Development and Inheritance

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

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

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

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

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

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

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

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

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

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

The Human Genome Project

•Mapped more than 38,000 of our genes

•Including some responsible for inherited disorders

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