OBTAINING NUTRIENTS VIA BLOOD VESSELS With regard to the way the embryo obtains its nutrients through contact with the maternal blood vessels, Barry Mitchell and Ram Sharma write: Due to the rapid growth of the embryo during the second week, there is a need for a more efficient means of nutritional and gaseous exchange. This is achieved when the embryonic blood vessels of the chorion come into contact with the maternal blood vessels of the decidua. ... [by the third week]... The exchange of nutrients, respiratory gases and waste products between the maternal and fetal blood takes place across the placental membrane within intervillous spaces. Maternal blood enters these spaces from the spiral arteries, branches of the uterine artery, bringing nutrients and oxygen for the embryo and fetus. This reinforces the validity of the meanings of `alaqah, and its evoking images of an entity obtaining its nutrients via blood. NEURULATION & THE FOLDING OF THE EMBRYO The `alaqah stage suggests the process of neurulation and the initial stages of the folding of the embryo. Neurulation comprises of the formation of the brain and the spinal cord from days 19 to 25 (approx.); and the folding of the embryo involves the head and the tail being brought closer together. The combination of these two physiological changes causes the embryo to resemble a leech-like substance
Posted on: Thu, 10 Oct 2013 11:51:57 +0000
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