progesterone, testosterone) and oestrogens

What does the zona fasciculata produce?

Glucocorticoids (e.g. cortisol)

What does the zona glomerulosa produce?

Mineralocorticoids (e.g. aldosterone)

What is noradrenaline synthesised from?

Dopamine

What are the major functions of catecholamines?

- Increase cardiac output

- Redistribution of blood to skeletal muscle

- Glycogenolysis and gluconeogenesis (to increase plasma glucose)

- Increase breakdown of triglycerides (to increase plasma fatty acids)

Why aren't steroid hormones stored locally?

They are very potent, so are produced on demand and very tightly regulated

Why are steroid hormones released with a plasma protein escort?

They are lipid soluble, so would easily enter the wrong tissue. They instead bind to a plasma protein to safely reach their destination before unbinding to enter it

What is the function of mineralocorticoids?

Regulate the concentrations of Na+ and K+ in the blood (so affect blood pressure)

Which proteins are mineralocorticoids bound to in the blood?

- Corticosteroid-binding globulin (CBG)

- Albumin

Where are mineralocorticoids and glucocorticoids inactivated?

In the liver

What is the major example of a mineralocorticoid?

Aldosterone

What is the half life of aldosterone?

20 mins

Describe the variation in secretion of glucocorticoids?

They have a circadian variation (vary through the day). Levels are higher in the morning and lower in the evening

What are the roles of glucocorticoids?

Catabolic steroids:

- Increase lipolysis

- Increase breakdown of skeletal muscle protein (provides substrates for gluconeogenesis)

Glucose metabolism:

- Promote gluconeogenesis in the liver

- Decrease glucose uptake by tissues (to divert glucose to the brain)

- Work with catecholamines to prepare for actions under stress

- Counteracts insulin

- Cause a negative calcium balance (due to effects on the kidney, bone and GI tract)

What is the major example of a glucocorticocorticoid?

Cortisol

What is the half life of cortisol?

70 mins (longer than aldosterone as it is more protein bound)

What is the role of cortisol?

- Part of the stress response, often released at the same time as adrenaline

- Affects carbohydrate, fat and protein metabolism

- Slows digestion

- Increased HR and RR

- Stimulates glycogenolysis

- Low levels are anti-inflammatory, high levels cause immunosuppression

How are glucocorticoids regulated?

- Released in response to stress

- Controlled by negative feedback loop (complex as it involves the hypothalamus (ACTHRH), the anterior pituitary gland (ACTH) and the adrenal gland. Loop explained in more detail in pituitary flashcards)

What are the functions of prolactin?

- Stimulate growth and differentiation of mammary tissue

- Stimulate milk production after parturition

- Important in maternal behaviour (including bonding)

- Increases prior to brooding in birds

How is prolactin regulated?

- Not just one thing which causes release of prolactin

- TRH (produced by hypothalamus) stimulates secretion

- Dopamine (produced by hypothalamus) inhibits secretion

- Suckling increases secretion

- Oestradiol increases secretion

Why do dairy cows continue to produce milk when no longer rearing a calf?

Being milked mimics suckling, so prolactin continues to be secreted. This causes more milk to be produced

What is melatonin involved with?

Seasonality in reproduction (production dependent on photoperiod (length of light in the day))

Where is leptin produced?

Adipose tissue

What family of hormone is leptin?

Adipokines

What is the role of leptin?

Plays a key role in regulating energy intake and expenditure, including appetite and hunger, metabolism and behaviour

How are leptin and triglyceride storage linked?

More triglycerides stored in adipocytes = more leptin produced