Endocrine

Tonic center

• continuous pulsatile releases of hormone from hypothalamus

Surge center

• hormones released all at once from hypothalamus

• not developed in male

Adenohypophysis (anterior pituitary)

• hormones released from hypothalamus into portal system

Neurohypophysis (posterior pituitary)

• neuropeptides travel along neurons, released directly into capillaries

Protein hormones

• bind to membrane receptors on outside of cell & activate signaling cascade

• ex: GnRH, LH, FSH, PRL, oxytocin

Steroid hormones

• directly cross plasma membrane to bind nuclear receptors & activate transcription

• derived from cholesterol, final form determined by packaging of enzymes

• metabolized by liver, excreted in urine or feces

• ex: progesterone, estradiol, testosterone

HPG in male

• GnRH stimulate LH + FSH

• LH stimulates Leydig cells to produce testosterone

  • testosterone gives negative feedback to LH via blood & supports spermatogenesis in Sertoli cells

• FSH stimulates Sertoli cells to mature sperm & produce ABP + inhibin

  • ABP secreted into lumen of seminiferous tubules & concentrates testosterone

  • inhibin gives negative feedback to FSH via blood

HPG in female

• follicular phase: FSH + LH stimulate pre-ovulatory follicles to produce estradiol

  • high estradiol triggers LH surge, causing ovulation

• luteal phase: FSH + LH stimulate corpus luteum to produce progesterone

  • progesterone gives negative feedback to GnRH + LH

• LH stimulates theca cells to produce androgens, which diffuse into granulosa cells

  • FSH stimulates conversion of androgens to estradiol & secretion of inhibin (negative feedback to FSH)

• estradiol has positive feedback effect w/low progesterone, negative feedback w/high progesterone

Y chromosome

• smallest chromosome, dozens of genes

• SRY required for male development, encodes testis determining factor

Genital ducts

• paramesonephric/Mullerian = female

  • fallopian tubes, uterus, cervix, cranial vagina

• mesonephric/Wolffian = male

  • epididymis, ductus deferens, seminal vesicles, ejaculatory duct

• differentiation requires hormones

  • anti-Mullerian hormone from Sertoli cells

  • Wolffian duct regresses without testosterone

External genitalia differentiation (males)

• testosterone in circulation converted to dihydrotestosterone in Anlage tissues

• DHT stimulates tissues to develop

External genitalia differentiation (female)

• differentiation occurs in absence of hormone but estrogen required to grow to normal size

• exogenous androgens can cause masculinization

External genitalia features

• genital tubercle = glans penis/clitoris

• genital swelling = scrotum/labia majora

• urethral folds = penile urethra + corpus spongiosum/labia minora

• urogenital sinus = prostate gland/caudal vagina & vestibule

Sexual differentiation of brain

• caused by estrogen

• males have constant gonadotropin release, females have cyclic release

• A-FetoProtein binds estradiol in female (can’t cross BBB), does not bind testosterone in males (can cross BBB)

  • testosterone converted to estradiol in brain by aromatase, surge center defeminized

Sperm capacitation

• physiological changes spermatozoa must undergo to be able to penetrate & fertilize an egg

  • removal of adherent seminal plasma proteins

  • reorganization of plasma membrane lipids & proteins

  • influx of extracellular calcium

  • increased cAMP

  • decreased intracellular pH

• occurs while in the female reproductive tract

• display hyperactive motility, able to bind zona pellucida, & undergo acrosome reaction

Acrosome reaction

• release of digestive enzymes that help sperm penetrate upon binding to zona pellucida

Oocyte maturation

• nuclear & cytoplasmic maturational events that result in acquisition of capacity for fertilization & development

  • LH surge triggers meiosis resumption/nuclear maturation & cortical granule migration/cytoplasmic maturation

  • first polar body released

  • ovulation of secondary oocyte

Fertilization

• union of two haploid gametes to form zygote-1, requires gamete transport to site of fertilization (ampulla of oviduct)

• secondary binding of sperm activates oocyte to resume meiosis & release second polar body

• male & female pronucleus form, fuse, & start mitotic divisions

Steps of fertilization

1. capacitated sperm bind zona pellucida (primary) & undergo acrosome reaction

2. sperm penetrates zona pellucida into perivitelline space

3. sperm bind to ooplasma (secondary)

4. secondary binding induces meiosis resumption & cortical granule exocytosis

5. cortical granules harden zona pellucida & block polyspermy

Polyestrus

• come into heat every 21-28 days

• ex: cattle, pigs, rodents

Seasonally polyestrus

• come into heat every 21-28 days during a specific season

• based on photoperiod

• ex: horses, goats, sheep

Photoperiod

• pineal gland makes more melatonin during dark periods

• melatonin promotes or inhibits reproduction

• long day breeder: melatonin inhibits cyclcity (GnRH)

• short day breeder: melatonin promotes cyclicity (GnRH)

Monoestrus

• come into heat once a year

• ex: dog, wolves, bears

Follicular phase (estrus)

• 20% of cycle, follicles are dominant ovarian structure, ends with ovulation

• primary hormone is estradiol

• GnRH causes release of LH + FSH (primarily FSH), which causes follicle to start growing & releasing estradiol

  • estradiol has positive feedback on FSH

• inhibin released when follicle reaches dominance to suppress FSH & allow LH surge

  • dominant follicles acquire receptor for LH

• theca cells secrete testosterone, converted to estradiol in granulosa cells, stimulates heat

• standing heat, sexually receptive

Proestrus

• transition from period of progesterone dominance to period of estrogen dominance

Estrus

• period of sexual receptivity & mating

Metestrus

• transition from estrogen dominance to progesterone dominance

Diestrus

• period of maximal luteal function

Anestrus

• condition when female no longer exhibits regular cycles

• ex: pregnancy, lactation, presence of offspring, season, stress, disease

Luteal phase (diestrus)

• 80% of estrus cycle, period from ovulation to corpus luteum regression

• primary hormone is progesterone from large + small luteal cells, blocks hormonal cascade

• if pregnancy doesn’t occur, prostaglandin lyses corpus luteum & continues cyclicity

Ovulation

• occurs due to LH surge

• basement membrane of follicle ruptures and creates corpus hemorrhagica

• theca cells become small luteal cells, granulosa cells become large luteal cells