Thorax Outline Week 12

• Thorax

Thorax Overview

• Located in the region between the neck and abdomen
• Superior Thoracic Aperture is commonly called the Thoracic Outlet
• The Superior Thoracic Aperture allows passage for structures between the head, neck, and upper extremities
• Superior Thoracic Aperture is bound posteriorly by the body of T1, laterally by Rib 1, and anteriorly by the manubrium of the sternum
• The Inferior Thoracic Aperture is closed by the diaphragm
• The Inferior Thoracic Aperture has three hiatuses: caval for the inferior vena cava, aortic for the aorta, and esophageal for the esophagus
• Inferior Thoracic Aperture allows passage for structures between the thorax and lower half of the body
• Inferior Thoracic Aperture is Bound posteriorly by the body of T12, laterally by the lower ribs and costal cartilages, and anteriorly by the xiphoid process of the sternum

Thoracic Cavity

• Enclosed by the ribs, thoracic vertebrae, and sternum
• The abdominal cavity separated from the Thoracic Cavity by the diaphragm
• Thoracic Cavity is composed of three spaces: the mediastinum, and the right and left pulmonary cavities
• The mediastinum is a central space that contains the heart, thymus, esophagus, trachea, major vasculature to the heart and lungs, vagus and phrenic nerves, and the thoracic duct
• Right and left pulmonary cavities contain the lungs

Thoracic Wall

• Includes the thoracic cage and muscles that extend between the ribs
• Thoracic Cage, composed of the thoracic skeleton, protects thoracic organs and some abdominal organs
• The functions of the thoracic wall include: protecting organs, resisting negative internal pressure related to lung recoil and inspiration, and providing attachment/support for the upper limbs

Thoracic Skeleton

• Includes 12 pairs of ribs and costal cartilages, 12 thoracic vertebrae and their IV discs, and the sternum

Thoracic Wall Muscles

• Superficial muscles
• Three layers of intercostal muscles

Ribs

• Ribs are curved, flat bones classified into three types: true, false, and floating
• True ribs (1-7) are vertebrosternal and attach directly to the sternum through their own costal cartilages
• False ribs (8, 9, 10) are vertebrochondral and have an indirect connection to the sternum through the cartilages of the ribs above
• Floating ribs (11, 12) do not have a connection to the sternum

Typical Rib Features

• Typical ribs (ribs 3-9) have a head with two facets
• One facet articulates with the vertebra of its corresponding number, and one for the superior vertebra
• Typical ribs feature a neck and a tubercle that articulates with the corresponding transverse process
• The body (shaft) of the rib is thin, flat, and curved
• The costal angle is the most marked curve where the rib turns anterolaterally
• The costal groove provides passage for the intercostal nerves and vessels

Atypical Ribs

• The 1st rib is broad, short, and most curved
• The 1st rib features a single articular facet for the T1 vertebra, a scalene tubercle for anterior scalene attachment and grooves for subclavian A/V
• The 2nd rib includes a tuberosity for the serratus anterior
• Ribs 10-12 have only one facet and articulate with a single vertebra
• Ribs 11 & 12 have no neck or tubercle
• Costal cartilage contributes to the elasticity of the thoracic wall

Thoracic Vertebrae

• The vertebral bodies feature costal facets for articulation with the heads of the ribs
• The transverse processes of thoracic vertebrae have costal facets for articulation with the tubercles of the ribs

Sternum

• Flat, elongated bone directly over the mediastinum
• The sternum has three parts: manubrium, body, and xiphoid process
• The manubrium includes the jugular notch and clavicular notches
• The body includes costal notches
• The xiphoid process is the inferior end, around the T10 level
• The Sternal Angle (Angle of Louis) is the junction between the manubrium and sternal body at the T4/T5 vertebral level
• The Sternal Angle (Angle of Louis) is an important landmark for Rib 2, the beginning of the aortic arch, tracheal bifurcation, and the pulmonary trunk

Joints of the Thoracic Wall

• The Sternoclavicular joint is a saddle-type synovial joint between the sternum and clavicle
• The Costochondral joint is a primary cartilaginous joint where the lateral end of costal cartilage articulates with the sternal end of rib
• The Sternocostal joint has varying types: the 1st joint is primary cartilaginous, while joints 2-7 are plane synovial
• Articulation of the 1st Sternocostal joint is between the 1st costal cartilage and the manubrium of the sternum
• Articulation of the 2nd-7th Sternocostal joints is between the costal cartilages and the sternum
• The Costovertebral joint is plane
• Articulation of head of the rib (2 facets, if present) with superior costal facet of a vertebra of the same number and with the inferior costal facet of the vertebral body superior to it
• Articulation of the costotransverse joint is between the tubercle of the rib and transverse process of vertebra of the same number
• Movements of the bony thorax include the pump-handle (rib/sternal elevation with increased A/P diameter) and bucket-handle (lower rib elevation with increased transverse diameter)

Intercostal Spaces

• Intercostal spaces separate ribs from one another
• There are 11 intercostal spaces, named for the superior rib
• The intercostal spaces are occupied by intercostal muscles and membranes, intercostal vessels, and nerves
• The space below the 12th rib is called the subcostal space
• The T12 spinal nerve is called the subcostal nerve
• Intercostal space contents run in the costal groove between the 2nd and 3rd layers of intercostal muscles: intercostal vein, intercostal artery, and intercostal nerve
• Endothoracic fascia separates the thoracic wall from parietal pleura

Thoracic Wall Muscles

• The superficial muscles originate from the upper extremity
• Deep muscles include the serratus posterior superior muscles, innervated by 2nd-5th intercostal nerves, elevate ribs 2-5 for inspiration
• Deep muscles include serratus posterior inferior muscles, innervated by 9th-11th intercostal nerves and the subcostal nerve (T12), depress ribs 9-12 for expiration
• Deep muscles include levator costarum, which run from transverse processes inferolateral to the tubercle or angle of ribs and are innervated by posterior rami of C8-T11 nerves, elevate ribs

Intercostal Muscles

• Includes subcostal muscles, usually well-developed only in lower thoracic wall
• Subcostal muscles extend from internal surface of the angles of ribs to the internal surfaces of inferior ribs, crossing 1-2 intercostal spaces
• Subcostal muscles run in the same direction as internal intercostals and have the same action
• Subcostal muscles are innervated segmentally by Intercostal Nerves (T1-T11)
• The Transversus thoracis consists of 4-5 slips superior and lateral radiating muscles from posterior aspect of inferior sternum, inferiorly continuous with transverse abdominis
• The act to weakly depress ribs, and are innervated segmentally by Intercostal Nerves (T1-T11)
• External intercostals: in intercostal spaces from tubercles to costochondral junctions, run inferior and anterior
• External intercostals are inferiorly continuous with external obliques and are most active during inspiration, innervated segmentally by Intercostal Nerves (T1-T11)
• Internal intercostals: in intercostal spaces from rib angles to sternum, run inferior and posterior
• Internal intercostals are inferiorly continuous with internal obliques and are most active during expiration, innervated segmentally by Intercostal Nerves (T1-T11)
• Innermost intercostals: similar to internal intercostals, are separated from intercostals by intercostal nerves and vessels, occupy the lateral most parts of intercostal spaces, and share the same action as internal intercostals
• Innermost intercostals are innervated segmentally by Intercostal Nerves (T1-T11)
• All intercostal muscles keep intercostal space rigid and prevent bulging of thoracic cavity during respiration
• Difficult to discern true individual roles in moving the ribs

Accessory Muscles of Respiration

• Muscles with attachments on the thoracic cage, assist with respiration
• Include: Scalenes, SCM, Pectoralis Major & Minor, Serratus Anterior, Abdominals

Thoracic Wall Arterial Supply

• Internal Thoracic A. is a branch of the Subclavian A.,
• Anterior & Posterior Intercostal Arteries are primary suppliers of the thoracic wall,
• Anterior branch of Internal Thoracic A, Posterior branch of Thoracic Aorta

Thoracic Wall Venous Drainage

• Drainage of the thoracic wall via Anterior and Posterior Intercostal Veins
• Posterior Intercostal Veins drain to the Azygos Vein
• Anterior Intercostal Veins drain to the Internal Thoracic Veins
• Azygos Vein drains into the Superior Vena Cava
• Internal Thoracic Veins drain into the Brachiocephalic Veins

Thoracic Wall Nerves

• 12 pairs of thoracic spinal nerves supply the thoracic wall, dividing into anterior and posterior rami
• Anterior rami T1-T11 are intercostal nerves, T12 is the subcostal nerve
• Posterior rami pass posteriorly to supply the joints, deep back muscles, and skin of thoracic region

Diaphragm

• Separates the thorax and abdomen, serving as the primary muscle of inspiration
• Descends for inspiration; is innervated by the Phrenic Nerve (C3-C5)
• Features openings for the Inferior Vena Cava, Esophagus, and Aorta
• Diaphragm Contraction = inhalation
• Flattens and increases thoracic volume = decreases intrathoracic pressure, creating a vacuum to pull air into the lungs
• Diaphragm Relaxation = exhalation
• Recoils into resting domed position, decreasing thoracic volume, with increased intrathoracic pressure, so forces air out of the lungs

Thoracic Cavity

• Enclosed by the thoracic wall, including right and left Pleural Cavities/lungs and the mediastinum (central)

Pleural Cavity

• Two independent cavities positioned on the right and left side of the mediastinum, surrounding the lungs
• Pleura is a mesothelial lining of the pleural cavity between the parietal and visceral pleural layers
• Parietal Pleura lines the wall of the pleural cavity
• Visceral Pleura lines the surface lungs

Lungs

• Functional organ of respiration Surrounded by the Pleural Cavity
• Structures include the Apex (top), Base (bottom), and Hilum
• Hilum is a medial portion with structures that enter and leave the lungs
• The structures passing through the hilum include the main bronchus, the pulmonary artery which carries deoxygenated blood to the lungs, the superior and inferior pulmonary veins which carry oxygenated blood from the lungs, and the bronchial arteries and veins which provide vascular supply/drainage
• Nerves: The Pulmonary Plexus provides parasympathetic and sympathetic innervation
• Sympathetic Trunks (T1-T4) are sympathetic, dilating the bronchioles and inhibiting bronchial secretions
• The Vagus Nerve is parasympathetic, constricting bronchioles and increasing bronchial secretions
• Lymphatics

Lung Lobes

• Right lung has 3 lobes
• The Horizontal Fissure separates the superior and middle lobes
• The Oblique Fissure separates the middle and superior lobe from the inferior lobe
• Left lung has 2 lobes
• The Oblique Fissure separates the upper and lower lobes
• Lingula is a tongue-like projection from the upper lobe
• Cardiac Notch is a depression for the apex of the heart

Bronchial Tree

• The trachea descends into the thorax from the neck and bifurcates at the T4/5 Level into R&L Main Bronchi
• The Right Primary Bronchus divides into the Superior, Middle and Inferior Secondary Bronchi
• The Left Primary Bronchus divides into the Superior and Inferior Secondary Bronchi
• Each secondary bronchi further divides into tertiary bronchi which continue to divide
• Smallest bronchi give rise to bronchioles which terminate in alveolar sacs, where gas exchange occurs

Bronchopulmonary Segments

• Anatomically, functionally, and surgically independent units of the lungs
• The Right Lung has 10 segments, and the Left Lung has 8-9

Heart

• Cone-shaped structure posterior to the sternum, with 1/3rd to the right and 2/3rds to the left
• Apex = inferior tip of the L ventricle
• Base = both atria, mostly L Atrium, lies primarily on the posterior surface of the heart
• Surrounded by the Pericardial Sac
• Parietal pericardium is the external covering
• Visceral pericardium covers the heart, also is the epicardium
• Pericardial cavity is the space between the serous pericardial layers

Heart Layers

• Epicardium is the outer layer, a loose connective tissue, adipose tissue and visceral pericardium
• Myocardium is the middle layer, with cardiac muscle responsible for contraction of the heart
• Endocardium is the inner layer of endothelial cells that line the inside of each heart chamber

Heart Chambers

• Two atria and two ventricles, that receive blood from circulation.
• Right Atrium: receives deoxygenated blood from systemic and coronary circulation, from the superior and inferior vena cava, and coronary sinus during systole
• Pumps blood to Right Ventricle through the Tricuspid Valve (Right AV) during diastole
• Structures of the Right Atrium include openings of the Inferior Vena Cava(IVC), Superior Vena Cava (SVC), and coronary sinus; the Fossa Ovalis (remnant of the foramen ovale in the fetus), the Right Auricle(an outpouching), and the Pectinate Muscle (ridges of myocardium)
• Left Atrium: receives oxygenated blood from pulmonary circulation
• Pumps oxygenated blood to the Left Ventricle
• The Left Atrium Structures include openings of Pulmonary Veins, the Left auricle, and the Pectinate Muscle

Heart Ventricles

• Two ventricles pump blood away from the heart
• Right Ventricle: pumps deoxygenated blood to the lungs through the Pulmonary Valve during systole
• Includes Trabeculae carnae (ridges of myocardium in the ventricle), Papillary muscles (elevations of myocardium that attach to the cusps to keep it closed during systole), and Chordae Tendineae (connect papillary muscles to the tricuspid valve cusps)
• Left Ventricle: pumps oxygenated blood to the rest of the body through the Aortic Valve during systole
• Important Structures of the Left Ventricle include Trabeculae Carneae, Papillary Muscles, and Chordae Tendineae

Heart Sides

• Right Side = pulmonary circuit
• Right atrium and ventricle receiving deoxygenated blood from circulation and sends to lungs
• Left Side = systemic circuit
• Left atrium and ventricle receiving oxygenated blood from pulmonary veins and pumps it into systemic and coronary circulation

Heart Valves

• 2 AV valves – open during diastole: Tricuspid and Mitral
• 2 Semilunar Valves – open during systole: Pulmonary/Pulmonic and Aortic
• Interconnected by a fibrous tissue ring which creates the cardiac skeleton
• Heart Sounds: S1 (lub) = closure of AV valves; S2 (dub) = closure of semilunar valves

Heart Coronary Arteries

• Supply oxygenated blood to the myocardium, maximal during diastole but minimal during systole
• L/R Coronary Arteries come from Ascending Aorta just above the aortic valve
• The Left Coronary Artery – supplies most of the left ventricle, left atrium, bundle of His, anterior interventricular septum
• The Left Anterior Descending (LAD), and important branch is of the LCA, supplying majority of Left ventricle and apex of the heart
• Circumflex A. supplies the left atrium and ventricle, where the L. Marginal A. supplies the L ventricle
• Posterior IV A. – Supplies R & L posterior ventricle
• The Right Coronary Artery supplies the right atrium, right ventricle, and SA node and AV node
• SA Nodal A. – supplies SA node
• R. Marginal A. – supplies R ventricle
• AV Nodal A. – Supplies AV node
• Posterior IV A. supplies R&L posterior ventricle

Cardiac Veins

• Drain deoxygenated blood from the myocardium
• Run with coronary arteries
• Drains into the Coronary Sinus, which drains into the Right atrium

Heart Conduction System

• Intrinsic conducting system consisting of noncontractile cardiac cells that initiate and distribute impulses throughout the heart
• Sinoatrial Node(SA Node)
• Located where the Right atrium meets the SVC, and is the pacemaker of the heart - initiates heartbeat
• Atrioventricular Node (AV Node)
• Located in the interatrial septum above the opening to the coronary sinus, it receives impulses from SA node and passes them to the Bundle of His
• Bundle of His: runs from AV node through the fibrous skeleton of the heart and divides into Right and Left Bundles
• Transmits impulses down interventricular septum and distributes to ventricular muscle through Purkinje Fibers

Heart Innervation

• Parasympathetic- Vagus Nerve
• Decreases heart rate and force of contraction via the medulla oblongata
• Sympathetic - Cardiac Splanchnic Nerves- Increases heart rate and force of contraction by T1-T4
• Visceral Afferents: Pain fibers follow sympathetic pathway back to spinal cord (T1-T4)
• Other visceral afferents information regarding stretch, baroreflexes, and chemoreflexes, etc follow the parasympathetic pathway and are conveyed to the brainstem via the Vagus N.

Great Heart Vessels

• Vessels for Pulmonary circulation
• Pulmonary Trunk – arise from Right ventricle, carrying deoxygenated blood
• R/L Pulmonary Arteries – carry deoxygenated blood to lungs
• Pulmonary Veins: Carry oxygenated blood from the lungs to the Left atrium
• Arteries for Systemic Circulation
• Aorta: Ascending begins at Left Ventricle
• Aortic Arch begins at the level of the 2nd rib arch, coursing upward and backward
• Includes the Brachiocephalic Trunk (divides into Right Common Carotid and Right subclavian), the Left Common Carotid Artery., and the Left Subclavian Artery.
• Descending (Thoracic) begins at the T4 vertebral level
• Veins for Systemic Circulation
• Right and Left Brachiocephalic Veins, where the internal jugular veins and subclavian veins meet
• Superior Vena Cava- Created by the joining of the Right and Left Brachiocephalic Veins
• Brings deoxygenated blood from the head, neck, and upper extremities to the Right atrium
• Inferior Vena Cava- Returning deoxygenated blood from the middle and lower regions of the body