Extraembyronic Tissues And Placenta - Lectures 17 & 18 Flashcards
What are the extraembryonic tissues?
Amnion (ICM - epiblast)
Yolk Sac (ICM hypoblast)
Chorion (fetal maternal interface)
Allantois (ICM)
What are the fetal maternal interface tissues and where do they derive from?
Placenta and Chorion
Derive from trophoblast
What are the functions of the amnion?
Buffer against mechanical injury
Accommadates growth
Allows normal movements
Protects fetus from adhesions
Hydramnios
Condition is associated with esophageal atresia and anencephaly
excessive amount of amnionic fluid - more than 2000 ml
Oligohydraminos
Too little amnionic fluid, less than 500ml
Renal agenesis - no kindeys, speaks to the importance of the fetus waste contribution to the fluid
What can you learn from testing A-fetoprotein, creatine and lecithin-to-sphingomyelin ratio??
α-fetoprotein is a amniotic fluid indicator of a neural tube defect
Fetal maturity and lung development can be assessed with creatine concentration and the lecthin-to-sphingomyelin ratio
What is phase I amnionic fluid and it’s source?
In the first 20 weeks of pregnancy
There’s free diffusion of electrolytes through fetal ectoderm
Maternal serum
Secreted by amionic membrane
Phase II amnionic fluid
Fetus added urine
Filtrate from vessels associated with chorion laeve
Filtrate from fetal vessels in umbilical cord is another possible source
Turnover rate in late pregnancy is every 3 hours or 500ml/hour
What are the possilbe functions of the yolk sac in mammals?
May concentrate: Folic acid and vitamins (A, B12 and E) - important source of nutrient for neuralation (histiotraphic nutrition)
Other functions: site of primordial germ cells and blood islands (origin of initial blood cells)
-extraembryonic hematopoesis
Meckels diverticulum - pouch of the ilium and represents the original attachment site of the yolk sac to the embryo
Development of the allantois
Allantoic (umbillical) vessel develop in the mesoderm of the allantois
Proximal part of allantois - formation of urinary bladder and becomes the median umbilical ligament (runs from bladder to umbilical cord)
4 Stages of Chorion Villi Development
previllous embryo - no villi have been formed on the trophoblast
primary villous stage - solid, cytotrophoblastic, ectodermal primary willi appear
secondary villous stage - mesodermal cores appears within the primary villi
tertiary villous stage - characterized by the appearance of blood vessels within the mesenchymal core of the secondary villi
Final Dev - cytotrophoblastic columns and shells and anchoring villi: villi achored to the cytotrohophoblastic shell
What are Hofbauer cells?
Fetal macrophages
Placental Development and Structure
Composed of two parts: fetal part and maternal part
Fetal part is chorionic plate and chorionic villi extended toward maternal.
Maternal part is the cytotrophoblastic shell, from the decidua basalis.
The intervillis space between the chorionic plate and cytotrophoblastic shell is filled with maternal blood
cytotrophoblastic columns are villus that extend from the chorionic plate to the cytotrophoblastic shell
if they connect to the shell then they are called anchoring villi, if they are unattached then- floating villi.
why is the human placenta known as the hemochorial type?
Because the maternal blood directly interfaces with the fetal chorion
This in not seen in all animals
What tissue in the mature placenta directly interfaces with the maternal uterine connective tissue?
the cytotrophoblast
Decidual Reaction
The stroma cells of the endometrium swell full of lipids and glycogen
decidua capsularia -sorrounds the embryo and chorion
decidua basalis - is between chorion and the uterine wall, becomes part of the placenta
decidua parietalis - decidua (endometrium tissue that underwent the decidual reaction) on sides without the embryo
What maternal tissues are lost at birth?
maternal decidua
What is the fate of the decidua capsularis?
it starts to degrade within the decidua parietalis, l
Layers of the womb
embryo amnion chorion - extraembryonic mesoderm synchtiotrophoblast cytotrophoblastic shell decidua capsularis
Maternal blood flow
Maternal blood flow - from spiral arteries into trophoblastic lacunae, the intervillus space of the placenta
Exchange in the the villi
back to maternal blood
Fetal Blood Flow
entirely enclosed in vessels
travels to capillary beds within placenta by umbilical arteries
Returns by umbilical vein
Erythroblastosis fetalis
Rh incompatibility between maternal and fetal blood. Mother is Rh- and baby is Rh+, mother makes antibodies against the Ph antigen and in all subsequent pregnancy those antibodies will attack and lyse fetal erythrocytes
Hydrops
How does hydrops fatalis relate to erthroblastosis fetalis?
hydrops fetalis: water accumulation in fetus
the bilirubin released from the lysed erthyocytes causes hydrops fetalis where the fetus takes on water, jaundice, brain damage and anemia
hydatiform mole
placenta villi swell into grape like appearance and fetus is either absent or not viable.
Happens from paternal imprinting causes the female pronucleus to sit the whole process out, or by duplication of the sperm dna, or two sperms.
Placenta previa
abnormal site for the placenta (ectopic pregnancy)
Functions of the Placenta
diffusion of oxygen and carbon dioxide
diffusion of foodstuff
excretion of waste
what’s the difference between the early placenta and the late placenta
early placenta is thick, has low permeability, small surface area with small diffusion conductance
the late placenta is thin, permeability, large surface area and great placental diffusion
THere’s a low pressure gradient between the mother and fetus at the end of pregnancy, why does adequate oxyengation occur?
fetal hemoglobin has a higher affinity for oxygen
fetal blood hemoglobin concentration is 50% greater than maternal
bohr effect - lower CO2 means more O
what is the double bohr effect?
the bohr effect is happening in both the fetus and mother but opposite
Human chorionic gonadotropin
Secreted by syncytial trophoblast cells into maternal fluids, measurable 8-9 days after ovulation, maximum secretion 10th-12th week of pregnancy
Prevent involutionof corpus luteum
Induces release of progestrone and estrogens by the corpus luteum
Corpus luteum growth
Has an interstitial cell-stimulating effect on the testes of male fetus
Estrogens
Secreted by syncytiotrophoblast cells of the placenta
At end of pregnancy secretion level is 30 times normal
Formed from androgenic steriod compounds, adrenal glands, and converted by trophoblast cells
Functions: Unterine enlargement Breast enlargement Growth of breast ductal structures Enlargement of maternal external genitalia Relaxation of pelvic ligaments Maybe affects fetal development
Higher in later pregnancy
Progestrone
Secreted in small amounts early in pregnancy by corpus luteum
In large amounts by placenta
Functions:
- caused decidual cells to develop
- decrease contractablility of the uterus
- increases secretion of fallopian tubes and uterus
- may help prepare breast for lactation
Higher in later pregnancy
Human Chorionic Somatomammotropin
Secreted by placenta in 5th week
Functions:
- decreased insulin sensitivity andd decreased utilization of glucose by mother
- general metabolic hormone
Secretion levels off on end of pregnancy
What are the theory’s on why the mother’s immune system doesn’t attack the fetus?
Placenta (syncytiotrophoblast and cytotrophoblast) don’t express MHC
Paralysis of mother’s immune system during preegnancy
Decidual immune barrier
Inactivation of mother’s immune system components by molecules formed on fetal placental surface
Fetal Alcohol Syndrome
Poor growth rate Microcephaly Mental retardation Heart defects Hypoplasia of facial features
