Fetal Development and Genetics Flashcards
1
Q
What is oogenesis?
A
- Process by which female gametes, or ova (eggs), are produced in the ovaries
- Begins before female fetus is born
2
Q
Describe oogenesis in the female fetus.
A
start to undergo first meiotic division to replicate DNA, but stop before it’s finished
3
Q
Describe oogenesis once puberty starts.
A
- hormonal changes stimulate the development of ovarian follicles
- each month (q28 days) 1 ooccyte completes first meiotic division
- results in:
- secondary oocyte (released during ovulation)
- small polar body (usually non-functional)
4
Q
Describe oogenesis during ovulation.
A
- secondary oocyte is released from the ovary during ovulation
- if fertilization occurs, it will proceed to complete meiosis II
5
Q
What is Spermatogenesis?
A
sperm formation
6
Q
What is Spermatogonium?
A
primitive sperm cells (male gametes) produced in the testes at onset of puberty
7
Q
Describe spermatogenesis during Meiosis I.
A
- primary spermatocyte undergoes meiosis I, resulting in two secondary spermatocytes
8
Q
Describe spermatogenesis during Meiosis II.
A
- results in a total of two haploid spermatids from one secondary spermatocyte
- each primary spermatocyte, four sperms are produced
9
Q
What is an ovum and where is it developed?
A
- mature egg released from the ovary during ovulation
- develops within a structure called the follicle
10
Q
What is the function of fimbriae?
A
- finger-like projections at the end of the fallopian tubes
- after ovulation, they help capture the released ovum and guide it into the uterine tube (fallopian tube) for potential fertilization
11
Q
What is the corpus luteum and what does it do?
A
- the remnants of the mature follicle transform into the corpus luteum
- secretes progesterone (a hormone used to prepare the endometrium (uterine lining) for possible fertilized egg)
12
Q
What are the two protective layers of the ovum?
A
- Zona Pellucida: surrounds the ovum, helping to protect the egg and facilitating the binding of sperm
- Corona Radiata: surround the zona pellucida and provide support and nutrients to the ovum.
13
Q
How long does the ovum have before needing to be fertilized?
A
- about 24 hours after it is released
- after, it degenerates and gets absorbed into body or expelled during menstrual cycle
14
Q
Describe quantity of sperm.
A
1tsp of semen = 200-500 million sperm
15
Q
What does the tail of the sperm do?
A
- the flagellum is responsible for its motility, allowing it to swim toward the ovum
- contains mitochondria, which provide the energy (ATP) needed for movement.
16
Q
What is the purpose of the head of the sperm?
A
- contains enzymes stored in a structure called the acrosome
- crucial for breaking down the zona pellucida, which allows for fertilization
17
Q
How long does sperm have to reach the ovum?
A
remain viable and capable of fertilization for up to 5 days after ejaculation
18
Q
What happens when sperm reaches ovum?
A
- meet in ampulla (outer third) of the uterine tube
- zona reaction (chemical reaction) prevents more than one sperm from entering the ovum
- restores the diploid number (23+23=46) to form zygote (fertilized egg)
19
Q
What is the greatest risk for an embryo (until 8 weeks)?
A
Teratogens
- Infections: Rubella, toxoplasma, TORCH
- Environmental exposures: heat, toxins
- Chemical exposures: alcohol, medications
20
Q
How does the placenta form?
A
- derived from the trophoblast cells of the blastocyst (outer layer of embryo)
- 2 layers:
- Syncytiotrophoblast: outer layer, invades uterine lining and establishes the maternal-fetal connection
- Cytotrophoblast: inner layer, provides support and structure
21
Q
How does circulation occur within the placenta?
A
- begins around day 17
- large network of blood vessels that invades maternal circulation through the uterine lining
22
Q
How does embryonic blood circulation occur within the placenta?
A
- occurs by day 21
- Intervillous spaces (allow for efficient exchange of substances)
- Maternal blood provides oxygen and nutrients
- Exchanges waste and carbon dioxide from the fetus
23
Q
How does the placenta contribute to endocrine and immune barrier function?
A
- Endocrine: placenta produces hormones (human chorionic gonadotropin (hCG), progesterone, estrogen), which maintains pregnancy and supports fetal development
- Immune Barrier (Semipermeable Membrane): placenta acts as a barrier that protects the fetus from certain pathogens while allowing the passage of antibodies and some immune cells from the mother to provide passive immunity
24
Q
Describe the mother’s side of the placenta.
A
- rough and convoluted
- due to the presence of decidual tissue and maternal blood vessels
- Dull red in color due to maternal blood
- vascularized with maternal blood, which is essential for providing oxygen and nutrients
25
Describe the fetus's side of the placenta.
- shiny and smooth
- *prevent adhesion to surrounding tissues and facilitates movement*
26
Describe placenta's growth.
- placenta grows in thickness and circumference until week 16
- after, only grows in circumference
- weighs about 1lb at term
27
Describe the blood inside the placenta.
- Contains approx. 500mL of blood at term
- Blood in the intervillous space is replenished 3-4 times every minute
28
What is amniotic fluid?
clear, slightly yellowish liquid that surrounds and cushions the developing fetus
29
What produces amniotic fluid and how much?
- fetal kidneys and lungs (at 10 weeks)
- at term, 1000mL
30
What are the functions of amniotic fluid?
- Maintains constant temperature
- Cushions fetus
- Allows movement and development
- Provide vitamins, proteins, IgG, electrolytes
- Antibacterial properties
- Important to fetal lung development
31
Describe the 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
- 30-90 cm in length, average 55cm
- Covered with Wharton’s jelly
- Centrally attached to the placenta
- Develops from the connecting stalk
32
What are Autosomal Chromosomal Abnormalities?
- involve changes in the non-sex chromosomes and can lead to a wide range of genetic disorders
- characterized by developmental and physical challenges
- Trisomy 21 (down syndrome)
33
What are Sex Chromosomal Abnormalities?
- changes in the X and Y chromosomes, affecting sexual development and function
- varied effects on physical and reproductive health
- Turner syndrome (45, X)
34
Describe multifactorial inheritance.
- Most common congenital conditions
- affects multiple genes and environmental interactions
- Examples: cleft lip, cleft palate, congenital heart disease
35
Describe unifactorial inheritance.
- caused by mutations in a single gene
- follows clear Mendelian inheritance patterns with predictable risks
36
List the types of genetic tests used in the perinatal period.
- Alpha-Fetoprotein (AFP)
- Cell-free DNA
- Fetal nuchal translucency (FNT)
- Preimplantation genetic testing
- Triple & Quad Screening
37
Describe Alpha-Fetoprotein (AFP), indications, and timing.
- Description: Maternal serum
- Indication: Increased levels associated with neural tube defect
- Timing: Between 15-18 weeks
38
Describe Cell-free DNA, indication, and timing.
- Description: Maternal plasma.
- Indication: Fetal sex, genotyping, Trisomy 13, 18, 21
- Timing: Approximately 10 weeks
39
Describe Fetal nuchal translucency (FNT), indication, and timing.
- Description: Vaginal probe ultrasound to measure fluid collection at base of fetal neck
- Indication: Associated with genetic disorders, trisomy 13, 18, 21, Turners syndrome
- Timing: Between weeks 10-14
40
Describe Preimplantation genetic testing, indication, and timing.
- Description: Genetic testing of embryos produced through IVF.
- Indication: Identify genetic alterations prior to implantation
- Timing: 3 days after egg retrieval or 2 days after fertilization
41
Describe Triple & Quad Screening, indication, and timing.
- Description: Maternal serum measure of AFP, estriol, beta-HCG and inhibin A.
- Indication: Identify risk for Down syndrome, NTD, other trisomy conditions
- Timing: Between weeks 15-18
