Hypothalamus and Pituitary

Posterior Pituitary

Storage and release site for vasopressin and oxytocin, produced in the PVN (paraventricular) and SON (supraoptic nerve).

Anterior Pituitary

Responsible for GH, Prolactin, TSH, ACTH, LH & FSH. All but one act as trophic hormones.

Trophic Hormones

Relay signals, not signaling directly to a gland. 

Prolactin

Not trophic hormone

Signal Control

Short loop and long loop

Short Loop Signal Control

Feedback from the hypothalamus on the trophic hormone (primary)

Long Loop Signal Control

Feedback from the hypothalamus on secondary or tertiary hormone.

Dwarfism

Growth hormone deficiency causes failure to grow with short stature, mild obesity, and delayed puberty. 

Cause of Dwarfism

1. Decreased secretion of GHRH due to hypothalamic dysfunction

2. Primary deficiencies of growth hormone secretion from the anterior pituitary 

3. Failure to generate somatomedins in the liver

4. Deficiency of growth hormone or somatomedin receptors in target tissues (growth hormone resistance)

Laron Dwarfism

A variant of dwarfism with elevated growth hormone levels but defective hormone receptors (treatment with growth hormone ineffective)

Gigantism

Before puberty, causing increased linear growth with increased hormonal stimulation at the epiphyseal plates

Acromegaly

After puberty, increasing periosteal bone growth, increased organ size, and increased enlargement of stuff. Insulin resistance and glucose intolerance.

Growth Hormone Excess

Due to growth hormone-secreting pituitary adenoma

Stimulating Growth Hormone

Decreased glucose, decrease free FA, arginine, fasting, hormones of puberty, exercise, stress

Inhibiting Growth Hormone

Increase glucose, increase free FA, obesity, somatostatin, growth hormone, pregnancy 

Syndrome of Inappropriate ADH

1. Excess ADH secreted from tumors

2. High levels of ADH cause excess water absorption, diluting body fluids

3. Decreases plasma osmolarity and Na2+ concentration, making urine concentrated.

4. Treated with ADH antagonists or water restriction

Nephrogenic Diabetes Insipidus

INcrease ADH with principle cells of collecting duct being responsive to ADH. Defective V₂ receptor, G_s protein, or adenylyl cyclase. Treated with loop diuretics.

Central Diabetes Insipidus

1. Caused by failure of the posterior pituitary to secrete ADH

2. Low ADH → impermeable collecting ducts to water → can’t concentrate urine

3. Produce large volumes of dilute urine

4. Body fluids become concentrated (increase serum Na+ concentration)

5. Treated with ADH analogue (desmopressin, dDAVP)

Stimulating ADH

Increased serum osmolarity, decreased ECF volume, pain, angiotensin II, nausea, hypoglycemia, nicotine, opiates, antineoplastic drugs

Inhibiting ADH

Decreased serum osmolarity, ethanol, alpha adrenergic agonist, ANP

Prolactin Deficiency

Destroys the entire anterior lobe of the pituitary and selectively destroys the lactotrophs. Results in a failure to lactate

Prolactin Excess

Causes destruction of the hypothalamus, interruption of the hypothalamic-hypophysial tract, and prolactin-secretin tumors

Stimulatory Factors of Prolactin

Pregnancy

Breast-feeding

Sleep

Stress

TRH

Dopamine antagonist

Inhibitory Factors of Prolactin

Dopamine

Bromocriptine

Somatostatin

Prolactin