Thorax
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- Thoracic Inlet
-
1) Manubrium sterni
2) 1st Rib
3) Thoracic Vertebra 1 - Thoracic Outlet
-
1) 12th Rib
2) Thoracic Vertebra 12
3) Costal Cartiliges 7-10 (costal margin)
4) Xiphoid Process
- closed by diaphragm - Components of Sternum
-
1) Manubrium
2) Body
3) Xiphoid Process - Manubrium
-
1) superior: T2 - Suprasternal (jugular) notch
2) lateral:
clavicle at clavicle notch
costal cartilage of 1st rib and part of 2nd rib
3) inferior: body of sternum at sternal angle (angle of Louis) at T4-T5 - Sternal Angle (of Louis)
-
- 2nd costal cartilage articulates via synovial joints with manubrium and body
1) T4 - T5, T4 Disc
2) bifurcation of trachea
3) aortic arch begins and ends
4) divides superior and inferior mediastinum
5) articulation of 2nd rib (start count here)
6) arch of azygous vein, entrance into SVC
7) thoracic duct crosses over (a duck between two gooses) R --> L Posterior to aorta
8) Vagus --> L recurrent laryngeal nerve
9) esophagus: junction between upper 1/3 and lower 2/3
10) ligamentum arteriosum - Body
-
- articulates with costal cartilages of ribs 2 to 7
- articulates above with the manubrium at the manubriosternal joint and with the xiphoid
- process below at the xiphisternal jont at T9 (on level with 6th rib - xihphoid process
- - cartilaginous in youth but ossified in adulthood
- Ribs
-
1) head articulates with same # vertebra and one above
Exceptions: 1, 10, 11, 12 only its own #
2) tubercle: transverse process of own vertebra
3) costal groove: VAN (superior to inferior) - true ribs
-
- ribs 1 to 7
- articulate with sternum by way of their costal cartilages - False Ribs
-
- ribs 8 to 12
- costal cartilages of ribs 8 to 10 articulates with cartilages above (dot directly with the sternum) - Floating Ribs
-
- ribs 11 to 12
- unattached anteriorly - Atypical Ribs
-
1st
2nd
10th
11th
12th - 1st rib
-
broadest, most curved, flat and shortest of the true ribs
- its superior surface has a scalene tubercle (for attachment of scalenus anterior) that
separates the groove for the subclavian vein anteriorly from the groove for the
subclavian artery (and lower trunk of the brachial plexus) posteriorly - 2nd rib
-
- articulates with TV1 and TV2 by its two articulate facets
- has a tuberosity for the serratus anterior muscle on its outer surface (posterior to this tuberosity is the insertion for scalenus posterior) - 10th rib
- - has one articular facet on its head for articulation with the body of TV10
- 11th and 12th
-
- each has one articular facet, no neck and no tubercle
- the 11th rib has a slight angle and a shallow costal groove whereas the 12th rib has no angle and no costal groove - external intercostalis
-
- “hand-in-front-pocket†fibers (directed obliquely inferiorly and anteriorly)
- extend from tubercle of ribs posteriorly to costochondral junction anteriorly
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- replaced by an anterior (external) intercostals membrane between costochondral
junction and the sternum
- originate from ribs above and insert into ribs below
- elevate ribs during inspiration (helping to increase thoracic volume)
- supplied by corresponding intercostal nerves - internal intercostalis
-
- middle layer
- fibers directed inferiorly and posteriorly (“hand-in-back-pocketâ€)
- extend from sternum to angle of ribs posteriorly
- replaced by the posterior (internal) intercostals membrane between the angle of rib and
the vertebral column
- depress ribs during expiration (except interchondral part that elevates ribs and is
inspiratory in function) - innermost intercostal
-
-laterally
-poorly developed (can be absent in upper 4 or 5 spaces)
- separated from the internal intercostals by intercostals vessels and nerve
(V.A.N)
- direction of fibers same as internal intercostal
- action unclear - subcostalis
-
-posterior
- better developed in lower thorax
- fibers bridge two intercostals spaces
- origin: inside angle of rib above
- insertion: inner surfaces of two ribs below
- elevates ribs - transversus thoracic
-
-anteriorly
- from posterior surface of xiphoid process and lower body of sternum upward
and laterally to costal cartilages of ribs 2-6
- depresses ribs during expiration
- innervated by intercostals nerves 3-6 - Diaphragm
-
- musculofibrous structure separating thoracic cavity from abdominal cavity
- most important muscle for inspiration
- its superior surface is covered by parietal pleura (primarily) and by fibrous
pericardium (centrally) which is adhered to its central tendon
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- its inferior surface is lined by parietal peritoneum except for that area where it is directly in contact with the bare area of the liver - origins of diaphragm
-
1. Sternal
- sternal portion originates from back of xiphoid process
- sernocostal hiatus (triangle) transmits superior epigastric vessels and is one site
for a diaphragmatic hernia
2. Costal
- arises from inner surfaces of lower 6 ribs and corresponding costal cartilages
3. Lumbar
a. arises from upper 2 or 3 lumbar vertebrae by way of two crura; the right
crus from the upper three and the left crus from the upper two lumbar
vertebrae right crus fibers form esophageal hiatus
b. some fibers also rise from medial and lateral acruate ligaments or
lumbocostal arches (thickened fascia of psoas major and quandratus
lumborum, respectively). The median arcuate ligament extends from
one crus to the other, passing infront of the aorta.
c. the lumbocostal (vertebrocostal) trigone contains loose connective
tissue that separates pleura above from suprarenal gland and superior pole
of kidney below. - insertion of diaphragm
- - central tendon of diaphragm (contains vena caval opening)
- Openings of diaphragm
-
1. Vena Caval Opening – T8
- transmit IVC and right phrenic nerve (left phrenic passes through
muscular part of hemidiaphragm)
2. Esophageal Opening (Hiatus) –T10
- transmits esophagus and vagus nerves
3. Aortic Opening (Hiatus) T12
- transmits aorta, azygos vein and thoracic duct
4. Sternocostal Hiatuses
- transmit the superior epigastric blood vessels
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5. Other
- sympathetic trunk passes under the medial arcuate ligament
- thoracic splanchnic nerves (greater, lesser and least) penetrate the crura
- hemiazygos vein pierces left crus of diaphragm - Blood supply of diagphragm
-
1. Arterial Supply
- superior surface by the pericardiacophrenic (internal thoracic),
musculophrenic (internal thoracic) and superior phrenic (thoracic aorta)
arteries
- inferior surface by the inferior phrenic (abdominal aorta)
2. Venous Drainage
- superior surface drained by corresponding veins primarily in the internal
thoracic vein
- inferior surface drained by inferior phrenic vein to the IVC on the right side
and to the left renal vein on the left side - Innervation of diagphragm
-
1. Motor
- phrenic nerve (ventral rami of C3, C4, C5)
- each hemidiaphragm supplied separately
2. Sensory (pleura and peritoneum)
- phrenic nerve supplies central portion (pain referred to shoulder and neck)
- lower intercostals nerves (7-11) supply periphery (pain referred to lower
thoracic and anterior abdominal walls) - Action of diaphragm
-
- the diaphragm descends when it contracts
- contraction increases thoracic volume and decreases intrathoracic pressure
during inspiration
- chief muscle of inspiration
- it also decreases the volume of the abdomen and increases intraabdominal
pressure (needed for defecation, parturition etc.) - diaphragmatic hernias
-
1. Congenital – most commonly through an incompletely closed embryonic
pleuroperitoneal canal (of Bochdalek), usually on the left side through costal part of
diaphragm
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2. Acquired – usually through the esophageal hiatus, referred to as a hiatal hernia - Inspiration
-
- occurs when the volume of the thoracic cavity is increased due to descent of the
diaphragm and elevation of the ribs
1. Quiet Inspiration
a. Diaphragm (increases vertical diameter of thorax when it contracts)
b. External Intercostals (elevate ribs, increasing anteroposterior (pump-handle)
and transverse (bucket-handle diameters of thorax)
c. (Interchondral portion of internal intercostals)
2. Forced Inspiration
a. Sternocleidomastoid* (elevates sternum to increase anteroposterior diameter)
b. Scalenes* elevate and fix ribs 1 and 2)
c. Pectoralis Minor* and Pectoral Major* (act from humeral insertion to
elevate ribs when arms are fixed – Patients in respiratory distress lean on
elbows to fix humeri)
d. Levator Scapula
e. Upper Trapezius
f. Rhomboids
g. Levatores costarum
h. Serratus Posterior Superior
i. (Erector Spinae)
j. (Latissimus Dorsi)
3. Deep Inspiration
Muscles of quiet inspiration plus:
a. Sternocleidomastoid
b. Scalenes
c. Levatores Costarum
d. Serratus Posterior Superior
Note: With exception of the diaphragm and external intercostals, the other muscles (e.g. SCM, scalenes etc) are accessory muscles of inspiration). - Expiration
-
- Depression of ribs and decrease in size of thoracic cavity
1. Quiet Expiration
- passive process accomplished by:
a. Elastic recoil of lungs (and costal cartilages)
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b. Relaxation of external intercostals (and diaphragm)
c. Gravity
2. Forced Expiration
- Active process accomplished by muscular effort
a. Internal Intercostals (decrease anteroposterior and transverse
diameters of thoracic cavity by depressing ribs)
b. Anterior abdominal Muscles (contract to compress the abdomen and
increase the intraabdominal pressure, pushing the diaphragm
upwards)
- Rectus Abdominis
- External Oblique
- Internal Oblique
- Transverse Abdominis
c. Quadratus Lumborum (lower 12th rib)
d. Serratus Posterior Inferior (depresses lower 4 ribs)
e. Transverse Thoracic (depresses rib 2-6)
Note: Accessory expiratory muscles are the anterior abdominal muscles, quadratus
lumborum and serratus posterior inferior - rib movements on inspiration
-
1. anterior ends elevated in a pump-handle fashion; increasing the A-P diameter
of the thorax
2. lateral parts elevated in a bucket-handle fashion; increasing the transverse
diameter of the thorax - arterial supply of thoracic wall
-
1. Internal thoracic (branch of subclavian)
- Branches include:
a. 1-6 anterior intercostals arteries
b. Superior epigastric (terminal branch)
c. Musculophrenic (terminal branch)
- gives off 7-11 anterior intercostals (i.e. lower 5)
d. Pericardiacophrenic artery (accompanies phrenic nerve)
e. Perforating branches (2-4 supply breast)
- Ends at 6th intercostals space, dividing into its two terminal branches
2. Highest (Supreme) Intercostal
- from costocervical trunk of subclavian artery
- gives rise to posterior intercostals 1 and 2
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3. Descending Thoracic Aorta
- gives rise to 3-11 (lower 9) posterior intercostals arteries
Note: Anterior Intercostals (to anterior thoracic wall) are derived from the internal thoracic
and its musculophrenic branch, whereas the posterior intercostals branch from the
highest intercostals (from costocervical trunk) and the thoracic aorta (primarily). - anastomoses of thoracic wall
-
1. Between superior epigastric (internal thoracic) and inferior epigastric (external
iliac). Collateral circulation between subclavian and external iliac arteries
2. Between anterior intercostals and posterior intercostals [collateral circulation
between subclavian (via internal thoracic) and aorta]
Collateral Circulation
The anastomoses described above provide an alternative route for blood flow if
the normal path is blocked as in coarctation (narrowing) of the aorta, for
example.
Coarctation of the aorta is a relatively common malformation characterized by
narrowing of the aorta proximal (preductal) or distal (postductal) to the ductus
arteriosus (i.e. the aorta narrows proximal to its descending thoracic part). So as
to reach the inferior parts of the body, arterial blood passes upward into the
subclavian artery, then circuitously through the internal thoracic artery to its
anterior intercostals branches and, through anastomoses channels, back to the
posterior intercostals arteries, to reach the descending aorta below the
constriction.
The intercostals arteries may significantly increase in size and notch the ribs.
These notches are diagnostic of coarctation of the aorta. - Venous Drainage of thoracic wall
-
- anterior intercostals veins drain into the internal thoracic vein (tributary of
brachiocephalic vein)
- the 1st right posterior intercostals vein drains into the right brachiocephalic
- the right 2nd, 3rd, and 4th intercostals veins form the right superior (highest
intercostals vein which then drains into the azygos
- the right 5-11 posterior intercostals drain directly into the azygos
- the 1st left posterior intercostals vein drains into the left brachiocephalic
- the 2nd and 3rd form the left superior intercostals vein which also drains into the left
brachiocephalic
- the left 4-11 posterior intercostals veins drain into the hemiazygos and accessory
hemiazygos veins and ultimately into the azygos; 4-8 to accessory hemiazygos and
11
9-11 to hemiazygos
Note: Anterior intercostals veins are tributaries of the internal thoracic vein whereas,
right posterior intercostals veins mostly drain into the azygos vein and left posterior
intercostals veins mostly drain into the hemiazygos and accessory hemiazygos veins.
The right subcostal vein drains into the azygos whereas the left one drains into the hemiazygos - lymphatic drainage of thoracic wall
-
A. PARASTERNAL (INTERNAL THORACIC) NODES
- 1 or 2 nodes in upper 4 or 5 intercostal spaces; along the upper part of the internal
thoracic artery
- receive afferent lymphatic vessels from medial part of breast, diaphragm, intercostals
spaces and costal pleura
- send efferents to bronchomediastinal trunk
- provide route by which cancer of the breast can spread to the lungs, mediastinum and
liver
B. PHRENIC (DIAPHRAGMATIC) NODES
- on thoracic surface of diaphragm
- receive afferent vessels from lower intercostals spaces, pericardium, diaphragm and liver
- efferent vessels sent to parasternal and posterior mediastinal nodes
C. INTERCOSTAL NODES
- 1 or 2 nodes found at vertebral end of intercostals spaces
- receive afferent vessels from pleura and associated structures
- nodes of upper spaces drain into thoracic duct while those of lower space drain into the
cisterna chili - innervation of thoracic wall
-
- they divide into small dorsal and large ventral primary rami
- dorsal primary ramus innervates dorsal musculature and skin of the back
- ventral primary rami (intercostals nerves) innervate intercostals muscles, skin and pleura
as well as abdominal muscles via T7 to T11 and posterior serratus muscles
A. INTERCOSTAL NERVES
- ventral primary rami of first eleven thoracic spinal nerves
- contain motor fibers, sensory fibers and postganglionic sympathetic fibers (to blood
vessels, sweat glands etc.)
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- innervate skin of chest and abdominal wall as well as intercostals and abdominal muscles
(via T7 to T11) and posterior serratus muscles (also innervate pleura)
- lateral cutaneous branch supplies skin on lateral chest wall (and mammary gland)
- anterior cutaneous branch supplies skin on the front of the thorax (and mammary
gland)
- 1st, 2nd and 3rd intercostals nerves supply thoracic wall and upper limb
- 7-11 intercostal nerves supply thorax and abdominal wall - T1
-
- primarily motor
- ventral ramus associated with brachial plexus has fine intercostals no lateral branch - intercostobrachial nerve
-
- lateral cutaneous branch of T2
- supplies skin on posterior medial side of arm - T3
- lateral cutaneous branch innervates axilla and medial side of arm
- T12
- dermatome above pubic symphysis
- T4
- dermatome in region of nipple
- T7
- dermatome in region of xiphoid process (epigastrium)
- T10
- dermatome of umbilicus
- thoracoabdominal nerves
-
- T 7-11
- muscles innervated by them include: intercostals, transverses abdominis, external and
internal obliques, rectus abdominis and serratus posterior inferior. They also provide
sensory innervation to the diaphragm, pleura and peritoneum.