Hypothalamus and Pituitary CIS

Question 1

What are anterior pituitary hormones stimulated by?

Answer 1

tropic hormones released by the hypothalamus

Question 2

Points about the HPS structure

Answer 2

Anterior pituitary hormones are stimulated by tropic hormones released by the hypothalamus.

Posterior pituitary hormones are neuroendocrine.

The blood supply is different between the anterior and posterior pituitary

The proximity to the optic chiasm can result in vision problems with pituitary adenomas.

Question 3

Pituitary hormones

Answer 3

Posterior pituitary hormones:

• Oxytocin
• ADH

Anterior pituitary hormones

• GH
• Prolactin (under negative inhibition by dopamine)
• LH/FSH
• TSH
• ACTH

Question 4

Causes of Hypopituitarism

Answer 4

Pituitary diseases:
Mass lesions
Pituitary surgery
Pituitary radiation
Infiltrative lesions (e.g. sarcoidosis, hemochromatosis)
Pituitary infarction
Pituitary apoplexy
Pituitary abscess
Genetic diseases

Hypothalamic disease:
Mass lesions
Hypothalamic radiation
Infiltrative lesions
Infections 

Traumatic brain injury

Stroke:
Ischemic stoke
Subarachnoid hemorrhage

Question 5

GH vs IGF-1

Answer 5

IGF-1 is responsible for most of the growth effects of GH

Question 6

Why are pregnant women susceptible to pituitary infarction?

Answer 6

lactotrophs are increasing dramatically during pregnancy. The increased demands for blood might not be met by the hypopysial system (can –> ischemic necrosis of the anterior pituitary)

Question 7

In some cases of Sheehan’s syndrome the posterior pituitary is relatively unaffected. How can you explain this finding?

Answer 7

It has its own blood supply.

Question 8

What else can stimulate ADH?

Answer 8

CRH

Question 9

Causes of hyperprolactinemia

Answer 9

Physiologic causes:
Pregnancy
Nipple stimulation
Stress

Pathologic causes:
Lactotroph adenomas
Decreased dopaminergic inhibition (Hypothalamic and pituitary disease, Drug use)

Other causes:
Estrogen
Hypothyroidism
Chest wall injury
Chronic renal failure
Idiopathic hyperprolactinemia
Macroprolactinemia
Genetic

Question 10

what to expect in prolactinoma

Answer 10

thyroid and cortisol would still be normal, FSH and LH would be low due to inhibition by prolactin

Question 11

Causes of acromegaly

Answer 11

Most common cause is a somatotroph adenoma of the anterior pituitary

Other causes included growth hormone-releasing hormone (GHRH) secretion from hypothalamic tumors or neuroendocrine tumors or ectopic GH secretion by neuroendocrine tumors (rare causes)

Question 12

Stimulation of growth hormone

Answer 12

deep sleep
fasting
sex steroids
stress
amino acids
hypoglycemia

Question 13

growth hormone actions (2)

Answer 13

stimulate growth

promote increase in blood glucose levels (a diabetogenic hormone; related to insulin resistance)

Question 14

suppression of growth hormone

Answer 14

obesity
glucocorticoids
High FFA
hyperglycemia
IGF-1

An excess of nutrients shuts down growth hormone

Question 15

How will pituitary tumors expand?

Answer 15

The pituitary gland is encased in the splenoid bone in the sella turcica
Pituitary tumors will expand upward and can press on the optic chiasm and other regions of the brain → causes dizziness and vision problems

Question 16

GH effects on metabolic pathways of fat, protein and glucose

Answer 16

Fat- lipolysis is increased- results in hyperlipidemia
Protein- protein synthesis is increased- increased lean body mass
glucose- GH opposes the effects of insulin which can result in type 2 diabetes

Mobilize fat, build protein, fight against insulin!

Question 17

Treatment strategies for acromegaly

Answer 17

Therapeutic strategies for acromegaly caused by a GH-secreting tumor of the anterior pituitary include:

• surgical resection of the neoplasm.
• stereotactic radiotherapy.
• lifelong medical therapy with the somatostatin analogue octreotide or the GH receptor antagonist pegvisomant.

Some visceral or soft tissue changes may subside but skeletal changes cannot be reversed.

Question 18

Diabetogenic effects of GH

Answer 18

decreases glucose uptake, increases blood glucose levels, increases lipolysis, increases blood insulin levels.

–> insulin resistance

Question 19

Increased protein synthesis and organ growth effects of GH

Answer 19

occur through the actions of IGF-1

increased amino acid uptake
increased DNA, RNA, protein synthesis
increased lean body mass and organ size

Question 20

increased linear growth by GH

Answer 20

through the actions of IGF-1

altered cartilage metabolism

When GH causes getting taller, it is called gigantism rather than acromegaly