L34 Flashcards
How long is the human gestation period from fertilization? What about from last menstrual cycle?
266 days from fertilization
280 days menstrual cycle
2 week different
what is the 3 stage of prenatal ?
pre-embryonic 0 to 2 week
embryonic 2 to 8 week
fetal periods 9 to birth
Obstetricians commonly split the gestation period into what?
trimerster
they divide the 9-month period of gestation into three trimesters.
what is the most critical stages of development
the first
trimester when embryonic and early fetal development is occurring
Where specifically does fertilization occur?
The ampula of the Fallopian tube
morula [ 12-16 cells ] form at which day ?
3 day after fertilazation
what happen at day 4 ?
Early blastocyst is formed (Morula hollows out, fills with fluid, and “hatches” from the
zona pellucida ZP)
what happen at day 7 ?
implanting blastocyst that consist of inner mass[ embryoblast ] and outer mass [ trophoblast]
and the The fertilization membrane (zona pellucida) has degenerated and disappeared in order for the trophoblast to implant into the uterus
during implantation the uterus is in which phase ?
secretory phase [ progesterone phase ]
Where exactly does the blastocyst implant?
On the posterior wall of the body of the uterus
what happen in day 8?
• The trophoblast at the embryonic pole differentiates into 2 layers:- Cytotrophoblast - Syncytiotrophoblast
•
cells of the inner cell mass (embryoblast) also differentiate into two layers: - Epiblast - Hypoblast
• At the same time, a small cavity appears in the epiblast called the amniotic cavity.
true or false
amniotic cavity apeers in hypoblast
false it appere in the epiblast
What happens at day 9?
Amniotic cavity expands
embryo is now a bilaminar disk (Epiblast and Hypoblast thicken)
Exocoloemic cavity (primary yolk sac) forms, and the Exocoelomic membrane, made from the Hypoblast, surrounds it (it is continuous with the Hypoblast)
What happens at days 11 and 12?
By the 11th- 12th day, the blastocyst is completely embedded in the endometrial stroma and uteroplacental circulation has been established.
- Extraembryonic mesoderm has been developed; soon large cavities formed in it then
become confluent to form extraembryonic coelom (chorionic cavity)………
the extraembryonic coelom [ chorionic cavity ] sorrounds?
the primary yolc sack and aminotic cavity
The somatic layer with cyto and syncytiotrophoblast form a membrane called ?
chorion
what is connecting stalk ?
the part where it does not cover by chrionic
This separates the extraembryonic mesoderm into 2 layers?
somatic layer (lining the cytotrophoblast from outside) and splamthic layer (or visceral layer) which spurrounds the primary yolk sac
etal blood vessels develop in the?
horionic villi which his sorrounded by intervillous space
^ the chorionic villi which remains form the placenta
what is the rule of 2?
A way to memorize in week 2 that
the trophoblast differentiates into 2 lyres [ cyto/syncytio - trophoblast ]
the embryoblast differentiates into 2 layers[ hypoblast / epiblast]
the extrareaByronic mesoderm splits into 2 layers [ somatic layer / splamthic layer]
there are 2 yolk sacs (prim and sec)
2 new cavities form[ aminotic and chronic]
Becoming trilaminar and establishing body axes happen in which week ?
third week
What is the first major event of week 3- and arguably the MOST important part of human development?
Gastrulation- meaning the formation of the gut
Formation of the 3 germ layers (Endo, meso, ecto)
Provides changes in the fate of the germ layers (differentiation) and start organogenesis
Establishing body axis (cranial- caudal left-right, etc)
Formation of x defined for the first time the major body axes.
What is x, and what body axes are they?
The primitive streak Cranial caudal (head-tail) Dorsal ventral (back belly) Medial lateral (left right)
what is the longitudinal midline structure in the epiblast ear the caudal end of the bilaminar disk?
primative streak
the X represent area where cells are leaving the Pramative streak and moving into the interior of the embryonic disc
primative groove
Epiblast cells migrate through the primitive streak by movement called ?
ingression
true or false
in week 2
PS moves through the midline of the Epiblast, (from caudal end - cranial) which makes the Epiblast cells migrate from the midline down towards the Hypoblast cells, and towards the lateral ends creating a primitive groove where they migrate.
The Hypoblast cells are displaced and the first layer is now the Endoderm 14 -15 days .
Afterwords, the Epiblast form another layer while migration creating the Mesoderrm
The Epiblast that remain, are now termed Ectoderm.
false
week 3
Thus the X through the process of gastrulation becomes the source of all three germ layers
WHAT IS X
epiblast is the source of 3 germ layers
What are the 2 membranes that have no mesoderm layers during the process of gastrulation?
The oropharyngeal membrane (cranial end and will become opening of mouth) Cloacal membrane (caudal end and will become opening of anal canal)
Notochord will form from the x and is on the y
x= primative node y= midline
What is the function of the notochord?
Primordial longitudinal axis of the embryo and gives it some rigidity.
2- Signals for the development of CNS.
What is the fate[ مصير] of the primitive streak?
The primitive streak diminishes in size and becomes an insignificant structure in the sacrococygeal regionof the embryo. Normally the primitive streak undergoes
degenerative changes and disappears by the end of week 4
What is sacrococygeal teratoma?
A disease caused by the remanence of the primitive streak
Causes a tumor to be formed which contains tissues from all germ layers as the primitive streak is remaint of Epiblast (pluripotent)
Only occurs in the sacrococygeal region
Good prognosis
In extreme cases, the deficiency in caudal development leads to fusion of the lower limb buds during early development resulting in a condition
called ?.
Sirenomelia
What is caudal dysgenesis?
A group of syndromes that occur because of INSUFFICIENT mesoderm formation in the caudal region of the embryo.
What are some characteristics of caudal dysgenesis?
Hypoplasia (poor formation of tissues and organs) and fusion of lower limbs
Anomalies of the lumber and sacral vertebrae
Agenesis of the kidney and urinary tract
Agenesis or internal genital organs EXCEPT GONADS
Imperforated anus
In EXTREME CASES - Sirenomelia (deficiency in caudal development leads to fusion of lower limb buds during early development
