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Colin Endo/Repro > CIS - Hypothalamic-Pituitary Relationships > Flashcards

CIS - Hypothalamic-Pituitary Relationships Flashcards

1
Q

What is another name for the pituitary gland?

A

Hypophysis

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2
Q

What is another name for the anterior pituitary gland?

A

Adenohypophysis

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3
Q

What is another name for the posterior pituitary?

A

Neurohypophysis

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4
Q

What is the name for the structure connecting the hypothalamus to the pituitary gland?

A

Hypophysial Stalk

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5
Q

What structures make up the posterior pituitary?

A

Posterior pituitary is a collection of axons

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6
Q

Where are the cell bodies that belong to the axons that make up the posterior pituitary located?

A

In the hypothalamus, specifically the Supraoptic Nucleus (SON) - which is located superior to the Optic Chiasm

And the Paraventricular Nucleus (PVN)

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7
Q

What are the signaling neuropeptides that are sent along the axons of the posterior pituitary and where do they come from?

A

ADH mostly comes from cell bodies in the Supraoptic Nucleus (SON)

Oxytocin mostly comes from cell bodies in the Paraventricular Nucleus (PVN)

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8
Q

What makes structures make up the anterior pituitary gland?

A

Endocrine cells

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9
Q

How does the hypothalamus communicate with the anterior pituitary gland?

A

Neurons of the hypothalamus secrete hormones into the Hypothalamic-Hypophysial Portal vessels, which signal the endocrine cells of the anterior pituitary to secrete different hormones into blood stream.

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10
Q

What hormones are secreted by the anterior pituitary endocrine cells?

A 
ACTH
LH
FSH
GH
TSH
Prolactin
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11
Q

What is a Primary Endocrine Disorder?

A

Low or high levels of hormone secreted due to a defect in the peripheral endocrine gland

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12
Q

What is a Secondary Endocrine Disorder?

A

Low or high levels of hormones secreted due to a defect in the pituitary gland

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13
Q

What is a Tertiary Endocrine Disorder?

A

Low or high levels of hormone secreted due to a defect in the hypothalamus

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14
Q

What cell type in the anterior pituitary secretes ACTH?

A

Corticotrophs

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15
Q

What cell type in the anterior pituitary secretes Prolactin?

A

Lactotrophs

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16
Q

What cell type in the anterior pituitary secretes GH?

A

Somatotrophs

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17
Q

What cell type in the anterior pituitary secretes FSH?

A

Gonadotrophs

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18
Q

What cell type in the anterior pituitary secretes TSH?

A

Thyrotrophs

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19
Q

What cell type in the anterior pituitary secretes LH?

A

Gonadotrophs

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20
Q

What is Acromegaly?

A

Rare disease caused by excessive, prolonged secretion of GH

Causes excessive growth of soft tissue, cartilage, and bones of the face, hands, and feet

Develops gradually, not recognized for many years

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21
Q

Describe the axis of regulation of GH

A

Hypothalamus secretes GHRH and Somatostatin

  • GHRH STIMULATES secretion of GH from the anterior pituitary, but INHIBITS secretion of GHRH from the hypothalamus
  • Somatostatin INHIBITS secretion of GH from the anterior pituitary

Anterior Pituitary secretes GH
- GH STIMULATES target tissues to secrete IGFs (Somatomedins), but also STIMULATES secretion of Somatostatin from the hypothalamus

Target Tissue secrete IGFs (Somatomedins)

  • IGFs STIMULATE secretion of Somatostatin from the Hypothalamus
  • IGFs INHIBIT secretion of GH from the anterior pituitary
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22
Q

What are three possible pathophysiologies of Acromegaly?

A

1) Excessive secretion of GH from anterior pituitary
2) Extrapituitary GH secreting tumor
3) Excessive GHRH secretion

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23
Q

When testing for acromegaly, what are you looking for and why?

A

Elevated IGF levels

Measuring GH is not useful as GH levels fluctuate throughout the day, whereas IGF-1 levels remain constant

You also conduct an oral glucose tolerance test. Normally, oral glucose will cause an initial drop in serum GH levels. If GH levels remain unchanged after oral glucose administration, acromegaly is confirmed.

Additionally, a pituitary MRI will be ordered to look for any pituitary mass. If no mass is found, Chest and abdominal CT are ordered and a GHRH serum level is measured

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24
Q

What happens if a pituitary tumor is found?

A

If the tumor is less than 1 cm, surgery is conducted through the nose via a transspenoidal approach (through sphenoid sinus)

If the tumor is less than 1 cm, radiation therapy is considered

25
Q

What medications may be prescribed for a patient with acromegaly?

A

Octeotide or Lanoreotide - Somatostatin analogs (inhibit anterior pituitary secretion of GH)

Pegvisomant - GH receptor antagonist

Bromocriptine or Cabergoline - Dopamine receptor agonists (may decrease GH secretion; but are generally only effective in 25% of acromegaly patients)

26
Q

What is the result of excessive GH secretion before puberty?

A

Gigantism

27
Q

What is the result of GH secretion after puberty?

A

Acromegaly

Increase periosteal bone growth
Increased organ size
Increased extremity size
Insulin resistance
Glucose intolerance
Coarsening facial features
28
Q

What are the metabolic functions of GH?

A

Causes insulin resistance, decreasing glucose uptake and utilization in target tissues

Causes Lipolysis in adipose tissue

Increase in protein synthesis and organ growth (via IGF)

Increases linear growth (via IGF)

29
Q

How does fasting affect GH, insulin, somatomedins, and metabolic functions?

A

Fasting causes:

  • Decrease in insulin
  • Decrease in IGF (somatomedins)
  • Increase in GH
  • Decrease in protein synthesis
  • Decrease in growth
  • Increase in caloric mobilization
30
Q

Decribe the axis of regulation of Prolactin

A

Hypothalamus secretes TRH and Dopamine

  • TRH PROMOTES secretion of TSH and Prolactin from the anterior pituitary
  • Dopamine (aka Prolactin-Inhibiting Factor) INHIBITS secretion of Prolactin from the anterior Pituitary

Anterior Pituitary Gland secretes Prolactin
- Prolactin INHIBITS GnRH from the hypothalamus

31
Q

How does CRH regulate hormone secretion in the pituitary gland?

A

CRH stimulates the secretion of both ACTH and MSH from the anterior pituitary gland

32
Q

How does Dopamine regulate hormone secretion in the pituitary gland?

A

Dopamine (aka Prolactin-inhibiting Factor) inhibits Prolactin from the anterior pituitary gland

33
Q

How does GHRH regulate hormone secretion in the pituitary gland?

A

GHRH stimulates GH secretion from the anterior pituitary gland

34
Q

How does GnRH regulate hormone secretion in the pituitary gland?

A

GnRH stimulates LH and FSH secretion from the anterior pituitary gland

35
Q

How does Prolactin regulate hormone secretion in the pituitary gland?

A

Prolactin stimulates secretion of Dopamine from the anterior pituitary gland

AND it inhibits the secretion of GnRH from the anterior pituitary gland

36
Q

How does Somatostatin regulate hormone secretion in the pituitary gland?

A

Somatostatin inhibits secretion of GH and TSH from the anterior pituitary gland

37
Q

How does TRH regulate hormone secretion in the anterior pituitary gland?

A

TRH stimulates TSH and Prolactin secretion from the anterior pituitary gland

38
Q

Whats the difference between a functioning and non-functioning pituitary adenoma?

A

Functioning tumor = secreting active hormone

Non-functioning tumor = not secreting active hormone

39
Q

How do you distinguish between a microadenoma and a macroadenoma?

A

Microadenoma is less than 1 cm in size

Macroadenoma is greater than 1 cm in size

40
Q

What are some symptoms of a Prolactinoma?

A

Hypogonadism (decreased size of gonads) due to excessive Prolactin inhibiting secretion of GnRH

Galactorrhea (spontaneous flow of milk from breast) due to excessive prolactin secretion

41
Q

What is Cushing’s disease?

A

A disease caused by an excessive secretion of ACTH from the anterior pituitary, resulting in increased secretion of Cortisol from the adrenal glands

42
Q

What results from a pituitary failure of GH secretion?

A

Children - short stature

Adults - no effect

43
Q

What results from a pituitary failure of FSH/LH secretion?

A

Men: Hypogonadism; decreased sperm count

Women: Hypogonadism; irregular menstrual cycle

44
Q

What results from a pituitary failure of TSH secretion?

A

Hypothyroidism

45
Q

What results from a pituitary failure of ACTH secretion?

A

Loss of pigmentation

Hypoadrenalism

46
Q

What results from a pituitary failure of ADH secretion?

A

Diabetes Insipidus

47
Q

What is Sheehan Syndrome

A

Sheehan syndrome is postpartum hypopituitarism due to necrosis of pituitary gland secondary to excessive depletion in blood pressure during or after birth.

Paitents can present with failure of lactation, amenorrhea (missed menstrual cycles), hypothyroidism, or other endocrine dysfunction

48
Q

What are the stages of oxytocin synthesis/secretion?

A

In cell bodies of the Paraventricular nucleus, Prepro-oxyphysin has its signal peptide cleaved (forming Pro-oxyphysin) and is packaged into transport vesicles.

While traveling down the axons in the hypothalamic-hypophyseal tract, the neurophysins are cleaved, forming Oxytocin.

Once in the posterior lobe of the pituitary, oxytocin is secreted into the blood, and targets the breast and uterus

49
Q

What are the stages of ADH synthesis and secretion?

A

In the cell bodies of the Supraoptic Nucleus, Prepropressophysin has its signal peptide cleaved (forming propressophysin) and is packed into transport vesicles

While traveling down the axons in the hypothalamic-hypophyseal tract, the neurophysins are cleaved, forming ADH.

Once in the posterior pituitary lobe, ADH is secreted into the blood, and targets the kidneys and arterioles

50
Q

What are the triggers of ADH secretion?

A

Decreased blood pressure

Increased blood osmolarity (MOST SENSITIVE)

Decreased arterial streatch due to decreased blood volume

Angiotensin II

Sympathetic Stimulation

51
Q

What is the signaling pathway for ADH secretion when blood pressure is decreased?

A

Cardiac and Aortic Baroreceptors detect decreased blood pressure

Sensory neuron sends signal to hypothalamus (Supraoptic Nucleus)

Signal from sensory neuron induces synthesis of ADH

ADH is secreted from posterior pituitary

52
Q

What is the signaling pathway for ADH secretion when arterial stretch is decreased due to decreased blood volume?

A

Arterial stretch receptors detect decreased stretch due to decreased blood volume

Sensory neuron sends signal to hypothalamus (Supraotpic nucleus)

Signal from sensory neuron induces the synthesis of ADH

ADH is secreted from the posterior pituitary

53
Q

What is the signaling pathway for ADH secretion when osmolarity is increased?

A

Osmoreceptors in the hypothalamus detect the increase in osmolarity

Hypothalamic interneurons send a signal to the Supraoptic Nucleus

Signal from interneurons induce synthesis of ADH

ADH is secreted from the posterior pituitary

54
Q

What are the actions of ADH and what receptors does it act on?

A

V2 Receptors - Promote water reabsorption from the collecting duct

V1 Receptors - Promote constriction of arterioles

55
Q

What is the mechanism of action of ADH on the collecting ducts?

A

ADH binds the a GPCR, with an Alpha-S subunit.

Once ADH is bound to receptor, GDP is phosphorylated to GTP, causing alpha-s subunit to remove itself from the G protein.

Alpha-S subunit interacts with Andylyl Cyclase, which converts ATP into cAMP

cAMP activates PKA, which activates the movement of Aquaporin-2 molecules to the apical membrane (facing the nephron lumen) and Aquaporin-3 molecules to the basolateral membrane (facing the blood)

56
Q

What is the pathophysiology of Diabetes Insipidus?

A

Lack of effect of ADH on the collecting ducts, promotes large volume of dilute urine (frequent urination)

57
Q

What is the difference between central and nephrogenic Diabetes Insipidus?

A

Central DI = Lack of ADH secretion (damaged pituitary or hypothalamus)
- Treatment: desmopressin (prevents water excretion)

Nephrogenic DI = Kidneys inability to respond to ADH (damage to kidney)
- Desmopressin is not an effective treatment

58
Q

What is SIADH?

A

Syndrome of Innapropriate ADH secretion

Excessive secretion of ADH causes retention of water

Colin Endo/Repro (12 decks)

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