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