Lecture 9: Placentation & Fetal-maternal Interactions Flashcards
What is the purpose of the Trophectoderm?
Forms the Placenta & external membranes
- produces hCG
- maintains Corpus Luteum (CL)
- CL produced progesterone —> maintains pregnancy by providing a stable environment in uterus that allows the implantation of embryo
How does an embryo signal its Mother to prepare for pregnancy?
- conceptus signals presence to mother
- timing of conceptus biochemical signal occurs prior to luteolysis (before corpus dies off)
What are different ways for Maternal Recognition in different species?
Human/Primate —> hCG
Cow/Sheep —> Interferon-tau
Pig —> Estrogen
Horse (Equine) —> Conceptus Movement; no hormone signals, the conceptus migrates and stops in different spots in the uterus
Why develop extraembryonic membranes?
Maternal body provides nutrients, oxygen, protection, defence from foreign substances
- fetus has different makeup so it will be recognized as foreign so membranes are formed
What are the 4 types of Fetal Membranes?
Aminion:
- made from extraembryonic ectoderm and somatic mesoderm
- suspends embryo within fluid filled ballon that protects from injury, accommodates growth, allows normal fetal movement
Yolk Sac:
- made from extraembryonic endoderm
- membrane outside embryo connected by a tube through umbilical opening to the embryo’s midgut that serves an early site for formation of blood
Allantois:
- made from trophoblast and mesoderm
- formation of umbilical cord and collects waste from fetus
Chorion:
- outermost of fetal membrane
- develops villi and gives rise to placenta to provide more surface area for nutrients exchange
What is the process of Amniocentesis?
- medical procedure to generate cells and amniotic fluid for detection of disease
Fluid - examined for proteins
Cells - determine sex, genetic defects
Describe the importance of the Placenta.
- transient (temporary) organ allowing metabolic interchange; nutrient uptake, gas exchange, produce hormones, fight against internal infection, etc.
- composed of fetal component from chorion and maternal components from uterine endometrium
- specific zones of metabolic exchange between chorion and endometrium
- placenta is expelled after birth —> even a little left behind can cause hemorrhaging
What is the Diffuse (horse, pig) Placenta?
- Entire surface of chorion involved in formation
- diffuse placenta in mares; many microcotyledons distributed
- diffuse placenta of sow: many chorionic villi distributed
What is the Cotyledonary (cow, sheep) Placenta?
- areas of attachment called cotyledons with patches of chorion with endometrium
- fetal portions —> cotyledons
- maternal contact sites —> caruncles
- no extensive branching within the cotyledon-caruncle complex
Convex (cow, giraffe):
- looks like a mushroom
-
Concave (sheep, goat):
- looks like a donut
- more invasive in the middle
What is the Discoid (human, primates, and rodents) Placenta?
- a single placenta formed in discoid shape
- round patch of chronic tissue forms fetal-maternal interface
- vessels from exchange zone merge to form umbilical vessels supplying blood to fetus
- chorion immersed in pools of blood where metabolic exchange takes place
What is the Zonary (dog, cat, seals, bears, and elephants) Placenta?
- form of a complete or incomplete band of tissue surrounding fetus
3 distinct zones:
1. Transfer zone (nutrient transfer)
2. Pigment zone (maternal hemorrhage important for iron transport)
3. Relatively non vascular zone
What is the Epitheliochorial (pig, horse) Placenta Barrier?
- epithelium of chorion in contract with uterine epithelium
- slowest nutrients exchange
- RED - Chronic capillaries
- RED - Chorionic interstitium
- RED - Chorionic epithelium
- YELLOW - Endometrial epithelium
- YELLOW - Endometrial interstitium
- YELLOW - Endometrial capillaries
What is the Syndesmochorial (cow, sheep) Placenta Barrier?
- uterine epithelium eroded locally; chorion enters uterine connective tissue
- rate of transfer is a little more faster due to loss of one layer
- RED - Chorionic capillaries
- RED - Chorionic interstitium
- RED - chorionic epithelium
- Endometrial epithelium ~ MAY OR MAY NOT BE PRESENT
- Endometrial interstitium
- Endometrial capillaries
What is the Endotheliochorial (pig, horse) Placental Barrier?
- erosion of uterine connective tissue; chorion in contact with maternal capillaries
- endometrial epithelium and CT are lost during placentation
- RED - Chorionic capillaries
- RED - Chorionic interstitium
- RED - Chorionic epithelium
- YELLOW - Endometrial interstitium
- Endometrial capillaries
What is the Hemochorial (human, primates, rodents) Placenta Barrier?
- further erosion of uterine blood vessel endothelium; chorionic villi in direct contact with maternal blood —> hemorrhaging could occur on maternal side
- highly invasive type of placentation —> full invasion of maternal side
- RED - Chorionic capillaries
- RED - Chorionic interstitium
- RED - Chorionic epithelium
RBC: Red Blood Cells
What Placental Classifications coordinate with each type?
What are the mechanisms of transport across the placenta?
What are the two types of Multiple Pregnancies?
Dizygotic:
Fraternal —> own membranes and placenta
Monozygotic:
Identical —> implant close but with their own sacs and placenta
- sharing one placenta can cause high risk —> competition of nutrients
What is Placenta Previa?
- if embryo implants too low down within uterus , placenta may lie across cervical Cana and obstruct delivery of baby
- can lead to premature separation of placenta from uterus and haemorrhage
What is Placenta Accreta?
- abnormal attachment of placenta to uterine wall —> chorionic villi invade abnormally into myometrium
3 grades of myometrial invasion by chorionic villi:
1. Placenta Accreta - chorionic villi in contact with myometrium (80% of cases)
- Treatments such as C-section through an historectamy to remove whole uterus to prevent hemorrhaging
2. Placenta Increta - chorionic villi invade into myometrium (15% of cases)
3. Placenta Percreta - chronic villi inside into serosa (5% of cases)
What is Placenta Abruption?
- separation of placenta from uterus before a baby is delivered, occurs in third trimester of pregnancy even sometimes earlier
- placenta abruption can be life threatening for mother, fetus, or both
- when there is lots of bleeding, baby needs to be delivered as soon as possible
