embryology

Question 1

Define pre-embryonic development

Answer 1

fertilisation-2nd week

Question 2

Define embryonic development

Answer 2

3rd week- 8th week

Question 3

Define foetal period

Answer 3

9th week- 38th week

Question 4

What changes take place as the zygote travels down the fallopian tube to the uterus

Answer 4

Zygote forms after spermatozoa fuses with the oocyte at the ampulla

1st cleavage forms to blastomeres

3 Further cleavages occur so by the time we have reached the end of the fallopian tube the morula(16 cells) forms

In the uterus morula turns into a blastocysts by compaction

Blastocyst hatches from zona pellucida and the trophoblast(outer layer of blastocyst) adheres and begins to implant into the endometrium

Takes 1 week

Question 5

Define zygote

Answer 5

fertilized egg cell that results from the union of a female gamete

Question 6

Define cleavage

Answer 6

the first few cellular divisions of a zygote

Question 7

Define zona pellucida

Answer 7

the glycoprotein membrane surrounding a mammalian ovum before hatching and implantation.
prevents anymore sperm getting in and prevent growth of blastomere/cyst

Question 8

Define morula

Answer 8

solid mass of blastomeres resulting from a number of cleavages of a zygote

Question 9

Define ovary

Answer 9

Female reproductive organ where ova are produced

Question 10

Define fallopian tube

Answer 10

pair of tubes in which ova from the ovaries travel to the uterus

Question 11

Define uterus

Answer 11

Female organ in which offspring are conceived and gestate before birth

Question 12

Formation and implantation of blastocyst

Answer 12

Cells within blastocyst secrete tissue fluid
this separates the cells into an outer (trophoblast) and inner mass (embryoblast)
as well as forming the blastocyst cavity

Question 13

Describe the formation of the bilaminar disc

Answer 13

The inner cell mass(embryoblast) flattens and differentiates into 2 layers the epiblast and the hypoblast.

Question 14

Define bilaminar disc

Answer 14

Bilaminar blastocyst or bilaminar disc refers to the epiblast and the hypoblast, evolved from the embryoblast

Question 15

Define germ layer

Answer 15

group of cells in an embryo that interact with each other as the embryo develops and contribute to the formation of all organs and tissues

Question 16

Define and state the derivatives of the ectoderm, mesoderm, endoderm

Answer 16

Ectoderm outermost layer of trilaminar disc, forms structures that maintain contact with outside world eg nervous system, epidermis, cornea and lens of the eye.

mesoderm middle layer of trilaminar disc forms supporting tissues eg muscle, cartilage, bone, vascular system(inc heart and vessels), smooth muscle, notochord

endoderm lower layer of trilaminar disc, forms internal structures eg epithelial lining of GI tract/urethra/bladder/etc, respiratory tract, parenchyma of glands, liver, pancreas.

Question 17

Define primitive streak

Answer 17

The faint streak on the trilaminar disk signalling gastrulation

Question 18

Define gastrulation

Answer 18

embryo transforms from a one-dimensional layer of epithelial cells (blastula) and reorganizes into a multi-layered and multidimensional structure called the gastrula
Turns bilaminar disk into trilaminar disk by migration and invagination of the epiblast

Process is controlled by the primitive streak

Cells of the epiblast break of and migrate towards the primitive pit penetrating through the epiblast to form ectoderm, mesoderm and endoderm.

Question 19

Define trilaminar embryonic disc

Answer 19

embryo which exists as three different germ layers - the ectoderm, the mesoderm and the endoderm.

Question 20

What are the 4 parts of the mesoderm and what do they differentiate into

Answer 20

paraxial mesoderm-head and somite
Somatic mesoderm-forms diaphragm and limb muscles
Intermediate mesoderm- forms kidneys
Splanchnic mesoderm- forms the muscle of the heart and viscera

Question 21

Describe formation of intra-embryonic coelom

Answer 21

During the third week of development,

the lateral plate mesoderm splits into a dorsal somatic mesoderm (somatopleure) and a ventral splanchnic mesoderm (splanchnopleure).

The resulting cavity between the somatic and splanchnic mesoderm is called the intraembryonic coelom
and is where the thoracic and abdominal cavity will form

Question 22

How does the mesoderm differentiate into the notochord

Answer 22

notochord forms from an aggregation of mesoderm that invaginates and extends inward from a surface indentation called the primitive pit, which subsequently elongates to form the primitive streak. As a result of these cell movements during gastrulation, the notochord comes to define the embryonic midline

Question 23

Fate of the notochord

Answer 23

Develops into the vertebrate column

Question 24

Formation of neural plate

Answer 24

Notochord directs via signalling molecules conversion of overlying ectoderm into neurectoderm by thickening it forming a slipper shape neural plate
The edges of which curl towards each other and form the neural tube

Question 25

Describe the head fold, tail fold and lateral fold

Answer 25

Head fold- bending of cranial aspect of the embryo ventrally. This process brings the mouth and heart into their ventral positions.

Tail fold-bending of the caudal aspect of embryo ventrally to reposition the cloaca and allantois

Lateral fold-the lateral edges of the embryonic disc flex sharply ventral. The edges of each germ layer make contact at head and tail regions and zipper toward the umbilicus. The ectoderm now covers the entire body surface except at the umbilical region where the connecting stalk and yolk sac merge.

Question 26

Describe the differentiation of somite

Answer 26

Each somite separate into these 3 cells

Dermatome-skin
Myotome-skeletal muscle
Sclerotome-vertebra and rib

Question 27

Use of dermatome and myotome in relation to innervate

Answer 27

Spinal nerve roots grow out of the nerve tube enter and innervate dermatomes and myotomes.

Clinically dermatome and myotome are used to describe an area of skin or muscle supplied from a single spinal nerve root.

Question 28

How many sommite’s do you have at the end of the 4-5 week period

Answer 28

31