Primary Chorionic Villi
Cytotrophoblast and Synctiotrophoblast
Secondary Chorionic Villi
Cytotrophoblast, Synchtiotrophoblast, and Mesenchymal Core
Tertiary Chorionic Villi
Cytotrophoblast, Synchtiotrophoblast, Mesenchyme, and Blood Vessels. Will have stem villi
Stem Villi and Anchoring Villi
A different classification of chorionic villi. Stem villi will be the site of gas/nutrient exchange, and anchoring villi will anchor the sac to the endometrium
Origin and Function of Decidua
All decidua comes from the mothers functional layer of the uterine endometrium. The decidua basalis becomes the mother's contribution to the placenta
Maternal part of the placenta. Located in contact with the chorion frondosum where the fetus attached to the uterine wall.
Originates from the maternal endometrium which "plugged" the area where the blastocyst invaginated on the uterine wall. In contact with the chorionic laeve which is on the abembryonic pole of the chorionic cavity. Gets stretch when the fetus starts to grow and extends into uterine cavity
Has no contact with chorionic sac. Functional layer of the uterine endometrium where there was no implantation
Origin and Function of Chorion
Extraembryonic mesoderm and the two layers of trophoblast and surrounds embryo and other membranes. Chorionic villi emerge from chorion, invade endometrium, and allow transfer of nutrients from maternal blood to fetal blood.
Located on embryonic pole of the chorionic cavity and is the site where tertiary villi will remain and give rise to the placenta. Becomes the fetal component of placenta
The abembryonic pole of the chorion, its villi will deteriorate. Will eventually fuse with the decidua capsularis, parietalis and amnion to create the mature amniotic sac
Fetal Component of Placenta
Tertiary villi of the chorionic frondosum. The fetal surface is the chorionic plate (chorion) from trophoblast and extraembryonic mesoderm
Maternal Component of Placenta
Decidua basalis. The maternal surface is the decidual plate.
Placental septa and formation of cotyledons
Around 4th and 5th months, the decidua basalis will extend projections, known as the placental septum, towards the chorionic plate creating cotyledons. These are compartmentalized sacs which do not fully close - intervillus space where villi is bathed in maternal blood
Amniochorionic Membrane Formation
Forms when amniotic cavity and fetus grow to point where decidua parietalis becomes continuous with both the decidua capsularis and the chorion laeve. At this point the amnion and the chorion fuse, which forms the membrane. the amniotic sac grows faster than the chorionic cavity, which allows it to "catch up" with it
Origin of Intervillus Space
When some of the cytotrophoblast creating the primary villus penetrates the synchtiotrophoblast making contact with the maternal epithelium, a cytotrophoblastic shell will be created. This shell creates the "roof" of the intervillus space with syncytiotrophoblast making contact with the maternal epithelium, a cytotrophoblastic shell will be created, making the roof of the space with the syncytiotrophoblast cells making the floor and the tertiary villi columns inside it.
What was the Intervillus Space Originally?
The lacunae of the syncytiotropholast
Main site of Gas Exchange in Placenta
Components of Placenta at 10 Weeks Blocking Passage to Fetal Bloody Supply
Syncytiotrophoblast, cytotrophoblast, mesencyme, and endothelial cells, which all must be crossed to get to fetal blood supply
Components of Placenta at 20 Weeks locking Passage to Fetal Bloody Supply
There is only syncytiotrophoblast and endothelial cells blocking passage
Functions of Placenta
Metabolism, Transportation, Endocrine Secretion
Synthesizes glycogen, cholesterol, and fatty acids
Gases, nutrients, and wastes. All of them using simple diffusion, facilitated diffusion, active transport or pinocytosis
Placental Endocrine Secretion
hcG, Somatomammotrophin (promotes breast milk production), hACT, Prolactin, relaxin, prostaglandins, progesterone, estrogen
Things that do pass the placental membrane
Gases: O2, CO2, CO; Nutrients: AAs, glucose, fatty acids, vitamins, electrolytes. IgG antibodies: Immunity to diptheria, smallpox, and measles; Drugs - Thalidomide causes defects in limb/ear; TORCH infection agents; Treponema pallidum (syphillis) (only bacterium); Waste products (urea, uric acid, billirubin)
Things that do not pass the placental membrane
Maternal cholesterol, triglycerides, or phospholipids; Protein hormones; Bacteria; Heparin; Transferrin; IgS, IgM (No immunity to pertussis or chickenpox)
Function of Amnion and Amniotic Fluid
Allows for unhindered fetal development. Permits free movement, symmetrical external growth of the fetus, also preventing adhesion of fetus to the amnion. Cushions the fetus against jolts and helps to control body temperature. Allows for normal fetal lung development
Origin of Amnion and Amniotic Fluid
Derived from maternal blood and the fetus swallows about 400ml/day after the 5th month. The fetus then contributes fluids to the amniotic fluid through urine and respiratory tract secretions.
Low amniotic fluid volume - can lead to Potter's syndrome
High amniotic fluid volume
The origin of the yolk sac
The Yolk sac (or Exocoelomic cavity) starts forming itself during the second week of the embryonic development, at the same time of the shaping of the amniotic sac. The hypoblast starts proliferating laterally and descending. In the meantime the Heuser membrane, located on the opposite pole of the developing vesicle, starts its upward proliferation and meets the hypoblast.
The function of the yolk sac
Transfer nutrients, during the 2nd and 3rd weeks before uteroplacental circulation is established. Also involved in hematopoiesis.
Fate of the yolk sac
Part of the yolk sac is incorporated into the midgut and the primordial germ cells arise from the yolk sac by the 3rd week. The yolk sac will degenerate some time after 6th week, detaching the vitelline duct.
Does everyone lose the vitelline duct?
Some people (2%) will not loose the vitelline duct which is seen as ileal diverticulum or Meckel's diverticulum.
Origin of allantois
Appears on day 16 as a small diverticulum from the caudal wall of the yolk sac extending into the connecting stalk
Function of allantois
Hematopoiesis during 3rd to 5th week.
Fate of allantois
Umbilical vein and arteries form from its blood vessels. Urachus tube becomes the median umbilical ligament after birth.
Also called the exocoelomic membrane is a short lived combination of hypoblast cells and extracellular matrix. It surrounds the exocoelomic cavity. It lines the inner surface of the cytotrophoblast
A cord or tube of epithelium connecting the apex of the urinary bladder with the allantois; its connective tissue.
Function of chorionic villi
Holds the placenta in place via the cytotrophoblastic shell, connecting the fetal part to the maternal part
The decidual layer that falls off at birth
Functional decidual basalis
This membrane breaks when your water "breaks"?
The turnover rate for amniotic fluid
Reason of fetal skin absorption of amniotic fluid
Fetal skin is non-keratinized and fluid can be diffused easily
The premordium of the bladder
Patent urachal fistula
Leakage of urine from the umbilicus