branchial arches Flashcards
what are branchial arches
structures which develop in the head and neck regions of the embryo and give rise to internal and external structures found on the head, neck and upper thorax
they appear at week 4 in humans following neurulation
what do the branchial arches form
pulmonary and cardiac vasculature
bone and cartilage structures of head and neck
musculature of head and neck
structures and bones of inner and outer ear
glandular structures including thyroid and thymus
what arches develop
initially 6 develop 5 is lost 4 and 6 fuses 4 remain form by lateral migration of neural crest cells
what are the outside indents called
clefts
what are the inside indents called
pouches
what forms from arch 1
outer - skin of jaw, salivary glands, tooth enamel, buccal cavity
inside - mandible maxilla
what forms from pouch 1
auditory tube
what forms from cleft 1
external components of middle ear and tympanum
what forms from arches 2-4
skin of ear and neck
what forms from pouch 2
tonsils and lymphatics
what forms from pouch 3
thymus and thyroid
what forms from pouch 4
thyroid
what does each branchial arch have
a nerve supply and capacity for neurogenesis
a bloody supply and capacity for driving angiogenesis
cartillage and connective tissue
what is each branchial arch
lined with ectodermal tissue on external surface, folds within tissues are called clefts
lined with endodermal tissue on internal surface, folds within tissue are called pouches
composed of mesoderm-derived mesenchyme tissue
neural crest cells
arise from ectoderm at margins of the neural tube
multipotent - differentiate to from different cell types
differentiation if regulated by growth factors that control slug/snail zinc finger transcription factors which controls gene expression factors and cell fate
neural crest cells drive branchial arch structural development
explanted neural crest stem cell experiments with varied growth factor combinations promote formation of different cell types
mesenchymal cells form….
branchial arch skeletal structure
bones of the skull and face including the inner ear bone
hyoid cartilage
cartilage, bone, dentin, tendon, sensory neurons, dermis, meninges and glandular stroma
humans and fish have some mirgration axes and in humans where gills would form, develop bones/ cartilage of the jaw, ear, neck and throat
origin of neural structures
the neural tube is segmented into rhombomeres during early development
hox genes determine segmentation and neural crest cell properties within each rhombomere
rhombomeres give rise to segmented brain structure and by migrating into specific branchial arches, cranial nerve 5, 7, 9 and 10
cerebellum, pons, medulla, cranial nerve 7 and 10 regulate breathing and heart rate
combinations of hox genes expression patterns in each rhombomere determines segmentation and neural crest cell properties
origin of vascular structures
branchial arches are located between the developing brain and heart
neural crest cells migrate to form the vascular arch within each branchial arch
anterior vascular arches from the major arteries of the head and neck
posterior vascular arches link together to form the aortic arch at junction with the heart
how does the heart form
3 populations of cardiac precursor cells - cardiac mesoderm cells - proepicardium - cardiac neural crest cells give rise to different lineages - pacemaker - atrial and ventricular cardiocytes - endocardial cells - valve components and connective tissues - smooth muscle cells - vascular endothelial cells
stages of heart development
- e6.5 mouse/ e13-15 human: mesoderm projenitors ingress through the primitive streak and form the first primitive heart feild
- e7.5 mouse/e19-20 human: ingress of cells from SHF form the outflow tract. the linear heart tube undergoes rightward looping to create the right and left ventricular chambers. at this stage primitive right and left atria are below ventricles
- e10.5 mouse/e28 human: completion of cardiac looping creates the right and left chambers. CNC and PE cells migrate to create specific cardiac lineages
- e14.5 mouse/e52 human: heart has 2 fully separated chambers and a separated outflow tract connected to the vascular structures which have arisen from branchial arches
creatinc cardiac cells of different lineages - signalling pathways
growth factor combinations determine mesoderm differentiation into cardiac lineages
BMP, NODAL-activin and SMAD, Wnt signalling, FGF
NODAL-activin signalling
conserves pluripotent cells state by activating SMAD phosphorylation and transcription factor activin
Wnt signalling
canonical - Wnt binds to frizzled receptor, activation induces dishevelled to bind and inactivate Axin/APC/GSK3 complex. subsequent dephosphorylation of b catenin results in its stabilisation, accumulation in cytosol and nuclear migration
in the nucleus b catenin is a coactivator of TCF/LEF which induces Wnt target gene expression
non canonical - 1. wnt/ calcium pathway: Dv1 stimulates ER calcium release activating PK-C, calmodulin dependent kinase 2 and transcription factor NFAT signalling. regulates cytokinesis
2. wnt/planar cell polarity signalling - mediated by GTPases RhoA and Ras which induces RHoA-RHo associated kinase or janus kinase cytoskeletal rearrangement and contraction
FGF signaling
FGF binds to TKRs
activates autophosphorylation of tyrosine kinase FGFR kinase domain
pattern of tyrosine auto-phosphorylation governs downstream signalling
