Embryology Flashcards
what is embryology
the study of origin and development of an organism
how long is a human pregnancy
38w-40w
when dose fertilisation occur
2 w after LMP
what is the embryotic period
first 8 w- all major organs formed in F
in the fetus when are all the major organs formed
embryotic period- first 8 weeks
what Is the fetal period
remaining 30w- organs grow larger and more complex
what is a zygote
fertilised egg- first in cycle
what is a 4-cell stage egg
4 cell egg- takes around 2 days to muture from a zygote- 2 stage
what is a morula
an egg cell that has divided mulitpule times- 3 days to mature from 4 cell stage- 3 stage
what is an early blastocycte
egg cell that has exited the F tube- 4 days to mature from a morula- 4 stage
what is an implementing blastocycte
egg implanted into utrus lining- 5 stage- 6 days to mature from early B
when dose cell dividion occur in the egg cell
as it travels down the F tube and enters the U
where is the site of fertilisation
F tube
what is a sex cell
gamete- ova or sperm only have 23 Chromsomes
what is a haploid number of chromsomes
half the number in a normal cell-
number of chromsomes in an ova
23- 12 pairs one sex cell, always X from mum can be either X or Y from dad
what sex cell do oocytes have
X only as they are produced by the ovary’s in the mother
what process is used to get a haploid number of chromsomes
Meiosis
what happens in the first w of conception
Zygote divides multiple times
morula- which is a cluster of 12-16 Blastomers forms at 72 hours
Day 4-late 60 cell morula enters the utrus- takes fluid and becomes a blasocyte
what are blastomers
daughter cells
when dose the embryo become deeply embedded in endometrium
Week 2
what occurs In W2
embryo deeply imbedded in endometrium,
Further development of trophoblast into placenta
Inner cell mass divides into epiblast and hypoblast
2 fluid filled sacs
Amniotic sac from epiblast
Yolk sac from hypoblast
Bilaminar embryonic disc: area of contact
what week dose the placenta develop
W2
what occurs in W3
Two layer germ disc Primitive streak forms Gastrulation forms tri-laminar embryo Neural induction Left-right asymmetry
how big is the fetus in W3
0.4mm - 2.0mm
what is gastralation
begins in 3 W- form the tri layer embryo- covers the 2 layers epiblasts in 3 germ layers
Ectoderm- outer layer
Mesoderm: middle layer
Endoderm: eventually most interior of embryo
how many layers is the embryo coverd with
3 germ layers via gastralation
what is the function of the Endoderm
inner most germ layer Via ge-lation-
generates the epithelial lining and associated glands of the gut, lung, and urogenital tracts
function of ectoderm
outside layer surrounding embryo- via Ga-lation, surrounds other layers later in development, generates skin and nervous tissue
function of Mesoderm
middle germ layer covering embryo via Gal-lation
, generates most of the muscle, blood and connective tissues of the body and placenta
when is the mesoderm formed
At gastrulation, primitive endoderm is replaced by definitive or embryonic endoderm
Then mesoderm is formed
what is Axial mesoderm
movement-mesoderm that passes through the node and migrates along the midline –forms the notochord
what is Paraxial mesoderm
mesoderm that passes just caudal to the node and migrates slightly laterally –forms cartilage, skeletal muscle, and dermis
what is Lateral plate mesoderm
mesoderm that passes more caudal and migrates more laterally –forms circulatory system and body cavity linings
what is Extraembryonic mesoderm
mesoderm that : passes most caudal and migrates most laterally –forms extraembryonic membranes and associated connective tissue & blood vessels.
which mesoderm forms the notochord
Axial
which mesoderm forms cartilage, skeletal muscle, dermis
paraxial
which mesoderm form circulatory system, body cavity linnings
lateral plate
which mesoderm forms extraembryonic membranes, connective tissue, blood vessels
Extraembryonic
function of the notochord and pre-chordal plate
important signaling centers that pattern the overlying ectoderm and underlying endoderm
how are the notochord and pre-chordal plate formed
develops from mesoderm arising from cells that passed directly through the node and migrated cranially along the midline- this is axial mesoderm
around what day is the notochord developed and what dose it form
day-16-18
Future site of the vertebral column
what is Neuralation
beginning Formation of spinal cord and brain
what causes Neuralation
Notochord signals overlying ectoderm
when dose the Closure of neural tube start
begins at end of week 3; complete by end of week 4 (folic acid important for this step)
when is Left-right asymmetry established
at gasturlaltion
what is Left-right asymmetry
Leftward beating of cilia at node moves some important protein molecules to the left side of embryo.
Causes left side genes to be expressed which then pattern developing organs.
what happens if cilia are defective in Left-right asymmetry
If cilia are defective, the important protein molecules can randomly end up on right side, resulting in reversal of symmetry, aka situs inversus
what happens if situs inversus occurs
organs can end up on the wrong side, this can be revered but only for a few organs
what dose diffraction of mesoderm in w 3 cause
Lateral to notochord, week 3
Extends cranially and caudally
how many regions do mesoderm divide into
3
Somites, Intermediate mesoderm, latral plate
function of Somites
division of mesoderm, 40 pairs of body segments (repeating units, like building blocks) by end week 4
function of Intermediate mesoderm
division of mesoderm, just lateral to somites- separates these two it is in the middle
function of lateral plate
splits to form coelom- will in turn form the serous cavities of the ventral body cavity:
Peritoneal
Pericardial
Pleural
what apposes these division of the mesoderm
Somatic mesoderm: apposed to the ectoderm
Splanchnic mesoderm: apposed to the endoderm
when dose folding begin and what happens
W4 day 23
Lateral folds will join ventrally
main difference between the 3 week embryo and the adult body- full developed fetus
embryo is still a flat disc
when is Placental formation
W4
what form the roof of the placenta
Chorionic plate-
what is the Chorionic plate made of
Syncitotrophoblast
Cytotrophoblast
Extraembryonic mesoderm with branches of umbilical vessels
what forms the floor From outside inwards of the plecenta
Basal Plate-
what is the Basal Plate made up of
Compact and spongy layer of decidua basalis
Cytotrophoblastic shell
Syncytiotrophoblast
how is the heart formed
Starts as two simple tubes
These fuse into different segments that will become different parts of the heart
The fused tubes then fold with the top part folding down in the front and the bottom part folding up behind this
when is the heart finished deloping by
W8
name some of the organs that are formed in Weeks 4 to 8
Formation of the main organ systems These include: Head and neck Brain Face Renal system Gastrointestinal system Limbs
what stages is the embryo suceptable from issues eg disease, bacteria, virus, toxins, chromsomes abnormlities
The embryo is susceptible at all stages of pregnancy
what are developed in Week 8 to 12
Some further development of ears, eyes and part of the palate
Main physical characteristics developing at this stage are genitalia
When are all the major body organs formed by
W4 to W8
