Organogenesis 1,2,3: ectoderm, endoderm, mesoderm

Question 1

Lineage

Answer 1

descent in line from common progenitor

Question 2

T or F: Organs are derived from only 1 germ layer

Answer 2

F: organs generally derived from 2-3 germ layers

Question 3

What does the ectoderm become?

Answer 3

1) Neural tube –> CNS (spinal cord)
2) neural crest –> PNS
3) outer epithelium of body (anterior pituitary, lens + cornea, inner ear, skin appendages)

Question 4

Steps of the formation of the neural tube

Answer 4

1) ectoderm (neural plate) thickens
2) neural plate folds
3) neural plate forms closed neural tube (CNS) with open lume
4) tube separates from ectoderm surface (delamination)

Question 5

The cells from the top of the DORSAL SIDE OF THE NT undergo (a) which then form (b)

Answer 5

a) EMT
b) neural crest cells

Question 6

Early NS formation from 18-23 days

Answer 6

edges of folding neural plate come together and join at mid-level along cranial-caudal axis then “zip” cranially and caudally, transiently leaving an open cranial (anterior) and caudal (posterior) neuropore

Question 7

rachischisis

Answer 7

closure defect of the neural tube

Question 8

Neural crest cells develop at the (a) aspect of the neural tube

Answer 8

a) dorsal

then undergo epithelial to mesenchymal transition and migrate to various locations

Question 9

Neural crest derviatives

Answer 9

1) PNS + glia
2) adrenal medullary cells (make epi)
3) skin pigment cells (melanocytes)

Question 10

What are the epidermal appendages?

Answer 10

mammary glands, sweat glands, sebaceous glands, hair, nails

Question 11

Epidermis starts as a (a) layer of (b) cells and then differentiates into (c)

Answer 11

(a- single)
(b- ectodermal)
(c- stratified squamous structure)

Question 12

What forms skin appendages?

Answer 12

DOWNGROWTH of epidermis into the dermis

Question 13

Experiments showing inductive interactions in the skin

Answer 13

ectoderm along and mesoderm alone DO NOT DIFFERENTIATION into epidermis/ dermis respectively

mesoderm derived determines the type it becomes

Question 14

enamel organ

Answer 14

ectodermal derivative

Question 15

dental pilla

Answer 15

cranial (neural) crest derivative

Question 16

ameloblasts

Answer 16

produce enamel (oral epithelial derivative)

Question 17

odontoblasts

Answer 17

produce dentin (neural crest derivative)

Question 18

Permanent teeth go through the (same or diff) development sequence of deciduous teeth

Answer 18

SAME

Question 19

What time does the endodermal germ layer start

Answer 19

14-15 days of gestation

Question 20

Major fates og endoderm

Answer 20

EPITHELIUM OF

gut (pancreas, liver, digestive tract, trachea, lungs)

urinary bladder

pharynx (thyroid, pharyngeal pouches)

Question 21

How the endoderm is shaped into the gut tube

Answer 21

while the ectoderm forms the neural tube, endoderm buds down to form gut tube, ectoderm closes around with endoderm and mesoderm in middle

Question 22

what derives from diverticululum

Answer 22

diverticulum= OUTPOUCHINGS of the gut tube

liver, pancreas, pulmonary system, thyroid

Question 23

What is this view called?

Answer 23

sagittal

Question 24

What view is this from?

Answer 24

transverse

Question 25

Fistula

Answer 25

failure of the normal separation of trachea and esophagus

Question 26

What happens if someone has blind esophageal pouch?

Answer 26

gastric air bubble

so spit up milk because no where for milk to go once swallowed

Question 27

Origin of Mesoderm cells

Answer 27

epiblast migrate down ventrally through primitive streak after endoderm is settled and end up in the middle

Question 28

Three divisions of the mesoderm

Answer 28

1) paraxial (closest to neural tube)
2) intermediate
3) lateral

Question 29

What does the paraxial mesoderm organize into?

Answer 29

somites (segmental blocks)

Question 30

What two layers does the lateral mesoderm split into?

Answer 30

1) somatic (parietal): lines body wall
2) splanchnic (visceral): organs

Question 31

What do somites (paraxial mesoderm) give rise to?

Answer 31

1) sclerotome (axial skeleton NOT appendicular)
2) myotome (skeletal muscle (both axial and limb))
3) dermatome (dermis at back of neck and back)

Question 32

What does the intermediate mesoderm give rise to?

Answer 32

urogenital system

Question 33

What does the lateral mesoderm give rise to?

Answer 33

somatic (parietal): lining of body wall

splanchnic (visceral): organ layer

dermis of trunk and neck

appendicular skeleton

wall of gut and respiratory tract

heart

Question 34

How do somites form?

Answer 34

mesenchymal to epithelial transition

Question 35

How do somites give rise to its 3 diff layers?

Answer 35

epithelial to mesenchymal (EMT)

Question 36

What is the fate of a somite cell determined by? What is an example?

Answer 36

determined by its location relative to various signal producing structures (INDUCTIVE INTERACTIONS)

ie. axial bone: SHH released in the floor plate of NT and notochord, goes and initiates Pax1 gene in the sclerotome cells…… regulates differentation of these cells into bone

Question 37

How sclerotome fuses to form vertebrae

Answer 37

sclerotome cells migrate around the spinal cord and notochord to merge with cells from the opposing somite on the other side of the neural tube…. originate in BOTH left and right side somits

vertebrae is fused of the caudal aspect of one sclerotome and the dorsal aspect of the cranial portion of the next one down

Question 38

What forms the intervertebral disc and the central portion?

Answer 38

cells remaining in the plane of division of each sclerotome form the intervertebral disc and the notochord forms the central portion

Question 39

What gene encodes for craniocaudal differences between vertebrae?

Answer 39

Hox genes!!! –> encode TFs which then contribute to anatomical structure of segment “identity”

Question 40

tooth development

Answer 40

surface ectoderm downgrowth

neural crest derived odontoblast produce dentine which stimulates downgrowth into mesenchyme, cells become ameloblasts and produce enamel