THORACIC CAVITY

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THORACIC CAVITY

• HEART

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Pericardial Cavity

• Heart is located in the middle inferior
  mediastinum within the pericardial cavity.

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Visceral Pericardium

• Serous membrane
• Fig 1.37, p 139)
• Referred to as epicardium.
• Arterial mesocardium.
• Venous mesocardium.

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Visceral Pericardium

• Transverse sinus
• Space between arterial and venous mesocardium.
• Oblique sinus
• Space between right and left pulmonary veins.

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Pericardium

• Pericardial cavity.
• Parietal (serous)
• Fused to fibrous pericardium.
• Fibrous
• Fused with central tendon of diaphragm
• Pericardiacophrenic ligament.
• Fused with sternum
• Superior and inferior sternopericardial
  ligaments.

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Pericardium

• Blood supply (Fig. 1.38, p 139)
• Pericardial arteries.
• Pericardiacophrenic arteries.
• Musculophrenic arteries.
• Nerve supply
• CN X.
• Phrenic nerve.
• Sympathetic trunk.

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Cardiac Projections

• Apex is down and to left.
• Base of heart is superior to apex
• Upside down triangle.
• Base projection
• Horizontal plane across sternum.
• Level of costal cartilage 3.
• Ends 2 cm to left of left parasternal line.

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Cardiac Projections

• Apex projection
• 5th intercostal space.
• 8 cm (interclavicular line) to left of median
  line of sternum.
• Pericardium extends up to sternal angle.

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Layers of the Heart

• External
• Epicardium
• Visceral layer of serous pericardium
  subserous layer of connective tissue.
• Middle
• Myocardium
• Thickest
• Cardiac muscle tissue.

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Layers of the Heart

• Inner
• Endocardium
• Endothelial layer

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Cardiac Skeleton

• 4 interlocking fibrous rings
• Annuli fibrosi.
• Interconnected with membranous portion of
  interventricular septum.
• Fig. 1.40B, p 143)

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Cardiac Skeleton

• Functions of annuli fibrosi
• Rigid attachment for cardiac muscle fibers.
• Support for valves.

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External Heart

• Base
• Posterior aspect of heart.
• Mostly left atrium small part of right
  atrium.
• Apex
• Located at intercostal space 5 medial to
  nipple.
• Formed from left ventricle
• Fig. 1.42A, p 146.

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External Heart

• Diaphragmatic surface
• Rests on diaphragm.
• Mostly left ventricle and a small part of
  right.
• Sternocostal surface
• Faces anteriorly.
• Mostly right ventricle.

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External Heart

• Left margin (border)
• Left side of heart formed mostly of left
  ventricle and left auricle.
• Inferior margin (border)
• Intersection of diaphragmatic and sternocostal
  surfaces.
• Formed mostly from right ventricle.
• Superior border
• Left and right atria and auricles.

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Anterior Surface of Heart

• CC common carotid A.
• AA aortic arch
• SC subclavian V.
• SVC sup. VC
• RPA right pulmonary artery.
• RPV right pulmonary veins.
• RCA right coronary A.
• IVC inferior vena cava.
• LA ligamentum arteriosum

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Anterior Surface of Heart

• LPA left pulmonary A.
• LPV left pulmonary V.
• CB circumflex branch of left coronary A.
• LM left marginal A.
• LAD left anterior descending A.

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Blood Supply to Heart

• Blood supply to heart is via two coronary
  arteries (Fig. 1.49AB, 157)
• Coronary arteries are the direct and only
  branches off the ascending aorta.

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Right Coronary Artery

• Passes between pulmonary trunk and right auricle.
• To coronary sulcus.
• Follows coronary sulcus to diaphragmatic surface.
• Anastomoses with left coronary artery.

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Right Coronary Artery Supplies

• Right atrium.
• Right ventricle.
• Posterior half of interventricular septum.

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Right Coronary Artery Branches

• Artery to SA node.
• Artery to AV node.
• Right marginal artery.
• Posterior interventricular artery
• posterior descending artery (PDA)

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Left Coronary Artery

• Passes between pulmonary trunk and left atrium.
• Supplies
• Left atrium.
• Left ventricle.
• Anterior half of interventricular septum.

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Left Coronary Artery

• Major branches
• Anterior interventricular artery ( left
  anterior descending LAD).
• Circumflex artery.
• Left marginal artery.

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Venous Drainage from Heart

• Fig. 1.51, page 159
• Coronary sinus
• Located in posterior coronary sulcus.
• Opens into right atrium.
• Direct continuation of great cardiac vein.
• Tributaries
• Great cardiac vein.
• Middle cardiac vein.
• Small cardiac vein.

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Right Atrium

• Fig. 1.43, p 148
• Receives blood from
• Superior vena cava.
• Inferior vena cava.
• Coronary sinus.
• Anterior cardiac veins.
• Large, thin-walled chamber.

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Right Atrium

• Sub-chambers
• Main posterior cavity
• Sinus venarum.
• Anterior cavity
• Auricle.
• Lined with pectinate muscles.

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Right Ventricle

• Fig. 1.44, p 149
• Receives blood from right atrium.
• Thicker walled than right atrium.
• Trabeculae carnae.
• Moderator band
• (septomarginal trabecula)
• Conveys right branch of atrioventricular
  bundle.

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Right Atrioventricular Valve

• Also called the tricuspid valve.
• Chordae tendinae.
• Papillary muscles.
• Fig. 1.45 BC, p 150

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Right Ventricle

• Pulmonary valve
• Formed from three semilunar cusps.
• Pulmonary trunk
• Divides into left and right pulmonary arteries.

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Left Atrium

• Left atrium (Fig. 1.46, p 152)
• Receives blood from four pulmonary veins.
• Smaller and thicker-walled than right atrium.
• Posterior smooth portion receives pulmonary
  veins.
• Anterior portion auricle
• with pectinate muscles.

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Left Ventricle

• Fig. 1.47, p 153
• Wall 2-3 x as thick as wall of right ventricle.
• Trabeculae carnae are less coarse than those of
  right ventricle.
• No moderator band.
• Two large papillary muscles
• Anterior and posterior.

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Left Atrioventricular/Aortic Valves

• Left atrioventricular valve
• bicuspid or mitral valve.
• Aortic valve
• Composed of three semilunar cusps.

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Conduction System of the Heart

• Composed of modified specialized cardiac muscle
  cells.
• No nervous tissue in heart.
• Fig. 1.52, p 163)

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Sinoatrial Node

• Referred to as pacemaker of heart.
• Located in right atrium near opening of SVC
• Superior end of sulcus terminalis.
• Receives direct stimulation from
• Sympathetic cardiac nerves.
• Parasympathetic vagus nerves.

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Conduction System of the Heart

• Atrioventricular node
• Located in interatrial septum near tricuspid
  valve.
• Interventricular bundle
• Descends through channel in fibrous skeleton.
• Reaches membranous interventricular septum.
• Only connection between myocardium of atria
  and that of ventricles.

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Conduction System of the Heart

• Interventricular bundle
• Divides into two bundles in membranous
  portion
• Right crus (bundle branches) passes through
  moderator band.
• Left crus (bundle branches)

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Conduction System of the Heart

• Purkinje fibers
• Terminal endings of bundle fibers.
• Embedded in myocardium of ventricle.

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Great Vessels

• Ascending aorta
• Runs behind sternum to sternal angle.
• Only branches are the two coronary arteries.
• Fig. 1.58, p 172

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Arch of the Aorta

• Lies within superior mediastinum.
• Arches to the left over the left pulmonary
  artery.
• Apex of the arch reaches the middle of the
  manubrium.
• Three main branches
• Brachiocephalic.
• Left common carotid.
• Left subclavian.

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Arch of the Aorta

• Anterior relationships
• Left phrenic nerve.
• Left vagus nerve.
• Superficial cardiac plexus.

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Arch of the Aorta

• Inferior relationships
• Left recurrent laryngeal nerve.
• Ligamentum arteriosum.
• Pulmonary trunk.
• Left primary bronchus.

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Arch of the Aorta

• Posterior relationships
• Trachea
• Left recurrent laryngeal nerve.

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Descending Aorta

• Lies within posterior mediastinum.
• Begins at level of sternal angle.
• Ends in front of thoracic vertebra 12.
• Continuous with abdominal aorta.

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Descending Aorta Branches

• Paired intercostal arteries.
• Paired subcostal arteries.
• Two or more bronchial arteries.
• Two to five esophageal arteries.

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Other Thoracic Vessels

• Supreme intercostal
• From costocervical trunk of subclavian artery.
• Supplies IC spaces one and two.
• Internal thoracics
• Arise within root of neck.
• Descend lateral to sternum.

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Internal Thoracic Arteries

• Branches
• Musculophrenic (terminal)
• To diaphragm
• To intercostal spaces 7-9
• Superior epigastric (terminal)

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Internal Thoracic Arteries

• Branches
• Pericardioacophrenic arteries
• Accompanies phrenic nerve.
• Supplies pericardium, mediastinal pleura,
  diaphragm.
• Perforating branches
• Accompany anterior cutaneous branches of
  intercostal nerves.
• Largest in intercostal spaces 2-4 in
  females.

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Right Brachiocephalic Vein

• From
• Right internal jugular.
• Right subclavian.
• Tributary
• Right internal intercostal vein.
• Fig. 1.64, p 182

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Left Brachiocephalic Vein

• Formed from
• Left internal jugular vein.
• Left subclavian vein.
• Tributaries
• Left internal thoracic vein.
• Left superior intercostal.
• Inferior thyroid veins.

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Superior Vena Cava

• Formed from
• Right brachiocephalic vein.
• Left brachiocephalic vein.
• Receives
• Azygos vein.

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Azygos System

• Drains most of blood from thoracic wall.
• Consists of longitudinal veins lying on either
  side of thoracic vertebral bodies.
• Variable.

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Azygos Vein

• Forms in abdomen
• From right subcostal and ascending lumbar veins.
• Drains all right posterior intercostal veins
  except first.
• Also receives blood from the bronchial and
  esophageal veins.

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Hemiazygos Vein

• Forms in abdomen
• From left subcostal and left ascending lumbar
  veins.
• Receives four posterior intercostal veins.
• Crosses over thoracic vertebrae at T8 level.
• Empties into azygos vein.

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Other Thoracic Vessels

• Accessory hemiazygos vein
• Drains intercostal spaces 4-7(8) on left side.
• Crosses over thoracic vertebrae at level T7.
• Empties into azygos vein.
• Note Intercostal space 1 is drained by the
  supreme intercostal vein emptying into the
  brachiocephalic vein.