5: The Endocrine System

Question 1

What are the three chemical classes of hormone?

Answer 1

Peptide, steroids, amino acid derivatives

Question 2

Discuss the mechanism of peptide hormones. Give examples

Answer 2

• Made of amino acids
• Released by exocytosis
• Cannot pass through plasma membrane because charged => bind to extracellular G-protein coupled receptor on target cell, causing signalling cascade
• Hormone = ‘first messenger’, receptor = ‘second messenger’

First messenger examples: ADH, insulin
Second messenger examples: cAMP, inositol triphosphate/IP3, calcium

Question 3

Sequence signal cascade w/ G-protein coupled receptor

Answer 3

G protein coupled receptor activates OR inhibits adenallyl cyclase => cAMP levels change accordingly

When present, cAMP binds to factors like protein kinase A
=> this phosphorylates transcription factors => exerts ultimate effect

Question 4

How long-acting are peptide hormones?

Answer 4

Generally short-lived b/c act through transient secondary messenger systems, which are easy to turn on/off

Question 5

Discuss the mechanism of steroid hormones. Give examples

Answer 5

• Derived from cholesterol; produced by gonads and adrenal cortex
• travel via transport protein; diffuse through membrane; intracell or intranuclear receptors; can bind directly to DNA!

Question 6

What is dimerization?

Answer 6

Pairing of two steroid receptor-hormone complexes

Question 7

How long lived are steroid hormones?

Answer 7

Slow but long-lived because change DNA/mRNA

Question 8

Discuss the mechanism of amino acid hormones. Give examples

Answer 8

• Less common than peptide/steroid
• Include: epinephrine, norepinephrine, thyroxine, triiodothyronine
• One or two aa, with additional modifications
• Chemistry unpredictable. epinephrine/norepinephrine bind to G coupled receptors. Thyroid hormones bind intracellularly

Question 9

What are catecholamines?

Answer 9

epinephrine, norepinephrine

Question 10

What is the difference between a direct hormone and a tropic hormone?

Answer 10

Tropic = require intermediate hormone to act, usually originate in brain/anterior pituitary

Question 11

KNOW ANT PIT TROPIC HORMONES

Answer 11

GnRH -> FSH/LH
Growth Hormone
TRH -> TSH
Corticotropin-releasing factor -> adrenocorticotropic hormone

Question 12

KNOW POST PIT HORMONES

Answer 12

Oxytocin

ADH

Question 13

KNOW ANT PIT DIRECT HORMONES

Answer 13

Prolactin - stimulares milk production in mammary glands

Question 14

What are triiodothyronine and thyroxine?

Answer 14

triiodothyronine = T3
thyroxine = T4

Both produced by iodination of tyrosine in follicular cells of thyroid

Question 15

KNOW PARATHYROID HORMONES

Answer 15

Produced by parafollicular cells/ C-cells

Good chart p. 173

Question 16

What are polyuria and polydipsia

Answer 16

Increased urination, increased thirst – common in diabetics

Question 17

What is somatostatin?

Answer 17

Inhibits insulin ad glucagon secretion. Stimulated by high glucose and aa concentrations. Also produced by hypothelamus; decreases GH secretion

Question 18

Discuss pineal gland hormones

Answer 18

Pineal gland = deep in brain

Secretes melatonin in response to retinal projections –> causes sleepiness

Question 19

What is erythropoietin?

Answer 19

Secreted by kidneys in response to low blood oxygen. Stimulates bone marrow to produce more RBC

Question 20

What is atrial natriuretic peptide / ANP?

Answer 20

Secreted by heart, when atrial cells are stretched from excess blood volume.
Promotes excretion of sodium -> increases urine volume -> lowers blood pressure

Question 21

What is thymosin?

Answer 21

Released by thymus. Stimulates T cell development / differentiation. Atrophies by adulthood.