Lecture 3 - Nuts And Bolts Of The Endocrine System

Question 1

What is the blood supply to pituitary gland?

Answer 1

Supplied by 2 arteries (both branches of internal carotid):

• Superior hypophyseal artery supplies the median eminance (at the top of the Infundibulum) and the upper park of the stalk
• inferior hypophyseal arteries supplies the neurohypophysis and lower part of stalk
• -> These two arteries anastamose

VEINS

• capillary plexuses in median eminance and stalk are drained by portal veins
• these veins then pass to the ant pituitary where they form a secondary capillary plexus
• provides a method for neurosecretory substance released from hypothalamus to also reach the anterior lobe

Question 2

Where is the thyroid gland located?

Answer 2

Bilobed gland in the neck, 2 lobes connected by isthmus

4×2 cms in size 30g

Runs from just below oblique line of thyroid cartilage to 5/6 trachea ring, immediately anterior to the trachea

Question 3

What is the thyroid gland derived from?

Answer 3

Endoderm, develops as a growth from the floor of the pharynx, near the base of the tongue

Question 4

What is the role of the thyroid gland?

Answer 4

Tissue metabolism, growth and development

Question 5

What is the artery supply to the thyroid?

Answer 5

Superior thyroid (from external carotid)
Inferior Thyroid (from subclavian)

Question 6

Venous drainage of the thyroid?

Answer 6

Drain from an extensive plexus into the internal jugular and brachiocephalic veins

Question 7

What is the nerve supply to thyroid

Answer 7

Recurrent nerve( from vagus nerve) which arches back over the aortic arch

Question 8

Why does care needs to be taken in thyroid surgery?

Answer 8

In crichothyrotomy (creating small gap between cricoid cartilage and thyroid to get emergency access to trachea) a small cut results in very perfuse bleeding due to the high vascularity of the area

Also the recurrent nerve can be damaged in surgery which could affect speech

Question 9

How big are the parathyroid gland? Where are they?

Answer 9

Small glands on posterior lateral of thyroid glands - 40mg each

4 - 2 Superior and 2 inferior

Question 10

How do the parathyroid glands develop?

Answer 10

Develop mostly from cells originating from the 3rd and 4th pharyngeal pouches

They migrate causally with the thymus

Question 11

What is the role of the parathyroid?

Answer 11

To secrete parathyroid hormone which regulates calcium and phosphate homeostasis

Question 12

Why is it vital to preserve the parathyroid glands in a thyroidectomy?

Answer 12

If the parathyroid are removed or damaged then calcium levels fall leading to muscles going into tetanic contraction and possible death

This occurs because a low calcium means sodium is more likely to enter the cell (Na and Ca are competitors) and an increase in intracellular Na leads to increased AP firing

Question 13

VAN of parathyroid?

Answer 13

V- superior, middle and inferior thyroid

A - primarily inferior thyroid (but also superior)

N - from middle and inferior cervical ganglions (these also supply the thyroids)

Question 14

Adrenal glands shape and origin?

Answer 14

Shape is pyramidal on right and semilunar on left

2-3 × 1 cm, 3.5-5g

Cortex is derived from modern and medulla is derived from neural crest cells

Question 15

What is the function of the adrenal cortex?

Answer 15

Secretes corticosteroids

Cells in superficial cortex secret mineralocorticoids

Deeper part of cortex - secretes glucocorticoids

Cortex also produces adrenal androgens e.g. testosterone

Question 16

What is the function if the adrenal medulla?

Answer 16

Chromaffin cells (Secretory cells of the medulla) develop from the same embryonic tissue as the sympathetic ganglia

The medulla is regarded as a modified sympathetic ganglion (ANS)

Medulla cells secret catecholamines and are involved in the flight or fight response

Question 17

What is the blood supply to the adrenal glands?

Answer 17

3 main

Question 18

What is the blood supply to the adrenal glands?

Answer 18

3 main sources - Superior suprarenal artery (from the inferior phrenic artery), middle suprarenal artery (from aorta) and inferior suprarenal artery (from the renal artery)

The arteries branch before entering the capsule and the rami supply the cortex and medulla of the gland

Cortical arteries give rise to subcapsular plexus and in turn cortical sinusoids that distribute blood to cortical cells

Medullary arteries pass through cortex to supply the medulla (thus hormones released by cortical cells influence activity of cells in the medulla e.g. cortisol mediates NA release)

Question 19

What Is the venous drainage of the adrenal glands?

Answer 19

Left adrenal vein drains into renal vein

Right adrenal vein drains into the IVC

Question 20

How is the fast response created in figjt/flight?

Answer 20

Some fibres bypass the sympathetic chain and go straight to medulla chromaffin cells creating a very fast reaction /release of hormones