Implantation and Early Embryonic Development

Study Notes

Implantation and Early Embryonic Development

Jam produces HCG as early as 4 weeks, which develops into the placenta and fetal membranes
Chorionic membrane (chorion) creates the sac for amniotic fluid
Amniotic membrane (amnion) also produces amniotic fluid; both are inner and outer layers
Proteolytic enzymes dissolve endometrial tissues, allowing blastocyst implantation
Embryoblast is the inner cell mass of the blastocyst, forming the embryo
Implantation, contact between the growing structure and uterine endometrium, happens ~8-10 days after fertilization
Implantation process has 3 stages:
- Apposition: the structure brushes against the endometrium
- Adhesion: the structure attaches to the endometrium
- Invasion: the structure settles into the endometrium, connecting with the endometrium's blood system
Implantation can occasionally cause light vaginal spotting due to ruptured capillaries
After implantation, the zygote becomes an embryo

Embryonic and Fetal Structures

Corpus luteum maintains function due to HCG secreted by trophoblast cells
Decidua is the Latin word for "falling off" and has three distinct parts:
- Decidua basalis: under the embryo, where trophoblast connects to maternal blood vessels
- Decidua capsularis: encloses the surface of the trophoblast
- Decidua parietalis/vera: remaining portion of the uterine lining
Chorionic villi are microscopic, finger-like projections with capillaries reaching into the uterine endometrium, initiating placenta formation (~11-12 days)
At term, ~200-300 chorionic villi form
Chorionic villi core is loose connective tissue containing fetal capillaries
Intervillous spaces are spaces between chorionic villi
By the 12th day, mature blood starts collecting in the intervillous space, and oxygen and nutrients diffuse from maternal blood to the embryo through the chorionic villi and umbilical cord (weeks 3-4)

Complications of Pregnancy

Hydramnios (Polyhydramnios)

Cause: Hyperglycemia (e.g., diabetes/gestational diabetes) causes fluid shifts into the amniotic space
Effects:
- Malpresentation (e.g., breech, floating)
- Cord prolapse: cord slips out of the vagina before fetal presentation. (Do not attempt re-insertion)
- Cord compression: leads to irreversible brain damage (avoid handling, position mother in Trendelenburg/knee-chest to prevent it)
- Fetal hypoxia: cold exposure causes arterial vasospasm and decreased uteroplacental blood flow
- Decreased fetal heart rate (normal range 120-160 bpm) due to vagal nerve stimulation (avoid handling)
Management:
- Administer oxygen to the mother
- Positioning (e.g., Trendelenburg/knee-chest) to prevent cord compression
- Manually elevate fetal head to prevent cord compression/nuchal cord
- Precipitate (fast) delivery may be needed

Oligohydramnios

Cause: Kidney agenesis (absence of kidneys) affects urine production
Effects:
- Cord compression
- Lack of fetal descent
Management: Left-side position may help relieve cord compression

Amniotic Fluid

Normal Color: Clear, colorless
Odor: Musky
Abnormal Colors & Odors:
- Yellowish: Blood incompatibility
- Greenish: Meconium staining (fetal distress, ARDS, meconium aspiration)
- Brownsh: Fetal death
- Reddish: Hemorrhage
- Grayish: Infection

Fetal Heart Rate (FHR) Decelerations

Early deceleration: ↓ FHR before uterine contraction (head compression, normal)
Variable deceleration: ↓ FHR during uterine contraction (cord compression, change positions)
Late deceleration: ↓ FHR after uterine contraction (uteroplacental insufficiency, stop oxytocin, left-side position, oxygen)

Description

Explore the fascinating process of implantation and early embryonic development. Learn about the roles of the chorion and amnion, the stages of implantation, and how these processes contribute to the formation of the embryo. This quiz will test your understanding of crucial concepts in embryology.