BMSC 6030E Module 5 Thorax PDF

BMSC 6030E Basic Human Anatomy for the Health Sciences Module 5: The Thorax Brett Szymik, PhD [email protected] BMSC 6030E Basic Human Anatomy — Module 5: Thorax Overview Overview of th...

BMSC 6030E Basic Human Anatomy for the Health Sciences Module 5: The Thorax Brett Szymik, PhD [email protected] BMSC 6030E Basic Human Anatomy — Module 5: Thorax Overview Overview of this Module The thorax, or chest region, forms much of the central part of the human body. It is largely enclosed by a system of bones that form a protective cage around a number of vital organs. The clinical importance of thoracic anatomy is too large and varied to summarize e ectively. Notably, the thorax contains the heart and lungs which are vital to life and frequent sites of disease. Learning Objectives 5. From studying this module on the thorax, a successful student will be able to: a. Identify anatomical features of the human thorax as seen from the surface. b. Identify the bones forming the thoracic cage and their relevant bony features and describe how these bones articulate with each other. c. Identify structures found in an intercostal space and describe their relations to each other. d. Identify structures of the heart and describe their basic functions, identify the great vessels, and outline the path of blood ow through these structures. e. Identify structures of the right and left lungs. Organization of this Module Overview Surface Anatomy of the Thorax Bones and Joints of the Thoracic Cage The Intercostal Space The Heart and Great Vessels The Lungs The Breast COA images from Moore, Dally, and Agur. Clinically Oriented Anatomy. 7ed. LWW images from Tank and Gest. Lippincott Williams & Wilkins Atlas of Anatomy. Marieb images from Marieb and Hoehn. Human Anatomy & Physiology. 8ed. Rohen images from Rohen, Lutjen-Drecoll, and Yokochi. Color Atlas of Anatomy. 7ed. Thieme images from Gilroy, MacPherson, and Ross. Atlas of Anatomy. 2ed. ff fl BMSC 6030E Basic Human Anatomy — Module 5: Thorax Surface Anatomy Surface Anatomy of the Thorax A lot of the surface anatomy of the thoracic region is on the posterior aspect of the body—your thoracic vertebrae and ribs are of course part of your thorax. But since we covered back anatomy in a previous module, this module will mostly focus on the anterior structures of the super cial thorax. Below are some commonly observable anatomical landmarks on the anterior aspect of the thoracic region. (The model in this photograph does not have developed breasts, but there are slides below dedicated to breast anatomy.) suprasternal (jugular) notch midclavicular line runs vertically down from the midpoint of the clavicle head of clavicle pectoralis major muscle manubrium areola and nipple body of sternum structures of Developed breast tissue (not seen here) overlays the sternum pectoralis major and typically overlays ribs 2–6. Surface anatomy of the breast is covered later in this module. serratus anterior muscle xiphoid process costal margin (black line) formed by the bottom of the rib cage and costal cartilages image: COA g. 1.25 fi fi BMSC 6030E Basic Human Anatomy — Module 5: Thorax Surface Anatomy Palpable Bony Structures of the Thorax Palpating structures of the thorax is clinically common and important. Notably, many clinical procedures require one to be able to count ribs correctly. The clavicle typically overlays rib 1 (the most superior rib). This means that the rst rib that one can reliably palpate is usually rib 2 (the rib just below rib 1). Starting from rib 2, one then counts up as you palpate down (i.e.: rib 3 is the next one down, then rib 4 is below that, and so on). Often, ribs are most reliably palpated near the sternum, where the rib’s costal cartilage connects the bone to the sternum. The word “costal” refers to ribs. head of clavicle clavicle (“collarbone”) purple = palpable manubrium rib 2 Rib 1 is mostly overlaid by the clavicle, so the rst rib that can be palpated is typically rib 2. This is important for counting ribs on a patient during body of sternum structures of clinical procedures, like placement of ECG leads. the sternum costal cartilages the anterior attachments of the ribs to xiphoid process the sternum, made of cartilage tissue costal margin the inferior border of the rib cage, traced here by the dashed line image: LWW plate 1.01A fi fi  BMSC 6030E Basic Human Anatomy — Module 5: Thorax Bones and Joints Structures of the Thoracic Cage The thoracic cage is formed by the thoracic vertebrae posteriorly, the ribs and costal cartilages, and the sternum anteriorly. The sternum (“breastplate”) is a at bony structure forming the anterior of the thoracic cage. It partially overlays the heart and is comprised of three separate bones: the manubrium, the T1 v i cle body of the sternum, and the xiphoid process. The clavicle articulates with the manubrium; cla T2 this is the only bony attachment of the upper limb to the axial skeleton. In advanced age, the 1 three bones of the sternum often ossify into a single bony structure. Costal cartilages also ossify with age, making them more brittle and less exible. manubrium 2 Di erent ribs articulate with the sternum di erently, and some don’t articulate with the sternum at all: true ribs each have their own costal cartilage: each true rib connects to the sternum 3 individually. Ribs 1–7 are true ribs. body of false ribs share a costal cartilage: multiple false ribs connect to the sternum via a sternum single, shared costal cartilage. Ribs 8–10 are false ribs. 4 oating ribs do not articulate with the sternum: oating ribs have no bony attachment costal cartilage 4 anteriorly. Ribs 11 & 12 are oating ribs. 5 Men and women have same number of ribs (12 pairs). It is possible to surgically remove one or both oating ribs, but I don’t know if this makes your abdomen look skinnier or increases 6 xiphoid your range of movement (I doubt both). In rare cases, a person may have one or more extra process ribs above rib 1. These are called cervical ribs because they articulate with cervical vertebrae 7 T11 of the neck. They are often asymptomatic, but can cause symptoms by compressing structures in the neck. intercostal space 7 8 T12 12 9 costal cartilage 7 Ribs 8, 9, and 10 connect to the sternum via rib 7’s costal cartilage. This makes ribs 8–10 false ribs. 10 true ribs 11 false ribs oating ribs Ribs 11 and 12 do not connect to the sternum at all. They are oating ribs. position of diaphragm image: COA g. 1.1 fl fl ff fl fi fl fl fl ff fl fl BMSC 6030E Basic Human Anatomy — Module 5: Thorax Bones and Joints Ribs Articulate with Thoracic Vertebrae Each pair of ribs articulates with the thoracic vertebrae of the back—there are 12 thoracic vertebrae and 12 pairs of ribs. The head of each rib primarily articulates with the body of the same numbered vertebra, i.e.: rib 1 (both left and right) primarily articulates with T1, rib 2 with T2, and so on. In addition, the tubercle of each rib articulates with the transverse process of the same numbered vertebra. This dual articulation—head and tubercle of the rib articulating with the body and transverse process of the vertebra, respectively—creates an axis along which the rib can pivot to allow the movements of inspiration and expiration. posterolateral view blue = articular surfaces articular surfaces for rib 7 costovertebral joint lateral view formed by the head of the rib articulating with the body of the same numbered vertebra head of rib 7 costotransverse joint formed by the tubercle of the rib articulating with the transverse process of the same the head of rib 7 articulates rib cle numbered vertebra body of mostly with the body of T7, 7 of ber T7 forming a costovertebral joint tu the tubercle of rib 7 articulates with T7 the transverse process of T7, of forming a costotransverse joint i ne sp red line: axis of rib rotation Circular arrows indicate how the rib rotates during inspiration. image: COA g. 1.5 fi BMSC 6030E Basic Human Anatomy — Module 5: Thorax Bones and Joints Costal Movements During Inspiration Inspiration occurs when muscles contract and the volume of the thoracic cage increases. That increase in volume causes air to be drawn into the thorax. Inspiration is an active process: muscular contraction is required. Expiration involves decreasing the volume of the thoracic cage. That decrease in volume causes air to be pushed out of the thorax. Normal, relaxed expiration is a passive process: muscles do not contract but instead the natural elastic recoil of tissues causes the rib cage to return to a resting position. Expiration can be active, however, with muscles used to forcefully expel air from the thorax The ribs rotate like a pump handle to The ribs rotate like a bucket handle to The overall movement of the raise the anterior aspect of the raise the lateral aspect of the thoracic ribs causes the volume of the thoracic cage during inspiration. cage during inspiration. thoracic cage to increase during inspiration. relaxed position inspired position During expiration, these inspiratory movements are simply reversed, returning the ribs and sternum to their relaxed positions, decreasing the volume of the thoracic cavity. image: COA g. 1.10 fi BMSC 6030E Basic Human Anatomy — Module 5: Thorax The Intercostal Space Muscles of the Thoracic Wall Most muscles of the anterior thoracic wall are associated either with movement of the upper limb or with movement of the ribs (for inspiration/expiration). A number of abdominal muscles attach to the lower rib cage to produce movement of the spine, and these will be covered in a di erent module. pectoralis minor pectoralis major deep to pectoralis major, originates on attaches to the clavicle, sternum, some of the ribs, then attaches to the and some of the ribs scapula to pull it down and forward serratus anterior attaches to some of the ribs, giving it its characteristic “serrated” appearance (like a serrated knife) intercostal muscles found between the ribs, hence “inter” “costal” abdominal muscles we’ll cover the abdominal muscles later, but image: COA g. 1.11 note that many of them originate on the ribs fi ff BMSC 6030E Basic Human Anatomy — Module 5: Thorax The Intercostal Space Intercostal Muscles Along with the diaphragm (which will be covered in a future module), the intercostal muscles are the primary muscles responsible for inspiration and expiration. Intercostal muscles are found in each intercostal space—the space between two ribs. The intercostal muscles come in two avors: external and internal. Per their names, external intercostal muscles are more super cial, and internal intercostal muscles are deep to the externals. In addition, the muscular bers of external and internal intercostal muscles run in di erent directions, giving them opposite actions. External intercostal muscles pull the ribs up and out, expanding the thoracic cage. Internal intercostals do the opposite, pulling the ribs down and in, compressing the thoracic cage. external intercostal muscles external intercostal muscles The most super cial intercostal muscles (hence “external”), their bers run downwards. Contraction of the external intercostals pulls the ribs up and out, expanding the ribcage for internal intercostal muscles inhalation. Some bers can be seen here on the front of the ribcage, but the internal internal intercostal muscles intercostals are mostly located deep to Found deep to the external intercostals the external intercostals. (hence “internal” and mostly not seen here), their bers run upwards and at a di erent angle. Contraction of the internal intercostals pulls the ribs down and in, compressing the ribcage for exhalation. image: COA g. 1.12 fi fi fi fi fi ff fi fl ff fi BMSC 6030E Basic Human Anatomy — Module 5: Thorax The Heart and Great Vessels Organs within the Thoracic Cavity The thoracic cavity is the area enclosed by the bony thoracic cage. The thoracic cavity is lled mostly by the lungs. The volume of the thoracic cavity changes as the ribs and diaphragm move during inspiration and expiration. After the lungs, the largest organ in the thoracic cavity is the heart and its great vessels (“great” as in large—the vessels associated with the heart are the biggest blood vessels in the body). In children and teenagers, the thymus gland resides in the upper anterior part of the thoracic cavity. The esophagus courses along the posterior of the thoracic cavity, coursing towards the stomach in the abdominal cavity below. There are also a number of nerves, vessels, and lymphatic structures within the thoracic cavity. thymus gland Large and active in children, immune cells go to the thymus gland to mature. As a person grows and their immune b 1 system develops, the thymus gland is less and less needed. r i By adulthood, it has atrophied and been replaced by manubrium connective tissue and fat. lung The thoracic cavity is mostly lled by the right and left lungs (retracted here to display the heart between them). Each lung is quite large— multiple liters in volume during inhalation! pericardium A sac that surrounds the heart, the pericardium is made of brous connective tissue and contains a small amount of uid that lubricates the movement of the heart. diaphragm The diaphragm separates the thoracic cavity diaphragm above from the abdominal cavity below. We’ll look at it in more detail during the abdominal module. image: Thieme g. 7.1 fi fi fi fl fi BMSC 6030E Basic Human Anatomy — Module 5: Thorax The Heart and Great Vessels Location of the Heart Your heart is a little bigger than your st and weighs less than one pound. It is located deep to the sternum and extends slightly to the left of the midline. base of the heart - The superior-posterior portion of the heart, where the great vessels enter and exit the heart. - Because it is anchored to the body by the great vessels, the base of the heart does not move much as the heart beats. apex of the heart - The “tip” of the heart, points anteriorly, inferiorly, and to the left. - Located ~3 or 4 inches left of the midline of the sternum, generally deep to intercostal space 5 - The apex of the heart is freely mobile and moves quite a lot with each heartbeat. You can probably palpate its movement or even see it moving from the surface of your body. 1 rib manubrium right lung (retracted) 2 left lung (retracted) body of sternum 3 4 5 6 apex of heart 7 midsternal line right dome of diaphragm left dome of diaphragm image: COA g. 1.44, 1.76 fi fi BMSC 6030E Basic Human Anatomy — Module 5: Thorax The Heart and Great Vessels Overview of the Heart and Circulatory System The heart is anatomically divided into right and left sides, and, importantly, blood does not mix between left and right side. Each side of the heart has two chambers: one atrium that receives blood into the heart and one ventricle that pumps blood out of the heart. pulmonary capillaries absorb O2 from the air into the blood, The right side of the heart receives blood from the tissues of the body. This blood has a low oxygen content release CO2 from the blood into the air and a high carbon dioxide content. The right heart delivers that blood to the lungs, where oxygen is brought into the blood from the air and carbon dioxide is released from the blood into the air. This “fresh” blood then returns to the heart’s left side. This is the job of the right side of the heart: pump blood to the lungs and back, i.e.: drive the pulmonary circuit. (“Pulmonary” means related to the lung.) pulmonary vein pulmonary artery pulmonary circuit high O2, low CO2 low O2, high CO2 The left side of the heart receives blood from the lungs. This blood has has a high oxygen content and low carbon dioxide content. The left heart delivers that blood to the tissues of the body, where oxygen will leave the blood to nourish the tissues and carbon dioxide will enter the blood as a waste product of the tissues. This blood then returns to the heart’s right side. This is the job of the left side of the heart: pump blood to the tissues of the body and back, i.e.: drive the systemic circuit. (“Systemic” as in the systems of the body.) ★ The systemic circuit is much larger than the pulmonary circuit, so the left side of the heart has to work harder than the right side. This is why the walls of the left ventricle are thicker and more powerful than the right left side systemic artery ventricle. Importantly, both the left and right sides of the heart pump the same volume of blood with each high O2, low CO2 systemic vein right beat, but the left side must create much greater pressure because the systemic circuit has a higher resistance low O2, high CO2 side to ow due to its large size. systemic circuit Arteries are vessels that send blood away from the heart, regardless of oxygen content. (artery = away) Veins are vessels that send blood towards the heart, regardless of oxygen content. Capillaries are microscopic vessels where nutrient and gas exchange takes place—where molecules like oxygen, carbon dioxide, and other nutrients and waste products enter and exit the blood. The gure on the right summarizes the path of blood through both sides of the heart and the two systemic capillaries cardiovascular circuits. Start at the star (right atrium), then follow the arrows to trace the path of blood, release O2 from the blood into the tissues, absorb CO2 from the tissues into the blood ending where you started. image: Marieb fl fi BMSC 6030E Basic Human Anatomy — Module 5: Thorax The Heart and Great Vessels Structures of the Heart and the Path of Blood Flow There’s a lot of anatomy associated with the heart! One of the best ways to learn the structures of the heart is to review those structures in the same order as blood ows through them. This turns a long list of structures into a story, and people remember stories better than lists. Be able to follow the path that a single red blood cell (RBC) will take as it ows through the heart and great vessels. A RBC will enter the heart from systemic circulation, ow through the right side of the heart, through pulmonary circulation, re-enter the heart on the left side, and eventually leave the heart via the aorta to return back to systemic circulation. Be able to trace each of the structures through which that RBC travels on this journey. arm s to head superior/inferior vena cava (SVC/IVC) ➤ right atrium ➤ tricuspid valve ➤ right ventricle ➤ pulmonary semilunar valve a d & & arms o m he ➤ pulmonary trunk ➤ pulmonary arteries ➤ lungs ➤ pulmonary veins ➤ left atrium ➤ bicuspid (mitral) valve ➤ left f r ventricle ➤ aortic semilunar valve ➤ ascending aorta Handy mnemonic for keeping the tricuspid and bicuspid (mitral) valves straight: if you follow the path of blood ow through the heart, you “tri it before you bi it”. SVC to left lung to right lung aorta from left lung PT left from right lung atrium right atrium left ventricle right ventricle IVC from lower body to lower body image: COA g. 1.49 fi fl fl fl fl BMSC 6030E Basic Human Anatomy — Module 5: Thorax The Heart and Great Vessels External Structures of the Heart The anterior surface of the heart shows us the right atrium, most of the right ventricle, nd arms to head a and some of the left ventricle. We also see many of the great vessels. anterior view from head and arms The superior vena cava (SVC) sends systemic venous blood from the head and arms into the right atrium, and the inferior vena cava (IVC) sends systemic venous blood from the lower body into the right atrium. The pulmonary trunk sends blood from the right ventricle out to the lungs. It branches aortic arch into pulmonary arteries. Pulmonary veins carry blood from the lungs into the left atrium. left pulmonary artery The aorta sends blood from the left ventricle out to the body. right pulmonary arteries SVC blood from the pulmonary trunk blood from the pulmonary trunk to the left lung to the right lung aorta Auricles are appy extensions of the atria. Their purpose is debated. pulm. left pulmonary veins blood from the left lung right pulmonary veins trunk into the left atrium Coronary arteries and veins send blood to and from the tissues of the heart itself. blood from the right lung into the left atrium Arrows show direction of blood ow through each vessel. Remember: artery = away. auricle of left atrium Note: Red and blue typically is used to denote high and low blood oxygen content, right coronary arteries and veins auricle of right atrium respectively. The purple color of the pulmonary trunk and pulmonary arteries and the atrium pink color of the pulmonary veins do NOT denote the oxygen content of the blood in left those vessels. If they were colored to denote oxygen content, what color would the ventricle pulmonary trunk and pulmonary arteries be? How about the pulmonary veins? right ventr icle Most of the anterior surface of the heart is comprised of the right ventricle. IVC aorta apex of heart points anteriorly, inferiorly, from lower and to the left body to lower body image: COA g. 1.52 fi fl fl BMSC 6030E Basic Human Anatomy — Module 5: Thorax The Heart and Great Vessels External Structures of the Heart to head and arms from head The posterior surface of the heart shows us almost all of the left atrium and left ventricle. and arms posterior view The right and left pulmonary veins converge on the left atrium to send blood from the lungs to the left side of the heart. The coronary sinus is the largest coronary vein. It sends venous blood from heart tissue aortic arch to the right atrium. SVC left pulmonary artery PT right pulmonary artery sending blood from the pulmonary trunk (PT) sending blood from the pulmonary trunk (PT) to the left lung to the right lung left pulmonary veins sending blood from the left lung left atrium into the left atrium right pulmonary veins sending blood from the right lung right into the left atrium atrium IVC from lower body left ventricle coronary sinus right ventricle blood from the tissues of the heart into the right atrium Most of the posterior surface of the heart is comprised of the left ventricle and the left atrium. apex of heart image: COA g. 1.52 fi  BMSC 6030E Basic Human Anatomy — Module 5: Thorax The Heart and Great Vessels Internal Structures of the Heart There are numerous structures inside the heart that are crucial to its proper function. The interventricular septum separates the right ventricle from the left ventricle, ensuring that blood in the two cardiovascular circuits does not mix. The interatrial septum does the same for the right and left atria. Valves ensure one-way ow of blood through the heart in the proper direction. The right and left atrioventricular valves separate each atrium from its associated ventricle so that blood only ows from the atrium into the ventricle. The pulmonary semilunar valve separate the right ventricle from the pulmonary trunk, and the aortic semilunar valve separates the left ventricle from the aorta. Both ensure that blood that has been ejected from the ventricles does not ow backwards back into the heart. anterior view of heart, left lateral view of heart, right ventricle cut open left atrium and left ventricle cut open pulmonary semilunar valve aorta prevents backwards ow of blood from pulmonary trunk into right ventricle. Here, it is cut open to PT show its three crescent-shaped cusps. aortic semilunar valve prevents backwards ow of blood from aorta into left ventricle. Here, it is not seen due to the thick muscle of the left ventricle. right interventricular septum atrium interventricular septum The wall of muscle that separates the left ventricle from the right ventricle, fossa ovalis helping to prevent mixing of high- and left A depression in the interatrial septum. In atrium the fetus, this was an open hole called the low-oxygen blood. foramen ovale. It is supposed to close at tricuspid valve (right birth, but that doesn’t always happen atrioventricular) completely. Some people have a “hole in prevents backwards ow of blood from their heart”, usually caused by incomplete right ventricle into right atrium closure of the foramen ovale. The hole chordae tendineae arrows: direction of proper blood ow allows mixing of high- and low-oxygen blood between the left and right sides of “heart strings” that support the AV valve the heart. to prevent it prolapsing papillary muscle chordae tendineae papillary muscles small muscles anchored to the inside of the heart that bicuspid valve (mitral, left atrioventricular) pull on the chordeae tendinae to support the valve prevents backwards ow of blood from left ventricle into left atrium image: Thieme g. 8.12 fi fl fl fl fl fl fl fl fl BMSC 6030E Basic Human Anatomy — Module 5: Thorax The Heart and Great Vessels Heart Valves atrioventricular valves - As the ventricle contracts, the blood inside the chamber is squeezed, causing it to ow. Heart valves are shaped such that backwards ow of blood causes them to close. The closure of valves ensures that blood only ows in the correct direction. The ventricles contract very strongly, so the atrioventricular valves must withstand high pressure. As such, they are anchored to the inner walls of the ventricles by papillary muscles and chordae tendineae. These tethers allow the valve to close, but support the cusps of the valve against prolapsing. A prolapsed valve is one that has closed too far and reopens backwards, allowing blood to ow backwards. semilunar valves - Semilunar valves do not have papillary muscles or chordae tendineae. Rather, the edge of each cusp is thickened where it contacts the other cusps. As with the AV valves, the shapes of the semilunar valves’ cusps cause the valve to open or close in accordance with the proper direction of blood ow. mitral valve (bicuspid, left atrioventricular) arrows: direction of blood ow valve cusp valve open valve closed Blood owing in the correct direction causes the valve’s cusps to open, allowing proper ow through the valve. Blood owing in the incorrect direction chordae tendineae causes the valve’s cusps to close, preventing backwards ow through the valve. chordae tendineae are slack chordae tendineae become taut and prevent the valve’s cusps from prolapsing, which would allow papillary muscle blood to ow backwards through the valve papillary muscles are relaxed papillary muscles contract to put more tension on the chordae tendineae, further preventing the valve’s cusps from prolapsing window cut into ventricle to show the structures of an atrioventricular valve image: Rohen plate 259, Marieb fl fl fl fl fl fl fl fl fl fl fl  BMSC 6030E Basic Human Anatomy — Module 5: Thorax The Heart and Great Vessels Pericardium The heart is surrounded by a sac called the pericardium (“peri-” as in “around”, like the word perimeter). The pericardium protects the heart and has a small amount of uid inside it that lubricates the movement of the heart as it beats. It also helps prevent over- lling of the heart by limiting how much the heart can expand. The pericardium is anchored to the great vessels. Here, the pericardium has been cut open to expose the outside of the heart. The pericardium is a tough membrane that encircles the heart like a bag. Between the inside of the pericardium and the outside of the heart is the pericardial cavity, which is lled with a small amount of serous uid that lubricates the movement of the beating heart. The pericardium has two layers: brous and serous. The brous pericardium is the thick outer layer that anchors the pericardium to the great vessels and given the pericardium its toughness and protective qualities. The serous pericardium is the thin inner layer that is smooth and helps lubricate the movement of the heart within the pericardial sac. The serous layer re ects back upon itself and becomes the outer layer of the heart wall, now called epicardium. Between the serous pericardium and the epicardium is the pericardial cavity, lled with serous uid. brous pericardium the two layers of the pericardium serous pericardium pericardial cavity, containing serous uid pulmonary trunk epicardium myocardium the three layers of the heart wall endocardium chamber of left atrium, containing blood image: COA g. 1.33, Marieb fi fi fi fi fi fi fl fl fl fl fi fl BMSC 6030E Basic Human Anatomy — Module 5: Thorax The Heart and Great Vessels Coronary Arteries and Veins If you have a resting heart rate of 60 beats per minute (a low normal rate), then your heart beats 86,400 times each day! That’s over half a million beats per week! That requires a lot anterior view of oxygen and nutrients and produces a lot of carbon dioxide. The heart has to deliver a left coronary artery (LCA) lot of blood to itself. delivers blood to tissues of the SVC left atrium and left ventricle rta The rst branches o of the aorta are coronary arteries that delivery systemic blood to a o pulm. left anterior descending artery (LAD) heart tissue. Coronary arteries are found on the surface of the heart, and send small right coronary artery (RCA) trunk delivers blood to most of the branches deep into the muscle of the heart wall. Occlusion (blockage) of a coronary artery delivers blood to tissues of the right interventricular septum and left ventricle right atrium and right ventricle can result in inadequate blood supply to heart muscle, called a myocardial infarction (MI, atrium le ft “heart attack”). ve nt ric The right coronary artery (RCA) delivers blood to the right atrium and right ventricle and right le parts of the heart’s electrical system. ventricle The left coronary artery (LCA) delivers blood to the left atrium and left ventricle and the large interventricular septum. A prominent branch of the left coronary artery is the left anterior descending artery posterior view (LAD). This branch of the LCA delivers blood to most of the left ventricle, including the interventricular septum. Occlusion of the LAD results in inadequate blood supply to large left areas of the left ventricle, perhaps causing the left ventricle to fail. When the left ventricle atrium fails, the whole body will not receive adequate fresh blood. This is quickly lethal. For this reason, the LAD is sometimes referred to as “the widow maker” because blockages of the rium LAD are both common and deadly. t at The coronary sinus is the largest coronary vein. It is located on the posterior surface of coronary sinus IVC righ vein that returns blood from the heart and delivers veinous blood from the heart tissues back to the right atrium. heart tissue to the right atrium lef tv en tric le icle e ntr htv rig image: Thieme g. 8.16 fi fi ff BMSC 6030E Basic Human Anatomy — Module 5: Thorax The Lungs Trachea Extending down through the chest is the trachea (“windpipe”), a hollow tube that we use to ventilate our lungs with air. The trachea is held open at all times—if it is ever occluded, you will know very quickly because you will not be able to breath. The trachea is held patent (open) by rings of sti cartilage call tracheal rings. Posterior to the heart, the trachea bifurcates into right and left primary bronchi, tubes that deliver air to the right and left lungs, respectively. The primary bronchi then branch many times to send air to all parts of each lung. Immediately posterior to the trachea is the esophagus, the muscular tube that sends food and drink down to the stomach in the abdomen. horizontal section through trachea and esophagus anterior view anterior larynx (“voice box”) tracheal cartilage (tracheal ring) horse-shoe shaped (i.e.: it’s not a complete circle), its sti ness maintains the patency (openness) of the airway horizontal section lumen of trachea (airway) trachea (“windpipe”) trachealis muscle connects to the ends of the tracheal ring and decreases diameter of airway when it contracts bronchial tree esophagus located immediately posterior to the trachea primary (main) bronchus posterior The trachea bifurcates into right and left primary bronchi, which go to the right and left lung, respectively. Inside the lung, each primary bronchus continues to divide into smaller image: Thieme g. 9.14, LWW plate 4-33B and smaller airways, collectively called the bronchial tree. ff fi ff  BMSC 6030E Basic Human Anatomy — Module 5: Thorax The Lungs Lungs Most of the thoracic cavity is occupied by lung tissue. The lungs are highly elastic, expanding and contracting with the movements of the diaphragm and ribs. Lung size varies from person to person, but it’s normal for each lung to be 2–3 liters in volume during maximum inspiration (that’s nearly a gallon each!). Each lung has multiple lobes, separated by deep grooves called ssures. Because the heart extends left of the midline, the left lung must make room for it. For this reason, the left lung is smaller than the right lung, only has two lobes, and has an indentation that accommodates the heart called the cardiac notch. right lung left lung superior lobe superior lobe horizontal ssure The right lung has three lobes separated by two ssures: horizontal and oblique. middle lobe cardiac notch The indentation in the left lung oblique ssure that accommodates the heart. oblique ssure inferior The left lung has only two lobes, so there can be only inferior one ssure separating them: the oblique ssure. lobe lobe image: Thieme g. 9.3 fi fi fi fi fi fi fi fi BMSC 6030E Basic Human Anatomy — Module 5: Thorax The Lungs Lung Hilum Below, the heart has been removed, but the great vessels are left intact. This demonstrates the relationships of the great vessels and airways to the lungs: all of the vessels and airways enter/ exit on the lung’s medial aspect, near the heart. This area is called the hilum of the lung. The structures that enter and exit the lung via the hilum are the only anatomical connections between the lung and the rest of the body: when a lung “collapses”, the de ated lung will dangle within the thoracic cavity by its hilum. SVC r ta ao intercostal muscles hilum of left lung (circled in black) rib PT The hilum of the lung is where everything enters and exits the lung: right lung the primary (main) bronchus, pulmonary arteries (purple), esophagus (retracted) pulmonary veins (pink), and lymphatic vessels (not shown). The left lung hilum is on the medial aspect of the lung, near the heart. It is the only anatomical connection of the lung to the body. (retracted) rib IVC location of liver (removed) diaphragm The liver sits inferior to the right lung, A dome-shaped muscle separating the thoracic cavity under the diaphragm. above from the abdominal cavity below. When it stomach contracts, it attens and drops downwards, increasing the volume of the thoracic cavity and causing inhalation. Here, we see the esophagus passing through the diaphragm to travel to the stomach. image: Thieme g. 9.6 fl fi fl BMSC 6030E Basic Human Anatomy — Module 5: Thorax The Lungs Pleural Cavities The lungs are not attached to the inside walls of the thoracic cavity. (Their only attachment to coronal section through the thoracic wall and the body is the hilum on the medial aspect near the heart where the bronchi and pulmonary inferior part of the right lung vessels enter/exit each lung.) In addition, the lungs are highly elastic and have little internal parietal pleura visceral pleura support structure. This means that the natural tendency of the lung is to collapse down upon membrane covering the inside surface membrane covering the outside surface itself via elastic recoil of its tissues. of the thoracic cavity wall of the lung pleural cavity The outside surface of each lung is covered in a membrane called visceral pleura (“visceral” The small space between the parietal pleura and visceral pleura. It contains a small amount of as in organ, the organ being the lung—think “visceral reaction” as in feeling something “in pleural uid. The uid lubricates movement of the your gut”). In addition, the inside surface of the thoracic cavity wall is covered in a similar lung and its surface tension helps to prevent the lung from collapsing. membrane called parietal pleura (“parietal” means wall, as in the wall of the thoracic cavity). right rib lung The visceral and parietal pleurae press up against each other but there are no connections diaphragm between the two membranes: there is a small amount of space between them. That space is the pleural cavity, separating the inside of the thoracic cavity wall from the outside of the lung. Each lung resides in its own pleural cavity. Normally, the lung is pressed up against the walls of the thoracic cavity, so the pleural cavity is very small. The pleural cavity is lled with a small amount of pleural uid. Pleural uid liver lubricates the movement of the lung against the thoracic cavity wall, and it has a high surface tension that sticks the outside of the lung to the inside of the thoracic cavity. When a lung “collapses”, the pleural cavity becomes quite large. This usually happens rib because air or blood or some other substance has lled the pleural cavity and separated the lung away from the inside wall of the thoracic cavity. image: Thieme g. 9.3, 9.2 fl fl fi fi fi fl fl BMSC 6030E Basic Human Anatomy — Module 5: Thorax Anatomy of the Breast Anatomy of the Breast The breast is a mass of tissue on the anterior thoracic wall that contains mammary glands. Both males and females have breast tissue and can develop breasts, but breasts typically only develop if female sex hormone levels rise (usually during female puberty). By volume, the breast is comprised mostly of adipose (fat) tissue and mammary lobes, the latter being the glandular tissue that produces milk during lactation. A system of lactiferous ducts delivers milk from the glands towards the nipple, where milk is ejected. Numerous suspensory ligaments (Cooper’s ligaments) course throughout the breast and help to support its tissues. sagittal slice through anterior thoracic wall and breast pectoralis major muscle Most of the breast sits on the super cial surface of surface anatomy of the breast the pectoralis major. The muscle can often be seen rib on a mammogram, which is an x-ray image taken of the breast. 2 adipose tissue By volume, most of the breast is adipose tissue, i.e.: fat. axillary tail of the breast suspensory ligaments (Cooper’s ligaments) It is common for some breast tissue 3 Whisps of dense brous connective tissue throughout the to extend into the axilla (“armpit”). breast that attach to the skin to support the breast tissues. nipple mammary lobes site of milk ejection from The glandular tissues that produce milk. In a lactating person, lactiferous sinuses the lobes often increase in size. lactiferous ducts areola Tubes that drain milk from the mammary glands towards pigmented tissue 4 the nipple during milk let-down. surrounding the nipple Breast tissue typically overlays most of the lactiferous sinus Many lactiferous ducts will converge at the nipple to form a small pectoralis major muscle and ribs 2–6, though this 5 number of lactiferous sinuses. The suckling infant will squeeze the can vary considerably depending on breast size. lactiferous sinuses to eject milk from the nipple into its mouth. 6 image: Thieme g. 6.32 fi fi fi BMSC 6030E Basic Human Anatomy — Module 5: Thorax