Lec 26: Formation of the Basic Body Plan

Question 1

What germ layer contains the notochord, and what does the notochord give rise to?

Answer 1

Mesoderm

give rise to intervertebral discs

Question 2

In early development, what layer makes up the embryo?

Answer 2

Only the epiblast makes the embryo (not hypoblast)

Question 3

What are the 2 membranes that will form the oral cavity and the urethral and anal openings?

Answer 3

Where ectoderm and endoderm meet (where the mesoderm does not separate them)

• oropharyngeal membrane (oral cavity)
• cloacal membrane (urethral and anal openings)

Question 4

What germ layer is the neural tube derived from, and what does it give rise to?

Answer 4

Derived from ectoderm

Gives rise to brain & spinal cord, and the neural crest

Question 5

What structures do the trunk of the neural crest give rise to?

Answer 5

• peripheral ganglia
• schwann cells
• pigment cells
• chromaffin cells of adrenal gland

Question 6

What structures does the cranial nerve crest give rise to?

Answer 6

• peripheral ganglia
• schwann cells
• pigment cells
• head cartilage and bone
• walls of the heart (heart outflow tract)

Question 7

What are somites derived from, and what do they give rise to?

Answer 7

Derived from mesoderm. Give rise to:

• vertebra (from sclerotome)
• skeletal muscle (from myotome)
• dermis of back (from dermatome)

Question 8

What are the two main groupings that the ectoderm gives rise to?

Answer 8

Outer epithelium of the body

Neural tube

Question 9

What germ layer is the outer epithelium of the body derived from, and what does it give rise to?

Answer 9

Derived from the ectoderm
Gives rise to:
-teeth
-epidermal appendages (i.e., hairs)
-sensory epithelium (of nose, inner ear, and lens)

Question 10

What are the main derivatives of the mesoderm?

Answer 10

• notochord
• somites
• intermediate mesoderm
• lateral mesoderm (parietal and visceral layer)

Question 11

What is the intermediate mesoderm a derivative of, and what does it give rise to?

Answer 11

A derivative of the mesoderm

Gives rise to urogenital organs (kidneys, gonads, ducts)

Question 12

What is the lateral mesoderm a derivative of, what are its 2 divisions, and what does each give rise to?

Answer 12

• Lateral mesoderm is a derivative of mesoderm
• Parietal layer and Visceral layer
• Parietal layer gives rise to body wall and limbs, connective tissues, and body cavity lining
• Visceral layer gives rise to precardiac mesoderm (precursor to heart and blood vessel lining), smooth muscle and connective tissue of mesoderm, serous membranes of visceral organs (respiratory, digestive, bladder/urethra)

Question 13

What is the inner epithelial lining of visceral organs derived from?

Answer 13

Derived from primitive gut tube endoderm

Question 14

What does the endoderm give rise to?

Answer 14

Epithelial lining of the gut tube (respiratory, digestive, bladder/urethra)

Question 15

What is the connective tissue and smooth muscle of the visceral organs derived from?

Answer 15

Visceral mesoderm

Question 16

What germ layer does the enteric nervous system that line the gut tube derive from?

Answer 16

From the neural crest of the neural tube of the ectoderm

Question 17

What does the mesoderm in the head give rise to?

Answer 17

Does NOT segment into somites

Ultimately gives rise to branchial arch muscles and extraocular muscles

Question 18

What visceral organs bud off of the primitive gut tube, and which develop as expanded regions of the original primitive gut tube?

Answer 18

Bud off: thyroid, trachea, lungs, liver
-stomach and intestines develop as expanded regions of the foregut and midgut, respectively; bladder is expansion of hindgut

Question 19

What do muscle innervation patterns represent?

Answer 19

early embryonic muscle position rather than the adult position

Question 20

What is the precursor of adult body cavities?

Answer 20

The coelomic cavity

Question 21

What structure ultimately contributes to formation of the diaphragm and liver?

Answer 21

Septum transversum

Question 22

What do the pericardial and pleural cavities derive from?

Answer 22

The bent cranial end of the coelomic cavity that surrounds the heart

Question 23

What are the 3 parts to the coelomic cavity?

Answer 23

• bent cranial end that surrounds the heart (gives rise to pericardial and pleural cavities)
• two pericardioperitoneal canals above the septum transversum
• two peritoneal regions that border the gut and open to chorionic cavity

Question 24

What closes the pericardioperitoneal canals?

Answer 24

closed by folds from posterior body wall called the pleuroperitoneal fold

Question 25

What 4 parts make up the diaphragm?

Answer 25

• septum transversum
• pleuroperitoneal folds
• esophagus and its mesentery
• muscle cells from somites

Question 26

What happens if there is a failure of the neural tube to close at the cranial neuropore? What about a failure to close at spinal cord levels?

Answer 26

Anencephaly (cranioschisis) is failure to close at brain levels
Myeloschisis is failure to close at spinal levels (aka spinal bifida aperta)

Question 27

What are the 4 types of incomplete bony encasement where neural tissue and/or meningeal sac may protrude through?

Answer 27

• Encephalocele: defect where brain tissue and meninges protrude through skull
• Myeloeningocele (spina bifida cystica): defect where there is protrusion of meninges and spinal cord through vertebral column
• Meningocele (spina bifida cystica): defect where only meninges protrude through vertebral column deficit
• Spina bifida occulta: defect from small number of vertebral arches fail to form on dorsal side; may not be evident.

Question 28

What causes a diaphragmatic hernia?

Answer 28

A pericardioperitoneal canal that remains open due to defective formation of pleuroperitoneal membrane
-with an incomplete diaphragm, viscera herniate into thoracic cavity and impair development of lungs and heart