embryology Flashcards
Define pre-embryonic development
fertilisation-2nd week
Define embryonic development
3rd week- 8th week
Define foetal period
9th week- 38th week
What changes take place as the zygote travels down the fallopian tube to the uterus
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
Define zygote
fertilized egg cell that results from the union of a female gamete
Define cleavage
the first few cellular divisions of a zygote
Define zona pellucida
the glycoprotein membrane surrounding a mammalian ovum before hatching and implantation.
prevents anymore sperm getting in and prevent growth of blastomere/cyst
Define morula
solid mass of blastomeres resulting from a number of cleavages of a zygote
Define ovary
Female reproductive organ where ova are produced
Define fallopian tube
pair of tubes in which ova from the ovaries travel to the uterus
Define uterus
Female organ in which offspring are conceived and gestate before birth
Formation and implantation of blastocyst
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
Describe the formation of the bilaminar disc
The inner cell mass(embryoblast) flattens and differentiates into 2 layers the epiblast and the hypoblast.
Define bilaminar disc
Bilaminar blastocyst or bilaminar disc refers to the epiblast and the hypoblast, evolved from the embryoblast
Define germ layer
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
Define and state the derivatives of the ectoderm, mesoderm, endoderm
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.
Define primitive streak
The faint streak on the trilaminar disk signalling gastrulation
Define gastrulation
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.
Define trilaminar embryonic disc
embryo which exists as three different germ layers - the ectoderm, the mesoderm and the endoderm.
What are the 4 parts of the mesoderm and what do they differentiate into
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
Describe formation of intra-embryonic coelom
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
How does the mesoderm differentiate into the notochord
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
Fate of the notochord
Develops into the vertebrate column
Formation of neural plate
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
Describe the head fold, tail fold and lateral fold
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.
Describe the differentiation of somite
Each somite separate into these 3 cells
Dermatome-skin
Myotome-skeletal muscle
Sclerotome-vertebra and rib
Use of dermatome and myotome in relation to innervate
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.
How many sommite’s do you have at the end of the 4-5 week period
31
