Hypothalamic-Pituitary-Adrenal Axis

Question 1

What 6 things does the hypothalamus regulate? How does it do this?

Answer 1

1. maintenance of homeostasis
2. reproduction
3. metabolism
4. eating and drinking behavior
5. energy utilization
6. osmolarity and blood pressure

secretes hormones via the pituitary

Question 2

What is the hypothalamic-pituitary-adrenal axis?

Answer 2

• hypothalamus secretes CRH to stimulate the anterior pituitary
• in response, anterior pituitary secretes ACTH, which stimulate cortisol metabolism and secretion from the adrenals
• increased cortisol in the bloodstream acts a negative feedback loop, which decreases CRH and ACTH production

Question 3

What are the 3 zones of the adrenal cortex? What hormones do they secrete?

Answer 3

1. zona glomerulosa - mineralocorticoids - aldosterone (SALT)
2. zona fasciculata - glucocorticoids - cortisol, corticosterone (SUGAR)
3. zona reticularis - sex hormones - androgens, estrogen (SEX)

Question 4

What hormones are secreted by the adrenal medulla?

Answer 4

catecholamines - epinephrine, norepinephrine

Question 5

What is responsible for cortisol release from the adrenal glands? What are 4 of its roles?

Answer 5

ACTH stimulation from the anterior pituitary

1. regulates macronutrient metabolism
2. maintain GI structure and function
3. maintain normal BP
4. stress adaptation - trauma, surgery, illness, pain, inflammation

Question 6

What is responsible for aldosterone release from the adrenal glands? What are 2 of its roles?

Answer 6

RAAS - increased serum K = increased aldosterone, decreased serum K = decreased aldosterone

1. increases ECF Na+ and H2O concentration
2. decreases ECF K+ concentration

Question 7

What is responsible for catecholamine release from the adrenal medulla? What are 5 of their roles?

Answer 7

stress, pain, injury, SNS stimulation = norepinephrine and epinephrine release

FIGHT OR FLIGHT

1. vasoconstriction
2. increased HR and contractility
3. vasodilation of smooth muscles (beta-stimulation)
4. glycogenolysis and gluconeogenesis to increase glucose availability
5. lipolysis, increased metabolic rate

Question 8

What are the likely results of pituitary tumors, adrenal cortical tumors, and adrenal medullar tumors?

Answer 8

increased ACTH = increased cortisol (Cushings)

increased cortisol (Cushing) and aldosterone (cats) secretion

(pheochromocytoma) excess and episodic release of catecholamines

Question 9

What is primary and secondary hypoadrenocorticism? How are they different?

Answer 9

non-functional pituitary gland = decreased cortisol, normal aldosterone = normal electrolytes

destruction of the zona glomerulosa and fasciculata = decreased cortisol and aldosterone = cortisol and mineralocorticoid deficiency (most common, dogs)

Question 10

What is the normal axis associated with growth hormone production? What are 3 aspects to its negative feedback loop?

Answer 10

• hypothalamus secretes GHRG, which stimulates the anterior pituitary gland
• in response, the pituitary gland secretes GH
• GH induced the liver to produce IGF-1

1. increased IGF-1 stops the production of GH from the pituitary and GHRH
2. increased GH self-regulates and decreases GHRH
3. somatostatin from the hypothalamus blocks this pathway

Question 11

What are 4 functions of growth hormone?

Answer 11

1. insulin antagonism
2. lipolysis
3. protein synthesis
4. epiphyseal growth

Question 12

What are 4 functions of IGF-1?

Answer 12

1. insulin-like activity
2. antilipolytic activity
3. protein synthesis
4. epiphyseal growth

Question 13

What is acromegaly?

Answer 13

pituitary tumor results in secretion of GH and increase in IGF-1 from the liver

Question 14

What hormones are produced by the posterior pituitary?

Answer 14

• ADH
• oxytocin