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Biology
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2. 39-3 The Reproductive System
Photo Credit: ©David M. Phillips/Photo Researchers Inc.
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Sexual Development
Sexual Development
In humans, the reproductive system produces, stores, and releases specialized sex cells known as gametes.
These cells are released to create the fusion of sperm and egg to form a zygote, the single cell from which all cells of the human body develop.
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Sexual Development
Puberty is a period of rapid growth and sexual maturation during which the reproductive system becomes fully functional.
When puberty ends, reproductive organs are fully developed.
Puberty usually begins between the ages of 9 and 15, and usually starts one year earlier in females than in males.
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Sexual Development
Puberty begins when the hypothalamus signals the pituitary to produce increased levels of two hormones that affect the gonads.
These hormones are follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
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6. The Male Reproductive System
Release of FSH and LH stimulates cells in the testes to produce testosterone.
FSH and testosterone stimulate the development of sperm.
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7. The Male Reproductive System
What is the main function of the male reproductive system?
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8. The Male Reproductive System
The main function of the male reproductive system is to produce and deliver sperm.
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9. The Male Reproductive System
A sperm cell consists of:
a head, which contains the nucleus
a midpiece, which contains energy-releasing mitochondria
a tail, which propels the cell forward
Head
Nucleus
Midpiece
Mitochondria
The sperm is the male gamete, or sex cell.
Tail
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10. The Male Reproductive System
Urinary bladder
Vas deferens
Pubic bone
Seminal vesicle
Urethra
Rectum
The main structures of the male reproductive system produce and deliver sperm. The main organs of the male reproductive system are the testes.
Penis
Prostate gland
Epididymis
Bulbourethral gland
Testis
Scrotum
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11. The Male Reproductive System
The testes are located in an external sac called the scrotum.
The scrotum is located outside the body cavity, where it is between 1 and 3 degrees cooler than normal body temperature. The lower temperature helps sperm development.
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12. The Male Reproductive System
Within each testis are clusters of hundreds of tiny tubules called seminiferous tubules.
Sperm are produced in the seminiferous tubules.
Sperm produced in the seminiferous tubules move into the epididymis, where they mature and are stored.
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13. The Male Reproductive System
From there, sperm move into a tube called the vas deferens, which extends up from the scrotum into the abdominal cavity.
This merges with the urethra, the tube that leads to the outside of the body through the penis.
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14. The Male Reproductive System
Glands lining the reproductive tract produce seminal fluid.
Seminal fluid nourishes sperm and protects them from the acidity of the female reproductive tract.
The combination of sperm and seminal fluid is called semen.
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15. The Female Reproductive System
The primary reproductive organs in the female are the ovaries.
The ovaries are located in the abdominal cavity.
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16. The Female Reproductive System
What is the main function of the female reproductive system?
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17. The Female Reproductive System
The main function of the female reproductive system is to produce eggs. In addition, the female reproductive system prepares the female's body to nourish a developing embryo.
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18. The Female Reproductive System
Fallopian tube
Ovary
Uterus
Cervix
Urinary bladder
Rectum
Pubic bone
The main function of the female reproductive system is to produce ova. The ovaries are the main organs of the female reproductive system.
Vagina
Urethra
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19. The Female Reproductive System
Puberty in females starts when the hypothalamus signals the pituitary gland to release FSH and LH.
FSH stimulates cells within the ovaries to produce estrogen.
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20. The Female Reproductive System
Egg Development 
Each ovary contains about 400,000 primary follicles, which are clusters of cells surrounding a single egg.
The follicle helps an egg mature for release into the reproductive tract, where it can be fertilized.
Eggs develop within their follicles.
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21. The Female Reproductive System
Egg Release
When a follicle has matured, its egg is released in a process called ovulation.
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22. The Female Reproductive System
The follicle breaks open, and the egg is swept from the ovary into one of the two Fallopian tubes.
While in the Fallopian tube, an egg can be fertilized.
After a few days, the egg passes from the Fallopian tube into the uterus.
If the egg is not fertilized it passes through the cervix, and finally out of the vagina.
The vagina leads to the outside of the body.
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The Menstrual Cycle
The Menstrual Cycle
The menstrual cycle is controlled by internal feedback mechanisms between the reproductive system and the endocrine system.
The cycle takes an average of 28 days.
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The Menstrual Cycle
During the menstrual cycle, an egg develops and is released from an ovary.
The uterus is prepared to receive a fertilized egg.
If the egg is fertilized, it is implanted in the uterus and embryonic development begins.
If the egg is not fertilized, it is discharged.
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The Menstrual Cycle
What are the four phases of the menstrual cycle?
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The Menstrual Cycle
The menstrual cycle has four phases:
follicular phase
ovulation
luteal phase
menstruation
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The Menstrual Cycle
Ovulation
Menstrual Cycle
The menstrual cycle is divided into four phases. Notice the changes in hormone levels in the blood, the development of the follicle, and the changes in the uterine lining during the menstrual cycle.
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The Menstrual Cycle
The follicular phase begins when estrogen levels in the blood are low.
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The Menstrual Cycle
The anterior pituitary secretes FSH and LH, which cause a follicle to develop to maturity.
As the follicle develops, cells surrounding the egg enlarge and produce more estrogen.
Estrogen causes the lining of the uterus to thicken.
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The Menstrual Cycle
Ovulation
This phase occurs midway through the cycle and lasts 3–4 days.
The pituitary gland produces more FSH and LH.
The release of these hormones causes the follicle to rupture, and a mature egg is released into one of the Fallopian tubes.
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The Menstrual Cycle
Luteal Phase 
The luteal phase begins after the egg is released.
As the egg moves in the Fallopian tube, the follicle turns yellow and is called the corpus luteum.
The corpus luteum continues to release estrogen but also begins to release progesterone.
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The Menstrual Cycle
Progesterone stimulates growth and development of the blood supply and surrounding tissue.
Within a few days of implantation, the uterus and the growing embryo will release hormones that keep the corpus luteum functioning for several weeks.
This allows the lining of the uterus to nourish and protect the developing embryo.
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The Menstrual Cycle
Menstruation
If fertilization does not occur, the corpus luteum will begin to disintegrate.
The follicle breaks down and releases less hormones, which makes the uterine lining detach.
This tissue, blood, and the unfertilized egg are discharged through the vagina.
This phase is menstruation, and it lasts 3–7 days.
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34. Sexually Transmitted Diseases
Diseases that spread from one person to another during sexual contact are called sexually transmitted diseases (STDs).
STDs are a serious problem in the U.S., infecting millions of people each year and accounting for thousands of deaths.
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35. Sexually Transmitted Diseases
STDs caused by bacteria include chlamydia, syphilis, and gonorrhea.
STDs caused by viruses include hepatitis B, genital herpes, genital warts, and HIV/AIDS.
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39-3
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39-3
Human male and female embryos are identical until they begin to differentiate at about
7 hours of development.
7 days of development.
7 weeks of development.
7 months of development.
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39-3
The process in which a mature egg is released from the follicle of an ovary is known as
fertilization.
ovulation.
menstruation.
meiosis.
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39-3
An egg passes from a Fallopian tube into the cavity of the
ovary.
vagina.
uterus.
cervix.
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39-3
Which statement best describes male sperm cells?
They are motile, produced in small numbers, and larger than most body cells.
They are motile, produced in large numbers, and smaller than most body cells.
They are nonmotile, produced in small numbers, and larger than most body cells.
They are nonmotile, produced in large numbers, and smaller than most body cells.
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39-3
The menstrual cycle is regulated by hormones that are controlled by
positive feedback mechanisms.
ovulation.
negative feedback mechanisms.
fertilization.
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