Cardiovascular System - Heart PDF

CARDIOVASCULAR SYSTEM - HEART Objectives: Students should be able to: i.iname the structures forming the walls of the thorax and define the terms “mediastinum” and “pleural cavities”; ii.describe the basic structure of the heart and state it position in the thorax; iii.define...

CARDIOVASCULAR SYSTEM - HEART Objectives: Students should be able to: i.iname the structures forming the walls of the thorax and define the terms “mediastinum” and “pleural cavities”; ii.describe the basic structure of the heart and state it position in the thorax; iii.define the terms “pericardium” and “pericardial cavity”; iv.name the chambers of the heart, their relationships to one another in the anatomical position and list the main features of each; v.name the valves of the heart, state their locations and outline how they function; vi.outline the coronary circulation and name the great vessels entering and leaving the heart; vii.outline the conducting system of the heart; viii.list the changes that occur in the heart at birth. The cardiovascular system functions to transport blood, nutrients and waste products of metabolism from one part of the body to another. For example, nutrients from the intestine are transferred to tissues and organs, while waste products of metabolism are transported to excretory organs such as the kidney. In order to perform its functions the cardiovascular system consists of a muscular pump, the heart, and a series of vessels. The latter carry blood from the heart to the tissues (arteries and arterioles), allow exchange of nutrients and waste products in the tissue (capillaries) and return blood from the tissues back to the heart (venules and veins). Outline of Thorax THORAX DIVISIONS & HEART LOCATION CORONAL SECTION Pleural cavity & lung Rib cage Heart in mediastinum Diaphragm  2 The heart and the main vessels entering and leaving it are situated in the thorax, a region bounded posteriorly by the thoracic vertebral column, laterally by the ribs and intercostal spaces, and anteriorly by the costal cartilages and sternum. Superiorly the thorax is continuous with the neck and inferiorly it is separated from the abdomen by the diaphragm. The thorax can be divided internally into right and left pleural cavities, occupied by the lungs, and between them a central area, the mediastinum, containing other structures, including the heart and some major vessels. THORAX HEART LOCATION EEr SAGITTAL SECTION THROUGH MEDIASTINUM EE Sternum Vertebral column Heart Pericardial cavity Diaphragm Heart (Introduction) The adult heart is a four-chambered muscular pump, serving two separate circulatory systems which function simultaneously. These are the pulmonary circulation, which involves the transport of blood to the lungs and back to the heart, and the systemic circulation, involving the transport of blood around the body and back to the heart. The four chambers of the heart are the right and left ventricles and the right and left atria. Deoxygenated blood is pumped to the lungs from the right ventricle via pulmonary arteries, and oxygenated blood leaving the lungs is returned to the left atrium by way of pulmonary veins. The left atrium communicates with the left ventricle by means of a bicuspid valve. Blood from the left ventricle is transported around the body via the aorta and its branches, and is returned to the right atrium via the superior and inferior venae cavae. The right atrium communicates with the right ventricle through a tricuspid valve. OX bloodleaving Deoxblood to left wings via pulmonary Ethereum'onant atrium arteries veins  3 ADULT HEART - GENERAL FEATURES ANTERIOR VIEW Aorta (artery) Superior vena cava Pulmonary trunk (vein) (artery) Left atrium Right Left atrium ventricle Right ventricle In the embryo and foetus, oxygen is derived from the maternal blood via the placenta. The lungs are non-functional so there is no need for a separate pulmonary circulation. As a result the primitive heart is a simple tube. However, at the moment of birth, separate and pulmonary and systemic circulations must be instantaneously established. The structural modifications that allow this to happen, notably partitioning of the heart tube into four chambers, take place in the embryo. CARDIOVASCULAR CIRCULATION – SCHEMATIC CARDIOVASCULAR CIRCULATION – SCHEMATIC ADULT FOETUS LUNGS LUNGS RA LA RA LA RV LV RV LV PLACENTA BODY BODY Adult Pericardium and Heart Pericardium Within the mediastinum the heart lies in its own cavity, the pericardial cavity (pericardial sac). The wall of the cavity consists of a fibrous sheet, the pericardium, the inner surface of which reflects on to the surface of the heart. The pericardial cavity is only a potential space since, in life, it contains only a thin film of fluid.  4 Inferiorly, the pericardium fuses with the diaphragm; and superiorly it merges with the outer layers of the vessels emerging from the heart. Heart As a result of the folding and twisting of the heart during development, the right atrium comes to form its definitive right border, with the superior and inferior venae cavae entering from above and below, respectively. A small ear-like projection from the right atrium, the right auricle, extends anteriorly. The right ventricle forms most of the anterior surface of the heart, with the pulmonary trunk (forms right and left pulmonary arteries) leaving it superiorly. The left border of the heart is formed by the left ventricle, ending inferiorly at the apex. The ventricles are separated by shallow an anterior and a posterior interventricular sulcus. The aorta emerges from the superior aspect of the left ventricle. The left atrium forms much of the posterior surface of the heart, with the left auricle often wrapping around the left border, on to the pulmonary trunk. The pulmonary veins (usually two right and two left) open into the atrium. The right and left atria are separated from the corresponding ventricles by a distinct groove, the atrio- ventricular (coronary) sulcus which encircles the heart. The base of the heart, consisting of parts of the right and left ventricles lies over the diaphragm. HEART - EXTERNAL FEATURES ANTERIOR VIEW Aorta sorner R. pulmonary artery 1319111 Superior L. pulmonary artery vena cava Pulmonary trunk Right Left auricle auricle Right Left atrium ventricle Atrioventricular think (coronary) sulcus Apex Em Coronary Right Anterior vessels ventricle interventricular sulcus interventricular VENTRILES btwn ItE v  5 HEART - SURFACE PROJECTION Clavicle Superior Sternum border Sternal angle Ribs & costal Left border cartilages Right border Apex SKIPPED Inferior border The outline of the heart can be approximately related to the surface of the thorax, as follows: Right border - 3rd costal cartilage to the 6th costal just to the right of the sternum. Inferior border - 6th right costal cartilage to the 5th left intercostal space about 8 cm from the midline. Superior border - 3rd right costal cartilage to the 2nd left costal cartilage just to the left of the sternum. Left border - a curved line joining the left superior and inferior borders. Internal Features Right atrium - internally, the thin wall consists of a posterior, smooth part (derived from the sinus venosus) and a roughened (trabeculated) area anteriorly. The trabeculated area (derived from the primitive atrium) includes the right auricle and contains cardiac muscle fibres, known as pectinate muscles (pectinate = comb-like). A prominent vertical ridge, the crista terminalis, forms the junction between the smooth and rough parts. Between the right and left atria is the smooth interatrial septum. It has a depression, the fossa ovalis, which marks the site of the embryonic foramen ovale. The opening of the coronary sinus is close to the interatrial septum, adjacent to the opening of the inferior vena cava,  6 The right atrium communicates with the right ventricle via the tricuspid valve, with three flaps (cusps). HEART - INTERIOR RIGHT ATRIUM VIEWED FROM RIGHT SIDE Superior vena cava Aorta Right auricle Pectinate untrue muscles Fossa Right ventricle ovalis Tiruated Interatrial septum part Crista terminalis Coronary Inferior sinus opening vena cava Left atrium - most of the wall is smooth, due to the absorption of pulmonary veins into it during development. Usually, there are four pulmonary veins (two right and two left) entering the chamber and the only trabeculated part is the left auricle. The left atrium HEART - INTERIOR RIGHT VENTRICLE ANTERIOR VIEW Aorta Superior Pulmonary trunk vena cava Pulmonary valve Right atrium Interventricular septum Cusps of tricuspid valve Left ventricle Chordae tendinae Septomarginal Papillary muscle (moderator) band Trabeculae carnae  chordal tri bicuspid trabeccarnell papillary muscles 7 tendinal values communicates with the left ventricle through the mitral (bicuspid) valve, with just two cusps. Ventricles - the walls are thicker and more muscular than those of the atria. In turn, the wall of the left ventricle is thicker than the right since the former must pump blood around the whole body whereas the right ventricle pumps blood only to the nearby lungs. The internal surfaces of the ventricular walls are raised into muscular ridges, or trabeculae carnae (trabecula = ridge, bar; carnae = meaty). Projecting from the trabeculae carnae are papillary muscles. Attached to the tips of the papillary muscles are tendinous strands, chordae tendinae, which, in turn, attach to the free edges of the cusps of the tricuspid and mitral valves. The ventricles are separated by the interventricular septum. The two ventricles become smoother superiorly, where the pulmonary trunk leaves the right ventricle and the aorta leaves the left ventricle. Their openings are guarded by the tricuspid (three-cusped) pulmonary and aortic valves, but there are no chordae tendinae attached to them. Churchee HEART - VALVES Thy SUPERIOR VIEW attach Pulmonary valve ANTERIOR to AV VALVES Aortic valve R. coronary L. coronary artery artery LEFT RIGHT Atrioventricular Atrioventricular (mitral) valve (tricuspid) valve Coronary sinus POSTERIOR With respect to valve function, when the atria contract blood is forced into the ventricles through the tricuspid and mitral valves, the cusps of which are directed into the ventricles. As the ventricles contract, back pressure forces the valves closed. Simultaneous contraction of the papillary muscles, with their attached chordae tendinae, prevent the valve cusps from being forced back into the atria. Since the ventricular blood cannot re-enter the atria, the only outlets are into the aorta and pulmonary trunk. When blood enters the aorta and the pulmonary trunk their valve cusps open in the direction of blood flow. At the end of ventricular contraction, back pressure of blood in the arteries pushes down on the cusps and closes the valves.  8 HEART – VALVE FUNCTION HEART – VALVE FUNCTION MITRAL & TRICUSPID VALVES PULMONARY & AORTIC VALVES Atrium Blood Atrium flow Backflow Valve cusp Valve cusp Chordae tendinae Blood Blood pressure flow Papillary Ventricle Ventricle Ventricle Ventricle muscle VALVE OPEN VALVE CLOSED VALVE OPEN VALVE CLOSED Coronary Circulation The heart has its own well developed blood supply. The right and left coronary arteries are the first two branches of the aorta, arising from the aortic sinus, a distended area just above the aortic valve. The right coronary artery passes between the right atrium and right ventricle, along the coronary sulcus, at first anteriorly, then posteriorly, before ending as a posterior interventricular (posterior descending) branch, which occupies the interventricular sulcus. The left coronary artery soon divides into two branches. The circumflex branch, passes posteriorly along the coronary sulcus, between left atrium and left ventricle. The second branch, the anterior interventricular (left anterior descending - LAD) artery passes anteriorly along the interventricular sulcus. Many small arteries leave the main vessels and supply the wall of the heart. There may be anastomoses (connections) between branches of the right and left coronary arteries. HEART - CORONARY ARTERIES ANTERIOR VIEW Superior Aorta vena cava rein Right coronary artery Left coronary artery yq.fm Circumflex stinkweed artery Inferior vena cava Anterior interventricular (left anterior descending) Posterior interventricular artery HHY (posterior descending) artery vein posterior  9 Most of the cardiac veins draining the heart enter the right atrium via the coronary sinus, located posteriorly, in the coronary sulcus. The great (left) cardiac vein accompanies the anterior interventricular artery before joining the coronary sinus, while a middle cardiac vein often accompanies the posterior interventricular artery before entering the sinus. A number of anterior cardiac veins pass from the right ventricle directly into the right atrium. HEART - CARDIAC VEINS ANTERIOR VIEW Superior vena cava Aorta Anterior cardiac veins Coronary sinus Great cardiac vein Inferior vena cava Middle cardiac vein Conducting System The heart has its own intrinsic beat, during which a wave of contraction passes through the heart muscle. The contraction is initiated at the sinu-atrial node, an area of specialized cardiac muscle at the upper end of the crista terminalis and spreads through the atria to the atrioventricular node, located in the interatrial septum, close to the opening of the coronary sinus. Here, impulses are transferred to a bundle of modified muscle cells, the atrioventricular bundle (bundle of His) which travel through the interventricular septum, into the ventricles, stimulating them to contract. The right bundle may form a distinct structure in the right ventricle called the (septo-)marginal or moderator band). HEART - CONDUCTING SYSTEM SECTION THROUGH ATRIA & VENTRICLES Superior Pulmonary trunk vena cava Sinoatrial Left node atrium Right Atrioventricular atrium bundle (of His) Left Atrioventricular ventricle node Interventricular septum Right atrioventricular valve Septomarginal Right (moderator) band ventricle  PSNS SNS new to plexus Cardiac 10 The nerve supply to the heart is by way of the cardiac plexus, formed by sympathetic and parasympathetic nerve fibres. The sympathetic fibres cause acceleration of and an increase in the strength of the heart beat. The parasympathetic nerves have the opposite effect. APPLIED ANATOMY 1. What would be the effect(s) if the interatrial septum failed to close at birth? 2. What is meant by the term heart attack? arthrosclerotic plaque causes a blockage which will a ect a large chunk of musculature, and then the heart FAILS if harsh enough pieces of the heart die, dont dissappear but hang in there and dont contribute to the hearts overall function and stays as necrotic Ischaemia and heath of heart muscle (infarct sire) due to occlusion of coronary artieries or branches  CARDIOVASCULAR SYSTEM - ARTERIES, VEINS & LYMPHATICS Objectives: Students should be able to: i. name the main arteries and veins of the body and state the areas they supply and drain; ii. outline the lymphatic system, state its functions and give examples of its clinical importance with regard to the spread of infection and cancer; iii. name the groups of lymph nodes to which pelvic, abdominal, thoracic, head and neck organs drain; iv. describe the path taken by lymph from extracellular fluid to the venous system; v. name the main lymph trunks and ducts of the body. Arteries Arteries are vessels that carry blood away from the heart. The pulmonary trunk, which quickly divides into right and left pulmonary arteries, carries blood to the lungs, and is involved in the pulmonary circulation while the aorta is the outflow into the systemic circulation. The aorta can be divided into three parts - ascending, arch and descending - each of which has its own branches, as follows: ARTERIES R. Common carotid L. Common carotid EEE R. Subclavian L. Subclavian iii archdin Brachiocephalic Pulmonary trunk p mail.it ARCH RIB VESSELS Coronary AORTA ASCENDING Intercostal BRONCHAL ASK Thoracic Diaphragm tf Coeliac DESCENDING a weeks i 412 Superior mesenteric Suprarenal Abdominal Be IM Renal BL Common iliac Gonadal L4 BL Internal iliac Inferior mesenteric single fiiQ pelvis Lumbar External iliac BL ANTERIOR VIEW femoral femoral  AORTA ASIENDING Right novonary artery 2 wof short Left rayedartery i. Ascending aorta - emerges from the heart and it very short. Its branches are the right and left coronary arteries which supply the heart. Superiormediastinum ii. Arch of the aorta - arches posteriorly and to the left in the upper part of the mediastinum, to reach the left side of the vertebral column. It gives rise to the following branches: i. brachiocephalic artery - short. It divides into the right common carotid artery, which arms supplies head and neck structures and the right subclavian artery. The latter supplies the right upper limb but also gives some important branches to the head and neck; 8B ftp ii. left common carotid artery; iii. left subclavian artery. 31 eiiiiigifaiiiiiii iii. Descending aorta - descends along the left side of the thoracic vertebral column before passing to the midline. Within the thorax it is sometimes referred to as the thoracic aorta and it gives the following branches: Hstal descendingi. intercostal arteries to the thoracic wall (intercostal spaces); Descendingaorta ii. bronchial arteries to the bronchi of the lungs. Ask 1131004kEur darashi ffmff.hn The descending aorta then passes through the diaphragm, still on the vertebral column, into the abdomen, where it is known as the abdominal aorta. It descends in the midline to roughly the L4 vertebral level, where it divides into right and left common iliac arteries. Its main branches in the abdomen are as follows: a) in the midline, as single arteries: i. coeliac artery (trunk) - a short artery arising immediately below the diaphragm. It has branches that supply the oesophagus, stomach, duodenum, pancreas, liver and spleen; ii. superior mesenteric artery - arising just below the coeliac trunk. It has branches to the duodenum, pancreas, small intestine and much of the large intestine; Him iii. inferior mesenteric artery - arises at about the L3 vertebral level. It supplies the distal part of the large intestine and the rectum. b) bilaterally: suprarenal anger i. suprarenal arteries - small arteries just superior to renal arteries. They supply the suprarenal (adrenal) glands; ii. renal arteries - arise at the L1 - L2 vertebral level. They supply the kidneys and give branches to suprarenal glands; iii. gonadal (ovarian or testicular) arteries - leave the aorta below the renal arteries and pass inferiorly to the pelvis, where they supply the ovaries or testes; iv. segmental lumbar arteries which supply the abdominal wall. Common Iliac Arteries (right and left) - each divides into external and internal iliac arteries at the pelvic brim; i. external iliac arteries (right and left) - enter and supply the lower limbs as the femoral arteries; ii. internal iliac arteries (right and left) - enter and supply the structures of the pelvis. A few branches also supply parts of the lower limb.  int ygular 3 IHrachioseph Isfen subclavian Veins Veins return blood to the heart. The blood within them is under less pressure than in arteries so they tend to have relatively thin walls and wide lumens (lumina). In order to aid the return of blood to the heart, some peripheral veins, notably in the limbs, contain valves that only allow blood flow towards the heart. A pair of pulmonary veins drains each of the lungs into the left atrium, while the superior vena cava and inferior vena cava drain systemic blood into the right atrium of the heart. VEINS R. Internal jugular L. Internal jugular R. Subclavian L. Subclavian R. Brachiocephalic L. Brachiocephalic Hemiazygos SUPERIOR VENA CAVA Iain Azygos nearest Heart my Intercostal Diaphragm Bronchial hemia INFERIOR VENA CAVA Hepatic R. Suprarenal I 2PETE L. Suprarenal R. Renal L. Renal R. Gonadal L. Gonadal Common iliac Lumbar Internal iliac External iliac ANTERIOR VIEW Tributaries of the Superior Vena Cava i. Internal jugular veins (bilateral) - accompany the common carotid arteries and drain head and neck structures; ii. Subclavian veins (bilateral) - drain the upper limbs; iii. Brachiocephalic veins (bilateral) - formed on each side by the union of the internal jugular and subclavian veins. The left brachiocephalic vein crosses to join the right brachiocephalic vein in the upper part of the thorax, to form the superior vena cava. Just before entering the right atrium, the superior vena cava is joined by the azygos vein. The latter passes along the right side of thoracic vertebral column, before entering the superior vena cava. It receives right intercostal veins, right bronchial veins and one or more hemiazygos veins in the thorax. Hemiazygos veins receive the left intercostal and bronchial veins. ASK  4 Tributaries of the Inferior Vena Cava i. Internal iliac veins (bilateral) - receive veins draining the pelvic and lower limb structures supplied by corresponding arteries; ii. External iliac veins (bilateral) - continuous with femoral veins which drain the lower limb. They travel with the corresponding arteries; iii. Common iliac veins (bilateral) - formed by the union of the internal and external iliac veins at the pelvic brim. The left and right common iliac veins join at about L5 vertebral level, to form the inferior vena cava. The latter ascends immediately to the right of the aorta, before passing through the diaphragm and immediately enters the right atrium. The inferior vena cava receives the following veins: i. right gonadal (ovarian or testicular) vein - drains right ovary or testis. It accompanies the corresponding artery. Note that the left gonadal vein drains into the left renal vein; ii. renal veins (bilateral) - drain the kidneys. The left renal vein receives the left gonadal and left suprarenal veins and crosses the aorta to reach the inferior vena cava; iii. right suprarenal vein - enters the inferior vena cava just superior to right renal vein; iv. hepatic veins - very short. They enter the inferior vena cava just before the latter pierces diaphragm (sometimes the inferior vena cava is enclosed by the liver). v. lumbar veins (bilateral, segmental veins) draining the abdominal wall. Much of the blood draining the gastrointestinal tract is directed through the liver via the hepatic portal vein, formed by the union of the splenic, superior mesenteric and inferior mesenteric veins. VEINS (Cont.) HEPATIC PORTAL VEIN Inferior vena cava Hepatic Liver Splenic f I Hepatic portal Inferior Superior mesenteric mesenteric Axillary IN Cephalic Basilic faster MY SUPERFICIAL VEINS Median OF UPPER LIMB cubital Some superficial veins are important with respect to drawing blood or giving injections. For example, on the anterior surface of the upper limb, in the region of the elbow, the median cubital  5 vein is usually visible, crossing the limb obliquely, from the cephalic vein, located laterally, to the basilic vein, on the medial side of the limb. The cephalic and basilic veins eventually drain into the axillary vein, which becomes the subclavian vein. Lymphatic System The cells of the body are bathed in extracellular fluid, from which they derive nutrients and into which they deliver products of metabolism. There is constant exchange between fluid in the extracellular spaces and the blood. A small portion of the fluid, termed lymph, does not enter the blood directly but instead passes into thin-walled lymph vessels (lymphatics) which form networks, or plexuses, that often accompany blood vessels. It is a low pressure system so the lymphatics contain numerous valves which prevent backflow of lymph. LYMPHATIC SYSTEM LYMPH NODE Afferent lymphatic Efferent lymphatic EXAMPLES OF MAJOR LYMPH NODE GROUPS Internal jugular vein Subclavian vein aments Axillary nodes Para-aortic nodes after Inguinal nodes Inguinal Aorta Interspersed along the lymph vessels are swellings, known as lymph nodes. They filter the lymph and are sites of lymphocyte and antibody production (part of the immune system). The vessels bringing lymph to the nodes are termed afferent lymphatics and those leaving them are called efferent lymphatics. The lymph nodes tend to lie in close proximity to blood vessels and usually form inter-connecting regional groups, some of which may be superficial e.g., inguinal lymph nodes in the groin, axillary nodes in the armpit, while others are related to deeper blood vessels, e.g., para-aortic and iliac nodes, associated with the abdominal part of the aorta and the iliac arteries. The size of the nodes varies considerably. For example, some superficial nodes are very small and normally cannot be felt (palpated) through the skin, while others are quite large and  6 easily palpated, such as those in the groin (inguinal nodes). In the event of disease, even small lymph nodes may enlarge considerably, and become palpable. In addition, disease can spread via the lymphatic system, passing from one lymph node to the next in the chain. It is therefore important to know the lymphatic drainage of specific organs, or regions, in order to: i) determine the extent of spread of a disease from a given site; ii) predict which lymph nodes could be affected as the result of a disease originating at a certain site. This knowledge is particularly important with respect to the spread of cancer through the lymphatic system. Malignant cells originating in a primary tumour are able to disassociate, enter lymphatics and form secondary tumours in lymph nodes along the drainage path. Breast cancer often spreads in this way. LYMPHATIC SYSTEM DRAINAGE OF THE BREAST ANTERIOR VIEW Axillary nodes (Para)sternal nodes Right breast Eventually, lymph vessels unite to form regional lymph trunks which ultimately drain into two lymph ducts. The main one is the thoracic duct (the only readily visible lymph channel in the cadaver). It begins in the abdomen, just below the diaphragm, as a dilated sac, called the cisterna chyli, which receives lymph from the abdomen, pelvis and lower limbs. It then passes through the thorax and into the neck, where it enters the venous system at the junction of the left subclavian and left internal jugular veins (origin of the left brachiocephalic vein). During its course, the thoracic duct receives the following lymph trunks: i) left broncho-mediastinal trunk (draining the left half of the thorax); ii) left jugular trunk (draining the left side of the head and neck); iii) left subclavian trunk (draining the left upper limb). In summary, the thoracic duct receives lymph from the abdomen, pelvis, lower limbs and left side of the body above the level of the diaphragm.  7 On the right side, the broncho-mediastinal, jugular and subclavian trunks often unite to form the right lymphatic duct, which enters the junction of the subclavian and internal jugular veins on the right side. The right lymphatic duct therefore drains lymph from the right side of the body, above the level of the diaphragm. LYMPHATIC SYSTEM LYMPH NODE Afferent lymphatic Efferent lymphatic MAJOR LYMPH VESSELS & NODES Internal jugular vein Jugular trunk Right lymph duct Subclavian trunk Subclavian vein Bronchomediastinaltrunk Axillary nodes Thoracic duct Cisternachyli Para-aortic nodes Trunks from abdomen, pelvis, lower limbs Inguinal nodes Aorta APPLIED ANATOMY 1. What is an aortic aneurysm? 2. Why are valves not as common in deep veins of the limbs? 3. Why are enlarged lymph nodes due to an infection painful, while enlarged lymph nodes resulting from cancer are not painful?  1 RESPIRATORY*SYSTEM! ! Objectives:! ! Students*should*be*able*to:* i.* define*the*terms*“pleural*cavity”,*“parietal*pleura”*and*“visceral*pleura”*and*name*the*subE divisions*of*parietal*pleura;* ii.* list*the*main*features*of*the*left*and*right*lungs;* iii.** list*the*structures*crossing*the*hilum*of*the*lung;* iv.* state*the*relationship*of*the*lungs*and*pleura*to*the*thoracic*wall*and*other*thoracic*viscera;** v.* outline*the*mechanisms*whereby*thoracic*volume*changes*during*respiration.** ! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Introduction** ! !!The!respiratory!system!consists!of!a!series!of!air!conducting!passages!and!numerous!thin4walled!sacs! which!allow!exchange!of!gases!between!the!air!in!the!sacs!and!blood!in!adjacent!capillaries.!!The! conducting!passages!include!the!nasal%cavities,%mouth,%pharynx,%larynx,%trachea,%bronchi%and% bronchioles.!!Some!of!the!bronchi,!the!bronchioles!and!all!the!respiratory!components,!or!alveoli,!where! gaseous!exchange!occurs,!occupy!the!lungs.!! !!(The!nasal!cavities,!pharynx!and!larynx!and!the!first!part!of!the!trachea!will!be!dealt!with!in!the!Head%&% Neck!section!of!the!course).!From!the!neck,!the!trachea!enters!the!mediastinum!in!the!midline,!anterior!to! the!oesophagus.!!At!about!the!T4!vertebral!level,!the!trachea!divides!into!the!right%and!left%primary% bronchi!which!leave!the!mediastinum!to!reach!the!lungs.!The!right!bronchus!is!more!vertical!than!the!left! and!rigid!horseshoe4shaped!bars!of!cartilage!in!the!walls!of!the!trachea!and!bronchi!help!to!keep!them! patent!(open).! THORAX TRACHEA, BRONCHI & LUNG LOCATION CORONAL SECTION Trachea Bronchus Pleural cavity Lung Heart Rib cage Visceral pleura Parietal pleura Diaphragm  2 Pleural*Cavities* ! !!The!lungs!occupy!the!right!and!left!pleural%cavities!which!are!lined!by!parietal%pleura.!!Where!the!bronchi! enter!the!lungs,!the!parietal!pleura!reflects!on!to!the!lungs!as!visceral%pleura.!!The!visceral!pleura! completely!covers!the!surfaces!of!the!lungs!so!that,!technically,!the!lungs!are!not!actually!“inside”!the! pleural!cavities.!!Rather,!the!pleural!cavities!are!potential!spaces!between!the!visceral!pleura!and!the! parietal!pleura,!the!two!layers!normally!being!separated!by!just!a!thin!film!of!fluid.!!! !!The!parietal!pleura!is!named!according!to!!the!area!it!lines!or!covers,!e.g.!costal%pleura!lining!the!ribcage,! mediastinal%pleura!covering!the!mediastinum!and!diaphragmatic%pleura!over!the!diaphragm.!!The!outline! of!the!pleural!cavities!can!be!related!to!the!surface!of!the!thorax.!!Towards!the!midline!of!the!body,!the! mediastinal!pleura!is!reflected!from!the!mediastinum!on!to!the!anterior!and!posterior!chest!wall.! Superiorly,!the!pleura!extends!slightly!into!the!neck,!as!cervical%pleura.!!The!lungs!do!not!fill!the!whole!of! the!pleural!cavities,!resulting!in!pleural%recesses,!potential!spaces!where!two!areas!of!parietal!pleura!are! juxtaposed,!without!any!intervening!lung.!!There!are!three!such!recesses:!i.!two!costo