Chapter 23Pregnancy, Growth, and

Development

Pregnancy is the presence of a developing offspring in the uterus

Growth is an increase in size. Involves increases in cell numbers and cell sizes

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

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Fertilization

Paths of the egg and sperm cells through the female reproductive tract

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Steps in Fertilization

• acrosome releases enzymes

• sperm cell penetrates zona pellucida

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

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Formation of Morula

• zygote• blastomeres• morula

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Early Human Development

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Implantation

•

• trophoblast will help form the placenta

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Summary of Stages and Events of Early Human Prenatal

Development• fertilized ovum

•

• zygote forms• cleavage

• • mitosis increases cell number

• morula• • solid ball of cell

• blastocyst•

• trophoblast and inner cell mass form

• gastrula•

• primary germ layers form 23-8

Hormonal Changes During Pregnancy

Mechanism that preserves uterine lining during early pregnancy

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Hormonal Changes During Pregnancy

Relative concentrations of three hormones in maternal blood during pregnancy

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Hormonal Changes During Pregnancy

• secretion of maintains corpus luteum• corpus luteum secretes estrogens and progesterone• • estrogens and progesterone stimulate and maintain uterine lining, inhibit FSH and LH, inhibit uterine contractions, and enlarge reproductive organs•

• placental lactogen • aldosterone promotes sodium retention• PTH

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Derivatives of Each Primary Germ Layer

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Embryos

• three weeks; dorsal view• three and a half weeks; lateral view• four weeks; lateral view

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Embryonic Development

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Changes During Embryonic Development

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Placenta

Consists of an embryonic portion and a maternal portion

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Placenta at Seventh Week

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Embryo at Eight Weeks

End of eighth week marks end of embryonic period

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Teratogens

•

• structures in developing embryo are sensitive to teratogens at different times

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Development

body portions change considerably

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Development of External Reproductive Organs

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Position of Full-Term Fetus

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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

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Major Events of Fetal Development

17th – 20th week• muscle movements stronger

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

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Fetal Circulation

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

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Fetal Cardiovascular Adaptations

• fetal blood has greater oxygen-carrying capacity• umbilical vein-• ductus venosus –

• foramen ovale –

• ductus arteriosis • umbilical arteries carry blood from internal iliac arteries to placenta

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Fetal Circulation

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Fetal Circulation Summary

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Prenatal Heart

Factors Contributing to the Labor Process

• as birth approaches, progesterone levels decrease• prostaglandins synthesized which may initiate labor• • • fetal head stretches uterus•

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Birth Process

A positive feedback mechanism propels the birth process

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Stages in Birth

• stage• stage• stage

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Milk Production

• 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

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Postnatal Period

Neonatal period• • newborn begins to carry on respiration, obtain nutrients, digest nutrients, excrete wastes, regulate body temperature, and make cardiovascular adjustments

Infancy• • • teeth begin to erupt• muscular and nervous systems mature• communication begins 23-38

Major Changes in the Newborn’s Cardiovascular

System

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Causes of Death

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Clinical Application

Preimplantation Genetic Diagnosis

Probes disease-causing genes in an eight-celled embryo

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