Germ Layer I & II

Question 0

At about __ days, the neural plate becomes visible as distinct region on surface of embryo. Through combination of cell proliferation & cell movements, neural plate becomes larger & starts to fold. The edges of neural plate are called the ___. The embryo is __mm

Answer 0

18; neural folds; 2mm

Question 1

Initially the ectoderm is an undifferentiated layer of tissue overlying the mesoderm. In response to signaling from ___, region of ectoderm is ___ via ___ signals to form neural tissue. This tissue is called the ___ & will develop into CNS (brain & neural tube). Peripheral neurons will grow out from neural tube during later development

Answer 1

notochord, induced; inductive signals; neural plate

Question 2

Neural tube closure first occurs in ___ of embryo & then proceeds __ & ___.

Answer 2

middle; cranially & caudally

Question 3

What is a neural tube defect? When does this occur in the embryo (time)?

Answer 3

failure of neural tube to fuse correctly results in rather common birth defects = NTDs

Question 4

What are 2 examples of NTDs. Where do they occur?

Answer 4

Anencephaly - caused by failure to fuse at cranial end

Spina bifida - caused by failure to fuse at caudal end

Question 5

Folic acid deficiency is correlated with what defect?

Answer 5

neural tube defect

Question 6

Embryonic tissues signal to adjacent tissues all the time & signaling change & are required for development.

Answer 6

Main point

Question 7

Development of sensory organs (eyes & ears) start very early - around ___ days. The ____ is visible as a thickening of the ectoderm. This occurs in response to signals from underlying neural tissue. As development proceeds, the ___ will invaginate & then differentiate into __ (non-neural) tissues of the eye

Answer 7

30-33 days; optic placode; optic placode; lens

Question 8

Human embryos show the optic pit at __ days

Answer 8

35

Question 9

What are neural crest cells?

Answer 9

remarkable group of cells that contribute to numerous embryonic structures including tissues of the face.

Question 10

Neural crests differentiate into bones of the ____. Parietal, occipital & bones at the back of the head are derived from ___ & ___

Answer 10

face; somites & somitomeres

Question 11

Neural crest cells originally develop at crest of ____, a position that also marks the extreme lateral edges of neural tissue. Neural crest cells do not begin to migrate UNTIL the neural tube is closed

Answer 11

neural folds.

Question 12

Neural crest cells develop into what types of cells?

Answer 12

most of bones & cartilage (not muscle) of face
pigment cells (melanocytes)
tooth papillae (pulp tissue & dentine inside the enamel layer)
CT of aortic arch arteries & septum separating aorta & pulmonary artery

Question 13

Cranial neural crest cells migrates through the ___

Answer 13

pharyngeal arches

Question 14

What is Treacher-Collins syndrome?

Answer 14

facial abnormalities due to deficiency of neural crest cells

Question 15

What is Waardenburg syndrome?

Answer 15

facial alteration - wide spaced eye & region lacking pigmentation in hair

At molecular level, mostly due to defects in SOX10 or Pax 3 genes

Question 16

What is fetal alcohol syndrome?

Answer 16

SOME problems cause by exposure of embryo to high alcohol result from neural crest defects
-facial abnormalities due to deficiency of neural crest cells. Children also commonly exhibit heart defects. Short nose, low nasal bridge & flat mid face

Question 17

What is neurofibromatosis?

Answer 17

Disease of neural crest cells affecting about 1/400 individuals
Defect of NF1 function (Ras)

Neural crest derivatives throughout body may grow tumors. Although tumors are mostly benign, they’re disfiguring & they an press on nerves & cause extreme pain.

Most commonly revealed as pigmentation defects - cafe au lait –> melanocytes

Question 18

Apart from neural tissues, embryonic ectoderm forms number of other tissues including

Answer 18

epidermis of skin including hair & nails

sensory epithelium of ear & nose & lens of eye

sweat glands, mammary glands & pituitary glands

enamel of teeth

Question 19

The mesoderm, lateral to notochord, is divided into ____, __ & __ at increasing distances from the midline

Answer 19

paraxial mesoderm, intermediate mesoderm & lateral mesoderm

Question 20

What does the paraxial, intermediate & lateral mesoderm form?

Answer 20

paraxial forms somites - repeating structures that form primitive musculature of embryo

intermediate will form urinary & reproductive system

lateral splits into 2 layers

• somatic (parietal) - in contact with ectoderm. This will form tissues of outer body wall including CT, bone, fat & tendon
• splanchnic (visceral) in contact with endoderm. It contributes to smooth muscle, mesothelia & supportive tissues of gut organs - liver & lungs & heart muscle

Question 21

The mesoderm closest to notochord forms epithelialized balls called ___. __ formation involves transient intermediate structures called ___. All except the __ cranial-most pairs of somitomeres go onto form somites. Somite formation commences cranially & progress caudally. Human embryo ultimately contains about ___ pairs of somites

Answer 21

somites; somites; somitomere; 7; 44

Question 22

The somite contains the precursor cells of 3 different tissues - ___, ___ & ___

Answer 22

myotome, dermatome & sclerotome

First, the lower medial portion of somite breaks & migrates away to form sclerotome –> vertebrae & ribs

Question 23

The repeating structure of somites is an example of ___

Answer 23

segmentation

Question 24

The ___ of the hindbrain are segmented structures

Answer 24

rhombomeres

repeating rhombomeres r1-r7

Question 25

Skeletal muscle arises from ___ component of somites. Muscle precursor cells are called ___. These cells express ___ genes. These TF will regulate expression of structural proteins of muscle (actin, myosin, tropomyosin)

Answer 25

myotome; myoblasts; myogenic determination genes

Question 26

Myoblasts migrate to site of muscle formation. Single myoblast cells fuse into multinucleate __. ___ containing contractile proteins then assemble

Answer 26

myotubes; myofibers

Question 27

What do cranial somitomeres form into? Limb muscle form from ___ surrounding the developing bones. These __ cells migrated into limb buds from myotome layer of somites

Answer 27

muscles of the face; neural crest cells contribute to bone of face

mesenchymal; mesenchymal

Question 28

Arms & legs form around __ days

Answer 28

34

Question 29

Smooth muscle of gut tissue is derived from ___. For most blood vessels, smooth muscle comes from ___. SM of iris, sweat glands & mammary glands come from ___. For ascending aorta & carotid vessels, SM derived from __

Answer 29

splanchnic mesoderm layer
somatic mesoderm
ectoderm
migrating neural crest cells

Question 30

SM development also involves myoblast precursor cell. SM cells do NOT fuse but remain ___

Answer 30

mononucleate

Question 31

Cells that will form heart muscle (myocardium) arise from ___ in cardiogenic region. This is sometimes called the ___.

Answer 31

splanchnic mesoderm; cardiac crescent

Question 32

One gene essential for heart development is ___.

Answer 32

Nkx2-5

Question 33

Cardiac precursor cells remain close to ___. Signal from endoderm is essential for ____.

Answer 33

endoderm; heart development

Question 34

Each heart primordium forms something like simple blood vessel with vascular layer (endocardium) surrounded by myocardial layer. The 2 heart primordia are brought together by lateral folding of embryo & fuse at midline

Answer 34

read over statement

Question 35

T/F The myogenic determination genes are NOT involved in cardiac muscle differentiation

Answer 35

true

Question 36

Most of bone in body forms from the ____ except the bones of the face which is formed from ___. The axial skeleton is formed from __. For the backbone, __ cells surround both notochord & neural tube. These cells then differentiate into bone.

Bone in limbs is generated from ___ cells that migrate into limb bus. These form cartilage & then bone

Answer 36

mesoderm; neural crest cells; scleretome; scleretome

mesenchymal cells

Question 37

In response to signal from adjacent tissues (GF), the ___ begins to differentiate into visceral organs. For the dorasl pancreas, signals from ___ are required to induce expression of pancreatic regulatory genes

Answer 37

endoderm; notochord

Question 38

Signals from developing ___ are required to induce liver formation

Answer 38

heart

** Note proximity of heart & liver primordium

Question 39

During early gastrulation, embryo is basically ___. As neural tissues develop, embryo elongates & ridges form on ___. Most rapidly growing structure is the ___. As it enlarges, it pushes forward (inside the amnion) & forms the head fold.

Answer 39

planar; dorsal surface; brain

Question 40

Growth of posterior tissues produces fold that causes embryo to arch into ____. Together the folding movements of head & tail produce the __, __, & ___.

Answer 40

amniotic space

foregut, midgut & hindgut

Question 41

The foregut ends at oral membrane - also called the ___ or __. Hindgut ends at ___

Answer 41

buccopharyngeal membrane or oropharyngeal membrane

cloacal membrane

Question 42

At same time, lateral folding is also occurring, primarily due to growth of somites. These movements enclose the endodermal tissue leaving only ___ duct as connection to yolk sac. The endodermal layer becomes completely enclosed in splanchnic mesoderm layer to form __. Mesoderm extending b/w gut tube & dorsal body wall forms the ___

Answer 42

vitelline duct; gut tube; dorsal mesentary

Question 43

What is Meckel’s diverticulum

Answer 43

bulge/pouch off SI. Remants of yolk sac stalk. 1/50 people

most don’t show symptoms although intestinal blockage/bleeding may sometimes result

Question 44

At month of development, how long is the embryo

Answer 44

5mm