Embryology Flashcards
What is the embryonic period?
First 8 weeks
During the 8 weeks what can be said about the organs?
They are all formed, but not developed
How long does it take the single fertilised egg to become a new human baby?
Normally 9 months
What is the conceptus stage?
Fertilisation to the end of week 3
What is the embryo stage?
Week 4 to week 8
What is the foetus stage?
Week 9 to birth
What is gametogenesis?
Germ cell formation
What two process take place during gametogenesis?
Oogenesis to oocyte (egg)
Spermatogenesis to spermatoza (sperm)
What is fertilisation?
The formation of the zygote
What is cleavage?
The period of rapid cell division
What forms after the Morula in cleavage?
Blastocyst
What is gastrulation?
The formation of the germ layers
What are the 3 germ layers?
Ectoderm, mesoderm, endoderm
At what stage are the body axes (head end and tail end) established?
Gastrulation
What is morphogenesis?
Formation of the body plan (embryonic folding (tube within a tube)
What is organogenesis and what weeks does it occur?
Primordia of all organ systems (weeks 4 - 8)
During what period does growth and weight gain occur?
Foetal period
During what period do tissues mature and become functional?
Foetal period
What period does overt sexual differentiation occur in?
Foetal period
What period is bone laid down and connections made in the CNS?
Foetal period
Processes underlying development: What are the 6 primary processes?
Cell division - increase in number of cells
Apoptosis - programmed cell death
Differentiation - change in appearance; adoption of new functions
Cell attachment - physical linkages between cells creating tissues
Induction - ability of one cell type to cause another to differentiate
Cell migration - movement from one location to another
Processes underlying development: What are the 3 secondary processes?
Axis formation/polarity
Folding/rotation - entire embryo or structures within
Increases/decreases in mass/dimension
What are the two sub processes of the secondary process increaseing/decreasing mass and dimension?
- Expansion - hypertrophy and hyperplasia
2. Compaction - decrease in cell mass with decrease in dimension, increase in cell number with no increase in dimension.
What is hypertrophy?
Increase in dimension with no increase in cell number
What is hyperplasia?
Increase in cell number with an increase in dimension
What 3 factors control development?
Genetic
Epigenetic
Environment
Where is the site of fertilisation?
Ampulla
What are the 4 stages of fertilisation?
- Sperm binds in a human specific interaction with the zona pellucida glycoprotein
- Acrosomal enzymes released from sperm head; the sperm digests its way into egg
- Egg and sperm plasma membrane fuse and sperm contents enter the cell
- Sperm entry triggers cortical granule release in egg cortex triggering formation of fertilisation membrane, which is impenetrable to sperm
What does sperm penetration of the egg also trigger?
Completion of the second meiotic division that leads to the formation of the haploid gamete.
What does fusion of the male and female pronuclei restore?
The diploid number of chromosomes = zygote (day 0)
Once the zygote is formed what does it then undergo?
A series of mitotic divisions which subdivide the fertilised egg into many smaller daughter cells called blastomeres.
Up to what stage blastomeres are thought to be totipotent?
Up to the 8 cell stage
What process forms blastocysts?
Compaction
What is the outer layer of a blastocyst?
Zona pellucida
At what day will the zygote attach to the uterus wall?
5.5 to 6 days
Name the 3 layers of the uterus from external to internal?
Myometrium
Perimetrium
Endometrium
What part of the blastocyst gives rise to the embryo?
Inner cell mass
What do the remaining cells in the inner cell mass of a blastocyst form once some have given rise to the embryo?
The trophoblast
What contributes to the placenta?
The trophoblast
Where are embryonic stem cells derived from?
The inner cell mass of blastocyst
Where does the embryo hatch from?
The zona pellucida
Once hatched, where does the embryo interact directly with?
Endometrial lining of uterus
Where are the normal implantation sites?
Middle or upper dorsal uterine wall
Name 6 abnormal sites for implantation
Ovary Ampulla Uterine tube Lower part of uterus Cervix Periotneum
What is another term for the outer cell mass of a embryo?
Trophoblast
Where do trophoblast cells of the embryo begin to invade?
The uterine epithelium
What has occured after 9 - 12 days?
The implanted embryo
By 9 - 12 days what has the syncytiotrophoblast done to the implanted embryo?
Extended and by erosion contacts maternal blood supply
Where is the amniotic cavity present in an implanted embryo?
Present above the bilayered embryonic disc and the definitive yolk sak below
What cavity other than the amniotic cavity has developed at 9 - 12 days (implanted embryo)?
Chorionic cavity
What does the chorionic cavity encircle?
The entire embryo
What streak has formed at the end of Week 2?
Primitive streak
At what end of the embryo is the primitive streak at?
Caudal
At what end of the embryo is the buccopharyngeal membrane at?
Cranial
During the formation of the germ layers, where do cells migrate through?
The primitive streak
What process is the movement of epiblast cells through the primitive streak to form the three primary germ layers?
Gastrulation
In gastrulation - what is the hypoblast replaced by?
Definitive endoderm
During gastrulation - where is the intraembryonic mesoderm formed between?
The endoderm and epiblast
During gastrulation what does the epiblast become?
Ectoderm
After 16 days what germ layer has formed?
Mesoderm
What is the fate of the ectoderm?
Epidermis of skin
Nervous system
What is the fate of the mesoderm?
Becomes subdivided
What is the fate of the endoderm?
Lining of the gut tube
Lining of respiratory tract
During the development of the mesoderm, it becomes three regions either side of what structure?
Notochord
What three regions does the mesoderm divide into?
Paraxial
Intermediate
Lateral plate (somatic mesoderm and visceral mesoderm)
What is the fate of the paraxial mesoderm?
Axial skeleton, parts of dermis, voluntary muscle
What is the fate of the intermediate mesoderm?
Urogenital symptoms
What is the fate of the lateral plate mesoderm?
Somatic part: lining of body wall, most of dermis, parts of limbs
Visceral part: Mesothelial covering of organs, cardiovascular system
What type of folding: converts the open coelom into a closed cavity, creating thoracic and abdominal cavities and closing fore and hind gut…mid gut is last to close?
Lateral folding
What type of folding: Forms the foregut and defines the thoracic cavity; developing heart tube displaced into thoracic cavity?
Cranial folding
What type of folding: Cloacal membrane and connecting stalk are displaced ventrally alongside the neck of the yolk sac, forming the hindgut, anus and umbilical cord?
Caudal folding
What four developments have occured in the 3rd month of foetal development?
Face more human looking (position of eyes and ears)
Limbs lengthen
First degree ossification centres in long bones and skull
Sex can be determined by external genitalia
What development occurs in months 4 and 5 of foetal development?
Rapid increase in length
What occurs in the 6th month to birth stage of foetal development?
Rapid increase in weight
At what stage is the critical neural development period?
weeks 3 - 16
At what stage is the critical period for heart development?
3.5 - 9 weeks
At what stage is the critical development period for upper limbs?
4 - 9 weeks
At what stage is the critical development period for lower limbs?
4.5 - 9 weeks
At what stage is the critical period of development for ears?
4.5 - end of 16 weeks
At what stage is the critical development period for eyes?
4.75 - end of 38 weeks
What is the critical development period for the palate?
6.5 - end of 9 weeks
What is the critical development period for teeth?
6.5 - End of 38 weeks
What is the critical development period for external genitalia?
7.5 - end of 38
What occurs in remodelling of the heart?
Going from a single tube to a four chambered structure
What 2 septa are grown during normal atrial septation?
Septum primum (flexible) Septum secundum (more rigid)
What does the communication between right and left atria occur through?
Foramen ovale
When does atrial septation one occur?
30 days
When does atrial septation 2 occur?
33 days
When does atrial septation 3 occur?
37 days
What valve is the septum primum?
Valve of foramen ovale
Function of foramen ovale: before birth - describe the pressures of the right and left atrium
Right atrium has higher pressure
Left atrium has lower pressure
Function of foramen ovale: describe the pressures of the right and left atrium after birth
Right atrium is lower pressure
Left atrium is higher pressure
After birth, in relation to the function of the foramen ovale, what closes off the shunt?
The septum primum (valve of foramen ovale) closes over the foramen ovale
Describe the growth of the muscular portion of normal ventricial septation?
Grows upwards from wall of expanding ventricle
Describe the growth of the membranous portion of normal ventricular septation?
Growth of tissue from endocardial cushions
What is ventricular septation closely related to?
Septation of the outflow tract
Name 4 types of congenital heart defects?
Atrial septal defect
Vebtricular defect
Outflow tract defects e.g. transposition of the great vessels
Combination of defects
What occurs as a result of excessive resorption of septum primum?
Atrial septal defects
What occurs as a result of absent septum secundum?
Atrial septal defects
What occurs when the septum primum and septum secundum fail to fuse and the mixing of blood is prevented due to pressure difference?
Prove patent foramen ovale
What 3 things occur in transposition of the great vessels?
Aorta exits right ventricle
Pulmonary trunk exits left ventricle
Deoxygenated blood pumped around the body
What is the patent ductus arteriosus?
Connection between pulmonary trunk and aorta
What are the 4 components of tetralogy of Fallot?
- Pulmonary stenosis
- Right ventricular hypertrophy
- Ventricular septal defect
- Over-riding aorta
