Microsoft PowerPoint 08 Placenta and Fetal Membranes total
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- Placenta
| 1 Placenta and Fetal Membranes Amnion - Epiblast / Extraembryonic Mesoderm Yolk Sac - Hypoblast / Extraembryonic Mesoderm Allantois - Embryonic Hindgut Chorion - Trophoblasts / Extraembryonic Mesoderm Placenta - Chorion / Maternal Decidua Amnion
Amnionic membrane is two cell layers 1) epiblast derived extraembryonic ectodermal layer 2) thin non-vascular extraembryonic mesoderm As the amnion enlarges it encompasses the embryo on the ventral side, merging around the umbilical cord. Amnion forms the epithelial layer of the umbilical cord With embryo growth the amnion obliterates the chorionic cavity
Amnionic sac is fluid filled called amnionic fluid: the embryo is bathed in the fluid Extraembryonic Tissues 8 days
9 days 14 days
Amnion 2 Amnion
Amnionic Fluid Up to week 20 - fluid is similar to fetal serum (keratinization) After 20 weeks – Contribution from urine, maternal serum filtered thru endothelium of nearby vessels, filtration from fetal vessels in cord Near birth - can contain fetal feces called meconium Near birth – amnionic fluid (500-1000 ml) exchanges every 3 hrs 1) across the amnion – exchange with maternal fluids. 2) fetal swallowing (20 ml/hour) – to gut – adsorption by fetus – out the umbilical cord to placenta. Hydraminos – Excess fluid (>2000 ml), esophageal atresia Oligohydramnios – Insufficient fluid (<500 ml), renal agenesis Amnion Function Mechanical protection: hydrostatic pressure Allows free movement - which aids in neuromuscular development Antibacterial Allow for fetal growth Protection from adhesions Amnion Band Syndrome (ABS) Placenta and Fetal Membranes Amnion - Epiblast / Extraembryonic Mesoderm Yolk Sac - Hypoblast / Extraembryonic Mesoderm Allantois - Embryonic Hindgut Chorion - Trophoblasts / Extraembryonic Mesoderm Placenta - Chorion / Maternal Decidua 3 Yolk Sac
Hypoblast - the primary yolk sac or Heuser's membrane. Day 12 - Second wave of cell migration - forms definitive yolk sac Composed of extrembryonic endoderm Early nutrition (2-3 weeks) for the embryo - later shrinking - nonfunctional – Meckels diverticulum (outpocketing of small intestine) Connects to midgut via the yolk sac stalk Derivatives: Early blood cells forms from blood islands Primordial germ cells The early gut, epithelium of the respiratory and digestive tracts
Placenta and Fetal Membranes Amnion - Epiblast / Extraembryonic Mesoderm Yolk Sac - Hypoblast / Extraembryonic Mesoderm
Chorion - Trophoblasts / Extraembryonic Mesoderm Placenta - Chorion / Maternal Decidua Allantois Endodermal origin – caudal outpocketing of the yolk sac Invades the connecting stalk (extraembryonic mesoderm) that suspends the embryo in the chorionic cavity Involved in early hematopoiesis (up to 2 months) The allantois blood vessels - artery and vein - becomes the umbilical vessels Remnants of Allantois becomes the urachus ligament that connects the belly button to the bladder Placenta and Fetal Membranes Amnion - Epiblast / Extraembryonic Mesoderm Yolk Sac - Hypoblast / Extraembryonic Mesoderm Allantois - Embryonic Hindgut Chorion - Trophoblasts / Extraembryonic Mesoderm Placenta - Chorion / Maternal Decidua Chorion
4 Chorion
Chorionic cavity (extraembryonic coelom)- lined with extraembryonic mesoderm Chorionic cavity expands separating amnion from cytotrophoblast Chorionic sac consist of: cytotrophoblastic layer syncytiotrophoblastic layer extraembryonic somatic mesoderm The Chorion / maternal endometrium forms the placenta Chorion forms stem villi Stem Villi Stem Villi Chorionic Plate – Stem villi extends from this tissue Primary stem villi (day 11-13) - finger-like protrusions into endometrium - contains syncytiotrophoblast, cytotrophoblast. Secondary stem villi (day 16) - extraembryonic mesoderm invasion into villi core. Tertiary stem villus (21 day) - extraembryonic vessels - chorionic arteries and veins derived from extraembryonic mesoderm. Hemichorial type placenta – maternal blood baths villi Stem Villi Cytotrophoblastic cell column – terminal villi, solid mass of trophoblast Cytotrophoblastic shell – surrounds embryo; direct contact with maternal decidual cells Anchoring Villi – give off cytotrophoblastic extensions - anchoring because they represent the real maternal- embryo link Floating Villi – branches off anchoring villi – dangles freely in maternal blood Chorion
5 Placenta and Fetal Membranes Amnion - Epiblast / Extraembryonic Mesoderm Yolk Sac - Hypoblast / Extraembryonic Mesoderm Allantois - Embryonic Hindgut Chorion - Trophoblasts / Extraembryonic Mesoderm Placenta - Chorion / Maternal Decidua Decidua
Decidual Reaction – stromal cells – accumulate glycogen and lipid, called Decidual Cells Decidua basalis - forms maternal component of the placenta; associates with the chorion frondosom Decidua capsularis - superfical layer overlying the entire embryoblast - this layer eventually degenerates; associates with the chorion laeve Decidua parietalis - all remaining parts of the endometrium - not associated with the embryo Deciduas
Making the Placenta By 8 weeks - chorionic stem villi over the entire surface of the chorionic sac Those villi associated with the decidua basalis increase in size and more villi form. Enlargement includes further branching of the anchoring villus - chorion frondosum. The villi continue to enlarge during most of gestation. The villi project into a blood filled intervillous space resulting from the erosion of the decidua basalis. Endometrial vessels - spiral arteries and endometrial veins Villi associated with the decidua capsularis degenerate - this region is called the chorion laeve Deciduas
Placenta The erosion of the decidua basalis is incomplete - uneroded regions called decidual septa. The decidual septa define regions of the placenta called cotyledon.
6 Placental Blood Flow Placental Anatomy Umbilical Cord One umbilical vein, two umbilical arteries Wharton’s jelly – mucoid connective tissue surrounding vessels Allantois Yolk Stalk (vitelline duct) and vitelline vessels (early) Intestinal loop – umbilical hernia (late)
Placental Circulation Fetal – Contained within vessels Umbilical Arteries – chorionic plate – branches to stem villi – capillaries in terminal villi – return via umbilical vein Maternal – Free-flowing lake Spiral arteries open into intervillous space and bath the villi 150 ml of maternal blood Exchanged - 3-4 times/minute Reduced blood pressure in intervillous space Oxygenated blood to the chorionic plate, return baths the villi Placental Anatomy 7 Placental barrier decreases with gestation Placental Barrier – syncytiotrophoblast + basal lamina, basal lamin + fetal capillary endothelium Syncytiotrophoblasts – many microvilli, no major histocompatibility antigens O 2
2 O Fe salts carbohydrates, amino acids, lipids vitamins, hormones, antibodies drugs, alcohol viruses (rubella, varicella-zoster, HIV) CO2
H2O salts
urea, uric acid creatinine bilirubin, hormones, RBC antigens Placenta as an Endocrine Organ Human Chorionic Gonadotropin – Corpus Luteum (declines after 8 weeks) Progesterone – High levels by the end of first trimester Estrogen – Synthesis involves enzymatic activity of fetal adrenal gland and liver Chorionic Somatomammotropin – Human Placental Lactogen – similar to GH (growth, lactation, lipid and carbohydrate metabolism) Placental Growth Hormone – similar to GH – Replaces materrnal GH by 15 wks – enhances blood glucose levels Chorionic Thyrotropin, Chorionic Corticotropin Multiple Pregnancies Monochorionic/Dichorionic Monoamnionic/Diamnionic Hydatiform Mole 8 Erythroblastosis fetalis Fetus / newborn - hemolytic disease (anemia) Rh factor is a RBC surface antigen Rh- mother with Rh+ 1st baby – Maternal antibodies are induced after birth At risk is second Rh+ baby Maternal Rh antibodies cross placenta Hemolysis of fetal Rh+ RBC Yüklə 33,1 Kb. Dostları ilə paylaş:
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