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31 Cards in this Set

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Define Reproductive physiology
def. The interactions among the reproductive organs,
hypothalamus, anterior pituitary, and target cells of the sex hormones that collectively lead
to the production and union of male and female gametes, and ultimately the production
and nourishment of offspring.
Primary reproductive organs (gonads)
1) produce gametes: sperm in males, ova (eggs) in females
2) secrete sex hormones: testosterone in males, estrogen and progesterone in females
Secondary sexual characteristics
External characteristics not directly involved with reproductive physiology
e.g. body configuration and hair distribution
Functions and anatomy of the reproductive tracts
Males (Figure 20-1):
1) spermatogenesis and semen production:
- scrotum and testis
- accessory sex glands: seminal vesicles, prostate gland, bulbourethral glands
2) deposition of sperm/semen in female:
- penis
- epididymis, ductus vas deferens, ejaculatory duct, urethra
Females (Figure 20-2):
1) oogenesis: ovaries
2) reception of sperm: vagina, cervical canal
3) fertilization (conception): oviducts
4) gestation (pregnancy): uterus, placenta
5) parturition (labor and delivery): uterus, cervix, vagina
6) lactation: mammary glands
Chromosomal distribution in sexual reproduction
Autosomal and sex chromosomes (Figure 20-1)
- males are XY
- females are XX
Sex differentiation
1) Genetic sex: determined by sex chromosomes
2) Gonadal sex:
- SRY (sex-determining region) of the Y chromosome masculinizes the gonads by
stimulating H-Y antigen secretion from early gonadal cells
- Without H-Y, undifferentiated gonadal tissue develops into ovaries (9th week)
3) Phenotypic (anatomical) sex:
- undifferentiated genitalia: genital tubercle, urethral folds, genital swellings
- differentiation into male genitalia induced by androgens (testosterone)
- Wolffian and Mullerian ducts
- males
- fetal testes secrete testosterone and Mullerian-inhibiting factor
- testosterone induces development of Wolffian duct into male reproductive tract
- DHT induces differentiation of the external genitalia into penis and scrotum
- Mullerian-inhibiting factor causes regression of the Mullerian ducts
- females in the absence of testosterone and Mullerian-inhibiting factor, the Wolffian
ducts regress and the Mullerian ducts develop into the female reproductive tract, and
undifferentiated genitalia differentiate into female external genitalia
Testicular descent
- occurs by 7th month of gestation, induced by testosterone
- failure can result in cryptorchidism (hidden testis)
- inguinal hernia: incomplete closure of the abdominal wall following testicular descent,
permits abdominal viscera to temporarily slip through
Testicular anatomy
Leydig cells; Germ cells, sperm; Sertoli cells
Effects of testosterone
1) the reproductive system before birth
2) sex-specific tissues after birth
3) secondary sexual characteristics
4) other reproductive functions
5) non-reproductive functions
Spermatogenesis
1) mitotic proliferation
2) meiosis
3) packaging
Sertoli cells
1) blood-testes barrier
2) nourishment
3) clear away extruded cytoplasm and destroy defective germ cell intermediates
4) secrete seminiferous tubule fluid
5) androgen binding protein retains testosterone within the seminiferous tubules lumen
6) site of action for control by testosterone and FSH
Control of testicular function by GnRH, LH and FSH
- GnRH levels are very low until puberty, as hypothalamic release of GnRH is inhibited
by both neural and hormonal mechanisms
- in adult males, GnRH is released from the hypothalamus in pulsatile bursts every 2-3 hrs
- GnRH stimulates both LH and FSH secretion
- LH acts on Leydig cells to regulate testosterone secretion
- FSH acts on seminiferous tubules to enhance spermatogenesis
Prostaglandins
Ubiquitous chemical messengers that regulate both male and female reproductive systems
Environmental estrogens
- Synthetic, hormone-like pollutants that can disrupt endocrine function
- May play a role in falling sperm counts, increased rates of testicular and prostate cancer,
increased rates of cryptochidism and hypospadia, and a decline in male/female birth ratios
Male sex act
1) Erection (Figure 20-12)
- engorgement of penis with blood
- spinal reflex triggered by tactile stimulation of the glans penis
- increase in parasympathetic supply:
para ->nitric oxide -> cGMP -> relaxation of penile arteriolar smooth muscle
- decrease in sympathetic supply
- impotence or erectile dysfunction
- very common, especially in men over 40
- may have psychological or physical causes
- can be treated with sildenafil (viagra), a PDE5 inhibitor
2) Ejaculation
- parasympathetic induced spinal reflex leading to smooth muscle contraction
- emission: contractile activity delivers prostatic fluid, sperm and seminal vesicle
fluid into the urethra
- expulsion: rhythmic contraction of skeletal muscle at base of penis expels the
semen
Male and female sex cycles
1) Excitement phase
2) Plateau phase
3) Orgasmic phase
4) Resolution phase
Oogenesis
Oogonia – the undifferentiated primordial germ cell in the fetal ovaries divides mitotically
up to 5th month gestation (~6-7 million), then begin the early steps of meiotic division but
do not complete it
Primary oocytes – along with granulosa cells make up primary follicles (~2 million)
Primary follicles are destine for either ovulation (~400) or atresia
The 1st meiotic division is completed just prior to ovulation, and the 2nd after fertilization
Ovarian Cycle
Ovarian Cycle – cycle time approximately 28 days
Follicular phase (Figures 20-14, 20-15)
Characterized by presence of maturing follicles, which secrete estrogen
Ovulation occurs at mid-cycle
Luteal phase
Characterized by presence of corpus luteum, which secretes progesterone and estrogen
*Correlation between hormonal levels and cyclical ovarian/uterine changes (Figure 20-16)
Hormonal regulation of ovarian cycle
Female gonadal function is directly controlled by anterior pit. hormones LH and FSH
LH and FSH are directly controlled by hypothalamic GnRH and feedback mechanisms
- Control of FSH and LH during follicular phase
- Control of LH surge at ovulation
- Control of LH during luteal phase
Menstrual cycle has three phases
Menstrual phase:
- discharge of blood and endometrial debris
- lasts 5-7 days
- coincides with termination of ovarian luteal phase/onset of follicular phase
Proliferative phase
- proliferation of epithelial cells, glands and blood vessels in endometrium
- endometrial layer increases in thickness from 1 to 3-5 mm
- ends at ovulation
Secretory (progestational) phase
- coincides with ovarian luteal phase
- endometrium is converted to a richly vascularized, glycogen-filled tissue
Puberty
Female reproductive system is quiescent until puberty, at about 12 years of age
At this time, GnRH secretion by hypothalamus increases
-> increased anterior pituitary gonadotropic hormones
-> increased ovarian activity
-> increased estrogen
Effects of increased estrogen
- growth and maturation of female reproductive tract
- development of secondary sexual characteristics i.e. fat deposition in the breasts,
buttocks and thighs
- closure of the epiphyseal plate
Pubertal effects not directly due to estrogen
- growth of axillary and pubic hair
- pubertal growth spurt
Menopause
Cessation of menstrual cycles – usually occurs at age 45-55
In part due to depletion of limited supply of ovarian follicles
Midlife hypothalamic failure may also play a role
Preceded by a period of irregular cycles and diminished estrogen levels
Effects of diminished estrogen levels:
- decrease in bone density, increase in osteoporosis
- increase in coronary artery disease
- HDL/LDL ratio
- loss of antioxidant activity
- increased proliferation of smooth muscle cells following vessel wall damage
- “Hot flashes” due to unstable control of blood flow
- possibly, depression and irritability
Fertilization and implantation
Fertilization normally occurs in the ampulla, the upper third of the oviduct. This requires
that both sperm and egg be transported to this site.
Fimbriae - end of the oviduct that picks up the egg after its release from the ovary.
Sperm transport to site is aided by thinning of the cervical mucus due to high estrogen
levels during the follicular phase, and by contractions of oviduct smooth muscle
Acrosome reaction - release of acrosomal enzymes by the sperm head upon contact with
corona radiata which subsequently break down the zona pellucida and permit sperm
binding to the egg plasma membrane.
Formation of zygote - the single sperm is internalized, stimulating the 2nd meiotic division,
and producing a zygote
Block to polyspermy – inactivation of sperm-binding proteins in zona pellucida
Morula – solid ball of cells, 3-4 days post-fertilization
Blastocyst – 4-5 days post-fertilization, contains the trophoblast, blastocoele and inner cell
mass (embryo/fetus). Implants in the endometrium of uterus, inducing the decidua
Ectopic pregnancy – fertilized egg implants in a different cavity instead of in the uterus.
Very risky pregnancy for mother.
Contraceptive techniques
Blockage of sperm transport to the egg
- natural contraception (rhythm method)
- coitus interruptus
- chemical contraceptives
- barrier methods
- condom
- diaphragm
- sterilization
Prevention of ovulation
- oral contraceptives (birth control pills)
- long-acting subcutaneous implantation
Blockage of implantation (*occurs post-fertilization)
- intrauterine device (IUD)
- morning-after pills
Future possibilities
Placenta
A special organ of exchange between maternal and fetal blood. The chorion and placental
villi project into the maternal blood pool and create an interface between maternal and fetal
blood supplies, which do not directly intermix. Umbilical cord supplies nutrients, O2 to the
fetus; removes metabolic wastes, CO2. Adverse compounds including thalidomide,
alcohol, agents in cigarette smoke, and AIDS virus can pass through the placental barrier.
Hormonal levels during pregnancy
Human chorionic gonadotropin
- secreted by developing chorion
- maintains the corpus luteum of pregnancy
- stimulates secretion of testosterone by developing testes in XY embryo
Estrogen
- secreted by corpus luteum and the placenta
- helps prepare mammary glands for lactation
- stimulates growth of myometrium, increasing uterine strength
Progesterone
- secreted by corpus luteum and the placenta
- suppresses uterine contractions
- promotes formation of cervical mucus plug to prevent uterine contamination
- helps prepare mammary glands for lactation
Gestation
Usually 38-40 weeks long. Uterus expands and increases in weight 20-fold (not counting
the baby). Mom’s blood volume increases 30% and respiration increases 20%.
Parturition (labor and delivery)
1) Dilation of the cervical canal to accommodate passage of fetus
2) Contractions of the uterine myometrium (*positive feedback cycle)
Lactation and breast-feeding
Milk, or equivalent, is essential for survival of the new baby. Multiple hormones increase
milk production from the mammary glands. Milk consists of water, fat, lactose, proteins,
vitamins, minerals, immune cells, antibodies, and immune-stimulating chemicals.
Colostrum is the milk produced for ~5 days postpartum and contains high concentrations
of immunoprotective components.
Postpartum depression
- “Afterbaby blues” that can persist for weeks to months following parturition
- Previously attributed to exhaustion associated with demands of raising an infant, and/or
the sudden, dramatic decrease in estrogen and progesterone levels
- New evidence suggests that the persistent drop in CRH levels following pregnancy may
play a role, as the stress hormone cortisol would otherwise help in coping with pregnancy
and parturition. A possibly related observation is that low CRH levels are often found in
patients with clinical depression.