7. Placental Physiology and Birth Adaptations Flashcards
(16 cards)
Define a mammal.
A mammal is defined by having mammary glands, three middle ear bones, hairy epithelium, and neocortex.
What types of placentas are found in different mammalian groups?
Marsupials have a temporary placenta; Monotremes have no placenta; Placental mammals have chorioallantoic placenta.
Describe the early development and structure of the human placenta.
Early embryonic development prioritizes placental formation. At embryonic day 50, the placenta is double the size of the embryo. It forms in one region of the chorion, connected by the umbilical cord. The maternal side has spiral arteries, while the fetal side contains villi with blood vessels covered by syncytiotrophoblast.
What is the size and weight of the placenta at term?
At term, the placenta is approximately 20 cm in diameter, 2 cm thick, and weighs about 0.5 kg.
What is the surface area of the placenta for gas exchange?
The surface area for gas exchange is approximately 10 square meters.
Compare the blood volumes and flow rates in the maternal and fetal sides of the placenta.
Maternal side: Blood volume ~150 ml; Blood flow 500-600 ml/minute. Fetal side: Blood volume ~120 ml; Blood flow 500-600 ml/minute.
What is the cellular structure of the placental barrier?
From maternal to fetal side: 1) Maternal blood in direct contact with syncytiotrophoblast; 2) Syncytiotrophoblast layer; 3) Cytotrophoblast layer; 4) Connective tissue; 5) Fetal endothelial cells; 6) Fetal blood.
What are the main functions of the placenta regarding nutrient and waste exchange?
Gas exchange, nutrient transport, waste removal, immune transfer, and heat regulation.
Describe the immunological functions of the placenta.
Syncytiotrophoblast produces TGF-β to block NK cell activation and neurokinin B to block interleukins. Trophoblast cells express unique MHC receptor (HLA-G) to prevent T-cell responses against fetal tissues.
Outline the endocrine functions of the placenta.
Human Chorionic Gonadotropin (hCG), Progesterone, Estrogens, and Prostaglandins.
Describe the structure and unique features of the umbilical cord.
The umbilical cord has two umbilical arteries and one umbilical vein, surrounded by Wharton’s jelly and covered by amniotic epithelium.
How are blood vessels in the placenta and umbilical cord kept dilated before birth?
Through the Prostaglandin E₂ pathway and the Nitric oxide pathway.
Describe the blood transfer from placenta to baby at birth and its importance.
30% of placental blood transfers to the newborn in the first 15 seconds; 60% within 2-3 minutes. This transfer is critical for maintaining adequate blood volume in the newborn.
Explain the vascular changes in the umbilical vessels at birth and their significance.
Within 1 minute of birth, placental blood flow reduces by ~80%. Arterial closure prevents blood flow to the placenta while venous patency allows blood return to the baby.
What triggers the vascular changes in umbilical vessels at birth?
Physical, chemical, and mechanical factors trigger rapid conversion from vasodilation to vasoconstriction.
Describe the importance of proper timing in umbilical vessel closure.
Arteries must close first to prevent blood flow to the placenta; veins must remain patent longer to allow blood return to the baby.
