Placenta, Cord & Membranes for KEATS PDF

Introduction to the placenta, cord & membranes The placenta attaches the embryo to the uterine wall. It metabolises the nutrients and gases required by the fetus from ~12/40, removes w...

Introduction to the placenta, cord & membranes The placenta attaches the embryo to the uterine wall. It metabolises the nutrients and gases required by the fetus from ~12/40, removes waste products and produces hormones to maintain the pregnancy The umbilical cord enables fetal blood to pass through the placenta Amniotic fluid is enclosed by double layered membranes (chorion and amnion) that maintain a stable 📷 @alexafayebirthstories environment and provide protection from external forces Functions of the placenta Five principal functions 1. Respiration – absorbs oxygen and excretes carbon dioxide for fetal metabolism as fetal lungs do not function until after birth 2. Nutrition – absorbs nutrients that the fetus needs and metabolises them for use. Some nutrients are stored ready for use e.g. glucose is stored as glycogen 3. Excretion – waste products produced by the fetus are excreted 4. Protection – most bacteria are not able to pass through the placental barrier. Some maternal antibodies are transferred to the fetus to support their early adaptive immunity 5. Hormone production- hCG, progesterone, oestrogen, human placental lactogen etc 📷 @hannahbphotographyuk Development of the placenta During implantation finger like projections (developing chorionic villi) from the trophoblast develop Once implanted in the decidua some of these villi proliferate to form the placenta and others degenerate to form the chorion As the villi penetrate the decidua, pools of blood are formed called sinuses as the walls of maternal blood vessels are eroded By 12/40 the placenta has fully formed from the chorionic villi Reproduced from: Essential Anatomy and Physiology in Maternity Care by Wylie Spiral artery conversion Maternal placental component (basal plate) is composed of the placental bed underneath the fetal component (chorionic plate) and the uteroplacental circulation These uteroplacental circulation is required to deliver large volumes of blood to the placental intervillous spaces The maternal blood vessels (spiral arteries) that supply the placental bed become dilated and flaccid (uteroplacental arteries) to reduce Fig. 8.7 Conversion of spiral arteries into the rate and pressure of the uteroplacental arteries. The maternal spiral arteries have thick muscular walls and are responsive to maternal blood to protect the vasoactive substances. They are remodelled by the delicate fetal villi trophoblastic cells in two waves, ultimately forming nonresponsive dilated vessels. Where remodelling is inadequate, a proportion of the vessels retain the structure of preimplantation or partially remodelled vasoresponsive vessels. Reproduced from: Anatomy and Physiology for Midwives by Coad et al Chorionic villi Chorionic villi float in the sinuses to allow gas and nutrient exchange between maternal and fetal blood Large surface area Fetal blood flows into the placenta from the fetal circulation to release waste products including carbon dioxide into the maternal Fig. 6.2 Chorionic villi. Reproduced from: Myles Textbook for Midwives by Marshall circulation and receive oxygen and nutrients from it Four layers of placental membrane prevent direct contact between fetal and maternal blood Fig. 8.11 Exchange of substances across the placenta occurs across a barrier consisting of four layers of tissue: syncytiotrophoblast, cytotrophoblast, mesoderm and fetal blood vessel wall. Reproduced from: Anatomy Intrauterine haematoma Intrauterine haematomas may be seen on ultrasound scan (USS) Incidence during 1st trimester = 4-22% Retroplacental haematoma – located behind the placenta and uterine wall Subchorionic haematoma – located between the chorion and uterine wall Associated with pregnancy complications including vaginal bleeding, miscarriage, preterm birth. Pregnancy induced hypertension, pre- eclampsia, gestational diabetes, intrauterine growth restriction (IUGR) and stillbirth The placenta at term Flat and round/oval ~20cm in diameter and ~2.5cm thick at the centre ~500g Placenta normally implant near the fundus on either the anterior or posterior surface (decidua is thicker) Maternal and fetal surfaces 📷 @littlerosephotography_ Maternal & fetal surfaces of the placenta Maternal surface The basal plate is attached to the decidua Deep-red bloody appearance due to maternal blood Up to 40 irregular lobes (cotyledons) divided by deep grooves (sulci) Each cotyledon is divided into numerous lobules which each contain one chorionic villus Fetal surface The chorionic plate lies next to the fetus Shiny appearance as covered by the amnion Umbilical cord usually arises from the centre of this side and is covered with a continuation of the amnion Blood vessels radiate outwards from the cord under the amnion with each cotyledon receiving its own branch of the umbilical artery and vein Fig. 6.4 The placenta at term. (A) Maternal surface. (B) Fetal surface. Reproduced from: Myles Textbook for Midwives by Marshall 8 Transverse section of placenta Fig. 12.7 Schematic drawing of a transverse section through a full-term placenta, showing the relation of the villous chorion (fetal part of the placenta) to the decidua basalis (maternal part of the placenta, the fetal circulation and the maternal placental circulation). Maternal blood flows into the intervillous spaces in funnel-shaped spurts from the spiral arteries, and exchanges of material between the mother and the embryo/fetus occur. The inflowing arterial blood pushes venous blood out of the intervillous space into the endometrial veins, which are scattered over the entire surface of the decidua basalis. Note that the umbilical arteries carry poorly oxygenated fetal blood (shown in dark grey) to the placenta and that the umbilical vein carries oxygenated blood (shown in light grey) to the fetus. Note also that the cotyledons are separated from each other by placental septa, projections of the decidua basalis. Each cotyledon consists of two or more main stem villi and their many branches. In this drawing, only one stem villus is shown in each cotyledon, but the stumps of those that have been removed are indicated. Reproduced from: Physiology in 9 Childbearing by Rankin Umbilical cord The umbilical cord develops to connect the placenta to the fetus at the umbilicus 1-2cm in diameter Average length = 50cm (30-90cm) Encloses two umbilical arteries and one umbilical vein surrounded by a connective tissue called Wharton jelly and a layer of amnion Spiral twist gives it additional 📷 @ingefotografie.nl strength Transports oxygen and nutrients to Fig. 6.7 Cross-section the fetus and removes waste through the umbilical cord. products Reproduced from: Myles Textbook for Midwives by Marshall Fetal membranes Double layer of membranes – chorion and amnion – that make up the amniotic sac which contains amniotic fluid The chorion is the opaque, thick and friable outer membrane lining the cavity of the uterus. Develops from the trophoblast and is continuous with the edges of the placenta 📷 @littlerosephotography_ The amnion is the transparent, smooth and stronger inner membrane closest to the fetus. Develops from the inner cell mass. It covers the fetal surface of the placenta and umbilical cord secreting amniotic fluid and prostaglandin E2 📷 @alexafayebirthstories Amniotic fluid (liquor) Clear alkaline and slightly yellowish fluid 99% water Amniotic fluid increases in volume as the fetus grows from 30ml at 10 weeks, 350ml at 20 weeks, to approximately 700–1000ml at 37 weeks before reducing to 600ml by 40 weeks Produced continuously by amnion, diffusion from maternal circulation across placenta, fetal tissue fluid through the skin, fetal urine, and fluid from the GI tract and lungs Amniotic Fluid Volume Dr Rachel Recycled continuously by fetal Reed swallowing and diffusion across the placenta into the maternal circulation Functions of amniotic membranes and fluid Protection from bumps to the abdomen Protection from infection Maintains a constant temperature Distends the amniotic sac creating space for symmetrical growth and allowing free movement, which is essential for symmetrical musculoskeletal development Assists normal lung development 📷 @ingefotografie.nl Helps fetal development of taste and smell Helps prepare the baby for breastfeeding Equalises pressure from contractions during labour Forewaters help transmit equal pressure across the cervix Lubrication to facilitate fetal descent during 2nd stage of labour