Fetal Development and Pregnancy Flashcards
Describe oogenesis.
- Production or development of an ovum (divides to give rise to embryo)
- Begins during embryological and fetal development of the female
Describe oogenesis in relation to the cell cycle.
- All potential eggs are established as an embryo: start to undergo first meiotic division to replicate DNA, but stop before its finished
- After onset of puberty, 1 oocyte matures q28 days and completes the first meiotic division
- 2 unequal cells – secondary oocyte and a small polar body
- Contain 22 autosomes and 1 X chromosome
- After ovulation, second meiotic division begins – completes only if fertilized
Describe spermatogenesis.
- Production or development of mature sperm
- Spermatogonium – primitive sperm cells produced in the testes at onset of puberty
Describe spermatogenesis in relation to the cell cycle.
- First meiotic division – 2 haploid secondary spermatocytes are formed
- Each contains 22 autosomes and 1 sex chromosome
- Secondary spermatocytes divide results in 4 sperm
Describe the ovum during fertilization.
- Fimbria of uterine tubes pulls ovum into tube
- Corpus luteum on the ovary produces progesterone
- Two protective layers: zona pellucida and corona radiate
- Viable for approx. 24 hours after ovulation
Describe the sperm during fertilization.
- Approx. 1tsp of semen = 200-500 million sperm
- Tail of sperm contain mitochondria
- Head of sperm contain enzymes that help get past those protective layers of the ovum
- Viable for up to 5 days
What happens during ovulation?
- Sperm and ovum meet in ampulla (outer third) of the uterine tube
- Chemical reaction prevents more than one sperm from entering the ovum – called the zona reaction
- Restores the diploid number to form zygote
What are embryo (until 8 weeks gestation) susceptible to?
Teratogens:
- Infections: Rubella, toxoplasma, TORCH
- Environmental exposures: heat, toxins
- Chemical exposures: alcohol, medications
Structure of the placenta?
- Derived from the trophoblast cells of the blastocyst, has 2 layers.
- Circulation begins around day 17
- Large network of blood vessels that invades maternal circulation
- Facilitates embryonic blood circulating by day 21
- Intervillous spaces
- Maternal blood provides oxygen and nutrients
- Exchanges waste and carbon dioxide from the fetus
Functions of the placenta?
- Endocrine
- Immune barrier (semipermeable membrane)
List additional information about the placenta.
- Maternal side is rough and convoluted
- Dull red in color due to maternal blood
- Fetal side is shiny and smooth
- Weighs about 1lb at term
- Until week 16 the placenta grows in thickness and circumference
- Remainder of pregnancy only grows in circumference
- Viral infections can influence thickness of placenta
- Contains approx. 500mL of blood at term
- Blood in the intervillous space is replenished 3-4 times every minute
Where is amniotic fluid produced? How much amniotic fluid is present at term?
- Produced by fetal kidneys & lungs at 10 weeks
- At term, approximately 1000 mL
What is the purpose of amniotic fluid?
- Maintains constant temperature
- Cushions fetus
- Allows movement and development of fetal limbs
- Provide vitamins, proteins, IgG, electrolytes
- Antibacterial properties
- Important to fetal lung development
Describe Polyhydramnios.
- Too much amniotic fluid
- Risk of cord prolapse upon rupture
Describe Oligohydramnios.
- Too little amniotic fluid
- Risk of poor fetal lung development;
fetal demise
What is the structure and function of umbilical cord?
- 3 vessels (AVA)
- 2 arteries – return blood to the placenta/chorionic villi
- 1 vein – carries nutrient and oxygen rich blood to the embryo/fetus
- Covered with Wharton’s jelly
What are Autosomes?
A chromosome that is not directly involved in determining the sex of an organism.
What is a Sex Chromosome?
A chromosome that determines whether an organism is male or female.
Describe Multifactorial inheritance.
- Typically complex disorders
- Most common congenital conditions
- Multiple genes and environmental interactions
- Examples: cleft lip, cleft palate, congenital heart disease, neural tube defects, and pyloric stenosis.
What causes Unifactorial inheritance?
Caused by mutations in a single gene (Mendelian genetics)
Compare the different types of Unifactorial Inheritance disorders.
- Autosomal dominant – only one mutated allele needed for expression (Marfan’s Syndrome)
- Autosomal recessive – two copies of mutant gene needed for expression (Sickle cell disease )
- X-linked dominant – dominant gene carried on X-chromosome (Fragile X)
- X-linked recessive – recessive gene carried on X-chromosome (Hemophilia)
List the types of genetic tests used in the perinatal period.
- Alpha-Fetoprotein (AFP)
- Fetal nuchal translucency (FNT)
- Triple & Quad Screening
- Preimplantation genetic testing
- Cell-free DNA
What is used in Alpha-Fetoprotein (AFP) testing?
Maternal serum
How is Fetal nuchal translucency (FNT) done?
Vaginal probe ultrasound to measure fluid collection at base of fetal neck
