1

1

Chapter 23 Pregnancy, Growth, and

Development

Pregnancy is the presence of a developing offspring in the uterus

Growth is an increase in size and entails increases in cell numbers and cell sizes

Development is the continuous process by which an individual changes from one life phase to another

2

Transport of Sex Cells •  fertilization is the union of an egg cell and a sperm cell •  figure shows paths of the egg and sperm cells through the female reproductive tract

3

Fertilization

•  sperm cell reaches corona radiata of egg

•  acrosome releases enzymes

•  sperm cell penetrates zona pellucida

•  sperm cell’s membrane fuses with egg cell’s membrane

2

4

Period of Cleavage

•  zygote •  blastomeres •  morula

5

Stages of Early Human Prenatal Development

6

Implantation

•  begins about the 6th day of development •  trophoblast will help form the placenta •  trophoblast secretes hCG which helps maintain the pregnancy

3

7

Summary of Stages and Events of Early Human Prenatal

Development •  fertilized ovum

•  12-24 hours after ovulation •  zygote forms

•  cleavage •  30 hours to third day •  mitosis increases cell number

•  morula •  third to fourth day •  solid ball of cell

•  blastocyst •  fifth day through second week •  trophoblast and inner cell mass form

•  gastrula •  end of second week •  primary germ layers form

8

Hormonal Changes During Pregnancy

Mechanism that preserves uterine lining during early pregnancy

9

Hormonal Changes During Pregnancy

Relative concentrations of three hormones in maternal blood during pregnancy

4

10

Hormonal Changes During Pregnancy

•  secretion of hCG maintains corpus luteum •  corpus luteum secretes estrogens and progesterone •  placenta secretes large amounts of estrogens and progesterone •  estrogens and progesterone stimulate and maintain uterine lining, inhibit FSH and LH, inhibit uterine contractions, and enlarge reproductive organs •  relaxin from corpus luteum inhibits uterine contractions and relaxes pelvic ligaments •  placental lactogen stimulates breast development •  aldosterone promotes sodium retention •  PTH maintains calcium concentrations in blood

11

Early Embryonic Stage Three primary germ layers form

12

Derivatives of Each Primary Germ Layer

5

13

Embryonic Development

14

Changes During Embryonic Development

15

Embryonic Membranes

As the amnion develops, it surrounds the embryo, and the umbilical cord begins to form from structures in the connecting stalk

6

16

Placenta

Placental membrane consists of

•  epithelial wall of an embryonic capillary •  epithelial wall of a chorionic villus

17

Placenta

Consists of an embryonic portion and a maternal portion

18

Placenta at Seventh Week

7

19

Embryo at Eight Weeks

End of eighth week marks end of embryonic period

20

Teratogens

•  factors that cause congenital malformations during embryonic development •  structures in developing embryo are sensitive to teratogens at different times

21

Fetal Stage •  begins at the end of the eighth week of prenatal development •  body portions change considerably during development

8

22

Development of External Reproductive Organs

•  differentiate from precursor structures

23

Position of Full-Term Fetus

24

Major Events of Fetal Development

9th –12th week •  ossification centers appear •  sex organs differentiate •  fetal limbs begin to move

13th – 16th week •  body grows rapidly •  ossification continues

9

25

Major Events of Fetal Development

17th – 20th week •  muscle movements stronger •  skin is covered with lanugo •  skin is covered with vernix caseosa

21st – 38th week •  body gains weight •  subcutaneous fat deposited •  eyebrows and eyelashes appear •  eyelids open •  testes descend

26

Stages of Prenatal Development

27

Fetal Blood and Circulation

•  oxygen and nutrients diffuse into the fetal blood from the maternal blood •  waste diffuses into the maternal blood from the fetal blood

10

28

Fetal Cardiovascular Adaptations

•  fetal blood has greater oxygen-carrying capacity •  umbilical vein carries oxygenated blood from placenta to fetus •  ductus venosus conducts half the blood from umbilical vein to inferior vena cava; liver is bypassed •  foramen ovale conveys blood from right atrium to left atrium; lungs are bypassed •  ductus arteriosis conducts some blood from pulmonary trunk to aorta; lungs are bypassed •  umbilical arteries carry blood from internal iliac arteries to placenta

29

Fetal Circulation

30

Birth Process

•  as birth approaches, progesterone levels decrease •  prostaglandins synthesized which may initiate labor •  stretching uterine tissue stimulates release of oxytocin •  oxytocin stimulates uterine contractions •  fetal head stretches uterus •  positive feedback results in stronger and stronger contractions and greater release of oxytocin

Factors contributing to the labor process:

11

31

Birth Process A positive feedback mechanism propels the birth process

32

Stages in Birth

•  fetal position before labor •  dilation of the cervix •  expulsion of the fetus •  expulsion of the placenta

33

Milk Production and Secretion

•  placental estrogens and progesterone stimulate further breast development •  estrogens cause ductile system to grow •  progesterone causes alveolar glands to develop •  placental lactogen also produces changes in breast •  prolactin is released about the 5th week of pregnancy •  breast production does not begin until after birth

12

34

Release of Milk

Myoepithelial cells contract to release milk from an alveolar gland

35

Mechanism of Milk Release

36

Hormonal Control of the Mammary Glands

13

37

Postnatal Period

Neonatal period •  birth to end of 4th week •  newborn begins to carry on respiration, obtain nutrients, digest nutrients, excrete wastes, regulate body temperature, and make cardiovascular adjustments

Infancy •  end of 4th week to one year •  growth rate is high •  teeth begin to erupt •  muscular and nervous systems mature •  communication begins

38

Postnatal Period

Childhood •  one year to puberty •  growth rate is high •  permanent teeth appear •  muscular control is achieved •  bladder and bowel controls are established •  intellectual abilities mature

Adolescence •  puberty to adulthood •  person becomes reproductively functional and emotionally more mature •  growth spurts occur •  motor skills continue to develop •  intellectual abilities continue to mature

39

Postnatal Period

Adulthood •  adolescence to old age •  person remains relatively unchanged anatomically and physiologically •  degenerative changes begin

Senescence •  old age to death •  degenerative changes continue •  body becomes less able to cope with demands placed on it •  death results from various conditions and diseases

14

40

Aging-Related Changes

41

Causes of Death

42

Causes of Death

15

43

Clinical Application Preimplantation Genetic Diagnosis

Probes disease-causing genes in an eight-celled embryo