Accessory Organs - Adrenal Glands

Question 1

What is the function of the adrenal glands?

Answer 1

To secrete steroid and catecholamine hormones.

Question 2

Anatomical location?

Answer 2

Located in the posterior abdomen, between the superomedial kidney and the diaphragm.

The right gland is pyramidal, whereas the left gland is semi-lunar in shape.

Renal fascia encloses the adrenal glands and the kidneys. This fascia attaches the glands to the crura of the diaphragm. They are separated from the kidneys by the perirenal fat.

Question 3

Anatomical relations - right adrenal gland?

Answer 3

Anterior:

• Inferior vena cava
• Right lobe of the liver

Posterior:

• Right crus of the diaphragm

Question 4

Anatomical relations - left adrenal gland?

Answer 4

Anterior:

1) Stomach
2) Spleen
3) Pancreas

Posterior:

1) Left crus of the diaphragm

Question 5

Anatomical structure?

Answer 5

It consists of an outer layer of connective tissue capsule, a cortex and a medulla. Veins and lymphatics leave each gland via the hilum, but arteries and nerves enter the gland at numerous sites.

The outer cortex and inner medulla are the functional portions of the gland. They are two separate endocrine glands, with different embryological origins:

• Cortex - derived from the embryonic mesoderm.
• Medulla - derived from the ectodermal neural crest cells.

Question 6

Adrenal glands - cortex?

Answer 6

It is yellowis in colour. It secretes two cholesterol derived hormones - corticosteroids and androgens. Functionally, the cortex can be divided into three regions (superficial to deep):

1) Zona glomerulosa - produces and secretes mineralocorticoids such as aldosterone.
2) Zona fasciculata - produces and secretes corticosteroids such as cortisol. It also secretes a small amount of androgens.
3) Zona reticularis - produces and secretes androgens such as dehydroepiandrosterone (DHES). It also secretes a small amount of corticosteroids.

Question 7

Adrenal glands - medulla?

Answer 7

This lies in the centre of the gland, and is dark brown in colour. It contains chromaffin cells, which secretes catecholamines (such as adrenaline) into the bloodstream in response to stress.

These hormones produce a ‘flight or fight’ response. Chromaffin cells also secrete enkephalins which function in pain control.

Question 8

Adrenal glands - vasculature?

Answer 8

There are three main arteries that supply the adrenal glands:

1) Superior adrenal artery - arises from the inferior phrenic artery
2) Middle adrenal artery - arises from the abdominal aorta
3) Inferior adrenal artery - arises from the renal arteries

Right and left adrenal veins drain the glands. The right adrenal vein drains into the inferior vena cava, whereas the left adrenal vein drains into the left renal vein.

Question 9

Innervation?

Answer 9

Adrenal glands are innervated by the coeliac and greater splanchnic nerves

Sympathetic innervation to the adrenal medulla is via myelinated pre-synaptic fibres, mainly from the T10 to L1 spinal cord segments.

Question 10

Lymphatics?

Answer 10

Lymph drainage is to the lumbar lymph nodes by adrenal lymphatic vessels. These vessels originate from two lymphatic plexuses - one deep to the capsule, and the other in the medulla.

Question 11

Clinical relevance: Phaeochromocytoma

Answer 11

This is a tumour of the adrenal medulla or preganglionic sympathetic neurones. It secretes adrenaline and noradrenaline uncontrollably, causing blood pressure to greatly increase. Patients may present with palpitations, headaches and diaphoresis (profuse sweating)

Phenoxybenzamine, a competitive. irreversible antagonist of adrenaline, can be used in treatment to reduce blood pressure by binding to adrenaline receptors, making less available for adrenaline to act upon.