Steroids Flashcards
What is the precursor molecule for steroid hormones?
cholesterol
Where does the body get cholesterol from?
the diet and from synthesis in the liver from acetyl CoA
What is the enzyme required for cholesterol synthesis?
HMG-CoA reductase
Where does the last stage of cholesterol synthesis occur?
in the endoplasmic reticulum
What enzyme is required to convert male sex steroids to female sex steroids?
aromatase
What are the two types of corticosteroids?
mineralocorticoids (aldosterone) and glucocorticoids (cortisol)
How are steroid hormones metabolised?
by CYP3A4 in the liver to form bile acids
How are sex steroids transported in the blood?
on sex steroid binding protein
Where is the receptor for sex steroids?
in the cell nucleus
Where is the receptor for adrenal steroids (glucocorticoids and mineralocorticoids)?
in the cell cytosol
Where does the activated steroid receptor bind?
to the hormone response element on DNA
What is cyproterone acetate and what is it used for?
an inhibitor of the nuclear androgen receptor - used to treat hirsuitism, male to female gender changes, prostate cancer, priapism and hypersexuality
What hormones in the hypothalamus and anterior pituitary lead to the release of adrenal steroids?
CRH and ACTH
What hormones in the hypothalamus and the anterior pituitary lead to the relase of sex steroids from the gonads?
GnRH and FSH/LH
What is the function of mineralocorticoids?
promote retention of sodium and water to increase blood pressure and blood volume
What stimulates the release of mineralocorticoids from the adrenal cortex?
angiotensin II (and also ACTH)
What hormone opposes cortisol?
DHEA
What are the actions of cortisol?
stimulate protein breakdown, inhibit protein synthesis, increase blood glucose, inhibits utilisation of glucose by adipose tissue, promotes lipid breakdown in most adipose tissue but also promotes fat deposition in the abdomen, head and chest, stimulates appetite and excessive eating, suppress cytokine synthesis to inhibit immune response
What is the goal of cortisol release?
get glucose to brain and muscle for a fight or flight response
What is dexamethasone and what are its uses?
a synthetic glucocorticoid - used to treat inflammatory and auto-immune conditions, counteract side effects in chemotherapy, chemotherapeutic agent in myeloma, promote maturation of foetal lungs, treat high altitude sickness, treat adrenal insufficiency
What is beclomethasone and what is it used for?
a synthetic glucocorticoid - used to treat the nasal symptoms of allergies
What is the steroid treatment for asthma?
prednisolone
Why do synthetic steroids require the dosage to be progressively reduced rather than suddenly stopped?
because it takes time to recover from the induced adrenal insufficiency due to the negative feedback
What is leuprorelin and what is it used for?
an analogue of GnRH - will overstimulate the receptor and will stop production of LH and FSH to completely inhibit production of oestrogen and progesterone in the ovaries and testosterone in the testes - can be used in treating breast, ovarian and testicular cancer
Where is progesterone secreted from?
the corpus luteum
What stimulates progesterone release?
LH
What is the function of progesterone?
maintains the endometrium
Describe the menstrual cycle
- the endometrium collapses - when there is no more oestrogen and progesterone
- low steroid is a signal for FSH - stimulates a follicle to produce oestrogen
- oestrogen builds up the endometrium - reaches a point to turn off FSH and turn on LH
- ovulate
- after ovulation - left with a corpus luteum which produces progesterone
- steroids give negative feed back - no more production of oestrogen and progesterone
- the cycle starts again
Where is testosterone produced?
in Leydig cells in men, in the ovaries and placenta in women, and in the zona reticularis of the adrenal gland in men and women
How do anabolic steroids increase muscle mass?
increase production of actin and myosin, block effects of cortisol so catabolism is reduced, increase BMR so deplete fat
What are the side effects of anabolic steroids?
liver damage, high blood pressure, jaundice, renal failure, acne, psychiatric effects, reduced sperm count, shrinking testicles, baldness, prostate cancer, infertility
What is DHEA?
the precursor for sex steroids
What stimulates DHEA release?
ACTH
