1. CHAPTER 39 – ENDOCRINE AND REPRODUCTIVE SYSTEMS

2. 39-1 – The Endocrine System

3. The endocrine system is made up of glands that release their products into the bloodstream. These products deliver messages throughout the body.

4. Hormones
Hormones – the chemicals that send messages from the endocrine system. They are chemicals released in one part of the body that travel through the bloodstream and affect the activities of cells in other parts of the body. Hormones bind to specific chemical receptors on those cells.
Target cells – cells that have receptors for a particular hormone

5. If a cell does not have receptors or the receptors do not respond to a particular hormone, the hormone has no effect on it.

6. Glands
A gland is an organ that produces and releases a substance, or secretion.
Exocrine glands – release their secretions through ducts directly to the organs that use them (sweat, tears, digestive juices)
Endocrine glands – release their hormones directly into the bloodstream.

7. The major endocrine glands in the human body:

8. Hormone Action
There are two groups of hormones: steroid hormones and nonsteroid hormones.
Steroid hormones are lipids and can cross cell membranes easily, passing directly into the cytoplasm and into the nuclei of target cells. Steroid hormones affect gene expression directly and can produce dramatic changes in cell and organism activity.
Nonsteroid hormones cannot pass through the cell membrane of their target cells.

9. Prostaglandins
Prostaglandins – modified fatty acids that are produced by a wide range of cells. They generally affect only nearby cells and tissues, and are known as “local hormones”
Some prostaglandins cause smooth muscles, such as those in the uterus, bronchioles, and blood vessels, to contract. Another group causes the sensation of pain in most headaches. Aspirin inhibits the synthesis of these prostaglandins.

10. Control of Endocrine System
The endocrine system is regulated by feedback mechanisms that function to maintain homeostasis.
For example, the thyroid gland releases a hormone called thyroxine which controls the rate of metabolism. A drop in thyroxine decreases the metabolic activity of cells. The activity of the thyroid gland is controlled by the hypothalamus and the anterior pituitary gland. The thyroid does not work alone.

11. Complementary Hormone Action
Sometimes two hormones with opposite effects act to regulate part of the body’s internal environment. Many endocrine functions depend on the complementary effects of two opposing hormones.

12. 39-2 Human Endocrine Glands

13. Endocrine glands are scattered throughout the body
The human endocrine system regulates a wide variety of activities. Any endocrine not functioning properly could result in a disease or a disorder.
The major glands of the endocrine system are the pituitary gland, the hypothalamus, the thyroid gland, the parathyroid glands, the adrenal glands, the pancreas, and the reproductive glands.

14. Pituitary Gland
Pituitary gland – a bean-sized structure that dangles on a slender stalk of tissue at the base of the skull. It is divided into two parts: the anterior pituitary and the posterior pituitary
The pituitary gland secretes nine hormones that directly regulate many body functions and controls the actions of several other endocrine glands.

17. Hypothalamus
The hypothalamus controls the secretions of the pituitary gland.

18. The thyroid gland is located at the base of the neck and wraps around the upper part of the trachea.
The thyroid gland has the major role in regulating the body’s metabolism.

19. Hyperthyroidism is when the thyroid produces too much thyroxine
Hyperthyroidism is when the thyroid produces too much thyroxine. It can result in nervousness, elevated body temperature, increased metabolic rate, increased blood pressure, and weight loss.
Hypothyroidism is when too little thyroxine is produced. This can result in lower metabolic rates and body temperature, lack of energy, and weight gain.

21. Parathyroid Glands
The four parathyroid glands are found on the back surface of the thyroid gland.
Hormones from the thyroid gland and the parathyroid glands act to maintain homeostasis of calcium levels in the blood.

22. Adrenal Glands
Adrenal glands are two pyramid-shaped structures that sit on top of the kidneys, one gland on each kidney.
The adrenal glands release hormones that help the body prepare for and deal with stress.

24. About 80% of an adrenal gland is its adrenal cortex
About 80% of an adrenal gland is its adrenal cortex. The adrenal cortex produces more than two dozen steroid hormones called cortiscosteroids. One of these hormones, called cortisol, helps control the rate of metabolism of carbohydrates, fats, and proteins.
The adrena medulla produces the “fight or flight” response to stress. This is the feeling you get when you’re excited or scared.

25. Pancreas
The pancreas produces enzymes that help breakdown food. The pancreas also produces hormones called insulin and glucagon.
Insulin and glucagon help to keep the level of glucose in the blood stable. When blood glucose levels rise after eating, the pancreas releases insulin, which takes glucose out of the bloodstream.

26. When the pancreas fails to produce or properly use insulin, a condition call diabetes mellitus occurs. In diabetes, the amount of glucose in the blood may rise so high that the kidneys actually excrete glucose in the urine. Very high blood glucose levels can damage almost every cell in the body, including the coronary artery.

27. There are two types of diabetes: Type I and Type II
Type I diabetes is an autoimmune disorder that usually develops in people before they turn 15. They’re bodies make little to no insulin. They must follow a strict diet and get daily injections of insulin to keep their blood glucose levels under control.
Type II diabetes commonly develops in people after the age of They produce low to normal amounts of insulin, however, their cells are unable to properly respond to the hormone because the interaction of the insulin receptors and the insulin is inefficient. In the beginning, it can be controlled with diet and exercise. Eventually, they may also need daily shots of insulin.

28. Reproductive Glands
The gonads are the body’s reproductive glands. The gonads serve two important functions: the production of gametes and the secretion of sex hormones.
The female gonads are the ovaries. They produce eggs (ova).
The male gonads are the testes. They produce sperm.

29. The gonads also produce sex hormones
The gonads also produce sex hormones. The ovaries produce estrogen and progesterone. Estrogen is needed for the development of eggs and for the formation of the physical characteristics associated with the female body, like the development of the female reproductive system, widening of the hips, and development of the breasts. Progesterone prepares the uterus for the arrival of a developing embryo.

30. The testes produce testosterone, which is needed for normal sperm production and the development of physical characteristics associated with the male body, like facial hair, increase in body size, and deepening of the voice.

31. 39-3 The Reproductive System

32. Sexual Development
For the first six weeks of development, human male and female embryos are identical in appearance. During the seventh week, major changes occur. The primary reproductive organs, testes or ovaries, begin to develop.

33. The testes produce testosterone, which is a male sex hormone needed for sperm production and the development of male physical characteristics.
The ovaries produce the female sex hormones estrogen and progesterone. Estrogen is needed for the development of eggs and for the formation of female physical characteristics. Progesterone prepares the uterus for the arrival of a developing embryo.
Neither the testes nor the ovaries are capable of producing active reproductive cells until puberty.

34. Puberty – a period of rapid growth and sexual maturation during which the reproductive system becomes fully functional.
By the end of puberty, the male and female reproductive organs are fully developed. When puberty begins is different for everyone but may occur any time between the ages of 9 and 15 and on average begins a year earlier in females than males.

35. The Male Reproductive System
The release of hormones FSH and LH stimulates cells in the testes to make testosterone. Testosterone produces a number of secondary sex characteristics that appear in males at puberty such as facial and body hair, increase in body size, and deepening of the voice.
The main structures of the male reproductive system are the testes, the epididymis, the vas deferens, the urethra, and the penis. These structures work together to produce and deliver sperm.

36. Scrotum – an external sac that contains the testes
Seminiferous tubules – tiny tubules in the testes that are tightly coiled and twisted together. Sperm is produced in them.

38. A sperm cell is made up of a head, which contains the nucleus, a midpiece, and a tail (flagellum) which propels the cell forward.

40. Epididymis – place where sperm fully mature and are stored.
From the epididymis, some sperm move into a tube called the vas deferens. The vas deferens merges with the urethra, which is the tube that leads to the outside of the body through the penis.
Sperm mixes with a nutrient-rich fluid called seminal fluid. This combination is called semen. Between 50 and 130 million sperm are present in 1 milliliter of semen.

41. The Female Reproductive System
The main structures of the female reproductive system are the ovaries, the Fallopian tubes, the uterus, and the vagina. In addition to producing eggs, the female reproductive system prepares the female’s body to nourish a developing embryo.

43. The ovaries usually produce only one mature ovum each month
The ovaries usually produce only one mature ovum each month. 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.
An egg is released about every 28 days. This is called ovulation. The egg is swept into the opening of one of the two Fallopian tubes. While an egg is in the Fallopian tube, it can be fertilized. Then the egg goes into the uterus. The lining of the uterus is ready to receive a fertilized egg.

44. The Menstrual Cycle
The menstrual cycle takes on average 28 days. It begins at puberty and continues until a female is in her mid-forties. The production of estrogen decreases and menstruation ends permanently at about 51, but can occur anytime from the late 30s to late 50s.

45. 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 the embryo develops. If the egg is not fertilized, it is discharged with the lining of the uterus.

46. The menstrual cycle has four phases: follicular phase, ovulation, luteal phase, and menstruation
The follicular phase begins when the level of estrogen in the blood is low. Hormones released cause a follicle to mature. The follicle produces estrogen. The estrogen causes the lining of the uterus to thicken in preparation of receiving a fertilized egg. The development of an egg in this stage takes about 10 days.

47. Ovulation is the shortest phase in the cycle
Ovulation is the shortest phase in the cycle. It occurs midway through the cycle and lasts three to four days. Hormones cause the follicle to rupture and a mature egg is released into one of the Fallopian tubes.
The luteal phase begins after the egg is released. The egg moves through the Fallopian tube. The follicle turns yellow and is now called the corpus luteum. The corpus luteum releases estrogen and progesterone.

48. During the first two days of the luteal phase, the chances that an egg will be fertilized are the greatest. If an egg is fertilized by a sperm, it will start to divide by the process of cell division known as mitosis. After several divisions, a ball of cells forms and implants itself in the lining of the uterus.

49. If fertilization does not occur, within two to three days of ovulation, the egg will pass through the uterus without implantation. The corpus luteum begins to disintegrate. Less estrogen and progesterone is released. 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. This is called menstruation. After a few days, the cycle begins all over again.

50. 39-4 Fertilization and Development

51. An egg is usually fertilized in a Fallopian tube
An egg is usually fertilized in a Fallopian tube. During sexual intercourse, sperm are released when semen is ejaculated through the penis into the vagina.
The egg is surrounded by a protective layer that contains binding sites to which sperm can attach. When a sperm attaches to a binding site, a sac in the sperm head releases powerful enzymes that break down the protective layer of the egg. The sperm nucleus enters the egg and chromosomes from the sperm and egg are brought together.

52. The process of a sperm joining an egg is called fertilization.
The fertilized egg is call a zygote.

55. Early Development
While still in the Fallopian tube, the zygote begins to undergo mitosis.
About six days after fertilization, the ball of cells, called a blastocyst, attaches to the wall of the uterus. This is called implantation.
During gastrulation, three layers are formed called the ectoderm, mesoderm, and endoderm. All organs and tissues will be formed from these layers.

56. Placenta – the mother and developing embryo and supplies the developing embryo with nutrients and oxygen. It also eliminates carbon dioxide and metabolic wastes.
The placenta is the embryo’s organ of respiration, nourishment, and excretion.

59. At 7 weeks, most of the organs have begun to form. The heart is beating. By 14 weeks, the hands, feet, and legs have reached their birth proportions. Eyes, ears, and nose are well developed. At full term, the fetus is fully developed and capable of living on its own.
About nine months after fertilization, the fetus is ready for birth. Contractions of the uterus force the baby out through the vagina. (Sometimes a caesarean section is needed).