Download File

Thoracic cavity & contents
Thorax Unit
Lecture 3 & 4
‫ حيدر جليل األعسم‬.‫د‬
Thoracic Cavity
Chest (thoracic) cavity is bounded by
chest wall and below by diaphragm. It
extends upward into the root of the
neck about one fingerbreadth above the
clavicle on each side. The chest cavity
can be divided into a median partition,
called the mediastinum, and the
laterally placed pleurae and lungs.
Mediastinum:
It is a movable median partition of chest
cavity that extends superiorly to thoracic
outlet and root of the neck and
inferiorly to diaphragm. It extends
anteriorly to sternum and posteriorly to
vertebral column.
Diaphragm:
It is a very thin muscle that (with pleura
and peritoneum) separates the chest
from the abdominal viscera.
Thoracic Cavity
Mediastinum is divided by an imaginary plane from anteriorly sternal
angle to posteriorly lower border of body of 4th thoracic vertebra, into:
A. Superior mediastinum: bounded by in front by manubrium sterni and
behind by first four thoracic vertebrae.
B. Inferior mediastinum: bounded in front by body of sternum and
behind by lower eight thoracic vertebrae. It is further subdivided into:
Middle mediastinum (pericardium and heart)
Anterior mediastinum (a space
between pericardium and sternum)
Posterior mediastinum (between
pericardium and vertebral column).
Contents of Mediastinum:
Thymus
Heart and large blood vessels.
Trachea
Esophagus.
Thoracic duct and lymph nodes.
Vagus, phrenic nerves & sympathetic trunks.
The Diaphragm
It is a thin muscular and tendinous septum
that separates chest cavity above from
abdominal cavity below. It is pierced by
structures that pass between chest and
abdomen. Diaphragm is the most
important muscle of respiration. It is dome
shaped & consists of a peripheral muscular
part, which arises from margins of thoracic
opening, and a centrally placed tendon.
Origin: can be divided into three parts:
A. Sternal part arising from posterior
surface of xiphoid process
B. Costal part arising from deep surfaces of
lower six ribs and their costal cartilages
C. Vertebral part arising by vertical
columns or crura & from arcuate ligaments
The Diaphragm
Right crus arises from the sides of bodies
of first three lumbar vertebrae and the
intervertebral discs.
Left crus arises from the sides of bodies of
first two lumbar vertebrae and the
intervertebral disc. Medial borders of the
two crura are connected by a median
arcuate ligament, which crosses over the
anterior surface of aorta. Lateral to crura
the diaphragm arises from medial and
lateral arcuate ligaments.
Medial arcuate ligament extends from side
of the body of 2nd lumbar vertebra to tip of
transverse process of first lumbar vertebra.
Lateral arcuate ligament extends from tip
of transverse process of first lumbar
vertebra to lower border of the 12th rib.
The Diaphragm
Insertion: diaphragm is inserted into a
central tendon, which is shaped like three
leaves. The superior surface of the tendon
is partially fused with the inferior surface of
the fibrous pericardium. Some of the
muscle fibers of the right crus pass up to
the left and surround the esophageal
orifice in a slinglike loop. These fibers
appear to act as a sphincter and possibly
assist in the prevention of regurgitation of
the stomach contents into the thoracic part
of the esophagus.
Shape of Diaphragm
Diaphragm curves up into right and left
domes, or cupulae.
Right dome: reaches as high as upper
border of fifth rib.
Left dome: may reach lower border of fifth
rib. (right dome lies at a higher level?)
Central tendon: at xiphisternal joint level
Openings in the Diaphragm
1. Aortic opening lies anterior to body of
12th thoracic vertebra between crura. It
transmits aorta, thoracic duct & azygos vein
2. Esophageal opening lies at level of 10th
thoracic vertebra in a sling of muscle fibers
derived from right crus (It transmits
esophagus, right and left vagus nerves,
esophageal branches of left gastric vessels
& lymphatics from lower 1/3 of esophagus
3. Caval opening lies at level of 8th thoracic
vertebra in central tendon. It transmits
inferior vena cava and terminal branches of
right phrenic nerve.
In addition to these openings:
Sympathetic splanchnic nerves pierce crura
Sympathetic trunks pass posterior to
medial arcuate ligament on each side
Superior epigastric vessels pass between
sternal and costal origins of diaphragm.
Nerve Supply of the Diaphragm
Motor nerve supply:
Right and Left phrenic nerves (C3, 4, 5)
Sensory nerve supply:
Central surfaces of diaphragm:
Right and Left phrenic nerves (C3, 4, 5)
Periphery of diaphragm:
Lower six intercostal nerves.
Action and fucntions of the Diaphragm
On contraction, diaphragm pulls down its
central tendon and increases vertical
diameter of thorax.
Therefore, functions of the diaphragm are:
1. Muscle of inspiration.
2. Muscle of abdominal straining.
3. Weight-lifting muscle.
4. Thoracoabdominal pump for blood &
lymph.
Pleura (Pleurae)
Pleurae and lungs lie on either side of
mediastinum within chest cavity.
Each pleura has two parts:
Parietal layer: lines thoracic wall, covers
thoracic surface of diaphragm and lateral
aspect of mediastinum, and extends into the
root of neck to line undersurface of
suprapleural membrane at thoracic outlet;
Visceral layer: completely covers outer
surfaces of lungs and extends into depths of
interlobar fissures.
The two layers become continuous with one
another by means of a cuff of pleura that
surrounds the structures entering and leaving
lung at hilum of each lung. To allow for
movement of pulmonary vessels and large
bronchi during respiration, pleural cuff hangs
down as a loose fold pulmonary ligament.
Parietal Pleura
Cervical pleura: lining undersurface of suprapleural membrane.
Costal pleura: lines inner surfaces of ribs, costal
cartilages, intercostal spaces, sides of vertebral
bodies, and back of sternum.
Diaphragmatic pleura: covers upper thoracic
surface of diaphragm.
Costodiaphragmatic recess is slit-like spaces
between costal and diaphragmatic parietal
pleurae that are separated only by a capillary
layer of pleural fluid. In quiet respiration,
costal & diaphragmatic pleurae are in
apposition to each other below lung border.
In deep inspiration, margins of lung base
descend and expand with in this recess.
Mediastinal pleura: covers and forms lateral
boundary of mediastinum.
Costomediastinal recess is a slit-like space situated
along anterior margins of pleura between mediastinal
and costal pleura which are separated by a capillary layer
of pleural fluid.
Pleural cavity
It is a slit-like space that separate parietal
and visceral layers of pleura. Pleural cavity
normally contains a small amount of
pleural fluid, which covers the surfaces of
pleura as a thin film and permits two
layers to move on each other with the
minimum of friction.
During full inspiration, lungs expand and
fill the pleural cavities. However, during
quiet inspiration the lungs do not fully
occupy pleural cavities at four sites:
right & left costodiaphragmatic recesses
right & left costomediastinal recesses.
Nerve Supply of Pleura
Parietal pleura is sensitive to pain,
temperature, touch, and pressure:
• Costal pleura is segmentally supplied
by intercostal nerves.
• Mediastinal pleura is supplied by
phrenic nerve.
• Diaphragmatic pleura is supplied over
the domes by phrenic nerve and
around periphery by lower six
intercostal nerves.
Visceral pleura is sensitive to stretch but
is insensitive to common sensations such
as pain and touch. It receives an
autonomic nerve supply from the
pulmonary plexus.
Lungs
Lungs are soft and spongy and very
elastic organs.
If the thoracic cavity were opened,
lungs would immediately shrink to one
third or less in volume. In children,
they are pink, but with age, they
become dark and mottled because of
inhalation of dust particles that
become trapped in phagocytes of the
lung.
Lungs are situated on each side of
mediastinum & separated from each
other by heart and great vessels and
other structures in mediastinum. Each
lung is conical, covered with visceral
pleura, and suspended free only by its
root in its own pleural cavity.
Lungs
• Apex : projects upward into the neck above the clavicle
• Concave base: (sits on diaphragm)
• Convex costal surface: corresponds to the concave chest wall
• Concave mediastinal surface: is molded to pericardium and other
mediastinal structures. At about middle of this surface is Hilum, a
depression in which bronchi, vessels, and nerves enter and leave the
lung forming the root of the lung.
Anterior border is thin & overlaps heart and on left lung, cardiac notch.
Posterior border is thick and rounded & lies beside vertebral column.
Lobes and Fissures of Lungs
Right Lung
Right lung is slightly larger than the left
and is divided by oblique and horizontal
fissures into 3 lobes:
upper, middle, and lower lobes.
Oblique fissure runs from inferior
border upward & backward across
medial & costal surfaces until it cuts
posterior border 2.5 inches below apex.
Horizontal fissure runs horizontally
across costal surface at the level of 4th
costal cartilage to meet oblique fissure
in midaxillary line. Middle lobe is thus a
small triangular lobe bounded by
horizontal and oblique fissures.
Left Lung
Left lung is divided by a similar oblique
fissure into 2 lobes: upper and lower
lobes. No horizontal fissure in left lung.
Bronchopulmonary Segments
Bronchopulmonary segments:
They are structurally and functionally
independent unit of a lung lobe and
are surrounded by connective tissue.
They are, anatomic, functional, and
surgical units of lungs.
Lobar (secondary) bronchus: passes to
a lobe of lung, gives off branches
Segmental (tertiary) bronchi to
bronchopulmonary segment.
Segmental bronchus is accompanied by
a branch of pulmonary artery, but the
tributaries of pulmonary veins run in
the connective tissue between
adjacent bronchopulmonary segments.
Each segment has its own lymphatic
vessels and autonomic nerve supply.
Blood Supply of Bronchi, connective tissue of lung & visceral pleura:
Bronchial arteries: branches of descending aorta).
Bronchial veins drain into azygos and hemiazygos veins.
Alveoli receive deoxygenated blood
from terminal branches of pulmonary
arteries. Oxygenated blood leaving
alveolar capillaries drains into
tributaries of pulmonary veins,
which follow intersegmental
connective tissue septa to the
lung root. Two pulmonary veins
leave each lung root to empty
into left atrium of the heart.
Lymph Drainage of Lungs
All lymph from lungs leaves hilum
And drains into tracheobronchial
nodes and then into
bronchomediastinal lymph trunks.
Nerve Supply: Sympathetic trunk & Vagus nerve (parasympathetic)
Thank You