1.5 Flashcards
As the chorionic villi develop, they become surrounded by maternal blood spaces. This provides a
Large surface are over which the foetus can obtain nutrients and exchange gases with the mother’s blood
Some of the cells in the blastocyst form
Chorionic villi that secrete enzymes to digest the outer layer of the endometrium
Chorionic villi =
Beginning of the placenta
the cells in the inner mass of the blastocyst differentiate into the
Many different kinds of cell that makes up tissues and organs
25 days after ovulation the embryo has a
Primitive bating heart
4 weeks after ovulation the
Brain is growing rapidly
The eyes and ears have started to form
Gut is beginning to develop
10 weeks after fertilisation the
Main body organs have formed and the embryo becomes a foetus
Main body organs have now formed
Foetus only about 35mm long from rump to head
The foetus is protected inside a sac called the
Amnion
Amnion secretes
Amniotic fluid
The umbilical cord connects the foetus to the placenta and carries
Blood between the two
Umbilical cord contains 2 umbilical arteries, carrying blood from the foetus to the placenta and an umbilical vein carrying blood
From the placenta to the vein
The foetus depends on the placenta for its development. Nutrients pass from the mother’s blood into the foetus’ blood in the placenta such as:
Glucose Amino acids Mineral ions Water Oxygen
Antibodies also pass from the mother to the foetus so that the foetus is protected from the same diseases as the
Mother
Immunity from these antibodies lasts for a short time after birth as the foetus does not
Produce it’s own memory cells
The placenta contains a large number of chorionic villi and the capillaries are separate from the maternal blood by a thin membrane that has
3 layers
3 layers of the membrane are:
- wall of the villus, consists of a thin layer of fused cells (micro villi which considerably increase surface area)
- a thin layer of connective tissue
- endothelium cells making up the capillary wall
The mothers blood and the foetal blood flow in opposite directions know as
Countercurrent flow
Countercurrent flow ensures that there is a
Concentration gradient all the way along the capillary
CCF - blood from the foetus arriving in the placenta has a very low oxygen concentration (0) but it receives oxygen by diffusion from the mothers blood which has a higher oxygen concentration:
(2)
the blastocyst and the developing placenta produce the hormone
Human chorionic gonadotrophin (hCG)
hCG is secreted in large amounts in the first 2 months of pregnancy and is
Present in the urine of pregnant women
Presence of hCG forms the
Basis of pregnancy tests
In the first 3 months of pregnancy, the corpus luteum continues to Secrete progesterone and a small amount of oestrogen. This inhibits
Contraction of the myometrium
Maintains the endometrium
After the first 3 months of pregnancy, the corpus luteum begins to
degenerate and the placenta secretes increasing amounts of progesterone together with some oestrogen
Progesterone also inhibits the production of FSH
from the pituitary gland
Screening in pregnancy :
Amniocentesis
Samples of chorionic villi
Amniocentesis a hypodermic needle is inserted through the mother’s abdomen and a small sample of amniotic fluid is extracted. This will
Contain some foetal cells
Amniocentesis the needle is guided into a suitable position by using an
Ultrasound scan
Amniocentesis the cells are extracted and stimulated so that they
Divide by mitosis
A spindle inhibitor is then added so that the cells do not complete
Mitosis
The cells are placed in a dilute salt solution so that they swell cupcake then chromosomes are photographed. The images of the chromosomes are then manipulated on a computer screen and
Arranged in homologous pairs - enables chromosome defects to be detected
Sample of chorionic villi involves using a plastic catheter inserted through the
Vagina
After 3-4 days zygote has formed a ball of cells called a
Morula
By about 5-6 days it has formed a
Blastocyst
The outer layer of cells on a blastocyst (trophoblast) will develop into the
Membranes around the embryo and the beginnings of the placenta
The inner cell mass of the blastocyst is the part from which the
Embryo will develop
The blastocyst reaches the uterus about a week after fertilisation takes a few days for
Implantation to occur
zona pellucida surrounding blastocyst breaks open and the trophoblast cells at one end of the embryo form villi that secrete enzymes-
Digest the outer layer of the endometrium releasing nutrients for the developing embryo
4 functions of the placenta:
- allows female mammals to carry young inside during early development
- during pregnancy, foetus receives all it’s nutrients via the placenta
- all the waste products in the foetus’ blood are removed via the placenta
- the placenta also produces hormones
Placenta consists of thousands of chorionic villi that project into the endometrium. The maternal blood vessels surrounding the chorionic villi break down forming
Maternal blood sinuses
Placenta is surrounded by capillaries which cause a larger surface area
CO2 from
O2 from
Chorionic villi to placenta
Placenta to chorionic villi
Placenta hormones
Human chorionic gonadotrophin
Progesterone
Oestrogen
Follicle stimulating hormone
Functions of placenta:
Barrier
Immune protection
Site of exchange
Placenta acts as a barrier
Limits the transfer of blood components from maternal blood to foetal system
Cells of the maternal immune system do not cross so reducing risk of immune rejection
Placenta act as a immune protection
Protective molecules cover the surface of the early placenta, ‘hiding’ it from the maternal immune system
Placenta acts as a site of exchange as
Of many dilutes between maternal and foetal systems
Foetus haemoglobin has a higher
Affinity for oxygen then maternal haemoglobin
Endocrine function
The placenta takes over the production of oestrogen and progesterone as the corpus luteum degenerates ensuring the endometrium is maintained
