Part 5: Heart and Major Vessels

Abby Brown

Related Learning Objectives

  • D4.6 Identify and differentiate pulmonary aa. from pulmonary vv. (and explain the observed latex coloration that may be present in the preserved specimen).
  • D4.9 Identify the various parts of the heart and associated major vessels; be able to trace/summarize the flow of blood into, through, and out of the heart.

IMPORTANT NOTE: As you proceed to study the heart, be sure to know/understand the blood flow pattern and general valve locations in addition to identifying the structures.

  1. In the middle part of the mediastinum, locate the heart and identify the fibroserous covering of the heart called the pericardium, often referred to as the pericardial sac. The pericardial sac is a specific part of the mediastinal pleura that is thin, but strong, and consists of three inseparable components: serous pericardium, fibrous pericardium, and pericardial mediastinal pleura. (See DG Fig. 3-9)

    • Incise the pericardial sac and open it to expose the heart.

  2. The heart has a base dorsally/cranially (where the great vessels are attached) and an apex ventrally/caudally (usually inclines to the left side). The surface of the heart facing the left thoracic wall is the auricular surface and the opposite surface (facing the right thoracic wall) is the atrial surface. (For heart diagrams, see DG Figs. 3-22, A & B, 3-23, and 3-24)

    • Identify the coronary groove (aka coronary sulcus) encircling the heart. This a groove between the atria and ventricles. The coronary groove contains coronary vessels and some amount of fat. (See DG Fig. 3-23)

    • There are two other ‘grooves’ but you will not need to identify them specifically on your specimen. These are the subsinuosal interventricular groove (sulcus) and the paraconal interventricular groove (sulcus). These grooves are shallow indentations separating the right and left ventricles of the heart. (See DG Figs. 3-22A and B)

      Related Learning Objective

      • D4.9

       

    • Identify the right atrium and right auricle. (See DG Figs. 3-22, A & B, and 3-23) The right atrium receives the blood from systemic veins and most of the blood from the heart itself. The right auricle is a flap-like (or ‘ear-shaped’), blind pouch that is part of the right atrium.

    • Re-identify the cranial vena cava and caudal vena cava. (The cranial vena cava is cranial to the heart, while the caudal vena cava is caudal to it.)

  3. Open the right atrium with a longitudinal incision, extending from the cranial vena cava to the caudal vena cava. Extend another small incision from this cut to the tip of the right auricle (this makes a ‘T’ or ‘J’ shaped incision into the right atrium and auricle). Open the right atrium and clean out any debris/latex found inside.

    • Dissection note: To make this process less messy, use paper towels to line the thoracic cavity before cleaning debris out of the heart. After you have finished cleaning out the heart, pull the paper towels (with latex/debris on them) out of the thorax.

    • The right atrium is divided into two parts, a main part and a blind pouch; the main part is the sinus venarum, and the blind pouch is the auricle.

        • Note the opening where the caudal vena cava enters the atrium caudally. Then, note the opening where the cranial vena cava enters the atrium cranially. Between these two openings there is a transverse ridge of tissue called the intervenous tubercle. This tubercle diverts incoming blood from the caval veins toward the right atrioventricular orifice. Identify this tubercle in your specimen. (See DG Fig. 3-22A)

            • Comment: Note that caudal to the intervenous tubercle you may see a slit-like depression called the fossa ovalis. (This is a remnant of an opening present in the fetus, the foramen ovale, which allowed blood to pass from the right atrium to the left atrium.) (See DG Fig. 3-22A)

        • Ventral to the opening of the caudal vena cava into the atrium, identify the coronary sinus. This is an opening that allows for venous return of most of the blood from the heart itself, via the great cardiac vein. (See DG Fig. 3-22A)

        • Comment: Note that there is an interatrial septum between left and right atria; this is within the dorsomedial wall of the sinus venarum.

    • The blind pouch of the right atrium is the right auricle. It’s tip faces cranially and to the left. (See DG Figs. 3-22A, and 3-23)

        • Comment: Note that the auricle is strengthened by interlacing muscular bands called pectinate muscles. (See DG. Fig. 3-22A) Pectinate muscles are also found on the lateral wall of the atrium proper.

  4. While still looking at the right atrium, identify the large opening (ventral and cranial to the coronary sinus) that allows the blood to pass from the right atrium into the right ventricle. This is the right atrioventricular (AV) orifice.

    • Comment: Note that all the internal surfaces of the heart are lined with a thin, glistening membrane called the endocardium.

      Related Learning Objective

      • D4.9

       

  5. Moving outside of the right atrium, identify where the right ventricle is located in relation to the right atrium. Identify the pulmonary trunk, which is the large vessel leaving the right ventricle cranially and angling to the left. (The pulmonary trunk then gives rise to the left and right pulmonary arteries.) (See DG. Figs. 3-22B, 3-23, and 3-24)

    • Make an incision through the wall of the pulmonary trunk at its base and continue this cut distally, through the wall of the right ventricle. (The cut should be made in the middle of the wall of the right ventricle,)

    • Reflect the right ventricular wall and remove any debris/latex found inside.

  6. Identify the right ventricle. Open the right ventricle and find the large atrioventricular orifice connecting the right atrium and the right ventricle. This opening contains the right atrioventricular (AV) valve (aka tricuspid valve) that allows the orifice to open and close. Identify the right AV valve and note that it has parietal and septal cusps. The parietal cusp is a short, wide flap arising from the parietal (wall) surface of the orifice. The septal cusp is a flap arising from the septal margin (septum between left and right sides). (See DG Figs. 3-22A, and 3-23)

    • Identify the chordae tendineae which are the stringy, fibrous bands that attach the cusps to the septal wall of the ventricle by attaching to the papillary muscles.

    • The papillary muscles are conical muscular projections in the septal wall of the ventricle that serve as attachment points for the chordae tendineae. Identify the papillary muscles seen in the right ventricle (usually 3-4). (See DG Fig. 3-23)

    • Comment: Note that you will see muscular irregularities of the interior walls of the ventricle; these are called trabeculae carneae. (See DG Fig. 3-23)

    • Dissection Note: There is a possibility that you will see a muscular strand extending across the lumen of the ventricle from the septal wall to the parietal wall. This structure is called the trabecula septomarginalis (aka moderator band). (These are not often seen in the cadavers because they get ripped/broken during the dissection process.)

    • Comment: The right ventricle terminates as the funnel-shaped conus arteriosus which then gives rise to the pulmonary trunk.

  7. At the junction of the right ventricle and pulmonary trunk, identify the pulmonary valve (aka pulmonic valve). The pulmonary valve consists of three semilunar cusps. (See DG Fig. 3-23)

    • Dissection Note: Also, closely associated with the pulmonary trunk, you may see the ligamentum arteriosum (fetal ductus arteriosus) connecting the pulmonary trunk and the aortic arch. This is a fibrous connection and may be difficult to see. (In the fetus this was the patent ductus arteriosus that shunts blood directly to the aorta to bypass the fetal lungs.) (See DG Fig. 3-22B)

      Related Learning Objective

      • D4.6

       

  8. Trace the pulmonary trunk and locate where it bifurcates into right and left pulmonary arteries, coursing toward the left and right lungs respectively; these in turn give rise to lobar pulmonary arteries. Attempt to re-identify the right and left pulmonary aa. in your specimen. Note that these arteries may be difficult to identify due to the removal of the lungs. (See DG Fig. 3-22B)

    • Comment: Note that on the isolated lungs, you may be able to see the lobar pulmonary arteries and also the lobar pulmonary veins. Note that the lobar pulmonary veins then enter the left atrium of the heart.

  9. On the left side of the heart, identify the left atrium and left ventricle. (The left atrium will have four or five openings/pulmonary veins entering it at the base of the heart.) (See DG Figs. 3-22B, 3-23, and 3-24)

    • Open the left side of the heart with one longitudinal incision through the middle of the left ventricle (mid-way between the paraconal interventricular and subsinuosal grooves) and another small (separate) incision through the left atrium and left auricle. Remove any debris/latex found inside.

  10. Open the left atrium and identify the left auricle. The atrium proper will be quite small; most of what is seen of the left atrium is the blind pouch of the left auricle.

    • Comment: Note that the left auricle also contains pectinate muscles as were seen in the right auricle.

    • While looking into the left atrium, identify the large opening that allows the blood to pass from the left atrium into the left ventricle. This is the left atrioventricular (AV) orifice.

      Related Learning Objective

      • D4.9

       

  11. Re-identify the left ventricle and note the significant difference in thickness of the left ventricular wall as compared with that of the right ventricle.

    • Open the left ventricle and find the large atrioventricular orifice connecting the left atrium and the left ventricle. This opening contains the left atrioventricular (AV) valve (aka mitral or bicuspid valve) that allows the orifice to open and close. Identify the left AV valve and note that it has parietal and septal cusps, but the division is not distinct. (See DG Fig. 3-24)

        • Note the (usually) two large papillary muscles and the chordae tendineae attached to the cusps. (See DG Fig. 3-24)

    • Comment: Note that the left ventricle will also have trabeculae carneae as the right ventricle did, but they are not as numerous in the left ventricle. (See DG Fig. 3-24)

  12. At the junction of the left ventricle and the aorta, attempt to find/see the aortic valve (aortic root region) and its three semilunar cusps. Since this region is difficult to see, you should also look at the available museum specimens to see this area. (See DG Fig. 3-24)

  13. Move outside of the heart and find the ascending aorta. Carefully, using blunt dissection, identify the right coronary artery as it leaves the ascending aorta and encircles the right side of the heart, following the coronary groove (and extending to the subsinuosal interventricular groove). The right coronary artery will send several branches out over the surface of the right ventricle as it travels around the heart. (See DG Figs. 3-17 and 3-25)

  14. Going back to the ascending aorta, identify the left coronary artery as it leaves the ascending aorta. The left coronary artery is about twice the size of the right coronary artery. It is a short trunk that then divides into two branches. Carefully dissect out the two branches, the circumflex branch and the paraconal interventricular branch. (See DG Figs. 3-17 and 3-25)

    • Identify the circumflex branch of the left coronary artery as it ‘circles’ the left side of the heart in the coronary groove, between the left atrium and left ventricle. (This branch terminates as the subsinuosal interventricular branch.) (See DG Fig. 3-25)

    • Identify the paraconal interventricular branch of the left coronary artery as it crosses the auricular surface of the heart, following the paraconal interventricular groove. (See DG Figs. 3-17 and 3-25)

    • Dissection Note: Note that both branches of the left coronary artery send multiple smaller branches out over the surface of the left ventricle.

  15. Locate and identify the great cardiac vein which begins in the paraconal interventricular groove and then follows the coronary groove to return blood supplied to the heart by the left coronary artery. The great cardiac vein empties this returned blood into the coronary sinus. (See DG Fig. 3-22B)

    • Re-identify the coronary sinus where the great cardiac vein empties into the right atrium (previously identified with the right atrium terms). (See DG Fig. 3-22A)

Be sure to visit the demo area to review the heart anatomy on the plastinated museum specimens as well. These plastinated models are frequently used on assessments, so we recommend being familiar with them!

Dissection Videos for this Section of Material

Heart and Major Vessels:

 

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Dissection Lab Guide for Dog and Cat Anatomy Copyright © by Abby Brown. All Rights Reserved.

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