General Embryology Flashcards
Write a short note on fertilisation .
Fertilisation is the process of fusion of two mature
germ cells, an ovum and a spermatozoon (haploid
cells) to form a single cell, zygote (diploid cell).
Fertilisation involves three basic steps:
1. Approximation of gametes
It involves transport of spermatozoa and ovum in
female genital tract towards the ampulla of uterine
tube (usual site of fertilisation).
- Contact and fusion of gametes
Sperm must break three barriers
(corona radiata, zona pellucida and vitelline
membrane) of secondary oocyte for fertilisation.
Capacitation is a process of maturation of spermatozoa during which coat of glycoprotein from head of spermatozoa is removed to enhance sperm motility. - Effects of fertilisation.
i) Completion of second meiotic division of secondary
oocyte .
ii) Restoration of a diploid number of chromosomes.
iii) Determination of chromosomal sex
iv) Initiation of cleavage.
Write a short note on Implantation.
Implantation is the process of penetration of blastocyst into the endometrium of uterus.
Implantation begins on 6th or 7th day after
fertilisation and completes by the 12th day.
Implantation occurs in the upper part of
body of the uterus usually in anterior or posterior uterine wall.
If blastocyst does not implant at the usual site, that
is, upper part of body of uterus in endometrium, it
is called abnormal or ectopic implantation and it
results in ectopic pregnancy.
Ectopic pregnancy or implantation are classified
according to their site of implantation as follows:
A.Uterine abnormal implantation.
• Placenta previa: It is an implantation in lower
uterine segment.
B. Tubal implantation: It is an implantation in uterine
tube. It is the most common extrauterine
implantation.
C. Abdominal implantation: It is a rare ectopic
implantation. It usually occurs in the ovary or
mesentery.
Write a note on placenta.
Placenta is an organ that performs exchange of nutrients and gases between mother and foetus.
Thus, the placenta is a foetomaternal organ.
Human placenta is discoid
Placenta has 2 components:
1) Maternal component - decidua which is derived from uterine endometrium.
2) Foetal component - chorion which develops from trophoblast and extraembryonic mesoderm.
Placenta with foetal membrane is also expelled out
of the uterus 30 minutes after childbirth.
Foetal surface of the placenta is shiny, grey and
translucent.
Maternal surface of the placenta is rough and dark
maroon.
Functions of placenta:
1. Gaseous exchange: O2 and CO2 exchange takes place
across placenta through simple diffusion.
2. Transport of nutrients such as glucose, fatty acids,
amino acids and electrolytes such as sodium,
potassium and chloride.
3. Excretion of urea, uric acid and creatinine from the
foetal blood into the maternal blood.
4. Passive immunity: Maternal antibodies (immunoglobulins) pass placental barrier by pinocytosis of
syncytiotrophoblast.
5. Placental barrier: It prevents entry of many drugs
and bacteria.
6. Endocrine function:
Placenta secretes following hormones:
– human chorionic gonadotropin
– placental oestrogen
– placental progesterone and
– placental lactogen.
Write a note on notochord.
Notochord is a midline embryonic structure that
develops during third week of development from
cells of primitive node, that is, epiblast.
Stages of formation of notochord:
1) Proliferation of cells of primitive knot.
2) Formation of primitive pit.
3) Formation of notochordal process around day 17 to 18.
4) Formation of notochordal canal.
5) Formation of neurentric canal.
6) Formation of notochordal plate
7) Formation of definitive notochord.
Primitive streak
On 15th day, primitive streak appears that induces
gastrulation.
Gastrulation is a process of convention of bilaminar
embryonic disc to trilaminar disc during the third
week of development.
Elevated cranial end of primitive streak form a
primitive node - Hensen’s node that surrounds a depressed pit called primitive pit.
What is chorion
Trophoblast and somatopleuric layer of extraembryonic mesoderm together form a chorion and
blastocystic cavity called the chorionic cavity.
Formed during second week of development.
Chorion is an extraembryonic membrane that helps in formation of placenta.
It develops from outermost layer of blastocyst know as trophoblast.
The chorion consists of two layers: the outer chorionic membrane and the inner chorionic plate.
Finger-like projections called chorionic villi develop from the chorionic plate and extend into the uterine lining.
Functions
1) Involved in formation and development of placenta.
2) Gas exchange
3) Protection from pathogens and mechanical shocks.
4) Immune tolerance
5) Hormone production like estrogen and progesterone.
What is amnion
Development -
1) Amnion develops during second week of embryonic development.
2) It arises from epiblast layer of the embryonic germ disc.
Structure -
1) Forms a transparent thin membrane.
2) It encloses fluid filled cavity called amniotic cavity.
3) The amniotic cavity sorrounds embryo during development.
Function and importance -
1) Act as protective barrier around developing embryo.
2) Amniotic cavity is filled with amniotic fluid which provides cushioning effect.
3) Amniotic membrane prevents foetus from adhering to surrounding tissues.
4) Rupture of membrane also called as breaking of water is normal process taking place during childbirth.
Amnion contributes to formation of amniotic sac which consist of amnion and amniotic fluid.
