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Placental mammals, including humans, have a chorioallantoic placenta that forms from the chorion and allantois. In humans, the placenta averages 22 cm (9 inch) in length and 2–2.5 cm (0.8–1 inch) in thickness, with the center being the thickest, and the edges being the thinnest. It typically weighs approximately 500 grams (just over 1 lb).
In humans, placentation takes place 7–8 days after fertilization. In humans, the placenta develops in the following manner. Chorionic villi (from the embryo) on the embryonic pole grow, forming chorion frondosum. Villi on the opposite side (abembryonic pole) degenerate and form the chorion laeve (or chorionic laevae), a smooth surface. The ...
The form of the human placenta is generally classified as a discoid placenta. Within this, the cotyledons are the approximately 15-25 separations of the decidua basalis of the placenta, separated by placental septa. [3] Each cotyledon consists of a main stem of a chorionic villus as well as its branches and sub-branches. [3]
The human allantois is a caudal out-pouching of the yolk sac, which becomes surrounded by the mesodermal connecting stalk or body-stalk. The vasculature of the body-stalk develops into umbilical arteries that carry deoxygenated blood to the placenta. [12] It is externally continuous with the proctodeum and internally continuous with the cloaca.
In humans, the circulatory system is different before and after birth. The fetal circulation is composed of the placenta, umbilical blood vessels encapsulated by the umbilical cord, heart and systemic blood vessels. A major difference between the fetal circulation and postnatal circulation is that the lungs are not used during the fetal stage ...
The human allantois is a caudal out-pouching of the yolk sac, which becomes surrounded by the mesodermal connecting stalk known as the body-stalk. The vasculature of the body-stalk develops into umbilical arteries that carry deoxygenated blood to the placenta. [5] It is externally continuous with the proctodeum and internally continuous with ...
Trophoblasts are present four days after fertilization in humans. [1] They provide nutrients to the embryo and develop into a large part of the placenta. [2] [3] They form during the first stage of pregnancy and are the first cells to differentiate from the fertilized egg to become extraembryonic structures that do not directly contribute to ...
During pregnancy, the syncytiotrophoblast cells of the placenta produce a polypeptide hormone, human placental lactogen (hPL), also known as human chorionic somatomammotropin (hCS). [17] in six weeks of gestation, production of hPL in maternal plasma is detected, then the concentration of hPL keeps increasing until week 30 of pregnancy. [17]