hi let's talk about the bronchial tree in this video we'll discuss the bronchial tree we'll
discuss its histology and how its histology changes according to the region of the tree
well also discuss what happens to the bronchial tree during a sympathetic response and we'll
talk about the bronchopulmonary segments so the bronchial tree requires very little imagination
to understand how it gets its name so if you were to take that image and rotate it
180 degrees you would say you know there's a trunk some branches some other branches
on those branches some foliage etc so this is most definitely an inverted tree like pathway
so the majority of the bronchial tree is conductive so the story of the let's just
call it the purely conductive portion of the respiratory pathway that isn't shared by the
digestive system begins in the larynx so the larynx is contiguous with the laryngopharynx
and it's there at the laryngopharynx that there's a decision made whether materials
are heading towards the respiratory system or the digestive system so if respiratory then materials
move through the lyrics or colloquially the voice box and then that lyrics articulates
with the trachea so the trachea there is the trunk of the bronchial tree and we can see
that it is comprised of numerous so generally about 13 C shaped hyaline cartilage so it's
incomplete in the posterior there's a little bit of smooth musculature there and that in
the trachea --less and then the trachea is going to bifurcate into the primary bronchi
so the primary bronchi or the main stem bronchi are the right and the left the right tends to
be a little larger and a little more vertically oriented whereas the left tends to be a little
smaller in diameter and a little more obliquely oriented those primary bronchi are then going to
divide into secondary bronchi and the secondary bronchi are what are known as the lobar bronchi
because these secondary bronchi serve lobes of the lung it's probably important to understand
or to recall that the right lung typically has three lobes whereas the left lung typically has
two lobes and so the right lung will have three secondary bronchi the left lung will have two
secondary bronchi multi-fork aiding off of these secondary bronchi are the tertiary bronchi also
known as segmental bronchi because they are what feed into bronchopulmonary segments which we'll
discuss shortly so if we look at this end a cast of a bronchial tree here I want you to keep in
mind that this is a posterior view so there's the trachea here are the main stem bronchi so this is
going to be left and this is going to be right so it's different than what was above here with
right and left we can see there's one two three and four secondary bronchi and then we can see
all of the the tertiary bronchi coming off of those secondary bronchi now from the tertiary
bronchi arise the bronchioles and the bronchioles are going to be an sequentially diminishing in
diameter pathway of airway and so the the first part of the of the bronchioles are the conducting
bronchioles and these quickly are going to divide into terminal bronchioles the terminal bronchioles
are named that because they are the terminus of the conducting zone so everything beyond
the terminal bronchioles is going to be in the respiratory zone whereas anything at that level
and proximal will be in the conducting zone now as we move through the bronchioles we're going to
notice that histologically the amount of hyaline cartilage embedded in the walls of these pathways
is going to diminish and the amount of smooth muscle is going to increase and so as we move
through the bronchioles the autonomic nervous system is going to be so much more important
with respect to regulating the the diameter of the airway now within that last part of the conducting
zone that terminal bronchioles area we have numerous club cells club cells are amazing they
do a lot for the for the respiratory system so they're protective they they contain enzymes that
they can break down pathogens and in other foreign bodies they produce surfactant or surfactant like
substance that helps to maintain that the patency of the airway they could even that they have micro
villi I on them so that they are in amongst the ciliated epithelium so they can help move mucus
and they can mitotically divide to produce more club cells to replace some of that that epithelium
along the pathway now what's interesting about these club cells it's sort of a a two-edged sword
is that they have an enzyme that can actually cleave a surface protein so hemagglutinin from
influenza virus and that actually activates the influenza virus and so these these club cells
where as they're very protective they are what actually will activate the the flu virus in the
the conductive pathway of the lung so there's that you know most wonderful things in life
carrying with them taxes and that's not too big a burden and so coming off of the the terminal
bronchioles are the the respiratory bronchioles the respiratory bronchioles are largely just
smooth muscle and during a sympathetic response smooth muscle is going to relax and so the the
respiratory pathway is going to dilate and that's going to allow for better ventilation now this is
also good to know because if a person has some sort of food allergy or is in danger
of anaphylaxis you can administer epinephrine and epinephrine is then going to work on that
same smooth muscle within the the bronchioles to to dilate it and to relax it to to ward off
anaphylaxis which is you know important for for staying alive now those tertiary bronchioles or
I'm sorry tertiary bronchi or segmental bronchi serve bro pulmonary segments and so here we can
see the the trachea dividing into the the primary bronchi and then into the secondary bronchi and
then everything that's colored here other than you know this blue color is a tertiary bronchus
and each tertiary bronchus corresponds to these bronchopulmonary segments so for instance one here
and one there is going to correspond to the apical or the apical posterior segments of the loan so to
there to the posterior segment of the superior lobe three the anterior segment of the superior
lobe four and five to the medial lobe six this is kind of an important we'll come back to this to
the superior segment of the inferior lobe and then you know everything else to the inferior lobe so
you see a little bit of variation between left and right lungs keeping in mind that the right lung is
going to have three lobes to it a superior a middle and an inferior whereas the left lung
simply has superior and inferior lobes so this is going to somewhat affect the distribution
of bronchopulmonary segments ever so slightly but I do want to draw your attention to these
superior segments of the inferior lobe so you can see a little bit of it there there and there
these superior segments of the inferior lobes are going to be important because they're
tertiary bronchi are posteriorly oriented and this is very unique amongst all of the tertiary
bronchi because they're the only ones that go posteriorly and what this means is that for a
person who is confided to their bed long-term so they're not elevated at all they're not up
and moving around fluid can accumulate in this superior segment of the inferior lobe so that is
a is a risk for pneumonia and that can be very problematic in terms of long-term prognosis so
that leads us to our assessment question for the video and that is bronchopulmonary segments
are directly and completely served by which elements of the bronchial tree bronchioles
primary bronchi secondary bronchi or tertiary bronchi well bronchopulmonary segments are
supplied by segmental bronchi those are tertiary bronchi correct answer is d secondary bronchi
those serve lobes primary bronchi serve lungs thank you very much for your time