Tissue Development, Repair, and Remodeling - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 685

However, branching pattern can vary [ 1392 ]. Branches can originate off an
unusual parent branch. A branch can miss and daughter branches spring directly
from the grandparent conduit. In addition, branching network size and architecture
differ among species.
Domain Branching
In mice, branches form in 4 domains: lateral, dorsal, medial, and ventral [ 1392 ]. The
first secondary branch from the left primary bronchus lineage buds off the lateral
sprout of the founder branch. Over the next 2 days, additional branches sprout distal
to the first secondary branch and create a row of lateral secondary branches. Then,
another row begins to form along the dorsal surface of the left primary bronchus. As
this domain develops, a third row starts to sprout from the medial surface of the left
primary bronchus. Afterward, a fourth domain eventually arises from the ventral
surface. This ventral domain often consists of a single distal branch. Secondary
branches off the distal portion of the right primary branch also arise by domain
branching, beginning with a row of lateral branches. The branch spacing in each
row is similar to the left pattern, but neither the row-initiation positions nor branch
number in each row are the same. 7
In domain branching, the main secondary daughter branches form in domains
at different positions around the wall circumference of the parent branch, like
rows of bristles on a bottle brush [ 1392 ]. However, each row is characterized by
an independently patterned domain. A patterning controller of domain branching
that directs the branching situation (either proximal or distal) is constituted of a
periodicity generator that regulates the sequence of branching within each domain.
A circumferential patterning controller specifies the positions of domains and the
order with which domains are used.
Planar and Orthogonal Bifurcations
Many ternary branches are constructed by domain branching. Nonetheless, some
ternary and higher-order generations arise from a different mode of tip expansion
and bifurcation. Planar bifurcation corresponds to branching with similar orien-
tation w.r.t. the founder branch, such as that of certain ternary and quaternary
branches [ 1392 ].
On the other hand, some ternary and most higher-order generations use a
third branching mode, the orthogonal bifurcation. Branches bifurcate as in planar
bifurcation, but between each round of branching with an approximately 90-
degree rotation of the bifurcation plane. The daughter tubes are thus arranged in
a rosette [ 1392 ].
7 The first right dorsal branch is proximal to the first right lateral branch, whereas the first left dorsal
branch is distal to the first left lateral branch.