15 Principles of Endocrine control

Question 1

Name the 3 main types of hormones and give an example to each type.

Answer 1

1. Proteins: insulin, glucagon, GH
2. Amino acid derivatives: tyrosine, T3, T4
3. Steroids: testosterone, estrogen, aldosterone, cortisol

Question 2

How do thyroid hormones cross the membrane?

Answer 2

They use MCT8 transporters to cross the membrane (monocarboxylate transporter 8)

Question 3

Genomic action of hormones
A. is long lasting
B. involves the activation or inactivation of genes
C. can be produced by signalling molecules that bind to cell surface receptors

Answer 3

All of the above

Question 4

What is non-genomic action of hormones?

Answer 4

Non-genomic action of hormones = generate secondary messenger inside the cell e.g. cAMP

Question 5

How can steroid hormones be administered?

Answer 5

Oral/ Percutaneous/ Transdermal route (will not be degraded by digestive hormones, resistant to heat)

Question 6

How can thyroid hormones be administered?

Answer 6

As they are amino acid derivatives, they can be administered by oral route (will not be degraded by digestive hormones, resistant to hear)

Question 7

How can GH be administered?

Answer 7

As GH is a protein hormone, it can only be administered by injection for IV infusion

Question 8

Plasma binding proteins are synthesized in the liver under partial ____________ control. (stimulated by __________ and inhibited by ____________)

Answer 8

Estrogenic

estrogen; androgen

Question 9

How does the above circumstances affect plasma binding protein levels?
A. GH excess
B. Liver cirrhosis
C. Pregnancy

Answer 9

A. less binding proteins available
B. high protein level > higher circulating level
C. pregnancy = high estrogen levels > increase in TBG (thyroxine binding globulin) production > increased levels of thyroxine T4 (increased in total hormone, not the biologically active hormone)

Question 10

Which of the following plasma binding protein has low affinity but high capacity?
A. Sex Hormone binding globulin
B. Cortisol binding globulin
C. Serum albumin
D. Thyroxine binding globulin

Answer 10

C

A: SHBG targets testosterone and estradiol
B. CBG targets cortisol and progesterone
D. TBG targets T3 and T4

all 3 of them have high affinity, low capacity

all 4 of them are plasma binding proteins for steroid and thyroid hormones

Question 11

Give 2 examples of plasma binding proteins for protein hormones.

Answer 11

1. Growth hormone binding proteins (GHBP): for GH, represents extracellular domain for GH receptor
2. Insulin-like growth factor binding proteins (IGFBP): for IGF

Question 12

Bioavailability of hormones = amount of free form. What is the exception?

Answer 12

Testosterone = free form + albumin bound

Question 13

Why does SHBG in females is higher than that in males?

Sex hormone binding globulin

Answer 13

This is because females have higher estrogen to stimulate the production of SHBG

Question 14

Which of the following features about protein hormones is correct?
A. They buffer changes in free hormone levels (if free form is used, bound form will dissociate to replenish)
B. Hormones are bound to plasma proteins to serve as a reservoir
C. Hormone-receptor complex as postreceptor binding action
D. They are unbound

Answer 14

D

A-C: for steroid and thyroid hormones
C: should be second messengers as postreceptors binding action

Question 15

_______________ is used as precursors in steroid hormones and thyroid hormones production.

Answer 15

Cholesterol

Question 16

Actions of trophic hormones e.g. ACTH, LH

1. Stimulate activity and expression of ___________________to accelerate cholesterol uptake into mitochondria
2. Induce expression of side chain cleavage enzyme and other steroidogenic enzymes
3. Stimulate activity of ___________ to speed up breaking down of cholesterol ester into cholesterol
4. Induce expression of __________

Answer 16

1. steroidogenic acute regulatory (StAR) protein
2. cholesterol esterase
3. LDL receptors

Question 17

What will happen when there is long-term elevated trophic hormone on steroidogenic endocrine gland?

Answer 17

Chronic stimulation by elevated trophic hormone may induce hypertrophy and hyperplasia of steroidogenic endocrine gland

Question 18

Which of the above are examples of of post-translational modification to yield bioactive hormones?

A. Insulin: forming disulphide bonds
B. Glycoprotein hormones (FSH, LH, TSH, hCG): glycolysation
C. inhibin/activin: form heterodimers/ homodimers

Answer 18

All of the above

B. for prolonging half life and reduce clearance

Question 19

Which of the examples demonstrates peripheral conversion of hormones?

A. Testosterone > dihydrotestosterone/ estradiol
B. Thyroxine > Triiodothyronine
C. Angiotensin I > Angiotensin II

Answer 19

All of the above

A: Dihydrotestosterone 80% from peripheral tissues, 20% from testis

C: by angiotensin converting enzyme

Question 20

Give an example to each of the below hormone conversions.

1. Activation
2. Inactivation/ Reactivation
3. Amplification pathway
4. Diversification pathway

Answer 20

1. Prohormone > bioactive hormone (e.g. Thyroxine > Triiodothyronine)
2. cortisol > cortisone: 11beta-HSD2 (so cortisol will not bind to mineralocorticoid receptor to produce mineralocorticoid effect)
3. testosterone > dihydrotestosterone by 5a-reductase
4. testosterone > estradiol by aromatase

Question 21

Why are finasteride/ dutasteride sed in the treatment of androgenetic alopecia/ benign prostatic hyperplasia?

Answer 21

They are 5a-reductase inhibitors. 5a-reductase is needed in the conversion of testosterone to dihydrotestosterone.

Question 22

Why are anastrozole used in the treatment of breast cancer?

Answer 22

It is an aromatase inhibitor which inhibits the conversion from testosterone to estrogen.

Question 23

What are the functions of the 2 enzymes 5’deiodinase and 5-deiodinase?

Answer 23

5’-deiodinase: for activation of T4 to T3

5-deiodinase: for inactivation of T4 to rT3

Question 24

Why is there a need for pulsatile pattern for hormone secretion?

Answer 24

Serves to avoid desensitization of target cells (too much) or down-regulation of hormone receptors (too little)

Question 25

What are the patterns of secretion of the below hormones?

A. ACTH and cortisol
B. GH

What is the abnormal pattern of secretion of them in certain diseases?

Answer 25

A: pulsatile; Cushing’s disease: no increase in early morning and no night time decrease

B: Acromegaly: always high, no increase in sleep

Question 26

What test should be used for excess glucocorticoid?

Answer 26

Dexamethasone suppression test

Question 27

What test should be used as a stimulatory test for GH?

Answer 27

insulin tolerance test/ glucagon stimulation test

GH: promote use of fat, raise blood glucose as energy source in order to spare protein form being metabolized.
Secretion of GH is stimulated by hypoglycemia

Question 28

When should an oral glucose tolerance test be ordered?

Answer 28

For diabetes/ excess GH

Question 29

When is a synacthen test ordered?

Answer 29

When there is insufficient hormones from adrenal cortex

*stimulation test for adrenal cortex

Question 30

What test should be used for suspected central/ nephrogenic DI?

Answer 30

Water deprivation test

Question 31

High target gland hormone level + High trophic hormone level =?

Answer 31

Secondary hyperfunction

Question 32

High target gland hormone level + Low trophic hormone level = ?

Answer 32

Primary hyperfunction

Question 33

Low target gland hormone level + High trophic hormone level =?

Answer 33

Primary hypofunction (primary failure of target endocrine gland)

Question 34

Low target gland hormone level + Low trophic hormone level =?

Answer 34

Secondary hypofunction