Reproduction

Fertility

the ability to conceive children

Infertility (clinical definition)

not being able to achieve pregnancy after 1 year of having regular, unprotected intercourse, or after 6 months if woman > 35yrs

Ways to assess/measure fertility

sperm count/quality, regularity of menstrual cycle, and possibility for implantation in uterus & maintenance of pregnancy over course of gestation

Main three factors affecting fertility

sex chromosomes, genes, and hormones

What are the sex chromosomes?

XX (female) or XY (male)

SRY gene

sex-determining region of the Y chromosome (partially directs formation of typical male sex organs)

What is Turner's syndrome?

XO (lack of second sex chromosomes)

What is Klinefelter syndrome?

XXY (extra X chromosome)

HPG axis

hypothalamus (GnRH) <-> anterior pituitary (LH & FSH) <-> gonads (androgens & estrogens) <-> effector tissues

Androgens

Testosterone and dihydrotestosterone (DHT)

Estrogens

estrone & estradiol

What is the precursor for all steroid hormones?

cholesterol

What enzyme converts androgens into estrogens?

aromatase

What enzyme converts testosterone to DHT?

5-alpha-reductase

What age range is considered pre-pubescent?

0-7 years

How is fertility changing during pre-pubescence?

not changing (infertile?

What is happening to gonadotropin levels during pre-pubescence?

LOWEST

Comparative gonadotropin levels @ pre-pubescence

FSH > LH

What age range does puberty typically occur?

Approximately 8-14 years

How is fertility changing during puberty?

Becoming physiologically capable of conceiving children

What physiological changes mark the onset of puberty?

Initial menses in females and growth of testes in males

What initiates puberty?

Onset of pulsatile GnRH

What is happening to gonadotropin levels during puberty?

increase

Comparative gonadotropin levels @ puberty

LH > FSH

What age range is considered the 'Reproductive Years'?

18-44 years

How is fertility changing during the Reproductive Years?

fluctuates w/ menstrual cycle (stays relatively high for sperm-producing individuals)

What is happening to gonadotropin levels during the reproductive years?

continue to increase

Comparative gonadotropin levels during reproductive years

LH > FSH

At what age range does the Climacterium period occur?

45-55 years

How is fertility/sexuality changing during the Climacterium period?

menstruation becomes more sporadic/less frequent & decreases/changes in libido

Hormonal changes during the Climacterium period

decrease in estrogen levels

At what age range does the Senescence period occur?

56+

How is fertility/sexuality changing during the Senescence period?

cessation of menstrual cycle/decrease in sperm count/motility

What is happening to gonadotropin levels during the Senescence period?

HIGHEST

Comparative gonadotropin levels during the Senescence period

FSH > LH

How does long term stress affect reproduction?

cortisol inhibits HPG axis (which can lead to amenorrhea (absence of menses), low libido, & erectile dysfunction)

What are the four phases of human sexual arousal?

excitement, plateau, orgasm, resolution

Describe the excitement stage of human arousal

increased blood flow to genitals (vasocongestion), vaginal lubrication & swelling of labia (females), testes swell & scrotum tightens (males)

Describe the plateau stage of human arousal

sexual excitement continues to grow

Describe the orgasm stage of human arousal

climactic short phase of sexual response, sensation of orgasms across sexes does NOT differ, & some females can vacillate between plateau & orgasm many times

Describe the resolution stage of human arousal

body slowly returns to its original unexcited states, refractory period occurs during male resolution phase (& for some females) in which individuals cannot becomes aroused for a period of time

What is the target of LH in males?

leydig cells of the testes for testosterone production

What is the target of FSH in males?

sertoli cells of the testes for inhibin & androgen-binding protein production

What is the target of LH in females?

theca cells of the ovaries for androgen (-> estrogen) & progesterone production

What is the target of FSH in females?

granulosa cells of the ovaries for estrogen & inhibin production

What occurs during spermatogenesis?

two meiotic divisions of one spermatogonium yield four spermatids which then develop into four mature sperm

What is the normal level of sperm concentration?

more than 20 million/mL

What level of sperm concentration is considered infertile?

less than 15 million/mL

Pathway for sperm development & ejaculation

Seminiferous tubules -> Epididymis -> Vas deferens -> Ejaculatory ducts -> None -> Urethra -> Penis (SEVEN-UP)

Features of sperm that allow fertilization

head (contains nucleus & acrosome (digestive enzymes for outer ovum)), midpiece (contains motor & mitochondria), tail (contains flagellum), & mucus (from semen, protects sperm during travel)

What is the common chemical used in spermicide?

Nonoxynol-9

What are the physiological effects of spermicide?

degrades acrosome & inhibits sperm motility

Oogenesis

growth process where primary egg cells (ova) become mature ova

What are the two separate cycles of the menstrual cycle?

ovarian cycle & uterine cycle

Three phases of the ovarian cycle

follicular phase, ovulation phase, and luteal phase

Simple desc of the follicular phase

follicular growth

Simple desc of the ovulation phase

one or more follicles have ripened; ovary releases oocyte(s)

Simple desc of the luteal phase

secretes hormones that maintain uterine lining (in case of fertilization/implantation)

Terms in order of follicle growth

primordial -> primary -> secondary -> antral

Hormone levels in early to mid-follicular phase

FSH > LH (both low); progesterone & inhibin low, estrogen (estradiol) high & increasing

What is happening during the early to mid-follicular phase?

estrogen downregulates GnRH, LH, & FSH but promotes estrogen secretion by the follicle; LH stimulates androgen secretion from thecal cells, and FSH stimulates granulosa cells to produce estrogens from the androgens via aromatase & AMH

Hormone levels during late follicular phase & ovulation

LH >> FSH (both spike); estrogen spikes before ovulation, after ovulation progesterone & inhibin rise

What is happening during the late follicular phase & ovulation?

LH stimulates thecal cells to produce androgens, FSH stimulates granulosa cells for high estrogen output (via androgens & aromatase), inhibin secretion, and progesterone release; Inhibin suppresses FSH, while estrogen & progesterone promote GnRH & LH

What directly induces ovulation?

surge of LH

What happens during ovulation?

follicle ruptures and egg (ovum) is released

Hormone levels during early to mid-luteal phase

LH > FSH (both very low), progesterone highest, estrogen & progesterone still @ moderate levels

What is happening during the early to mid-luteal phase?

Corpus luteum secretes increased estrogen progesterone, and inhibin, which shut off FSH & LH

Hormone levels during late luteal phase

estrogen, progesterone, and inhibin return to low levels, and LH & FSH begin increasing (FSH > LH)

What is happening during the late luteal phase?

Corpus luteum dies, which decreases estrogen and progesterone; as LH & FSH increase again, FSH stimulates new follicle development

Zygote

fertilized egg

Blastocyst

fertilized egg after a week that implants into uterine lining (endometrium) during pregnancy

10-12 days after fertilization, what does the blastocyst become?

an embryo

8 weeks after fertilization, what does the embryo become?

fetus

Site of fertilization

uterine/fallopian tube

Pathway for sexual differentiation in XY male

SRY blocks DAX1 -> upregulates gene expression of SOX9 & SF1 which bind to the promotor region of AMH -> inhibits development of female reproductive tract (or Mullerian ducts)

Pathway for sexual differentiation in XX female

no SRY gene, no blockage of DAX1 -> suppresses gene expression of SOX9 & SF1 -> AMH absent which enables development of female reproductive tract (Mullerian ducts)

Function of testes

make sperm (spermatogenesis)

Function of epididymis & vas deferens

store and concentrate sperm, increase sperm motility & fertility

Function of seminal vesicles

supply fructose for energy

Function of prostate gland

Produces alkaline fluid that enhances sperm motility & can neutralize vaginal secretions

Function of bulbourethral glands

secrete mucus for lubrication

Function of ovaries

secrete sex steroids (estrogen, progesterone, & inhibin) & produces oocytes

What causes internal sexual differentiation at birth?

presence/absence of SRY gene, AMH, & testosterone (presence causes males (Wolffian ducts -> epididymis & vas deferens) & absence causes females (Mullerian ducts -> uterine tube & uterus))

What causes external sexual differentiation at birth?

presence/absence of strong androgens (DHT) (presence causes males (genital tubercle becomes glans of penis; labioscrotal fold becomes scrotum) & absence causes females (genital tubercle becomes clitoris; labioscrotal fold becomes labia majora))

Simple desc of CAIS

complete androgen insensitivity syndrome (androgens present but no action - female phenotype but male internal structures)

What happens to a CAIS XY individual at birth?

SRY gene still present, so fetal testes develop, and AMH, DHT, & T are present but have no action so no Wolffian ducts or male reproductive tract development

What happens to a CAIS XY individual at puberty?

no uterus so no menses, but no male secondary sex characteristics; breasts develop b/c aromatase & estrogen receptors are still working

Simple desc of Guevedoces

5-alpha-reductase deficiency (T does not get transformed into DHT)

What happens to a Guevedoces XY individual at birth?

SRY present so fetal testes develop & AMH present (no Mullerian ducts), and T is present so Wolffian ducts develop into male internal repro tract, but no DHT so not strong enough response to develop penis, scrotum, and prostate

What happens to a Guevedoces XY individual at puberty?

testes develop & eventually produce enough T to compensate for lack of DHT, leading to the development of penis & scrotum (external genitalia) at puberty

Simple desc of CAH

congenital adrenal hyperplasia (mutation in 21-hydroxylase, the enzyme that makes glucocorticoids)

What happens to a CAH XX individual at birth?

no SRY, so fetal ovaries develop, & no AMH so Mullerian ducts present & develop into uterus, uterine tubes, & inner vagina; adrenal glands are stimulated to make excess androgens in absence of glucocorticoids which enlarges the external female genitalia

What happens to a CAH XX individual at puberty?

may experience early puberty (nothing else unordinary)

What happens to a Turner's syndrome individual at birth?

no SRY genes so fetal ovaries develop, but female repro tract is underdeveloped

What happens to a Turner's syndrome individual at puberty?

relatively short stature, smaller breasts, and no menses

What happens to a Kleinfelter individual at birth?

SRY present so male internal & external structures develop; testicular atrophy may occur

What happens to a Kleinfelter individual at puberty?

taller stature, breasts may develop, feminized hair growth