Abnormal implantation sites (ectopic pregnancy)

Abnormal
implantation sites (ectopic pregnancy)

Occasionally
implantation in the uterus itself may lead to serious complications. This is
particularly so when the blastocyst implants close to the internal os. At later
stages of development the placenta overbridges the os (placenta previa), and
causes severe bleeding in the second half of pregnancy and during delivery. Not
infrequently implantation sites are found outside the uterus, resulting in extra-uterine or ectopic pregnancy. This may occur
at any place in the abdominal cavity, ovary or Fallopian tube. Most frequently
in the abdominal cavity the blastocyst attaches itself to the peritoneal lining
of the recto-uterine cavity (Douglas pouch). This also may take place in the
peritoneal covering of the intestinal tract or to the omentum.

Sometimes
the blastocyst develops in the ovary proper, causing a primary ovarian pregnancy. More commonly an ectopic
pregnancy is lodged in the Fallopian tube (tubal
pregnancy). In the latter case, the tube ruptures at about the
second month of pregnancy, resulting in severe internal hemorrhaging by the
mother.

So, there are two types of ectopic pregnancy intra-uterine and extra-uterine,
the last one includes tubal ovarial and peritoneal ones.

Ectopic pregnancy usually leads to death of embryo and severe bleeding by the
mother during the second month of pregnancy.

HISTIOTROPHIC AND
HEMATOTROPHIC

PERIODS OF EMBRYOGENESIS

In
different stages of embryogenesis embryo has different types of nutririon.
During
the first 30 hours after fertilization it posseses nutrients from the yolk
inclusions of the oocyte.
Without fertilization oocyte may be alive three days thanks to the yolk. It is so called “vitelotrophic nutrition” (vitelum – from greece “yolk”). After that “histiotrophic nutrition” begins thus during
the first month of pregnancy embryo is fed with surrounding tissues and their
secretion. At that period of embryogenesis hormone progesteron is necessary
very much because of it influence on this secretory process.

At the
begining of the 5^th week trophoblast enzymes solve the wall of
uterine mucosa vessels and new type of nutrition begins. It is “hematotrophic nutrition”, because the embryo
receives all the necessary products from the mother blood.

specific
processes of embryogenesis

Ooplasmatic segregation – redistribution of the oocyte cytoplasm components which
result in formation of presumptive zones
(portion of an oocyte from which some exact structure may develop).

Proliferation
is a process of cells amount increase by means of their devision.

During the
embryogenesis the cells may influence one to each other and produce some
differences between themselves. Thus the induction
results in differentiation. At the same
time being developing in some way the embryonic cells have lost their
possibility to be changed in different way. This process is named a comition. Gens expression and repression are the
basic points of these processes.

EXTRACORPORAL FERTILIZATION

During
last period of time in medical practice of many countries of the world
so-called extracorporal (artifitial) fertilization is used very often in
the case of male or female infertility.

It was in
1976 in Great Britain,
Luisa Brawn was born thanks to the efforts of embryologists Edwards and
Stantow.

There are
some advances of such extracorporal fertilization:

1. It is possible to choice the future
sex of baby.

2. The sperm may be reached with
spermatozoa, abnormal onces may be picked out.

3. Abnormal sites of implantation are
almost impossible in such case (f.e., tubal pregnancy).

Real-life situations to be solved

1. There is a cross
section of spermatozoon in anelectron micrograph.. Mitochondrial sheath
wrapped around the axial filaments is seen. What part of spermatozoon is sected
?

2. In histologic
specimen of a human oocyte there is a small amount of yolk inclusions, settled
uniformly in cytoplasm. What type of oocyte is this?

3. Human oocyte was
fertilized with spermatozoon with Y-chromosome. What sex will baby have?

4. Human spermatozoa are
moving toward to oocyte and tunics of both cell join into contact. What
process takes place?

5. After spermatozoon
penetration into human oocyte other ones can't do that. What kind of
fertilization is this? What structure prevents penetration of numerous
spermatozoa into oocyte?

6. At the 6-7-th day of
embryogenesis em brio implantation had occurred in the uterine tube. What will
happen in such case of abnormal implantation site?

7. Cavity appears in
human embryo and blastomers differentiation begins. What structures will appear
as a result of this differentiation?

» Implantation. By the end of first week of development