10/22/14

Question 1

What are the levels of prolactin during and after pregnancy?

Answer 1

• During pregnancy, high circulating concentrations of estrogen increase prolactin levels by 10- to 20-fold. However, at the same time, estrogen, as well as progesterone, inhibit the stimulatory effects of prolactin on milk production. It is the abrupt drop of estrogen and progesterone levels following delivery that allows prolactin — which temporarily remains high — to induce lactation.
• After childbirth, prolactin levels fall as the internal stimulus for them is removed. Sucking by the baby on the nipple then promotes further prolactin release, maintaining the ability to lactate. The sucking activates mechanoreceptors in and around the nipple. These signals are carried by nerve fibers through the spinal cord to the hypothalamus, where changes in the electrical activity of neurons that regulate the pituitary gland cause increased prolactin secretion. The suckling stimulus also triggers the release of oxytocin from the posterior pituitary gland, which triggers milk let-down
• Prolactin controls milk production (lactogenesis) but not the milk-ejection reflex; the rise in prolactin fills the breast with milk in preparation for the next feed.

Question 2

What is the material inside the lumen of the thyroid follicular cells called? What are the newly synthesized thyroid hormones attached to?

Answer 2

Colloid; T3 and T4 are attached to THYROGLOBULIN

Question 3

What is the major secretory product of the thyroid gland? Why?

Answer 3

T4; the coupling reaction of DIT+DIT is faster than MIT+DIT (T3)

Note T3 is physiologically active form.

Question 4

How is iodine transported into the follicular epithelial cells of the thyroid gland? What regulates it?

Answer 4

Na-I contransport

Low levels of [I-] stimulate the pump, high levels of [I-] inhibit pump

Thiocyanate and Perhchlorate inhibit pump

Question 5

This enzyme oxidizes iodine in the follicular epithelial cell lumen of the thyroid (+ organifies I onto tyrosine of thyroglobulin and couples MIT/DIT reactions)

Answer 5

Thyroid Peroxidase

Inhibited by Propylthiouracil (PTU)

Question 6

When the thyroid gland is stimulated, how does T3/T4 get released from thyroglobulin?

Answer 6

Iodinated thyroglobulin is endocytosed and T4/T3 are hydrolyzed by lysosomal enzymes. MIT/DIT are deiodinated by thyroid deiodinase and recycled.

Question 7

Wolf-Chaikoff Effect

Answer 7

Intake of lots of iodine will inhibit organification and synthesis of thyroid hormones (cause transiet hypothyroidism)

Question 8

What doe thyroid hormones bind to in circulation? What happens to this during pregnancy?

Answer 8

TBG – Thyroxine-binding globulin (produced by liver)

High levels of estrogen increase TBG (transiently lower plasma levels cause increased stimulation of thryoid hormone, but levels of free physiologically active thryoid hormones reaches normal levels)

Question 9

What happens to thyroid hormones in starvation?

Answer 9

Normally, 5’iodinase converts T4 to T3 in tissues; starvation inhibits this iodinase (more is converted fto reverse T3, which is inactive) in all tissues EXCEPT brain

Naturally, this will decrease oxygen consumption and BMR during starvation for muscles, etc.

Question 10

Describe the negative feedback mechanism of thyroid hormones

Answer 10

Free T3 (converted from T4) down-regulates the TRH receptor on thyroid gland when the levels of T4/T3 in the blood are HIGH

Question 11

Levels of TSH in Graves Disease

Answer 11

Graves Disease – Antibodies against TRH receptor causes HYPERthryoidism and trophic effect on thryoid gland
TSH levels are actually quite low because of the negative feedback from increased T3/T4 in circulation

Question 12

What is the effect of T3 on BMR?

Answer 12

Increased oxygen consumption
Increased body temperature

In all tissues EXCEPT brain, spleen, gonads

How? Increases activity of Na-K pump (need more ATP, need more O2, more exothermic heat being released…)

Question 13

How does T3 affect metabolism?

Answer 13

If we are taking in more oxygen and want to produce more ATP, we need more substrates for metabolism, which means there is an INCREASE in lipolysis, gluconeogenesis, glycogenolysis, and glucose absorption in the gut, but there is a net CATABOLIC state because, well, cellular respiration is a happening.

Also increases synthesis of key metabolic enzymes

Question 14

How does T3 increase cardiac output?

Answer 14

Induces synthesis of B1-adrenergic receptors, which increase heart rate and contractility
Also induces synthesis of cardiac myosin and sarcoplasmic reticulum Ca2+ ATPase

Question 15

How does T3 promote growth?

Answer 15

Synergistic affects with GH
Promote ossification and fusion of bone plates and bone maturation
Hypothyroidism will cause bne age to be LESS than actual age

Question 16

What happens if there is hypothyroidism in the perinatal period?

Answer 16

Irreversible mental retardation

Question 17

What causes proptosis in Graves disease?

Answer 17

Autoantibodies target fibroblasts in the eye muscles, which can differentiate into fat cells; become infalmed and causes “proptosis” or swelling of the eye; also causes edema from the local vasculature that can’t properly drain

Question 18

What is the effect of hypothyroidism on CNS?

Answer 18

Listlessness, slowed movement, somnolence, impaired memory, and decreased metnal capacity.

Also causes hyperexcitability, hyperreflexia, and irritability.