Placenta, cord & membranes Flashcards
Functions of the placenta
- Respiration - The placenta absorbs oxygen and excretes carbon dioxide for fetal metabolism
- Nutrition - absorbs the nutrients the fetus needs, breaks them down with enzymes into simpler molecules for use in fetal cells. Some nutrients are stored by the placenta, to be used as the need arises. E.g. Glucose is stored by the placenta as glycogen
- Excretion - Wastes produced by the fetus are removed from fetal blood and excreted by maternal organs
- Protection - The placental barrier is limited, but it does prevent the passage of most bacteria. Small micro-organisms such as viruses, however can pass through and may affect the developing fetus.
- Hormone production- The placenta acts as a complex endocrine gland producing many different hormones. Human chorionic gonadotrophin ( hCG) is produced by the early villi in large amounts to maintain the corpus luteum- until the placenta has developed sufficiently to take over. hCG levels later fall.
What is the placenta?
Is the organ that attaches the embryo to the uterus wall. Week 10-placenta fully formed. Weighs: 600 g → normally weighs ⅙ th of the weight of the fetus.
12-20 weeks gestation the placenta weighs more than the fetus and carries out all the metabolic reactions.
What are blastocyst & trophoblast
Implantation process: Act of planting or setting in
Blastocyst: very early in the pregnancy about a week after conception, the outer layer (trophoblast) develops into the placenta and chorion; the inner cell mass; projecting into the cavity, develops into the fetus and amnion
Trophoblast: The outer covering of the blastocyst from which the placenta and chorion develops.
Chorionic villi
During the implantation process, the blastocyst begins to develop finger-like projections from the trophoblast over its entire surface.
By 10 week of pregnancy, the placenta has formed from these closely packed villi.
Fetal surface of a healthy placenta
lies next to the fetus and is covered by the amniotic membrane.
White and shiny covered by the amniotic membrane
The maternal surface of the healthy placenta at term is
Dark red and separated into lobules
Attached to the decidua (modified mucosal lining of the uterus known as the endometrium that forms in preparation for pregnancy) which is arranged into lobes called cotyledons and are divided by grooves called suci → each cotyledons is divided into numerous lobules each of which contains one chorionic villus. → CREATING A LARGE SURFACE AREA (allowing nutrients and gases to exchange
The approximate healthy volume of amniotic fluid at term is
800-1000ml
The umbilical cord
Develops to connect the placenta to the fetus at the fetal umbilicus.
At term it is 50 cm long and 2 cm wide
AVA
2 arteries
1 vein
What are the membranes?
THE CHORION: outer membrane lining the cavity. It develops from the trophoblast of the early embryo. It has an opaque appearance and continuous with the edges of the placenta.
THE AMNION: the membrane closest to the fetus and secrets amniotic fluid. It is smooth, transparent and stronger than the chorion. It also covers the fetal surface of the placenta and the umbilical cord.
Amniotic fluid
Produced continuously by the amnion and is recycled constantly by fetal swallowing, urination and lung fluids add to its composition.
1000 ml of amniotic fluid is the right amount for a full term baby.
What is Polyhydramnious?
Where there is 1500 ml of AF.
Membranes can rupture early
Usually associated with a congenital defect in the fetus- oesophageal atresia or an open neural tube defect.
Risk of placental abruption is when the placenta separates early from the uterus, in other words separates before childbirth.
OR prolapsed umbilical cord- In a prolapse, the umbilical cord drops (prolapses) through the open cervix into the vagina ahead of the baby.
What is Oligohydramnious?
Less than 500 ml of AF.
Associated with fetal abnormalities such as an absence of kidneys
Dries out the fetus.
What is Succenturiate lobe?
A small extra lobe of placenta that develops alongside the main placenta
Blood vessels will run through the membrane into the lobe which can cause:
Intrapartum bleed: may be caused if vessels in the membrane rupture and are located near the cervix.
During the delivery of the placenta, the lobe may be retained causing infection or secondary haemorrhage.
The midwife may spot the lobe after examining the placenta and finding a hole.
What is Vasa praevia?
Where blood vessels lie over the cervical os. check membranes before artificially rupturing membranes (vaginal examination)- risk: haemorrhage at any time.
What is Placenta accreta and percreta?
Placenta embeds itself in the lining of the uterus, placenta accreta is when it grows further than the lining of the uterus.
Placenta percreta is when placenta grows further than the lining of the uterus into the endometrium muscles.
