Lecture 2: Pituitary gland

Question 1

What are the parts of the pituitary?

Answer 1

• Neurohypothesis
  
  • Median eminence
  • Infundibular stalk
    
    • upper
    • lower
  • Infundibular process (Pars nervosa)
• Adenohypothesis
  
  • Pars intermedia
  • Pars tuberalis
  • Pars distalis

Bolded = posterior lobe

Italicised = anterior lobe

Question 2

Draw the pituitary and it’s portions!

Answer 2

***note where the dividing line between the hypothalamus and the pituitary

Question 3

Where does the pituitary sit?

Answer 3

• In the pituitary fossa within the sphenoid bone
• Contained by the Sella Turcica

Question 4

What is the covering of the pituitary gland?

Answer 4

• Dura mater which has an opening for the stalk
• Splits and puts a tissue sheath over the top called the diaphragma sella

Question 5

Origin of the anterior and posterior pituitary?

Answer 5

• Rathke’s pouch, which is a pouch in the primitive mouth cavity, moves up as neurohypophsyeal bud grows down
• Rathle’s pouch part –> anterior lobe after it breaks off
• Neurohypophyseal part –> infundibulum + posterior lobe
• Anterior = epithelial origin
• Posterior = neural origin

Question 6

What arteries supply the pituitary portal system?

Answer 6

The superior hypophyseal and inferior hypophyseal arteries Which come of the Internal Carotids.

Superior hypohyseal: comes in at the top. Feeds a portal system to the pars distalis (therefore the median eminence and infundibular stalk)

Inferior hypophyseal: comes in under the post. pituitary. Feeds vessels in the lower capillary bed + PP capilaries (neurohypophysis and a little bit of the stalk)

Question 7

Short axons go into the __________

Long axons go into the _________

Answer 7

Short axons go into the upper capillary bed of the pituitary

Long axons go into the lower capillary bed of the Pituitary

Question 8

What branches off the Superior Hypophysial artery, and what does it supply?

Answer 8

The Trabecular Artery.

Goes straight into the Pars Distalis, bypassing he upper capillary bed to go to the lower cappilary bed.

**Therefore doesn’t supply the ant. pituitary as previously thought!

Question 9

What are the blood supply summary points?

Answer 9

1. Pars Distalis lacks direct arterial supply
2. Median Eminence has an arterial supply but lacks significant venous drainage; other then the portal system to the pars distalis.
3. Ample venous drainage from Pars Distalis
4. The neural lobe; (pars nervosa) has it’s own arterial supply and venous drainage

**not all of the blood flow is one way, some of it flows back from the pituitary to hypothalamus in a short feed-back loop.

Question 10

How does the axis function

Answer 10

• Neurohypothesis:
  
  • neurons secrete hormones straight into the systemic circulation
• Adenhypothesis
  
  • Adenocytes secrete into portal vessels
• Alternative pathway:
  
  • Where the axons go not to the portal system, but to the 3rd ventricle, get into the fluid and run down primitive nerve cells tanycytes who’s fat axons go down to the anterior pituitary.

Question 11

What are the types of cells in the pars distalis (2)?

Answer 11

• Chromophobes
• Chromophils
  
  • Acidophils (oragne G)
    
    • Somatotrophs → Produce Growth Hormone (GH)
    • Lactotrophs → Produce Prolactin (PRL)
  • Basophils (magenta)
    
    • Gonadotrophs → LH and FSH
    • Thyrotrophs → thyroid stimulating Hormone
    • Corticotrophs → ACTH

Question 12

Clinical correlation of chromatophils?

Answer 12

1. In pregnancy there’s a marked proliferation of acidophils (prolactin) to help develop other body tissues for birth
2. Tumour of acidophils (in pituitary): lead to acromegaly if there’s excess GH
3. Basophil Adenoma: cushings syndrome due to excess ACTH