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Cell and Developmental biology > branchial arches > Flashcards

branchial arches Flashcards

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1
Q

what are branchial arches

A

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

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2
Q

what do the branchial arches form

A

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

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3
Q

what arches develop

A 
initially 6 develop
5 is lost 
4 and 6 fuses 
4 remain
form by lateral migration of neural crest cells
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4
Q

what are the outside indents called

A

clefts

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5
Q

what are the inside indents called

A

pouches

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6
Q

what forms from arch 1

A

outer - skin of jaw, salivary glands, tooth enamel, buccal cavity
inside - mandible maxilla

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7
Q

what forms from pouch 1

A

auditory tube

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8
Q

what forms from cleft 1

A

external components of middle ear and tympanum

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9
Q

what forms from arches 2-4

A

skin of ear and neck

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10
Q

what forms from pouch 2

A

tonsils and lymphatics

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11
Q

what forms from pouch 3

A

thymus and thyroid

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12
Q

what forms from pouch 4

A

thyroid

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13
Q

what does each branchial arch have

A

a nerve supply and capacity for neurogenesis
a bloody supply and capacity for driving angiogenesis
cartillage and connective tissue

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14
Q

what is each branchial arch

A

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

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15
Q

neural crest cells

A

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

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16
Q

mesenchymal cells form….

A

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

17
Q

origin of neural structures

A

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

18
Q

origin of vascular structures

A

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

19
Q

how does the heart form

A 
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
20
Q

stages of heart development

A
  1. e6.5 mouse/ e13-15 human: mesoderm projenitors ingress through the primitive streak and form the first primitive heart feild
  2. 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
  3. 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
  4. 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
21
Q

creatinc cardiac cells of different lineages - signalling pathways

A

growth factor combinations determine mesoderm differentiation into cardiac lineages
BMP, NODAL-activin and SMAD, Wnt signalling, FGF

22
Q

NODAL-activin signalling

A

conserves pluripotent cells state by activating SMAD phosphorylation and transcription factor activin

23
Q

Wnt signalling

A

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

24
Q

FGF signaling

A

FGF binds to TKRs
activates autophosphorylation of tyrosine kinase FGFR kinase domain
pattern of tyrosine auto-phosphorylation governs downstream signalling

25
Q

origin of the cardiac pacemaker

A

early heart chamber is not yet formed
cardiac myocytes contract fromRA/LA to RV ina peristaltic wave
in a chambered heart:
RA/LA contract before LV/RV, resulting in ecg pattern
ecg contraction moves atrial to ventricular chambers
onset of coordination of heart contraction - 21 days
fetal heart rate = 170 bpm at 7 weeks

26
Q

origins and properties of cardiac pacemaker cells

A

originate as specialised cardiomyocytes with a primitive non contractile phenotype
transcription factor islet1 maintains primitive state and promotes cell migration into the heart tube to form the pacemaker and cell cluster
express pacemaker-specific ion channels and gap junction proteins which allow for action potential propagation
hcn4 channel: sodium/ potassium hyperpolarisation - activated- cyclic nucleotide - gated channel 4
connexins 45 and 30.2 are gap junction proteins
differential gene expression defines and restricts pacemaker cell phenotype
T box trancription factors TBX18, TBX5 and TBX3
homeobox protien NKX2.5
short stature homeobox 2 (SHOX2)
islet1
Tbx3 and Nkx2.5 have a central antagonistic funtion in pacemaker differentiation
Isl1 maintains monocyte precursor state, favouring pacemaker phenotype

27
Q

gene expression patterns defining pacemaker and cardio myocytes cells

A 
progenitor cells
pacemaker precursors
myogenic precursor
mature cardio myocytes 
(LEARN PATHWAYS)
28
Q

branchial arch abnormalities

A

crouzon syndrome - defective branchial arch 1 formation, jaw and dental malformation, failure to fuse skull bone

golden har syndrome - defective branchial arch 1 and 2 formation, incomplete development of ear nose and soft palate, lip and mandible usually one side of the body, internal organs lose symmetry

di George sydrome - malformation of 3rd and 4th pouches, failure of thymus and parathyroid gland development. range of heart defects - failure to close ventricular septum and thickening of the right ventricle

29
Q

dextro-transposition of great arteries

A
  • venous return to right ventricle pumped directly though the aorta by-passing the lungs
    left ventricle pumps O2 blood back into lungs
    creates separate circular circulatory systems that operate in parallel
    infants turn blue
30
Q

levo-transposition of great arteries

A

aorta transposed so it is anterior and left of the pulmonary artery
LV and RV are transposed

31
Q

simple and complex TGV

A

intracardiac shunts

Cell and Developmental biology (13 decks)

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