Early embryology Flashcards
What is a blastomere?
When the fertilised oocyte splits into two cells
What is a morula?
When there are 16 cells- 4 cell divisions
What is the trophoblast?
The outer cell mass- contacts with the endometrium of the uterus to facilitate implantation and the formation of the placenta
What is the embryoblast?
The inner cell mass- responsible for the formation of the embryo itself
What are the two cell types that form from the trophoblast?
Syncytiotrophoblast and cytotrophoblast
What are the two layers of the bilaminar disc?
Epiblast and hypoblast (divisons of the embryoblast)
What layer of the embryo becomes continuous with the uterus?
Syncytiotrophoblast
What is the primitive streak?
A groove in the midline of the epiblast.
Where is the primitive pit?
Within the primitive node, which lies at the cranial end of the primitive streak
What layer of the bilaminar disc does the trilaminar disc form from?
The epiblast
What are layers of the trilaminar disc?
Endoderm, mesoderm, ectoderm
What structures are derived from the endoderm?
Lining of digestive, respiratory, and urogenital tract, liver and pancreas
What structures are derived from the mesoderm?
Notochord, musculoskeletal system, muscular layer of stomach, intestine etc, circulatory system, urogenital system
What structures are derived from the ectoderm?
Epidermis of skin, cornea and lens of eye, nervous system
What are the somites derived from?
Paraxial mesoderm
How many pairs of somites are formed?
44- but 13 break down leaving 31
What is a dermatome?
A strip of skin innervated by a single spinal nerve
What is a myotome?
A group of muscles innervated by a single spinal nerve root
What nerve roots give rise to achilles reflex?
S1,S2
What nerve roots give rise to the patellar reflex?
L3,L4
What nerve roots give rise to biceps and brachiradialis reflex?
C5,C6
What nerve roots give rise to the triceps reflex?
C7,C8
How many pharyngeal clefts are there?
4
Which pharyngeal cleft gives rise to a permanent structure?
1
What does the 1st pharyngeal cleft give rise to?
The external auditory meatus
What do the 2nd, 3rd and 4th pharyngeal clefts form?
Temporary cervical sinuses
How many pharyngeal arches are there?
5
What does the 1st pharyngeal arch give rise to?
Eustachian tube and middle ear cavity
What does the 2nd pharyngeal arch give rise to?
Lining of the palatine tonsils
What does the 3rd pharyngeal arch give rise to?
Inferior parathyroid glands and thymus
What does the 4th pharyngeal arch give rise to?
Superior parathyroid glands and ultimobranchial body
What does the 5th pharyngeal arch give rise to?
Nothing!
What nerve is the first pharyngeal arch associated with?
Trigeminal
What nerve is the second pharyngeal arch associated with?
Facial
What nerve is the third pharyngeal arch associated with?
Glossopharyngeal
What nerve is the fourth pharyngeal arch associated with?
Superior laryngeal branch of vagus
What nerve is the sixth pharyngeal arch associated with?
Recurrent laryngeal branch of vagus
