All Guyton Endocrine

Question 1

Name the hormones produced by the anterior pituitary and each of their main functions

Answer 1

1. Growth hormone - protein formation, cell multiplication, cell differentiation
2. ACTH - controls secretion of some adrenocortical hormones (glucocorticoids, androgens), which affect metabolism of glucose, proteins, fats
3. TSH - controls secretion rate of T3 and T4
4. Prolactin - mammary gland development and milk production
5. FSH and LH - growth of overlies and testes

Question 2

What are hormones secreted by the posterior pituitary and their main functions?

Answer 2

ADH/vasopressin - controls rate of water excretion into urine
Oxytocin - helps express milk from glands, helps in uterine contraction during baby delivery

Question 3

What controls hormone release from the anterior pituitary/

Answer 3

Hypothalamic releasing and inhibitory hormones

Question 4

What are the main functions of growth hormone?

Answer 4

Increases rate of protein synthesis in most cells of body
Increases mobilization of fatty acids to form adipose, increases FFA in blood and increases use of FFA for energy
Decreases rate of glucose utilization throughout body

Question 5

What is the most important somatomedin?

Answer 5

IGF1 aka somatomedin C

It is produced predominantly in the liver in response to GH, and attaches strongly to a carrier protein in the blood and is released slowly from the blood to the tissues

Its slow release prolongs growth promoting effects of bursts of GH

Question 6

What stimulates GH secretion?

Answer 6

Decreased BG and FFA, increased AA, starvation/fasting, protein deficiency, trauma, stress (catecholamines), exercise, testosterone/ estrogen, deep sleep GHRH, ghrelin

Question 7

What inhibits GH secretion?

Answer 7

Increased BG and FFA, aging, obesity, GHIH (somatostatin), exogenous GH, somatomedins

Question 8

What are the physiological functions of ADH?

Answer 8

ADH causes the collecting ducts to be permeable to water which results in resorption of water and concentrated urine. In the absence of ADH, the luminal membrane of tubular cells of the collecting ducts are impermeable to water and this results in dilute urine

ADH binds with membrane receptors that activate Adenylyl Cyclades —> formation of cAMP inside the tubule cell —> phosphorylation of elements of special vesicles —> vesicles insert into apical cell membrane —> increase water permeability

Question 9

What regulates ADH secretion?

Answer 9

Osmoreceptors (neuron receptors in or near the hypothalamus) sense increased ECG osmolarity —> fluid is pulled by osmosis out of osmoreceptors to cause additional secretion of ADH (vice versa if ECF is dilute)

If ECF is concentrated —> ADH neurons in supraoptic nuclei transmit impulses to the posterior pituitary —> release large amount of ADH into blood —> effects collecting ducts of nephron

Low blood vol and BP also stimulate ADH secretion —> increased ADH stimulates vasoconstriction of arterioles throughout body and increased BP
Decreased stretch of baroreceptors of the carotid and aortic and pulmonary regions also stimulate ADH secretion (decreased stretch indicates under filling, hemorrhage, etC)

Question 10

What is the predominant metabolically active hormone secreted by the thyroid gland?

Answer 10

93% is T4

Remaining is T3

Question 11

What is the most potent thyroid hormone secreted by the thyroid gland?

Answer 11

T3 is 4x more potent than T4 but persists for a much shorter time

Almost all T4 is eventually converted to T3 in tissues

Functions of both hormones are the same, but T3 is more potent and has a faster onset of action

Question 12

What is the thyroid gland composed of?

Answer 12

Follicles, which contain colloid

Question 13

What is a major constituent of colloid?

Answer 13

Thyroglobulin, which contains the thyroid hormones

Question 14

What is required for formation of thyroxine?

Answer 14

Iodine

Question 15

What transports iodides from the blood into the thyroid and follicles?

Answer 15

1. Sodium iodide symporter - cotransports one iodide along with 2 Na ions across the plasma membrane into the cell.

The energy for transporting iodide against a concentration gradient comes form Na/K ATPase which creates a low intracellular Na concentration and gradient for facilitated diffusion of Na into the cell
TSH stimulates the activity of the iodide pump

2. Iodide trapping - process of concentrating the iodide in the cell, rate of this is determined by TSH

Iodide is transported out of thyroid cells across the apical membrane into the follicle by a chloride iodide ion counter transporter molecule (I.e. PENDRIN)

Question 16

What are the major substrates that combine with iodine to form thyroid hormones?

Answer 16

Tyrosine

ER and Golgi apparatus of thyroid cells create a glycoprotein called thyroglobulin, which contains multiple tyrosine AA

Question 17

How does iodide combine with tyrosine?

Answer 17

It is oxidized by the enzyme peroxidase and its accompanying hydrogen peroxide on the apical membrane of the cell or attached to it

Question 18

What is the process of organification in regards to thyroid hormone synthesis?

Answer 18

Bidding of iodine with thyroglobulin

Tyrosine is first iodized to form monoiodotyrosin then diiodotyrosine, then couple to make T3 and T4

Question 19

How are T3 and T4 released into blood from thyroid gland?

Answer 19

T3 and T4 are cleaved from thyroglobulin molecule prior to being released
The apical surface of the thyroid cell sends out a pseudopod extension that closes around a small portion of colloid forming a pinocytic vesicle released into cell

Lysosomes in the cell cytoplasm fuse with these vesicles to form digestive vesicles containing digestive enzymes

Multiple proteases among the enzymes digest thyroglobulin and release T4 and T4 in free form
T3 and T4 diffuse through the base of the thyroid cell into blood

3/4 of tyrosine in thyroglobulin never becomes thyroid hormones. They are used in the recycling process

Question 20

Which is more strongly protein bound: T3 or T4?

Answer 20

T4

Question 21

What is the general effect of thyroid hormones?

Answer 21

Activate mic;ear transcription of large numbers of genes, which leads to:
1. Synthesis of protein enzymes, structural proteins, etc — generalized functional increase in activity throughout the body

Thyroid hormones act intracellular/ intranuclear on DNA transcription

Question 22

What is the mechanism of action of methimazole?

Answer 22

Prevents formation of thyroid hormone from iodides and tyrosine (partly blocks peroxidase enzyme needed for iodinating of tyrosine and partly blocks coupling of 2 iodinated tyrosines)

Question 23

What are the three layers of the adrenal cortex?

Answer 23

Zona glomerulosa - 15% of cortex, contains aldosterone synthase, which allows for aldosterone secretion
Zona fasciculata - middle and widest zone ~75% of cortex - secretes glucocorticoids (cortisol, corticosterone) and small amounts of adrenal androgens and estrogens - secretion controlled via ACTH. Cortisol has some mineralocorticoid activity. 90-95% of cortisol in plasma binds to plasma proteins

Zona reticularis - inner thin zone, secretes adrenal androgens and small amounts of estrogens. ACTH also regulates secretion here, but other factors such as androgen stimulating hormone from the pituitary also regulate

Question 24

What is the rate limiting step in formation of adrenal steroids?

Answer 24

Cholesterol desmolase cleavage of cholesterol to form pregnenolone

Cholesterol enters adrenal cell —> delivered to mitochondria —> cleaved by cholesterol desmolase —> pregnenolone

Question 25

What is the function of aldosterone?

Answer 25

Mineralocorticoid Increases renal tubular resorption of Na and secretion of K This occurs in the principal cells of the collecting tubule (less so in distal and collecting ducts)

Question 26

What is aldosterone escape?

Answer 26

Excess aldosterone results in increased ECF volume which results in increased blood pressure Increased BP results in increased renal excretion of Na and water (I.e. pressure natriuretic and dieresis) to return renal output of Na and water back to normal This return to normal of Na and water excretion by the kidneys as a result of pressure natriuretic and dieresis = aldosterone escape This will balance the intake and output of na and water, but increased BP will persist as long as high levels of aldosterone remain present

Question 27

What are consequences of exposure to excess aldosterone?

Answer 27

Hypokalemia Hypertension Muscle weakness

Question 28

What regulates aldosterone secretion by the adrenal?

Answer 28

Increased potassium concentration in the ECF increases aldosterone secretion Increased Angiotensin II in the ECF increases aldosterone secretion Increased NA concentration in the ECF will very slightly decrease aldosterone secretion ACTH from the anterior pituitary is necessary for aldosterone secretion Potassium concentration and the RAAS are the most potent in regulating aldosterone secretion

Question 29

What effects does cortisol have on metabolism?

Answer 29

Stimulates gluconeogenesis Increases protein breakdown from muscle Antagonizes insulin Causes decreased glucose utilization by body Causes an increase in liver and plasma proteins Increases mobilization of FFA for energy

Question 30

What are the three cell types in the islets of langerhans and what do these cells secrete?

Answer 30

Beta - 60% of cells - secrete insulin and Amy Lin Alpha - 25% of cells - secrete glucagon Delta - 10% of cells - secrete somatostatin

Question 31

What are the major effects of insulin?

Answer 31

Promotes muscle glucose uptake and metabolism Promotes liver uptake and storage and use of glucose Promotes conversion of excess glucose into FFA and inhibits gluconeogenesis by the liver Promotes fat storage and synthesis (inhibits hormone sensitive lipase to prevent hydrolysis of triglycerides)