Placenta - Anatomy & Physiology
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The placenta is an apposition of foetal and parental tissue for the purposes of physiological exchange. There is little mixing of maternal and foetal blood, and for most purposes the two can be considered as separate.
Exchange
Histotrophic
- Nutrition supplied by uterine secretions/debris - 'Uterine milk'
- Often maintained by progesterone
- Nourishment of the embryo before implantation when there is no established placenta.
- Maintained for long period of time in ungulates, since implantation is late
- Horse: day 35
- Ruminants: day 15-20
- Pig and horse: pinocytosis persists via areolae
- Sheep,cow,dog and cat: pinocytosis persists via haemophagous zones that break down and release iron to the placenta.
Haemotrophic
- Direct transfer of nutrients from the maternal to foetal blood via the placenta. By Simple Diffusion, Facillitated Diffusion, Active Transport and Complex Diffusion
Placental Blood Supply and Drainage
Umbillical Arteries
- Arise from Iliac arteries along with vesicular arteries to the bladder.
- Form the ventral ligament of the bladder in the adult.
- Carry deoxygenated blood from the bladder.
Umbillical Veins
- Join the hepatic portal vein
Shunts
Vascular Dynamics
Protection
Physical
Teratogens