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227 .205 (15)

Comparative placentation lecture notes for 2nd year vet

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227 .205
Peter Davie

Comparative placentation Baby in uterus is covered by membranes. Umbilical cord connects the fetus to the uterus. Placenta -is the only organ that is expelled out - Is required for nutrient exchange, gas exchange and elimination of waste products. - Allows exchange to mother Uterus –i) myometrium- muscles for expulsion of fetus. - Strongest muscle in the body ii)endometrium- endometrial glands- important for pregnancy - for histotrophs, before proper development of artery, histotroph provide nutrient. -Develops more during pregnancy -Endometrial BV - endometrial epithelium -endometrial stroma(connective tissue) -iii)uterine lumen Fetus- in the first month, the urinary bladder and urethra not developed -elimination of products is by urachus. Urachus is the urethra for the first few months. Membranes- amnion- contains amniotic fluid. -it contains fetal urine and secretion of gut tube(poo). The poo is not like adults. - excretion from gut and from urethra. During delayed delivery(dystocia)- fetus inhales the amniotic fluid (which contains the excretion) straight into lungs. fetus wont survive. Yolk sac- provide nutrition Allantois- is predominantly fetal urine and fetal waste products. - In cattle it is big and in human it is small Urethra connects – 50% to amnion and 50% to allantois. - Contains urine - May contain hippomanes/allantoic calculi It is a normal, incidental finding in horses. They are not faeces, and are not formed within the amniotic cavity. To-u-ch- a l-am-b u-umbilical cord ch-chorion aL-allantois am-amnion b- baby Chorion- endometrium and chorion is for exchange. do fetal membranes fuse- yes they do the allantois and chorion fuse to form the allantochorion. It is a single functional unit. Alllantochorion=chorioallantois Functions of the fluid-filled sacs are i) Cushioning- for the fetus -for the mother from the kicking baby ii) exchange- gas exchange, nutrient exchange and waste removal allantois has BV on it, the BV converge and become veins and umbilical artery. For exchange at the chorion. The BV of endometrium are close to chorion, so the exchange occurs easily between the BV of endometrium and the BV chorion. Amnion covers fetus Allantochorion blood vessels go into the fetus via the umbilical cord. During delivery, the fetaus is delivered through the allantochorion as the allantochorion ruptures and the allantochorion turns inside out in the process. The allantochorion ruptures at the point of the cervix. The allantochorion is very thin at the cervix. If it doesn’t break at the cervix, fetus can die of dystocia. Can be seen star shaped during delivery. Red bag delivery- occurs when there is premature detachment of the allantochorion from the uterus also known as red bag delivery.. Can see being delivered is a starshaped red bag which is the thicker side. This is an obstetric emergency since the foal will rapidly die of hypoxia before the vet can arrive. The bag should be torn and fetus removed immediately. Where the allantochorion overlies the entrance to the cervix there is no endometrium, hence no placental exchange takes place here. This area is thinner and weaker and is part that breaks during parturition. The puckered, star shaped entrance to the cervix leaves an imprint on the allantochorion called cervical star. An intact cervical star in an afterbirth is an abnormal finding. An intact cervical star should not be found when placental membranes are examined Placental classification 1) By fetal membrane contribution a)fetal choriovitelline placenta forms when the b) a fetal chorioallantoic placenta forms when yolk sac combines with the chorion in early the allantoic and chorionic connective tissue gestation/ it is fully functional but temporary fuse. It is the definitve placenta in all domestic placenta in all domestic animals animals. the yolk sac is important for angiogenesis(= development of new blood vessels)and haematopoiesis in early gestation, but these functions are assumed by other organs in later gestation and postnatal life. In horses a choriovitelline placenta is present thought the first sex weeks of gestation. Angiogenesis and haematopoiesis. First blood vessels(yolk sac) then spleen/liver then after birth bone marrow. What happens to the yolk sac once it is no longer the primary contributor to the placenta.The yolk sac regresses and is passed out during delivery. Possible to see a persistent yolk sac remnant. 2)by barriers between fetal and maternal blood. The chorion forms chrorionic villi in order to maximize contact area between the fetal membranes and endometrium( increase surface area) The chorion is fused to the allantois, for the allantochorion. It is the allantois, not the chorion that supplies the blood vessels to the allantochorion. Barriers lie between the maternal capillary and the fetal capillary. 1) Epitheliochorial placenta - 6 barriers in ruminants, pigs and horse. 2) Endotheliochorial placenta-4 layers in carnivores. 3) Haemochorial placenta- 3 layers in primates and rodents. How does t
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