Placenta and Fetal Membranes Flashcards
What are the fetal membranes?
Chorion
Amnion
Allantois
Umbilical vesicle
What makes up the fetal part of the placenta?
Chorionic sac - villous chorion
What makes up the maternal part of the placenta?
Derived from endometrium - decidua basalis
What is the outermost fetal membrane?
Chorionic sac
What occurs at the placenta?
Exchange of nutrients and oxygen between maternal and fetal bloodstreams
What connects the placental circulation with the fetal circulation?
Vessels in the umbilical cord
What are the parts of the Decidua?
- Decidua Basalis
- Decidua Capsularis
- Decidua Parietalis
What is the Decidua?
Functional layer of the endometrium
Decidua Basalis location?
Forms deep to conceptus (embryo) = placenta
What portion of the Decidua forms the maternal part of the placenta?
Decidua Basalis
Decidua Capsularis location?
Superficial and overlies the conceptus (embryo) = chorion
Decidua Parietalis location?
Remaining parts of the decidua = walls of uterus
During implantation, the trophoblast layer differentiates into what 2 layers?
Cytotrophoblasts (inner layer)
Syncytiotrophoblasts (outer layer)
What layer of cells displaces the decidual cells of the endometrium?
Syncytiotrophoblasts
Lacunae
Spaces that appear in the syncytiotrophoblasts that will fill with blood and secretions and eventually fuse
- diffusion of oxygen and nutrients here until actual circulation is formed!
What makes up the chorionic sac?
Extraembryonic somatic mesoderm
Cytotrophoblasts
Syncytiotrophoblasts
What is the amnion?
Membrane that surrounds embryo and amniotic fluid
What will the amnion eventually do and form?
Obliterate the chorionic cavity and form epithelial covering of the umbilical cord
What is the function of amniotic fluid?
Cushion and protect fetus and permit fetal movements
Does the volume of amniotic fluid increase as gestation continues?
Yes; should be around 700-1000 mL by week 37
Polyhydramnios
(include fetus and mother signs)
EXCESS amniotic fluid
- Fetus symptoms = CNS abnormalities
- Mother symptoms = breathlessness, pain, swelling, bloating
Oligohydramnios
(include fetus and mother signs)
Insufficient amniotic fluid (<400 mL)
- Fetus symptoms = anomalies like renal agenesis, not permitted to move very much
- Mother symptoms = abnormal placenta or HBP
The cytotrophoblasts proliferate towards the endometrium starting from where?
Chorionic plate
The cytotrophoblasts extend through what and attach to what?
Extend through syncytiotrophoblasts
Attach to decidua basalis
As the cytotrophoblasts proliferate and extend towards the decidua basalis, what will they form surrounding the chorionic sac?
Cytotrophoblastic shell
Once the cytotrophoblastic shell is formed, what is created beneath it?
Intervillous space
What flows in the intervillous space at week 11-14?
Maternal blood
The intervillous space is also a continuation of?
Lacunae network
What span the intervillous space?
Chorionic villi
What fuse to form the placenta?
Villous chorion and decidua basalis
Decidual erosions produce placental septa. What do the septa divide?
Villous chorion into irregular areas
Once the placental septa divide the villous chorion into irregular areas, what are those areas called?
Cotyledons
What do villi associated with the decidua capsularis become?
Compressed and degenerate to form the
= Smooth Chorion
What do villi associated with the decidua basalis become?
Villi branch extensively to form bushy area known as
= Villous Chorion
Primary chorionic villi
Cytotrophoblasts grow into syncytiotrophoblasts
Secondary chorionic villi
Extraembyronic mesoderm grows into primary villi
Tertiary chorionic villi
Extraembryonic mesoderm differentiates into capillaries and blood vessels
Main stem villi
Extend from chorionic plate
Branch villi
Extend off the main stem villi and increase surface area
What type of villi make up the location where the main exchange occurs between fetus and mother?
Branch villi
Anchoring villi
Villi that attach to maternal tissues through the cytotrophoblastic shell
Cotyldeons have what type of villi?
At least 2+ main stem villi and multiple branch villi
As the embryo grows, what decidua layer bulges into the uterine cavity?
Decidua capsularis
What decidua layer will degenerate and allow the amnion and chorion to fuse?
Decidua capsularis
Once the amnion and chorion fuse, what is created and what will it fuse with?
Amniochoriotic membrane
It will fuse with the decidua parietalis on the opposite wall
After 20 weeks gestation, what in the villi degenerates?
Cytotrophoblasts
What things are NOT allowed to cross the placenta?
- Protein hormones (ex. pituitary hormones)
- Bacteria
- Drugs with amino acid like structures
What makes up the umbilical cord?
Mucous tissue (“wharton’s jelly”)
2 umbilical arteries
1 umbilical vein
Allantois proper
In the umbilical cord, the umbilical arteries contain what type of blood?
De-oxygenated
In the umbilical cord, the umbilical vein contains what type of blood?
Oxygenated
Connecting stalk covered with amnion makes?
Umbilical cord
Absence of an umbilical artery can result in?
Fetal anomalies and can impact labor outcomes
Placenta Previa
Placenta implants in lower uterine segment or cervix
- often leads to serious 3rd trimester bleeding
- Predisposure = prior placenta previa or C section
Placenta Accrete/a
Partial/complete absence of decidua and villous chorion adheres to myometrium
- severe postpartum bleeding
Hydatidiform mole
Replacement of villi with dilated translucent vesicles
Partial mole
Portion of villi are edematous
- FETAL TISSUE PRESENT
- one ovum fertilized by 2 sperm
Complete mole
ALL villi are edematous
- NO fetal tissue present
- NO ovum, all DNA is PATERNAL
Invasive mole
Complete mole that penetrates uterine wall
- Increased hCG in blood
Gestational choriocarcinoma
Invasive metastatic tumor that arises from trophoblast cells
- Increased hCG
Dizygotic twins arise from ____ zygotes
2
Dizygotic (fraternal) twins likely have 2 of what?
2 chorions
2 amnions
Possible 2 placentas
Monozygotic twins arise from _____ zygote
1
The earlier the split for monozygotic twins the?
More separate the membranes and placentas will be
