Make your own free website on

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


The cervix dilates and fetus moves toward cervical canal


The cervix completes dilation and fetus emerges


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





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



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


Male climacteric



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



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