2.3 Hormones Flashcards
What are sex chromosomes responsible for? (2)
Sex chromones are the location of genes responsible for gonad development<div><br></br><div>Determine the primary source and type of sex hormones (Male: Androgen; Female: Estrogen, Progesterone)<br></br></div></div>
What determines development of sex tissue? (1)
SRY Gene: Transcription factor that determines the development of male gonadal tissues<div><ul> <li>XX: Female</li> <li>XY: Male (SRY is on Y)</li></ul></div>
Difference between sex steroids and sex hormones? (2)
“Steroid hormones are <span>lipid-soluble </span>so pass through membranes into all cells (i.e.,manipulating steroids = change in fairly large area)<div><br></br></div><div>Sex hormones are <span>water-soluble </span>so cannot pass through membranes<br></br></div>”
Biosynthesis of sex steroids? (Image)
“<div><img></img><br></br></div> <div>Cholesterol = Common Precursor</div><div>Primary source = Gonads (Minor source: Adrenal cortex)</div><div>Testoseterone > 5-alpha-dihydrotesterone = Androgens Testosterone > Estradiol = Estrogens</div>”
How doesgonadal steroid synthesis in males (2) change across the lifespan?
<ul> <li>Early (pre-birth; second trimester) transient synthesis of testosterone causes masculinisation of genitalia.</li> <li>Levels increase at puberty to (relatively) constant adult levels.</li></ul>
How doesgonadal steroid synthesis in female (4) change across the lifespan?
<ul> <li>(No early transient synthesis of estrogen)</li> <li>Circulating estrogens (and progesterone) are <strong>low</strong> until puberty</li> <li>Cyclical patterns of synthesis during adulthood</li> <li>Decreased synthesis in menopause</li></ul>
Brain regulation of gonadal steroid synthesis (2)
“<ul> <li>Circulating hormone levels (‘negative’ <strong>feedback circuits</strong>) and other brain inputs drive<strong>Hypothalamus</strong> activity.</li> <li><strong>Hypothalamus</strong> drives <strong>pituitary gland</strong>, which determines levels and pattern of sex hormones (<strong>FSH/LH</strong>) secretion released into the bloodstream </li><ul> <li>If high enough, they start making steroids</li> </ul> </ul><div><div><img></img><img></img></div></div>”
Role of genetics vs sex steroids:Gynandromorphs (1)
Mixture of genetically male and female tissues but both sides of the brain will be exposed to the same circulating hormones, so any differences between sides must be due to genes. (Same brain both sides)
Role of genetics vs sex steroidsMammals (1)
50 genes are expressed at different levels in male vs. female brains BEFORE gonad formation. (Some regions differ on both sides)
Define sexual dimorphism (1)<br></br><br></br><br></br>
Permanent anatomical, physiological and behavioural differences between sexes
How do organisational effects arise? (1)
Anatomical and physiological differences (which define sexually dimorphic behaviours) are initiated by exposure to/deprivation of steroids during critical developmental periods
Do all areas become sexually dimorphic? (1)
Only a minority of regions become sexually dimorphic because steroid receptors have discrete pattern of localisation in the developing and adult nervous system
Organizational effects: Mechanism of steroid action? (3)
“<span>Direct, Genomic/ ““Classic genomic””</span><div><ol> <li> <div>Steroid (androgen/estrogen) binds to its specific cytoplasmic receptor (AR/ER)</div> </li> <li> <div>Steroid-receptor complex translocate to the nucleus to activate specific response elements.</div> </li></ol><div><img></img><br></br>E2 (Steroid) to ER (Receptor)<br></br>ER complex (Steroid-Receptor Complex) goes to nucleus (ERE), where transcription occurs<br></br></div></div>”
“Outcome of ““Classic Genomic”” (1)Organizational effects of steroids”
Slow onset and offset (Hours to days)
What if a neuron expresses aromatase? (3)Organizational effects
“<ul> <li> <div>Testosterone is converted to estradiol: Actions can occur via estrogen receptors or via androgen receptors or via both receptor types (Depending on which classes of steroid receptors are expressed in the neuron)</div> </li> <li> <div>In males, in neurons that express aromatase, the transient rise in <strong>circulating</strong> T during development causes a transient, <strong>local, intracellular</strong> rise in E in those neurons.</div> </li> <li> <div>These neurons also express estrogen receptors (ERs), so the effects of this intracellular increase in E will actually be mediated by estrogen</div> <ul><li><img></img><br></br></li></ul></li></ul><div><ul><li>Testosterone is converted to Estrodial (E2) via. aromatase</li><li>Actions depends on what ER is (Androgen/Estrogen/Both Receptor)</li><li>But because there is a rise in Estradiol in development, the neurons also express estrogen receptors.</li></ul></div><div><br></br></div><div><br></br></div><div><br></br></div>”
