2. Concept 46.5: The interplay of tropic and sex hormones regulates mammalian reproduction
Human reproduction is coordinated by hormones from the hypothalamus, anterior pituitary, and gonads
Gonadotropin-releasing hormone (GnRH) is secreted by the hypothalamus and directs the release of FSH and LH from the anterior pituitary
FSH and LH regulate processes in the gonads and the production of sex hormones

3. The sex hormones are androgens, estrogens, and progesterone
Sex hormones regulate:
The development of primary sex characteristics during embryogenesis
The development of secondary sex characteristics at puberty
Sexual behavior and sex drive

4. Hormonal Control of the Male Reproductive System
FSH promotes the activity of Sertoli cells, which nourish developing sperm and are located within the seminiferous tubules
LH regulates Leydig cells, which secrete testosterone and other androgen hormones, which in turn promote spermatogenesis
Animation: Male Hormones

5. – – – Hypothalamus GnRH Anterior pituitary FSH LH Sertoli cells
Fig –
Hypothalamus
GnRH – –
Anterior pituitary
FSH LH
Negative feedback
Negative feedback
Sertoli cells
Leydig cells
Figure Hormonal control of the testes
Inhibin
Spermatogenesis
Testosterone
Testis

6. Testosterone regulates the production of GnRH, FSH, and LH through negative feedback mechanisms
Sertoli cells secrete the hormone inhibin, which reduces FSH secretion from the anterior pituitary

7. The Reproductive Cycles of Females
In females, the secretion of hormones and the reproductive events they regulate are cyclic
Prior to ovulation, the endometrium thickens with blood vessels in preparation for embryo implantation
If an embryo does not implant in the endometrium, the endometrium is shed in a process called menstruation

8. Hormones closely link the two cycles of female reproduction:
Changes in the uterus define the menstrual cycle (also called the uterine cycle)
Changes in the ovaries define the ovarian cycle

9. Degenerating corpus luteum
Fig
(a)
Control by hypothalamus
Inhibited by combination of estradiol and progesterone
Hypothalamus –
Stimulated by high levels of estradiol 1
GnRH +
Anterior pituitary
Inhibited by low levels of estradiol – 2
FSH LH
(b)
Pituitary gonadotropins in blood 6 LH
FSH
FSH and LH stimulate follicle to grow
LH surge triggers ovulation 3
(c)
Ovarian cycle 7 8
Growing follicle
Maturing follicle
Corpus luteum
Degenerating corpus luteum
Follicular phase
Ovulation
Luteal phase
Estradiol secreted by growing follicle in increasing amounts
Progesterone and estradiol secreted by corpus luteum 4
(d)
Ovarian hormones in blood
Peak causes LH surge 5
Figure The reproductive cycle of the human female 10
Estradiol
Progesterone 9
Estradiol level very low
Progesterone and estra- diol promote thickening of endometrium
(e)
Uterine (menstrual) cycle
Endometrium
Menstrual flow phase Proliferative phase
Secretory phase
Days | | | | | | | | 5 10 14 15 20 25 28

10. Degenerating corpus luteum
Fig a
(a)
Control by hypothalamus
Inhibited by combination of estradiol and progesterone
Hypothalamus –
Stimulated by high levels of estradiol
GnRH +
Anterior pituitary
Inhibited by low levels of estradiol –
FSH LH
(b)
Pituitary gonadotropins in blood LH
FSH
FSH and LH stimulate follicle to grow
LH surge triggers ovulation
Figure The reproductive cycle of the human female
(c)
Ovarian cycle
Corpus luteum
Degenerating corpus luteum
Growing follicle
Maturing follicle
Follicular phase
Ovulation
Luteal phase
Days | | | | | | | | 5 10 14 15 20 25 28

11. Ovarian hormones in blood Peak causes LH surge
Fig b
(d)
Ovarian hormones in blood
Peak causes LH surge
Estradiol
Progesterone
Estradiol level very low
Ovulation
Progesterone and estra- diol promote thickening of endometrium
(e)
Uterine (menstrual) cycle
Endometrium
Figure The reproductive cycle of the human female
Menstrual flow phase Proliferative phase
Secretory phase
Days | | | | | | | | 5 10 14 15 20 25 28

12. The Ovarian Cycle
The sequential release of GnRH then FSH and LH stimulates follicle growth
Follicle growth and an increase in the hormone estradiol characterize the follicular phase of the ovarian cycle
The follicular phase ends at ovulation, and the secondary oocyte is released
Animation: Ovulation

13. Animation: Post Ovulation
Following ovulation, the follicular tissue left behind transforms into the corpus luteum; this is the luteal phase
The corpus luteum disintegrates, and ovarian steroid hormones decrease
Animation: Post Ovulation

14. The Uterine (Menstrual) Cycle
Hormones coordinate the uterine cycle with the ovarian cycle
Thickening of the endometrium during the proliferative phase coordinates with the follicular phase
Secretion of nutrients during the secretory phase coordinates with the luteal phase
Shedding of the endometrium during the menstrual flow phase coordinates with the growth of new ovarian follicles

15. A new cycle begins if no embryo implants in the endometrium
Cells of the uterine lining can sometimes migrate to an abnormal, or ectopic, location
Swelling of these cells in response to hormone stimulation results in a disorder called endometriosis

16. Menopause
After about 500 cycles, human females undergo menopause, the cessation of ovulation and menstruation
Menopause is very unusual among animals
Menopause might have evolved to allow a mother to provide better care for her children and grandchildren

17. Menstrual Versus Estrous Cycles
Menstrual cycles are characteristic of humans and some other primates:
The endometrium is shed from the uterus in a bleeding called menstruation
Sexual receptivity is not limited to a timeframe

18. Estrous cycles are characteristic of most mammals:
The endometrium is reabsorbed by the uterus
Sexual receptivity is limited to a “heat” period
The length and frequency of estrus cycles varies from species to species

19. Concept 46.6: In placental mammals, an embryo develops fully within the mother’s uterus
An egg develops into an embryo in a series of predictable events

20. Conception, Embryonic Development, and Birth
Conception, fertilization of an egg by a sperm, occurs in the oviduct
The resulting zygote begins to divide by mitosis in a process called cleavage
Division of cells gives rise to a blastocyst, a ball of cells with a cavity

21. The blastocyst implants
Fig 3
Cleavage
Cleavage continues 4
Ovary 2
Fertilization
Uterus
The blastocyst implants 5 1
Ovulation
Endometrium
(a) From ovulation to implantation
Figure Formation of the zygote and early post-fertilization events
Endo- metrium
Inner cell mass
Cavity
Trophoblast
Blastocyst
(b) Implantation of blastocyst

22. After blastocyst formation, the embryo implants into the endometrium
The embryo releases human chorionic gonadotropin (hCG), which prevents menstruation
Pregnancy, or gestation, is the condition of carrying one or more embryos in the uterus
Duration of pregnancy in other species correlates with body size and maturity of the young at birth

23. Pregnancies can terminate spontaneously due to chromosomal or developmental abnormalities
An ectopic pregnancy occurs when a fertilized egg begins to develop in the fallopian tube

24. First Trimester
Human gestation can be divided into three trimesters of about three months each
The first trimester is the time of most radical change for both the mother and the embryo
During implantation, the endometrium grows over the blastocyst

25. During its first 2 to 4 weeks, the embryo obtains nutrients directly from the endometrium
Meanwhile, the outer layer of the blastocyst, called the trophoblast, mingles with the endometrium and eventually forms the placenta
Blood from the embryo travels to the placenta through arteries of the umbilical cord and returns via the umbilical vein

26. Fig
Maternal arteries
Maternal veins
Placenta
Maternal portion of placenta
Umbilical cord
Chorionic villus, containing fetal capillaries
Fetal portion of placenta (chorion)
Maternal blood pools
Figure Placental circulation
Uterus
Umbilical arteries
Fetal arteriole
Fetal venule
Umbilical cord
Umbilical vein

27. Splitting of the embryo during the first month of development results in genetically identical twins
Release and fertilization of two eggs results in fraternal and genetically distinct twins

28. The first trimester is the main period of organogenesis, development of the body organs
All the major structures are present by 8 weeks, and the embryo is called a fetus

29. Changes occur in the mother
Growth of the placenta
Cessation of ovulation and the menstrual cycle
Breast enlargement
Nausea is also very common

30. (a) 5 weeks (b) 14 weeks (c) 20 weeks Fig. 46-17
Figure Human fetal development
(a) 5 weeks
(b) 14 weeks
(c) 20 weeks

31. Fig a
Figure Human fetal development
(a) 5 weeks

32. Fig b
Figure Human fetal development
(b) 14 weeks

33. Fig c
Figure Human fetal development
(c) 20 weeks

34. Second Trimester During the second trimester
The fetus grows and is very active
The mother may feel fetal movements
The uterus grows enough for the pregnancy to become obvious

35. Third Trimester
During the third trimester, the fetus grows and fills the space within the embryonic membranes
A complex interplay of local regulators and hormones induces and regulates labor, the process by which childbirth occurs

36. from fetus and mother’s posterior pituitary
Fig
Estradiol
Oxytocin +
from ovaries
from fetus and mother’s posterior pituitary
Induces oxytocin receptors on uterus
Positive feedback
Stimulates uterus to contract
Stimulates placenta to make +
Figure A model for the induction of labor
Prostaglandins
Stimulate more contractions of uterus

37. Placenta Umbilical cord Uterus Cervix Dilation of the cervix 1
Fig
Placenta
Umbilical cord
Uterus
Cervix
Figure The three stages of labor
Dilation of the cervix 1

38. Expulsion: delivery of the infant
Fig
Figure The three stages of labor
Expulsion: delivery of the infant 2

39. Delivery of the placenta
Fig
Uterus
Placenta
(detaching)
Umbilical
cord
Figure The three stages of labor
Delivery of the placenta 3

40. Expulsion: delivery of the infant
Fig
Placenta
Umbilical cord
Uterus
Cervix
Dilation of the cervix 1
Expulsion: delivery of the infant
Figure The three stages of labor 2
Uterus
Placenta (detaching)
Umbilical cord
Delivery of the placenta 3

41. Birth, or parturition, is brought about by a series of strong, rhythmic uterine contractions
First the baby is delivered, and then the placenta
Lactation, the production of milk, is unique to mammals

42. Maternal Immune Tolerance of the Embryo and Fetus
A woman’s acceptance of her “foreign” offspring is not fully understood
It may be due to suppression of the immune response in her uterus

43. Contraception and Abortion
Contraception, the deliberate prevention of pregnancy, can be achieved in a number of ways
Contraceptive methods fall into three categories:
Preventing release of eggs and sperm
Keeping sperm and egg apart
Preventing implantation of an embryo

44. A health-care provider should be consulted for complete information on the choice and risks of contraception methods

45. Figure 46.20 Mechanisms of several contraceptive methods
Male
Female
Method
Event
Event
Method
Production of sperm
Production of primary oocytes
Vasectomy
Combination birth control pill (or injection, patch, or vaginal ring)
Sperm transport down male duct system
Oocyte development and ovulation
Abstinence
Abstinence
Condom
Female condom
Coitus interruptus (very high failure rate)
Sperm deposited in vagina
Capture of the oocyte by the oviduct
Tubal ligation
Spermicides; diaphragm; cervical cap; progestin alone (as minipill, implant, or injection)
Sperm movement through female reproductive tract
Transport of oocyte in oviduct
Figure Mechanisms of several contraceptive methods
Meeting of sperm and oocyte in oviduct
Morning-after pill; intrauterine device (IUD)
Union of sperm and egg
Implantation of blastocyst in endometrium

46. The rhythm method, or natural family planning, is to refrain from intercourse when conception is most likely; it has a pregnancy rate of 10–20%
Coitus interruptus, the withdrawal of the penis before ejaculation, is unreliable
Barrier methods block fertilization with a pregnancy rate of less than 10%
A condom fits over the penis
A diaphragm is inserted into the vagina before intercourse

47. Intrauterine devices are inserted into the uterus and interfere with fertilization and implantation; the pregnancy rate is less than 1%
Female birth control pills are hormonal contraceptives with a pregnancy rate of less than 1%

48. Sterilization is permanent and prevents the release of gametes
Tubal ligation ties off the oviducts
Vasectomy ties off the vas deferens
Abortion is the termination of a pregnancy
Spontaneous abortion, or miscarriage, occurs in up to one-third of all pregnancies
The drug RU486 results in an abortion within the first 7 weeks of a pregnancy

49. Modern Reproductive Technologies
Recent advances are addressing reproductive problems

50. Detecting Disorders During Pregnancy
Amniocentesis and chorionic villus sampling are invasive techniques in which amniotic fluid or fetal cells are obtained for genetic analysis
Noninvasive procedures usually use ultrasound imaging to detect fetal condition
Genetic testing of the fetus poses ethical questions and can present parents with difficult decisions

51. Treating Infertility
Modern technology can provide infertile couples with assisted reproductive technologies
In vitro fertilization (IVF) mixes eggs with sperm in culture dishes and returns the embryo to the uterus at the 8 cell stage
Sperm are injected directly into an egg in a type of IVF called intracytoplasmic sperm injection (ICSI)

52. Video: Ultrasound of Human Fetus 1 Video: Ultrasound of Human Fetus 2

53. Gametogenesis Spermatogenesis Oogenesis n n n n n n n n n n n n n n
Fig. 46-UN1
Gametogenesis
Spermatogenesis
Oogenesis
Primary spermatocyte
Primary oocyte 2n 2n n
Polar body
Secondary spermatocytes
Secondary oocyte n n n n n n n
Spermatids n n n n
Sperm n
Polar body
Fertilized egg n

54. Fig. 46-UN2

55. You should now be able to:
Distinguish between asexual and sexual reproduction
Explain how hermaphroditism may be advantageous to animals that have difficulty encountering a member of the opposite sex
Describe various ways in which animals may protect developing embryos
Using diagrams, identify and state the function of each component of the male and female reproductive systems

56. Describe oogenesis and spermatogenesis; describe three major differences between them
Explain how the uterine and ovarian cycles are synchronized and describe the functions of the hormones involved
List the various methods of contraception, how each works, and how effective each is
Describe techniques that allow us to learn about the health and genetics of a fetus