Exercise 20 Gross Anatomy of the Heart

Laboratory Objectives tissue layer that is fused to adjacent structures (the diaphragm, sternum, costal cartilages of ribs, thoracic vertebrae, and the On completion of the activities in this exercise, you "'rill be able to: great vessels emerging from the heart). The inner serous peri­ Describe the anatomical relations of the heart with other cardium is a delicate serous membrane that forms a double­ structures in the thoracic cavity. layered sac around the heart. It consists of the parietal Provide details on the arrangement of the connective tissue pericardium, which covers the deep or inner surface of the fi­ layers (the pericardium) that surround the heart. brous pericardium, and the visceral pericardium, which forms • Identify important structures on the surface of the heart. the outer surface of the heart wall. The potential space between Locate the major internal structures of the heart. the parietal and visceral pericardial membranes is the Identify the tissue layers of the heart wall. pericardial cavity (Figure 20.1c). The cavity is filled with a wa­ • Describe the coronary circulation. tery fluid produced by the epithelial cells lining the serous peri­ Describe the flow of blood through the heart. cardium. The fluid helps to reduce friction when the two serous • Dissect a sheep heart and compare its structure with the membranes rub against each other as the heart beats. human heart. Materials CLINICAL CORRELATION Anatomical models or figures of the human heart Inflammation of the pericardia I membranes, known as peri­ • Plastic bags carditis, increases the friction between the two membranes and Cotton or cheesecloth causes an overproduction of fluid. As the fluid accumulates in the Colored pencils pericardial cavity it inhibits the normal movements of the heart Preserved sheep hearts wall and restricts cardiac output, leading to a condition called Dissecting trays cardiac tamponade. • Dissecting tools Dissecting gloves Protective eyewear ACTIVITY 20.1 Examining the Organization • Face mask of the Pericardium

1. Obtain a large, clear plastic bag and close off the he heart is a two-sided, double-pumping organ. The left side open end. (the left pump) controls the flow of blood to all tissues and 2. With a heart model, push the inferior pOinted tip (the T cells in the body, where oxygen and nutrients are delivered apex of the heart) into the wall of the closed plastic bag. and metabolic wastes are taken away. The right side (the right This action is similar to pushing a fist into the bag as illus­ pump) sends blood to the lungs, where oxygen stores in red blood « trated in Figure 20.1c. cells are replenished and carbon dioxide, a metabolic waste, is re­ 3. Notice that as you push the heart deeper into the closed leased. To keep blood circulating throughout the body, the heart bag, two layers of plastiC, separated by a space, cover the beats approximately 100,000 times and pumps between 7000 and organ (Figure 20.1c). 9000 liters of blood each day. By any standard, this is an arduous 4. Continue pushing the heart into the bag until you reach workload, but the fact that the heart can maintain this level of ac­ the great vessels that are attached to the superior aspect of ti\-ity for decades, without stopping, is nothing short of remarkable. the heart (aorta, pulmonary trunk, superior vena cava). In this exercise, you will examine the special anatomical fea­ 5. The plastiC layers represent the serous pericardium tures that reflect the enduring and efficient functioning of the (Figure 20.lc), as follows: heart. You will focus your examination on gross anatomical lructure. If you would like to review the light microscopic • The inner plastiC layer that is in contact with heart wall st ru 'LU re of cardiac muscle, see Activity 10.2. represents the visceral pericardium. • The outer layer of plastiC represents the parietal pericardium. • The space between the two plastic layers is the pericar­ The Pericardium dial cavity. The heart is enclosed by a membranous sac called the peri­ Notice that the two layers of plastiC are continuous cardium (Figure 20.1c) . This structure consists of two parts. with each other at the great vessels. In other words, The outer fibrous pericardium is a tough, fibrous connective the visceral pericardium is continuous with the

355 356 EXERCISE TWENTY

parietal pericardium where the great vessels are con­ What important function does the fibrous peri­ nected to the heart (Figure 20.1c). cardium serve? 6. Wrap a layer of cotton or cheesecloth over the outer plas­ tic laye r (the parietal pericardi u m). This layer represents the fibrous pericardium which is attached to the connec­ tive tissue layers that surround adjacent structures.

Thyroid gland Right lung _ _ -- First rib (cut)

Aorta (segment removed)

Left pleural cavity

(a)

Right pleural cavity

Rig ht pulmonary -1:-11k------.~f":::9:">C-•..__~~..;f artery

Right pulmonary vein

Superior vena cava Base of Right heart atrium Parietal Epicardium (visceral pericardium pericardium) Cut edge of parietal pericardium (b)

Fibrous tissue of Wrist (corresponds Inner wall pericardial sac ~ ~ w~ to base of heart) (corresponds Pericardial to visceral cavity Areolar tissue pericardium) containing , Parietal , Mesothelium } pericardium pericardial Air space fluid (corresponds Cut edge of epicardium to pericardia I Outer wall (visceral pericardium) cavity) Fibrous ---'-­ (corresponds Apex of heart attachment to parietal Balloon to diaphragm pericardium) (c)

Figure 20.1 The anatomical relations of the heart. a) Anterior view of the thoracic cavity, showing the heart within the mediastinum and between the two lungs; b) transverse section of the thoracic cavity showi ng the position of the heart in relation to other structures; c) the relationship of the heart, pericardium, and pericar­ dial cavity.

------GROSS ANATOMY OF THE HEART

Arch of aorta Gross Anatomy of the Heart Ligamentum arteriosum The heart is a four-chambered organ that is shaped roughly like Descending an inverted pear. On average, it is approximately 14 em long and aorta Ascending --#!!!jii!~I! 9 em wide, or slightly larger than a clenched fist. Its weight aorta Left pulmonary artery ranges from 230 to 280 grams in females and 280 to 340 grams ___:--_ Pulmonary in males. The hea rt and its surrolU)ding pericardial cavi ty are lo­ cava trunk Auricle of ---"jl---­ cated within the mediastinum, a centrally located area within right atrium the thoracic cavity. Two thirds of the organ is pOSitioned to the left of the midline. It is bordered laterally by the pleural cavities, Fat in anterior Fat in ....'--~,. which surround the lungs, anteriorly by the sternum, and pos­ coronary interventricular sulcus teriorly by the esophagus and thoracic vertebrae (Figures 20.1a and b)

\1I:1~ITiiHt' LE

ACTIVITY 10.1 Examining the Gross Anatomy

(a) of tbe Human Heart

Pericardium External Anatomy Ascending Pulmonary Auricle of trunk left atrium 1. Examine a model of the heart from an anterior view (Figures 20.2a and b) and make the following observations. Superior • The heart is divided into left and right sides. Each side contains two chambers: a superior atrium that receives Auricle of blood and an inferior ventricle that discharges blood. right atrium RIGHT Identify the four heart chambers: right atrium, right ATRIUM ventricle, left atrium (best observed from a posterior view), and left ventricle. • The apex of the heart (Figure 20.1c) is formed by Coronary sulcus the inferior tip of the left ventricle. It is located at the level of the fifth intercostal space, 7 to 9 cm to the RIGHT VENTRICLE left of the median plane. Locate this position on a Pericardiu skeleton. to diaphragm interventricular LEFT sulcus VENTRICLE • Extending off the main body of each atrium is a medial appendage known as an auricle. Locate the auricles of (b) each atria.

Left pulmonary artery WHATS IN A WORD The term auricle is derived from auricular, Left pulmonary ""':::::----:;;d'l!!!llllllll~to.. the Latin word for "external ear." The auricles of the atria were veins Superior given that name because early anatomists noted their resem­ vena cava blance to the external ear. Fat in coronary --7::.,;.z.==jIo.-:-' ~ ~..~~--i'T"-Right • Identify the atrioventricular (coronary) groove (sul­ sulcus pulmonary Coronary -j&---'+-----:::;=~ veins cus), which divides the atria, superiorly, from the ven­ sinus tricles, inferiorly. • From the atrioventricular groove, identify the anterior interventricular groove as it travels toward the apex Inferior along the anterior surface of the heart. It forms a border vena cava bet\veen the left and right ventricles. • Locate the ascending aorta, which receives blood from ~••~.""'~Fat in posterior interventricular the left ventricle. The ascending aorta gives rise to the sulcus arch of the aorta. The aortic arch gives off three (e) branches in the following order: the brachiocephalic artery, the left common carotid artery, and the left e 20.2 External anatomy of the heart. a) Diagram, and b) dissec­ subclavian artery. -- ",~ :erio r view; c) diagram, posterior view. EXERCISE TWENTY

• Locate the pulmonary trunk. It is located anterior to sure of the foramen oval is, called an atrial septal defect, allows the ascending aorta and receives blood from the right oxygenated blood in the left atrium to mix with deoxygenated ventricle. The pulmonary trunk gives rise to the right blood in the right atrium. This malformat.ion can be repaired surgi­ and left pulmonary arteries. cally to prevent the two blood supplies from blending. • Locate the superior vena cava and inferior vena cava where they empty into the right atrium. 3. In the right atrium, identify the following distinct regions. 2. Examine a model of the heart from a posterior view • The anterior wall is defined by the rough surface formed (Figure 20.2c) and make the following observations. by the pectinate muscles. The pectinate muscles con­ • Identify the relative positions of the four hean cham­ tinue onto the wall of the right auricle, the par-shaped, bers. Notice that the left atrium is more easily identified muscular pouch that extends medially from the atrial from a posterior view. wall (Figure 20.2a). This portion of the atrium is de­ • The base of the heart is at the heart's posterior and su­ rived from the embryonic heart. perior aspects, and is formed primarily by the left • The posterior wall lacks pectinate muscles and is atrium. It is located beneath the second pair of ribs and smooth. Verify that the openings for the superior vena the sternal angle (junction of the sternal body and cava and inferior vena cava are located along the smooth manubrium), and extends from T6 to T9 vertebrae. Lo­ portion of the atrial wall. The posterior atrial wall is de­ cate this position on a skeleton. rived from embryonic veins. At the inferior end of the • Once again, identify the atrioventricular (coronary) right atrium, the right atrioventricular (AV) orifice groove as it continues along the posterior surface of the leads into the right ventricle. heart. Notice that it forms a complete circle around the 4. Similar to the right atrium, the left atrium has two distinct heart, and forms a border between the atria and vent rides. regions with similar embryonic origins. The small anterior • Locate the posterior interventricular groove. Like the wall is dominated by the left auricle. Identify the pectinate anterior interventricular groove, the posterior groove de­ muscles in this region. The posterior wall is smooth and scends toward the apex from the atrioventricular groove, relatively large. Verify that the four pulmonary veins drain and forms a border between the left and right ventricles. into the left atrium from this region. Identify the left atri­ • Observe the four pulmonary veins-two on each oventricular (AV) orifice, at the inferior end of the left side-as they enter the left atrium. atrium, leading into the left ventricle. • Once again, identify the superior and inferior vena 5. Identify the two inrerior chambers, the right and left ventri­ cavae entering the right atrium. cles. Place the thumb and index finger of one hand on either side of the wall that separates the two ventricles. This struc­ Internal Anatomy ture is the interventricular septum (Figure 20.3). Notice that this wall is much thicker than the interatrial septum. 1. On the heart model, open the heart wall to expose the in­ Once again, identify the anterior and posterior interventricu­ ternal structures (Figure 20.3). lar grooves. Verify that these grooves delineate the anterior 2. Identify the two superior chambers, the right and left atria. and posterior margins of the interventricular septum. With one hand, place your thumb on one side and your in­ dex finger on the other side of the wall that separates the two atria. Your fingers are holding the interatrial septum. CLINICAL CORRELATION Identify the fossa ovalis, an oval depression along the in­ The inferior portion of the interventricular septum is a thick mus­ teratrial septum within the right atrium. cular wall. The superior portion is a thin, membranous partition and, consequently, is a more likely site for ventricular septal defects. Because blood pressure in the left ventricle is higher CLINICAL CORRELATION than in the right ventricle, a ventricular septal defect will result in The wall that separates the right and left atria is called the a left-to-right shunt of blood. This malformation, left unrepaired, interatrial septum. Inside the right atrium, along the interatrial can cause pulmonary disease and heart failure. septum, there is an oval depression called the fossa ovalis (Figure 20.3). This depression marks the site of the foramen 6. Within the right ventricle, the following distinct regions ovaIe, an opening that connects the atria in the fetal heart. The can be identified. foramen ovale has a valve that allows blood to travel from the right • The inferior portion receives the blood from the right atrium to the left atrium but not in the reverse direction. This spe­ atrium. Its walls are covered by an irregular network of cialization in the fetal circulation allows most of the oxygenated muscular elevations called the trabeculae carneae. blood coming from the placenta to bypass the nonfunctional lungs • Superiorly, the right ventricle narrows into a cone­ and the pulmonary circulation, and to pass directly to other vital or­ shaped chamber, the conus arteriosus, which leads to gans via the systemic circulation. At birth, the foramen ovale closes the pulmonary trunk. The wall of the conus arteriosus is when the valve fuses with the interatrial septum. Incomplete clo­ smooth and, consequently, lacks trabeculae carneae. GROSS ANATOMY OF THE HEART

Figure 20.3 Internal anatomy of Aortic arch the heart. Internal structures of the Superior heart chambers are revealed in a vena cava coronal section. The arrows indicate Ligamentum arteriosum the direction of blood fl ow. Pulmonary trunk

Ascending ----f--"'-' aorta

- -i"'I------Interatrial septum coronary sinus r.:r--tt-+--.J~-_ Aortic semilunar valve

Pectinate Cusp of left AV (bicuspid) valve Conus arteriosus LEFT VENTRICLE Cusp of right AV (tricuspid) valve

Chordae tendineae --=::::::--Ir.-:~"--' - ...... t-~~---::~- Interventricular septum Papillary muscle ---+-"\.-"-'''':''I...... ~ lI'.+,,=",,---,~-.:QI!:!L--"::"-I~:::"" Trabeculae carneae RIGHT VENTRICLE ---+--....._~'

Inferior vena cava -----!:~ Moderator band

~P------Descending aorta

7. Inside the left ventricle, the arrangement of rough- and the atria when the ventricles contract. As a result, back­ smooth-walled sections is similar to what is found in the flow of blood into the atria is prevented. right ventricle. The wall along the inferior portion of the • The two semilunar valves can be identified at the junc­ left ventricle is rough, due to the presence of the trabecu­ tion of each ventricle to its respective great artery. The lae carneae. The aortic vestibule is the smooth-walled, pulmonary semilunar valve is situated at the junction superior region that leads to the aorta. of the right ventricle and the pulmonary trunk, and the S. Identify the two pairs of heart valves, which are strategi­ aortic semilunar valve is located at the junction of the cally located to regulate blood flow through the heart and left ventricle and the aorta (Figure 20.3). Each semilu­ into the great arteries (aorta and pulmonary trunk). nar valve has three crescent-shaped cusps that are exten­ • The two atrioventricular (AV) valves are positioned sions of the great arterial walls. The operation of these between the atria and ventricles at the atrioventricular valves is also controlled by changes in pressure, this orifices. These valves open and close as a result of pres­ time between the ventricles and great arteries. They sure differences between the atria and ventricles during open when the ventricles pump blood into the arteries. the pumping action of the heart. The right valve is They close when the pumping action is complete to pre­ called the tricuspid valve because of its three cusps. vent backflow into ventricles. The left valve is named the bicuspid (mitral) valve be­ cause it possesses only two cusps. The cusps on the AV WHAT'S IN A WORD The bicuspid valve is often referred to as valves are membranous extensions of the endocardium the mitral valve, because when it is closed, the cusps resemble that reach into the ventricular chambers. Fibrous cords, the tall pointed hat, with front and back peaks, worn by bishops known as chordae tendinae, connect the inferior free and other members of the clergy. This ceremonial headdress is margins of the cusps to papillary muscles located on called a mitre (miter). the ventricular walls. The chordae tendinae and papil­ The term semilunar means "half moon. " The name refers ItO lary muscles prevent the cusps from swinging back into the half-moon shape of the cusps in the semilunar valves. EXERCISE TWENTY

The Heart Wall Why are the walls of the ventricles much thicker 1. Observe the left ventricular wall on a heart model and than the walls of the atria? identify the three layers of the heart wall (Figure 20.4) . • The inner endocardium is a thin, serous membrane of connective tissue and a simple squamous epithelium. It lines the internal walls of the heart chambers. • The middle myocardium is the thickest layer and com­ prises the bulk of the heart wall. It is composed prima­ rily of cardiac muscle fibers, separated by connective Coronary Circulation tissue containing capillaries and nerves. Contractions of Like any other organ, the heart must have an adequate blood cardiac muscle fibers are responsible for the pumping supply that delivers sufficient amounts of oxygen and nutrients action of the heart. to cardiac muscle cells and carries away carbon dioxide and • Similar to the endocardium, the outermosl epicardium other metabolic wastes. The right and left coronary arteries is a serous membrane of connective tissue and a simple branch directly off the ascending aorta. These arteries and their squamous epithelium. This layer is also called the branches deliver blood to all regions of the heart. Blood is visceral pericardium. drained from the heart wall by a number of cardiac veins which 2. Examine the relative thickness of the walls surrounding empty, directly or indirectly, into the right atrium. the heart chambers (Figure 20.3). Observe that the atrial walls are much thinner than the ventricular walls. 3. Compare the thickness of the two ventricular walls and ACTIVITY 20.3 Identifying the Blood Vessels observe that the left ventricular wall is thicker than the right ventricullar wall. of the Coronary Circulation 1. Identify the following coronary arteries on a heart model (Figure 20.5). CLINICAL CORRELATION • The right and left coronary arteries branch off the as­ Microbial infection of the endocardium can cause tissue inflam­ cending aorta just superior to the aortic semilunar valve. mation or endocarditis. This condition often causes damage • The left coronary artery travels to the left side, along the to the heart valves and could impede normal blood flow atrioventricular groove and posterior to the pulmonary through the heart. In severe cases, blood clots can form along trunk (Figure 20.Sa). Soon after it emerges from behind the walls of the ventricles. These clots can break off and travel the pulmonary trunk, it gives rise to two main branches: to other blood vessels where they can bring about organ fail­ the circumflex artery and the anterior interventricu­ ure, heart attacks, or strokes. lar artery (Figure 20.Sa).

Figure 20.4 Organization of the pericardium and heart wall. The re­ lationship of the heart wall (epicardium, Dense fibrous layer myocardium, and endocardium) with the pericardium and pericardial cavity is illustrated. Note that the epicardium and / CO""""" l;""ffi the visceral pericardium are the same structure.

MYOCARDIUM ~-~--~-+,. , (cardiac muscle MesotheliUm} EPICARD. IUM tissue) ,.,..-_ _ Areolar (visceral tissue pericardium)

Areolar tissue ENDOCARDIUM . { Endothelium --= .~ GROSS A ATOMY OF T H E HEART

Aortic • The circumflex artery travels along the atrioventricular arch groove. It curves around the left side (Figure 20.5a) and continues onto the posterior surface Left (Figures 20.5b and c). coronary • The anterior interventricular artery descends toward artery the apex along the anterior interventricular groove (Figure 20.5a). • The right coronary artery travels to the right along the atrioventricular groove (Figure 20.5a). It curves around the right side and continues onto the posterior surface Atrial y-- ,.­ Great (Figure 20.5b). arteries cardiac vein Anterjor The right coronary artery and the circumflex artery form cardiac an anastomosis (a natural connection between two veins blood vessels) on the posterior surface of the heart. Small Marginal • Just before the right coronary artery curves around cardiac artery (a) vein to the posterior surface, it gives off a branch called the marginal artery. The marginal artery descends Great Circumflex along the right margin of the right ventricle cardiac artery Coronary (Figure 20.5a). • On the posterior surface of the heart, the right coronary artery gives off a second major branch, the posterior in­ terventricular artery. This artery descends toward the apex along the posterior interventricular groove (Figures 20.5b and c). • Near the apex of the heart, attempt to identify an anas­ Posterior tomosis between the anterior and posterior interventric­ cardiac vein ular arteries. This anastomosis may not be demonstrated on the models that are available in your laboratory. 2. Identify the following cardiac veins on the heart model (Figure 20.5).

Middle cardiac Marginal • On the posterior surface of the heart, the coronary si­ vein artery nus is a large dilated sac that runs along the atrioven­

(b) tricular groove and empties into the right atrium (Figures 20.5b and c) . It drains most of the venous blood from the heart wall. Left pulmonary veins Left pulmonary artery • The great cardiac vein ascends along the anterior inter­ Circumflex Right pulmonary ventricular groove, running alongSide the anterior inter­ artery ~artery ventricular artery (Figure 20.5a). At the atrioventricular / _~ ./ Superior Great cardiac V vena cava groove it travels with the circumflex artery to the poste­ vein Right pulmonary rior surface, where it drains into the coronary sinus veins (Figures 20.5b and c). Posterior cardiac Left atrium • The middle cardiac vein ascends along the posterior in­ terventricular groove, traveling with the posterior inter­ Right atrium ventricular artery. It drains into the coronary sinus as it Inferior approaches the base of the heart (Figures 20.5b and c). vena cava • The smaU cardiac vein runs alongSide the marg.inal Coronary sinus artery as it travels toward the atrioventricular groove Middle cardiac vein (Figure 20.5a). At the atrioventricular groove, it trav­ els with the right coronary artery to the posterior sur­ Right ventricle face and drains into the coronary sinus (c) (Figure 20.5b). anterior cardiac veins Figure 20.5 The coronary circulation. The major arteries and veins that • The are small veins that travel a 5 JPply and drain the heart wall are illustrated. a) Anterior view of the heart with short distance along the anterior surfac e of the right :ne pulmonary trunk removed to reveal the left coronary artery; b) posterior ventricle. They drain directly into the right atrium . eo;! of the heart; c) dissection of the heart, posterior view. (Figure 20.5a). EXE .E TWEN n

Durin" the previous activity, you identified two ar­ ACTIVITY 20.4 Tracing the Flow of Blood terial "lOmoses in the coronary circulation. Through the Heart Chambers I ci o you think "the functional Significance of these arterial _ nnections in the heart? (Hint: Consider what must occur if 1. On a model of the heart, trace the pathway of blood blood flow to a particular region of the heart is partially blocked.) through the pulmonary circuit by reviewing steps one through five in Figure 20.6. 2. On a model of the heart, trace the pathway of blood through the systemic circuit by reviewing steps six through nine in Figure 20.6.

Blood Flow Through the Heart If the left ventricle is damaged and is not pump­ ing its normal volume of blood into the aorta, it The heart functions as a two-sided muscular pump that regulates will lag behind the pace of the right ventricle and eventually two separate blood circulatory loops. The right side of the heart blood will back up in the pulmonary circulation. This condi­ controls the pulmonary circulation, which is the flow of blood to tion is called congestive heart failure. Explain how restric­ and from the lungs. The left side of the heart controls the systemic tions in blood flow from the left ventricle and into the systemic circulation, which is the flow of blood to and from all body tissues circulation can have a negative effect on blood flow in the pul­ (Figure 20.6). The sequence of events that defines one pumping monary circuit. cycle of the heart is known as the cardiac cycle. During the cardiac cycle, the two atria relax and contract together and the t"vo ventri­ cles relax and contract together. Thus, the flow of blood through pulmonary and systemic circuits is occurring simultaneously

Pulmonary circulation: Deoxygenated blood enters the right atrium via the venae cavae, coronary • sinus, and anterior cardiac veins. Blood passes through the tricuspid valve and enters the right ventricle.

Right ventricle pumps blood through the o pulmonary semilunar valve into the o ~- pulmonary trunk. Blood is transported to the lungs via the o pulmonary arteries and their branches. In the lungs, the blood is oxygenated.

Oxygenated blood is transported to the left atrium of the heart via the pulmonary veins.

Systemic circulation:

Oxygenated blood passes through the bicuspid valve and enters the left ventricle.

Left ventricle pumps blood through the G aortic semilunar valve into the aorta.

Oxygenated blood is transported by the o aorta and its branches:

Blood is distributed to the head, neck and upper extremities via branches of the aortic arch.

Blood is distributed to the thorax, abdomen, pelvis and lower extremities ure 20.6 Overview of the pulmonary and systemic circulations. via branches of the descending aorta. ~ - :: . ~ , ven tricle pumps blood into the pulmonary trunk to begin the pul­ - : - 3 . :ircu lation. Th e left ventricle pumps bl ood into the ascending aorta to Deoxygenated blood returns to the right - :: ~ - :-e systemic circuit. atrium. GROSS A N ATOMY OF THE H EART

2. By making a cut in the pericardial sac, you have exposed the The Sheep Heart outside surface of the heart wall. . otice that the heart waIl is The sheep heart is remarkably similar to the human heart and covered by a thin, translucent membrane. With forceps, lift a thus represents an excellent model for studying cardiac struc­ portion of this membrane off the heart's surface. This is the ture. As you dissect, have models, illustrations, or photographs visceral pericardium. Recall that the visceral pericardium of the human heart readily available so that you can make struc­ and epicardium are the same structure. The space between lural comparisons. the parietal pericardium and visceral pericardium is the peri­ cardial cavity. Identify this space by placing a probe into it.

External Anatomy of the Heart ACTIVITY 10.5 Dissection of the Sheep Heart 1. Carefully remove the pericardial sac to expose the entire Organization of the Pericardium heart. This can be accomplished by continuing your initial l. Identify the pericardial sac if it is present. This structure scissors CUl toward the base of the heart and detaching the includes the fibrous pericardium and parietal pericardium. pericardial sac's attachments to the great vessels. The fibrous pericardium is a thick outer layer of fibrous 2. Observe the major sulci (grooves) that travel along the connective tissue and fat that encloses the heart. With a surface of the heart (Figures 20.7a and b) . They can best pair of scissors, cut along the pericardial sac for a short be identified by the large amount of fat that is located distance (about 2.5 cm or 1 inch) and fold it back to ex­ along their paths. pose its inner surface. The thin, shiny layer along this sur­ • The atrioventricular groove travels around the heart's cir­ face is the parietal pericardium. cumference and separates the atria from the ventricles.

Right atrium

Right atrium Pulmonary veins entering left atrium

Right ventricle Coronary sinus Anterior Posterior interventricular interventricular sulcus sulcus

Right ventricle

(al (b)

Aorta

Aortic semilunar valve Tricuspid Left atrium

Bicuspid valve

Chordae tendineae

Papillary muscle

Left ventricle

Figure 20.7 Anatomy of the sheep heart. a) Anterior view; b) posterior view; c) corona l section. (e) EXERCISE TWENTY

• The ante.rior interventricular sulcus (groove) travels be­ 3. Identify the interatrial septum that separates the left and tween the left and right ventricles on the anterior surface. right atria. The shallow, oval depression along the right • The posterior interventricular sulcus (groove) does the atrial side of the septum is the fossa ovalis. Inside the same on the posterior surface. atrial chambers, identify the pectinate muscles. Locate the 3. The atria on the sheep heart are quite small, and are com­ atrioventricular orifices that lead into the ventricles. These parable to the auricles on the human heart. Often, during openings mark the locations of the atrioventricular valves, commercial preparation of the heart, these chambers are which will be examined later. partially removed, leaving the internal structures exposed. 4. Identify the interventricular septum that divides the two Consequently, the venae cavae leading into the right ventricles. Notice how the inferior portion is thick and mus­ atrium and the pulmonary veins to the left atrium are usu­ cular, and the superior portion is thin and membranous. ally absent. Identify the base of the heart by locating what 5. Beginning at the apex, cut through the interventricular remains of the atrial walls (Figure 20.7). septum with a scalpel or scissors. Continue cutting 4. Hold the sheep heart so that the anterior surface is facing through the interatrial septum until you have completed a you (Figure 20.7a). At the inferior tip of the left ventricle, coronal section of the heart (Figure 20.7c). identify the apex of the heart. Identify the two great arter­ 6. In the coronal section, identify the following structures ies-the pulmonary trunk and the aorta. From an anterior (Figure 20.7 c). view, the pulmonary trunk is anterior to the aorta. Locate • The atrioventricular (AY) valves are located between the the anterior interventricular groove once again. Realize atria and ventricles. The tricuspid valve, with three that this groove forms a boundary between the right and cusps, is on the right side and the bicuspid valve, with left ventricles (Figure 20.7a). two cusps, is on the left. For each valve, observe that the 5. As described earlier, fat depOSits are found along the ma­ cusps are connected to the papillary muscles by the jor grooves on the heart's surface. In order to identify chordae tendinae. the blood vessels that travel along the grooves, it is nec­ • The trabeculae carneae are muscular elevations along the essary to remove this fat. With forceps, carefully strip walls of both ventricles. Notice that they are found pre­ away the fat from a small section along one of the dominately in the inferior portions of these chambers. grooves to verify the presence of blood vessels. Review • The superior portions of the ventricles are narrow, the names of the blood vessels that travel in each groove smooth-walled corridors that lead to the great arteries. (Figure 20.5). In the right ventricle, the conus arteriosus leads to the 6. Hold the sheep heart so that the posterior surface is facing pulmonary trunk. In the left ventricle, the aortic you (Figure 20. 7b). Along the atrioventricular groove, vestibule leads to the aorta. carefully remove the fat to reveal a thin walled, dilated 7. From the severed free margins of the aorta and pulmonary blood vessel that empties into the right atrium. This vessel trunk, cut along the walls of these blood vessels toward the is the coronary sinus (Figure 20.7b). ventricles until you reach the semilunar valves. Observe that each valve is composed of three crescent-shaped cusps. Internal Anatomy of the Heart 8. Along the wall of the aorta, just superior to the aortic 1. Expose the interior of the right atrium and ventricle in the semilunar valve, use a blunt probe to find the openings to folloWing manner. the right and left coronary arteries. • Insert the blunt end of a pair of scissors into the supe­ rior vena cava. H the superior vena cava is not present, The Heart Wall insert the scissors into the opening where the blood ves­ 1. Observe the left ventricular wall and identify the three lay­ sd drains into the right atrium. ers of the heart wall (Figure 20.7c). • Cut along the [ateral margin of the right atrium. • The inner endocardium is a thin serous membrane. It • Continue to cut along the lateral margin of the right appears as a smooth, shiny surface lining the internal ventricle to the apex. Be sure to cut through the entire walls of the heart chambers. thickness of the ventricular wall but avoid damaging in­ • The middle myocardium is the thickest layer. It is com­ ternal structures. posed primarily of cardiac muscle fibers. 2. Expose the interior of the left atrium and left ventricle in • The outer epicardium, which is the visceral peri­ the following manner. cardium, is also a serous membrane. • Using a scalpel or the sharp end of a pair of scissors, 2. Examine the relative thickness of the walls surrounding make a small incision in the lateral wall of the left atrium. the heart chambers (Figure 20.7 c). Observe that the atrial • Insert the blunt end of the scissors into the incision and '..valls are much thinner than the ventricular walls. cut along the lateral margin of the left atrium. 3. Compare the thickness of the two ventricular walls and • Continue to cut along the lateral margin of the left ven­ observe that the left ventricular wall is thicker than the tricle to the apex. right ventricular wall. GROSS ANATOMY O F THE H EART

2. Provide an explanation to account for the fact that the 1. On a model of the human heart, observe the heart wall is thicker in the left ventricle than in the right thickness of the heart wall in the various cham­ ventricle. bers. In terms of relative thickness, how do the heart walls in the chambers of the human heart compare with the sheep heart? Exercise 20 Review Sheet Name ______~______Lab Section ______Gross Anatomy of the Heart Date ______~______

Questions 1-4: Define the following terms. 1. Mediastinum

2. Atria versus ventricles

3. Apex of the heart

4. Base of the heart

5. Describe the circulatory pathways and the primary functions of the pulmonary and sys­ temic circulations.

6. Describe the three tissue layers that comprise the heart wall.

7. Describe the organization of the pericardium.

Questions 8-11: Each heart valve is located at the junction of an atrium and ventricle, or a \'entricle and great artery. Use this concept to describe the location of the heart valves. 8. Bicuspid valve

9. Tricuspid valve EXERCISE TWENTY

10. Pulmonary semilunar valve

1l. Aortic semilunar valve

12. Describe the function of the chordae tendinae and papillary muscles.

Questions 13-16: Complete the following table.

Artery Vessel from which Artery Branches Groove in which Artery Travels Regions Supplied by the Artery

13. Ascending aorta Right side of the heart

14. Anterior interventricular artery 15. Left coronary artery Left ventricle and left atrium

16. Posterior interventricular groove

Questions 17-20: Match the coronary artery in column A with the cardiac vein in column B that travels with it. The answers in column B may be used more than once or not at all.

A B

17. Marginal artery a. Great cardiac vein

~ 18. Anterior interventricular artery b. Middle cardiac ve.in 19. Circumflex artery c. Small cardiac vein 20. Posterior interventricular artery d. Coronary sinus

~ ------GROSS ANATOMY OF THE HEART

Questions 21-31: In the following diagram, identify the structures by labeling with the color that is indicated. 2l. Right atrium = yellow 22. Left ventricle = gray 23. Aorta = red 24. Left atrium = green 25. Pulmonary trunk = blue 26. Superior vena cava = purple 27. Right ventricle = orange 28. Inferior vena cava = pink 29. Coronary sinus = blue 30. Pulmonary arteries = brown 3l. Pulmonary veins = black

Questions 32-41: In the following diagram, identify the labeled structures. Select your an­ swers from the follOWing list.

32. a. Apex of the heart 33. b. Cusp of tricuspid valve 37 34. c. Inferior vena cava

35. d. Chordae tendinae 38 33 36. e. Middle cardiac vein 39 37. f. Trabeculae carneae 34

38. g. Papillary muscle 35 40 39. h. Interventric.ular septum 41 40. i. Great cardiac vein 36 4l. j. Cusp of bicuspid valve k. Ascending aorta I. Coronary sinus