DEVELOPMENT

Question 1

what is gastrulation ?

Answer 1

It is a process by which the embryo changes from being a single layer of cells to a multilayer of cells.

Question 2

What events happen after fertilization ?

Answer 2

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

Question 3

what is the full term in pregnancy in weeks ?

Answer 3

38 weeks counted from the last menstrual period

Question 4

when is development counted from ?

Answer 4

from fertilization

Question 5

What cells are affected by mutations occurring later on ? give an example

Answer 5

Somatic cells and will have no effect on subsequent generations and evolution eg DMD, brain tumour

Question 6

what cells are affected by mutations occurring early on ? give an example

Answer 6

affects both somatic and germ cell lines and therefore the mutation can be passed on eg haemophilia

Question 7

why are the pituitary glands called the adenohypophysis(anterior) and the neurohypophysis (posterior) ?

Answer 7

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

Question 8

how long is pre-organogenesis and what happens

Answer 8

12-24 hours between cleavages and is the formation of 2 layers, bilaminar germ disc

Question 9

what is the bilaminar germ disc ?

Answer 9

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

Question 10

when are these two layers distinct in embryos

Answer 10

from day 8

Question 11

what is a conceptus ?

Answer 11

a hollow ball of cells within an embryonic pole

Question 12

what is an embryo ?

Answer 12

called an embryo when organ structures are present

Question 13

what happens during gastrulation and when does it happen ?

Answer 13

organogenisis and when the embryo is 15 days. Get the basic body plan

Question 14

what is the fetus

Answer 14

period of rapid growth and refinement eg going from a hand plate to fully formed fingers as well as cellular function.

Question 15

define oocyte

Answer 15

sex cell that has not finished undergoing meiosis

Question 16

define ovum

Answer 16

mature sex cell. completes meiosis on fertilization

Question 17

define zygote

Answer 17

fertilized ovum with male and female nuclei. Two sets of information in the nucleus

Question 18

define morula

Answer 18

ball of cells. no cell growth. hyperplasia only ( enlargement of a tissue without increasing in size )

Question 19

define compaction

Answer 19

process of creating a tight ball of cells

Question 20

define blastomere

Answer 20

individual cell that makes up the morula

Question 21

define balastocyst

Answer 21

hollow ball of cells with a thickening at one end when viewed as a cross section

Question 22

define blastocoel

Answer 22

the fluid filled hollow withing the blastocyst

Question 23

what triggers the formation of an ovum

Answer 23

triggered by fertilization and forms an ovum and a polar body

Question 24

what is the purpose of the polar body

Answer 24

damaged set of chromosomes sent to the polar body. the polar body has little cytoplasm and will apoptose (programmed cell death )

Question 25

which part of the uterine tube does fertilization take place ?

Answer 25

ampulla

Question 26

what is the zona pellucisa and till when is it present

Answer 26

it is the thick extracellular coat around the zygote and is present till it reaches the uterus

Question 27

does cell division increase the size of the cell

Answer 27

no it increases only the number of cells

Question 28

where does implantation take place and what is implanted

Answer 28

the blastocyst is implanted in the upper quadrant of the uterus

Question 29

what is the inner cell mass and when is it identifiable

Answer 29

group of cells that contribute to the embryo. It is identifiable at 4-6 days of human gestation

Question 30

what is the epiblast

Answer 30

outer layer of cells that go on to form embryonic tissue. surrounded by the amniotic cavity

Question 31

what is the hypoblast

Answer 31

primitive endoderm ( inner layer). Gives rise to extraembryonic tissue and faces the yolk sac

Question 32

functions of extraembryonic tissues

Answer 32

nourishment, protection, waste disposal

Question 33

types of extraembryonic tissue and their functions

Answer 33

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

Question 34

what are the critical periods for development and why

Answer 34

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

Question 35

what are the critical periods for organ system developments

Answer 35

neural- embryonic period | heart

Question 36

when does gastrulation take place

Answer 36

12-15 days

Question 37

what are the three layers in the gastrula and where they are found

Answer 37

ectoderm(outer)- skin and nervous system mesoderm(middle)-internal organs endoderm(inner)- internal linings eg blood vessels,gut lining

Question 38

what is the primative streak and what is its function

Answer 38

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

Question 39

what happens to the cells during gastrulation

Answer 39

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

Question 40

what is hypertrophy

Answer 40

cellular growth which creates thickened tissues as the cells grow in size

Question 41

what is hyperplasia

Answer 41

cell division which increases cell number

Question 42

how do cells know whether they are outside or inside

Answer 42

cells outside the blastocyst have contacts on 2 sides whereas cells in the inner cell mass have more contacts

Question 43

what happens during long range signalling

Answer 43

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.

Question 44

what happens during short range signalling

Answer 44

cells can react to their own signals (autoregulation) or to signals from neighbouring cells. this local signalling can be inhibitory or inducing