1. Section 1: The Endocrine System
How does the endocrine system control body processes?
What are the endocrine glands?
How does negative feedback control hormone levels?

2. The Endocrine System
The endocrine system produces chemicals called hormones that control many of the body’s daily activities.
The endocrine system also regulates long-term changes such as growth and development.

3. Functions of Endocrine Glands
The endocrine glands include the hypothalamus, pituitary, thyroid, parathyroid, adrenal, thymus, and pancreas.

4. Functions of Endocrine Glands
The ovaries in females and testes in males are also endocrine glands.

5. Functions of Endocrine Glands
The pituitary gland communicates with the hypothalamus to control many body activities.

6. Negative Feedback
Through negative feedback, when the amount of a particular hormone in the blood reaches a certain level, the endocrine system sends signals that stop the release of that hormone.

7. End of Section: The Endocrine System

8. Section 2: The Male and Female Reproductive Systems
What is sexual reproduction?
What are the structures and functions of the male and female reproductive systems?
What events occur during the menstrual cycle?

9. Sexual Reproduction
Sexual Reproduction involves the production of egg cells by the female and sperm cells by the male.

10. Sexual Reproduction
The egg and sperm join together during fertilization, forming a fertilized egg (also called a zygote). From the 2-cell stage until the 8th week of development, it is called an embryo.

11. Sexual Reproduction
Humans have 46 chromosomes (23 pairs) in almost all of their cells. However, the sex cells (sperm and egg) only have 23 chromosomes (23 singles).

12. Sexual Reproduction
During fertilization, the 23 single chromosomes from the sperm (male) combine with the 23 single chromosomes from the egg (female) to eventually produce a child with 23 PAIRS of chromosomes (or 46 total).

13. Male Reproductive System
The male reproductive system is specialized to produce sperm and the hormone testosterone. The structures of the male reproductive system include the testes, scrotum, and penis.

14. Male Reproductive System
Sperm cells have a “head” (which contain the 23 chromosomes) and a “tail” (a flagellum that whips around and allows it to swim). Glands produce other fluids called “semen” that give the sperm nutrients and allow them to swim.

15. Male Reproductive System
The oval-shaped testes are the organs of the male reproductive system. They are responsible for producing sperm cells and the male sex hormone testosterone.

16. Female Reproductive System
The role of the female reproductive system is to produce eggs and, if an egg is fertilized, to nourish a developing baby until birth. The organs of the female reproductive system include the ovaries, fallopian tubes, uterus, and vagina.

17. Female Reproductive System
The human egg (also called “ovum”) can be fertilized by a single sperm cell. The egg also includes enough nutrition to feed itself from the moment of fertilization until the development of the umbilical cord.

18. Female Reproductive System
The oval-shaped ovaries produce and store the eggs. They also produce the female sex hormone estrogen.

19. The Menstrual Cycle
During the menstrual cycle, an egg develops in an ovary. At the same time, the uterus prepares for the arrival of an embryo.

20. End of Section: The Male and Female Reproductive Systems

21. Section 3: Pregnancy, Development, and Birth
What are the changes that occur to the zygote, embryo, and fetus during development?
How is the developing embryo protected and nourished?
What happens during childbirth?
What changes occur as a person develops from infancy to adulthood?

22. Development Before Birth
The zygote develops into an embryo and then into a fetus. Differentiation leads to specialized cells, tissues, and organs.
Zygote

23. Development Before Birth
The zygote develops into an embryo and then into a fetus. Differentiation leads to specialized cells, tissues, and organs.
Zygote
Eight-Cell Stage
Hollow Ball

24. Development Before Birth
The zygote develops into an embryo and then into a fetus. Differentiation leads to specialized cells, tissues, and organs.
Zygote
Eight-Cell Stage
Hollow Ball

25. Development Before Birth
The zygote develops into an embryo and then into a fetus. Differentiation leads to specialized cells, tissues, and organs.
Zygote
Eight-Cell Stage
Hollow Ball
Stage When Folding Begins

26. Development Before Birth
The zygote develops into an embryo and then into a fetus. Differentiation leads to specialized cells, tissues, and organs.
Zygote
Eight-Cell Stage
Hollow Ball
Stage When Folding Begins
Embryo With Three Layers

27. Cell Differentiation
Differentiation is the process by which cells change and become specialized (have specific jobs).
Specialization is permanent. Once the cell becomes specialized, it can not change into another cell.

28. Fetal Development
From the 9th week of pregnancy until birth, the developing human is called a fetus.

29. Protection and Nourishment
The membranes and other structures that form during development protect and nourish the developing embryo, and later the fetus.

30. Twins: Identical vs. Fraternal

31. Twins: Identical vs. Fraternal

32. End of Section: Pregnancy, Development, and Birth