W9- Lecture 48- Basic Embryology

Question 1

name the stages from fertilisation onwards in embryonic development

Answer 1

Fertilisation

Zygote

Cleavage

Morula

Blastocyst

Gastrulation
(Ectoderm, Mesoderm ,Endoderm)

Organogenesis

Question 2

describe the cleavage stage of embryonic development

Answer 2

Cleavage- cells half the size of progenitor cell
alternate type of mitosis
After cleavage only one of the daughter cells contains lepton however the other doesn’t
Leptin stimulates production of gene transcription

Question 3

what is a zona pellucida ?

+ function

Answer 3

the thickmembrane surrounding an ovum before implantation.

barrier for cell division takes place in
And restricts size of replication
Will Strech and expand a certain size but restricts

Question 4

what is a morula ?

Answer 4

early-stage embryo consisting of 16 cells (called blastomeres) in a solid ball contained within the zona pellucida.
eventually secrete fluid

Question 5

Differnce between blastocyst and morula ?

Answer 5

Morula ball of cells smaller

Blastocyst contains fluid filled sac called blastocoel and also more cell no

Question 6

when does hatching from the zona pellucida take place ?( +what process causes)

where ?

Answer 6

Hatching takes the same amount of time that is does for the fertilised ball of cells takes to move from the ampulla to the uterus
Hatching occurs when the blastocyst stage pumps too much liquid and the zona pellucida breaks open

hatching will occur in the uterus

Question 7

when does gastrulation takes place ?

what is it

Answer 7

gastrulation takes place

Formation of there germ layers
Commitment into different developmental paths

Question 8

what is Organogenesis?

how does this aid Foetal development

Answer 8

organs are formed so when foetal

development happens the organs only have to increase in size and complexity

Question 9

describe the distribution of some cellular products e.g., leptin.

Answer 9

unequal due to cleavage producing blastomeres(2 cells )

Question 10

what is rotational cleavage/ what does it produce ?

Answer 10

each successive replication happens in a diff place

produces cell at 8-cell stage

Question 11

what is compaction ?

what does it form ?

Answer 11

Flattening of blastomeres(outside cells of embryo ) maximising cell-cell contacts.

Formation of tight junctions.
+ 16-cell morula

Question 12

what day do we expect the embryo enters the uterine cavity ?

Answer 12

approx day 6

Question 13

what is the trophoblast ?

Answer 13

– inner cell membrane

inside zona pellucida

Question 14

what do the external polarised cells cells develop into ?

Answer 14

Trophectoderm;

Question 15

what do the Internal non-polar cells develop into ?

Answer 15

Inner cell mass (ICM

Question 16

formation of which structure leads to hatching ?

Answer 16

Formation of blastocoel (fluid filled cavity )

Question 17

Trophectoderm develops into

Answer 17

syncytiotrophoblast(forms gap junctions) - spreads around blastocyst

Question 18

the Inner cell mass (ICM) develops into

Answer 18

Epiblast & Hypoblast

Question 19

what does the epiblast form ?

Answer 19

Embryonic epiblast then the
embryo
Amniocytes. Secrete fluid which form the amnion

Question 20

what does the hypoblast form ?

Answer 20

lines blastocoel form the yolk sac

Question 21

name all the structures the three germ layers form
Ectoderm
Mesoderm
Endoderm

Answer 21

Ectoderm
Epidermis
Nervous system
Pigment cells

Mesoderm	
Kidneys
Gonads
Bones
Muscle
Heart
Blood cells
(Part of most internal organs)

Endoderm
Lining of gut
Respiratory system

Question 22

what is pattern formation ?
+ examples
what does this involve ?

Answer 22

is the process by which a spatial and temporal pattern of cell activities is organized within the embryo” (Wolpert, 2002).

E.g.: Axis specification, formation of germ layers.

Involves the co-ordination of a variety of mechanisms of cellular communication

Question 23

what is induction of cells

Answer 23

Cell types specified under influence of other cell types.

Production of signals that bring about response in target cells.

Question 24

what is Morphogenesis?

e.g

what influences this

Answer 24

The achievement of developmental diversity by formation of different structures from the same initial structure.

E.g.: Gastrulation, neurulation, limb formation etc.

by signalling

Question 25

what is Juxtacrine or paracrine signalling ?

Answer 25

Juxtacrine (next to) or paracrine (longer distance) signalling

Question 26

what is a Morphogen?

name three

Answer 26

Morphogen is a signalling molecule that forms (an extracellular) concentration gradient.

E.g.’s include Hedgehog, Wingless, Activin

Question 27

what do qualities must receiving cells of a morphogen have ?

Answer 27

a) be competent to respond
b) detect inducing agent
c) quantify level of inducing agent.(to meet threshold )