1. The Reproductive System
Sexual Development

2. The Reproductive System
What would happen to you if…
Your lungs collapsed.
Your heart stop pumping.
Your brain stop firing impulses.
Your immune system failed.
Your reproductive system failed.
An individual can lead a healthy, happy life without reproducing.
However, the reproductive system could be though of as the single most important system. Why?
It ensures the continuation of the species, without it no species could produce another generation.

3. Sexual Development
For the first six weeks of development, human male and female embryos are identical in appearance.
During the 7th week, the testes in males and the ovaries in females begin to develop.
Tissues of the embryo respond to the hormone testosterone, produced by the testes, by developing into the male reproductive organs.
Ovaries produce estrogen, if the embryo is female, to trigger tissue to develop the female reproductive organs.

4. Sexual Development

5. Sexual Development

6. Sexual Development
After birth, the gonads produce small amounts of sex hormones that continue to influence the development of the reproductive organs.
However, neither the testes nor the ovaries are capable of producing active reproductive cells until puberty.
Puberty is a period of rapid growth and sexual maturation during which the reproductive system becomes fully functional.
The onset of puberty varies considerably among individuals.
It usually occurs any time between the ages of 9 and 15.
On average, it begins about one year earlier in females than males.

7. What Begins Puberty?
Puberty begins when the hypothalamus signals the pituitary gland to produce increased levels of two hormones that affect the gonads.
Follicle-stimulating hormone (FSH) stimulates follicle development in ovaries and sperm development in testes.
Luteinizing hormone (LH) triggers ovulation, causes ruptured follicle to become the corpus luteum, and stimulates testosterone production in males.

8. Male and Female Develop very similar structures of sex glands.
Two genital tubes.
Manufacture the hormones of the other sex.
Hormones of one sex are often used to treat illness in the other sex.
Both sexes have reproductive organs call genitals or genitalia, designed for the purpose of intercourse and conception.

9. The Male Reproductive System
The role of the male reproductive system is to produce sperm and to deliver them to the female gamete, so that fertilization can occur.

10. Structure of Sperm
A sexually mature human male produces millions of sperm each day.
The cells that give rise to sperm are initially diploid, but they undergo meiosis reducing the number of chromosomes in the developing sperm cell by half.
After meiosis, a sperm matures for several weeks, becoming a highly specialized DNA delivery cell.
Maturation: 72 days
Average swimming speed: 8 inches per hour
Survival time in a woman: 2-7 days

11. Structure of Sperm Consists of a head with a highly condensed nucleus.
A sperm cell has a long tail and has discarded most of its cytoplasm and organelles.
Mitochondria remain in the sperm cell, clustered around the top part of the tail, to provide energy for the tail to whip back and forth.
A cap of digestive enzymes forms at the tip of the sperm’s head enabling the sperm to penetrate the egg.

12. The Path Traveled by Sperm
Sperm are produced in two oval-shaped organs called testes or testicles.
The testes are located in the scrotum, a loose sac hanging below the base of the penis where the temperature is about 3º lower than the normal body temperature.
Within each testis are clusters of hundred tiny tubules called seminiferous tubules where sperm are produced.

13. The Path Traveled by Sperm
After formation, sperm mature and are stored in the epididymis, a coiled tube attached to the surface of each testis.
If uncoiled, an epididymis would be about 20 ft long.

14. The Path Traveled by Sperm
The lower of each epididymis gradually unwinds to become the vas deferens.
The walls of the vas deferens contain a thick layer of smooth muscle which contracts during ejaculation or the process by which sperm leave the male body.
Sperm moves into a tube that leads into the urethra, the tube that leads to the outside of the body through the penis.
Ejaculation is regulated by the autonomic nervous system, so it is not completely voluntary

15. One Exit, Two Substances
During ejaculation, the tube from the bladder is closed off by a small valve.
This valve keep urine and semen separated.
Prevents urination during ejaculation.

16. Sperm is not Semen
As they travel through the vas deferens and urethra, sperm are bathed in fluids that are produced by glands along the route of travel.
The seminal vesicles are two small glands located near the bladder that produce a fluid that nourishes sperm.
The bulbourethral gland is located just past the prostate gland and secretes a thick, clear, alkaline fluid that becomes part of the semen.
The prostate gland secretes an alkaline fluid that counteracts the acids found in the male urethra and in the female vagina.
These secretions mix with sperm to form semen, which is expelled from the penis during ejaculation.

17. All for One, and One for Me
About 2-6 ml of semen are released in an average ejaculation.
Ejaculation releases up to 300 million sperm at once.
Between million sperm are present in 1 ml of semen.
There is about 2.5 million sperm in a drop of semen.
The chances of a single sperm fertilizing and egg, if there is one available, are quite good.

18. Cryptorchidism
Condition when testes do not descend into the scrotum at birth.
Can be corrected with surgery or hormones administered before puberty.
If not treated, it is likely to result in infertility.

19. The Female Reproductive System
The female reproductive system must play two biological roles
Produce ova or eggs.
Prepare the female’s body to nourish a developing embryo.

20. The Female Reproductive System
Females gametes are called ova, or eggs.
The ovaries are the organs responsible for producing eggs.
Located in the lower part of the abdomen.
Each ovary contains about 400,000 primary follicles.
An egg released from an ovary moves into a Fallopian tube, which carries the egg into the uterus.

21. That’s a lot of Eggs
At birth, a human female has between 200,000 and 400,000 primary follicles, which are clusters of cells surrounding a single eggs, in her ovaries.
By puberty, that number will have dwindle to about 10,000.
Of those, about 400 will be released at the rate of about 1 every 28 days.
Maturing eggs become large, highly complex cells, growing to be nearly 200,000 times larger than a sperm.
Although many eggs begin to mature each month, usually only one egg completes the process and is released.

22. The Female Reproductive System
The uterus is a hollow, muscular organ about the shape and size of pear.
During pregnancy, the uterus expands to many times its usual size.
The lower part of the uterus is a tubular ring of strong muscles known as the cervix.

23. The Female Reproductive System
The vagina is a muscular tube that receives the penis and any sperm ejaculated by a male during intercourse.
The lower end of the vagina opens to the outside of the body, and the upper end connects to the cervix.
During birth, the baby passes through the cervix and the vagina, also called the birth canal.

24. The Female Reproductive Cycle
The two reproductive tasks of the female are accomplished in two overlapping cycles.
The ovarian cycle.
The uterine cycle.
Together, these cycles allow for the maturation and release of female gametes and the accommodation of the egg, whether fertilized or not.
A series of hormones produces these changes in a sequence of events known as the menstrual cycle.
The menstrual cycle has four phases: follicular phase, ovulation, luteal phase, and menstruation.

25. Menstrual Cycle

26. The Ovarian Cycle Prepares a mature egg for fertilization.
In a female, egg release occurs only at a specific time once a month in a process called ovulation.
If the egg is not fertilized, the ovaries prepare another egg for release the next month.

27. Uterine Cycle
Each month, the uterus prepares to receive and nourish a fertilized egg, or embryo, in a cycle of changes called the uterine cycle.

28. Follicular Phase Takes about 10 days.
Begins when the level of estrogen in the blood is relatively low.
The hypothalamus reacts by producing a releasing hormone that stimulates the anterior pituitary to secrete FSH and LH.
In the ovaries, these hormones cause a follicle to develop to maturity.
As the follicle develops, the cells surrounding the egg enlarge and begin producing estrogen.
Estrogen causes the lining of the uterus to thicken in preparation for receiving the fertilized egg.

29. Ovulation Shortest phase in the cycle.
Occurs about midway through the cycle and last 3-4 days.
Hypothalamus sends a large amount of releasing hormone to the pituitary gland causing it to produce FSH and LH.
The follicle ruptures, and a mature egg is released into one of the Fallopian tubes.

30. Luteal Phase
Begins after the egg is released and moves through the Fallopian tube.
Back at the ovary:
The follicle turns yellow and is know known as the corpus luteum.
The corpus luteum continues to release estrogen but also begins to release progesterone.
Progesterone adds the finishing touches by stimulating the growth and development of the blood supply and surrounding tissue.
It is during the first two days of the luteal phase, that the chances that an egg will be fertilized are the greatest.
Usually from 10 to 14 days after the completion of the last menstrual cycle.

31. Menstruation
If the egg is not fertilized, it will passed through the uterus without implantation.
Back at the ovary:
The corpus luteum begins to disintegrate.
As the old follicle breaks down, it releases less estrogen and progesterone.
When the level of estrogen falls below a certain point, the lining of the uterus begins to detach from the uterine wall.
This tissue, along with blood and the unfertilized egg, are discharged through the vagina during menstruation.
Menstruation lasts about 3-7 days on average and it usually starts 14 days after ovulation.
A new cycle begins with the first day of menstruation.
A few days after menstruation ends, levels of estrogen in the blood are low enough to stimulate the hypothalamus.

32. END