Relaxation and refractory period: Refractory period increases with age.
Regulation of Male Sex Hormones
- Hypothalamus: secretes GnRH "Gonadotropic Releasing Hormone"
- Anterior Pituitary: Releases two gonadotropic hormones:
- FSH (follicle stimulating hormone):
As FSH rises, so does spermatogenesis in the seminiferous tubules
- LH (Luteininzing hormone):
As LH rises, increased production of testosterone and other androgens
in the interstitial cells
- Blood testosterone rises, LH production by AP falls
- Blood testosterone falls, LH production by AP rises
to restore testosterone levels
- As they produce sperm, seminiferous tubules produce inhibin:
As inhibin rises. FSH production AP falls
- Large rise in basal level of testosterone at puberty
Female reproductive system
- Ovaries::
produce eggs and the sex hormones
estrogen and progesterone
- Ovary contains 400,000 follicles at puberty -
immature egg cells (oocytes)
- Follicles are sacs containing the oocytes
- Oocytes in primary follicles meiotically divides --->
secondary follicles ----> Graafian follicle ---> ovulation
- The egg consists of the secondary oocyte surrounded by the
zona pellucida
- The left over structures in the follicle become the
Corpus Luteum
- If fertilization occurs the Corpus Luteum lasts 3-6 months;
Otherwise lasts about 10 days
- Follicles and the Corpus Luteum are responsible for
secreting female sex hormones
- Oviduct:
Conducts eggs to the uterus; Fertilization frequently occurs here
- When eggs are expelled from the uterus they are
collected by extensions of the oviduct called fimbriae
- Cilia lining the oviduct sweep the egg towards the uterus
- Uterus: Houses and nurtures the developing fetus
- Muscular organ ~5 cm wide
- Oviducts enter at the top
- Cervix:
the entry to the vagina at the bottom at ~90 degrees
- Lining called the endometrium:
Two layers: a basal layer and functional layer that
varies in thickness depending on the stage of the menstrual cycle
- Vagina:
Receives penis during sexual intercourse; acts as birth canal
Lined by a mucous membrane and very elastic walls to facilitate sexual
intercourse and birth
- External genitalia: the vulva consists of the
labia majora and the labia minora:
- Protects the clitoris, erectile tissue
- Labia minor and clitoris involved in sexual arousal...
- Female orgasm is more complex and has a much wider range of
"normal" response then in the male
Female sex hormones
- Hypothalamus secretes GnRH, Gonadotropic Releasing Hormone
- Anterior Pituitary releases gonadotropic hormones FSH and LH
- Ovaries secrete estrogen and progesterone
- Estrogen at puberty stimulates maturation of uterus and vagina;
secondary sex characteristics, wider hips, more body fat
- Progesterone stimuates thickening of endometrium
in latter part of each menstrual cycle
- Both estrogen and progesterone needed for normal breast development
Ovarian Cycle
Average time is 28 days but varies widely in normal healthy women
Stages of cycle:
- Days 1-13 FSH from AP increases under the influence of GnRH
- Causes follicle to develop from
primary -> secondary -> Graafian
- Causes increased secretion of estrogen;
As estrogen levels in the bloodstream rise,
secretion FSH by AP decreases
(negative feedback): follicular development ceases
- Ovulation occurs around the 14th day.
- Day 15-28 AP increases secretion of LH;
LH maintains the Corpus Luteum, which secretes progesterone;
Increased progesterone in blood, AP production, LH falls
- Day 28 in the absence of fertilization -> menstruation;
At this point both estrogen and progesterone levels are low
Uterine cycle
- Days 1-5 estrogen and progesterone still low;
Endometrium disintegrates and sloughs off - menstruation
- Days 6-13 i.e. the follicular phase of the ovarian cycle:
- Under the influence of estrogen the endometrium thickens
- Increases vascularization:
"The proliferative phase" of the uterine cycle.
- Day 14: Ovulation
- Days 15-28: progesterone from Corpus Luteum causes the endometrium
to continue thickening and start to secrete a thick mucoid layer:
"secretory phase" of uterine cycle
- If no fertilization, by day 28 estrogen and progesterone are low;
start over again
Fertilization
- Basic seminal fluid tends to neutralize the acidic vaginal environment
- Cervical mucous becomes more watery 3-4 days before ovulation and day
of ovulation allowing sperm to penetrate more easily
- Egg is viable for 3-4 days after ovulation
- Uterine contractions transport sperm most of the way to the egg;
- Prostaglandins in sperm promote contractions
- Sperm swim the rest of the way up the oviduct,
5 - 30 minutes to get there after intercourse
- Only one sperm can fertilize one egg.
Implantation
- After fertilization, fertilized egg transported down oviduct
into uterus: it embeds itself in the endometrium
- Membrane surrounding developing embryo secretes human chorionic
gonadotropic hormone
- HCG prevents degeneration of the Corpus Luteum
- Corpus Luteum produces greater quantities of progesterone
- Progesterone inhibits motility of the uterus;
With estrogen prepares the breast for lactation
- Corpus Luteum is maintained for as long as 6 months
Placenta
- Placenta has components of both maternal and fetal tissue
- Location of exchange of gases and nutrients
between maternal and fetal blood
- Once formed, placenta produces HCG, estrogen and progesterone
- Shuts down AP - no new follicles produced
- Uterine lining maintained: Corpus Luteum no longer needed
- Menstruation usually ceases for duration of pregnancy
Menopause
- Between ages of 45 and 55 , the uterine and ovarian cycles cease.
- Ovaries no longer respond to gonadotropic hormones
(FSH & LH) from the AP.
- Ovaries no longer secrete estrogen or progesterone
- While the body adapts to hormonal changes women may
experience any of circulatory irregularities (hot flashes),
dizziness, insomnia, sleepiness and depression.
- Great variation among women, hormone replacement therapy may help some.
Birth Control
- Sterilization
- Most effective form of birth control
- In males vas deferens is cut off and sealed:
the vasectomy
Only affects sperm content of semen so minimal side effects
- In females tubal ligation or tying off the oviducts:
Used to be quite invasive, new techniques e.g. laparoscopy
makes it much easier
- Disadvantages of sterilization - hard to reverse
- "The pill": combination of estrogen & progesterone given for
21 days of 28 day cycle
- Effectively shuts down FSH and LH production so
follicles do not develop.
- Many early problems have been sorted out; side
effects possible (as are side benefits)
- Norplant & Depo-Provera:
synthetic progesterone prevents ovulation
- Norplant - sub-cutaneous time release capsules
- Depo-Provera - injections every three months
- IUD's: Best for women who've had 1 pregnancy, middle to older,
& are at low risk for STD's
- Barrier methods: diaphragms, cervical caps, vaginal sponges, condoms
- Most effective when used with a spermicide
- Some give protection against STD's
- "Natural family planning" (periodic abstinence):
- Requires knowledge of the day of ovulation
- Avoid 4 days either side of ovulation
to account for unusually long-lived sperm or eggs.
- Women need exceptionally regular cycles to be effective
- "Basal" body temperature measurements (T rises at ovulation),
vaginal pH measurements (more alkaline),
mucus thickness can help time ovulation.
- "Morning after pills"
- Most are essentially a controlled overdose of normal
birth control pills
- RU-486 now distributed by Planned Parenthood.
- Blocks progesterone receptors causing uterine lining to
slough off taking embryo with it.
- Many people have ethical problems with these pills since they
remove fertilized eggs i.e. after "conception" has occurred.