Chapter 29, part 1
Development and Inheritance
Learning Objectives
Explain the relationship between differentiation and development and specify the various stages of development
Describe the process of fertilization
List the three prenatal periods and describe the major events associated with each
Discuss the importance of the placenta as an endocrine organ
Learning Objectives
Discuss the structural and functional changes in the uterus during gestation
List and discuss the events that occur during labor and delivery
Relate basic principles of genetics to the inheritance of human traits
SECTION 29-1 An Overview of Topics in Development
Differentiation and development
Development
Gradual modification of physical and physiological characteristics
Differentiation
The creation of different types of cells
Stages of development
Prenatal development
Embryological
Changes occurring the first two months after fertilization
Fetal
Begins at the start of the ninth week and continues until birth
Postnatal development
Commences at birth and continues to maturity
SECTION 29-2 Fertilization
Fertilization (conception)
Occurs in the uterine tubes
Within a day of ovulation
Spermatozoa cannot fertilize an ovum until after capacitation
Figure 29.1 Fertilization
Figure 29.1 Fertilization
The Oocyte at Ovulation
Oocyte is in meiosis II
Surrounded by the corona radiate
Spermatozoa release hyaluronidase and acrosin
Enzymes required to penetrate corona radiate
Single spermatozoan contacts oocyte, fertilization begins
Oocyte activation
Oocyte activation
Oocyte completes meiosis II
Functionally mature ovum
Female pronucleus and male pronucleus fuse (amphimixis)
Polyspermy prevented by membrane depolarization and cortical reaction
SECTION 29-3 The Stages of Prenatal Development
Embryonic and Fetal Periods
Induction
During prenatal development differences in cytoplasmic composition trigger changes in genetic activity
Gestation periods
Three trimesters
SECTION 29-4 The First Trimester
The First Trimester
Cleavage
Zygote becomes a preembryo then a blastocyst
Implantation
Blastocyst burrows into uterine endometrium
Placentation
Blood vessels form around blastocyst and placenta develops
Embryogenesis
Formation of a viable embryo
Cleavage and blastocyst formation
A series of cell divisions that subdivides the cytoplasm of the zygote
Trophoblast – outer layer of cells
Inner cell mass – cluster of cells at one end of blastocyst
Figure 29.2 Cleavage and Blastocyst Formation
Implantation
Occurs about 7 days after fertilization
Trophoblast enlarges and spreads
Maternal blood flows through open lacunae
Gastrulation
Embryonic disc composed of germ layers
Endoderm
Mesoderm
Ectoderm
Figure 29.3 Stages in Implantation
Figure 29.4 The Inner Cell Mass and Gastrulation
Germ layers
Gastrulation
By day 12 surface cells move toward the primitive streak
A third germ layer forms
The three germ layers are:
Ectoderm – superficial cells that did not migrate
Endoderm – cells facing the blastocoele
Mesoderm – migrating cells between ectoderm and endoderm
Extraembryonic Membranes
Four extraembryonic membranes:
Yolk sac
Amnion
Allantois
Chorion
Figure 29.5 Extraembryonic Membranes and Placenta Formation
Figure 29.5 Extraembryonic Membranes and Placenta Formation
Figure 29.5 Extraembryonic Membranes and Placenta Formation
Embryo Anatomy
Yolk sac
Important site of blood cell formation
Amnion
Encloses fluid that surrounds and cushions developing embryo
Allantois
Eventually becomes bladder
Chorion
Figure 29.6 A Three-Dimensional View of Placental Structure
Placentation
Chorionic villi extend into maternal tissue
Forms intricate branching network for maternal blood
Umbilical cord connects fetus to placenta
Hormones of the placenta
Trophoblast secretes hormones to maintain pregnancy
HCG
Estrogens
Progesterone
hPL
Placental prolactin
relaxin
