Download We have a box, the thorax. Floor is the diaphragm. Roof is

We have a box, the thorax. Floor is the diaphragm. Roof is thoracic inlet.
Framework has three components
Vertebrae – T1-T12
Sternum – 3 parts manubrium, body, and xiphoid process
Ribs
Now build a wall, most rigid yet extensible in the body. Protect organs (heart, lungs, vessels) and for
respiration. Normal resting breathing is done mostly with the diaphragm. Intercostals and other
accessory mm come into play with exerted breathing. Expansion in AP and lateral directions, increasing
the volume of the space, pressure goes down, air flows in (vacuum).
Mm also make up the walls of the box, start with the skin, subcutaneous CT, then fascia. Ventral rami,
which are intercostal nerves, innervate the outer surface, skin, CT and fascia. Terminate in lateral and
anterior cutaneous branches.
B/t the ribs we have intercostal mm, 3 layers, external, internal and innermost. Innermost run the same
direction as the internal. Put hands in pockets for direction of external intercostal. Neurovascular
bundle found under the rib in the costal groove, VAN. Small collateral branches run on top of the rib,
but not as important. Careful when we insert chest tubes, needles, etc. Start them on top of the rib and
angle up.
Other mm of respiration:
Transversus thoracic – start on posterior of sternum fan out to lower ribs and costal cartilage
Subcostals – run down to lower ribs, believe go down two spaces
Pectoralis minor and major
Serratus Anterior
Levator costarum part of the thorax as well, only lifts the ribs
Serratus Posterior – superior and inferior
All these muscles, except lev costarum, are capable of moving ribs both up and down depending on
what is anchored. Where ever the anchor is, that is the direction the ribs will move
Angle of Louis – T2 directly behind it, arch of aorta
Vertebra – articulate with ribs in 3 places, the rib above the one it is on and articulation with the
transverse process of the vertebra
Endothoracic fascia lines the entire thorax. Pleura only surrounds the pleural space surrounding the
lungs and bronchi.
Break the thorax down into smaller units. Start with the pleural space, continuous around the lungs and
bronchi. Set this box aside for now. Now go to middle mediastinum, heart, pericardium and roots of
GVs.
Pericardium – 3 layers – fibrous, parietal serous, pericardial space, then visceral serous pericardium (aka
epicardium), then myocardium, then endocardium. IVC/SVC enter into the box on the right and enter
the right atrium. Tricuspid valve separate RA from RV. From RV through pulmonary trunk via
pulmonary valve to the L/R pulmonary arteries. Give up CO2, pick up some O2 in the lungs and come
back to the heart via the Sup/Inf L/R pulmonary veins in to the LA. Go through the mitral valve
(bicuspid) to the LV to the aorta through the aortic valve. Go through the ascending aorta, to the aortic
arch to brachiocephalic , L common carotid and L subclavian.
Looking at the heart, coming out of the LV, the aorta, conduit for O2 blood to go to the body, first
branches are the R/L coronary arteries. Left coronary splits to circumflex and left marginal node. Left
coronary supplies A/V node as well. Right main coronary, first branch is SA nodal artery, 2nd branch is R
marginal artery then posterior intraventricular artery. Where the PIA comes from sets the dominance of
the heart. Want PIA coming from RMC or codominant heart. If PIA comes from LMC, LMC more likely to
have an occlusion. Bad to have left dominant heart.
GCV runs w/ AIA and becomes coronary sinus as it runs with circumflex artery. MCV runs with PIA. SCV
runs with R marginal artery.
What makes the heart beat? Myocytes have their own natural rhythm, automaticity, from 3rd week of
embryo development. Cardiac plexus controls the heartbeat. Made up of sensory nerves (T1-T4),
sympathetics and cardiac branches of the vagus nerve (parasympathetics). Symp speed the heart up,
parasymp slows it down. Common way of cutting these nerves? Heart transplant, have to have a
pacemaker with your transplant. Anytime we stick something in the thorax we run a risk of damaging
these nerves that control the heart. Common to hit the stellate ganglion (superior most sympathetic
and inferior cervical ganglion that fuse), cause Horner syndrome immediately. Sympathetics and
sensory nerves indicate a heart attack. Sympathetics can carry referred pain.
Periphery of diaphragm innervated partially by intercostal nerves. Mainly innervated by phrenic nn. ID
the phrenic nn first during surgery, cut both and patient is now on a ventilator.
Next box is in front of the heart, anterior mediastinum, thymus was here. Turns to fat as an adult, need
this to develop T cells. Pathology here? Thymoma. Left internal thoracic artery is used for bypass
surgery.
Next we go to the superior mediastinum. Aorta lives here, with its branches, brachiocephalic, L common
carotid, and l subclavian. Brachiocephalic branches to R common carotid and R subclavian. Coronary
arteries come off the aorta in the middle mediastinum. Pulmonary trunk and R/L pulmonary arteries are
here too. Truncus arteriosus here, but in the adult now the ligamentum arteriosum. Thoracic duct goes
from inferior to superior of the thorax, drains the entire body except rt arm, neck and head (right sides).
Accompanying the L common carotid we have L IJV, following the LSC artery is the LSC vein, same on the
right side. The R SCV and R IJV join together to make the innominate vein (brachiocephalic). On the left,
the same SCV and IJV join to make the left brachiocephalic vein. The brachiocephalic veins join together
to make the SVC.
Right thoracic trunk dumps in to the right junction of the IJV and SCV. Left thoracic duct dumps into the
junction of the L IJV and L SCV.
Arch of the azygos joins the posterior side of the SVC. Azygos runs on the right side of the posterior
thorax (starts in superior mediastinum). Also have trachea and esophagus. Esophagus lying behind the
trachea. Also, vagus and phrenic nerves run through here too.
R vagus nerve, branches off to R recurrent laryngeal. R vagus cont to esophagus and becomes the
posterior vagal trunk. L vagus, branches to L recurrent laryngeal, becoming the anterior vagal trunk.
Next move on to the posterior mediastinum, sympathetic trunk is the new portion, thoracic duct here,
azygos system, esophagus, vagus nn (phrenic runs from superior to middle mediastinum, not in the
posterior). Vertebrae here, spinal column, made up of vertebrae and IVDs. Running down the side of
the spinal column, Sympathetic chain ganglia, 2nd order neurons for the sympathetics live here. Primary
neurons for sympathetics live in the lateral horn (intermediolateral). The sympathetic chain ganglia are
connected by presynaptic axons, travelling up and down the trunks. How do we get from spinal cord to
target, start in IML (lateral horn) through the ventral horn through the spinal nerve, through ventral
rami, then leave via the white rami (more myelin, faster tx) to a sympathetic chain ganglion. Once in
ganglion, have three choices: synapse in that ganglion and leave via the gray ramus to the ventral rami
proximal to where the white rami was located, some fiber will go posteriorly, but most runs anteriorly to
give body wall sympathetic innervation; enter via white ramus to ganglion, then descend (PrS axon) (or
ascend) down if going to say T11, but had entered at T7, then synapse in T11 ganglion and out the way
previously described via gray ramus; last choice is, say come in via white rami at T6, pass into the
ganglion, then leave without doing anything (can do this at T6/7/8) becoming splanchnic (internal
organs), T5-T12 splanchnic nn innervate GI tract, renal system and down to splanchnic section of bowel.
These will synapse on their target organs.
Somatic nervous system, one neuron system, from CNS to target.
Azygos vv, posterior intercostals feed into these. Can bypass IVC by going through the azygos system,
patient would have very large veins on their back. Hemiazygos and accessory hemizygous drain the left
side. IVC also here, on right side of the column.
Thoracic aorta runs in here too, posterior intercostal arteries branch off at T5. Branches to bronchial
arteries as well. Esophageal arteries here too branching off thoracic aorta.
Cisterna chyli found just inferior to diaphragm on the right side on vertebral column.
What connects posterior mediastinum to middle mediastinum? IVC
4th intercostal space to left of the sternum, enter the thorax, then into the middle mediastinum, heart is
here, lots of damage. So know where the different compartments are located for injuries.
Say midaxillary line, right side 6th intercostal space, what is not at risk? Can you hit the heart,
esophagus, sympathetic trunk, lung (all yes), liver too (cannot hit trachea, already split and terminated
to the lungs)
Say pt has MI, need a pacemaker, tried to put the pacemaker leads in the left subclavian vein and while
threading, the tip got caught in an opening right at the top of the SVC and pushed thorugh it, just went
through the azygos v.
Pt in automobile accident, old car, seatbelts optional, doesn’t have airbags, and no collapsible steering
column. Pt bounced his chest/sternum off the steering wheel, fractured the sternal ends of ribs 3 and 4
4 inches out from the midline, displacing them internally on the left side, hit the RV wall, lung tissue, no
major vessels here, if you go through the heart you could hit the thoracic aorta, but wouldn’t matter,
already dead.
Connect all the boxes and think about the relationships b/t them.
Embryology tomorrow and cases.