1. Lesson Overview Lesson Overview The Reproductive System Lesson Overview 34.3 The Reproductive System

2. Lesson Overview Lesson Overview The Reproductive System THINK ABOUT IT An individual can lead a healthy life without reproducing. But is there any other system that is more important for the continuation of a species? Without the reproductive system, no species could produce the next generation, and the species would come to an end. In a certain sense, this may be the most important system in the body.

3. Lesson Overview Lesson Overview The Reproductive System Sexual Development What effects do estrogens and testosterone have on females and males?

4. Lesson Overview Lesson Overview The Reproductive System Sexual Development What effects do estrogens and testosterone have on females and males? In girls, the effects of the sex hormones include breast development and a widening of the hips. In boys, they result in the growth of facial hair, increased muscular development, and deepening of the voice.

5. Lesson Overview Lesson Overview The Reproductive System Sexual Development During the seventh week of development, male and female embryos start to develop differently. The male pattern of development is triggered by the production of testosterone in the embryo’s gonads. In female embryos, testosterone is absent and the female reproductive system develops under the influence of estrogens produced in the gonads.

6. Lesson Overview Lesson Overview The Reproductive System Sexual Development Estrogens and testosterone are steroid hormones primarily produced in the gonads. In addition to shaping the sexual development of the embryo, these hormones act on cells and tissues to produce many of the physical characteristics associated with males and females.

7. Lesson Overview Lesson Overview The Reproductive System Sexual Development Puberty is a period of rapid growth and sexual maturation during which the reproductive system becomes fully functional. Puberty actually begins in the brain, when the hypothalamus signals the pituitary to produce hormones that affect the gonads—follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

8. Lesson Overview Lesson Overview The Reproductive System The Male Reproductive System What are the main functions of the male reproductive system?

9. Lesson Overview Lesson Overview The Reproductive System The Male Reproductive System What are the main functions of the male reproductive system? When puberty is complete, the reproductive system is fully functional, meaning that the male can produce and release active sperm.

10. Lesson Overview Lesson Overview The Reproductive System The Male Reproductive System The release of LH stimulates cells in the testes to produce increased amounts of testosterone. Testosterone causes the physical changes in males associated with puberty, such as facial hair, increased muscular development, and deepened voice. Testosterone and FSH stimulate the development of sperm.

11. Lesson Overview Lesson Overview The Reproductive System The Male Reproductive System When puberty is complete, the reproductive system is fully functional: the male can produce and release active sperm. This figure shows the structures of the male reproductive system.

12. Lesson Overview Lesson Overview The Reproductive System Sperm Development Within each testis are clusters of hundreds of tiny tubules called seminiferous tubules where sperm develop. Specialized diploid cells within the tubules undergo meiosis and form the haploid nuclei of mature sperm.

13. Lesson Overview Lesson Overview The Reproductive System The Female Reproductive System What are the main functions of the female reproductive system?

14. Lesson Overview Lesson Overview The Reproductive System The Female Reproductive System What are the main functions of the female reproductive system? The main function of the female reproductive system is to produce egg cells, or ova (singular: ovum). In addition, the system prepares the female’s body to nourish a developing embryo.

15. Lesson Overview Lesson Overview The Reproductive System The Female Reproductive System The primary reproductive organs of the female are the ovaries. Puberty in females starts when the hypothalamus signals the pituitary gland to release FSH and LH. FSH stimulates cells within the ovaries to produce increased amounts of estrogens and to start producing egg cells.

16. Lesson Overview Lesson Overview The Reproductive System Female Reproductive Structures At puberty, each ovary contains up to 400,000 primary follicles. The follicles help an egg mature for release into the reproductive tract. About 400 eggs are released in a woman’s lifetime. The figure shows the other structures of the female reproductive system.

17. Lesson Overview Lesson Overview The Reproductive System The Menstrual Cycle One ovary usually produces and releases one mature ovum every 28 days or so. The process of egg formation and release occurs as part of the menstrual cycle, a regular sequence of events involving the ovaries, the lining of the uterus, and the endocrine system.

18. Lesson Overview Lesson Overview The Reproductive System The Menstrual Cycle The menstrual cycle is regulated by hormones made by the hypothalamus, pituitary gland, and ovaries; it is controlled by internal feedback mechanisms.

19. Lesson Overview Lesson Overview The Reproductive System The Menstrual Cycle During the menstrual cycle, an egg develops within a follicle and is released from an ovary. In addition, the uterus is prepared to receive a fertilized egg. If an egg is not fertilized, it is discharged, along with the lining of the uterus. If an egg is fertilized, embryonic development begins and the menstrual cycle ceases. The menstrual cycle includes the follicular phase, ovulation, luteal phase, and menstruation.

20. Lesson Overview Lesson Overview The Reproductive System Pregnancy If a sperm fertilizes an egg, the fertilized egg completes meiosis and immediately undergoes mitosis. After several divisions, a ball of cells will form and implant itself in the lining of the uterus. The uterus and embryo begin to release hormones that keep the corpus luteum functioning for several weeks. This prevents the menstrual cycle from starting again.