Embryology Flashcards
If something goes wrong with the development of an embryo, what may happen?
The child may be born anatomically different to other children.
If abnormalities occur at a very early stage, this is usually ………… and will not result in a ……….. ……..
fatal
live birth
Between which stages does embryology not occur?
Fertilisation and implantation
After fertilisation, the ovum divides many times to produce smaller cells. What is this bundle of cells called?
Morula
What is the Morula attached to?
Nothing, it is floating freely in the uterus, therefore is getting no nutrition.
The morula cannot grow but it can develop. What does it develop into?
It develops into a blastocyst.
Around what day can a blastocyst be seen?
day 5-7
What is a blastocyst, and what is inside?
It is a sphere of cells, containing an inner cell mass (a collection of cells at one side of the ring) and a space in the middle.
Another space (amniotic cavity) forms within the inner cell mass. What does the inner cell mass become?
It becomes the embryo.
What is a trophoblast?
It is the outer layer of cells on the blastocyst that later form the placenta.
To form the placenta, the trophoblast grows into the ……….
Uterus
What is the ectoderm?
The most exterior of the three primary germ layers formed in the early embryo.
Another layer of cells forms around the space in the blastocyst. What is it called?
The endoderm.
As we develop, an …………. ………. is formed between the cell mass (embryo) and the placenta.
extracellular matrix
The cells of the extracellular matrix secrete chemicals, causing them to break down into ……….. between the endoderm and ………….
holes
placenta
What is the developing placenta called?
Cytotrophoblast
What 8 things will the ectoderm develop into?
Epidermis of skin, hair and nails Mammary, sweat and sebaceous glands Central nervous system Peripheral nervous system Enamel of teeth Lens of eye and parts of inner ear Sensory epithelium of nose, ears and eyes
At what stage is the earliest that we start to call the cells an embryo?
When the bilaminar disk is formed.
What is the conceptus?
The fertilised tissue.
Which is the only bit of the conceptus which will develop into the live birth?
The bilaminar disk (embryo).
What is the primitive streak?
A groove on top of the ectoderm that appears as the embryo develops.
What happens to cells from the base of the primitive streak?
They break off and migrate to lie in the space between the ectoderm and endoderm, creating the mesoderm.
What does the mesoderm develop into?
Whole musculoskeletal system Deep layers of skin Abdominal and chest walls and lining Walls of bowel (not lining) Urogenital system
By day …….. there is a trilaminar disk.
17
In which two places does the mesoderm not separate the ecto and endoderm?
The head end of the embryo and an area at the back of the other end of the embryo.
What will the joining of the ecto and endoderm at the head of the embryo go on to develop into?
The mouth.
What will the joining of the ecto and endoderm at the back of the embryo go on to develop into?
The anal canal and the orifice for the urethra.
And in female embryo the vagina.
What does the endoderm develop into?
Epithelial lining of GI tract, respiratory tract and urinary bladder
Parenchyma of thyroid gland, parathyroid gland, liver and pancreas
Epithelial lining of tympanic cavity & auditory tube
Plays a part in development of notochord
How does the notochord form?
A tube develops from the end of the primitive streak and extends towards the cranial end.
the tube fuses with the endoderm to become a groove in the endoderm layer. The plate then folds to become a tube again- the notochord.
What does the notochord go on to priduce?
It plays a central role in further development of the midline.
Cells on the ectoderm start to develop differently once the notochord forms. What is this development driven by?
Chemicals released from the notochord.
………….. tissues differentiate from the ectoderm and thicken into the neural plate.
Neuroectodermal
The neural plate ……….. separates the ectoderm from the neural plate.
border
What does the neural plate develop into?
The brain and spinal chord.
What does the neural plate border develop into?
The sensory part of the nervous system.
Why does folding of the neural plate occur?
As the cells grow, there isn’t enough space on the outer surface of the embryo to accommodate all the cells.
As the neural plate bends dorsally, the two neural plate borders meet, fusing together to form neural crest cells. Below this, the ………… ……… forms.
Neural tube
After the fusing of neural plate borders, what happens to the ectoderm and what does it become?
The ectoderm fuses on top of the neural crest cells, and becomes the skin (epidermis).
What do the neural crest cells form?
The sensory parts of the nervous system.
What does the neural tube develop into?
The brain and spinal chord (CNS).
What happens if the fusion/closure of the neural tube doesn’t take place at the lower end of the spine?
The child has spina bifida.
What happens if the fusion/closure of the neural tube doesn’t take place at the upper end of the spine?
The brain doesn’t develop properly. The child is born without the cerebral cortex (anencephaly)- fatal.
What are somites?
Blocks of mesoderm that are located on either side of the neural tube
What is each somite supplied by?
A single spinal nerve.
What do somites/paraxial mesoderm become?
The myotomes (muscles), sclerotome (cartilage and bone) and dermatome (dermis of skin).
Paraxial mesoderm.
What is the mesoderm closest to the notochord known as?
What is the mesoderm slightly further away from the notochord known as?
Intermediate mesoderm.
What is the mesoderm furthest away from the notochord known as?
Lateral mesoderm.
As mesoderm develops, where do Intra-embryonic body cavities develop?
In the layer of mesoderm on inside of ectoderm and outside of endoderm.
The space between the ectoderm/mesoderm and mesoderm/endoderm forms the …….
space surrounding the lungs, heart and bowel in body (pleura, pericardium and peritoneal cavity).
As the intraembryonic cavities grows, what happens to the somites?
They are developing into separate groups of cells which will form different parts of the body.
The ……………. mesoderm develops into the urogenital system (the kidneys, gonads & respective duct systems).
Intermediate
What does the lateral mesoderm develop into?
It splits into 2 layer:
outer layer- covers inside of chest & abdominal walls (somatic parietal layer)
other layer- covers organs in thorax & abdomen (splanchnic visceral layer).
Folding of the embryo must take place for development. Why does the embryo fold?
Some surfaces grow quicker than others. The ectoderm grows faster than the endoderm, and that is why it folds to form the CNS.
How does the embryo with skin all around form?
More lateral folding takes place. The upper layer of ectoderm wraps downwards around the entirety of the embryo.
How does the amniotic sac form?
When the ectoderm fully wraps around the other parts of the embryo, an extraembryonic cavity forms.
As the cells grow at different ………., the embryo undergoes further folding. The heart, brain and mouth move into position.
Rates
Summarise what happens in the 1st week
Fertilization
Formation of morula and blastocyst
Summarise what happens in the 2nd week
Implantation of blastocyst
Formation of bilaminar embryonic disc & early placenta
Summarise what happens in the 3rd week
Differentiation of cell layers to form trilaminar embryonic disc
Summarise what happens in the 4th week
Folding of embryo and continuing development of 3 germ layers
Summarise what happens in the 5th-8th week
Development of all organs
Summarise what happens by end of 8th week
Embryo looks like an adult and is called foetus
Growth becomes prominent feature.
