01-13 Pituitary Structure/Function

Question 1

What two effects do pituitary hormones have on their target tissues?

Answer 1

1. maintain organ size

2. end target hormone secretion

Question 2

Describe the embryonic development of the ANTERIOR pituitary

Answer 2

—develops out of Rathke’s pouch (invagination of oral ectoderm)
—migrates to come into contact w/ primitive hypothalamus
—”pouch cells undergo an orderly series of differentiation steps resulting in the terminally differentiated, hormone-specific cell types that comprise the pituitary gland. Each of these steps is controlled by a series of specific transcription factors. Understanding this process has shed light on the pathogenesis of genetic hypopituitarism syndromes and of pituitary tumors that secrete more than one hormone.”

Question 3

hormone synthesis in ant vs. post pituitary
—which hormones?
—where made?

Answer 3

ANT:
—FLAT-P(I)G: FSH, LH, ACTH, TSH, Prl, GH
—RELEASING factors from hypothalamus are delivered via portal circulation to Ant Pit
—control STIMULATING hormone production in the Ant Pit.

POST:
—just ADH and oxytocin
—doesn’t actually synth hormones
—stores EFFECTOR hormones made in hypothal and delivers them via axonal transport through neurons

Question 4

Systemically think about expansion of the pituitary
—structures damaged?
—resulting clinical manifestations?
**SUPERIORLY?
**LATERALLY?
**INFERIORLY?

Answer 4

Two categories of problems: endocrine and neuro

SUPERIORLY
—tentorium sella → h/a (highly innervated!)
—optic chiasm → visual field ∆s
—pit stalk/hypothal impinge → hypothal obesity/apetite stimulation; temperature dysreg; low ADH (central DI); excess prolactin

LATERALLY
—carotids usu. not affected
—cavernous sinus: II, IV, VI → disconj gaze
—(CN V usu not affected)
—medial temporal lobe → temporal lobe szs

INFERIORLY
—sphenoid sinuses → CSF rhinorrhea, meningitis

Question 5

What type of visual field defect do you usually see with pituitary tumors?

Answer 5

bitemporal hemianopsia

Question 6

H-P-A Axis

Answer 6

CRH (from hypothal) oscillatory 24hr cycle →
ACTH → (from POMC in ant pit)
—zona fascic → cortisol → feedback 2 levels
—zona retic → androgens

Note: the zona glomerulosa is ACTH independent in its production of aldosterone

Question 7

What are the layers of the adrenal cortex?
—What do they produce?
—Mnemonic?

Answer 7

Adrenal cortex layers, superficial to deep:
Zona Glomerulosa: produces aldosterone
Zona Fasciculata: produces mostly cortisol
Zona Reticularis: produces mostly androgens
—Margarita: Salt, sugar, sex

Question 8

Thyroid Axis

Answer 8

Hypothal: TRH ↑s TSH, Somatostatin ‪↓‬s TSH
Ant pit: TSH
Thyroid: T4&raquo_space; T3
**Both T4 and T3 feedback at both a.p. and hypothal levels, but T3 more potently?

Question 9

Levothyroxine = T?

Answer 9

T4

Question 10

Gonadal Axis

Answer 10

Hypothal: GnRH ↑s FSH/LH, Somatostatin ‪↓‬s

Ant Pit: FSH & LH

In OVARIES
—LH: estradiol, progesterone → dual feedback
—FSH: ovulation

In TESTES:
—LH: testosterone & inhibin → dual feedback
—FSH: spermatogenesis

**In ♀: oscillator; programmed senescence

Question 11

Growth Hormone Axis

Answer 11

Hypothal: GHRH ↑s GH, Somatostatin ‪↓‬s GH
Ant Pit: GH → dual feedback
Liver: IGF-1 (1° effector) → also dual feedback

Question 12

Prolactin Axis

Answer 12

Control seemingly completely inhibitory:
—DA* from hypothal blocks ant pit’s Prl
~~TRH at very high levels can also stim Prl (thus we sometimes see galactorrhea is 1° hypothyroidism)
—Prl → breast

*not a neuropeptide as w/ other axes

Question 13

Which hormones are glycoprotein hormones?
—structure
—implications

Answer 13

FSH, LH, TSH & hCG

STRUCTURE
—heterodimers of same α and a unique β chain
—glycosylated via post-translational modif

IMPLICATIONS
—errors in either prot synth or post-translation processing can cause problems
—have to test for the β chain

Question 14

Testing for suspected panhypopituitarism

—what would you order?

Answer 14

HPA Axis: ACTH stimulation test or 24hr urine cortisol

Thyroid Axis: free T4, TSH

Growth Axis: GH and IGF-1

♀ Gonadal Axis: mens. status, estrogen, LH, FSH

♂ Gonadal Axis: test., LH, FSH

ADH: 24hr urine volume; dehydration test (do ADH and urinary osmolarity levels rise?)

Oxytocin: not tested

Question 15

Pituitary apoplexy
—presentation
—cause?
—mgmt?

Answer 15

PRESENTATION
—worst h/a of life; sudden bitemp hemianopsia and/or diplopia; acute panhypopituitarism

CAUSE
—acute bleed into pre-existing pituitary adenoma

MGMT
—medical: cortisol stat (pre-anesthesia)
—surgery: drain it!