Embryology Flashcards
What time period is covered by the term conceptus?
Fertilisation to end of week 3
What time period is covered by the term embryo?
Week 4-week 8
What is happening with regards to organs in an embryo?
They are all present but not yet matured
What time period is covered by the term foetus?
Week 9- birth
What does gametogenesis phase comprise?
Germ cell formation (formation of egg and sperm)
What does the fertilisation phase comprise?
Formation of sperm and oocyte to form the zygote
What is a zygote?
Single cell embryo
What is the period of cell division with no size increase as a protein coat is forming known as?
Cleavage
What is a blastocyte?
First point where differentiation can be seen in cells
Which cells in the cluster of a blastocyte will form embryo structures?
Cells in the centre of the cluster
What happens in gastrulation?
Germ layers and formed and body axis determined
What are the 3 germ layers?
Ectoderm- outer
Mesoderm- middle
Endoderm- inner
What happens in organogenesis?
Formation of organs and organ systems
The basis of organs and organ systems will all be in place by ? and will continue developing through ?
Embryonic period/foetal period
What are 5 things which happen in the foetal period?
- Growth and weight gain
- Tissues mature and become functional
- Sexual differentiation
- Bone laid down
- Connections made in CNS
When are you able to tell the sex of a foetus?
12 weeks
What is the ability of one cell type to cause another one to differentiate known as?
Induction
What 3 factors control development?
Genetic, epigenetic and environmental
What is the difference between genetic and epigenetic control?
Genetic- expression of genes
Epigenetic- preferential expression of maternal or paternal genes
What is Angelman syndrome?
Deletion of maternal chromosome 15 which leads to mental retardation and poor motor development
What is Prader-Willi syndrome?
Deletion of paternal chromosome 15 which leads to mental retardation, obesity and hypogonadism
Where does fertilisation take place?
Ampulla of the fallopian tube
What does the sperm first bind with?
Glycoproteins of the zona pellucida
What happens before the sperm nucleus enters the egg?
Sperm and zona pellucida membranes fuse
What does sperm entry trigger?
Completion of meiosis 2 and release of cortical granules to prevent fertilization from a second sperm
After fertilisation, the zygote undergoes mitotic divisions to produce daughter cells known as what?
Blastomeres
What is the point where are cells are confined within the zona pellucida known as?
Compaction
What will the outer cells closer to the zona pellucida form?
Extensive gap junctions
Is the zona pellucida impermeable?
No
As early events of week 1 take place, where is the embryo moving towards?
Uterine cavity
How long does it take the embryo to reach the uterine cavity and what forms when it does?
About 4-5 days, forms the blastocyte
What is the function of the zona pellucida?
Protection
When is the zona pellucida lost?
When the embryo reaches the uterine cavity and it blocks entry to here
Where are the normal sites of implantation?
Middle/upper dorsal uterine wall
Where are abnormal sites of implantation?
Ovary, ampulla, uterine tube, lower uterus, cervix, peritoneum
What does implantation in abnormal sites lead to?
Ectopic pregnancy
Implantation is an active process driven by what?
Trophoblast
At around 7.5 days, the embryo divides into 2 cell layers, what are these?
Epiblast- dorsal surface of an embryo
Hypoblast- ventral surface of an embryo
What else begins to form during implantation, and when does implantation finish?
Amniotic cavity
Finishes around day 9
What do the epiblast and hypoblast become during gastrulation?
Hypoblast- endoderm
Epiblast- ectoderm
What does the endoderm become?
Lining of GI tract, respiratory tract, bladder and urethra
What does the ectoderm become?
Epidermis of skin, hair, nails, associated glands, nervous system
Somatic and visceral coverings of organs are derived from what?
Mesoderm
What does lateral folding create?
Thoracic and abdominal cavities
What does lateral folding close?
Foregut and hindgut
Which gut is the last to close?
Midgut
What happens during cranial folding?
Formation of the foregut and defines the thoracic cavity, developing heart tube is displaced into the thoracic cavity
What is formed during caudal folding?
Hindgut, anus and umbilical cord
When does the heart begin to develop?
Week 4
What is the normal development of the atrial septum?
Grows as 2 septa (primum/secundum),
When does communication between the 2 atrial septa continue until and what does this communication occur through?
Continues until birth through the foramen ovale
What are the relative pressures of the atria before and after birth?
Before: right higher, left lower
After: right lower, left higher
What are three causes of an atrial septal defect?
Excessive resorption of septum primum
Absent septum secundum
Patent foramen ovale
What are the 2 different types of ventricular septal defect?
Muscular defect- most common and least severe
Membranous defect- less common and most severe
What happens in transposition of the great vessels?
Aorta exits right ventricle and pulmonary trunk exits left ventricle causing deoxygenated blood to be carried around the body
What are the 4 factors in Tetralogy of Fallot?
Pulmonary stenosis, hypertrophy of right ventricle, VSD, overriding aorta
