DEVELOPMENT Flashcards
what is gastrulation ?
It is a process by which the embryo changes from being a single layer of cells to a multilayer of cells.
What events happen after fertilization ?
The fertilised egg starts to divide (cleavage) and creates a
hollow ball of cells which undergoes the process of gastrulation. Organs begin to form (organogenesis) and then will continue to grow and refine after hatching (fetal period in humans). Metamorphosis, the process of becoming sexually
mature can be thought of as being equivalent to puberty. When mature,gametes are produced to allow the cycle to begin again
what is the full term in pregnancy in weeks ?
38 weeks counted from the last menstrual period
when is development counted from ?
from fertilization
What cells are affected by mutations occurring later on ? give an example
Somatic cells and will have no effect on subsequent generations and evolution eg DMD, brain tumour
what cells are affected by mutations occurring early on ? give an example
affects both somatic and germ cell lines and therefore the mutation can be passed on eg haemophilia
why are the pituitary glands called the adenohypophysis(anterior) and the neurohypophysis (posterior) ?
Because the adenohypophysis (anterior pituitary) and neurohypophysis originate from different embryonic structures. This explains how the structure and function differ in the two regions of the pituitary gland. the anterior is fromed from the mouth area and the posterior from the developing brain tissue
how long is pre-organogenesis and what happens
12-24 hours between cleavages and is the formation of 2 layers, bilaminar germ disc
what is the bilaminar germ disc ?
formed when the inner cell mass forms two layers seperated by an extracellular basement membrane. The outer one is called the epiblast and the inner one is called hypoblast go on to form the embryo
when are these two layers distinct in embryos
from day 8
what is a conceptus ?
a hollow ball of cells within an embryonic pole
what is an embryo ?
called an embryo when organ structures are present
what happens during gastrulation and when does it happen ?
organogenisis and when the embryo is 15 days. Get the basic body plan
what is the fetus
period of rapid growth and refinement eg going from a hand plate to fully formed fingers as well as cellular function.
define oocyte
sex cell that has not finished undergoing meiosis
define ovum
mature sex cell. completes meiosis on fertilization
define zygote
fertilized ovum with male and female nuclei. Two sets of information in the nucleus
define morula
ball of cells. no cell growth. hyperplasia only ( enlargement of a tissue without increasing in size )
define compaction
process of creating a tight ball of cells
define blastomere
individual cell that makes up the morula
define balastocyst
hollow ball of cells with a thickening at one end when viewed as a cross section
define blastocoel
the fluid filled hollow withing the blastocyst
what triggers the formation of an ovum
triggered by fertilization and forms an ovum and a polar body
what is the purpose of the polar body
damaged set of chromosomes sent to the polar body. the polar body has little cytoplasm and will apoptose (programmed cell death )
which part of the uterine tube does fertilization take place ?
ampulla
what is the zona pellucisa and till when is it present
it is the thick extracellular coat around the zygote and is present till it reaches the uterus
does cell division increase the size of the cell
no it increases only the number of cells
where does implantation take place and what is implanted
the blastocyst is implanted in the upper quadrant of the uterus
what is the inner cell mass and when is it identifiable
group of cells that contribute to the embryo. It is identifiable at 4-6 days of human gestation
what is the epiblast
outer layer of cells that go on to form embryonic tissue. surrounded by the amniotic cavity
what is the hypoblast
primitive endoderm ( inner layer). Gives rise to extraembryonic tissue and faces the yolk sac
functions of extraembryonic tissues
nourishment, protection, waste disposal
types of extraembryonic tissue and their functions
amnion- protective, allows the embryo to float. prevents drying out and provides protection from mechanical damage
allantois- waste disposal/collection
chorion- blood vessels for exchange with external environment
placenta- organ with maternal and fetal blood vessels
what are the critical periods for development and why
pre-organogenesis- week 2, death can occur
embryonic period- week 3-8, major malformations may occur
fetal period- week 9-38, functional defect and minor malformations
what are the critical periods for organ system developments
neural- embryonic period
heart
when does gastrulation take place
12-15 days
what are the three layers in the gastrula and where they are found
ectoderm(outer)- skin and nervous system
mesoderm(middle)-internal organs
endoderm(inner)- internal linings eg blood vessels,gut lining
what is the primative streak and what is its function
primative streak-it is a structure that forms during early stages and is like a groove. cells move through the streak to form the mesoderm and endoderm
what happens to the cells during gastrulation
the epiblast cells converge on the primative streak
the individual poliferating cells move through the primative streak and displace the hypoblast to create the endoderm
later cells move through to create the mesoderm
what is hypertrophy
cellular growth which creates thickened tissues as the cells grow in size
what is hyperplasia
cell division which increases cell number
how do cells know whether they are outside or inside
cells outside the blastocyst have contacts on 2 sides whereas cells in the inner cell mass have more contacts
what happens during long range signalling
long range signals often creates gradients where cells will behave differently based on where they are on the gradient. this type of signal is a morphogen.
what happens during short range signalling
cells can react to their own signals (autoregulation) or to signals from neighbouring cells. this local signalling can be inhibitory or inducing
