Chapter 29, part 2
Development and Inheritance
SECTION 29-5 The Second and Third Trimesters
Second and Third Trimesters
Second trimester
Organ systems increase in complexity
Third trimester
Many organ systems become fully functional
Fetus undergoes largest weight change
At end of gestation fetus and uterus push maternal organs out of position
Figure 29.9 The Second and Third Trimesters
Figure 29.10 Growth of the Uterus and Fetus
Figure 29.10 Growth of the Uterus and Fetus
Developing fetus totally dependent on maternal organs
Maternal adaptations include increased
Respiratory rate
Tidal volume
Blood volume
Nutrient and vitamin uptake
Glomerular filtration rate
Structural and Functional Changes in the Uterus
Progesterone inhibits uterine muscle contraction
Opposed by estrogens, oxytocin and prostaglandins
Multiple factors interact to produce labor contractions in uterine wall
Figure 29.11 Factors Involved in the Initiation of Labor and Delivery
SECTION 29-6 Labor and Delivery
Goal of labor is parturition
Stages of labor
Dilation
The cervix dilates and fetus moves toward cervical canal
Expulsion
The cervix completes dilation and fetus emerges
Placental
Ejection of the placenta
Figure 29.12 The Stages of Labor
Other labor and delivery situations
Premature labor
True labor begins before fetus has completed normal development
Difficult deliveries
When the fetus faces the pubis rather than the sacrum
The legs or buttocks enter the vaginal canal first (breech births)
Multiple births
Twins, triplets, etc.
Dizygotic or monozygotic situations
SECTION 29-7 Postnatal Development
Postnatal life stages
Neonatal period
Infancy
Childhood
Adolescence
Maturity
Senescence begins at maturity and ends in death
The neonatal period
From birth to one month
Respiratory, circulatory, digestive and urinary systems adjust
Infant must thermoregulate
Maternal mammary glands secrete colostrum first few days
Milk production thereafter
Both secretions are released via the milk let-down reflex
Body proportions change during infancy and childhood
Figure 29.13 The Milk Let-Down Reflex
Figure 29.14 Growth and Changes in Body Form
Adolescence
Begins at puberty
The period of sexual maturation
Ends when growth is completed
Puberty marked by
Increased production of GnRH
Rapid increase in circulating FSH and LH
Ovaries and testes become sensitive to FSH / LH
Gamete production initiated
Sex hormones produced
Growth rate increases
Hormonal changes at puberty produce gender specific differences in system
Differences are retained throughout life
Adolescence continues until growth completed
Further changes occur when sex hormones decline
Menopause
Male climacteric
Senescence
Aging affects functional capabilities of all system
SECTION 29-8 Genetics, Development, and Inheritance
Genes and chromosomes
Every somatic cell carries copies of the 46 original chromosomes in the zygote
Genotype – Chromosomes and their component genes
Phenotype – physical expression of the genotype
Patterns of inheritance
Somatic cells contain 23 pairs of chromosomes
Homologous chromosomes
22 pair of autosomes and one pair of sex chromosomes
Chromosomes contain DNA
Genes are functional segments of DNA
Figure 29.15 Human Chromosomes
Various forms of a gene are called alleles
Homozygous if homologous chromosomes carry the same alleles
Heterozygous if homologous chromosomes carry different alleles
Alleles are either dominant or recessive depending on expression
Punnett square diagram predicts characteristics of offspring
Figure 29.16 Predicting Phenotypic Characteristics by Using Punnett Squares
Inheritance
Simple inheritance
Phenotypic characteristics are determined by interactions between single pair of alleles
Polygenic inheritance
Phenotypic characteristics are determined by interactions among alleles on several genes
Sources of individual variation
Genetic recombination
Gene reshuffling
Crossing over and translocation
Occurs during meiosis
Spontaneous mutations
Random errors in DNA replication
Figure 29.17 Crossing over and Translocation
Sex-linked inheritance
Sex chromosomes are X chromosome and Y chromosome
Male = XY
Female = XX
X chromosome carries X-linked (sex linked) genes
Affect somatic structures
Have no corresponding alleles on Y chromosome
Figure 29.18 X-Linked inheritance
The Human Genome Project
Mapped more than 38,000 of our genes
Including some responsible for inherited disorders
Figure 29.19 A Map of the Human Chromosomes
You should now be familiar with:
The relationship between differentiation and development, and the various stages of development
The process of fertilization
The three prenatal periods and describe the major events associated with each
The importance of the placenta as an endocrine organ
You should now be familiar with:
The structural and functional changes in the uterus during gestation
The events that occur during labor and delivery
The basic principles of genetics as they relate to the inheritance of human traits
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
