Hypothalamus, Pituitary, Thyroid

Question 1

Neurosecretory Cell

Answer 1

Neuron that acts as an endocrine cell and produces neuropeptides.

Question 2

What do hypothalamic neuropeptides do? How are they transported?

Answer 2

They are transported through the hypothalamic pituitary portal system to the anterior pituitary, where they cause AP hormone release.

Question 3

Lactotrophs, Somatotrophs, Gonadotrophs, Corticotrophs, Thyrotrophs

Answer 3

Release: Prolactin, GH, LH and FSH, ACTH, and TSH.

Question 4

Posterior Pituitary hormones

Answer 4

Vasopressin and oxytoxin. Stored in PP, made in hypothalamus.

Question 5

3 Hormone Classes

Answer 5

Peptides, Amino acid derivatives, Steroids. Most hormones are peptides. Only steroids like cortisol are lipid soluble and bind to intracellular receptors.

Question 6

What do FSH, GH, LH, Prolactin, TSH, ACTH, and Vasopressin stimulate?

Answer 6

Ovary (estrogen), liver (IGF-1), testicles (testosterone), breasts (milk), Thyroid (thyroxine), adrenals(cortisol), kidneys (hold onto water). Products in parentheses negatively feedback onto initial hormone.

Question 7

Examples of endocrine positive feedback

Answer 7

Breast feeding causes additional prolactin release. Ovulation causes increases in estrogen.

Question 8

Hypothalamic inhibitory neuropeptides

Answer 8

Somatostatin (stops GH), dopamine (stops prolactin).

Question 9

What creates a target cell?

Answer 9

Presence of receptors

Question 10

Explain:

Answer 10

When GnRH is given continuously, receptors downregulate and cause less release of LH and FSH

Question 11

Which hormone’s circadian rhythms does this represent?

Answer 11

Cortisol

Question 12

What hormone does this represent?

Answer 12

Testosterone

Question 13

Why are prolactin and growth hormone so similar?

Answer 13

They are in the same gene family. Both use Jak/Stat pathway.

Question 14

Jak Stat Pathway

Answer 14

Tyrosine-kinase associated receptors. Binding of substrate causes dimerization and phosphorylation of Jak and STAT. STAT moves into the nucleus and acts as a transcription factor to upregulate certain genes of increased growth and metabolism.

Question 15

Ghrelin. How does it work?

Answer 15

Produced by stomach, activates NPY neurons and activates the pituitary. Associated with hunger. Works by stimulating growth hormone release.

Question 16

Direct Actions of Growth Hormone

Answer 16

Are counter-regulatory to insulin. GH increases gluconeogenesis and lipolysis. GH also activates IGF-1, which uses GH’s breakdown products to create stuff.

Question 17

Stimulators and inhibitors of GH

Answer 17

Stimulators: Exercise and Puberty, Ghrelin

Inhibitors: Obesity and advanced age.

Question 18

Indirect actions of GH

Answer 18

All through IGF1. IGF1 is a growth factor for muscle and bone. In bone, it stimulates osteoblasts and inhibits osteoclasts.

Question 19

Why is Regulation of Prolactin Unique?

Answer 19

Because it’s mostly tonic inhibition by dopamine released from hypothalamus. This inhibition is overcome in pregnancy and breast feeding. Prolactin causes milk production.

Question 20

Where is the thyroid located?

Answer 20

Wrapped tightly around the trachea below the cricoid cartilage.

Question 21

How is the thyroid stimulated?

Answer 21

By TSH from anterior pituitary.

Question 22

Thyroid Feedback Mechanism

Answer 22

TRH from hypothalamus stimulates TSH from AP, which stimulates T4/T3 release from Thyroid gland.

T4/T3 negatively regulate AP activity.

Question 23

How are TSH, HCG, LH, and FSH related?

Answer 23

They are part of the same hormone family. They are all glycoproteins (protein w/carbohydrate antenna).

Question 24

TSH, FSH, LH, HCG structure

Answer 24

All have identical alpha subunit, unique beta subunit that conferrs specificity for their individual receptors.

Question 25

HCG

Answer 25

Secreted from chorion in pregnancy. Very high levels of HCG can stimulate the TSH receptor, causing T3 and T4 release. Sometimes an HCG secreting tumor can cause hyperthyroid-like symptoms.

Question 26

TSH glycosylation

Answer 26

In order to function correctly, TSH must be glycosylated. However, our assays are not sensitive enough to determine if TSH in the blood is glycosylated correctly, so it often goes undetected. So, we measure **improperly** glycosylated TSH in blood.

Question 27

What does TSH do when it binds its receptor?

Answer 27

Induces hormone synthesis and secretion. Also stimulates thyroid cell growth and differentiation.

Question 28

T3 and T4

Answer 28

T3 (triiodothyronine)- 20% of Thyroid secretions. Can be created by T4 in tissues via peripheral conversion. Very potent. T4 (Thyroxine)- 80% of thyroid secretions. Circulating precursor. Long half-life.

Question 29

Peripheral Conversion. How does it occur?

Answer 29

The process of converting T4 to T3 in tissues. 75% of T3 is created this way. Type I and Type II deiodinases remove one iodine from the outer iodine to create T3. Type III deiodinases will create rT3 by removing the inner iodine.

Question 30

Thyroid Follicle Structure

Answer 30

Sits next to blood vessel, follicular epithelial cells surround lumen (colloid).

Question 31

Thyroglobulin (T3 and T4 synthesis)

Answer 31

A carrier molecule with attached tyrosines made in follicular epithelial cells. Once transported into colloid, will pick up Iodine (I2) to make DITs and MITs on surface. Transported back into epithelial cell, releases DIT and MIT, and is recycled. DIT+DIT = T4, DIT+MIT=T3.

Question 32

How is iodide transported into the follicular epithelial cell?

Answer 32

Via a Na-I cotransporter.

Question 33

What do DIT and MIT stand for?

Answer 33

Diiodotyrosine, monoiodotyrosine.

Question 34

Radioactive Iodine

Answer 34

Can take a picture of thyroid, destroy thyroid tissue, or treat thyroid cancer.

Question 35

Wolff-Chaikoff Effect (High doses of Iodine)

Answer 35

High doses of Iodine will down-regulate Na-I cotransporter, so less I is pumped into colloid. Less T3 and T4 made. Treats hyperthyroidism.

Question 36

TBG

Answer 36

Thyroxine-binding globulin. 99.97 of T4 circulates bound to TBG.

Question 37

Once T3 is in the cell, what happens?

Answer 37

Binds to nuclear receptor which brings it inside, binds to DNA, acts as a TF.

Question 38

Effect of T3 and T4.

Answer 38

Growth- Bone and cells CNS- Maturation BMR- Increase Na-K pump, increase O2 consumption, increase heat production, increase BMR Metabolism- Increased glucose absorption, increased glycogenolysis, increased gluconeogenesis, increased lipolysis Cardiovascular- Increased cardiac output, Cholesterol regulation

Question 39

Thyroid hormone effect on cholesterol

Answer 39

Promotes bad cholesterol excretion, and increases HDL levels.

Question 40

Why does paleo diet increase cholesterol?

Answer 40

Resembles starvation, which lowers thyroid hormone levels.

Question 41

Thyroid Hormone effects on vasculature and kidney

Answer 41

Promotes vasodilation, increase of RAAS system, which promotes sodium reabsorption and increase in blood volume. In kidney, increases sodium reabsorption. In heart, increases inotropy and chronotropy, increases BP. **INCREASES GFR.**