Fetal Development & Genetics

Question 1

Stages of Fetal Development

Zygotic Stage

fertilization of sperm and egg (conception)

Answer 1

• Ovulation occurs on DAY 14 of menstrual cycle
  
  • Sperm are either X or Y ← sex determiner
• Fertilization occurs in the fallopian tube
• Zygote is transported from fallopian tube to uterus via tubular movement
• Zygote undergoes cleavage → turns into morula
  
  • Morula reaches uterine cavity 72 hours after fertilization
  • When nutrient rich fluid enters uterine cavity, BLASTOCYST forms

Question 2

Stages of Fetal Development

Blastocyst Stage

*morula divides into solid mass of cells and attaches to uterus

(more cleaved zygote)

Answer 2

• Inner surface of blastocyst forms embryo and amnion
• Trophoblast - outer layer surrounding blastocyst
  
  • Attaches itself to endometrium for more nourishment
  • Will eventually attach itself to upper fundus d/t rich blood supply in area
  • Trophoblast develops into chorion and helps form placenta

*morula divides into solid mass of cells and attaches to uterus

Question 3

Stages of Fetal Development

Embryonic Stage

End of 2nd to 8th Week

Answer 3

Major structures and organs begin to develop, main external features

Question 4

Stages of Fetal Development

Fetal Stage

8th Week

Answer 4

differentiation and structures specialize by end of 8th week until birth

Question 5

What is the role of the amniotic fluid?

Function, Sources

Answer 5

Function
* Thermoregulation for fetus
* Permit symmetric growth and development
* Cushion for fetus from trauma
* Allows umbilical cord to be relatively free of compression

Derived from 2 sources:
* Fluid from maternal blood across amnion
* Fetal urine

Question 6

Amnitoic Fluid

Oligohydramnios

Answer 6

Oligohydramnios - decreased amniotic fluid due to uteroplacental insufficiency
fetal renal abnormality.

• <500 at term

Diagnostic test: ultrasound

Fetus at risk for:
* Low birth weight
* Surgical birth

Question 7

Amniotic Fluid

Polyhydramnios

Answer 7

Polyhydramnios - too much amniotic fluid as a result of maternal diabetes, neural tube defects, chromocomsal deviations, malformations of GI or CNS.

• > 2000mL at term

Diagnostic Test: Ultrasound

*indicative of fetal GI issue (fetal esophageal sphincter is open, fetus is “vomiting” amniotic fluid out

Question 8

Umbilical Cord

Answer 8

• Formed form amnion
• Contains 1 large vein and 2 small arteries
• Wharton Jelly

*surrounds all 3 blood vessels in umbilical cord to prevent compression, which would cut off blood supply and nutrients to fetus; White jelly like substance; Maternal uterine artery delivers nutrients to placenta; Maternal uterine veins carry fetal waste products away

Question 9

Placenta

Functions, Characteristics

Answer 9

Fuctions
* Serves as interface between mother and fetus
* Produces hormones to control physiology of mother to ensure fetus is supplied with adequate nutrients and O2 for growth
* Protect fetus from immune attack by the mother
* Remove waste products from fetus
* Inducing mother to bring more nutrients to placenta
* Promotes hormones that mature into fetal organs

Characteristics
* Formed by week 12
* Shine side is faced towards baby
* Rough side is faced towards mother (the amniotic membrane)

Question 10

Fetal Circulation

Shunt

Answer 10

Deliver oxygen rich venous blood to systemic circulation and ensure that oxygen poor venous blood bypasses pulmonary circulation.

• Lung development finishes after birth
• Placenta acts as lungs during gestation; fetal lungs are NONFUNCTIONAL

Question 11

Fetal Circulation

Pathway

*While the baby is still inside the uterus.

Answer 11

• Oxygen rich blood carried from placenta to fetus via umbilical vein
  
  • Half goes to hepatic capillaries, other half goes to ductus venosus into IVC
  • Blood from vena cava deflected via foramen ovale into LA → LV → ascending aorta → head and upper body
• Deoxygenated blood goes
  
  • from SVC → RA → RV → pulmonary artery → (MAJORITY) ductus arteriosus → descending aorta → placenta (for oxygenation)
  • Only 5-10% of blood goes to lungs d/t pulmonary resistance b/c fetal lungs are filled with fluid and nonfunctional

Question 12

What happens to circulation at birth?

Answer 12

• Infants’ first breath inflates the lungs, leads to increase in blood flow to lungs from RV
• Pressure in LA increases
  
  • Left side of foramen ovale to press against opening and create functional separation between two atria
• Blood goes to RV as it can no longer be bypassed
  
  • Reason for increased blood flow to lungs
• RV pumps blood into pulmonary artery, which goes to the lungs
• PDA, ASD, and VSD closes