Follicle-stimulating hormone ( FSH ): promotes sperm production and secretion of inhibin
Luteinizing hormone ( LH ): stimulates production of Testosterone which is essential for development and maintenance of reproductive organs, male secondary sex characteristics, and spermatogenesis
Negative Feedback Regulation of Spermatogenesis
Both testosterone and inhibin feed back to hypothalamus and pituitary to inhibit FSH and LH secretion
Sperm production maintained at a relatively constant level (note: testosterone also needed for sperm production)
Male Reproductive System:
1. Epididymus :
Large coiled tube (23 ft long) that surrounds testes.
Stores sperm (about 20 days).
During ejaculation, about 400 million sperm cells are propelled from epididymus.
2. Vas Deferens:
Long muscular ducts from scrotum to back of bladder.
During ejaculation, the sperm pass from epididymus into these two ducts.
* Vasectomy: Each vas deferens is cut to prevent sperm from entering urethra.
3. Ejaculatory Duct :
Short duct after two vas deferens ducts unite.
4. Urethra :
Deliver sperm to the exterior.
In males, urine and sperm pass through the urethra.
maintains temperature (lower than body) that sperm require for normal development
Accessory Glands : Produce semen.
Functions of semen :
Activate sperm cells
Provide nutrients for motility
Counteract acidity of vagina and male urethra
A. Seminal vesicles (2): Secrete fluid that nourishes sperm. Contribute about 60% of semen volume.
B. Prostate gland : Produces a thin milky secretion.
Largest of semen secreting glands.
Contributes 30% of semen volume.
C. Bulbourethral glands
Secrete a clear mucus that neutralizes acid from urine in urethra.
Front View of Male Reproductive System
Major Organs of Male Reproductive System:
6. Testes: Paired male gonads.
Produce sperm through spermatogenesis , which occurs in a vast system of hollow tubes called seminiferous tubules .
Each mature sperm has a head, a midpiece, and a flagellum.
Sperm head has an acrosome , which produces enzymes that help it penetrate the egg.
Human sperm cannot develop at body temperature, the scrotum helps regulate temperature.
Spermatogenesis Occurs in Seminiferous Tubules of Testes
Sperm Cell Structure
Fertilization: Sperm Cell Penetrates Egg with Acrosomal Enzymes
Reproductive System of Humans
Reproductive Functions of Female:
Produces eggs (ova)
Incubates and nourishes the embryo and fetus
Produces milk for young
All of these processes are regulated and coordinated by hormones secreted by:
Pituitary gland (anterior portion)
Major Organs of Female Reproductive System:
1. Ovaries: Produce ova (egg) and sex hormones.
Size and shape of large almond.
* Follicles : A single egg with surrounding cells that nourish and protect it. Women are born with all of their follicles (40,000 to 400,000).
Side View of Female Reproductive System
Major Organs of Female Reproductive System:
2. Oviducts (Fallopian Tubes ): Transport the egg from the ovary to the uterus . Fertilization occurs here.
Has thick walls of smooth muscle responsible for uterine contractions and cramps.
Inner mucous lining, which thickens each month in preparation for pregnancy. If fertilization does not occur, breaks down and is discharged during menstruation .
If fertilization occurs, the egg implants and helps support growth until the placenta develops.
4. Cervix: Lower portion of the uterus, which projects into the vagina.
* Pap smear: Examination of cervical tissue to detect abnormalities. Recommended yearly.
* Cervical cancer: Most cases caused by a viral infection.
5. Vagina : Thin walled, muscular chamber.
Receives the sperm and penis
Acid pH kills bacteria and sperm cells
Part of birth canal
Frontal View of Female Reproductive System
Hormone Regulation of Female Reproductive System
Hypothalamus secretes gonadotropin-releasing hormone (GnRH) that stimulates anterior pituitary to secrete:
Follicle-stimulating hormone (FSH): promotes follicle development in ovary
Luteinizing hormone (LH): stimulates ovulation and development of corpus luteum
Pituitary Hormones Regulate Follicular Development of Ovaries
Feedback Regulation of Oogenesis
feedback regulation of female reproductive cycle is negative and positive
leads to female cycles
hypothalamus and pituitary control ovaries
ovarian hormones control uterus
Two Parts to Female Reproduction
1. Uterine Cycle
Days 1-5 – Menstruation (“no” steroids)
Days 6-13 - Proliferative phase (Estrogen effect)
Day 14 – Ovulation (LH effect)
Days 15-28 - Secretory phase (Progesterone effect)
2. Ovarian Cycle
Follicular Phase - FSH promotes development of an ovarian follicle containing an egg ready to be ovulated
secretes increasing levels of estrogen
Luteal Phase –LH promotes ovulation and development of corpus luteum that secretes progesterone
Ovarian Hormones Regulate Uterine Endometrium
Estrogen stimulates proliferation for implantation of embryo
Progesterone stimulates secretion to nourish embryo until implantation
Female Sex Hormone Effect on Endometrium
also has effects on breast and other body tissues
PMS: “hormone withdrawal”
Female Menstrual Cycle /Uterine Cycle : Approximately 28 days.
Menstruation: Days 1-5 of cycle.
Walls of endometrium break down.
Caused by falling levels of progesterone and estrogen.
Can last 3 to 7 days.
Pre-Ovulatory / Proliferative phase (Estrogen effect) : Starts around day 6 of cycle .
Rising estrogen levels cause the endometrium to start thickening.
Ovulation (LH effect) : Occurs around day 14 of cycle.
FSH stimulates growth of ovarian follicle.
LH causes follicle to finish meiosis I (secondary oocyte) and to be released by ovary.
Corpus luteum : Starts to secrete estrogen and progesterone .
Post-ovulatory Secretory phase (Progesterone effect) : Starts around day 15.
Endometrium continues to grow in response to rising estrogen and progesterone.
If no fertilization occurs, corpus luteum degenerates and menstruation occurs.
If fertilization occurs, embryo maintains corpus luteum.
Stages of Female Reproductive Cycle
Sperm remain viable for up to 48 hours within the female reproductive tract
Sperm swim up the female reproductive tract, aided by muscular contractions of the uterus
The oocyte may also secrete a chemical that attracts sperm
There is a three day “window” for intercourse to result in fertilization: two days before to one day after ovulation
Fertilization usually takes place in the fallopian tube.
Sperm undergo a functional change in the female tract – called capacitation
During this process the membrane around the acrosome becomes fragile, and its enzymes are released.
It requires the combined action of many sperm to allow one sperm to penetrate the oocyte.
When the first sperm enters the egg, the cell depolarizes causing the release of calcium ions inside the cell.
This stimulates the release of granules that cause changes in the zona pellucida to prevent entry of other sperm.
Secondary oocyte completes division, and nuclei of ovum and sperm unite to form a zygote.
Zygote the fused sperm and egg cell. This cell undergoes rapid mitotic cell division, but these do not increase the size of the zygote
Morula Cleavage produces a solid sphere of cells, still surrounded by zona pellucida.
Blastocyst At 4.5 to 5 days, cells have developed into a hollow ball of cells. At this stage the cell enters the uterus.
Most animals proceed
through these stages
Early cleavage stages
The blastocyst remains free in the uterus a short time, during which the zona pellucida disintegrates.
Blastocyst nourished by glycogen from glands of the endometrium.
At about 5 days after ovulation blastocyst implants – orients cell mass toward endometrium, and secretes enzymes which allow it to penetrate (digest) the endometrial wall. This nourishes the blastocyst for about a week after implantation.
Fertilization and Early Embryonic Development
Primary germ layers found in between the yolk sac and the amniotic cavity is the embryonic disc, which gives rise to the primary germ layers:
Endoderm form the digestive tract, lungs kidneys, liver & pancreas
Mesoderm forms skin, bones, muscles, heart, blood & spleen
Ectoderm forms nervous system, eye, hair & mammary glands
The chorion develops into the fetal part of the placenta.
The chorionic villi connect the fetal circulation to the placenta
Composed of both fetal and maternal tissues
Functions of the placenta:
1. Transfer gases
2. Transport nutrients
3. Excretion of wastes
4. Hormone production – temporary endocrine organ – estrogen and progesterone
5. Formation of a barrier – incomplete, nonselective – alcohol, steroids, narcotics, anesthetics, some antibiotics and some organisms can cross