Physiology of Hypothalamus and Pituitary

Question 1

What does the hypothalamic-pituitary unit regulate and control?

Answer 1

• regulates thyroid, adrenal and reproductive glands
• controls growth, milk ejection and osmoregulation

Question 2

what connects the hypothalamus to the pituitary?

Answer 2

infundibulum

Question 3

What are the two nuclei of the posterior pituitary and what do they release?

Answer 3

• supraoptic nuclei → AVP
• paraventricular nuclei → Oxytocin

Question 4

What are the 5 cell types and the hormones they secret from the anterior pituitary gland?

Answer 4

• Thyrotrophs (TSH)
• Gonadotrophs (FSH, LH)
• Somatotrophs (GH)
• Lactrotrophs (PRL)
• Corticotrophs (ACTH)

Question 5

What is the difference between the anterior and posterior pituitary hormone delivery?

Answer 5

• anterior: hypothalamus secretes releasing or inhibiting hormones into the hypothalamic-hypophyseal portal system
• posterior: hormones are made in the hypothalamus and released directly from axon terminals

Question 6

What does the hypophesial-portal vessels of the anterior pituitary allow?

Answer 6

• delivery of hypothalamic hormones directly and in high concentrations to the AP
• hypothalamic hormones are not seen in the arterial circulation

Question 7

What protects the hypothalamus and what does the unprotected portion of the hypothalamus allow for?

Answer 7

• blood brain barrier
• hormonal feedback loops

Question 8

What hormones are not controlled by the hypothalamus?

Answer 8

PTH
Insulin
Glucagon
Calcitriol

Question 9

What are the two hypothalamic inhibitory hormones?

Answer 9

• Prolactin-inhibiting Hormone (dopamine)
• Growth Hormone Inhibitory Hormone (somatostatin)

Question 10

How do hormones diffuse into the anterior pituitary cells via the portal capillaries?

Answer 10

capillaries are fenestrated (have pores) to allow easy hormone passage and diffuse based on concentration gradients

Question 11

What are AVP and Oxytocin synthesized from and where?

Answer 11

larger precursor molecules prepropressophysin and preprooxyphysin in the nuclei located in the hypothalamus

Question 12

What causes the release of AVP and what are the receptors it binds too?

Answer 12

• increased plasma osmolarity
• increased blood volume
• decreased blood pressure
• drugs or tumors (SIADH)
• V1 (blood vessels) and V2 (kidneys)

Question 13

What is SIADH?

Answer 13

Syndrome of Inappropriate Antidiuretic Hormone Secretion
- a condition in which there is excessive release of ADH leading to water retention and dilutional hyponatremia (low sodium)

Question 14

What are the diabetic conditions that are associated with AVP and what do they cause?

Answer 14

• Central Diabetes Insipidus: failure to release AVP
• Nephrogenic Diabetes Insipidus: decrease response to AVP in the kidneys
  *** both lead to dilute urine and hyperosmotic plasma

Question 15

What is the mechanism of Oxytocin and what are its main 3 functions?

Answer 15

increases intracellular calcium via G-alpha-q pathway to induce smooth muscle contractions for
- uterine contractions during parturition
- milk let down and ejection from breasts
- promotes maternal and social bonding behavior

Question 16

What does suckling cause?

Answer 16

stimulate the release of oxytocin (let down) and prolactin (production) and inhibit the release of dopamine

Question 17

What can inhibit the release of prolactin and what happens if inhibition is not working properly?

Answer 17

dopamine
- hyperprolactinemia occurs which can lead to galactorrhea and hypogonadism

Question 18

What is the most common pituitary adenoma?

Answer 18

prolactinoma

Question 19

What is the role of estrogen during pregnancy?

Answer 19

estrogen increases breast tissue, but inhibits prolactin’s action on milk production –> after birth, when estrogen and progesterone levels drop, prolactin is finally able to trigger milk secretion

Question 20

What can excess/deficiency in GH (somatotropin) lead to?

Answer 20

• acromegaly or gigantism
• dwarfism

Question 21

What is responsible for the release of GH?

Answer 21

• puberty –> ventromedial and arcuate nuclei –> GHRH –> adenylyl cyclase and PLC –> GH

Question 22

What is SRIF?

Answer 22

Somatostatin released from periventricular neurons that inhibits GH release from the anterior pituitary

Question 23

what are the direct effects of GH?

Answer 23

• ↑ Protein synthesis
• ↑ Fatty acid mobilization
• ↓ Glucose utilization by tissues
• ↑ Glucose production by liver
• ↑ Insulin secretion → may cause insulin resistance (“diabetogenic effect”)

Question 24

What is IGF-1 and what are its effects?

Answer 24

GH stimulates liver to release IGF-1 (Insulin-like Growth Factor 1, a somatomedin) and acts on:
- muscle to ↑ amino acid uptake, protein synthesis
- bone to ↑ chondrocyte mitosis, collagen production → bone growth
- Adipose to ↑ lipolysis, ↓ glucose uptake –> can lead to ketosis

Question 25

What are the mechanism that GH can increase protein synthesis?

Answer 25

- ↑amino acid transport into cells - ↑mRNA transcription and translation by ribosomes - ↓catabolism of protein and amino acids

Question 26

what are the acute and chronic conditions that can lead to GH secretions?

Answer 26

- Acute stimulus: hypoglycemia is a powerful short-term trigger - Chronic stimulus: protein deficiency or malnutrition triggers long-term GH increase *** with malnutrition tissues become desensitized and cause growth delays in children

Question 27

What is the outcome of GH strongly stimulating osteoblasts?

Answer 27

leads to growth of the jaw, skull, hands, and feet, as seen with acromegaly

Question 28

What is the anabolic effect of GH?

Answer 28

promotes protein synthesis → increases lean muscle mass through - ↑ Amino acid uptake - ↑ mRNA transcription and translation - ↓ Protein breakdown

Question 29

what is GH dependent on?

Answer 29

carbohydrates and insulin are required to support GH’s anabolic effects - without insulin (e.g., if pancreas is removed), GH cannot build muscle effectively which shows GH’s actions are insulin-dependent, even though GH itself can cause insulin resistance in excess

Question 30

What is the pulsatile pattern of GH?

Answer 30

GH is not released constantly — instead, it is secreted in bursts (pulses) throughout the day where the largest bursts occur: - After strenuous exercise - During the first 2 hours of deep sleep (especially stages 3 and 4 of non-REM sleep)

Question 31

What is IGF-1?

Answer 31

released by the liver in response to GH and - follows GH secretion - binds tightly to plasma proteins → acts like a buffer - has a long half-life (20 hours) → its effects last much longer than GH pulses

Question 32

Why is the pulsatile pattern important?

Answer 32

- Although GH levels spike briefly, the slow and prolonged release of IGF-1 allows for sustained effects on growth, metabolism, and repair - IGF-1 acts on bones, muscles, and other tissues long after the GH pulse is gone

Question 33

What can the inability to make IGF-1 cause?

Answer 33

poor growth obesity hypogenitalism

Question 34

What is Panhypopituitarism?

Answer 34

decreased secretions of all anterior pituitary hormones