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Flashcards in Pituitary Gland Deck (77)
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1
Q

Intra-uterine growth

Factoids

A
  • Acting hormones are: growth hormone, IGF-II (early in gestation), IGF-I (late in gestation), and insulin (large newborn in diabetic mother)
  • Smoking decreases placental vascularity and decreases birth weight
  • The worldwide leading cause of low birth weight is poor maternal nutrition
2
Q

Post-natal growth (Pre-pubertal)

Factoids

A
  • Acting hormones are: growth hormone, insulin and thyroid hormone
  • Steroids have no role in growth in this period but their excess will slow growth
  • Congenital hypothyroidism will cause cretinism, but does not decrease the birth weight (every newborn should be screened for thyroid hormones)
  • Hypersecretion of growth hormone in this period will cause giantism, with delay in pubertal changes and subsequent hypogonadism
3
Q

Growth Hormone deficiency (pre-pubertal)

Causes

A
  • Congenital deficiency
  • Idiopathic deficiency due decrease in GHRH secretion
  • Acquired deficiency due to hypothalamic-pituitary tumor
4
Q

Dwarfism

Cause

A

Growth Hormone deficiency (pre-pubertal)

5
Q
Laron Dwarfism (Laron syndrome)
(Cause)
A

Tissue resistance to growth hormone (Increased growth hormone, and decreased IGF-I)

6
Q

Growth Hormone deficiency (pre-pubertal)

Stimulation test

A

Arginine infusion

7
Q

Growth Hormone deficiency (pre-pubertal)

Treatment

A

Simple replacement of GH

8
Q

Growth Hormone deficiency (post-pubertal)

Effects and Treatment

A
  • Decrease in lean body mass

- Replacement therapy is now considered an acceptable treatment

9
Q
Laron Dwarfism (Laron syndrome)
(Treatment)
A

Mecasermin (recombinant IGF) or synthetic IGF

10
Q

Growth Hormone

Factoids

A
  • Released from the anterior pituitary
  • Peptide hormone
  • Anabolic and catabolic
  • Tesamorelin is an analog that is used to treat HIV-associated lipodystrophy
11
Q

Growth Hormone

Anabolic effects

A
  • Direct: growth by Increasing amino acid uptake by the cells
  • Indirect: growth via growth factors (especially IGF-I)
12
Q

Growth Hormone

Catabolic effects

A
  • Decreases uptake of glucose in fat and muscles (raises blood glucose)
  • Mobilizes fats by by increasing the activity of hormone sensitive lipase (raises free fatty acids) [Not cAMP]
13
Q

Insulin-like growth factor-I (IGF-I)

Factoids

A
  • Peptide similar in structure to insulin
  • Pulsatile secretion (more likely during the night in stages III and IV (non-REM) sleep
  • Half-life is 15-20 minutes
  • Circulates bound to plasma proteins (regulated by GH), thus long half-life (24 hr marker of growth hormone secretion)
  • Decreases in catabolic states
14
Q

Insulin-like growth factor-I (IGF-I)

Effects

A
  • Increases cartilage growth (chondrogenesis) in bones

- Increases lean body mass

15
Q

Growth Hormone

Regulation

A
  • Secretion requires the presence of normal plasma levels of thyroid hormone
  • Deep sleep, puberty, hypoglycemia, exercise and amino acids like arginine and leucine promote GH secretion
  • IGF-I and elevated glucose inhibit GH release
  • Secretion is through GHRH (hypothalamus)
  • Inhibition is through Somatostatin (hypothalamus)
  • IGF-I stimulates somatostatin
  • GH inhibit GHRH and stimulates somatostatin
16
Q

Puberty

Reproductive changes

A
  • Hypothalamic pulse generator (LH) increases activity just before physical changes at puberty
  • First noted sign in females is breast development; first by estrogen (promotes duct growth), then progesterone (promotes development of milk-producing alveolar cells)
  • First noted sign in males is enlargement of testes (FSH stimulating seminiferous tubules)
  • Pubic hair development in both sexes is dependent on androgens
17
Q

Puberty

Physical changes

A

During puberty, androgens promote secretion in the following sequence:

  • If T4 is normal, increased androgens (males from testes and females from adrenals [adrenarche] —> increased GH —> increased IGF-I
  • Near the end of puberty, androgens promote mineralization (fusion or closure) of the epiphyseal plates of long bones. Estrogen can also promote this even in males
  • Growth spurt in females begins early in puberty and is nearly complete by menarche. In males it begins near the end of puberty
18
Q

Acromegaly

Causes

A

Excess growth hormone secretion post-puberty due to:
- Anterior pituitary macro-adenoma (> 1 cm) (almost always)
- Ectopic GHRH secretion (very rare)
Note: some tumors contain lactotrophs and elevated prolactin can cause hypogonadism and galactorrhea

19
Q

Acromegaly

Diagnosis

A
  • Elevated IGF-I level (somatomedin C)
  • Failure of suppression of GH/IGH-I after giving glucose
  • MRI shows lesion in the pituitary
20
Q

Acromegaly

Treatment

A
  • First surgical removal by trans-sphenoidal approach
  • If surgery fails, use GH receptor antagonist (pegvisomant) or octreotide (synthetic somatostatin). If both failed then use Cabergoline (dopamine agonist)
  • If all the above treatments failed then we use radiation
21
Q

Hypothalamic-Anterior Pituitary Axis

Hormone synthesis

A
  • Hypothalamic hormones are synthesized in neuron cell bodies, packaged in vesicles, and transported down the axons to be stored and released from nerve terminals (in median eminence region [the stalk])
  • The hormones are then secreted into the hypophyseal-portal system and transported to the anterior pituitary
22
Q

Hypothalamic-Anterior Pituitary Axis

Hormone types

A

All hormones in this system are water-soluble

23
Q

Hypothalamic-Anterior Pituitary Axis

Anatomy

A
  • Pituitary is located in the bony sella turcica at the base of skull
  • It hangs from the hypothalamus by a stalk (infundibulum)
  • Dura membrane (diaphragm sellae) separate the pituitary gland and prevents cerebrospinal fluid from entering sella turcica
  • Optic chiasm is 5-10 mm above this diaphragm
24
Q

Hypothalamic-Anterior Pituitary Axis

Hormone secretion type

A

All hormones are released in a pulsatile pattern except for TRH

25
Q

Hypothalamic Arcuate Nucleus

Secreted Hormones

A
  • Dopamine (prolactin inhibitory factor [PIF])

- Growth hormone releasing hormone (GHRH)

26
Q

Hypothalamic Preobtic Nucleus

Secreted Hormones

A

Gonadotropin releasing hormone (GnRH)

27
Q

Hypothalamic Paraventricular Nucleus

Secreted Hormones

A
  • Thyrotropin releasing hormone (TRH)
  • Corticotropin releasing hormone (CRH)
  • Somatostatin
28
Q

Thyrotropin releasing hormone (TRH)

Pituitary target, Target percentage of pituitary, Target hormone secretion

A
  • Thyrotrophs
  • 10%
  • Stimulates TSH and prolactin secretion
29
Q

Corticotropin releasing hormone (CRH)

Pituitary target, Target percentage of pituitary, Target hormone secretion

A
  • Corticotrophs
  • 10-25%
  • ACTH
30
Q

Gonadotropin releasing hormone (GnRH)

Pituitary target, Target percentage of pituitary, Target hormone secretion

A
  • Gonadotrophs
  • 10-15%
  • LH and FSH
31
Q

Growth hormone releasing hormone (GHRH)

Pituitary target, Target percentage of pituitary, Target hormone secretion

A
  • Somatotrophs
  • 50%
  • GH
32
Q

Dopamine (prolactin inhibitory factor [PIF])

Pituitary target, Target percentage of pituitary, Target hormone secretion

A
  • Lactotrophs
  • 10-15%
  • Prolactin
33
Q

Somatostatin

Pituitary target, Target percentage of pituitary, Target hormone secretion

A
  • Somatotrophs
  • 50%
  • Inhibits GH secretion
34
Q

Gonadotropin releasing hormone (GnRH)

High frequency vs. Low frequency pulses Effects

A
  • High favors LH secretion

- Low favors FSH secretion

35
Q

Hypothalamic-Anterior Pituitary Axis

Effect of severing the connection at the pituitary stalk

A
  • All anterior pituitary hormones will be decreased

- Except for Prolactin which will increase because it was under chronic source of inhibition (dopamine [PIF])

36
Q

Hypothalamus

Hormones

A
  • TRH
  • CRH
  • GHRH
  • GnRH
  • Somatostatin
  • Dopamine (PIF)
37
Q

Anterior Pituitary

Hormones

A
  • TSH
  • ACTH
  • GH
  • LH
  • FSH
  • Prolactin
38
Q

Hypopituitarism

Causes

A
  • Inherited
  • Acquired:
  • Head trauma (most common)
  • Tumors (mass effect)
  • Inflammation
  • Vascular damage
  • Hydrocephalus can also affect the hypothalamus
  • Isolated deficiency:
  • GH: sporadic or familial
  • GnRH: Kallman syndrome (low LH,FSH and sex steroids, anosmia, and renal agenesis [50%])
  • ACTH, TSH and prolactin extremely rare (usually a sign of panhypopituitarism)
  • Craniopharyngioma (most common tumor in children)
39
Q

Hypopituitarism

Loss of function sequence

A
  • GH and GnRH
  • TSH
  • ACTH
  • Prolactin
    Note: typically trophic hormones are in the normal range; but their level is inadequate to stimulate peripheral glands adequately
40
Q

Hypopituitarism

Stimulation tests [Academic perspective]

A
  • GnRH —> LH and FSH
  • TRH —> TSH and Prolactin
  • Insulin infusion (hypoglycemia) —> GH and ACTH
41
Q

Sheehan syndrome

Cause

A

Severe post-partum hemorrhage —> shock —> arteriolar spasm of the already enlarged pituitary (due to pregnancy) —> ischemic necrosis

42
Q

Pituitary Adenomas

Types and Presentation

A
  • Microadenomas (< 1 cm in diameter): present as a hormonal excess like Cushing disease
  • Macroadenomas (> 1 cm in diameter): mass effect that present as panhypopituitarism and visual loss
43
Q

Pituitary Adenomas

Microadenomas Prevalence

A
  • Hyperprolactinemia 60% (hypogonadism and galactorrhea)
  • Acromegaly 20%
  • Cushing disease (ACTH) 10%
44
Q

Pituitary Adenomas

Association

A

MEN 1

45
Q

Posterior Pituitary

Hormones

A
  • Arginine vasopressin (ADH)

- Oxytocin

46
Q

ADH

Synthesis and Secretion

A
  • Synthesized in supraoptic and paraventricular nuclei of the hypothalamus
  • Stored and released from the posterior pituitary
47
Q

ADH

Release regulators

A
  • Osmoreceptors in the hypothalamus (respond to 1% change in osmolarity)
  • Volume receptors (stretch and baroreceptors) [respond to 10-15% change in volume). In conditions of weightlessness like space or water immersion to the neck, there will be net shift of blood from limbs to abdomen and chest which lead to greater stretch of baroreceptors, thus suppressing ADH release
  • Ethanol inhibits it
  • Cortisol and thyroid hormones decrease its release
48
Q
Osmolarity point 
(Resetting Conditions)
A
  • Pregnancy
  • Menstrual cycle
  • Volume depletion
    Note: in all these conditions there will be downward resetting
49
Q

ADH

Action

A
  • Reabsorption of water at renal collecting tubules (via V2 receptors) by placing aqua pores into the luminal membrane
  • Increased urea reabsorption (with water)
  • In severe hemorrhage, high levels of ADH via V1 receptors on vascular smooth muscle cause a vasoconstriction
50
Q

Atrial Natriuretic Peptide (ANP)

Source

A

Hormone secreted by the heart as a whole but mainly right atrium

51
Q

Atrial Natriuretic Peptide (ANP)

Release regulators

A
  • Stretch of atria (independent of nervous involvement)
  • Increased salt intake
  • CHF and all fluid overload states
52
Q

Atrial Natriuretic Peptide (ANP)

Action

A
  • Causes loss of water and sodium from the kidneys by
  • Increases GFR by causing dilatation of afferent arteriole and constriction of efferent arteriole
  • Decreases water and sodium reabsorption in the collecting ducts
  • Inhibits aldosterone
  • It works through cGMP
53
Q

Atrial Natriuretic Peptide (ANP)

Uses

A

Normal ANP level is used to exclude CHF as a cause of dyspnea

54
Q

Brain Natriuretic Peptide (BNP)

Source

A

Hormone secreted from heart mainly from ventricles

55
Q

Brain Natriuretic Peptide (BNP)

Release regulators

A
  • Stretching of ventricles

- Normally very little but increased markedly in patients with dilated hearts

56
Q

Free Water Clearance

Equation

A
  • CH2O = V - ([Uosm * V)] / Posm)
  • Uosm: urine osmolarity
  • Posm: plasma osmolarity
  • V: urine flow rate
57
Q

Positive Water Clearance

Interpretation

A
  • Uosm / Posm < 1
  • Losing water
  • Decreased ADH
58
Q

Negative Water Clearance

Interpretation

A
  • Uosm / Posm > 1
  • Retaining water
  • Increased ADH
59
Q

Negative Water Clearance, High ADH, High Posm

Diagnosis

A

Dehydration

60
Q

Negative Water Clearance, High ADH, Low Posm

Diagnosis

A

SIADH

61
Q

Positive Water Clearance, High ADH, High Posm

Diagnosis

A

Nephrogenic DI

62
Q

Positive Water Clearance, Low ADH, High Posm

Diagnosis

A

Neurogenic DI

63
Q

Positive Water Clearance, Low ADH, Low Posm

Diagnosis

A

Primary Polydipsia

64
Q

Sectioning of Pituitary stalk

Effects on ADH

A

Triphasic respones

  • DI
  • SIADH (release of ADH from dying cells)
  • DI
65
Q

Hyperprolactinemia

Presentation

A
  • In females: galactorrhea, amenorrhea and infertility

- In males: decreased libido and impotence

66
Q

Panhypopituitarism

Causes

A

Any pituitary tumor that destroys more than 75% of the gland like:

  • Pituitary adenomas
  • Sheehan syndrome
  • Craniopharyngiomas
67
Q

Visual field changes in hypothalamic disorders

Association

A
  • Pituitary adenoma
  • Craniopharyngioma
  • Midline hamartoma
  • Langerhans histiocytosis
  • Inflammatory processes like sarcoidosis and meningitis
68
Q

Pineal Gland

Diseases

A
  • Dystrophic calcification
  • Tumors:
  • Seminomas (most common)
  • Teratomas
69
Q

Prolactin

Actions

A
  • Stimulates milk production in breasts

- Inhibits ovulation in females and spermatogenesis in males by inhibiting GnRH synthesis and release

70
Q

Prolactin

Secretion regulators

A
  • It is tonically inhibited by dopamine from hypothalamus
  • Prolactin inhibits its own secretion by increasing dopamine synthesis and secretion from hypothalamus
  • TRH increases its secretion (like in primary and secondary hypothyroidism)
  • Sight/cry of baby will inhibit the hypothalamic dopamine inhibition of prolactin, thereby increasing its secretion
  • Dopamine inhibitors will cause increase in prolactin secretion like
  • Medication: most antipsychotics, estrogens like OCPs and pregnancy, methyldopa and verapamil
  • Chest wall injury (via ANS)
  • Nipple stimulation
  • Estrogen also directly stimulates pituitary release of prolactin
  • Renal failure will increase prolactin (by reducing its elimination)
71
Q

Prolactinoma

Treatment

A
  • First line: Dopamine agonists like bromocriptine or cabergoline (more tolerable) after excluding pregnancy
  • Second line: Transsphenoidal resection (if medical Rx failed or there is compressive effects)
72
Q

Nelson Syndrome

Pathophysiology

A

Enlargement of existing ACTH-secreting pituitary adenoma after bilateral adrenalectomy for refractory Cushing disease (due to removal of cortisol feedback mechanism)

73
Q

Nelson Syndrome

Presentation

A
  • Hyperpigmentation
  • Headaches
  • Bitemporal hemianopia
74
Q

Nelson Syndrome

Treatment

A
  • Pituitary irradiation

- Surgical resection

75
Q

Acromegaly

Associations

A
  • Impaired glucose tolerance (insulin resistance)

- Increased risk of colorectal polyps and cancer

76
Q

Empty Sella Syndrome

Description

A
  • Atrophy or compression of pituitary
  • Often idiopathic
  • Common in obese women
77
Q

Pituitary Apoplexy

Description

A
  • Sudden hemorrhage of pituitary gland, often in presence of adenoma
  • Presents as sudden severe headache, bitemporal hemianopia or diplopia, and features of hypopituitarism