The document presents information on the anatomy and physiology of the placenta and membranes. It defines the placenta and membranes, describing their structure and functions. The placenta acts as the lungs, kidneys, and endocrine organ for the fetus, exchanging gases, nutrients, and waste. The amnion and chorion comprise the membranes surrounding the fetus and amniotic fluid. Variations like succenturiate lobes or short/long cords can impact delivery. In summary, the document outlines the key roles and features of the placenta and membranes in sustaining fetal development.

1. PRESENTED BY M. JONAZI
22/01/2014
ANATOMY AND PHYSIOLOGY OF
PLACENTAAND MEMBRANES

2. OBJECTIVES
 Define the placenta, and membrane.
 Describe the placenta and membranes .
 Explain the functions of the placenta and
membranes.
 Describe anatomical variations of the
placenta, membranes and the cord.

3. Definitions
The placenta
• The Placenta is a connecting link between the baby
and the mother (Sellers, 2007).
Membrane
 Is a thin layer of tissue surrounding an organ or tissue
lining a cavity or separating adjacent structures or
tissues (Sellers,2007).

4. Description of the placenta and
membranes
Placenta
• The placenta is a complex organ , which originates
from the trophoblastic layer of the fertilized
ovum(Fraser, & Cooper, 2009).
 The placenta is completely formed and functioning 10
weeks after fertilization.

5. Description cont’
• At term, the placenta is a round flat mass about 20 cm
in diameter and 2.5 cm thick at its centre.
Weighs approximately 1/6 of the baby’s weight(about
500g).
• It has two surfaces namely the maternal and foetal
surfaces(Sellers, 2007; Fraser,&Cooper, 2009).

6. Cont’
Maternal surface
• This surface is composed of the decidua basalis and of
thousands of chorionic villi containing fetal blood,
which are embedded in the decidua basalis.
• Maternal surface is divided into 16-20 lobules or
cotyledons which are separated by deep grooves or
sulci into which the decidua dips down.
• Maternal blood is present in the intervillous
spaces(Sellers, 2007).

7. THE MATERNAL SURFACE CONT’
 Maternal blood gives the surface dark red colour.
 Sometimes deposits of lime salts may be present on the
surface making it slightly gritty.
 This has no clinical significance(Fraser, & Cooper,
2009).

8. THE FETAL SURFACE
• This surface faces the foetus during pregnancy, and
has the umbilical cord inserted into it.
• It is covered with the amniotic membrane (the
amnion) which gives it a smooth shiny appearance.
• The amnion can be stripped away from the surface, up
to the insertion of the cord(Sellers, 1993).

9. FETAL SURFACE CONT’
 Foetal blood vessels can be seen radiating from the
insertion of the umbilical cord, out towards the edges
of the placenta.
 These blood vessels are branches of the umbilical vein
and the two umbilical arteries.
 The two membranes attached to the placenta are the
chorion and amnion(Sellers, 2007).

10. Description cont’
The membranes
The chorion
• This is an outer thick opaque friable membrane derived
from the trophoblast(Fraser, & Cooper, 2009).

11. THE MEMBRANES
The chorion cont.
 The chorion is continuous with the edge of the
placenta, because they both have developed from the
trophoblast(Sellers, 2007).
 The chorion should have no blood vessels running
through it.

12. Description cont’
The amnion
 This is an inner smooth tough membrane of the foetal
sac, and lines the amniotic cavity.
 The membrane contains the liquor amnii
 It lines the chorion and the surface of the placenta
continuing over the outer surface of the umbilical cord.

13. Description cont’
When first formed, the amnion is in contact with the
embryo, but 4-5 weeks after conception the amniotic
fluid begins to accumulate within it(Fraser, & Cooper,
2009).
The amnion is the foetal sac which contains the foetus
and liquor amnii during pregnancy.
Also known as the amniotic membrane.

14. Cont’
 The amnion can be stripped off the chorion and the
fetal surface of the placenta, up to the insertion of the
cord(Sellers, 1993).
 After delivery the amnion also has a hole in it, through
which the baby has been born(the fenestrum).
 The amnion has no blood vessel(Sellers, 2007).

15. Description cont’
Amniotic fluid
 It is a clear alkaline and slightly yellowish liquid
contained within the amniotic sac.
 The source is thought to be both foetal and maternal.
 It is secreted by the amnion, especially the part
covering the placenta and umbilical cord.

16. Cont’
 Amniotic fluid increases in volume as the foetus
grows.
 The volume is greatest at approximately 38 weeks’
gestation when there is about one litre.
 It then diminishes slightly until term when
approximately 800 ml remains.

17. Cont’
 If the total amount of liquor exceeds 1500 ml, the
condition is known as polyhydramnious.
 If less than 300 mls it is called oligohydramnious.
 Such abnormalities are often associated with
congenital malformations of the foetus(Fraser, &
Cooper, 2009).

18. Cont’
Fetal urine also contributes to the volume from the tenth
week of gestation onwards.
Function of amniotic fluid
 Distends the amniotic sac allowing for growth and
free movement of the foetus.
 Maintains a constant intrauterine temperature.
 It equalizes pressure and protects the foetus from
injury.

19. Cont’
 It also aids in effacement of the cervix and dilatation of
the uterine os, particularly where the presenting part is
poorly applied.
 In labour, as long as the membranes remain intact, the
amniotic fluid protects the umbilical cord and the placenta
from pressure of the uterine contractions(Fraser, &
Cooper, 2009).

20. THE UMBILICAL CORD
 The umbilical cord connects the foetus with the
placenta.
 The cord extends from the foetal surface of the
placenta to the umbilical area of the foetus and is
formed by the 5th week of pregnancy.
 The cord is approximately 1-2cm in diameter and 40-
50 cm in length(Fraser, & Cooper, 2009).

21. Cont’
 The cord contains two smaller, thick-walled arteries
and one large, thin-walled vein (Sellers, 1993; Fraser,
& Cooper, 2009).
Function of the umbilical cord.
• The umbilical cord transports oxygen and
nutrients to the developing foetus, and
removes waste products(Fraser, & Cooper,
2009).

22. FUNCTIONS OF THE PLACENTA
Functions of the placenta
Nutrition
 It provides the embryo with nourishment necessary for
development, growth and survival, such as glucose,
amino acids, vitamins and mineral salts, which are
transferred from the mother, across the placental
membrane, to the fetus.

23. Nutrition cont’
 Glucose for energy and growth.
 Amino acids for body building.
 Calcium and phosphorus for bones and teeth.
 Iron and other minerals for blood formation.
 These nutrients are actively transferred from the
maternal to the foetal blood through the walls of the
villi(Fraser, & Cooper, 2009).

24. Functions cont’
Excretory
 The main substance excreted from the foetus is carbon
dioxide.
 Waste products , such as creatinine, bilirubin are
transferred from the foetal bloodstream across the
placental membrane to the mother’s blood circulation for
excretion(Sellers, 2007).

25. FUNCTIONS CONT’D
Respiration
 The placenta acts as the respiratory organ for the fetus.
 During intrauterine life, no pulmonary exchange of
gases can take place so the foetus must obtain oxygen
and excrete carbon dioxide through the placenta.

26. Functions cont’
RESPIRATION CONT’D
 Oxygen is transferred , through the placental
membrane from the mothers’s blood in the intervillous
spaces, to the foetal blood and circulation, for foetal
utilization.
 The carbon dioxide is then transported back to the
placenta and transferred across the placental membrane
into the maternal blood circulation(Sellers, 2007).

27. Cont’
 It is then exhaled via the maternal lungs(Sellers,
2007;Fraser, & Cooper, 2009

28. Functions cont’
Endocrine
 The placenta is a temporary endocrine organ.
 The placenta produces hormones which are essential
for the maintenance of the pregnancy(Sellers, 2007).

29. Functions cont’
 Also responsible for the preparation of the maternal
body for pregnancy, labour and for feeding the
newborn baby.
Major hormones produced by the placenta.
Human Chorionic Gonadotrophin (hCG) which
stimulates the growth and activity of the corpus
luteum.

30. Functions cont’
 Peak levels of hCG achieved between the 7th and 10th
week.
Excreted in the mother’s urine(Fraser, & Cooper, 2009).
Oestrogens which are growth stimulating hormones.

31. Functions cont’
Human Placental Lactogen(hPL) which plays a role in
glucose metabolism in pregnancy.
Progesterone
 Made in the syncytial layer of the placenta in
increasing quantities until immediately before the
onset of labour when its level falls.

32. Functions cont’
 Main function of progesterone is to act on tissues that
have already been receptive to oestrogen(Fraser, &
Cooper, 2009).

33. FUNCTIONS CONT’D
Protection
 The placenta provides a limited barrier to infection.
 Few bacteria can penetrate.
 Substances including alcohol, chemicals associated
with smoking cigarettes and several types of viruses
are not filtered out(Fraser, & Cooper, 2009).

34. Functions cont’
Enzymal function
• Every enzyme known to exist in the human body has been
found in the placenta.
• These enzymes are necessary for:
 the synthesis of proteins.
 the functioning of fetal tissue, such as respiratory
enzymes.
 Steroid conversion, to produce progestrone and
oestrogens(Sellers, 1993)..

35. Functions cont’
Storage
 The placenta metabolizes glucose , stores it in the form
of glycogen and reconverts it to glucose as required.
 It can also store iron and the fat-soluble
vitamins(Fraser, & Cooper, 2009).

36. Anatomical variations of the placenta,
membranes and cord
A. Succenturiate lobe of the placenta.
 This is the most significant of the variations.
 A small extra lobe is present separate from the main
placenta and joined to it by blood vessels which run
through the membranes to reach it.

37. Anatomical variations cont’
Succenturiate lobe
 The danger is that this small lobe may be retained in
utero after the placenta is delivered, and if it is not
removed, it may lead to infection and severe
postpartum haemorrhage(Fraser, & Cooper, 2009).

38. Cont’
Placenta bipartita or tripartita
 The placenta has developed as two or even three
separate lobes.
 The blood vessels from the separate lobes unite at one
umbilical cord.
 This is different from the two placentas in twin
pregnancy Sellers, 2007;Fraser, & Cooper, 2009

39. Anatomical variations cont’
Placenta circumvallata
The chorion (and sometimes the amnion as well) has
folded back upon itself around the edge of the
placenta, before continuing over the edge of the
placenta to form the foetal sac.
The danger of this placenta is that the chorion or part of
it, can become detached from the edge of the placenta
and can be retained in the uterus(Sellers, 2007).

40. Anatomical variations cont’
Placental infarcts
• True infarcts of the placenta are areas of necrosis
where the chorionic villi have been damaged.
• This could be due to vasospasm of the maternal
circulation .
• Large parts of the placenta have a whitish, anaemic
appearance.
• Can cause placental insufficiency(Sellers, 2007).

41. Cont’
Placental oedema
 A large pale placenta may indicate that the mother has
diabetes mellitus.
 On the other hand, a large pale placenta can be due to
maternal syphilis(Sellers, 2009).

42. Placenta accreta
 A condition where the trophoblastic villi have
penetrated through the basal layer of the decidua and
become attached to the myometrial cells.

43. Anatomical variations cont’
The membranes and cord
Battledore insertion of the cord
 The cord in this case is attached at the very edge of the
placenta in the manner of a table tennis bat(Sellers,
2007;Fraser, & Cooper, 2009).

44. Anatomical variations cont’
Placenta velamentosa
• The cord is inserted into the membranes instead of
into the foetal surface of the placenta.
• The umbilical blood vessels branch from the insertion
of the cord and then run through the chorion to and
from the placenta.
• Significant if the placenta is low-lying(Sellers,
2007;Fraser, & Cooper, 2009).

45. Cont’
A short cord
 A short cord , is any cord less than 400mm.
 Danger is it could delay or even prevent descent of the
foetus during labour; there could be early separation of
the placenta causing foetal anoxia.

46. Cont’
A very long cord
 Cords of 1 500mm(1,5m). Long cords may become
wound two or three times around the neck of the
foetus at birth resutting in reduced blood flow and then
foetal death(Sellers, 2009).

47. Cont’
True notes in the cord
 Caused by the foetus passing through a loop of cord
and forming a knot in the cord.
 Most likely to occur with a long cord.
 Danger is that during delivery, the knot could be drawn
tight as the foetus descends, causing anoxia and even
foetal death (Sellers, 2009).

48. References
Fraser, D.M., & Cooper, M.A.(2009). Myles Textbook
for Midwives (15th ed. ).Edinburgh; Churchill
Livingstone Elsevier.
Sellers, P.M. (2007). Midwifery: A Textbook and
Reference Book For Midwives in Southern Africa
Volume 1 Lansdowne: Juta and Co, Ltd.