Early Development Flashcards
What is fertilisation/conceptual age?
The time from the point of fertilisation
Assumed to be one day from the last ovulation
What is gestational age?
The time from the beginning of the last menstrual period
Fertilisation age +14 days
Can be measured by comparing embryo size charts
What is carnegie stage?
This is a measure of 23 stages of embryo development by comparing embryo features (i.e. first heart beat)
State are the 3 stages in embryo development
Embryogenic
Embryonic
Fetal
What occurs during the embryogenic stage (give time)
2 weeks post fertilisation
This is the establishment of the early embryo
There are 2 cell populations: pluripotent embryonic cells and extraembryonic cells
What is occurs during the embryonic stage (give time)?
2-8 weeks after fertilisation
The establishment of the 3 germ layers and the body plan
What occurs during the fetal stage and when?
Trimesters 2+3
The formation of organ systems
Migration of organs to final destination
Acquisition of fetal viability
Outline the cell stages of development (include cell numbers)
Ovulated oocyte - 1 cell Fertilised zygote - 1 cell Embryo cleavage - 2-8 cells Morula - 16 cells Blastocyst - 200-300 cells
What is the maternal to zygotic transition?
A shift away from maternal to zygotic RNA at the 4-8 cell stage
What occurs during compaction?
Outer cells become compressed and more wedge shaped as the inner cells grow and compress against the zona pellucida
2 cell populations form - inner and outer
Which 2 cell jucntions form during contraction?
Desmosomes and tight junctions
Which type of stem cells make up the inner cell mass?
Pluripotent stem cells - contribute to final organism
What is contained within the blastoceal?
Na+ ions which drive water to follow in
What is the role of the zona pellucida?
Protects early embryo
Prevents polyspermy
What occurs during blastocyst hatching?
There are cellular contractions and enzymatic digestions - allow embryo to continue to grow
Briefly outline the role and formation of the syncitotrophoblast
It arises from the trophectoderm
The fusion of trophectoderm cells froms the syncitiotrophoblast
It invades the maternal endometrium and breaks capillaries to establish a blood supply
What is the role of the cytotrophoblast?
They provide a source of syncitiotrophoblast cells
What 2 things does the inner cell mass divide into?
Epiblast - form the fetal tissue
Hypobalst - forms the yolk sac
Which hormone is released from the syncitiotrophoblast?
beta hCG
Describe bilaminar disc formation?
Amniotic cavity separates the cells of the epiblast
The upper layer forms the amnion and cells of epiblast and hypoblast are separated by amniotic cavity
What is gastrulation?
The formation of the 3 germ layers and establishment of the body axis
What occurs during gastrulation?
Primitive streak form through the bilaminar disc
Cells from the epiblast move through the streak and it becomes a pit
This forms the definitive endoderm and hypoblast is displaced
Cells in the middle and top become the mesoderm and ectoderm respectively
Which organs arise from the endoderm?
Liver Pancreas Lung GI tract Thyroid
What arises from the ectoderm?
Tooth enamel
Skin epithelia
CNS
Neural crest
What arises from the mesoderm?
Blood Muscles Gonads Adrenal cortex Kidneys Bone and cartilage
What is the notochord and where does it develop?
It is a rod like structure made from cartilage like cells.
It is the organising centre for neurulation
Develops on the ectoderm
Outline what occurs during neurulation?
Notochord releases signals which cause the ectoderm to invaginate, forming the neural crest. Neural ridges form and they move over the neural grove and eventually fuse
What cells are found in the neural folds?
Neural crest cells which eventually migrate from the folds
When do the head and tail ends close?
Head closes at d23
Tail closes at d 27
What 2 conditions arise due to failure of the neural plates to fuse?
Anencephaly - failure to close at the head end (born without brain and most of skull)
Spinal bifida - failure to close at the tail end (lower spine)
What do neural crest cells migrate into?
Cranial NC Cardiac NC Sacral NC Vagral NC Trunk NC
What defects can arise due to failure to migrate?
Deafness
Pigmentation disorders
Cardiac and facial defects
Gut innervation failure
What are somites and what is somitogenesis
Somitogenesis is the production of somites
Somites are paired blocks of mesoderm
What is rate of budding in humans?
1/90mins
What type of development measuring can somite number be used in?
Carnegie staging
What 2 types of tissue do somites form initially?
Sclerotome - vertebrae and rib cartilage
Dermomyotome - dematome is skin, fat and connective tissue; myotome is muscle
What 2 types of folding occur in primitve gut formation?
Ventral folding - head and tail end curl together
Lateral folding - the two sides of the embryo roll
What is the result of this folding?
Pinches off part of the yolk sac which forms the fore/mid/hindgut
What are the derivatives of the primitive gut?
Foregut - upper duodenum, pancreas, liver, gall bladder, stomach, esophagus
Midgut - lower duodenum, rest of SI, ascending colon, 2/3 of transverse colon
Hindgut - 1/3 of transverse colon, descending colon, rectum and upper anal canal
Describe the derivation of the heart
From the mesoderm
Heartbeat detectable from 6 weeks
Describe the derivation of the lungs
Arises from the endoderm - lung bud
Lung bud progressively splits into 2 from 4 weeks
Describe the derivation of the gonads
Arises from the mesoderm as bipotential - not committed to male or female - forms gonadal ridge
XY embryos - SRY gene triggers sertoli cells to develop into testes and leydig cells from
XX embryos - absence of SRY gene causes granulosa formation and ovary formation - reinforced by FOXL2 gene
