Lecture 2: Hormones And Steroids Flashcards
Steroid hormones
- Small ( synthesized from a common precursor, a cholesterol subunit)
- not stored ( fat soluble and easy to move across cell membranes, therefore signal to produce is signal to release).
- not soluble in blood ( must bind to water soluble carrier proteins transfer )
- slow acting (hours to days)
-long half-life (due to carrier proteins, hours to days)
Steroid hormone mechanism of action
1). Pass through cell membrane
2). Bind to steroid receptor- in cytosol or nucleus
3). Hormone - receptor complex is a transcription factor and signal is transduced to nucleus
4). Nucleus receives signal and transcribes DNA to mRNA which is then translated to a protein
Leads to changes in gene expression over the course of hours or days
Anabolic androgenic steroid
Male side effects: gynecomastia, testicular atrophy
Female side effects: hirutism, clitoral hypertrophy
- makes men develop female secondary sex traits, and women vice versa
Key steroid hormones
- Testosterone (t)
- glucocorticoids (gc)
- estrogen
- progesterone
Key peptide hormones
- Vasopressin
- prolactin
- oxytocin
What are hormones? Neuronal vs hormonal communication
- chemical messengers
- produced and released by endocrine glands
- released into bloodstream
- Act on target cells which are at a distance away: neural communication is at very short distances and does not need to be carried to a target through a medium like blood.
Hormonal actions
1). Activation:exposure-effect-exposure-effect
2). Organizational: exposure (critical period like puberty) - effect crescendos
Endocrine glands
Pineal gland
Hypothalamus
Pituitary gland
Thyroid and parathyroids
Adrenal glands
Pancreas
Ovaries
Testes
Hormone regulation
1). Negative feedback: endocrine secretes hormone- target cells produce product-
Increased [product] signals endocrine to make less hormone
2). Positive feedback: increased [product] cause endocrine to increase hormone secretion
Peptide hormones
- Large hormones (made up of amino acids)- few aa- peptide hormone, many aa - protein hormones/polypeptide hormones
- not fat soluble, stored in endocrine cells,released by exocytosis
- blood soluble
- Can’t pass easily through cell membranes
- fast acting ( millisec to min)
- short half-life ( couple of minutes)
Erythropoietin (epo)
- Peptide hormone
- produced by adrenals in response to hypoxia
- p.e.d
- targets bone marrow cells to increase red blood cell production
Monoamines
- Related to peptide hormones
- derived from a single amino acid
1). Catecholamines: adrenal, derived from tyrosine ( epinephrine, norepinephrine, dopamine)
2). Indoleamines: pineal gland, derived from tryptophan ( melatonin, serotonin)
H.p.g axis
1). Brain signals hypothalamus to secrete gonadotropin - releasing hormone g.n.r.h
2). G.n.r.h acts on anterior pituitary (+)
3). Pituitary produces luteinising (l.h.) hormone and follicle stimulating hormone (f.s.h)
4). L.h makes t in male testes and f.s.h makes sperm
L.h and f.s.h make estradiol and progesterone in females
5). Increased testosterone, estradiol, progesterone (-) feedback to hypothalamus and anterior pituitary
Why do steroids make males more feminine and males more masculine?
1). Androgens such as t are masculinizing but not exclusively male
2). Estrogens are not exclusively female
- why?
Chemically similar, cross-conversion, cross-reactivity
* making body produce more t unnaturally leads to (-) feedback and less t is naturally generated
* t is catabolized by aromatase into estrogen and [estrogen] is increased
- in women, increased t levels (-) feedback and less L.h. Less f.s.h but extra t from steroid remains producing male traits. The t is converted to estrogen which leads to even more (-) feedback
