The Pericardium - TeachMeAnatomy The Pericardium Last Updated: August 18, 2016 Revisions: 36 © 2015-2017 TeachMeAnatomy.com [CC-BY-NC-ND 4.0] Fig 1.0 – Orange peel and the pericardium, not much in common? If the heart is the fun, interesting inside bit of an orange, the pericardium could be compared to the peel around it. Like peel, it can seem vaguely unexciting – that is until you learn some of its very important (appeeling. ahem.) physiological functions 1. In scientific terms, the pericardium is a fibroserous, fluid filled sack that surrounds the muscular body of the heart and the roots of the great vessels (the aorta, pulmonary artery, pulmonary vein and the superior and inferior vena cava). This article will give an outline of its functions, structure, innervation and its clinical significance.

Functions The pericardium has many physiological roles, the most important of which are detailed below Fixes the heart in the mediastinum and limits its motion – this is due to its attachment to the diaphragm, the sternum and the tunica adventitia (outer layer) of the great vessels Prevents overfilling of the heart – The relatively inextensible fibrous layer of the pericardium prevents the heart from increasing in size too rapidly, thus placing a physical limit on the potential size of the organ Lubrication – A thin film of fluid between the two layers of the serous pericardium reduces the friction generated by the heart as it moves within the thoracic cavity Protection from infection – The fibrous pericardium serves as a physical barrier between the muscular body of the heart and adjacent organs prone to infection, such as the lungs. © 2015-2017 TeachMeAnatomy.com [CC-BY-NC-ND 4.0] Fig 1.4 – Anterior view of the pericardium. Note the attachments to the diaphragm, and the roots of the great vessels.

Anatomical Structure The pericardium is made up of two main layers – a tough external layer known as the fibrous pericardium, and a thin, internal layer known as the serous pericardium (to overextend the orange metaphor, the outer peel could be thought of as the fibrous layer, with the inner white stuff being the serous layer). Fibrous Pericardium Continuous with the central tendon of the diaphragm, the fibrous pericardium is made of tough connective tissue and is relatively non-distensible. This rigidity prevents rapid overfilling of the heart, but can have several serious clinical consequences (see cardiac tamponade). Serous Pericardium Enclosed within the fibrous pericardium, the serous pericardium is itself divided into two layers – the outer parietal layer which lines the internal surface of the fibrous pericardium and the internal visceral layer which forms the outer layer of the heart (also known as the epicardium). Each layer is made up of a single sheet of epithelial cells, known as mesothelium.

Found between the outer and inner serous layers, is the pericardial cavity, which contains a small amount of lubricating serous fluid. This fluid serves to minimize the friction generated by the heart as it contracts and moves about within the thoracic cavity. © 2015-2017 TeachMeAnatomy.com [CC-BY-NC-ND 4.0] Fig 1.0 – Overview of the layers of the heart wall. The order of these layers can be easily remembered using the acronym Fart Police Smell Villains. F – Fibrous layer of the pericardium P – Parietal layer of the serous pericardium S – Serous fluid V – Visceral layer of the serous pericardium Clinical Relevance: Transverse Pericardial Sinus Formed as a result of the embryological folding of the heart tube, the transverse pericardial sinus is a passage through the pericardial cavity. It is located: Posteriorly to the ascending aorta and pulmonary trunk. Anteriorly to the superior vena cava. Superior to the left atrium.

In this position, the transverse pericardial sinus separates the arterial vessels (aorta, pulmonary trunk) and the venous vessels (superior vena cava, pulmonary veins) of the heart. This can be used to identify and subsequently ligate the arteries of the heart during coronary artery bypass grafting. © 2015-2017 TeachMeAnatomy.com [CC-BY-NC-ND 4.0] Fig 1.2 – The Transverse pericardial sinus, separating the major arteries and veins. Also note the close relationship of the fibrous pericardium and the diaphragm Innervation The phrenic nerve (C3-C5) is responsible for the innervation of the pericardium, as well as providing motor and sensory innervation to the diaphragm. Originating in the neck and travelling down through the thoracic cavity, the phrenic nerve is a common source of referred pain, with a key example being shoulder pain experienced as a result of pericarditis.

Clinical Relevance By James Heilman, MD [CC-BY-SA-3.0], via Wikimedia Commons Fig 1.3 – Radiograph of a pericardial effusion – note the enlarged heart shadow. The relatively inextensible fibrous pericardium can cause problems when there is an accumulation of fluid, known as pericardial effusion, within the pericardial cavity. This rigidity means that the heart is subject to the resulting increased pressure. The chambers can become compressed, thus compromising cardiac output. The causes of tamponade are many and varied, and include haemopericardium (blood in the pericardium) and pericarditis, which is detailed below. Pericarditis Pericarditis, or inflammation of the pericardium, has myriad of causes, including bacterial infection and myocardial infarction. The main symptom is chest pain, but it can also cause acute cardiac tamponade due to an accumulation of fluid in the pericardial cavity. 1 The exciting functions of orange peel are documented at length in academic literature – for instance, did you know that the juice from orange peel is highly flammable?

Rate This Article Human Heart – Diagram and Anatomy of the Heart Heart, Posterior Full Heart Description [Continued from above] . . . pulmonary arteries and veins, and the vena cava. The inferior tip of the heart, known as the apex, rests just superior to the diaphragm . The base of the heart is located along the body’s midline with the apex pointing toward the left side. Because the heart points to the left, about 2/3 of the heart’s mass is found on the left side of the body and the other 1/3 is on the right. Anatomy of the Heart Pericardium The heart sits within a fluid-filled cavity called the pericardial cavity. The walls and lining of the pericardial cavity are a special membrane known as the pericardium. Pericardium is a type of serous membrane that produces serous fluid to lubricate the heart and prevent friction between the ever beating heart and its surrounding organs. Besides lubrication, the pericardium serves to hold the heart in position and maintain a hollow space for the heart to expand into when it is full.

The pericardium has 2 layers—a visceral layer that covers the outside of the heart and a parietal layer that forms a sac around the outside of the pericardial cavity. Structure of the Heart Wall The heart wall is made of 3 layers: epicardium, myocardium and endocardium. Epicardium. The epicardium is the outermost layer of the heart wall and is just another name for the visceral layer of the pericardium. Thus, the epicardium is a thin layer of serous membrane that helps to lubricate and protect the outside of the heart. Below the epicardium is the second, thicker layer of the heart wall: the myocardium. Myocardium. The myocardium is the muscular middle layer of the heart wall that contains the cardiac muscle tissue . Myocardium makes up the majority of the thickness and mass of the heart wall and is the part of the heart responsible for pumping blood. Below the myocardium is the thin endocardium layer. Endocardium. Endocardium is the simple squamous endothelium layer that lines the inside of the heart.

The endocardium is very smooth and is responsible for keeping blood from sticking to the inside of the heart and forming potentially deadly blood clots. The thickness of the heart wall varies in different parts of the heart. The atria of the heart have a very thin myocardium because they do not need to pump blood very far—only to the nearby ventricles. The ventricles, on the other hand, have a very thick myocardium to pump blood to the lungs or throughout the entire body. The right side of the heart has less myocardium in its walls than the left side because the left side has to pump blood through the entire body while the right side only has to pump to the lungs. Chambers of the Heart The heart contains 4 chambers: the right atrium , left atrium , right ventricle , and left ventricle . The atria are smaller than the ventricles and have thinner, less muscular walls than the ventricles. The atria act as receiving chambers for blood, so they are connected to the veins that carry blood to the heart. The ventricles are the larger, stronger pumping chambers that send blood out of the heart.

The ventricles are connected to the arteries that carry blood away from the heart. The chambers on the right side of the heart are smaller and have less myocardium in their heart wall when compared to the left side of the heart. This difference in size between the sides of the heart is related to their functions and the size of the 2 circulatory loops. The right side of the heart maintains pulmonary circulation to the nearby lungs while the left side of the heart pumps blood all the way to the extremities of the body in the systemic circulatory loop. Valves of the Heart The heart functions by pumping blood both to the lungs and to the systems of the body. To prevent blood from flowing backwards or “regurgitating” back into the heart, a system of one-way valves are present in the heart. The heart valves can be broken down into two types: atrioventricular and semilunar valves. Atrioventricular valves. The atrioventricular (AV) valves are located in the middle of the heart between the atria and ventricles and only allow blood to flow from the atria into the ventricles.

The AV valve on the right side of the heart is called the tricuspid valve because it is made of three cusps (flaps) that separate to allow blood to pass through and connect to block regurgitation of blood. The AV valve on the left side of the heart is called the mitral valve or the bicuspid valve because it has two cusps. The AV valves are attached on the ventricular side to tough strings called chordae tendineae . The chordae tendineae pull on the AV valves to keep them from folding backwards and allowing blood to regurgitate past them. During the contraction of the ventricles, the AV valves look like domed parachutes with the chordae tendineae acting as the ropes holding the parachutes taut. Semilunar valves. The semilunar valves, so named for the crescent moon shape of their cusps, are located between the ventricles and the arteries that carry blood away from the heart. The semilunar valve on the right side of the heart is the pulmonary valve , so named because it prevents the backflow of blood from the pulmonary trunk into the right ventricle.

The semilunar valve on the left side of the heart is the aortic valve , named for the fact that it prevents the aorta from regurgitating blood back into the left ventricle. The semilunar valves are smaller than the AV valves and do not have chordae tendineae to hold them in place. Instead, the cusps of the semilunar valves are cup shaped to catch regurgitating blood and use the blood’s pressure to snap shut. Conduction System of the Heart The heart is able to both set its own rhythm and to conduct the signals necessary to maintain and coordinate this rhythm throughout its structures. About 1% of the cardiac muscle cells in the heart are responsible for forming the conduction system that sets the pace for the rest of the cardiac muscle cells. The conduction system starts with the pacemaker of the heart—a small bundle of cells known as the sinoatrial (SA) node. The SA node is located in the wall of the right atrium inferior to the superior vena cava . The SA node is responsible for setting the pace of the heart as a whole and directly signals the atria to contract.

The signal from the SA node is picked up by another mass of conductive tissue known as the atrioventricular (AV) node. The AV node is located in the right atrium in the inferior portion of the interatrial septum. The AV node picks up the signal sent by the SA node and transmits it through the atrioventricular (AV) bundle. The AV bundle is a strand of conductive tissue that runs through the interatrial septum and into the interventricular septum. The AV bundle splits into left and right branches in the interventricular septum and continues running through the septum until they reach the apex of the heart. Branching off from the left and right bundle branches are many Purkinje fibers that carry the signal to the walls of the ventricles, stimulating the cardiac muscle cells to contract in a coordinated manner to efficiently pump blood out of the heart. Physiology of the Heart Coronary Systole and Diastole At any given time the chambers of the heart may found in one of two states: Systole. During systole, cardiac muscle tissue is contracting to push blood out of the chamber. Diastole.

During diastole, the cardiac muscle cells relax to allow the chamber to fill with blood. Blood pressure increases in the major arteries during ventricular systole and decreases during ventricular diastole. This leads to the 2 numbers associated with blood pressure—systolic blood pressure is the higher number and diastolic blood pressure is the lower number. For example, a blood pressure of 120/80 describes the systolic pressure (120) and the diastolic pressure (80). The Cardiac Cycle The cardiac cycle includes all of the events that take place during one heartbeat. There are 3 phases to the cardiac cycle: atrial systole, ventricular systole, and relaxation. Atrial systole: During the atrial systole phase of the cardiac cycle, the atria contract and push blood into the ventricles. To facilitate this filling, the AV valves stay open and the semilunar valves stay closed to keep arterial blood from re-entering the heart. The atria are much smaller than the ventricles, so they only fill about 25% of the ventricles during this phase. The ventricles remain in diastole during this phase.

Ventricular systole: During ventricular systole, the ventricles contract to push blood into the aorta and pulmonary trunk. The pressure of the ventricles forces the semilunar valves to open and the AV valves to close. This arrangement of valves allows for blood flow from the ventricles into the arteries. The cardiac muscles of the atria repolarize and enter the state of diastole during this phase. Relaxation phase: During the relaxation phase, all 4 chambers of the heart are in diastole as blood pours into the heart from the veins. The ventricles fill to about 75% capacity during this phase and will be completely filled only after the atria enter systole. The cardiac muscle cells of the ventricles repolarize during this phase to prepare for the next round of depolarization and contraction. During this phase, the AV valves open to allow blood to flow freely into the ventricles while the semilunar valves close to prevent the regurgitation of blood from the great arteries into the ventricles. Blood Flow through the Heart Deoxygenated blood returning from the body first enters the heart from the superior and inferior vena cava .

The blood enters the right atrium and is pumped through the tricuspid valve into the right ventricle. From the right ventricle, the blood is pumped through the pulmonary semilunar valve into the pulmonary trunk . The pulmonary trunk carries blood to the lungs where it releases carbon dioxide and absorbs oxygen. The blood in the lungs returns to the heart through the pulmonary veins . From the pulmonary veins, blood enters the heart again in the left atrium. The left atrium contracts to pump blood through the bicuspid (mitral) valve into the left ventricle. The left ventricle pumps blood through the aortic semilunar valve into the aorta. From the aorta, blood enters into systemic circulation throughout the body tissues until it returns to the heart via the vena cava and the cycle repeats. The Electrocardiogram The electrocardiogram (also known as an EKG or ECG) is a non-invasive device that measures and monitors the electrical activity of the heart through the skin. The EKG produces a distinctive waveform in response to the electrical changes taking place within the heart.

The first part of the wave, called the P wave, is a small increase in voltage of about 0.1 mV that corresponds to the depolarization of the atria during atrial systole. The next part of the EKG wave is the QRS complex which features a small drop in voltage (Q) a large voltage peak (R) and another small drop in voltage (S). The QRS complex corresponds to the depolarization of the ventricles during ventricular systole. The atria also repolarize during the QRS complex, but have almost no effect on the EKG because they are so much smaller than the ventricles. The final part of the EKG wave is the T wave, a small peak that follows the QRS complex. The T wave represents the ventricular repolarization during the relaxation phase of the cardiac cycle. Variations in the waveform and distance between the waves of the EKG can be used clinically to diagnose the effects of heart attacks, congenital heart problems, and electrolyte imbalances. Heart Sounds The sounds of a normal heartbeat are known as “lubb” and “dupp” and are caused by blood pushing on the valves of the heart.

The “lubb” sound comes first in the heartbeat and is the longer of the two heart sounds. The “lubb” sound is produced by the closing of the AV valves at the beginning of ventricular systole. The shorter, sharper “dupp” sound is similarly caused by the closing of the semilunar valves at the end of ventricular systole. During a normal heartbeat, these sounds repeat in a regular pattern of lubb-dupp-pause. Any additional sounds such as liquid rushing or gurgling indicate a structure problem in the heart. The most likely causes of these extraneous sounds are defects in the atrial or ventricular septum or leakage in the valves. Cardiac Output Cardiac output (CO) is the volume of blood being pumped by the heart in one minute. The equation used to find cardiac output is: CO = Stroke Volume x Heart Rate Stroke volume is the amount of blood pumped into the aorta during each ventricular systole, usually measured in milliliters. Heart rate is the number of heartbeats per minute. The average heart can push around 5 to 5.5 liters per minute at rest.

Prepared by Tim Taylor, Anatomy and Physiology Instructor Pericardium Pericardium Human Anatomy » Body Systems » Cardiovascular System » Pericardium Pericardium is a fibroserous sac, which encloses the heart and roots of great vessels. It has two primary functions. Firstly, it restricts excessive movements of the heart so that injury to this vital organ of human body is avoided. Secondly, it serves as a lubricated container in which different parts of the heart can contract. The pericardium lies within the middle mediastinum, posterior to body of sternum and anterior to fifth to eighth thoracic vertebrae. The pericardium consists of two parts: fibrous pericardium and serous pericardium. Fibrous pericardium: It is the strong fibrous part of pericardium, which is attached firmly to the central tendon of diaphragm below. It fuses with the outer coats of great blood vessels that pass through it. These blood vessels are: Aorta, Superior vena cave, Inferior vena cave, Pulmonary trunk, Pulmonary veins.

Fibrous pericardium is attached in front to the sternum be means of sternopericardial ligaments. Serous pericardium: This part of pericardium coats the heart and lines the fibrous pericardium on the inside. It is composed of two layers: Parietal and Visceral. Parietal layer of serous pericardium: It lines the fibrous pericardium and is reflected around the roots of great blood vessels. At the region of reflection, it becomes continuous with the visceral layer of serous pericardium, which covers the heart closely. Visceral layer of serous pericardium: This layer is closely applied to the heart and is often called the epicardium. There exists a slit like space between the parietal and visceral layers of serous pericardium. This space is known as pericardial cavity and it contains a small amount of tissue fluid called pericardial fluid. Pericardial fluid acts as a lubricant to facilitate the movements of heart.

Pericardial sinuses: On the posterior surface of the heart, the reflection of the serous pericardium around the large veins form a recess called oblique sinus. There is another sinus on the posterior surface of the heart, which is called transverse sinus. Transverse sinus is in the form of a short passage that lies between the reflection of serous pericardium around the aorta and reflection around large veins. The pericardial sinuses form as a consequence of the way the heart bends during development. They don’t have any clinical significance. Nerve supply of the pericardium: Fibrous pericardium and the parietal layer of serous pericardium are supplied by phrenic nerves. The visceral layer of serous pericardium has different innervations than the parietal layer. It is innervated by branches of sympathetic trunks and vagus nerves.

Share this page: Exercise 30: Anatomy of the Heart Flashcards | Easy Notecards PROVIDE NUTRIENT BLOOD TO THE HEART MUSCLE CORONARY ARTERIES LINING OF THE HEART CHAMBERS ENDOCARDIUM ACTUAL "PUMPS" OF THE HEART MYOCARDIUM DRAINS BLOOD INTO THE RIGHT ATRIUM CORONARY SINUS WHAT IS THE FUNCTION OF THE VALVES FOUND IN THE HEART? THE VALVES ENFORCE A ONE-WAY BLOOD FLOW THROUGH THE HEART CHAMBERS. PREVENTS BACK-FLOW OF BLOOD. 17 WHAT IS THE ROLE OF THE CHORDAE TENDINEAE? THEIR CALLED HEART STRINGS, AND ANCHOR THE CUSPS TO THE VENTRICULAR WALLS. 18 A SIMPLE SCHEMATIC OF GENERAL CIRCULATION IS SHOWN. WHAT PART OF THE CIRCULATION IS MISSING FROM THIS DIAGRAM? ____1_____ ADD TO THE DIAGRAM AS BEST YOU CAN TO MAKE IT DEPICT A COMPLETE SYSTEMIC/PULMONARY CIRCULATION. LABEL THE SYSTEMIC AND PULMONARY CIRCULATION 1.

PULMONARY CIRCULATION 19 Ok, so you’re using my notecards which is great. I am glad I could help you out cause I wish I had someone to help me out when I took this course. I know Anatomy is super hard. I only ask that if you find these notecards helpful, you join Easy Notecards and create at least one notecard set to help others out. It can be for any subject or class. Thanks and don’t forget to rate my helpfulness! 20 DURING THE SHEEP HEART DISSECTION, YOU WERE ASKED INITIALLY TO IDENTIFY THE RIGHT AND LEFT VENTRICLES WITHOUT CUTTING INTO THE HEART. DURING THIS PROCEDURE, WHAT DIFFERENCES DID YOU OBSERVE BETWEEN THE TWO CHAMBERS? LEFT VENTRICLE FELT THICK AND SOLID, AND THE RIGHT FELT MORE THINNER AND EASILY MOVED AND FLABBY. 21 WHEN YOU MEASURED THICKNESS OF VENTRICULAR WALLS, WAS THE RIGHT OR LEFT VENTRICLE THICKER?

LEFT VENTRICLE 22 KNOWING THAT STRUCTURE AND FUNCTION ARE RELATED, HOW WOULD YOU SAY THIS STRUCTURAL DIFFERENCE REFLECTS THE RELATIVE FUNCTIONS OF THESE TWO HEART CHAMBERS? THERES A GREATER DEMAND ON THE LONGER SYSTEMIC CIRCULATION (L. VENTRICLE) AND HAS A HIGHER RESISTANCE THEN THE PULMONARY CIRCULATION (R. VENTRICLE) 23 SEMILUNAR VALVES PREVENT BACKFLOW INTO THE __1__; MITRAL AND TRICUSPID VALVES PREVENT BACK-FLOW INTO THE __2__. 1. VENTRICLES 2. ATRIA 24 USING YOUR OWN OBSERVATIONS; EXPLAIN HOW THE OPERATION OF THE SEMILUNAR VALVES DIFFERS FROM THAT OF THE MITRAL AND TRICUSPID VALVES. THE MITRAL VALVE (ANCHORD TO CHORDAE TENDINEAE) ALLOWS THE BLOOD TO FLOW FROM THE LEFT ATRIUM INTO LEFT VENTRICLE, TRICUSPID VALVE STOPS BACKFLOW OF BLOOD BETWEEN THE TWO (MITRAL AND TRICUSPID VALVES).

THE SEMILUNAR VALVES (DONT HAVE CHORDAE TENDINEAE)PERMIT BLOOD TO BE FOCED INTO THE ARTERIES BUT PREVENT BACKFLOW OF BLOOD FROM THE ARTERIES INTO THE VENTRICLES 25 COMPARE AND CONTRAST THE STRUCTURE OF THE MITRAL AND TRICUSPID VALVES. THE MITRAL VALVE CONTAINS 2 FLAPS, AND THE TRICUSPID VALVE HAS A THREE FLAPPED VALVE. 26 TWO REMNANTS OF FETAL STRUCTURES ARE OBSERVABLE IN THE HEART - THE LIGAMENTUM ARTERIOSUM AND THE FOSSA OVALIS. WHAT WERE THEY CALLED IN THE FETAL HEART, WHERE WAS EACH LOCATED, AND WHAT COMMON PURPOSE DID THEY SERVE AS FUNCTIONING FETAL STRUCTURES? LIGAMENTUM ARTERIOSUM- CALLED (DUCTUS ARTERIOSUS) IN FETAL HEART, LOCATED BETWEEN PULMONARY TRUNK AND AORTIC ARCH. IN ADULTS LIGAMENT THERE NOW. ALLOWS BLOOD TO FLOW FROM THE PULMONARY TRUNK TO SYSTEMIC CIRCULATION.

FOSSA OVALIS - CALLED (FORAMEN OVALE) IN FETAL HEART, LOCATED ON RIGHT ATRIUM WALL (ALSO WALL OF RIGHT VENTRICLE). ALLOWED BLOOD TO ENTER THE LEFT ATRIUM FROM THE RIGHT ATRIUM. 27 DIFFERENTIATE CLEARLY BETWEEN THE ROLES OF THE PULMONARY AND SYSTEMIC CIRCULATIONS. DIFFERENCE IS THAT PULMONARY CIRCULATION IS STRICTLY TO PROVIDE GAS EXCHANGE IN THE LUNGS; WHEREAS THE SYSTEMIC CIRCULATION PROVIDES THE FUNCTIONAL BLOOD SUPPLY TO ALL BODY TISSUES.

28 CIRCULATION OF A RED BLOOD CELL IN THE HUMAN BODY: RIGHT ATRIUM THROUGH THE TRICUSPID VALVE TO THE __1__, THROUGH THE __2__ VALVE TO THE PULMONARY TRUNK, TO THE __3__, TO THE CAPILLARY BEDS OF THE LUNGS, TO THE __4__, TO THE __5__ OF THE HEART, THROUGH THE __6__ VALVE TO THE __7__, THROUGH THE __8__ VALVE TO THE __9__, TO THE SYSTEMIC ARTERIES, TO THE __10__ OF THE TISSUES, TO THE SYSTEMIC VEINS, TO THE __11__, __12__, AND __13__ ENTERING THE RIGHT ATRIUM OF THE HEART. 1. RIGHT VENTRICLE 10. CAPILLARY BEDS (BODY & HEART) 11. SUPERIOR VENA CAVA 13. CORONARY SINUS & CARDIAC VEINS 29 IF THE MITRAL VALVE DOES NOT CLOSE PROPERLY, WHICH CIRCULATION IS AFFECTED?

PULMONARY CIRCULATION 30 WHY MIGHT A THROMBUS (BLOOD CLOT) IN THE ANTERIOR DESCENDING BRANCH OF THE LEFT CORONARY ARTERY CAUSE SUDDEN DEATH? A THROMBUS IN THE CORONARY ARTERY CAN CUT OFF THE BLOOD SUPPLY TO THE HEART, RESULTING IN THE VERY RAPID DEATH. 31 HOW WOULD YOU DISTINGUISH THE STRUCTURE OF CARDIAC MUSCLE FROM THAT OF SKELETAL MUSCLE? SKELETAL MUSCLE IS LONG, SYLINDRICAL, MULTINUCLEATED CELLS AND HAS OBVIOUS STRIATIONS. BUT CARDIAC MUSCLES ARE BRANCHING, STRIATED, HAVE USUALLY UNI-NUCLEATED CELLS THAT INTERDIGITATE AT THE JUNCTIONS (INTERCALATED DISCS) 32 DESCRIBE THE UNIQUE ANATOMICAL FEATURES OF CARDIAC MUSCLE. WHAT ROLE DOES THE UNIQUE STRUCTURE OF CARDIAC MUSCLE PLAY IN ITS FUNCTION? THE UNIQUE FEATURE IS THE INTERCALATED DISCS.

THE INTERCALATED DISCS HAVE TWO IMPORTANT FUNCTIONS: 1. IT HOLDS THE MYOCYTES TOGETHER SO THAT THEY DO NOT PULL APART WHEN THE HEART CONTRACTS; 2. IS TO ALLOW AN ELECTRICAL CONNECTION BETWEEN THE CELLS, WHICH IS VITAL TO THE FUNCTION OF THE HEART AS A WHOLE. ALSO HAS MANY MITOCHONDRIA THAT PROVIDE ENERGY REQUIRED FOR CONTRACTION. 33 Chapter 24: Blood vessels, lymphatic drainage and nerves of the thorax Chapter 24: Blood vessels, lymphatic drainage and nerves of the thorax Pulmonary circulation The pulmonary trunk and arteries carry deoxygenated blood, but they are arteries in the sense that they transmit blood away from the heart at a relatively high pressure (20 to 30 mm of mercury) and in a pulsatile manner and in the sense that they have elastic walls like the aorta. The pulmonary trunk extends from the conus arteriosus of the right ventricle to the concavity of the arch of the aorta, to the left of the ascending aorta, where it divides into the right and left pulmonary arteries.

The point of division is approximately at the left side of the sternal angle. The pulmonary arteries and their branches are largely responsible for the normal shadows seen radiographically in the roots and hili of the lungs. The right pulmonary artery, longer and wider than the left, passes inferior to the arch of the aorta and enters the hilus of the lung (see fig. 22-4 ). The left pulmonary artery is connected to the arch of the aorta by the ligamentum arteriosum (fig. 24-1 ), which is the fibrous remains of a prenatal vessel, the ductus arteriosus. A pulmonary vein arises in each lobe of the lung. The right upper and middle veins usually unite, so that four veins, upper and lower on each side, enter the left atrium. Systemic circulation The aorta. The systemic supply of the thorax is derived mainly from branches of the aorta, the chief systemic artery of the body. The aorta is divided into the ascending aorta, arch of the aorta, and descending aorta. The part of the descending aorta in the thorax is called the thoracic aorta.

The aorta is an elastic artery that withstands the systolic blood pressure and provides elastic recoil. The walls of the ascending aorta and arch contain pressure receptors, which are reflexly connected to aortic depressor fibers in the vagi (slowing the hear in response to increased blood pressure). The ascending aorta begins at the root of the aorta, where the three aortic sinuses are located. Its branches are the right and left coronary arteries. It ascends to the level of the sternal angle. The arch of the aorta (the term aortic arch is better reserved for special embryonic vessels) runs posterior on the left side of the trachea and esophagus and superior to the left main bronchus (see figs. 22-5 and 24-1 ). The arch of the aorta, in proceeding backward, lies in an almost sagittal plane in the superior mediastinum, behind the lower part of the manubrium sterni (see fig. 23-21 ). It is visible radiographically as the aortic knob, or knuckle (see fig. 23-16 ).

The arch is related on its inferior side to the bifurcation of the pulmonary trunk and is connected to the left pulmonary artery by the ligamentum arteriosum. The left recurrent laryngeal nerve hooks inferior to the arch. There are three main branches of the arch (situated posterior to the left brachiocephalic vein): the brachiocephalic trunk, left common carotid artery, and left subclavian artery. Immediately distal to the last-named branch, the aorta is slightly constricted (isthmus). A severe constriction (coarctation of the aorta) may occur here during development, in which case the adequacy of the collateral circulation depends on the relationship of the constriction to the opening of the ductus arteriosus (which connects the pulmonary trunk and aorta). The brachiocephalic trunk. The brachiocephalic trunk divides behind the right sternoclavicular joint into the right subclavian and right common carotid arteries. The left common carotid and left subclavian arteries enter the neck behind the left sternoclavicular joint.

Variations in the branches of the arch of the aorta may be encountered, e.g., a common origin of the brachiocephalic trunk and left common carotid artery. Sometimes an aortic ring may encircle the trachea and esophagus and press on them. The right subclavian artery may arise from the thoracic aorta and be retro-esophageal (fig. 24-1 B), which is frequently stated to cause dysphagia (difficulty in swallowing). The thoracic aorta descends in the posterior mediastinum and traverses the diaphragm to become the abdominal aorta. It begins to the left of the vertebral column, gradually moves arteriorly and to the right (where it lies behind the esophagus), and enters the abdomen in the median plane. The branches of the thoracic aorta are parietal and visceral. The parietal include several posterior intercostal arteries and the subcostal and some phrenic arteries. The visceral branches are the bronchial, esophageal, pericardial, and mediastinal. Brachiocephalic veins.

Each brachiocephalic vein is formed by the confluence of the subclavian and internal jugular veins behind the corresponding sternoclavicular joint. The right vein descends vertically, whereas the left crosses in an oblique orientation anterior to the branches of the arch of the aorta. Near the level of the sternal angle, the two brachiocephalic veins unite to form the superior vena cava (fig. 24-1 ). The superior vena cava descends on the right side of the ascending aorta, receives the azygos vein, and ends in the right atrium. Rarely, a left superior vena cava may persist: it comprises parts of the left brachiocephalic vein, left superior intercostal vein, oblique vein of the left atrium, and coronary sinus (fig. 24-2 B). The azygos system. The azygos system consists of veins on each side of the vertebral column, which drain the back as well as the walls of the thorax and abdomen. These veins are highly variable, but they end in the azygos, hemiazygos, and accessory hemiazygos veins (fig. 24-2 ).

The azygos vein (Gk, a zygon, "unpaired") is formed by small vessels (such as the right subcostal and right ascending lumbar veins), and it ascends through the posterior and superior mediastinum. It arches anteriorward over the root of the right lung and ends in the superior vena cava. It receives the hemiazygos, accessory hemiazygos, and a number of posterior intercostal veins. The hemiazygos and accessory hemiazygos veins form a very variable arrangement on the left side. The hemiazygos vein arises in a manner comparable to that of the azygos. The accessory hemiazygos vein corresponds to the upper portion of the azygos vein. The vertebral venous system. The vertebral venous system consists of plexuses that drain the back, vertebrae, and structures in the vertebral canal. They communicate above with the intracranial veins and below with the portal system, and they empty into the vertebral, posterior interosseous, lumbar, and sacral veins.

The veins in the vertebral plexus are valveless: blood may flow in either direction, and pressure in them is reflected in the cerebrospinal fluid. Reversed blood flow permits tumor cells to be transported from the breast, thorax, abdomen, or pelvis to the vertebrae, spinal cord, or brain. Veins of the thoracic wall (such as the thoraco-epigastric veins, which are superficially placed) connect the superior and inferior venae cavae and can provide a collateral circulation in obstruction of one of the venae cavae. Extensive anastomoses among the caval, azygos, and vertebral systems provide multiple routes for the return of blood to the heart. In effect, the azygos and vertebral systems bypass the caval system and these veins dilate in caval obstruction. Lymphatic drainage Lymph nodes The parietal nodes of the thorax are the parasternal, phrenic, and intercostal. The visceral nodes drain the lungs, pleurae, and mediastinum.

The nodes in the roots and hili of the lungs are arranged in several groups: pulmonary along the larger bronchi, bronchopulmonary mainly at the hilus, and tracheobronchial near the bifurcation of the trachea (fig. 24-3 ). Lymph nodes in the roots of the lungs tend to be involved secondarily in infections, such as tuberculosis, and in tumors of the lungs and mediastinum. Their density may increase so that they become visible radiographically, especially if they become calcified. The tracheobronchial nodes drain into the tracheal (or paratracheal) nodes. Mediastinal nodes are scattered in the superior mediastinum, and they receive vessels from the thymus, pericardium, and heart. The efferents of the tracheal and mediastinal nodes form a bronchomediastinal trunk on each side of the trachea. There are also posterior mediastinal nodes, most of which drain directly to the thoracic duct.

Lymphatic vessels All of the lymphatic drainage of the thorax is directed toward the bronchomediastinal trunks, thoracic duct, and descending intercostal lymphatic trunks (fig. 24-3 ), but the actual lymphatic trunks themselves are highly variable. The thoracic duct extends from the abdomen to the neck, where it ends in one of the large veins (figs. 24-3 and 24-4 ). It begins as either a plexus or a dilatation called the cisterna chyli, passes through or near the aortic opening of the diaphragm, and ascends in the posterior mediastinum between the aorta and the azygos vein. Next it crosses obliquely to the left, posterior to and then along the left side of the esophagus. Finally it passes posteiror to the left subclavian artery, enters the neck (where it forms an arch above the level of the clavicle), and commonly ends in the left internal jugular vein (fig. 24-3 ). Variations are common.

The thoracic duct receives the left subclavian and jugular trunks and often the left bronchomediastinal trunk. Most of the lymph in the body reaches the venous system by way of the thoracic duct (figs. 24-4 and 24-5 ), but anastomoses are so extensive that no serious effects result if the thoracic duct is ligated. On the right side, the bronchomediastinal trunk forms various combinations with the subclavian and jugular trunks. Rarely, all three unite to form a right lymphatic duct, which then empties directly into the junction of the internal jugular and subclavian veins. Thymus The thymus is partly in the neck and partly in the thorax. It comprises one to three lobes, each of which consists of numerous lobules containing lymphocytes, which are important in the development and maintenance of the immune system. The cervical part of the thymus lies on the anterior and lateral sides of the trachea, whereas the thoracic part lies posterior to the superior portion of the sternum. The organ has a profuse blood supply and lymphatic drainage.

The thymus reaches its greatest size at puberty and then begins to regress. Much of its substance is replaced by fat and fibrous tissue, but thymic tissue never disappears completely. The thoracic nerves are described in the discussion of the thoracic wall. The phrenic nerves. The phrenic nerves supply the diaphragm. These nerves usually arise from cervical nerves 3-5. (The contribution of the C5 nerve root to the phrenic nerve often arises from the nerve to the subclavius, and it may enter the thorax separately as an accessory phrenic nerve.) After descending on the anterior surface of the anterior scalene muscle in the neck, the phrenic nerves enter the thorax and pass anterior to the roots of the lungs. Each givesrise to sensory branches to the pericardium and pleura and then divides into several branches, which pierce the diaphragm and supply that muscle, as well as part of the peritoneum, from below. The phrenic (fig.

24-6 ) nerves contain (1) motor fibers to the diaphragm, (2) pain fibers from the pericardium, pleura, and peritoneum, and (3) sympathetic vasomotor fibers. Pain is usually referred to the skin over the trapezius muscle that is normally innervated by cervical nerves 3 and 4. Pain sometimes refers to the region of the ear innervated by C2 and 3. The vagi. The vagi descend through the neck and enter the thorax, where they contribute to the pulmonary plexuses and then form the esophageal plexus. They then continue as anterior and posterior vagal trunks, which pass through the esophageal opening of the diaphragm. Each vagus has a recurrent laryngeal branch and a variable number of cardiac branches in the neck and thorax. The right recurrent laryngeal nerve arises as the vagus crosses anterior to the subclavian artery, hooks around that vessel, and ascends between the trachea and esophagus.

The left recurrent laryngeal nerve arises as the vagus crosses the left side of the arch of the aorta, hooks around the inferior side of the arch (to the left of the ligamentum arteriosum), and then ascends on the right side of the arch between the trachea and esophagus. The left recurrent laryngeal nerve is liable to damage from disorders of the aorta (e.g., aneurysms) or of the mediastinum (e.g., tumors), resulting in hoarseness. It is believed that both recurrent laryngeal nerves owe their adult relationships to their embryonic arrangement caudal to the sixth aortic arches. The vagi contain (1) parasympathetic fibers (e.g., to the heart), (2) sensory fibers (many of which are concerned with cardiovascular and pulmonary reflexes; others, in the mucosa of the bronchial tree, cause coughing), and (3) motor fibers to the pharynx and larynx (fig. 24-7 ), in the head and neck. The sympathetic trunks. The sympathetic trunks (figs.

24-8 and 32-5 ) descend through the neck and enter the thorax, where they lie anterior to the necks of the ribs (see figs. 20-2 , 20-3 , and 20-5 ). The thoracic part of each trunk has about a dozen ganglia, the first of which is often fused with the inferior cervical ganglion to form the stellate ganglion. The sympathetic trunks enter the abdomen by piercing the crura of the diaphragm or by passing posterior to the medial arcuate ligaments. The trunks and ganglia are connected with the thoracic ventral rami by rami communicantes, which convey preganglionic and postganglionic fibers. Preganglionic fibers from segments T1 to 6 of the spinal cord supply the heart, coronary vessels, and bronchial tree. Apart from cardiac and pulmonary branches, the main visceral branches are the three splanchnic nerves.

The greater, lesser and least splanchnic nerves (from superior to inferior) traverse the lower thoracic ganglia, pierce the crura of the diaphragm, and end in ganglia and plexuses (celiac and renal) in the abdomen. The sympathetic trunks and their branches contain pain fibers from the thoracic and abdominal viscera and from blood vessels. These sensory fibers traverse the sympathetic trunks and rami communicantes to reach the spinal nerves, dorsal roots, and spinal cord. Many branches of the vagi and sympathetic trunks form plexuses in the thorax, e.g., the cardiac, pulmonary, esophageal, and aortic plexuses. Additional reading Clemens, H. J., Die Venensysteme der menschlichen Wirbelsiiule, de Gruyter, Berlin, 1961. Well-illustrated account of vertebral venous system. Jacobsson, S.-I., Clinical Anatomy and Pathology of the Thoracic Duct, Almquist and Wiksell, Stockholm, 1972. An excellent, concise monograph on anatomy. Pontes, A.

de P., Arterias supra-aorticas, University of Brazil, Rio de Janeiro, 1963. A study of the arch of the aorta and variations in its branches. Questions 24-1 How does (a) the right pulmonary artery differ from the left and (b) the left bronchus differ from the right? 24-1 The pulmonary trunk, ascending aorta, and superior vena cava lie in that order from left to right. The right pulmonary artery has to cross posterior to the aorta and vena cava (see fig. 23-18 ) to reach the right lung. The right pulmonary artery, therefore, is longer than the left; it is also wider. In contrast, the left bronchus has to cross anterior to the esophagus and descending aorta (see fig. 24-1 ) to reach the left lung, and so it is longer than the right; it is also narrower. 24-2 What is the ligamentum arteriosum? 24-2 The ligamentum arteriosum is a fibrous band connecting the left pulmonary artery to the arch of the aorta.

It is the remains of a prenatal vessel, the ductus arteriosus (see fig. 23-13 ), which shunts most of the relatively deoxygenated blood from the pulmonary trunk to the aorta (and thence to the placenta for oxygenation). 24-3 Which structure hooks around the arch of the aorta? 24-3 The left recurrent laryngeal nerve (from the vagus) hooks around the arch of the aorta immediately posterior to the ligamentum arteriosum (see fig. 24-1 ). In contrast, the right recurrent laryngeal nerve hooks around the right subclavian artery. This is attributed to the embryonic position of the nerves, namely caudal to aortic arch 6, the distal portion of which disappears on the right side (allowing the nerve to hook around aortic arch 4, which contributes to the right subclavian artery). On the left, aortic arch 6 forms the ductus arteriosus (forcing the nerve to assume its adult position, hooking around the ligamentum arteriosum at its attachment to the arch of the aorta).

24-4 What is a retro-esophageal right subclavian artery? 24-4 A retro-esophageal right subclavian artery (see fig. 24-1 B) arises from the descending aorta instead of, as in the vast majority, from the brachiocephalic trunk. It is frequently stated to cause dysphagia. It is attributed to a variation in the development of the aortic complex (persistence of the right dorsal aortic root and disappearance of right aortic arch 4). 24-5 Which regions of the body are drained by the thoracic duct? 24-5 All regions of the body except the right upper limb and right side of the head, neck, and thorax (see fig. 24-5 ) are drained by the thoracic duct into one of the large veins of the neck, e.g., the left internal jugular vein. 24-6 What is the origin of the phrenic nerves? 24-6 The phrenic nerves arise from cervical nerves 3 to 5. These segments also supply the skin over the trapezius, and pain may be referred from the diaphragm to the shoulder.

Figure legends Figure 24-1 A, The three arteries (1, 2, 3) usually given off by the arch of the aorta. Also shown are the brachiocephalic and superior caval veins in outline (as if transparent) and the trachea, esophagus, and phrenic and vagus nerves. Note the different course of the recurrent laryngeal nerves on the two sides, the left nerve being related to the ligamentum arteriosum. Cf. fig. 50-17 . B, An instance in which a retro-esophageal right subclavian artery (asterisk) arises as the last branch of the arch of the aorta. Figure 24-2 A, Scheme of the main connections of the azygos, caval, and vertebral systems of veins. Connections of the azygos and hemiazygos veins with the posterior intercostal veins also occur. B, The main veins of the thorax. An interrupted blue line indicates the course of a left superior vena cava (a rare anomaly) on its way to the coronary sinus. Figure 24-3 The visceral lymph nodes and collecting trunks of the thorax.

Figure 24-4 The thoracic duct. It commonly crosses the vertebral column at T.V.5 or 6. (Based on Davis.) Figure 24-5 All except the shaded area is drained by the thoracic duct. Figure 24-6 Functional components of the phrenic nerve. For purposes of simplification, each component is shown as a single fiber. Afferent (blue), efferent (red), and sympathetic (black) fibers are distinguished. Figure 24-7 Functional components of the vagus nerve. For purposes of simplification, each component is shown as a single fiber. Afferent (blue), efferent (red), and parasympathetic (interrupted) fibers are distinguished. The distinction between accessory and vagal components is not shown. Figure 24-8 Functional components of the sympathetic trunk, showing the origin of preganglionic fibers and the sites of ganglion cells. Afferent (mostly pain) fibers from viscera are indicated in blue.

Jump to: Pulmonary arteries and veins - Anatomy and Function | Kenhub Pulmonary Arteries and Veins Contents Anatomy Embryologically, the pulmonary arteries originate from the truncus arteriosus (as does the aorta ), and in the developed heart , the pulmonary trunk (pulmonary artery or main pulmonary artery) begins at the base of the right ventricle . The pulmonary trunk is a short and stout (wide) structure that is about 5 cm in length and 3 cm in diameter, which branches into 2 pulmonary arteries; the left and right pulmonary arteries, which act to deliver deoxygenated blood to its respective lung . On the other hand, pulmonary veins are large blood vessels that receive oxygenated blood from the lungs to delivery to the rest of the body. There are 4 total pulmonary veins—with 2 pulmonary veins coming from each lung, left and right—that empty into the left atrium of the heart. Two pulmonary veins emerge from the hilus of each lung, and each pulmonary vein receives blood from 3-4 bronchial veins apiece before draining into the left atrium . The pulmonary veins are fixed to the pericardium travel alongside the pulmonary arteries.

The right superior pulmonary vein passes in front of and a tad below the pulmonary artery at the root of the lung, and the inferior pulmonary vein is situated at the lowest part of the lung hilum . In reference to the heart, the right pulmonary veins pass behind the right atrium and superior vena cava return, and the left pulmonary veins pass in front of the descending thoracic aorta. Finally, the bronchus is located behind the pulmonary artery. Recommended video: Pulmonary arteries Anatomy and function of the left and right pulmonary arteries. Function While veins usually carry deoxygenated blood from tissues back to the heart, in this case, pulmonary veins are among the few veins that carry oxygenated blood instead. Oxygenated blood from the lungs is circulated back to the heart through the pulmonary veins that drain into the left atrium. Once blood is pumped from the left atrium through the mitral valve into the left ventricle , this oxygenated blood will then be pumped from the left ventricle through the aortic valve to the rest of the body’s organs and tissues through the aorta.

Deoxygenated blood that has circulated through the system will be collected from the superior vena cava and inferior vena cava , which drain into the right atrium of the heart. Once deoxygenated blood is pumped from the right atrium through the tricuspid valve into the right ventricle, contraction of the right ventricle will push blood through the pulmonic valve into the pulmonary artery that will carry deoxygenated blood to the lungs. Within the lungs, the blood passes through capillaries adjacent to alveoli and becomes oxygenated through respiration (breathing). Branches of the pulmonary artery travel closely alongside the bronchial tree on their way to the alveoli. However, the bronchial tree itself is supplied by the bronchial artery, which arises from the aorta and carries systemic blood. Each alveolus is surrounded by a nest of blood capillaries that are supplied by small branches of the pulmonary artery. In summary, the pulmonary circuit begins with the pulmonary trunk, which is a large vessel that ascends diagonally from the right ventricle and branches into the right and left pulmonary arteries.

As the circuit approaches the lung, the right pulmonary artery branches into two arteries, and both branches enter the lung at a medial indentation called the hilum of the lung. The upper branch is the superior lobar artery, which feeds into the superior lobe of the lung. The lower branch divides again within the lung to form the middle lobar and inferior lobar arteries that supply the lower 2 lobes of the lung, since there are 3 lobes of the right lung. The left pulmonary artery is more variable in number and gives off several superior lobar arteries that feed into the superior lobe before entering the hilum of the lung to branch off into inferior lobar arteries that feed the left lower lung lobe. Histology of Arteries and Veins Large veins have diameters greater than 10 mm. They have some smooth muscle in all three tunics. They have a relatively thin tunica media with only a moderate amount of smooth muscle; the tunica externa is the thickest layer and contains longitudinal bundles of smooth muscle. Large veins include the venae cavae, pulmonary veins, internal jugular veins, and renal veins.

Since the pressure of the pulmonary veins cannot be easily measured, the pulmonary capillary wedge pressure is used instead, and the normal range is 2-15 mmHg. The pulmonary arteries have thin distensible walls with less elastic tissue than the systemic arteries. Thus, they have a blood pressure range of 15-30 mmHg systolic, and 4-12 mmHg diastolic. Get me the rest of this article for free Create your account and you’ll be able to see the rest of this article, plus videos and a quiz to help you memorize the information, all for free. You’ll also get access to articles, videos, and quizzes about dozens of other anatomy systems. References: Kenneth Saladin, Anatomy & Physiology: The Unity of Forma and Function, 6th edition, McGraw-Hill Science/Engineering/Math, Chapter 19, 20. Anne M Gilroy, Brian R MacPherson, Lawrence M Ross and Michael Schuenke, Atlas of Anatomy, 2nd edition, Thieme. Keith L Moore, A M R Agur, and Arthur F Dalley. Essential Clinical Anatomy, 4th edition, Lippincott Williams & Wilkins.

Author: trunk pulmonary veins superior vena cava and inferior vena - ANAT - 1625 View Full Document 2. musculophrenic artery ( branch of internal thoracic artery ) 3. bronchial arteries ( branches of descending thoracic aorta ) 4. esophageal arteries ( branches of descending thoracic aorta ) 5. superior phrenic artery ( branch of descending thoracic aorta _ 6. coronary arteries ( branches of ascending aorta ) Veins drain into the pericardiacophrenic veins, which open into the internal thoracic vein Nerve supply of pericardium 1. phrenic nerve ( sensory ) 2. vagus nerve 3.

sympathetic trunk ( vasomotor ) Heart Is a suction and pressure pump, propels blood to all parts of the body The right side of the heart receives poorly oxygenated ( venous ) blood from the body through the superior vena cava and inferior vena cava and pump it through the pulmonary trunk to the lungs for oxygenation The left side of the heart receives well-oxygenated ( arterial ) blood from the lungs through the pulmonary veins and pumps it into the aorta for distribution of the body The heart has four chambers 1. right atrium 2. left atrium 3. right ventricle 4. left ventricle The wall of each heart chamber consists of three layers 1. endocardium is a thin internal layer, lining the membrane of the heart 2. myocardium, is a thick middle layer, composed of cardiac muscle 3.

epicardium, a thin external layer, formed by the visceral pericardium Right atrium Forms the right border of the heart, receives venous blood from superior vena cava, inferior vena cava and coronary sinus Right auricle Is a ear-like conical muscular pouch that projects from the right atrium Interior of the right atrium has two parts 1. posterior, smooth, thin walled part ( sinus venarum ) 2. anterior, rough, muscular part Sinus venarum part Has the openings of superior vena cava, inferior vena cava and coronary sinus, which 20 bring poorly oxygenated blood into the heart Anterior part Is composed of pectinate muscles Sulcus terminalis Is a shallow vertical groove externally, separation the smooth and rough walls of the right atrium Crista terminalis Is the vertical ridge internally, corresponding to sulcus terminalis This preview has intentionally blurred sections. Sign up to view the full version. Heart 1. Epicardium (visceral pericardium) is described above 2. Myocardium consists of multiple interlocking layers of cardiac muscle tissue with associated connective tissue, blood vessels and nerves. 3.

Endocardium is the inner lining of the heart. It is continuous with the endothelium that lines the blood vessels. Cardiac Muscle Tissue Cardiac muscle cells form a branching, network of cells bound strongly to one another by intercalated discs. Intercalated discs are regions of close attachment between cardiac cells that enable the cardiac muscles to work together during a contraction. This is because desmosomes at the discs physically bind the cell membranes; contractile fibers within the cells in turn attach to the desmosomes; and gap junctions at the discs enables rapid communication between cells. Fibrous Skeleton The fibrous skeleton of the heart consists of four fibrous rings that surround the valve orifices and two triangular fibrous connections between these rings, the right and left fibrous trigones. The valves include the aortic and pulmonary semilunar valves and the right and left atrioventricular valves. The fibrous skeleton physically supports the valves, provides independent attachment for the atrial and ventricular myocardium, and acts an electrical insulator between the atria and ventricles. Orientation and Superficial Anatomy of Heart 1. The heart lies slightly to left of midline.

The base of the heart is formed mainly by the left atrium, and, to a small extent, by the back part of the right atrium. The apex is the inferior rounded tip. 2. The heart at oblique angle to longitudinal axis. Because of this tilt, the apex points obliquely toward the left. This tilt in the orientation of the heart also causes the horizontal and vertical borders of the heart to be as follows: 3. The inferior border is formed by the inferior wall of the right ventricle. 4. The left border is formed by the left ventricle and a small portion of the left atrium. 3. The heart rotated slightly toward left. Because of this rotation: The surface of the heart underneath the sternum and the ribs on the left side, the sternocostal surface, is that of the right atrium and ventricle. The surface of the heart that rests on the diaphragm, which curves directly behind the heart, is called the diaphragmatic surface, and is formed by the posterior walls of the right and left ventricles The atria have thin muscular walls that are distended as they receive blood. When contracted, the anterior walls form flaps that are called auricles.

A deep groove between the atria and ventricles is called the coronary sulcus. The boundary between the right and left ventricles is indicated externally by a shallow groove on the anterior surface, the anterior interventricular sulcus, and the posterior surface, the posterior interventricular sulcus. Internal Anatomy and Organization of the Heart The atria and ventricles are side by side and share a common wall (like adjoining apartments). The common wall between the atria is the interatrial septum and the common wall between the ventricles is the interventricular septum. The internal anatomy of the four chambers reflects the functional demands placed on each chamber as blood flows through it. Right Atrium The right atrium receives deoxygenated blood from superior vena cava, inferior vena cava and coronary sinus. Parallel ridges of muscle called pectinate muscles are found in the interior of the right auricle. In the fetus, there is an oval opening called the foramen ovale in the interatrial septum. Forty-eight hours after birth, the foramen ovale closes and becomes a oval depression called the fossa ovalis.

Right Ventricle The deoxygenated blood from right atrium enters the right ventricle through an opening bounded by three flaps, or cusps, of the right atrioventricular (tricuspid) valve. The free edges of the cusps are attached to strings of connective tissue called the chordae tendineae. The chordae tendineae are anchored to the ventricular wall by papillary muscles that are conical projections from the wall. The inner surface of the right ventricles has irregular, muscular folds called trabeculae carneae. The moderator band is a band of muscle that extends from the interventricular septum to the anterior wall of the right ventricle. The superiorly right ventricle tapers into a funnel-shaped passage, the conus arteriosus, where blood is ejected into the pulmonary trunk. Backflow of blood is prevented by three half-moon flaps attached to the base of the pulmonary trunk that forms the pulmonary semilunar valve. The pulmonary trunk branches into the right and left pulmonary arteries. Left Atrium The left (2) and right (2) pulmonary veins drain oxygenated blood from the lungs into the left atrium.

The auricle of the left atrium lacks pectinate muscles. The oxygenated blood enters the left ventricle through a valve with two flaps, the left atrioventricular (a.k.a. bicuspid, mitral) valve. Left Ventricle The left ventricle, as explained below, has a thicker wall than the right. It also differs from the right in lacking a moderator band and having more prominent trabeculae carneae. As oxygenated blood is ejected from the left ventricle is passes through the aortic semilunar valve and enters the ascending aorta. Sac-like expansions at the base of the ascending aorta are called aortic sinuses. The aortic sinuses prevent the flaps of the semilunar valves from adhering to the walls of the aorta and permits blood to flow unimpeded into the right and left coronary arteries that originate from the aortic sinuses. Conducting cells distribute the contractile stimulus throughout the myocardium. Conducting System of Heart The sinoatrial node is the cardiac pacemaker of the cardiac cycle. This node is located near the entrance of the superior vena cava in the wall of the right atrium.

This node has the most rapid autorhythmicity, as isolated cells generate 80 -100 impulses per minute. Because of the dominance of parasympathetic innervation, the actual heart rate is slower at 70 � 80 beats per minute. An abnormally low heart rate is called bradycardia. An abnormally high heart rate is called tachycardia. The impulse that originates from the SA node travels to the atrioventricular (AV) node by way of internodal fibers that stimulate the myocardial cells of the atria to contract. The impulse passes more slowly through the AV node which is located in the interatrial septum near the opening of the coronary sinus. The impulse slows as it goes through the AV node and travels through the interventricular septum by way of the AV bundle (bundle of His). The AV bundle divides into right and left bundles that go to the apex. Then branches at the apex radiate on inner surfaces of ventricles and Purkinje cells finally distribute the impulse to the myocardial cells of the ventricles.

Electrocardiogram ECG (EKG) The electrical impulses generated and distributed by the conducting system create electrical impulses that spread through the body. These impulses can be measured by electrodes placed on the surface of the body. Depending on the placement of the leads, various traces are produced that reflect the electrical activity of the heart.

Question: What organ of the body has a pericardium, pulmonary trunk, and superior vena cava?
Answer: Heart