Read e-book online Life's Vital Link: The Astonishing Role of the Placenta PDF

By Y.W. Loke

ISBN-10: 0199694516

ISBN-13: 9780199694518

The advance of the placenta was once a pivotal occasion in evolution. The lengthy and tortuous evolutionary highway which led from egg-laying reptiles to present-day placental mammals like ourselves was once an epic trip spanning over three hundred million years. with out the placenta, we'd nonetheless be laying eggs, rather than giving beginning to stay offspring.

In Life's very important Link, Y. W. Loke presents a fascinating examine this outstanding organ, tracing the lifetime of the placenta from the instant it's created inside of a fertilized egg, via its short yet eventful remain in the womb-usually round 270 days. Loke describes the elemental gateway functionality of the placenta, telling the way it actively encourages the passage of gear which are invaluable to the child whereas barring those who are in all probability destructive. It transfers oxygen and meals from mom to child and returns carbon dioxide and waste items within the opposite path, thereby performing because the baby's lungs, kidneys and digestive tract suddenly. Loke additionally unearths different interesting features of this organ. for example, the placenta is genetically "foreign" to the mummy, making it resemble an alien transplant in her womb. by means of rights, it's going to be rejected by way of the mother's immune approach, however it is not-a secret which, if solved, may also help transplant sufferers steer clear of organ rejection. Loke additionally issues out that, in comparison to different mammals, the human placenta is very intrusive, penetrating deep into the liner of the mother's womb to acquire meals for the baby-highly invasive habit that has stuck the attention of oncologists, trying to find clues into the invasive nature of melanoma.

Life's important Link is the 1st e-book to provide common readers an account of this awesome organ, an creative tool thousands of years within the making.

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19 Unlike the monotremes, which are represented by only three 28 IN T HE BEGINNING species, there are approximately 260 living species of marsupials, the majority of which dominate the mammalian fauna of Australasia, such as the kangaroo and opossum. A few species are also found in the Americas. Although no longer egg-laying, marsupials nevertheless have a most unusual mode of reproduction. They are viviparous and do have a placenta but the young are born very immature, naked, and blind (known as joeys) and need to be nurtured for a further period in a pouch where they obtain nutrients via breast milk secreted by the mother, hence, ‘marsupium’ meaning pouch.

It looks as if our ancestral placenta started off being invasive and then changed its mind and withdrew to become less invasive. We do not know why this happened. Environmental pressures from different habitats could provide the evolutionary stimulus to select the most appropriate placental type for individual species. 27 Named Juramaia, it is estimated to be 160 million years old, and therefore predates Eomaia by 36 million years. Since Juramaia is now the oldest recorded eutherian, the split between marsupials such as kangaroos and eutherians like ourselves must have occurred at least 160 million years ago during the Jurassic period, much further back in evolutionary time than first thought.

51 L IFE ’ S V I TA L L INK Inner cell mass Zona Trophectoderm figure 7 A blastocyst with the inner cell mass that will become the embryo and the trophectoderm that will give rise to trophoblast cells of the placenta. This early separation of the trophectoderm from the ICM to produce a distinct trophoblast lineage is unique to mammals. 34 Two genes known as Nanog and Oct 4 are switched on very early in the ICM while another gene called Cdx2 is the first to be activated in trophectoderm. These genes point out the developmental direction the initial primitive collection of cells should follow: either to become the ICM or the trophectoderm, that is, to be baby or placenta.

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Life's Vital Link: The Astonishing Role of the Placenta by Y.W. Loke

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