(03) ST: Human Development Flashcards
what is embryogenesis?
the first eight weeks of development after fertilisation
transforming from single cell to organism with multi-level body plan
what four things are achieved in embryogenesis?
PATTERNING - cells acquire identity
MAJOR AXIS - anterior / posterior, dorsal (back) / ventral (tummy) defined
THREE GERM LAYERS
RUDIMENTS OF MAJOR ORGANS
name and define the three germ layers
ECTOderm = outside, skin + nervous system tissue
MESOderm = between (skeleton / muscle)
ENDOderm = inside (typically the gut)
Name the steps in the process of embryogenesis
Fertilisation
Cleavage + formation of blastocyte
Implantation
Development of Trophoblast
Gastrulation
Embryonic folding
Foetal Development
What is fertilisation?
Sperm + oocyte fuse, producing a DIPLOID zygote
path of sperm cell
corona radiata - the somatic cells outside of the egg
zona pellucida - fibrous mat, activates sperm
fuses with plasma membrane of secondary oocyte
through cytoplasm of secondary oocyte to get to the nuclei
what is cleavage?
relatively rapid type of cell division that occurs after fertilisation
the cell size DOES NOT INCREASE! literally cleaves
what is the morula?
a loosely packed ball of cells by day four of cleavage
(comes from the greek word for raspberry)
process from morula to blastocyst
cells pack closer together, greater adhesion, first epithelial layer forms as water flows inside ball of cells
some cellular differentiation - embryoblasts (inner cell mass) –> embryo, tropoblast cells (outside) eventually give rise to extra-embryonic tissues
processes from morula to blastocyte
cells packed, greater adhesion
first epithelial layer forms as water flows inside ball of cells
cellular differentiation - embryoblasts (inner) give rise to the embryo, tropoblast cells (outer) give rise to extra-embryonic tissue
describe blastocyst
ball of cells with a blastocyst cavity
embryoblasts = inner cell mass, trophoblasts on the outside
function of blastocyst cavity
gives some room for stuff to move around in relation to each other
where does fertilisation and cleavage occur?
fertilisation occurs in the uterine tube
early cleavage events also occur in the tube
developed into a blastocyst by the time it reaches the uterine cavity
implantation must occur in the uterine wall, about 6 days after fertilisation
development of trophoblast cells after implantation
forms the chorionic villi of the foetal placenta (required for nutrient / gas exchange with mother)
role = secrete enzymes to allow embryo to burrow into wall
keeps wall intact (secretes enzyme human chorionic gonadotropin (HCG) prevents menstruation)
what is gastrulation?
the developmental process where a blastula (1D layer of epithelial cells) transforms to a gastrula (multilayered and multidimensional)
basically, the formation of the three germ layrs
what is gastrulation?
the developmental process where a blastula (1D layer of epithelial cells) transforms to a gastrula (multilayered and multidimensional)
basically, the formation of the three germ layers
what is the bilaminar embryonic disc
two different tissue types in the inner cell mass - hypoblast (internal = primitive endoderm) and epiblast (external = primitive ectoderm)
gives rise to the embryo itself
describe the development of the amnion and yolk sac
the amnion develops from the epiblast, and the yolk sac from the hypoblast
(the bilaminar disc remains sandwiched in the middle of the two lobes - they are extraembryonic)
what is the connecting stalk
connects the bilaminar disc to the tropho / ectoderm cells
visible signs of the beginning of gastrulation
the formation of the primitive streak on the dorsal side of the embryo
in posterior to anterior direction
where is the future posterior of the embryo
where the bilaminar disc connects to the extra embryonic tissue by the connecting stalk is the future posterior
what happens in the process of the formation of the primitive streak
ectoderm cells rising up, moving in, and displacing the endodermal tissue underneath, forming the mesodermal layer
(three germ layers established)
what is the notochord
thick of rod of cells develops in mesoderm layer, defines where future backbone develops
describe the processes of embryonic folding
anterior and posterior folding (like a comma)
ectodermal lateral fold forming tube - gut on the inside, ectoderm on the outside, mesoderm in the middle, pinching off the yolk sac
the amnion now completely surrounds the embryo
by what time have all key organs been formed?
by around 8 weeks
define cell differentiation
the process were immature unspecialised cells take on individual characteristics, reaching their mature form and function
differentiated cells have limited divisions
what do stem cells do
replace themselves AND generates differentiated daughter cells
what are stem cells needed for?
growth
renewal
repair
name the four layers of the Stem Cell Hierarchy
totipotent
pluripotent
multipotent
nullipotent
example of a totipotent cell
zygote - capable of giving rise to ALL types of cells of the body and extra-embryonic tissue
examples of pluripotent cells
inner cell mass cells of blastocyst (or embryonic stem cell) - some divisions have taken place and cells have become committed to certain differentiation pathways
capable of giving rise to ALL cells in the body (but not extraembryonic tissue), or for trophoblasts, vice versa
examples of multipotent cells
within organs - can only give rise to a particular type of tissue or organ
eg. haematopoietic stem cell gives rise to all different types of cells in blood
define and give examples of nullipotent / unipotent stem cells
can only give rise to one cell type
eg. keratinocyte stem cells present in skin
