Costanzo Endocrine Part 5

Front 1

Describe prolactin

Back 1

1. The major hormone responsible for lactogenesis

2. Participates, with estrogen, in breast development

3. Is structurally homologous to growth hormone

Front 2

Describe the regulation of prolactin secretion by hypothalamic control

Back 2

1. Through dopamine and thyrotropin-releasing hormone (TRH)

2. Prolactin secretion is tonically inhibited by dopamine [prolactin-inhibiting factor (PIF)] secreted by the hypothalamus. Thus, interruption of the hypothalamic-pituitary tract causes increased secretion of prolactin and sustained lactation

3. TRH increase prolactin secretion

Front 3

Describe the regulation of prolactin secretion by negative feedback control

Back 3

Prolactin inhibits its own secretion by stimulating the hypothalamic release of dopamine

Front 4

Describe the actions of prolactin

Back 4

1. Stimulates milk production in breast (casein, lactabumin)

2. Stimulates breast development (in a supportive role with estrogen)

3. Inhibits ovulation by decreasing synthesis and release of gonadotropin-releasing hormone (GnRH)

4. Inhibits spermatogenesis (by decreasing GnRH)

Front 5

Describe prolactin deficiency

Back 5

1. From destruction of the anterior lobe

2. Results in the failure to lactate

Front 6

Describe prolactin excess

Back 6

1. Results from hypothalamic destructiion (due to loss of the tonic "inhibitory" control by dopamine) or from prolactin-secreting tumors (prolactinomas)

2. Causes glactorrhea and decreased libido

3. Causes failure to ovulate and amenorrhea because it inhibits GnRH secretion

4. Can be treated with bromocriptine, which reduces prolactin secretion by acting as a dopamine agonist

Front 7

List the factors that increase prolactin secretion

Back 7

-Estrogen (pregnancy)
-Breast-feeding
-Sleep
-Stress
-TRH
-Dopamine antagonists

Front 8

List the factors that decrease prolactin secretion

Back 8

-Dopamine
-Bromocriptine (dopamine agonist)
-Somatostatin
-Prolactin (by negative feedback)

Front 9

Which hormones are produced by the posterior pituitary?

Back 9

1. ADH
2. Oxytocin

Front 10

Describe the structure of the hormones produced by the posterior pituitary

Back 10

ADH and oxytocin are homologous nonapeptides

Front 11

Describe the synthesis and release of hormones from the posterior pituitary

Back 11

1. Synthesized in hypothalamic nuclei and are packaged in secretory granules with their respective neurophysins

2. Travel down the nerve axons from secretion by the posterior pituitary

Front 12

Describe ADH

Back 12

1. Originates primarily in the supraoptic nuclei of the hypothalamus

2. Regulates serum osmolarity by increasing H2O permeability of the late distal tubules and collecting ducts

Front 13

Describe the actions of ADH

Back 13

1. Increased H2O permeability of the principle cell of the late distal tubule and collecting duct (via a V2 receptor and an adenylate cyclase-cAMP mechanism)

b. Constriction of vascular smooth muscle (via a V1 receptor and an IP3/Ca2+ mechanism)

Front 14

List the factors that increase ADH secretion

Back 14

-Increased serum osmolarity
-Volume contraction
-Pain
-Nausea (powerful stimulant)
-Hypoglycemia
-Nicotine, opiates, antineoplastic drugs

Front 15

List the factors that decrease ADH secretion

Back 15

-Decreaesd serum osmolarity
-Ethanol
-α-agonists
-ANP

Front 16

Describe oxytocin

Back 16

1. Originates primarily in the paraventricular nuclei of the hypothalamus

2. Causes ejection of milk from the breast when stimulated by suckling

Front 17

Describe regulation of oxytocin by suckling

Back 17

1. Is the major stimulus for oxytocin secretion

2. Afferent fibers carry impulses from the nipple to the spinal cord. Relays in the hypothalamus trigger the release of oxytocin from the posterior pituitary

3. The sigh or sound of the infant may stimulate they hypothalamic neurons to secrete oxytocin, even in the absence of suckling

Front 18

Beyond suckling, what other stimuli cause increased secretion of oxytocin

Back 18

Dilation of the cervix and orgasm

Front 19

Describe the actions of oxytocin

Back 19

1. Contraction of myoepithelial cells in the breast
-Milk is forced from the mammary alveoli into the ducts and delivered to the infant

2. Contraction of the uterus
-During pregnancy, oxytocin receptors in the uterus are upregulated as parturition approaches, although the role of oxytocin in normal labor is uncertain
-Oxytocin can be used to induce labor and reduce postpartum bleeding