Hypothalamic Pituitary Axis

Question 1

What does corticotropin releasing hormone do?

Answer 1

It induces the release of ACTH

Question 2

What does Gonadotropin-releasing hormone do?

Answer 2

Induces the release of LH and FSH

Question 3

What does Growth Hormone Releasing Hormone do?

Answer 3

Induces release of GH…BIG STRETCH

Question 4

What does Somatostatin do?

Answer 4

Inhibits the release of GH and TSH

Question 5

What does Dopamine do?

Answer 5

Inhibits the release of prolactin

Question 6

What does Thyrotropin do?

Answer 6

Induces the release of TSH and prolactin

Question 7

Effect of cortisol on hypothalamic hormones

Answer 7

inhibits CRH

Question 8

Effect of the sex hormones testosterone and progesterone on hypothalamic hormones

Answer 8

Inhibit GnRH (Gonadotropin releasing hormone)

Question 9

What does GHRH do to other hypothalamic hormones?

Answer 9

Trick question, it just inhibits itself.

Question 10

What does prolactin do to hypothalamic hormones?

Answer 10

Inhibits GnRH but stimulates dopamine

Question 11

What do somatomedins do to hypothalamic hormones?

Answer 11

Stimulate Somatostatin release

Question 12

Effect of growth hormone on hypothalamic hormones

Answer 12

Stimulates somatostatin

Question 13

Discuss the two types of Empty Sella Syndrome

Answer 13

In primary ESS, increased pressure in the sella turcica flattens the pituitary along the walls of the cavity

In secondary ESS, we see a regression of the pituitary secondary to injury or radiation. Both give the impression of an empty sella on imaging.

This syndrome occasionally results in endocrine dysfunction

Question 14

What is the embryonic origin of the anterior pituitary (adenohypophysis)

Answer 14

Forms from the embryonic invagination of pharyngeal epithelium (oral ectoderm) called the pouch of Rathke

Question 15

What is the embryonic origin of the posterior pituitary (neurohypophysis)

Answer 15

Forms from the neuroectoderm derived from the hypothalamus. During development, it fuses with the pouch of Rathke

Question 16

Discuss the response types we see in the anterior and posterior pituitary

Answer 16

With the anterior pituitary, we get activation by circulating hormones from the hypothalamus.

With the posterior pituitary, since it is composed of neural tissue, we get release of hormones in response to neurotransmission.

Question 17

All anterior pituitary hormones are what type of hormone?

Answer 17

Peptide hormones

Question 18

What does adenocorticotropic hormone do?

Answer 18

ACTH induces synthesis of adrenal cortical hormones (cortisol, androgens, aldosterone) in response to CRH. It regulates the size, integrity, and synthetic function of the adrenal cortex

Question 19

What does Follicle Stimulating hormone do?

Answer 19

FSH stimulates follicle growth in ovaries and spermatogenesis in testes

Question 20

What does luteinizing hormone do?

Answer 20

LH Promotes testosterone synthesis in testes, promotes estrogen/progesterone synthesis in the ovaries.

Surge causes ovulation and maintains the corpus luteum

Question 21

What does growth hormone do when released from the anterior pituitary?

Answer 21

Promotes protein synthesis and tissue growth

Question 22

What does Thyroid Stimulating Hormone do?

Answer 22

Stimulates growth of the thyroid gland and synthesis and secretion of thyroid hormones

Question 23

What does Prolactin do when released from the anterior pituitary?

Answer 23

Promotes additional breast development during pregnancy in preparation for milk secretion, and directly stimulates lactation.

It also inhibits ovulation indirectly by inhibiting GnRH

Question 24

ACTH is inhibited by ____

Answer 24

Cortisol

Question 25

FSH is inhibited by ____, ____, and ____

Answer 25

Inhibin, estrogen, progesterone

Question 26

LH is stimulated by ___ and inhibited by ___, ___, and ___.

Answer 26

Inhibited and stimulated by estrogen Inhibited by testosterone and progesterone

Question 27

Growth hormone is inhibited by ____

Answer 27

Somatomedins

Question 28

Thyroid Stimulating Hormones are inhibited by _____

Answer 28

Thyroid hormones

Question 29

Prolactin is stimulated by ____ and ____ and inhibited by ___

Answer 29

Stimulated by TRH and the action of suckling and inhibited by Dopamine

Question 30

Cell populations of the anterior pituitary can be subdivided even further on imaging by using special stains. Periodic Acid Schiff (PAS) stains can identify three groups. Discuss the acidophil group

Answer 30

Stains Orange Somatotropes (GH) and lactotropes (Prolactin)

Question 31

Cell populations of the anterior pituitary can be subdivided even further on imaging by using special stains. Periodic Acid Schiff (PAS) stains can identify three groups. Discuss the basophil group

Answer 31

Stains purple B-FLAT Gonadotropes - FSH, LH Corticotropes - ACTH Thyrotropes - TSH

Question 32

Cell populations of the anterior pituitary can be subdivided even further on imaging by using special stains. Periodic Acid Schiff (PAS) stains can identify three groups. Discuss the chromophobe group

Answer 32

No stain reaction. We see this with empty cells, meaning they lack cytoplasmic granules so there is no stain. Former acidophils and basophils do this when they have released all of their hormone-containing granules.

Question 33

Effect of damage to the pituitary stalk

Answer 33

Damage to the pituitary stalk can lead to decreased secretion of pituitary hormones secondary to disruption of the hypophyseal portal system (anterior pituitary) and hypothalamic neurons (posterior pituitary). The exception is prolactin secretion, which is increased in a situation of damage.

Question 34

Discuss the link between growth hormone and IGF-1

Answer 34

GH acts directly on tissues to decrease glucose uptake and mobilize fatty acids. Its growth promoting effect is primarily mediated via insulin-like growth factor-1 (IGF-1), formerly known as somatomedin, and it stimulates protein synthesis at the organ level and in chondrocytes for linear growth. IGF-1 is made in the liver in response to GH. Both hormones independently stimulate protein synthesis in muscle and increase lean body mass.

Question 35

Discuss what we mean by counterregulatory hormone

Answer 35

These are hormones released during non-homeostatic conditions to restore a balance of some kind, and usually refers to hypoglycemic response hormones GH, for example, is released in response to hypoglycemia to increase serum glucose levels by promoting glycogenolysis, gluconeogenesis, lipolysis, and ketogenesis

Question 36

Discuss the structure and formation of ACTH

Answer 36

Synthesized from a larger precursor, POMC (proopiomelanocortin), which also derives Beta lipotropin and Beta endorphin. A bioactive moiety, alpha-MSH (melanocyte stimulating hormone) is present on the N-terminal end of ACTH.

Question 37

Discuss the structural homology of the 6 major hormones of the anterior pituitary

Answer 37

The anterior pituitary gland produces six major hormones that can be classified into three groups based on structural homology 1. Glycoproteins - FSH, LH, TSH - All have an identical alpha subunit but a unique beta unit 2. Somatomammotropins - GH and Prolactin (PRL) - Structurally related peptides that belong to the same cytokine-hematopoietin family 3. ACTH-related peptides - ACTH, MSH, lipotropin - all formed by cleavage of POMC

Question 38

_____ shares the same alpha subunit with FSH, LH, and TSH

Answer 38

hCG

Question 39

Discuss synthesis and release of hormones from the posterior pituitary

Answer 39

Hormones of the posterior pituitary are synthesized in hypothalamic neurons (called magnocellular neurons due to their large cell bodies) and transported via axoplasmic flow to axon terminals in the posterior lobe of the pituitary. Oxytocin and ADH are synthesized from larger precursors (prohormones) which are cleaved within the vesicles to produce active forms.

Question 40

What hypothalamic nuclei are responsible for hormone production?

Answer 40

Paraventricular nucleus and the supraoptic nucleus

Question 41

Discuss the actions of Oxytocin and how we release it

Answer 41

Two main actions: - Promotes contractions of the uterine myometrium during labor - Stimulates contraction of myoepithelial cells in the breast, facilitating milk release to suckling infant Exogenous stimuli drive oxytocin secretion. Signals include suckling infant and dilation of the cervix as seen in childbirth

Question 42

Discuss ADH osmolarity regulation

Answer 42

The osmotic concentration of extracellular fluid is sensed by specialized neurons within or adjacent to the hypothalamus. The size of these neurons changes with extracellular osmolality, resulting in nerve signals increasing or decreasing ADH secretion as appropriate. Increase in ADH occurs when we have a high osmolality. ADH increases water reabsorption and decreases plasma osmolality. ADH also responds to huge decreases in blood volume, unlike the RAS, which reacts to small changes. ADH also constricts arterioles.

Question 43

How does ADH decrease plasma osmolality?

Answer 43

ADH increases permeability to water in the distal tubules and collecting ducts of the kidney, thereby increasing water reabsorption and decreasing plasma osmolality. It stimulates membrane bound V2-receptors, triggering an increase in intracellular cAMP. Special vesicles containing aquaporins (permeable water pores) are inserted into the luminal aspect of the cell membrane. Free diffusion of water occurs from tubule to peritubular fluid, decreasing ECF osmolality.

Question 44

How does ADH constrict arterioles?

Answer 44

At high concentrations, ADH constricts arterioles by acting through the V1 receptor, and is consequently referred to as arginine vasopressin

Question 45

Discuss how ADH responds to large changes in blood volume

Answer 45

ADH is secreted in response to >10% changes in blood volume. Secretion is stimulated by signals from atrial stretch receptors and baroreceptors. Hypovolemia with resultant reduced atrial stretch results in decreased secretion of atrial natriuretic peptide (ANP). Low levels of ANP support increased secretion of ADH. Baroreceptors of the aortic and carotid sinus sense decreased arterial pressure due to hypovolemia, resulting in decreased afferent signals to the medulla and consequent increase in ADH secretion and sympathetic stimulation.