Embriology 2-2.pdf

CARDIOVASCULAR SYSTEM • A simple built heart is formed in the cardiogenic zone. • Primitive blood vessels originate from it and gradually grow at the base of each organ. • The blood vessels of the embryo through the embryonic stalk (which will be incorporated into the umbilical cord) are connecte...

CARDIOVASCULAR SYSTEM • A simple built heart is formed in the cardiogenic zone. • Primitive blood vessels originate from it and gradually grow at the base of each organ. • The blood vessels of the embryo through the embryonic stalk (which will be incorporated into the umbilical cord) are connected to the extraembryonic blood vessels created in the extraembryonic mesenchyme of the chorionic plate. • In the fourth week, the heart begins to contract and push blood through the blood vessels. CARDIOVASCULAR SYSTEM • Establishing the blood flow is a prerequisite for intensive mitotic and metabolic processes during the histogenesis and morphogenesis of the rest of the organs. • Intracorporeal and extracorporeal blood circulation - enables the supply of oxygen and nutrients and the release of harmful metabolites. • The placenta plays a major role in this process. PLACENTA • The placenta is the organ through which it the exchange of nutrients and gases between mother and fetus is enabled. • The tissues of both organisms (the mother and the fetus) are built in the placenta: • Fetal part (placentafoetalis) -is created by the chorionic membrane, and consists of chorion frondosum. • Maternal part (placenta maternalis)originates from the endometrium and consists of decidua basalis. PLACENTA PLACENTA • Discoid shape, diam~18 cm, weight 500 g, thickness~ 3 cm • It occupies 30% of the inner surface of the uterus. • It gets thinner towards the ends and continues in the other envelopes of the foetus (together they comprise Sacus embryonalae). • During childbirth, the placenta is peeled off and thrown out - then iwe can recognize fetal and maternal side. A. Fetal side C. Maternal side FETAL SIDE (PLACENTAFOETALIS) Smooth and shiny amniotic epithelium Blood vessels of the chorionic plate Umbilical cord Amniotic membrane PLACENTA FOETALIS • Amnionic epithelium (single-layered cylindrical) • Chorionic plate (chorion frondosum fused with the amnion) is the mesenchyme through which the chorionic blood vessels pass • Chorionic villi- grow from the chorionic plate and branch out towards placenta maternalis. • The space between the villi is called the intervillous space. Main stem PLACENTAFOETALIS Syncytiotrophoblast Mesenchyme Fetal capillaries Cytotrophoblast Hofbauer-this cell Development of chorionic villi • Free villi-they swim in the intervillous space • Anchored villi-penetrate intodecidua basalis through the cytotrophoblast coat PLACENTA FOETALIS • Cytotrophoblast coat (shell)-a barrier between genetically different organisms at a place of morphofunctional connection. • It is covered with basal decidua, through its cracks pass the uteroplacental blood vessels from the mother MATERNAL SIDE (PLACENTA MATERNALIS) Lobulated, bloody, rough surface Decidua basalis Lobes of the placenta By‫ دوﻟﻪ‬- ‫ ﺗﻤﺮه دﻫﻦ‬-Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php? curid=31121431 Placental lobe (cotyledon) PLACENTA MATERNALIS • Basal plate- contact between fetal and maternal tissues (decidua basalis, cytotrophoblast cover and syncytiotrophoblast) • Decidua basalis- between horionfrondosum and the myometrium of the uterus. Contains decidual cells (functionally altered stromal endometrial cells) • Placental septa- incomplete- division of lobes or cotyledons INTERVILLOUS SPACE • It contains the mother's blood which comes from the spiral endometrial arteries, which pass through the punctures of the basal plate and lose the wall, flowing into the intervillous space. • This space is drained through endometrial veins. • The villi are continuously flushed with the mother's blood. PLACENTAL CIRCULATION • The blood poor in oxygen leaves the fetus through the umbilical arteries, which go to the placenta as chorionic arteries, which branch to calipers in the chorionic villi. • Oxygenation and metabolite exchange occur in the intervillous space. • Oxygenated fetal blood goes to the villous veins and the veins of the chorionic plate, then into the veins of the umbilical cord to the fetus, bringing it oxygenated blood. PLACENTAL MEMBRANE • Up to 20 weeks: -syncytiotrophoblast -cytotrophoblast -connective tissue - endothelium • After 20 noworks: -syncytiotrophoblast -cytotrophoblast - endothelium ABNORMAL INSERTION FUNCTIONS OF THE PLACENTA • Transport function • Endocrine function-syncytiotrophoblasts -protein hormones:hCG,placental lactogen, human chorionic thyrotropin, human chorionic corticotropin -steroid hormones: Estrogens and porgesterone • Metabolic function-synthesis of glycogen, cholesterol and mask acids UMBILICAL CORD (FUNICULUS UMBILICALIS) • 30-90cm length, diameter 1-2 cm • Central or velamentous-marginal insertion AMNION AND AMNIOTIC FLUID COMPOSITION • 90% water • Desquamated fetal epithelial cells • Organic and inorganic salts CIRCULATION • Every 3 hours it is exchanged through the amnio-chorionic membrane into the maternal tissues via the uterine capillaries or with fetal blood via the funiculus umbilicalis and where the amnion abuts the chorionic plate • The fetus swallows 400 ml of amniotic fluid per day at the end of pregnancy. After resorption, it returns with the fetal bloodstream through the placental membrane in the intervillous spaces into the mother's blood, and with excretion through the kidneys back into the amniotic fluid. • Oligohydramnios (for example400ml) and Polyhydramnios (for example2000 ml)