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Endocrine First Aid > Hypothalamic Pituitary Axis > Flashcards

Hypothalamic Pituitary Axis Flashcards

1
Q

What does corticotropin releasing hormone do?

A

It induces the release of ACTH

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2
Q

What does Gonadotropin-releasing hormone do?

A

Induces the release of LH and FSH

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3
Q

What does Growth Hormone Releasing Hormone do?

A

Induces release of GH…BIG STRETCH

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4
Q

What does Somatostatin do?

A

Inhibits the release of GH and TSH

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5
Q

What does Dopamine do?

A

Inhibits the release of prolactin

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6
Q

What does Thyrotropin do?

A

Induces the release of TSH and prolactin

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7
Q

Effect of cortisol on hypothalamic hormones

A

inhibits CRH

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8
Q

Effect of the sex hormones testosterone and progesterone on hypothalamic hormones

A

Inhibit GnRH (Gonadotropin releasing hormone)

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9
Q

What does GHRH do to other hypothalamic hormones?

A

Trick question, it just inhibits itself.

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10
Q

What does prolactin do to hypothalamic hormones?

A

Inhibits GnRH but stimulates dopamine

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11
Q

What do somatomedins do to hypothalamic hormones?

A

Stimulate Somatostatin release

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12
Q

Effect of growth hormone on hypothalamic hormones

A

Stimulates somatostatin

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13
Q

Discuss the two types of Empty Sella Syndrome

A

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

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14
Q

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

A

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

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15
Q

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

A

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

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16
Q

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

A

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.

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17
Q

All anterior pituitary hormones are what type of hormone?

A

Peptide hormones

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18
Q

What does adenocorticotropic hormone do?

A

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

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19
Q

What does Follicle Stimulating hormone do?

A

FSH stimulates follicle growth in ovaries and spermatogenesis in testes

20
Q

What does luteinizing hormone do?

A

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

Surge causes ovulation and maintains the corpus luteum

21
Q

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

A

Promotes protein synthesis and tissue growth

22
Q

What does Thyroid Stimulating Hormone do?

A

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

23
Q

What does Prolactin do when released from the anterior pituitary?

A

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

It also inhibits ovulation indirectly by inhibiting GnRH

24
Q

ACTH is inhibited by ____

A

Cortisol

25
Q

FSH is inhibited by ____, ____, and ____

A

Inhibin, estrogen, progesterone

26
Q

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

A

Inhibited and stimulated by estrogen

Inhibited by testosterone and progesterone

27
Q

Growth hormone is inhibited by ____

A

Somatomedins

28
Q

Thyroid Stimulating Hormones are inhibited by _____

A

Thyroid hormones

29
Q

Prolactin is stimulated by ____ and ____ and inhibited by ___

A

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

30
Q

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

A

Stains Orange

Somatotropes (GH) and lactotropes (Prolactin)

31
Q

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

A

Stains purple

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

32
Q

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

A

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.

33
Q

Effect of damage to the pituitary stalk

A

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.

34
Q

Discuss the link between growth hormone and IGF-1

A

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.

35
Q

Discuss what we mean by counterregulatory hormone

A

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

36
Q

Discuss the structure and formation of ACTH

A

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.

37
Q

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

A

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
38
Q

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

A

hCG

39
Q

Discuss synthesis and release of hormones from the posterior pituitary

A

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.

40
Q

What hypothalamic nuclei are responsible for hormone production?

A

Paraventricular nucleus and the supraoptic nucleus

41
Q

Discuss the actions of Oxytocin and how we release it

A

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

42
Q

Discuss ADH osmolarity regulation

A

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.

43
Q

How does ADH decrease plasma osmolality?

A

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.

44
Q

How does ADH constrict arterioles?

A

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

45
Q

Discuss how ADH responds to large changes in blood volume

A

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.

Endocrine First Aid (16 decks)

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