Embryology Lecture 4 Placental and Fetal Membranes Flashcards
What does the placenta do?
During that 9 month period it provides nutrition, gas exchange, waste removal and endocrine and immune support for the developing fetus
What are the 2 components to the placenta?
Maternal Component:
Derived from decidua basalis of uterine endometrium
¤At birth:
Dark red in color
Oozes blood due to torn vessels at the time of birth
Fetal Component:
¤Derived from trophoblast and extraembryonic mesoderm:
Chorion frondosum
At birth:
Smooth, shiny, light blue or blue pink color because amnion covers the surface
5-8 large chorionic blood vessels are present
What are the 3 types of decidua?
¤Portion of decidua where blastocyst is implanted:
decidua basalis
¤Part of decidua that separates embryo from uterine lumen:
decidua capsularis
¤Part lining rest of uterine cavity:
decidua parietalis (vera)
Desribe the chorion frondosum
Consists of tertiary chorionic villi derived from trophoblasts (cytotrphoblasts and syncytiotrophoblasts) and extraembryonic mesoderm which collectively known as villous chorion (Chorion frondosum)
¨Villi are the functional units of placenta
¨When first formed they are spread around the chorion
¨ Later villi in the region of decidua capsularis degenerate and the chorion becomes smooth:
¨ chorion laeve
¨ Villi in the region of decidua basalis proliferate and expand giving rise to a bushy chorion:
¨ chorion frondosum
Relationships between the embryo and maternal decidua (pink) from the early weeks of pregnancy through the fifth month and the formation of chorion frondosum and chorion laeve
8.5.6
Describe the stages of villi
8.5.6
¨Late 2nd week and beginning of 3rd week cytotrophoblasts have grown into syncytiotrophoblasts to form primary villi
¨Later, extraembryonic mesoderm grows into the primary villi and the villi are now known as secondary villi
¨By the end of 3rd week blood cells and vessels develop in the mesoderm core. The villi are now known as tertiary villi
Summary slide of villi
8.5.6
Formation of Cytotrophoblastic Shell
Cytotrophoblast cells in the villi penetrate the overlying syncytium until they reach the maternal decidua
¨Here they make contact with similar extensions of neighbouring villi to form the outer cytotrophoblastic shell:
¤Attaches fetal part of placenta to maternal part
¤Attaches the chorionic sac to the maternal endometrium
¨Anchoring Villi/Stem villi
¤Chorionic villi that attach firmly to the decidua basalis through the cytotrophoblastic shell
¤Extend from chorionic plate to decidua
¨Free Villi/Terminal Villi:
¤Branch from the sides of stem villi
¤Exchange of nutrients and gas occur through free villi
Overall view of a 5-week-old embryo illustrating the relationships of the chorionic plate, villi, and outer cytotrophoblastic shell
8.5.6
What is the function of the placental barrier and what is it made out of?
Separates maternal blood from fetal blood
Composition:
¤Syncytiotrophoblast, cytotrophoblast, connective tissue (extra-embryonic mesoderm), endothelium of fetal capillaries - early pregnancy
¤Syncytiotrophoblast, endothelium of fetal capillaries - late pregnancy
Acts as a selective barrier (some substances freely cross, whereas other substances don’t)
What are the partitions of a mature placenta called?
decidual/placental septa
What does the placenta look like? (maternal vs fetal)
Maternal Surface:
¨Rough and divided into 8-10 cotyledons
¨ Dark red in color and oozes blood due to torn maternal blood vessels
Fetal Surface:
¨ Smooth and shiny
covered by amnion
¨ The attachment of the umbilical cord is usually eccentric
Establishing the Uteroplacental Circulation
This is accomplished by MODIFICATION OF THE SPIRAL ARTERIES:
¤Specialized invasive cytotrophoblast cells, migrate out from the cytotrophoblast shell
¤I_nvade the spiral arteries_ (but not the veins) and displace the endothelial cells of the spiral arteries forming hybrid arteries. This leads to:
Widening of spiral arteries
Blood escaping from their open ends leaves easily at a much lower pressure than normal arterial pressure
As the embryo grows, these arteries provide an increasing flow of blood into the intervillous space
Functions of Placenta Summary
¨Exchange of Gases:
¤Transport oxygen, carbon dioxide and carbon monoxide by simple diffusion
Exchange of Nutrients and Electrolytes:
¤ Amino acids, carbohydrates, vitamins etc
Transmission of Maternal Antibodies:
¤IgG for passive immunity
Hormone Production:
¤Human chorionic gonadotropin (hCG), somatomammotropin / placental lactogen (provides fetus priority on maternal blood glucose), progesterone (maintains the endometrium during pregnancy) and estrogen for mammary gland development and uterine growth
Excretion:
¤Metabolic waste products produced by fetus
Barrier:
¤Prevents many bacteria and other harmful substances from reaching the fetus
______ is contain 2 -3 separate lobes
____ is a asmall part of placenta is separated from rest of it and sometimes retained inside uterus and cause postpartum hemorrhage
______ is peripheral edge of placenta is covered by decidua
¨Duplex or triplex placenta
¨Placenta succenturiata
¨Circumvallate placenta
Implantation and Placentation
The placenta is derived from the trophoblast cells that further differentiate and invade maternal tissues
–Cytotrophoblast: stem cell population
–Syncytiotrophoblast: invasive fused cells (syncytium) derived from cytotrophoblast
–Invasion process breaks into maternal capillaries, trophoblastic lacunae fill with maternal blood
