Difference between revisions of "Placenta - Anatomy & Physiology"

Revision as of 19:37, 11 July 2011

Introduction

The formation of the placenta is referred to as the "second" or "embryonic" period of pregnancy (after the implantation period) and describes the establishment of a fully functional placenta. 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.

Formation

The placenta consists of a foetal portion formed by the chorion and a maternal portion formed by the decidua basalis. The uteroplacental circulatory system begins to develop from approximately day 9 via the formation of vascular spaces called "trophoblastic lacunae".

Maternal sinusoids develop from capillaries of the maternal side which anastamose with these trophoblastic lacunae. The differential pressure between the arterial and venous channels that communicate with the lacunae establishes directional flow from the arteries into the veins resulting in a uteroplacental circulation.

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

Immunological

Endocrine

Endocrine Function

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 ==Introduction==
-The formation of the placenta is referred to as the "second" or "embryonic" period of pregnancy and describes the establishment of a fully functional placenta. 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.
+The formation of the placenta is referred to as the "second" or "embryonic" period of pregnancy (after the implantation period) and describes the establishment of a fully functional placenta. 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.
 ==Formation==