endocrine- pituitary Flashcards
where is the anatomical location of the pituitary gland?
inferior to diencephalon. Rests in sella turcica, close proximity to optic nerves & chiasm
Connected to hypothalamus via infundibulum
(Neural & vascular)
what are the embryologic origins of the two pituitary lobes?
Posterior-neurohypophysis (ectoderm) - nervous nature
Anterior-adenohypophysis (mesoderm) - glandular in nature
what does the posterior pit. do?
Posterior secretes ADH(aka vasopressin) & oxytocin
what does the anterior pituitary do?
Anterior produces & secretes TSH, ACTH, FSH/LH (gonadotropins), GH, & prolactin
if the hypothalamus- pituitary axis is interrupted, how will hormone levels change?
ALL will decrease except prolactin which will increase
hormones that will increase: GH, TSH, ACTH, LH, FSH
why will prolactin increase if the hypothalamus-pituitary axis is interrupted?
the major control of prolactin is inhibitory in nature (dopamine) so if we stop this, we get an uncontrolled increase in prolactin
what are the hormones from the hypothalamus and what hormone in the anterior pituitary do they each produce?
(percentages of each given for extra info)
20% somatotrophs (GH) 15% corticotrophs (ACTH) 15% gonadotrophs (FSH & LH) 15% lactotrophs (prolactin) 5% thyrotrophs (TSH)
how would we txt the most common pituitary tumor?
most common pit. tumor is a prolactin secreting tumor (dopamine inhibits this so we use dopamine to txt these tumors)
what are the three types of endocrine disorders?
primary, secondary and tertiary
what constitutes a primary endocrine disorder?
Primary disorders involve the gland responsible for producing the hormone in question
ex/ Total thyroidectomy produces primary hypothyroidism
what constitutes a secondary endocrine disorder?
Secondary disorders involve problems with the pituitary stimulation, target gland is normal
ex/Destruction of pituitary (source of TSH is gone) produces secondary hypothyroidism
what constitutes a tertiary endocrine disorder?
Tertiary disorders involve problems with the hypothalamus, pituitary & target glands are not stimulated
ex/ hypothalamus destroyed by tumor - tertiary hypothyroidism
hypo- and hyper-pituitarism is always referring to the anterior or posterior pituitary?
anterior
what is “simmond’s disease”?
type of hypopituitarism:
Loss of one or more of the hormones from the adenohypophysis (ant pit. hormones)
simmond’s dz:how much of the pituitary mass must be lost for clinical changes to occur?
Requires loss of 75% of the adenohypophysis (of pit mass) before clinical changes (b/c many in circulation)
what is “panhypopituitarism”?
Panhypopituitarism is loss of most or all of the hormones of the adenohypophysis.
** Underdiagnosed & deadly
loss of ant. pituitary hormones follow what kind of “predictable sequence”?
GH (“I don’t feel good”)
FSH/LH (“My sex drive is gone”)
TSH + ACTH (life-threatening)
4 kinds of pituitary destruction that can cause panhypopituitarism?
Adenoma- squeeze out normal pit cells.
Surgery- removal of pit.
Radiation
Trauma
postpartum pituitary necrosis that can cause panhypopituitarism?
**“Sheehan’s syndrome”
From hemorrhagic shock (low flow- ischemia) during complicated delivery
what is empty sella syndrome?
Arachnoid herniation into sella turcica
- Slowly crushes gland
explained: hypophysis has roof of dura w/ a hole that allows infundibulum thorough- but some people this is too big = herniation of arachnoid into pit.
3 ways one can get panhypopituitarism?
- pituitary destruction
- postpartum necrosis
- empty sella syndrome
panhypopituitarism: variable symptoms: loss of GH ?
accelerates body wasting (atherosclerosis)
panhypopituitarism: variable symptoms: loss of prolactin
prevents lactation after childbirth
panhypopituitarism: variable symptoms: loss of TSH
produces secondary hypothyroidism
panhypopituitarism: variable symptoms: loss of ACTH
secondary adrenal insufficiency (deadly) - need cortisol to live
how do you dx panhypopituitarism?
- stimulate the gland, a lack of hormone response = positive Dx
- example: CRH, ACTH, or TRH stimulation - brain MRI
testing for panhypotituitarism by giving them synthetic ACTH, why would there be no response?
- no response = positive Dx
- if they haven’t had ACTH in a really long time , adrenal cortex atrophies, so will have NO response to ACTH
txt for panhypopituitarism?
hormone replacement and surgical resection of adenoma
hyperpituitarism: what is it and what are the 3 usual causes?
Too much of one (or two) of the hormones from the adenohypophysis
Usual cause(s)
1. Autonomous overproduction-pituitary adenoma
2. Excess/under production of hypothalamic RH/RIH
3. Loss of feedback inhibition from destruction/removal of other glands
pituitary adenoma: what are the sizes for microadenoma vs macroadenoma?
Microadenomas < 1 cm
Macroadenomas ≥ 1 cm
presentation of pituitary adenoma (2)
- Hormone excess (functional) or deficit from destruction of remaining gland
- Visual problems-monocular blindness or bitemporal hemianopsia (can’t see peripheral vision in either eye) -smashes optic chiasm - crushed crossing optic fibers
Incidental “enlarged sella turcica” on skull films- what would this indicate?
pituitary adenoma
how do you test for hyperpituitarism ? (2)
- May require a “suppression” test-lack of suppression may indicate autonomous production (tumor)
- head CT/MRI
what are the two major ways we induce hormone suppression to test hyperpituitarism?
- Low-dose dexamethasone suppression
- High-dose dexamethasone suppression (usually will suppress a pituitary ACTH-oma)
- dexamethasone- a potent glucocorticoid.
- low dose:isnt enough to suppress the ACTH-oma, its used as a screen.
- high dose: suppression- reduce ACTH levels, used if you suspect the disease
what does a prolactinoma cause (men vs women) ?
Prolactin-producing pituitary adenoma (anterior lobe)…
Men-impotence, loss of libido, obesity
Women-amenorrhea, galactorrhea, infertility, obesity
what may cause hyperprolactinemia other than a prolactinoma?
dopamine antagonists
-if you inhibit dopamine - take away the inhibitory effect- stimulatory effect (TRH) stays = hyperprolactinemia
2 txt options for prolactinoma
Bromocriptine (dopamine agonist)
Surgery or gamma knife
GH aka somatotropin: what does it do? (2)
- Promotes linear growth & protein synthesis
2. Causes insulin resistance & increase in insulin levels
actions of growth hormones (somtatotropins) are regulated by what?
mediated by liver-derived somatomedins (insulin-like growth factors, IGF)
- can stimulate hypothalamus or inhibit ant. pitutary to control GH levels
where does growth hormone come from?
hypothalamus secretes:
GHRH –> stimulates ant. pituitary release of GH
(*also negative feedback to hypothal)
somatostatin (SRIF) –> inhibits ant. pituitary release of GH
where does prolactin come from?
hypothalamus secretes:
TRH –> stimulates ant. pituitary release of prolactin
dopamine –> inhibits ant. pituitary release of prolactin
what is gigantism? (signs)
excess GH before puberty (before epiphyseal closure)
- Height > 7 ft (200 cm)
what is acromegaly? (signs- kinda weeds)
excess GH after epiphyseal closure
- Huge hands, tongue, brow, & jaw (prognathism)
- Oily skin
- Secondary diabetes
- Osteoporosis
- Increased coronary risk
- Early mortality
what usually causes gigantism or acromegaly?
pituitary macroadenoma
Dx of gigantism/acromegaly? (2 ways)
- Spot IGF-1 (normal levels essentially rule out)
2. GH suppression test
2 ways to txt gigantism/acromegaly?
- Surgical removal
2. Somatostatin analogue (octreotide)-reduces tumor size
GH suppression test for acromegaly explained (Weeds)
Growth hormone (hGH) suppression by a glucose load is the classic screening test for acromegaly Failure to suppress hGH is diagnostic of acromegaly when coupled with elevated IGF1 and clinical signs of excess growth hormone.
cushing’s syndrome vs cushing’s disease
Cushing’s syndrome (Cushingism)-excess glucocorticoids (cortisol)
Cushing’s disease (Cushingism) caused by overproduction of ACTH by pituitary adenoma
what can cause cushing’s disease
ACTH-oma (Microadenomas)
dx of cushing’s disease
microadenoma: Not suppressed by low-dose dexammethasone
Usually can be suppressed by high-dose dexamethasone
txt of cushing’s disease?
surgical removal
posterior pituitary disorders: what can cause suppression of each of the two hormones secreted here?
- Lithium therapy & alcohol use: suppress ADH secretion
2. No known syndromes: oxytocin excess/deficiency
what hormone regulates plasma osmolarity?
ADH
what prompts the secretion of ADH from the post. pituitary?
increased osmolarity or decreased plasma volume
decreased plasma volume causes what changes that effect ADH/vasopressin?
Acts on renal collecting ducts to increase water reabsorption
- water retention into blood = concentrated urine
- Higher concentrations ADH/vasopressin = produce vasoconstriction (hence “vasopressin”)
how is hypothalamus prompted to secrete ADH or increase thirst?
it has osmoreceptors that read plasma osmolarity (normal 270-280)
- if they sense 300+ osmolarity- secrete ADH to decrease it.
what is diabetes insipidus? two types?
Deficiency of ADH or normal ADH with decreased response
- Neurogenic (central) - lack of response from neuro system
- Nephrogenic - lack of response from kidney
what causes diabetes insipidus?
head trauma or brain surgery
what are the signs of diabetes insipidus?
Polyuria, polydipsia
-3-20 L/day, dilute
what is the test for diabetes inspidus? (what do you do?what do results mean? how do you distinguish between central and nephrogenic?)
“water deprivation test”
- Measure plasma/urine osmolarity, restrict water overnight, re-measure (trying to raise osmolality - can also do by giving them hypertonic saline)
- Dx: Failure of urine osmolarity to increase
- Adding ADH assays before & during distinguishes between central & nephrogenic
neurogenic (central) diabetes inspidus: txt
usually incomplete lack of hormone (not complete lack of ADH) so..
- can Auto-regulate based on thirst
- Synthetic ADH (dDAVP, Desmopressin) for chronic or severe cases
txt for nephrogenic DI
- if you can’t remove the cause–> TZD diuretics
- drinking more water prevents hyperosmotic
what causes SIADH? (persistent vs transient)
persistent: ectopic ADH production (rarely a pituitary problem)
* *Oat cell lung carcinoma (most common ectopic ADH)
transient: may be caused by head injury or brain surgery
what is syndrome of inappropriate ADH? (SIADH)?
Continual ADH production regardless of plasma osmolarity
- Persistent water reabsorption, plasma hypotonicity (hyponatremia - low Na+ conc., dilute blood)
- concentrated urine
- Hyponatremia leads to seizures & death
5 Dx criteria for SIADH?
- Hypotonic hyponatremia
- Natriuresis (urine sodium > 20 mEq/L)
- Urine osmolarity > plasma osmolarity
- Absence of volume depletion & edema
- Normal renal, adrenal, & thyroid function
best txt for SIADH?
water restriction-make the “inappropriate ADH” appropriate
3 other txt options for SIADH?
- Normal saline + furosemide to promote free water clearance
- Lithium & demeclocycline poison collecting duct ADH receptors
- Newer ADH-receptor antagonists (conivaptan, tolvaptan)
what can be used to txt SEVERE cases of SIADH? what precautions to take with this?
Hypertonic saline (3%)
Too much, too fast can cause central pontine myelinolysis (neuronal issues —> death)
- 0.5 mEq/L/hr
Most non-thyroid endocrine diseases will require ________ or ________ for diagnosis
“stimulation” or “suppression” test
