Implantation + placental function Flashcards
what is the placenta, where and how is it made?
placenta is a temporary organ that forms in uterus during pregnancy. It attaches to uterine wall and provides nutrients/oxygen to baby through the umbilical cord
trophectoderm (trophoblast cells make placenta from fetal side) is the part of the conceptus that initiates uterine contact and, after transformation to become the trophoblast, uterine invasion
what is a conceptus?
conceptus= is the embryo in the uterus, especially during the early stages of pregnancy.
what is the function of the placenta
- temperature regulation + immune function
*hormone production + secretion
*nutrient uptake + delivery;
-H2O + electrolytes via simple diffusion
-glucose via facilitated diffusion thru GLUTs
-amino acids via active transport via transporter proteins
-fatty acids via simple diffusion
-large proteins + cells via pinocytosis (but v large molecules like heparin + insulin will NOT get thru placenta)
*waste removal (urea via simple diffusion)
*exchange of o2/co2
*maternal adaptation to pregnancy (so that foetus is not rejected)
other things placenta will pass on to foetus:
-IgG antibodies (googoo gaga)
-hormones
-antibiotics
-sedatives
-some viruses e.g. rubella, zika
-some organisms e.g. treponema pallidum (syphilis), toxoplasmosis, listeria
Fertilisation and initial development of embryo takes place in fallopian tube. Cell divisions create a solid mass of cells known as []. Around 4 days after fetilisation the [] enters the uterus
on the 5th day this [] turns into a blastocyst and on the 8th day this blastocyst implants in the []
Fertilisation and initial development of embryo takes place in fallopian tube. Cell divisions create a solid mass of cells known as morula. Around 4 days after fetilisation the morula enters the uterus
on the 5th day this morula turns into a blastocyst {outer single layer of trophoblast cells creates placenta and foetal membranes; inner cell mas is the embryo} and on the 8th day this blastocyst implants in the endometrium (blastocyst hatching + development of placenta begins)
n.b. implantation is regulated by a interactions between trophoblast + endometrium
what is blastocyst hatching?
release of the embryo from the zona pellucida is carried out at the stage of the blastocyst and is called zona hatching/blastocyst hatching (happens around day 5/6 after fertilisation). During zona hatching the blastocyst breaks the zona pellucida and performs active movements to escape through a gap formed in the zona.
the zona pellucida degenerates and decomposes, to be replaced by the underlying layer of trophoblastic cells.
n.b. With hatching, the syncytiotrophoblast cells produce hCG, estradiol, and EGF which signal to the uterine epithelium that a blastocyst is about to implant (
Implantation begins with apposition of the blastocyst at the uterine epithelium, generally about 2-4 days after the morula enters the uterine cavity; describe the 4 stages of implantation and how many days after fertilisation do these occur?
implantation= rapidly dividing ball of cells — (blastocyst) — has begun to burrow into the uterine lining (endometrium) {‘implanting itself’}. Within the blastocyst, the inner group of cells will become the embryo
blastocyst hatching** (day 5/6)
**apposition (day 6/7)= blastocyst will position itself + release adhesion molecules e.g. growth factors/IL-6/prostaglandin E2 (around blastocyst u have throphoblast cells which will divide and differentiate into cytotorophoblasts which can also fuse and become a synctiotrophoblast)
adhesion** (day 7/8)= cells of trophoblast fix to maternal tissues; the cytotrophoblasts release laminin + fibronectin which bind to receptors on endometrial wall and stick/ adhere the trophoblast (outer layer of foetus) to the wall
**invasion (day 8/9)= blastocyst is FULLY/COMPLETELY EMBEDDED IN maternal decidua + ENDOMETRIAL WALL; lots of cytotrophoblasts will multiply quickly to remodell the spiral arteries and make them larger– this is done as trophoblast releases proteolytic enzymes
what hormone does the foetus release to send signals to mother to prevent the corpus luteum degenerating
If a pregnancy occurs, then the pregnancy hormone (hCG) produced by trophoblast cells keeps the corpus luteum alive (stop it from degenerating) as it resembles LH; it maintains the progesterone + oestrogen levels which supports the pregnancy (building up spiral coily arterioles) for the next 6–8 weeks until the placenta takes over and the corpus luteum disappears (the corpus luteum will degenerate around week 12)
during day 6-7 apposition step of implantation takes place; the trophoectoderm differentiates into 2 different cells {describe them}
during day 6-7 apposition step of implantation takes place; positioning of blastocyst within the uterine cavity
the trophoectoderm differentiates into:
- cytotrophoblasts= have a single nucleus, divide rapidly
- synctiotrophoblast= form from fused cytotrophoblast, mutlinucleated cell, do NOT divide, fuses with pinopods
BOTH OF THESE ARE KNOWN COLLECTIVELY AS ‘TROPHOBLASTS’
before fertilisation (2 days after LH surge) the endometrial wall becomes hairy.. 8 days after LH surge a structure called [] is produced that can interact with the blastocyst
pinopodes= large plasma membrane protrusions of uterine epithelial cells that transiently project toward the uterine lumen during the “window of implantation.”
what are some signalling/adhesion molecules produced by foetus in uterine wall + their function
IL-6 (LIF)= inhibits hyperactivity of mother immune system
Growth factors (vascular endothelial growth factor VEGF, epidermal growth factor) increase angiogenesis in placenta
heparin-binding epidermal growth factor (HB-EGF) involved in attachment + invasion of blastocyst
prostaglandin E2 (PGE2)= dilation of smooth muscle of blood vessels and relaxing uterus] n.b. COX-2 {cyclooxygenase-2} converts arachidonic acid to PGE2
Human leukocyte antigen-G (HLA-G) inhibits antigen-specific lymphocytes response + decreases NK cell function (avoids early rejection)
all of this facilitates implantation
what is decidua?
decidua is the specialized layer of endometrium that forms the base of the placental bed. The corpus luteum of the ovary (and later, the placenta itself) produces progesterone that induces endometrial stromal cells to undergo cellular modifications and vascular alterations termed the ‘decidual reaction
trophoblasts invades the endometrial blood vessels and form [] filled sinuses
trophoblasts invades the endometrial blood vessels and form intertrophoblastic filled sinuses
what hormone stimulate fetal growth?
IGF-I stimulates fetal growth when nutrients are available, thereby ensuring that fetal growth is appropriate for the nutrient supply. The production of IGF-I is particularly sensitive to undernutrition. IGF-II plays a key role in placental growth and nutrient transfer
Insulin-like growth factor-1 is the primary growth stimulator of the fetus. The maternal catabolic phase of pregnancy is marked by a decelerated fasting metabolism.
what is chorionic villi formation
Chorionic villi sprout from the chorion{a membrane that surrounds a developing fetus in conjunction with the amnion} after their rapid proliferation in order to give a maximum area of contact with the maternal blood. These villi invade and destroy the uterine decidua while at the same time they absorb nutritive materials from it to support the growth of the embryo and establish foeto-maternal circulation
*the embryonic tissue + maternal blood remain separated by a layer of cytotrophoblasts and syncytiontrophoblasts
*chorionic villi are the main functional units of placenta
*by the 3rd week of gestation the embryonic mesoderm differentiates into blood vessels developing in the umbilical cord + embryo= thus forming tertiary villi
*until week 12/13 there is v little maternal blood so embryo in relative hypoxic environment
protecting women + babies w anti-D Immunoglobulin
Anti-D prophylaxis means giving a medicine called anti-D immunoglobulin to prevent a D - negative woman producing antibodies against D - positive blood cells and so prevent the development of HDFN in an unborn baby; IN SHORT if woman is Rh- and her bby is Rh+ the mother will produce antibody against babies antigens HARMING BABY RED BLOOD CELLS (especially if the woman has a second baby; meaning second immune response) to avoid this they give them anti-D Immunoglobulin to protect the baby which is injected at week 28
Hemolytic disease of the fetus and newborn (HDFN) is a blood disorder that causes your baby’s red blood cells to break down quickly
