Reproduction Notes
The Reproductive system
In this unit we are going to get into the reproductive systems of both male and females. You know me I like to save the awkward part for last, so let’s try not to get too many giggle session in this unit! Here we go!
1. Male Reproductive System:
The Male Reproductive system includes the following parts:
Organ / FunctionTestes / Produce sperm and sex hormones
Epididymides / Ducts where sperm mature and are stored
Vas Deferens / Conduct and also store sperm
Seminal Vesicle / Contribute Nutrients and fluid to semen
Prostate Gland / Contributes Basic Fluid to semen
Urethra / Conducts Sperm and Urine
Bulbourethral Glands / Contribute viscous fluid to semen
Penis / Organ of Sexual Intercourse
Scrotum / maintains testes at cooler temperature than the abdominal cavity. This is necessary for producing viable sperm.
Seminiferous Tubules / Produce sperm
2. Male Gonads, the testes
The testes (sometimes still called "testicles" Testes actually comes from the latin word meaning "witness") are paired organs that develop from gonads within abdomen of foetus. They subsequently descend through a canal into scrotal sacs (a pouch of skin located below the pelvic region) during the last 2 months of fetal development
Scrotum maintains testes at cooler temperature than the abdominal cavity. This is necessary for producing viable sperm. It does this by moving the testes either closer to the body or further away from the body depending on needed temperature.
Sterility, due to too high body temperature, results if testes fail to descend; can be corrected by surgery
3. Sperm Cells
àProduced inside seminiferous tubules in testes. Testes contains sections called lobules, each with one to three coiled seminiferous tubules with total length of 250 meters
àsperm mature in tubular epididymis behind each testes.
àOnce mature, sperm propelled into vas deferens by muscle contractions.
àMove from storage in vas deferens to urethra for ejaculation
Sperm: Three Parts produced throughout a male's lifetime; composed of:
a) head: contains 23 chromosomes within a nucleus,
b) covered by the acrosome, which contains enzymes that facilitate penetration of the egg. An egg is 100,000 times bigger than a sperm!
c) middle-piece: contains mitochondria to produce energy for sperm motility.
d) tail: provides motility, which is a flagellum composed of a 9 +2 pattern of microtubules
Sustentacular (Sertoli) cells support, nourish and regulate cells that generate sperm cells.
Types of Cells
a) spermatogonia: lie inside outer wall, divide mitotically to form...
b) primary spermatocytes: enlarged spermatogonia undergo meiosis to form 2...
c) secondary spermatocytes: each has 23 chromosomes and divides to form 2...
d) spermatids: has 23 chromosomes at end of 2nd meiotic division forming...
e) spermatozoa: has 23 chromosomes. Nourished and supported by seritoli cells
4. The Penis
àthe penis is a cylindrical-shaped organ in that hangs in front of scrotum.
àSpongy tissue inside shaft of penis is flaccid (soft) with normal blood flow in the penis.
àErection occurs from increased blood flow filling spongy tissue.
Impotency is failure to become erect
5. Semen
Semen is a thick white substance produced for ejaculation. Seminal secretions come from three different organs:
a. Seminal Vesicles: Two seminal vesicles join two vas deferens; secrete nutrients for sperm at time of ejaculation.
b. Prostate Gland: surrounds urethra below bladder; secretes milky alkaline fluid that aids sperm motility and survival (helps to neutralize the acidic environment in the vagina).
à Prostate gland enlargement is common in older men; constricts urethra and makes urination difficult. Prostate cancer is 3rd largest cancer killer of men
c. Bulbourethral Glands (Cowper’s Glands): make mucus secretions with a lubricating effect.
Ejaculatory duct is single duct leading from two vas deferens; carries semen to urethra
6. Ejaculation
àa process in which semen is forced from the penis
àsexual arousal can cause an erection, and ejaculation occurs when sexual arousal reaches its peak.
àafter sperm enters the ejaculatory duct, the seminal vesicles, prostate gland, and Cowper's gland release their secretions.
àRhythmical contractions of the ejaculatory duct and urethra expels semen from the penis. This (and accompanying physiological and psychological sensations) is known as male orgasm.
àRefractory period is typical time following ejaculation during which erection cannot occur. This time tends to increase as a man ages.
7. Hormones and Testes
The testes also produce hormones which are involved with sex in males.
a. the hypothalamus controls the testes by releasing Gonadotropic- Releasing Hormone (GnRH)
b. GnRH triggers the aniterior pituitary to release two hormones: FSH and ICSH
c. Follicle-stimulating hormone (FSH) promotes spermatogenesis in seminiferous tubules; tubules release hormone inhibiting in a negative feedback cycle
d. Interstitial cell-stimulating hormone (ICSH) (called luteinizing hormone (LH) in females), controls production of testosterone by interstitial cells
e. Interaction of hormones maintains fairly constant production of sperm and testosterone
8. Testosterone
Testosterone is the male hormone responsible for secondary sex characteristics in males.
· Growth of beard, underarm, and pubic hair. Larynx and vocal cords enlarge causing voice change.
· Stimulates muscle growth.
· Increases sex drive and probably aggressiveness.
· Stimulates sweat and oil glands causing acne and body odour.
Testosterone is also necessary for the production of sperm! Is produced by interstitial cells of the testes.
9. Anabolic Steroids
Used to increase muscle mass! Extremely dangerous for your kidneys and your circulatory system:
Summary of Male Reproductive System
Structure / FunctionTestes / Produce sperm cells and male sex hormones (i.e. testosterone)
Seminiferous Tubules / Produce immature sperm cells.
Epididymis / Matures and stores sperm cells in coiled tubules.
Vas deferens / Carries sperm from the epididymis to its junction with the urethra.
Seminal vesicle / Secretes fructose into the semen which provides energy for the sperm.
Prostate Gland / Secretes an alkaline buffer into the semen to protect the sperm from the acidic environment of the vagina.
Cowper's Gland (Bulbourethral glands) / Secretes mucus-rich fluids into the semen that may protect the sperm from acids in the urethra
Penis / Deposits sperm into the vagina during ejaculation.
10. The Female Reproductive System
Ovaries / are to each side of uterus in pelvic abdominal cavity. Produce eggs and sex hormonesOviducts (Fallopian Tubes) / extend from near ovaries into uterus; sweep up eggs from ovary using cilia lining and wafting fimbria at end of oviducts. Conduct egg to uterus. They are also the site of fertilization.
Uterus / is thick-walled muscular organ for nurturing embryo (fetus develops here); opening in cervix leads to vagina.
Cervix / located at back of vaginal canal, the cervix contains opening to uterus.
Vagina / is a muscular tube with mucosa lining; serves in intercourse (receives penis during sexual intercourse) and as birth canal.
11. Ovaries and Oviducts
àOvaries measure about 3 cm by 1 cm in size. Are held in place by ligaments to oviduct and uterus.
àEach month, an ovary produces an egg that bursts from ovary during ovulation.
àOviducts are tubes to the uterus, and extend from near ovaries into uterus.
àFimbriae are fingerlike ends of the oviducts that sweep up eggs from ovary. Muscular contractions and cilia lining the oviducts waft the egg toward uterus.
àFertilization of egg, oogenesis, and zygote formation usually occurs in oviduct ("Tubular pregnancies" occur when embryo implants in oviduct. Ectopic pregnancy is any implantation outside central body of uterus).
12. Uterus and Vagina
àUterus is about the size and shape of inverted, flattened pear. It lies above and slants forward over urinary bladder.
àIt can stretches from 5 cm wide to over 30 cm with growing baby.
àEndometrium lining forms placenta with basal layer and functional layer that varies with uterine cycle.
àHysterectomy is removal of uterus.
àVagina is a tube with mucosa lining. It makes 45º degree angle with small of back. Serves in intercourse, and at the end of pregnancy, its wall extends greatly as birth canal.
Females also have External Genitals
àVulva is term for collective external genitalia.
àMons pubis is fatty prominence under pubic hair.
àLabia majora enclose following structures:
a. Labia minora extend from vaginal opening to encircle clitoris at front.
b. Clitoris is homologous to penis, and has a shaft of erectile tissue capped by a pea-shaped gland. It has many sensory nerve receptors which makes it sexually sensitive and is prominent in the processes of female orgasm.
c. Hymen is ring of tissue that may partially close the vaginal opening. If unbroken as a child it is broken by the first sexual intercourse.
13. Regulation of Female Hormones!
àHypothalamus secretes gonadotropic-releasing hormone (GnRH).
àGnRH triggers anterior pituitary to produce two hormones:
a. Follicle-stimulating hormone (FSH) stimulates follicles in ovary to produce eggs.
b. Luteinizing hormone (LH) is involved in uterine cycle.
àOvaries secrete estrogen and progesterone
14. The Ovarian Cycle
Stages of Follicle Development
a. Primary follicle oocyte duplicates and divides in first part of meiosis to form secondary oocyte at side of fluid-filled cavity.
b. Release of oocyte (egg) is called ovulation.
c. Second meiotic division does not occur until fertilization occurs.
d. Remaining follicle cells in ovary develop into corpus luteum which degenerates in ten days if pregnancy does not occur.
e. If pregnancy occurs, corpus luteum persists for 3 - 6 months; secretes estrogen and progesterone.
f. Follicular phase: during first half of 28-day cycle (day 1 - 13), FSH from anterior pituitary stimulates follicular development in ovary which increases estrogen release into blood; ends with ovulation on about 14th day.
g. Luteal phase: during second half of 28-day cycle (day 15 - 28), LH from anterior pituitary promotes development of corpus luteum, which secretes progesterone; high progesterone inhibits (negative feedback) LH secretion from anterior pituitary so that corpus luteum begins to degenerate; as luteal phase ends, progesterone drops and menstruation begins
h. so LH hormone causes the development of the corpus luteum in females and testosterone production in males.
15. Menstruation Cycle
Days 1 - 5: low levels of estrogen and progesterone cause endometrium to disintegrate, blood vessels (menses) rupture and flow out of vagina during menstruation.
Days 6 - 13: endometrium becomes thicker and more vascular due to increased amounts of estrogen; called proliferative phase.
Ovulation usually occurs on day 14 of 28-day cycle.
Days 15 - 28: endometrium doubles in thickness, uterine glands mature and secrete mucus due to production of progesterone by corpus luteum; readies uterus to receive developing embryo.
If not pregnant, corpus luteum degenerates; lower hormone levels cause uterine lining to break down
16. Fertilization and Pregnancy
a. Fertilized egg develops as travels down oviduct to uterus.
b. Embryo embeds in endometrial lining (implantation) several days after fertilization.
c. Placenta forms from both maternal and fetal tissues: provides exchange of molecules between fetal and maternal blood.
d. Placenta first produces HCG (human chorionic gonadotropic hormone) to prevent degeneration of corpus luteum.
e. With development of placenta, estrogen and progesterone are produced to maintain endometrium lining of uterus and shut down anterior pituitary so no new follicles mature.
17. The Birth Process
a. Foetus rotates with head pointed toward cervix.
àIf not in position, breech birth (bum first) may require Caesarean section.
àEnd of ninth month, foetus averages 525 mm (20 inches) and 3,380 grams (7.5 pounds).
b. Mild, indiscernible contractions occur throughout pregnancy; become stronger and more frequent near end of pregnancy
àtrue labor involves contractions lasting over 40 seconds occurring every 15 - 20 minutes.
c. Trigger of childbirth involves prostaglandins and oxytocin (though we don't have all the details worked out yet) from mother's pituitary; both hormones can induce birth.
àOxytocin is made in the hypothalamus and stored in the posterior pituitary. It causes the uterus to contract and is used to artificially induce labour. It also stimulates the release of milk from the mammary glands for nursing. Oxytocin involves a positive feedback loop.
d. Just before birth, the growing baby's head exerts pressure against the cervix. This pressure triggers sensory nerves to send a signal to the pituitary to release more oxytocin. The oxytocin causes stronger uterine contractions, which causes greater stimulation of the sensory nerves, which causes more oxytocin to be released, which causes stronger uterine contractions, and so on. The cycle ends when the baby is pushed out of the uterus, stopping the stimulation of sensory nerves to the pituitary.
Parturition includes labor and expulsion of fetus; involves three stages:
Stage 1: Cervix dilates; mucus plug from cervical canal is expelled; amniotic membrane ruptures to release amniotic fluid (i.e. "water" breaks); stage ends when cervix is fully dilated.
Stage 2: Baby emerges from uterine contractions that occur every 1 - 2 minutes, lasting one minute each; if vagina cannot expand enough, an episiotomy is performed and baby is born. Umbilical cord is cut, shriveling and leaving scar that becomes navel.
Stage 3: Placenta (afterbirth) is expelled from uterus about 15 minutes after delivery of baby.
18. Estrogens and Progesterone
At puberty, estrogen stimulates the growth of the uterus and vagina and is necessary for egg maturation. Estrogen also causes and maintains secondary sex characteristics at puberty:
Growth of body, underarm, and pubic hair in female pattern.
Stimulates fat deposit under skin for more rounded body.
Stimulates breast development.
Stimulates wider pelvic development and female proportions.
What do Estrogen and Progesterone do for breast milk?
Breasts contains one to two dozen lobules, each with many mammary ducts that end in blind sacs called alveoli.
Areola (pigmented area of nipple) lacks hair and sweat glands but has saliva-resistant lubricant.