L11- Early embryology 2

Question 1

outline the broad stage of early embryology

Answer 1

1. fertilisation and implantation
2. gastrulation
3. neurulation
4. segmentation- somites
5. folding

Question 2

a zygote

Answer 2

single cell formed when egg and sperm cell fuse- fusion is known as fertilisation

Question 3

cleavage- first cell division- occurs

Answer 3

within 24-30h after fertilisation

Question 4

by late cleavage what is formed

Answer 4

morula (32 cells)

Question 5

when does blastulation occur

Answer 5

day 4

Question 6

blastulation

Answer 6

2 types of cell are produced

• outer cell- trophoblast cells
• inner cell mass

Question 7

compaction

Answer 7

first cavity forms within blastocyst- blastocoel- pushes inner cell mass to one side

Question 8

after blastulation

Answer 8

blastocyst hatches from zona pellucida

Question 9

inner cell mass differentiates into

Answer 9

epiblast- aminiotic cavity

hypoblast- primitive yolk sac

Question 10

implantation occurs

Answer 10

on day 6-7

Question 11

summary of zygote to embryoblast

Answer 11

Question 12

gastrulation starts on

Answer 12

day 16 (week 3)

Question 13

during gastrulation what occurs

Answer 13

production of germ layers

Question 14

name the germ layers

Answer 14

ectoderm

mesoderm

endoderm

Question 15

ectoderm

Answer 15

epidermis, hair, nails, brain, spinal cord, peripheral NS

Question 16

mesoderm

Answer 16

muscle, bone, connective tissue, notochord, kidney, gonads, circulatory system

Question 17

endoderm

Answer 17

epithelial lining of the digestive tract

Question 18

first step of gastrulation

Answer 18

formation of primitive streak

Question 19

primitive streak determines the

Answer 19

midline of the body

• should have mobile cilia which mean the body structures are on the right side of the body

Question 20

prior to gastrulation the embryonic disk is

Answer 20

bilaterally symmetrical

• but int he body clear differenc ebetween left and right side

Question 21

situs invetus

Answer 21

• Complete mirror image viscera
• Commonly exults in immobile cilia
  
  • Infertile
• No associated morbidity
• Problems arise if there is both normal and mirror image disposition

Question 22

immotile cilia during gastrulation mean

Answer 22

waft organs into the right direction

Question 23

during gastrulation the hyboblast is replaced and the epiblast differentitated into the trilaminar disk

Answer 23

ectoderm

mesoderm

endoderm

Question 24

directly beneath the primitive the streak in the mesoderm what is formed

Answer 24

the notochord

Question 25

when does the notochord form

Answer 25

week 4

Question 26

the notochrod

Answer 26

notorchord helps define major axis of the body and are important in neurulation (triggers it)

Question 28

neurulation occurs

Answer 28

in two stages

Question 29

stage 1

Answer 29

formation of neural tube

Question 30

second stage of neurulation

Answer 30

Notochord also causes the mesoderm to subdivide and differentiate

Question 31

in the first stage the notochord causes the ectoderm above to

Answer 31

thicken

Question 32

neural tube formation

Answer 32

1. Triggered by signals from the notochord 2. Just above the notochord the ectoderm thickens (neural plate) and forms a fold producing a neural groove 3. On either side of the neural groove folds will form 4. Neural folds come together until the two-fold touch each other 5. Neural tube found in the mesoderm dissociates from the rest of the ectoderm and the rest of the ectoderm will seal itself back together

Question 34

neural tube will become the

Answer 34

brain stem

Question 35

second stage of neureulation

Answer 35

Notochord also causes the mesoderm to subdivide and differentiate

Question 36

notochord comes from the

Answer 36

axial meosderm

Question 37

somites will come from the

Answer 37

paraxial mesoderm

Question 38

somites differentiate into

Answer 38

muscle, cartilage, bone, and dermis myotomes and dermatomes

Question 39

intermediate mesoderm si the

Answer 39

original of urogenital sysrtem- kidney, gonads, adrenal glands

Question 40

lateral plate mesoderm

Answer 40

heart, blood vessels, muscle in our organs

Question 41

after neurulation

Answer 41

segmentation and organisation of the mesoderm--\> giving rise to somites

Question 42

somites

Answer 42

organisation of oparaxial mesoderm into segements

Question 43

how many somite pairs

Answer 43

31

Question 44

first pair of somites appear

Answer 44

on day 20 in the occipital region

Question 45

somites give rise to

Answer 45

repeating structures such as... - vertebrae - ribs - intercostal muscle - spinal cord segments

Question 46

somites guide

Answer 46

innervation by myotomes

Question 47

somite derivative

Answer 47

dermatome myotome sclerotome

Question 48

dermatome

Answer 48

skin section - dermis

Question 49

myotome - muscles

Question 50

sclerotome

Answer 50

hard tissue section - bone

Question 51

31 somites and 31

Answer 51

spinal nerves

Question 52

why is embryonic folding important

Answer 52

before embryonic folding, the mouth is at the same level as the heart

Question 53

aim of folding

Answer 53

to present only ectoderm to the otuside world

Question 54

what folding achieves

Answer 54

Draws together the margins of the disk * Creating a ventral body wall * Pilling amniotic membranes around the disc * Embryo becomes suspended within the amniotic sac * Pulling connecting stalk enthralling * Also creates the primordium of the gut, put the heart and the primordium of the diaphragm in the right place and creates a new cavity within he embryo (GI tract)

Question 55

explain folding brefiled

Answer 55

the cranial (head) and caudal (back) fold in towards eachother - the endoderm (GI tract) folds into the middle, with the ectoderm covering around it - when the tract is formed, the defintitve yolk sac will be coming out from it - this yolk sac will be pinched off

Question 56

diagram of folding con..

Answer 56

Question 57

by the end of the 4th week

Answer 57

* Nervous system has started to form * Segments have appeared * Assigning tasks to specific cells * Embryo has folded, putting everything in right place