15 Principles of Endocrine control Flashcards
Name the 3 main types of hormones and give an example to each type.
- Proteins: insulin, glucagon, GH
- Amino acid derivatives: tyrosine, T3, T4
- Steroids: testosterone, estrogen, aldosterone, cortisol
How do thyroid hormones cross the membrane?
They use MCT8 transporters to cross the membrane (monocarboxylate transporter 8)
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
All of the above
What is non-genomic action of hormones?
Non-genomic action of hormones = generate secondary messenger inside the cell e.g. cAMP
How can steroid hormones be administered?
Oral/ Percutaneous/ Transdermal route (will not be degraded by digestive hormones, resistant to heat)
How can thyroid hormones be administered?
As they are amino acid derivatives, they can be administered by oral route (will not be degraded by digestive hormones, resistant to hear)
How can GH be administered?
As GH is a protein hormone, it can only be administered by injection for IV infusion
Plasma binding proteins are synthesized in the liver under partial ____________ control. (stimulated by __________ and inhibited by ____________)
Estrogenic
estrogen; androgen
How does the above circumstances affect plasma binding protein levels?
A. GH excess
B. Liver cirrhosis
C. Pregnancy
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)
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
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
Give 2 examples of plasma binding proteins for protein hormones.
- Growth hormone binding proteins (GHBP): for GH, represents extracellular domain for GH receptor
- Insulin-like growth factor binding proteins (IGFBP): for IGF
Bioavailability of hormones = amount of free form. What is the exception?
Testosterone = free form + albumin bound
Why does SHBG in females is higher than that in males?
Sex hormone binding globulin
This is because females have higher estrogen to stimulate the production of SHBG
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
D
A-C: for steroid and thyroid hormones
C: should be second messengers as postreceptors binding action
_______________ is used as precursors in steroid hormones and thyroid hormones production.
Cholesterol
Actions of trophic hormones e.g. ACTH, LH
- Stimulate activity and expression of ___________________to accelerate cholesterol uptake into mitochondria
- Induce expression of side chain cleavage enzyme and other steroidogenic enzymes
- Stimulate activity of ___________ to speed up breaking down of cholesterol ester into cholesterol
- Induce expression of __________
- steroidogenic acute regulatory (StAR) protein
- cholesterol esterase
- LDL receptors
What will happen when there is long-term elevated trophic hormone on steroidogenic endocrine gland?
Chronic stimulation by elevated trophic hormone may induce hypertrophy and hyperplasia of steroidogenic endocrine gland
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
All of the above
B. for prolonging half life and reduce clearance
Which of the examples demonstrates peripheral conversion of hormones?
A. Testosterone > dihydrotestosterone/ estradiol
B. Thyroxine > Triiodothyronine
C. Angiotensin I > Angiotensin II
All of the above
A: Dihydrotestosterone 80% from peripheral tissues, 20% from testis
C: by angiotensin converting enzyme
Give an example to each of the below hormone conversions.
- Activation
- Inactivation/ Reactivation
- Amplification pathway
- Diversification pathway
- Prohormone > bioactive hormone (e.g. Thyroxine > Triiodothyronine)
- cortisol > cortisone: 11beta-HSD2 (so cortisol will not bind to mineralocorticoid receptor to produce mineralocorticoid effect)
- testosterone > dihydrotestosterone by 5a-reductase
- testosterone > estradiol by aromatase
Why are finasteride/ dutasteride sed in the treatment of androgenetic alopecia/ benign prostatic hyperplasia?
They are 5a-reductase inhibitors. 5a-reductase is needed in the conversion of testosterone to dihydrotestosterone.
Why are anastrozole used in the treatment of breast cancer?
It is an aromatase inhibitor which inhibits the conversion from testosterone to estrogen.
What are the functions of the 2 enzymes 5’deiodinase and 5-deiodinase?
5’-deiodinase: for activation of T4 to T3
5-deiodinase: for inactivation of T4 to rT3
Why is there a need for pulsatile pattern for hormone secretion?
Serves to avoid desensitization of target cells (too much) or down-regulation of hormone receptors (too little)
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?
A: pulsatile; Cushing’s disease: no increase in early morning and no night time decrease
B: Acromegaly: always high, no increase in sleep
What test should be used for excess glucocorticoid?
Dexamethasone suppression test
What test should be used as a stimulatory test for GH?
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
When should an oral glucose tolerance test be ordered?
For diabetes/ excess GH
When is a synacthen test ordered?
When there is insufficient hormones from adrenal cortex
*stimulation test for adrenal cortex
What test should be used for suspected central/ nephrogenic DI?
Water deprivation test
High target gland hormone level + High trophic hormone level =?
Secondary hyperfunction
High target gland hormone level + Low trophic hormone level = ?
Primary hyperfunction
Low target gland hormone level + High trophic hormone level =?
Primary hypofunction (primary failure of target endocrine gland)
Low target gland hormone level + Low trophic hormone level =?
Secondary hypofunction
