Lecture 8: development of the pharyngeal apparatus

Pharyngeal Arches

a series of tissue bulges that appear on the ventro-lateral side of the embryonic head

first pharyngeal arch

arch gives rise to the maxillary arch and mandibular arch

Pharyngeal cleft

• separates pharyngeal arches on the outside

• indentation between pharyngeal arches on their external surfaces

• lined by the ectoderm

• 4 pairs

Pharyngeal pouch

• Indentation between pharyngeal arches on their internal surfaces

• Lined by endoderm

• 4 pairs

Neural crest-derived mesenchyme

the yellow

Mesoderm mesenchyme

The green

Pharyngeal arch artery

purple dots

part of the vascular endothelium

• make up the aortic arch artery, and aortic arch

• embedded in the mesenchyme of the pharyngeal arches

• derived from splanchnic mesoderm

Angioblasts

the purple border with the white in the middle

part of the vascular endothelium

• Precursor of blood vessels

• from paraxial mesoderm and splanchnic mesoderm

Nerves

Orange

Pharyngeal Endoderm

• component of the pharyngeal arch

• wall of the pharyngeal gut

• covers the internal surface of the pharyngeal arches, and lines the pharyngeal pouches

Surface Ectoderm

• component of the pharyngeal arch

• covers the external surface of the pharyngeal arches, and lines the pharyngeal clefts

Neural Crest-Derived Mesenchyme

called ectomesenchyme or mesctoderm to distinguish it from the mesoderm mesenchyme

• Contains cranial neural crest cells (NCC) and Cardiac NCC

Cranial NCC (neural crest cells)

• from forebrain, midbrain, and hindbrain

• Only those in the midbrain and hindbrain enter the pharyngeal arches

• becomes skeleton and connective tissue

Cardiac NCC (neural crest cells)

• part of the neural crest-derived mesenchyme

• from mid-otic placode to the level 3rd somite (2nd pharyngeal cleft - 6th arch)

• Contributes to heart and blood vessels

Rhombomeres

the embryonic hindbrain is organized into 8 segments called what?

R1, R2

which rhombomeres that are the only ones of the eight that are in the midbrain go to the 1st pharyngeal arch

R4

Rhombomere that goes to the 2nd pharyngeal arch, part of the hindbrain

R6, R7

Rhombomeres that go to the 3rd, 4th, and 6th pharyngeal arches

R3, R5

Which two rhombomeres produce only very few cardiac neural crest cels, which joins the streams from neighboring R

paraxial, splanchnic

The mesoderm mesenchyme is mostly from blank mesoderm, and some blank mesoderm

Mesoderm core

at the center of each pharyngeal arch, mostly becomes skeletal muscles of the face and neck

part of the mesoderm mesenchyme

Second heart field

• part of the mesoderm mesenchym

• splanchnic mesoderm

• at the junction of the pharyngeal arches and the heart

• becomes part of the heart (cardiac muscles)

1st pharyngeal arch

which arch gives rise to Trigeminal (cranial nerve 5)

2nd pharyngeal arch

which arch gives rise to Facial (cranial nerve 7)

3rd pharyngeal arch

which arch gives rise to Glossopharyngeal (cranial nerve 9)

4th and 6th pharyngeal arch

which arch gives rise to vagus (cranial nerve 10)

Pharyngeal Ectoderm

Regulates development of the neural crest mesenchyme

Fibroblast growth factor (FGF) and bone morphogenetic protein (BMP)

The major signaling molecules produced by the ectoderm.