Special Topics: 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 (stomach/tummy)
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?
the outermost layer of cells or tissue of an embryo in early development, or the parts derived from this
What is the mesodermal germ layer?
the middle layer of cells or tissues of an embryo, or the parts derived from this
What is the endodermal germ layer?
the innermost layer of cells or tissue of an embryo in early development, or the parts derived from this
What germ layers is the integumentary system derived from?
Ectoderm and mesoderm
What germ layers is the skeletal system derived from?
Ectoderm and mesoderm
What germ layers is the nervous system derived from?
Ectoderm
What germ layers is the endocrine system derived from?
Ectoderm, mesoderm and endoderm
What germ layers is the respiratory system derived from?
Ectoderm and endoderm
What germ layers is the digestive system derived from?
Ectoderm and endoderm
What germ layers is the muscular system derived from?
Mesoderm
What germ layers is the cardiovascular system derived from?
Mesoderm
What germ layers is the lympathic system derived from?
Mesoderm
What germ layers is the urinary system derived from?
Mesoderm and endoderm
What germ layers is the reproductive system derived from?
Mesoderm and endoderm
Example of structures the ectoderm gives rise too
epidermis of the skin, nervous tissue including brain and spinal cord
Example of structures the mesoderm gives rise too
dermal layer of the skin, muscles, cardiovascular system, lymphatic system, kidneys, skeleton..
Example of structures the endoderm gives rise too
gut, reproductive cells, some glands
What is the first stage of Embryogenesis?
Fertilisation
What occurs after fertilisation?
Cleavage of the zygote and formation of the blastocyst
What is a sperm?
Male gamete
What is an egg?
Female gamete
How many sperm reach the egg?
200
What is capacitation?
removal of inhibitory molecules from the surface of the sperm that causes them to swim harder and faster towards the egg, which they are attracted to by chemotaxis and thermotaxis
What structural features does a sperm have that allows it to get inside an egg?
Enzymes, a tail and head
What layers does the sperm have to penetrate to reach the cytoplasm of the oocyte?
- Corona Radiata
- Zona Pellucida
- Plasma membrane of secondary oocyte
- Cytoplasm of secondary oocyte
What is the egg bigger than the sperm?
Because it contains all the developmental material for an embryo
What is the corona radiata?
outside layer of cells around secondary oocyte
What is the zona pellucida?
the fibrous mat structure between corona radiata and plasma membrane of secondary oocyte
What does the zona pellucida prevent?
ectopic pregnancy (when embryo starts developing outside of uterus)
What phase is the oocyte in when fertilisation occurs?
Metaphase II
Where does fertilisation occur?
Fallopian/uterine tube
What is polyspermy?
is the fertilization of an egg by multiple sperm, and the results of such unions are lethal
What is the second stage of Embryogenesis
Cleavage of the zygote and formation of the blastocyst
What occurs after the cleavage of the zygote and formation of the blastocyst
Implantation
What is cleavage?
the rapid mitotic division post fertilisation
What is formed on the first day post fertilisation?
A blastomere
What is a blastomere?
the two smaller cells that are produced from the division of the fertilised egg
Does the volume of a cell change during cleavage?
No, it has the same volume but more cells are produced in a smaller space
What is formed on the fourth day post fertilisation?
A Morula
What is a morula?
a loosely packed ball of cells
What is formed on the fifth day post fertilisation?
A blastocyst
What is a blastocyst?
Hollow ball of cells which contains 2 tissue types. It is a tighter ball of cells/increased adhesion to form the first epithelial layer
What are the two tissue types in a blastocyst and what do they create?
The inner cell mass (ICM) which creates the embryo and the Trophoblast cells which create embryonic tissues like the placenta
What is the hollow part of the blastocyst called?
The blastocyst cavity
How is the blastocyst cavity formed?
sodium pump puts water into blastocyst via osmosis which forms a cavity
What is the main visual difference between the morula and blastocyst?
Blastocyst has cavity
What is the third stage of Embryogenesis?
Implantation
What occurs after implantation
development of the trophoblast
What is the endometrium?
Inner lining of the uterus
What happens to the endometrium if fertilisation does not occur?
It sheds away in menstruation
What helps the oocyte move into the uterus
Muscular and cilia movement in the fallopian tube
What happens to the blastocyst 5-6 days after fertilisation?
Blastocyst hatches out of zona pellucida to plant into the endometrium layer of the uterine cavity
How does the blastocyst get into the uterine wall?
It secretes enzymes that allow it to burrow into the uterine wall and eventually become fully surrounded by maternal tissue
What is the fourth stage of embryogenesis?
Development of the trophoblast
What happens after the development of the trophoblast?
Development of the bilaminar embryonic disc
What is the trophoblast?
Outer layer of the blastocyst
What is the placenta made of?
both maternal and embryonic tissues
What does the trophoblast differentiate into around 1 week postt fertilisation?
It differentiates into Syncytiotrophoblast and
Cytotrophoblast
What are Syncytiotrophoblast
cells that secrete enzymes to allow blastocyst to firmly implant into the uterine lining
What is the Cytotrophoblast?
Inner cellular layer of the trophoblast
What do Syncytiotrophoblast and Cytotrophoblasts give rise too?
form the chorion (the embryonic portion of the placenta - extra embryonic tissue)
What is function of the placenta?
to create the interface between the mother and the child, and allows for exchange of materials between the two. Villi within the chorion create a large surface area to facilitate this
What is the uterine endometrium?
the uterine wall
What hormone does trophoblast release?
human chorionic gonadotropin
What is human chorionic gonadotropin
A hormone that prevents the endometrium from shedding in menstruation which allows the embryo to implant
What does a pregnancy test test fo
human chorionic gonadotropin in urine
What is the fifth stage of embryogenesis?
the development of the bilaminar embryonic disc
What occurs after the development of the bilaminar embryonic disc
the development of the yolk sac
What does the ICM form?
the bilaminar embryonic disc
What are the two types of internal cells in the ICM bilaminar embryonic disc?
Hypoblasts and epiblasts
What does the hypoblast form?
the endoderm
What does the epiblast form?
the ectoderm
What germ layer is not present when the bilaminar embryonic disc is developing?
the mesoderm
What is the amnion cavity?
A small cavity that appears in the epiblast
How is the amnion cavity formed?
epiblasts divide to form a dome made of simple squamous epithelium which fills with fluid
What is the amnion?
Layer of simple squamous cells that are formed by the epiblast, enclosing the amniotic cavity which eventually forms the amniotic sac
What is the function of the amniotic sac + fluid?
protection, regulates body temperature, prevents embryo from drying out, prevents tissues of embryo from joining to anything else, this is the region where you can get DNA
What is the amniocentesis
the process where the amniotic fluid from the amniotic sac is tested for abnormalities and infections
When does the Extraembryonic mesoderm start to form?
During the development of the bilaminar embryonic disc (day 12 post fertilisation)
What will the Extraembryonic mesoderm form?
the mesoderm germ layer and help form the placenta and chorion
Where is the blastocyst during the development of the bilaminar disc
buried right into the endometrium wall
day 12
What is the 6th stage of embryogenesis?
The development of the yolk sac
What occurs after the development of the yolk sac?
Gastrulation
What cell migrate, proliferate and cover the inner wall of the blastocyst cavity at day 9?
Hypoblasts
What is the exocoelomic membrane
the thin membrane lining the blastocyst cavity made of hypoblast cells that will form the yolk sac
What does the embryo sit between
the yolk sac and amniotic cavity
What is the function of yolk sac?
Supplies nutrients and energy, source of blood cells, contains first germ cells for gonads, forms part of the gut, shock absorption, prevents desiccation
What are lacunar networks?
the small holes in the Syncytiotrophoblast and eventually they invade and form the complete structure with the maternal sinusoid (blood network) creating the placenta.
Why does the placenta have a large surface area?
The placenta has a very large surface area to allow for max exchange of materials between the mother and foetus
What is the maternal sinusoid?
are maternal capillaries close to where the embryo is implanting. These are encouraged to expand to form sinusoids and they fuse with lacunar networks. Network connects the embryo to the maternal blood supply. Beginning the formation of the placenta (nutrients in and waste out)(also releases hormones that prevent the rejection of the embryo because the embryonic tissue is genetically different from the mother)
What is the 7th step of embryogenesis?
gastrulation
means “to form gut”
What occurs after gastrulation
the formation of the notochordal process
What is gastrulation
When the 3 germ layers are laid down and the dramatic movement of cells so 2D disc forms 3D structure
What is the connecting stalk?
bilaminar embryonic disc is attached to trophoblast cells by connecting stalk (embryo is still attached to the ectoderm)
What indicates the gastrulation is about to occur?
the formation of the primitive streak
What is the primitive streak?
A faint groove on the dorsal surface of the epiblast
How is the primitve streak formed?
the dorsal surface of epiblast elongates from the posterior to the anterior of embryo – it establishes where the head and tail will be. It starts as a faint groove which elongates.
Where do cells from the ectoderm migrate to in gastrulation?
Cells from the ectoderm migrate to lie above the underlying endodermal cells to form mesoderm
What is invagination?
When cells of the epiblast move below the primitive streak and detach from the epiblast forming the mesoderm (this is a loosely organised connective tissue)
What is the 8th stage of embryogenesis?
The formation of the notochordal process
What occurs after the notochordal process
neurulation
What is the primitive node?
A swelling at the head end of the primitive streak
What is the notochordal process
it is the precursor to the notochord that is a hollow tube of cells
How is the notochordal process formed
About 16 days post fertilisation mesodermal cells migrate towards the head end and form a hollow tube of cells in the midline called the notochordal process
What is the notochord?
At day 22-24, the notochordal process forms a solid rod of cells (the notochord)
Function of notochord
It is an inducer - tells tissues what organ to become by releasing chemicals. Causes mesodermal cells to become ventral bodies and ectoderm above to form the neural plate
What is the neural plate?
the ectoderm cells above the notochord that thickin
What does the neural plate develop into?
Flat group of ectodermal cells that develop into the brain and spinal cord
What is organogenesis
Phase of embryonic development which causes the formation of organs (caused by the notochord)
What is the 9th stage of embryogenesis?
neurulation and somites
What occurs after neurulation and somites
embryonic folding
What is neurulation?
the formation of the neural tube (started by notochord)
What begins neurulation?
the formation of the neural groove
How is the neural tube formed?
Neural plate thickens and depresses to form the neural groove, the edges rise up to form the neural folds and eventually it sinks down and pinches off as a separate neural tube (BELOW ectoderm)
What does the neural tube form
brain and spinal cord
What are neural press cells?
cells that migrate away from the neural tube when it is fully submerged in the mesodermal layer and will form tissues like melanocytes (skin pigment etc.)
What happens to the neural tube 4 week post fertilisation
anterior end of the neural tube gives rise to 3 enlarged areas which will give rise to the brain i.e. the forebrain, the midbrain and the hindbrain.
What is the notochord making form at the same time of the formation of the neural tube
the lateral mesoderm (either side of the notochord) is forming somites
What are somites?
cuboidal like structures that form in parallel pairs either side of the notochord and they will eventually form the vertebrae of backbone and muscle in back. Differentiates into three different structures/regions
What is the dermatomes?
top of the somite which will give rise to connective tissue
What is the myotomes?
middle of somite which will give rise to skeletal muscles on our back, neck and limbs
What is the sclerotome?
lower somite will give rise to vertebrae and ribs
What is the 10th stage of embryogenesis?
Embryonic folding
What happens as the embryo begins to fold?
the gut is formed
How does embryo fold to form a tube?
Embryo folds laterally
How is the gut formed?
lateral folding of the ectoderm – it folds down and around the central column, surrounding the mesodermal layer with the endoderm in the middle which will form the gut
What is the connecting stalk the precursor of?
the umbilical cord
What is a cranial fold?
when the head bends down
What is a caudal fold?
when the back bends down
What parts of the gut are formed due to embryonic folding and in what order
The mid gut is formed first (where the yolk sac is)
Afterwards, the fore and reargut are formed
What is the dorsal ectodermal layer continuous with in embryonic folding?
Amnion
What is the endodermal ventral layer continuous with in embryonic folding?
Yolk sac
What happens to the cloacal membrane at 7 weeks post fertilisation
it dissolves (where anus will be)
What happens to the Oropharyngeal membrane at 4 weeks post fertilisation
it dissolves (where the mouth will be)
What merges to form future umbilical cord?
Connecting stalk and yolk sac
what is the embryo completely surrounded by due to lateral folding?
the amniotic cavity
What does lateral folding mean?
Lateral folds come down from the amniotic layer and invade the yolk sac and the two sides of the fold connect which means the gut has formed a complete tube
What are the pharyngeal arches and how many are there?
pouches on the outside of the embryo (form either side of the future head and neck) that give rise to structures in the head
there are 6 pharyngeal arches (4 obvious and 2 less obvious)
What does the otic placode give rise too?
makes the ear
What does the optic/lens placode give rise too?
makes the eye
What does the first pharyngeal arch give rise to?
The mandible
What is within the pharyngeal arches?
pharyngeal pouches
What does the pharyngeal pouches do?
connects to the oesophagus which gives rise to the pharynx (throat)
What is the heart prominence
A ventral projection at 28 days post fertilisation
