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The placenta (pl.: placentas or placentae) is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation.It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate maternal and fetal circulations, and is an important endocrine organ, producing hormones that regulate both maternal and fetal ...
One theory is that velamentous cord insertion may arise from the process of placental trophotropism, which is the phenomenon where the placenta migrates towards areas which have better blood flow with advancing gestation. The placenta grows in regions with better blood supply and portions atrophy in regions of poor blood flow.
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 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. The embryonic allantois becomes the fetal urachus, which connects the fetal bladder (developed from cloaca) to the yolk sac.
In Type 2, unprotected vessels run between lobes of a bilobed or succenturiate lobed placenta. In Type 3, a portion of the placenta overlying the cervix undergoes atrophy. In this type, there is a normal placental cord insertion and the placenta has only one lobe. However, vessels at a margin of the placenta are exposed.
The part of the ovary where the funiculus attaches is referred to as the placenta. In botany, the term placentation most commonly refers to the arrangement of ovules inside an ovary. Placentation types include: Basal: The placenta is found in mono to multi carpellary, syncarpous ovary. Usually a single ovule is attached at the base (bottom).
The vestibular glands, also known as the female accessory glands, are the Bartholin's glands, which produce a mucous fluid for vaginal lubrication, and the Skene's glands for the ejaculation of fluid as well as for lubricating the meatus.
During pregnancy changes in the placenta involve the disappearance of the greater portion of the stratum compactum, but the deeper part of this layer persists and is condensed to form what is known as the basal plate.