1. Reproduction and Embryonic Development
Chapter 27
Reproduction and Embryonic Development

2. Baby Bonanza The increased use of fertility drugs
Baby Bonanza
The increased use of fertility drugs
Has caused an increase in the number of multiple births in the United States

3. Fertility drugs
Are sometimes too effective

4. ASEXUAL AND SEXUAL REPRODUCTION
27.1 Sexual and asexual reproduction are both common among animals
In asexual reproduction
One parent produces genetically identical offspring

5. Asexual reproduction
Enables an individual to produce many offspring rapidly

6. Reproduction in some animals is accomplished through external fertilization
In which the parents release their gametes into the environment where fertilization occurs
Eggs
Figure 27.1E

7. Sexual reproduction
May enhance reproductive success in changing environments

8. 27.2 Reproductive anatomy of the human female
HUMAN REPRODUCTION
27.2 Reproductive anatomy of the human female
Both sexes in humans
Have a set of gonads where gametes are produced
Have ducts for delivery of the gonads and structures for copulation

9. Contain follicles that nurture eggs and produce sex hormones
A woman’s ovaries
Contain follicles that nurture eggs and produce sex hormones
Oviduct
Ovaries
Follicles
Corpus luteum
Wall of uterus
Uterus
Endometrium
(lining of uterus)
Cervix
(“neck” of uterus)
Vagina
Figure 27.2A

10. Oviducts convey eggs to the uterus Where the eggs develop
Oviducts convey eggs to the uterus
Where the eggs develop
Egg
cell
Ovary
LM 200
Figure 27.2B

11. The uterus opens into the vagina
Which receives the penis during intercourse and forms the birth canal

12. Other structures of the female reproductive system include
Other structures of the female reproductive system include
Labia, the clitoris, Bartholin’s glands, and the cervix
Oviduct
Ovary
Uterus
Urinary bladder
(excretory system)
Pubic bone
Urethra (excretory system)
Shaft
Glans
Prepuce
Clitoris
Labia minora
Labia majora
Vaginal opening
Anus
(digestive system)
Bartholin’s gland
Vagina
Cervix
Rectum
Figure 27.2C

13. 27.3 Reproductive anatomy of the human male
27.3 Reproductive anatomy of the human male
A man’s testes
Produce sperm
Rectum
(digestive system)
Seminal vesicle
Vas deferens
Ejaculatory
duct
Prostate gland
Bulbourethral gland
Epididymis
Testis
Scrotum
Urinary bladder
(excretory
system)
Pubic bone
Erectile
tissue of
penis
Urethra
Glans of penis
Prepuce
Penis
Figure 27.3A

14. Contribute to the formation of fluid that nourishes and protects sperm
Several glands
Contribute to the formation of fluid that nourishes and protects sperm
Urinary bladder
(excretory
system)
Prostate gland
Bulbourethral
gland
Erectile tissue
of penis
Vas deferens
Epididymis
Testis
Seminal
vesicle
(behind
bladder)
Urethra
Scrotum
Glans of
penis
Figure 27.3B

15. During ejaculation
Sperm and the nourishing fluid, called semen, are expelled through the penis
Sphincter
contracts
Urinary
bladder
Urethra region here
expands and fills
with semen
Contractions
of vas deferens
of prostate
gland
of seminal
vesicle
of epididymis
First stage
Sphincter remains
contracted
of muscles
around base
of penis
relaxes
Contractions of urethra
Second stage
Semen expelled
Figure 27.3C

16. A negative feedback system of hormones Controls sperm production
A negative feedback system of hormones
Controls sperm production
Stimuli from other areas in the brain
Hypothalamus
Releasing hormone
Anterior pituitary
Negative feedback
FSH LH
Androgen production
Sperm production
Testis
Figure 27.3D

17. Developing sperm cells (haploid; single chromatids)
Primary spermatocytes, which are diploid, are made continuously in the testes
And undergo meiosis to produce haploid sperm
Primary spermatocyte
Differentiation and onset of Meiosis I
Meiosis I completed
Meiosis II
Differentiation
(in prophase of Meiosis I)
Secondary spermatocyte
(haploid; double chromatids)
Developing sperm cells (haploid; single chromatids)
Sperm cells
(haploid)
Center of seminiferous tubule n 2n
Testis
Scrotum
Penis
Epididymis
Seminiferous tubule
Cross section of seminiferous tubule
Diploid cell
Figure 27.4A

18. Each month one primary oocyte
Each month one primary oocyte
Matures to form a secondary oocyte, which can be fertilized
Completes meiosis and becomes a haploid ovum
Diploid cell
In embryo 2n
Differentiation and onset of Meiosis I
Primary oocyte
(arrested in prophase of Meiosis I)
Present at birth
Completion of Meiosis I and onset of Meiosis II
Secondary oocyte
(arrested at meta- phase of Meiosis II; released from ovary) n
Entry of sperm triggers completion of Meiosis II
Ovum
(haploid)
Second polar body
First polar body
Figure 27.4B

19. The development of an ovarian follicle
The development of an ovarian follicle
Involves many different processes
Corpus luteum
Degenerating corpus luteum
Start:
Primary oocyte
within follicle
Growing follicles
Mature follicle
Ovary
Ruptured follicle
Ovulation
Secondary oocyte
Figure 27.4C

20. 27.5 Hormones synchronize cyclic changes in the ovary and uterus
27.5 Hormones synchronize cyclic changes in the ovary and uterus
The ovarian cycle includes
Changes in the ovary that occur about every 28 days
The menstrual cycle
Involves changes that occur in the uterus

21. An Overview of the Ovarian and Menstrual Cycles
An Overview of the Ovarian and Menstrual Cycles
Events in the menstrual cycle
Are synchronized with the ovarian cycle, which occurs about every 28 days

22. Uterine bleeding, called menstruation
Includes the breakdown of the endometrial lining
Usually persists for 3–5 days
After menstruation
The endometrium, the lining of the uterus, regrows

23. Synchronize the events in the ovarian cycle
Five hormones
Synchronize the events in the ovarian cycle
Table 27.5

24. Hormonal Events Before Ovulation
Hormonal Events Before Ovulation
Approximately every 28 days
The hypothalamus signals the anterior pituitary to secrete FSH and LH
FSH and LH
Trigger the growth of a follicle

25. As the follicle grows, it secretes estrogen
Which causes a burst in FSH and LH levels, leading to ovulation

26. Hormonal Events at Ovulation and After
Hormonal Events at Ovulation and After
After ovulation
The follicle becomes the corpus luteum
The corpus luteum secretes both estrogen and progesterone
Which exert negative feedback on the hypothalamus and pituitary, causing a decline in FSH and LH levels

27. As FSH and LH levels drop
The hypothalamus can once again stimulate the pituitary to secrete more FSH and LH, and a new cycle begins

28. Control of the Menstrual Cycle
Control of the Menstrual Cycle
The menstrual cycle
Is directly controlled by estrogen and progesterone

29. If fertilization of an egg occurs
A hormone from the embryo maintains the uterine lining and prevents menstruation

30. The ovarian and menstrual cycles
Control by hypothalamus
Inhibited by combination of
estrogen and progesterone
Stimulated by high levels
of estrogen
Hypothalamus
Releasing hormone
Anterior pituitary 1
FSH LH B
Pituitary hormones
in blood 4
LH peak triggers
ovulation and
corpus luteum
formation 6 LH
FSH 2
FSH LH C
Ovarian cycle 5
Corpus
luteum
Degenerating
corpus luteum
Growing follicle
Mature
follicle
Ovulation
Pre-ovulatory phase
Post-ovulatory phase
Estrogen
Progesterone
and estrogen D
Ovarian hormones
in blood 3 7
Estrogen 8
Progesterone
Estrogen
Progesterone
and estrogen E
Menstrual cycle
Endometrium 5 10 20 25 28
Days
Figure 27.5
Menstruation

31. 27.6 The human sexual response occurs in four phases
27.6 The human sexual response occurs in four phases
The excitement phase
Prepares the sexual organs for coitus
The plateau phase
Is marked by increases in breathing and heart rate

32. Orgasm follows
Characterized by rhythmic contractions of the reproductive structures
The resolution phase
Completes the cycle and reverses the previous responses

33. 27.7 Sexual activity can transmit disease
CONNECTION
27.7 Sexual activity can transmit disease
Sexual intercourse
Carries the risk of exposure to sexually transmitted diseases (STDs)

34. STDs common in the United States
STDs common in the United States
Table 27.7

35. 27.8 Contraception can prevent unwanted pregnancy
CONNECTION
27.8 Contraception can prevent unwanted pregnancy
Contraception
Is the deliberate prevention of pregnancy
Table 27.8

36. Contraception can be accomplished Through various methods
Contraception can be accomplished
Through various methods
Skin patch
Diaphragm
Spermicide
Condom
Birth control pills
Figure 27.8

37. PRINCIPLES OF EMBRYONIC DEVELOPMENT
27.9 Fertilization results in a zygote and triggers embryonic development
Embryonic development begins with fertilization
The union of sperm and egg to form a diploid zygote

38. The Properties of Sperm Cells
The Properties of Sperm Cells
Only one sperm
Fertilizes an egg
Colorized SEM 500
Figure 27.9A

39. A sperm releases enzymes from the acrosome that pierce the egg’s coat
During fertilization
A sperm releases enzymes from the acrosome that pierce the egg’s coat
Plasma membrane
Middle piece
Head
Neck
Mitochondrion (spiral shape)
Nucleus
Acrosome
Tail
Figure 27.9B

40. The Process of Fertilization
The Process of Fertilization
Sperm surface proteins bind to egg receptor proteins
Sperm and egg plasma membranes fuse, and the two nuclei unite

41. Changes in the egg membrane
Prevent entry of additional sperm
The fertilized egg (zygote)
Develops into an embryo

42. The process of fertilization
The sperm approaches the egg 1
The sperm’s acrosomal enzymes digest the egg’s jelly coat 2
Proteins on the sperm head bind to egg receptors 3
Sperm
The plasma membranes of sperm and egg fuse 4
Nucleus
Sperm head
The sperm nucleus enters the egg cytoplasm 5
Acrosome
Plasma membrane
Acrosomal enzymes
A fertilization envelope forms 6
Receptor protein molecules
Plasma membrane
Sperm nucleus
Vitelline layer
Cytoplasm
Egg nucleus
Jelly coat
The nuclei of
sperm and egg
fuse 7
Egg cell
Zygote nucleus
Figure 27.9C

43. 27.10 Cleavage produces a ball of cells from the zygote
27.10 Cleavage produces a ball of cells from the zygote
Cleavage is a rapid series of cell divisions
That results in a blastula, a ball of cells
Zygote
2 cells
4 cells
8 cells
Many cells (solid ball)
Blastula (hollow ball)
Cross section of blastula
Blastocoel
Figure 27.10

44. 27.13 Changes in cell shape, cell migration, and programmed cell death give form to the developing animal
Cells of the ectoderm
Fold inward during neural tube formation
Ectoderm
Figure 27.13A

45. Programmed cell death, or apoptosis
Programmed cell death, or apoptosis
Is a key developmental process in which cells die
Apoptosis
Dead cell engulfed and digested by adjacent cell
Figure 27.13B

46. 27.14 Embryonic induction initiates organ formation
27.14 Embryonic induction initiates organ formation
In a process called induction
Adjacent cells and cell layers influence each other’s differentiation via chemical signals

47. Induction during eye development
Future brain
Optic vesicle
Lens ectoderm
Optic stalk
Optic cup
Cornea
Lens
Future retina
Figure 27.14 1 2 3 4

48. 27.15 Pattern formation organizes the animal body
27.15 Pattern formation organizes the animal body
Pattern formation
Is the emergence of the parts of a structure in their correct relative positions

49. HUMAN DEVELOPMENT
27.16 The embryo and placenta take shape during the first month of pregnancy
Pregnancy, or gestation
Is the carrying of developing young within the female reproductive tract

50. An Overview of Developmental Events
An Overview of Developmental Events
Human development
Begins with fertilization in the oviduct
Cleavage starts
Fertilization of ovum
Oviduct
Secondary oocyte
Ovulation
Ovary
Blastocyst (implanted)
Endometrium
Uterus
Figure 27.16A

51. Cleavage produces a blastocyst
Cleavage produces a blastocyst
Whose inner cell mass becomes the embryo
Endometrium
Inner cell mass
Cavity
Trophoblast
Figure 27.16B

52. The blastocyst’s outer layer, the trophoblast
Endometrium
Future embryo
Future yolk sac
Blood vessel (maternal)
Multiplying cells of trophoblast
Trophoblast
Uterine cavity
Figure 27.16C
The blastocyst’s outer layer, the trophoblast
Implants in the uterine wall

53. Meanwhile, the four extraembryonic membranes develop
Meanwhile, the four extraembryonic membranes develop
The amnion, the chorion, the yolk sac, and the allantois
Amniotic cavity
Amnion
Mesoderm cells
Chorion
Yolk sac
Allantois
Chorionic villi
Embryo:
Ectoderm
Mesoderm
Endoderm
Figure 27.16D, E

54. Roles of the Extraembryonic Membranes
Roles of the Extraembryonic Membranes
About a month after conception
The extraembryonic membranes are fully formed
Mother’s blood vessels
Allantois
Yolk sac
Placenta
Amniotic cavity
Amnion
Embryo
Chorion
Chorionic villi
Figure 27.16F

55. The embryo floats in a fluid-filled amniotic cavity
Surrounded by the amnion
The chorion and mesoderm cells from the yolk sac
Form the embryo’s part of the placenta

56. The allantois
Forms part of the umbilical cord

57. The Placenta The placenta’s chorionic villi
The Placenta
The placenta’s chorionic villi
Absorb food and oxygen from the mother’s blood to nourish the embryo

58. 27.17 Human development from conception to birth is divided into three trimesters
Human development is divided into three trimesters
Each about three months in length

59. The First Trimester The most rapid changes
The First Trimester
The most rapid changes
Occur during the first trimester
Figure 27.17A

60. The embryo is called a fetus
By 9 weeks
The embryo is called a fetus
Figure 27.17B

61. Second Trimester The second trimester
Second Trimester
The second trimester
Involves an increase in size and general refinement of the human features
Figure 27.17C

62. The fetus is about 19 centimeters long, and weighs half a kilogram
At 20 weeks
The fetus is about 19 centimeters long, and weighs half a kilogram
Figure 27.17D

63. Third Trimester The third trimester
Third Trimester
The third trimester
Is a time of rapid growth, which ends in birth
Figure 27.17E

64. 27.18 Childbirth is hormonally induced and occurs in three stages
27.18 Childbirth is hormonally induced and occurs in three stages
The birth of a child
Is brought about by a series of strong, rhythmic contractions of the uterus, called labor

65. Estrogen makes the uterus more sensitive to oxytocin
Estrogen makes the uterus more sensitive to oxytocin
Which acts with prostaglandins to initiate labor
Estrogen
Oxytocin
from ovaries
from fetus and pituitary
Induces oxytocin receptors on uterus
Stimulates uterus to contract
Stimulates placenta to make
Prostaglandins
Stimulate more contractions of uterus
Positive feedback
Figure 27.18A

66. Labor occurs in three stages
Dilation, expulsion, and delivery of the placenta
Placenta
Umbilical cord
Uterus
Cervix
Placenta (detaching)
Figure 27.18B
Dilation of the cervix 1
Expulsion: delivery of the infant 2
Delivery of the placenta 3

67. 27.19 Reproductive technology increases our reproductive options
CONNECTION
27.19 Reproductive technology increases our reproductive options
New techniques
Can provide help to infertile couples
Figure 27.19

68. Some of these methods
Raise important ethical and legal questions