The Adrenal Gland

Question 1

What are the main groups of steroid hormones according to their physiological effects and the endocrine cell types that secrete them?

Answer 1

1. Mineralocorticoids – involved in regulation of Na+ and K+ and produced within the ‘zona glomerulosa’
2. Glucocorticoids – involved in regulation of blood glucose and produced in the ‘zona fasciculata’
3. Sex steroids

Question 2

What are the main pathways and cellular compartments involved in the synthesis of steroid hormones?

Answer 2

All steroid hormones are derived from cholesterol

The different types of hormones produced are due to different enzymes being present in the different zones of the adrenal cortex, i.e. glomerulosa, fasciculata, reticularis.

E.g. enzymes needed to make aldosterone (21-hydroxylase) are only found within the zona glomerulosa.

Enzymes needed to make cortisol (21-hydroxylase) are found in zona fasciculata.

Zona reticularis produces the sex hormones

Question 3

What is the structure of the adrenal gland, highlighting its zonation, vascularisation and innervation?

Answer 3

1. Zonation:
   
   1. Glomerulosa
   2. Fasciculata
   3. Reticularis
2. Vascularisation:
   
   1. Right adrenal vein drains directly into IVC
   2. Left adrenal vein drains into the left renal vein
   3. Supplied by:
      
      1. Superior adrenal artery – branch of inferior phrenic artery
      2. Middle adrenal artery – branch of abdominal aorta
      3. Inferior adrenal artery – branch of renal arteries
   4. Innervated by:
      
      1. Coeliac plexus

Question 4

In what way is the adrenal cortex essential for survival of the individual while the adrenal medulla is not?

Answer 4

1. The adrenal cortex is the part of the gland which produces cortisol and aldosterone – the 2 stress hormones that are essential for life!
2. Cortisol is crucial in maintaining safe levels of blood glucose and ensuring that the brain is not affected by hypoglycaemia.
3. Aldosterone is also crucial as it allows individuals to maintain their extracellular fluid volume.

Question 5

What is the normal circadian basal rhythm in plasma total cortisol concentration?

Answer 5

Cortisol levels peak between 6-9am

Lowest levels of cortisol occur around 12pm

Question 6

What do the following terms mean?

1) Plasma protein binding globulin
2) Plasma free corisol

Answer 6

Plasma protein bound cortisol – 95% of cortisol that circulates in the blood is bound to the cortisol binding globulin (cbg) which is a carrier protein

Plasma free cortisol – the cortisol which is not bound to cortisol binding globulin (cbg).

Question 7

What effect on plasma glucose does cortisol have? What are the target sites and processes underlying this effect?

Answer 7

1. Cortisol decreases the effectiveness of insulin, meaning that blood glucose levels will rise in the presence of cortisol.
2. Where does cortisol act in order to have an anti-insulin affect?
   
   1. Muscles
   2. Adipose tissue
   3. Liver
   4. Immune system
3. At most of these sites, cortisol promotes the breakdown of fat and muscle to release FFA’s into the blood stream.
4. Cortisols main purpose is to PREVENT Hypoglycaemia by
   
   1. Promoting gluconeogenesis in the Liver
   2. Breaking down skeletal muscle proteins which provide the substrate required for gluconeogensis.

Question 8

What are the clinical features and biochemical diagnosis of the hyperfunction syndromes of the adrenal cortex and medulla?

Answer 8

1. Cushing’s syndrome:
2. The source of cushings can be tested by dexamethasone test
   
   1. Clinical features:
      
      1. Moon face
      2. Wasting of the extremities
      3. Excess fat on trunk
   2. Biochemical diagnosis:
      
      1. Decreased ACTH

Question 9

What are the clinical features, diagnosis and management of adrenal hypofunction (Addison’s disease)?

Answer 9

1. Clinical features:
   
   1. Abdo pain, weakness, weight loss, darkening of the skin
2. Diagnosis:
   
   1. Synachten (synthetic ACTH)
3. Management:
   
   1. Corticosteroids, e.g. hydrocortisone
   2. Fludrocortisone (fluid – helps with ecf balance (Na+ K+),

Question 10

What is the importance of glucocorticoids in acute stress?

Answer 10

Glucocorticoids are important during acute stress as they ensure that the brain is not starved of energy.

They do this by having a positive action on glucagon to release glucose if the blood glucose has dropped significantly during the acute stress.