Specials - Early Human Development Flashcards
What is the function of embryogenesis?
To carry out patterning, define major axis, define three germ layers, form the rudiments of major organs
What is patterning in embryogenesis?
the process where cells acquire identity in space and time (laying down 3 main germ layers)
What are the major axis defined in embryogenesis
anterior (head), posterior (tail), dorsal (back), ventral (belly)
What process produces the three germ layers?
Gastrulation
What colour is the ectoderm on a fate map?
Blue
What colour is the mesoderm on a fate map?
Red
What colour is the endoderm on a fate map?
Yellow
What is the ectodermal germ layer?
Outside
Will give rise to the tissues on the outside of organs
Eg epidermis (Skin), spinal cord and brain
What is the mesodermal germ layer?
Between ectoderm and endoderm
Gives rise to all internal structures
Eg: Skeletal, CVS, lymphatic, kidneys and dermis
What is the endodermal germ layer?
Inside
Gives rise to the gut, reproductive cells and glands
What is fertilisation defined as?
The fusion of the nucleus of the sperm and nucleus of the egg to form a zygote
What is the process of fertilisation?
Sperm penetrates egg
Sperm and egg are both haploid, once fertilisation occurs, the nuclei fuse and form a zygote
Millions of sperm are released, but only approx 200 reach the egg
As sperm swim through female reproductive system, they undergo capacitation
What is capacitation?
A process which takes off inhibitory molecules present on the sperm, encourages them to swim harder and faster towards the egg
Due to what cues is the sperm able to move towards the egg?
Chemoattractant and thermotatic cues released by the corona radiata
This is how the sperm knows which Fallopian tube to enter into (every month an egg is released from alternating sides of the Fallopian tube and hence the sperm does not waste any energy going from one side to to the other)
What is the head of the sperm covered by?
The acrosome
What is the function of the acrosome?
Contains enzymes which allows the sperm to penetrate the layers surrounding the egg
Ie the corona radiata and zona pellucida
What does the mid piece of the sperm contain?
Many mitochondria, provides lots of energy for sperm to swim to egg
What is the corona radiata?
First layer of cells surrounding the egg which the sperm must penetrate
What is the purpose of the corona radiata?
Releases hormones which act as a chemoattractant (mentioned previously)
What is the role of zona pellucida?
To prevent multiple sperm penetrating the egg
What is the path of the sperm cell?
Corona radiata —>
Zona Pellucida —>
Plasma membrane —>
Cytoplasm of oocyte
What happens on day 0?
Fertilisation
what happens of day 1?
A process called cleavage
What is cleavage?
It is defined as rapid mitotic division which occurs post fertilisation.
It divides the embryo into smaller and smaller blocks so in the next stage it can cause some interesting patterns and shapes (lego block analogy)
What happens on day 2?
The zygote divides to produce two smaller cells called blastomeres
On what day are blastomeres formed?
Day 2
What happens on day 3?
The blastomeres divide again forming a total of 4 cells
What happens on day 4?
By day 4, a loosely packed ball of small cells called the morula are produced
What happens on day 5?
By day 5, a densely packed ball of cells called the blastocyst is formed
On what day are blastocysts formed?
Day 5
How is the blastocyst cavity formed?
Sodium pumps in the cells pump sodium ions into the blastocyst which causes water to follow by osmosis
This forms the blastocyst cavity
When is the morula formed?
day 4
What 2 cell types does the blastocyst form?
Inner cell mass (embryo blast)
Trophoblast
What is the trophoblast?
Cells on the OUTSIDE which produce the placenta, chorion and extra embryonic tissues
TROPHOBLAST DOES NOT CONTRIBUTE TO THE DEVELOPMENT OF THE EMBRYO
What does the inner cell mass do?
Produces the embryo (provides nutrients and support for the embryo)
The cavity allows the cells to move around and produce a 3d embryo
What type of epithelia is present in the Fallopian tube?
Ciliated simple columnar epithelium
In order to move the egg
Describe the process of implantation
- The fertilised egg wafts by cilia into the fallopian tube- Contains ciliated simple columnar epithelium (thus has cilia for movement)
- Cleavage occurs when the fertilised embryo moves down the fallopian tube
- Implants into the wall of the of the endometrium
What would happen if two eggs were released at the same time?
non-identical twins would be produced
What would happen if a single egg splits
identical twins are formed
On what day does implantation occur?
day 6
What is developed during week 2?
Trophoblast Bi-laminar embryonic disc Amniotic cavity yolk sac lacunae
Describe the development of the trophoblast
OUTSIDE
The trophoblast gives rise to the placenta
The cells in the trophoblast give rise to two other cells:
Syncitiotrophoblast and cytotrophoblast
Both of these cell types will give rise to the placenta and
release enzymes which will help them burrow into the uterine wall
They also release HCG which prevents shedding of the endometrium and is detected in pregnancy tests (urine or blood)
Describe the development of the bi-laminar embryonic disc
Contributes to the development of the embryo
The inner cell membrane differentiates into the EPIBLAST AND HYPOBLAST to form this bi-laminar layer
What does the epiblast do?
gives rise to the ectoderm (blue)
What does the hypoblast do?
gives rise to the endoderm (yellow)
Describe the development of the amniotic cavity
The cells of epiblast divide and form a dome like structure
It gives rise to the amniotic cavity which will fill with fluid
What is the function of the amniotic fluid?
Regulate body temp, protect, prevents the embryonic tissue sticking to other tissues and drying out (keeps it MOIST)
It eventually will envelop the developing embryo
Describe the development of the yolk sac
During implantation, cells in the hypoblast proliferate and migrate around the inner wall of the blastocyst cavity
This forms the yolk sac
What is the function of the yolk sac?
To provide nutrients to the developing embryo
Where is the yolk sac located?
Within the blastocyst cavity
What is the yolk sac the source of?
Primordial germs cells, blood cells and the gut
How are the lacunae formed?
The syncitiotrophoblast forms small spaces called lacunae
These lacunae eventually fuse forming lacunar networks
What are maternal sinusoids?
Dilated maternal capillaries close to where the embryo is implanting
What is the function of the maternal sinusoids?
To connect the embryo to the maternal blood supply
Allows nutrients to be deliver to the embryo and waste products to be removed
What happens in weeks 3-4?
Gastrulation Notochordal process Neurulation Embryonic folding Pharyngeal arches
What is gastrulation?
The process in which the 3 germ layers are established
Describe the process of gastrulation
Begins by the development of the primitive streak (a groove on the dorsal surface of the ectoderm)
During gastrulation, cells from the ectoderm migrate down to lie above the endoderm. These migrating cells form the mesoderm
The mesoderm is loosely packed unlike ecto & endoderm
Describe the notochordal process
As the primitive streak forms, the ectodermal cells migrate down to produce the mesodermal cells
This induces the notochordal process by moving towards the head of the embryo
What is the notochordal process (structure of it)?
Is a hollow tube of cells which eventually form a solid rod of cells called the notochord
What is the function of the notochord?
It can tell other tissues what to become
It causes the induction of tissue differentiation as the notochord sends signals to develop into certain organs
How is the neural plate formed?
Thickening of the ectodermal cells above the notochord
These cells become tall and column like
What does the notochord induce?
Neurulation
What is neurulation?
Neurulation is the formation of the neural tube
Describe how the neural tube forms
Neural plate thickens
Neural groove forms
Neural fold forms
Neural folds connect up and fuse to form the neural tube
What does the neural tube eventually give rise to?
The brain and spinal cord
What does the notochord instruct to produce somites?
The lateral mesoderm
What 3 structures do the somites develop into?
Myotome
Dermatome
Sclerotome
What does the dermatome develop into?
Connective tissue (DERMIS)
What does the Myotome develop into?
Back and neck
What does the sclerotome develop into?
Vertebrae and ribs
Describe embryonic head and tail folding?
Becomes a 3d structure
Folding of lateral sides, head and tail come together to from a comma shape
Folds around itself
Head and tail end fold in to each other, future mouth
Clocal = anus
The yolk sac and connecting stalk come together to form the future umbilical cord
Describe lateral folding of the embryo
Lateral sides of the amniotic fluid cavity come down to form a tube
Causes embryo to be enveloped within the amniotic cavity
This will give rise to the gut
What is the 10th stage of embryogenesis?
Embryonic folding
What is a cranial fold?
When the head bends down
What happens to the cloacal membrane at post 7 weeks fertilisation?
It dissolves (where anus will be)
What are pharyngeal arches?
Pouches on the outside of the embryo
Gives rise to structures in the head (JAW)
Will form either side of the head and neck that
How many pharyngeal arches are there/
6
4 are obvious
2 are less obvious
What does the otic placode give rise to?
The ear
What does the optic placode give rise to?
The eye
What does the first pharyngeal arch give rise to?
The mandible (JAW)
What do pharyngeal pouches do?
Connect oesophagus which gives rise to the pharynx (throat)
What is the heart prominence?
A ventral projection at 28 days post fertilisation
