106. formation of germ layers107.108.109. germ derivatives

Question 1

When does the embryonic period/ period of organogenesis occur from

Answer 1

3-8th week
this is when the germ layers give rise to different organs

Question 2

ectoderm derivatives: neuralation

Answer 2

neural plate
neural groove
neural fold
neural tube - CNS
neural crest - ganglion ridge - PNS

neural pores so neural tube can communicate with the amniotic cavity

Question 3

ectoderm derivatives: neural crest

Answer 3

cells from the neuroectoderm begin to dissociate =neural crest
*autonomic ganglia
* glial cells
* melanocytes
*meninges of the brain
* craniofacial skeleton
* Schwann cells
* dentine of teeth

Question 4

ectoderm derivatives: outer+neural tube

Answer 4

outer ectoderm
* epidermis
*hair+nails
*sebacous glands
*mammary glands
*lens,cornea

neural tube
*spinal cord
*motor neurons
*retina
*brain
*posterior pituitary

Question 5

mesoderm derivatives: what happens on the 17th day to the mesoderm layer

Answer 5

PARAXIAL MESODERM- future somites

INTERMEDIATE MESODERM- furute excretory units

LATERAL PLATE MESODERM- parietal/somatic mesoderm layer,visceral/sphlanchnic mesoderm layer, intraembryonic cavity

Question 6

what is derived from the paraxial mesoderm

Answer 6

vertebral column
skeletal/cardiac muscle tissue
dermis and subcutaneous tissue

Question 7

What is derived from the intermediate mesoderm

Answer 7

urogenital structures eg kidney and nephric tubules
nephrotomes
nephrogenic cord

Question 8

what is derived from the lateral plate of mesoderm

Answer 8

parietal/somatic:
lateral/ventral body wall
costal cartligaes
limb muscles

visceral/sphlancnic:
wall of gut tube
serous membranes
endothelial
spleen

Question 9

derivatives of mesenchyme

Answer 9

develops from mesoderm, contains collagen bundles and fibroblasts

smooth muscle tissue
connective tissue
blood and hemopoietic tissue
blood vessels
microglia

Question 10

derivatives of endoderm

Answer 10

The majority of the gastrointestinal tract
 The respiratory tract
 The endocrine glands and organs (Thyroid and thymus, islets of langerhans)
 Auditory system (epithelium of the auditory tube and tympanic cavity)

Question 11

Establishment of the body form begins when

Answer 11

20-21 days

external features seen eg somites
pharangeal arches
formation of organs-ears nose eyes

Question 12

it goes from flat trilaminar embryomic disk to a cyclinder. How?

Answer 12

This is embryonic folding

folding in horizonal plane and median plane- thats why differing rates of organ formation

horizontal/cephalocaudal folding- forms head and tail
lateral folding- forms rounded body form

Question 13

as embyonic folding continues the endoderm moves to midline and fuses to form what

Answer 13

primitave gut tube
-foregut
-midgut
-hindgut

Question 14

what ruptures by the 4th week to form the mouth

Answer 14

oropharyngeal membrane

Question 15

how is the connection between the yolk sac and the placenta maintained

Answer 15

Through vitelline duct and umbilical cord respectively

Question 16

what is formed by the end of the 4th week

Answer 16

upper limbs, lower limbs, fingers and toes

Question 17

when is the fetal period

Answer 17

9th week to birth

Question 18

What are the quantative changes during the foetal period

Answer 18

crown rump length approx 5cm/month month 2-5
weight approx 700g/month last 2 months

Question 19

what are some of the monthly changes during foetal period

Answer 19

3rd month:
 face (eyes, ears) 
become more human-looking
 limbs rich their relative length
 external genitalia
 liver – major hemopoietic organ

 4th-5th month:
 fetus lengthens rapidly
 fetal movements recognized
 fine hair – lanugo, vernix caseosa
 eyebrows and head hair visible
 fetus weight – less than 500 g

 6th month:
 organ systems are able to function
 fetus weight ~800 g

 7th month – weight ~1300 g

 8-10th months:
 organ systems specialization and coordination
 adaptation to the environment conditions