human reproduction biology 269. previous sessions: discussed normal embryonic and fetal development....

HUMAN REPRODUCTIONBIOLOGY 269

Previous sessions: discussed normal embryonic and fetal development.

Unfortunately, things don't always go right.

More than 150,000 children born each year with birth defects, or congenital malformations.

They are present in , and later become apparent in . Thus, they affect approximately

More than 4,000 different forms of birth defects known

Can affect any organ and Often affect multiple organs

They can be mild severe

Many possible causes:

However, cause is unknown ~ half the time

Chromosomal abnormalities:

Either:

Since all cells of all organs have same chromosomes, chromosomal abnormalities often affect many different organs

Incidences of chromosomal abnormalities in spontaneously aborted fetuses and live births

No. per 100 % surviving aborted to birth.... 3-4 sets of chromosomes 10 - 17 <0.01

Extra sex chromosome <1 >99Missing sex chromosome 10 < 1

Extra autosome 20 - 40 3Missing autosome 1 0

Damaged chromosome 2 - 3 35

Chromosomal abnormalities:

Already talked about

Can involve sex (X or Y) chromosomes or autosomal (other 44) chromosomes

Chromosomal abnormalities:

Trisomy 21, or Down's Syndrome~ 1 out of 660 live births

Abnormal face,Abnormal hands, feetHeart defectsDeafnessMarked mental retardation

Chromosomal abnormalities:

Turner's syndrome: X-~ 1 out of 500 live births

Short female; Poorly developed sexual characteristicsNever enters puberty therefore sterile.Defects in heart, lungs, vessels, bonesOccasionally mentally retarded

Chromosomal abnormalities:

Abnormality (missing piece) of chromosome #5Cri du chat syndrome

Abnormal crySmall head & faceEye abnormalitiesDamage to brainMarked mental retardation

Drugs taken by mother; Cross placenta to embryo

Hundreds of drugs known to cause birth defects.

Potential for birth defects = most common reason drugs restricted

Best known = (sedative):

Limb abnormalities Absent (whole or part), Short, MalformedDefects in heart, lungs, digestive system

Thalidomide

Examples of other drugs linked to birth defects:

Aminopterin Defects of brain, nerves, or skeleton (often limbs) Methotrexate eyes, heart (antitumor agents)

Diethylstilbesterol Defects of uterus, vagina( ↓ miscarriage)

Vitamin A Defects of brain, spinal cord, face (cleft palate/lip), heart Streptomycin Deafness from damage to(antibiotic) inner ear

Defects of

Diseases and infections of mother may cause birth defects, including many diseases which are relatively mild to her

Bacteria, viruses, etc. may cross placenta to embryo orAntibodies produced by mother's immune system may cross placenta and damage embryo

Some common diseases linked to birth defects

Defects of head & face, brain, eyes, other organs

Defects of eyes, brain, heart Deafness

Defects of eyes, head, brain

Examples of chemicals in food, air, water linked to birth defects Cross placenta to embryo

Defects of brain, nerves, heart Defects of skeleton (often limbs) Blindness, deafness Spasticity Mental retardation

Defects of heart, brain Blindness, deafness

Decreased fetal growth Defects of face (cleft palate/lip) Emotional & learning problems

Methylmercury poisoningMinamata Japan, 1930s-1950s

Physical trauma to fetus can cause defects:

Dislocated hip, shoulder Deformed limbs Deformed skull

Amputation of limbs

Leg and foot deformities

Inadequate amniotic fluid and uterine pressure

Cord around neck

Again: Cause