Endocrinology: Pituitary Gland (Hypophysis)

Front 1

Anatomy of the Pituitary Gland

Back 1

-located at the base of the skull in the sella turcica (saddle-shaped cavity in the sphenoid bone)
-dura forms the roof over & lines the sella
-pituitary stalk extends from hypothalamus through dura & connects pituitary to hypothalamus
-2 parts: anterior & posterior

Front 2

Posterior Pituitary

2 hormones associated

Back 2

-extension of the nervous system
-hormones made in cell bodies w/in hypothalamic nuclei
-axons extend from cell bodies into posterior pituitary via pituitary stalk
-hormone travels down axons to posterior pituitary where stored and released into circulation as needed

1. ADH (vasopressin): controls H2O balance, inhibits diuresis (urine output)
2. Oxytocin: controls uterine contractions & breast milk let down

Front 3

Anterior Pituitary

Back 3

"master gland"
-contains several cell types that make & release different hormones
-production regulated by hypothalamic hormones delivered directly to ant pit by special portal venous system in pituitary stalk
-hypothalamic hormones not measurable in general circulation (based on ant pit)

Front 4

Hypothalamic Hormones

Back 4

-peptide hormones
-secreted in pulses: pulses affected by input from higher brain centers (affected by stress)
-pit. response depends on hypothalamic hormone pulse timing & amplitude
-not easy to replace in hypothalamic disease

+: TRH, CRH, GnRH, GHRH
-: dopamine, somatostatin

Front 5

Hormones of the Anterior Pituitary
-their cell type
-their target

Back 5

Peptide hormones: secreted in pulses, can measure in blood:

TSH - thyrotrophs: thyroid
ACTH -corticotrophs: adrenal cortex
LH - gonadotrophs: ovary or testis
FSH - gonadotrophs: ovary or testis
GH -somatotrophs: liver, all tissues
Prolactin - lactotrophs: breasts

Front 6

Hypothalamic-Anterior Pituitary Axis

Back 6

Hypothalamus releasing hormone --> ant. pit. via hypothalamic-pituitary portal system --> release ant. pit hormones to targets via circulation

Front 7

Thyroid Feedback Loops

Adrenal Feedback Loops

Back 7

X

Front 8

Gonad Feedbacks Loops

Growth Feedback Loops

Back 8

X

Front 9

Primary Disease

Secondary Disease

Tertiary Disease

Back 9

1: problem w/ the target gland

2: problem w/ the pituitary gland

3. problem with the hypothalamus

Front 10

Pituitary Tumor Effects

Back 10

-stretched dura = headache
-optic chiasm damage = visual field (loss of peripheral vision, tunnel vision)
-cranial nerve defects
-erosion into sinuses
-excess pituitary hormones:
GH = acromegaly/gigantism
ACTH = excess cortisol (cushings disease)
TSH (rare) = hyperthyroidism
Prolactin = breast milk, no menses, infertility
FSH/LH = only fragments, no disease
*many tumors don't produce hormones

Front 11

Prolactin Feedback Loops

Back 11

X

Front 12

Pituitary Treatments on:
1. Tumor Mass
2. Hormone Excess
3. Hormone Deficient

Back 12

1. surgery, radiation therapy

2. inhibitor of pit. secretion, pit. hormone receptor antagonist (block receptor)

3. target gland hormone replacement, pit hormone replacement

Front 13

Disorders of Pituitary Failure

Back 13

Hypopituitarism
-individual cell type failures
-entire gland failure (panhypopituitarism)
-causes: tumor, surgery, radiation, infarction (postpartum), infiltration (iron deposits), infection (TB), immune

-if mass present = usually GH, FSH & LH lost 1st then TSH, ACTH, & prolactin last (inhibition lost)
-pit hormones low & target organ hormones low

Front 14

Targets Associated with Pituitary Failure

Back 14

low ACTH & cortisol = can't handle medical stress
low TSH & thyroid: hypothyroidism
low FSH, LH & sex hormones = no menses, impotence, infertility, low libido
low prolactin = no lactation
low GH & IGF-1 = growth failure in children

Front 15

Hormone Replacement

Back 15

Target gland hormones:
-thyroid hormone
-cortisol
-estrogen or testosterone

Pituitary Hormones:
-LH, FSH (if fertility desired)
-GH in childhood
-GH in adults?

Front 16

Causes of Excess Prolactin

Back 16

-pituitary tumor (prolactinoma)
-pit. stalk damage (dopamine can't reach pit)
-chest wall trauma
-kidney failure
-drugs (esp. antidepressents)
-Hypothyroidism

Front 17

Treatment of Excess Prolactin

Back 17

-maybe no treatment if only mild increase
-treat if: pit. tumor (prolactinoma) is large, cause non-pregnancy related milk production, prolactin inhibiting fertility (supress GnRH)
-Dopamine inhbits prolactin secretion & cause tumor to shrink
-treatment = dopamine agonist (shorter 1/2 life)

Front 18

Metabolic Consequences of Excess Growth Hormone

Bone Consequences of Excess GH

Back 18

-more DNA, RNA, & protein synthesis
-increase insulin resistance: less glucose used, may develop diabetes
-increase free FA mobilization: fat becomes a better fuel source

-Acromegaly: in adults, enlargement of acral tissues (acral = tip of extremity)
-Gigantism: if onset before puberty
-bones thicken
-lengthen if before puberty
-bony overgrowth of skull (enlarged sinuses, prominent brow ridges - frontal bossing)
-enlarged lower jaw (prognathism) widely spaced teeth
-huge hands and feet
-bone changes are irreversible

Front 19

Effects of Excess GH on Soft Tissues

Back 19

-CT increased: painful joints, trapped ligaments, thick tongue & tracheal cartilage (sleep apnea, thick palms & soles)
-viscera: internal organs, enlarged, colon polyps
-muscles: enlarged, weakens/fatigue (fiber atrophy, nerves trapped)
-skin: thick, skin tags, large sweat glands
-Hypertension: heart disease
-Mass effects: headache, pit. insufficiency

Front 20

Tests for Acromegaly

Back 20

-high IGF-1
-GH > 1 ug/ml after oral glucose (should lower GH but not in acromeg)
-skull, hand and foot xrays
-pit MRI or CT scan

Front 21

Acromegaly Treatment

Back 21

1. Surgery: esp. if threating vision
2. somatostatin analogs: suppress GH secretion
3. GH receptor antagonist
4. Radiation therapy: long time, can wipe out pituitary decrease fertility)
** GOAL = supressed GH & normal IGF-1