Lecture 12: Placenta and Fetal Membranes Flashcards
During week one the trophoblast contacts the endometrium and differentiates into which 2 important cell layers; what is the function of each?
1) Cytotrophoblast (inner layer)
- Stem cell layer
- Mitotically active
2) Syncytiotrophoblast (outer layer)
- Proteolytic enyzmes, hCG
- Responsible for implantation and intitial sign of pregnancy
Where is the amnion and amniotic cavity arising from?
Epiblast of the Inner Cell Mass
What is the Decidua reaction?
- Changes of the endometrium as it is being invaded by the syncytiotrophoblasts
- Endometrium cells are being lysed and nutrients are being spilled out and provided to the developing embryo
- Also creates an immunologically privileged site
Where is the extraembryonic mesoderm and primary/secondary yolk sac (umbilical vesicle) arising from during week 2; what will the extraembryonic mesoderm eventually give rise to?
- Hypoblast
- Give rise to the Placenta
What are the 3 derivatives of extraembryonic mesoderm; which kind is part of each?
1. Connecting Stalk
- Extraembryonic somatic mesoderm
2. Primitive Blood
- Extraembryonic splanchnic mesoderm
3. Chorion
- Extraembryonic somatic mesoderm + Cytotrophoblast + Syncytiotrophoblast
Where does fertilization occur and when/where does implantation occur?
- Fertilization occurs in the ampulla of uterine tube
- Implantation on posterior body wall by 6 and continues until week 2
What is Ectopic Pregnancy; where does it occur most frequently?
- Implantation of the blastocyst outside uterine cavity
- Occurs most frequently in the ampulla or isthmus of the oviduct (tubal pregnancy)
What is a Complete Hydatidiform Mole; how is it cases?
- Abnormal trophoblastic proliferation; excessive amounts of hCG produced
- Fertilization of an empty oocyte by one sperm, follwed by duplication
- Fertilization of an empty oocyte by two sperm
What is a Partial Hydatidiform Mole?
- Abnormal trophoblastic proliferation; excessive amounts of hCG produced
- Fertilization of a normal oocyte by 2 sperm, zone reaction did not occur to block polyspermy
What are the clinical features of Hydatidiform Moles?
- Vaginal bleeding
- Pelvic pressure or pain
- Enlarged Uterus
- Hyperemesis Gravidarum (from excessive hCG)
What can occur if a Hydatidiform Mole is not found and removed?
- They are typically benign
- If not removed can eventually cause a Choriocarcinoma, which is a very malignant tumor
What are the 3 ways that Amniotic Fluid is formed?
- Cells of the Amnion will secrete fluid
- Maternal blood and Interstitial Fluid
- Fetal Urine
What is the compostion of Amniotic Fluid?
- Ions and small molecules
- Glycophospholipids
- Steroid hormones
- Particulates
What are the functions of Amniotic Fluid?
- Cushions fetus inside uterus
- Maintains temperature
- Provides space for fetal movements
- Provides diagnostic information (amniocentesis)
What is Oligohydramnios and what can cause this?
- Insufficient amniotic fluid
Caused by:
- Renal agenesis
- Pulmonary hypoplasia
- Placental abnormality or maternal HBP
What is Polyhydramnios and what can cause this?
- Excessive amniotic fluid
Caused by:
- Anencephaly (CNS defect)
- Esophageal atresia
- Maternal diabetes
- Multifetal gestations
- Hypoplastic lungs
What is amniotic band syndrome?
- Parts of the amnion tear off and create bands that can wrap around limbs, face, fingers, and toes
- Caused by trauma to the mother and/or insuffiecient blood flow to amnion causing it to slough off
What 3 layers make up the Chorion?
- Extraembryonic somatopleure
- Cytotrophoblast
- Syncytiotrophoblast
When do the Primary Chorionic Villi arise and what is formed?
- Days 13-14 (week 2)
- Syncytiotrophoblasts invading the endometrium will form trophoblastic lacuna (intervillous spaces) for Mom’s blood to fill up
- Cytotrophoblasts begin projecting upwards forming villi
When do Secondary Chorionic Villi arise and what is formed/the components?
- Days 15-18 (week 3)
- Extraembryonic mesoderm extends into the primary villi
- Cytotrophoblasts form the Cytotrophoblastic shell, which firmly secures the placenta to the mother’s endometrium called the decidua basalis
- Outer syncytiotrophoblast layer
When do Tertiary Chorionic Villi arise and what are the components?
- Days 19-21
- When the extraembryonic mesoderm differentiates into villous capillaries and blood vessels
- Core of extraembryonic mesoderm w/ capillaries, middle cytotrophoblast layer, and outer syncytiotrophoblast layer
Which chorionic villi contain capillaries?
Tertiary
How is the intervillous space (lacuna) formed and what are the stem/anchoring villi and branching villi?
- Chorionic villi invade the decidua basalis and erode the decidual tissue forming the intervillous space
Stem/anchoring villi: attach to the maternal tissue through the cytotrophoblastic shell
Branching villi: grow from the sides of stem villi and participate in nutrient/gas exchange
The chorionic villi cover the entire chorionic sac until?
Beginning of week 8
What is the Decidua and the 3 components; which is Mom’s contribution?
- Functional layer of endometrium that separates from the remainder of uterus after child birth
1. Decidua Basalis: deep to the conceptus, forms maternal part of the placenta
2. Decidua Capsularis: superficial and overlying the conceptus
3. Decidua Parietalis: the remaining part of the decidua
How is the smooth chorion formed?
- With growth, villi associated with the Decidua Capsularis become compressed
- Blood supply is reduced
- Will degenerate and leave an avascular bare area, the smooth chorion
How is the villous chorion formed?
- Villi associated with the Decidua Basalis rapidly increase
- Branch profusely and enlarge
- Form busy area of the chorionic sac, villous chorion
As the fetus continues to grow and enlarge the decidua capsularis begins to bulge into the uterine cavity, what does this cause?
- Lack of blood supply causes decidua capsularis to degenerate and fuse with the decidua parietalis
- Smooth chorion then fuses with the decidua parietalis
- Leads to obliteration of the uterine cavity
The amniotic sac grows faster than the chorionic sac, what does this cause and where will this fuse?
- Formation of the amniochorionic membrane
- Membrane will fuse with decidua capsularis
- Adhere to the decidua parietalis
What are the early placental layers (before week 20) from outside the fetus to inside?
- Syncytiotrophoblast
- Cytotrophoblast
- Villi connective tissue
- Endothelium of fetal capillaries
What are the late placental layers (after week 20) from outside the fetus to inside?
- Syncytiotrophoblast
- Vasculosyncytial placenta membrane
- Endothelium of the capillaries
Identify numbers 7-9?
7) Mesenchymal core
8) Cytotrophoblast cells
9) Syncytiotrophoblast cells
Identify A-B
A) Mesenchyme core
B) Hofbauer cell
C) Syncytiotrophoblast cells
Identify 10-14
10) Intervillous Space
11) Syncytiotrophoblast Cells
12) Trophoblastic bud/Syncytial Knot
13) Cytotrophoblast Cells
14) Hofbauer Cells (placental macrophages)
Identify 1-6
1) Chorionic Villi
2) Intervillous space (lacuna)
3) Capillaries
4) Syncytiotrophoblasts
5) Cytotrophoblast cells
6) Placental macrophages (Hofbauer cells)
What are Cotyledon’s; what do they consist of?
- Erosion of decidual tissue produces placental septa, which divide the fetal part of the placenta into irregular and convex areas called cotyledon’s
- Consist of 2+ main stem villi and multiple branch villi
What forms the fetal vs. maternal part of the placenta?
Fetal part: formed by the villous chorion, which project into the intervillous space containing maternal blood
Maternal part: formed by the decidua basalis, almost entirely replaced by the fetal part of the placenta (4th month)
What’s Placenta Accreta, Increta, and Percreta?
Placenta Accreta: abnormal adherence of chorionic villi to myometrium
Placenta Increta: chorionic villi penetrate into the myometrium
Placenta Percreta: chorionic villi penetrate through the myometrium to uterine serosa or adjacent organs
*May be due previous uterine surgery (i.e., C-section) or scar tissue
What organs are common attachment sites seen in Placenta Percreta?
Bladder and/or rectum
What is Placenta Previa?
- Vaginal bleeding beyond 20 weeks gestation
- Abnormal extension of the placenta over or/close to internal opening of the cervical canal
What is Marginal, Partial, and Total Placenta Previa?
Marginal: margin of placenta lies close to internal cervical os
Partial: edge of placenta extends across part of internal ostium
Total: placenta entirely convers internal cervical ostium
What are things that can cross the placenta?
- Nutrients
- Some hormones (i.e., testosterone, progestins, thyroxin)
- Small Ab’s (IgG)
- Waste products (i.e., urea, uric acid, conjugated bilirubin)
- Drugs (almost all of them)
- Infectious agents (cytomegalovirus, rubella, coxsackieviruses, variola, measles, herpes, syphilis, toxoplasma gondii, listeria)
What can NOT cross the placenta?
- Protein hormones such as insulin or pituitary hormones
- Large Ab’s (IgD, IgE, IgM, IgA)
- Drugs w/ structural similarities to AA’s such a heparin
- Infectious agents (i.e., most but not all bacteria)
What vessels are found within the umbilical cord; what protects these vessels; what surrounds the umbilical cord itself?
- 2 umbilical arteries + 1 umbilical vein
- Extraembryonic mesoderm (“Whartons Jelly”) protects the vessels from pressure
- Umbilical cord is surrounded by the amnion
Where is the Extraembryonic Coelom?
Hollow cavity outside of the embryo, eventualy forms body cavity
Where is the Extraembryonic Somatic Mesoderm?
Lining the trophoblast and covering the amnion
Where is the Extraembryonic Splanchnic Mesoderm?
Lining the yolk sac (umbilical vesicle)
Absence of the umbilical arteries may be associated with what?
Chromosomal and fetal abnormalities
Dizygotic twins will have what type of membranes and placenta?
- Two amnions & two chorions
- But chorions & placentas may be fused
What are dizygotic twins?
- Two different eggs are fertilized by 2 different sperm
- Twins that originate from 2 different zygotes
What are monozygotic twins; how can they split?
- Twins that originate from one zygote (identical)
- Can split at the 2-cell, 4-cell, or 8-cell stage
What is a 2-cell split creating monozygotic twins; what splits; what week; what is formed?
- Early separation of embryonic blastomeres during week 1
- 2 different: placenta, chorion, and amnion
What is a embryoblast split creating monozygotic twins; what splits; what week; what is formed?
- Trophoblast already established, but inncer cell mass divides around day 7
- Formation of 2 amniotic sacs; 1 chorionic sac; shared placenta
* Since trophoblast was already established it will give rise to a single placenta and chorionic membrane. With splitting of the inner cell mass we get 2 separate amnions.
Identify these structures
Chorionic Villi
