Anatomy

ANATOMY & PHYSIOLOGY

Mammalian Heart Dissection Investigation Manual

MAMMALIAN HEART DISSECTION

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Table of Contents

2 Overview 2 Outcomes 2 Time Requirements 2 Key 3 Background 7 Materials 8 Safety 9 Preparation 10 Activity 1 11 Disposal and Cleanup 12 Glossary

Overview The heart is the center of the cardiovascular system. It pumps oxygenated blood throughout the body, and deoxygenated blood to the capillaries of the lungs. In this investigation, the student will be guided through the dissection and close examination of an adult mammalian heart.

Outcomes •   Identify external and internal anatomical features of the heart. •   Apply anatomical terminology while performing a heart

dissection. •   Describe the functions of the chambers, valves, and major

vessels of the heart. •  Distinguish between pulmonary and systemic circulation. •  Trace the flow of blood through the heart.

Time Requirements Preparation 10 minutes Activity 1: Dissection of a Mammalian Heart 40 minutes

Key Personal protective equipment (PPE)

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Background The body is made up of organ systems, each with a specific role in maintaining life. Each  organ system consists of a number of organs that operate collectively to carry out certain body functions. At every level of organization, whether at the cellular, tissue, organ, or organ- system level, each structure always reflects its function and vice versa. This concept is known as the principle of complementarity of struc- ture and function. In this activity, a sheep heart will be examined and dissected to understand the relationship between structure (anatomy) and function (physiology).

Organ systems do not operate independently, but rather are coordinated for the organism to survive. The interdependence of organ systems needed for homeostasis–the dynamic equilibrium the body sustains when in good health–must be considered and understood. For example, the heart is part of the circulatory system and is involved in transportation of mate- rials, including nutrients; hormones; and gases, such as oxygen and carbon dioxide, throughout the body.

The circulatory system is composed of a network of vessels lined with endothelium, a type of epithelium (covering and lining tissue). The walls of blood vessels may include connec- tive tissue and smooth muscle. The heart is an expanded region of the circulatory system, so it is not surprising to find that it is made up  of tissues very similar to those found in blood vessels. The interior spaces are lined with endocardium, endothelial tissue of the heart. Some components, such as the valves, contain connective tissue, and the heart is enclosed in an outer connective tissue layer

called the epicardium. The walls of the heart are composed mainly of cardiac muscle, an involuntary type of striated muscle tissue. The middle, muscular layer of the heart wall is termed the myocardium.

The mammalian four-chambered heart allows for two cardiovascular pathways: the pulmo- nary circulation and the systemic circulation (Figure 1). Together, these two pathways carry blood throughout the body while maintaining separation of oxygenated and deoxygenated blood. The pulmonary circulation carries deoxy- genated blood away from the heart through the capillaries in the lungs, and then returns oxygen- ated blood to the heart. The systemic circulation is responsible for providing this oxygen-rich blood to the rest of the body and returning it to the heart so it can enter the pulmonary circula- tion. These two interdependent circulatory loops enable mammals to use oxygen efficiently. 

Heart Structure and Function The mammalian heart (Figure 2) consists of four chambers: two atria (receiving chambers) and two ventricles (powerful pumping chambers). Blood enters the right and left atria and leaves the heart via the right and left ventricles. When the atria contract, they push blood a short distance into the ventricles. From the ventricles, the blood is forced into the arteries and out of the heart. The muscular walls of the ventricles are much thicker than those of the atria; thus, ventricular contraction creates high pressure to send blood a greater distance. The walls of the left ventricle are particularly thick due to its role in propelling the systemic circulation.

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MAMMALIAN HEART DISSECTION

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Background continued The aorta is the main vessel conveying oxygen- ated blood from the heart into the rest of the systemic circulation (see Figure 1). The curved region of the aorta near its attachment to the heart is known as the aortic arch. The brachiocephalic trunk (also known as the brachiocephalic artery) is a major branch from the aortic arch that splits

apart to form the right subclavian artery, supplying the right forelimb, and right common carotid artery, supplying the right side of the head and neck. The left common carotid artery branches from the aortic arch to supply the left side of the head and neck, and the left subclavian artery branches afterward to supply the left forelimb.

Figure 1. Capillaries of the upper body (head and arms)

O2CO2

CO2O2 LungsJugular vein Carotid artery

Capillaries of the lungs

Superior vena cava

Pulmonary artery

Pulmonary vein

Aorta Right atrium

Left atrium Inferior vena

cava Left ventricle

Right ventricle Lymph node Liver

Hepatic portal veinHepatic vein Digestive

tract

Mesenteric arteriesLymphatic

vessel Renal vein Renal artery

KidneysIliac vein Iliac artery

O2CO2

Capillaries of the lower body (trunk and legs)

To understand pulmonary and systemic circulation more clearly, the path of the blood must be traced through the heart, as shown in Figure 2. Deoxygenated blood returning to the heart from the rest of the body enters the right atrium via the superior and inferior vena cavae. When the atrial muscle contracts, blood is pushed into the right ventricle. When the right ventricle contracts, blood is forced into the pulmonary trunk, which branches to form the right and left pulmonary arteries. These two arteries carry blood to the lungs. As the blood enters capillary beds in the lungs, carbon dioxide diffuses out of the  blood and into air sacs, and oxygen diffuses from the air sacs into the  blood. This oxygenated blood returns to the heart through the pulmonary veins. This constitutes the pulmonary circulation.

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The pulmonary veins empty blood into the left atrium, which contracts at the same time as the right atrium. Blood from the left atrium is forced into the left ventricle. As the ventricles contract, blood in the left ventricle is forced into the aorta. The aorta conveys blood to arteries that branch to transport the oxygen-rich blood through the body. Oxygen is delivered to the various tissues of the body, and deoxygenated blood is conveyed back toward the heart through veins that eventually lead back to the vena cavae. This pathway of blood constitutes the systemic circulation.

These two cardiovascular pathways carry blood simultaneously. The heart chambers contract rhythmically to ensure that blood continues on its proper course. This rhythmic contraction and relaxation of the heart muscle is called the cardiac cycle. During this cycle, the atrial walls

contract. This contraction forces blood into the relaxed ventricles. As the atria relax, the muscular walls of the ventricles contract. Both ventricles then relax, completing the cycle.

Blood moving from an atrium to a ventricle must flow through an atrioventricular valve. There are two atrioventricular valves: the bicuspid valve (also known as the mitral valve) on the left side of the heart, and the tricuspid valve on the right. These valves allow for one-way flow of blood. When the ventricle contracts, the  valve prevents blood from being forced back into the atrium. The valves are flaps, or cusps,  of connective tissue anchored by strong fibers.  These fibers are known as chordae tendinae, and prevent the valves from opening during ventricular contraction. The chordae tendinae are anchored by papillary muscles found in the walls of the ventricles.

Figure 2. Oxygenated blood to body

Deoxygenated blood from body Aorta

Superior vena cava Left pulmonary arteryRight pulmonary artery Pulmonary trunkDeoxygenated blood to lungs Oxygenated blood from lungs

Right pulmonary veins Left pulmonary veins

Left atrium Right atrium Bicuspid valve

Pulmonary valve

Aortic valve

Left ventricle Inferior vena cava

Right ventricleTricuspid valve continued on next page

MAMMALIAN HEART DISSECTION

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Background continued When blood is forced from the ventricles, it passes through semilunar valves. One semi- lunar valve, called the aortic valve, is located where the aorta leaves the left ventricle; the other, called the pulmonary valve, can be found where the pulmonary trunk leaves the right ventricle. Once the ventricles have relaxed, the semilunar valves keep blood from moving back into the ventricles.

Because the heart is a continuously working muscle, it needs a constant supply of nutrients

and oxygen. However, oxygen in the blood does not have time to diffuse across the thick  endothelial lining of the chambers. The heart, therefore, has its own series of blood vessels that provide nourishment. The coronary artery branches from the aorta as it leaves the heart. It then branches into arteries that carry oxygenated blood to the capillary beds within the heart walls. Cardiac veins return oxygen-poor blood from the walls of the heart to the pulmonary circula- tion. The cardiac veins return blood to the coro- nary sinus, which opens into the right atrium.

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Materials Included in the materials kit:

Pig heart preserved in Carolina’s Perfect Solution® OR Sheep heart preserved in Carolina’s Perfect Solution® (as specified by instructor)

Heart dissecting mat Disposable dissecting tray

Self-locking storage bag

Absorbent pad

Needed from the dissection set:

Scalpel Probe Forceps

Needed from the safety set:

Safety goggles Lab apron Disposable gloves

Needed from the equipment kit:

Hand lens (optional)

Needed but not supplied: •   Paper towels •    70% isopropyl alcohol (rubbing alcohol) or

other non-bleach disinfectant •    Digital camera or mobile device capable of

taking digital photos

Reorder Information: A replacement Carolina’s Perfect Solution® Sheep Heart (item number 228774), Mammalian Heart Dissection set (item number 580183), or Caro- lina’s Perfect Solution® Pig Heart (item number 228564), or Mammalian Heart Dissection (Pig) (item number 228564) can be ordered from Carolina Biological Supply Company.

Call 800-334-5551 to order.

MAMMALIAN HEART DISSECTION

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Safety This investigation requires safety goggles, disposable gloves, and a lab apron.

Follow the instructions for this activity closely and observe established laboratory safety prac- tices, including appropriate personal protective equipment (PPE); safety glasses or goggles, gloves, and lab aprons must be worn when dissecting. Do not eat, drink, or chew gum while performing the dissection. Use proper hygiene practices before, during, and after the lab, including washing your hands before and after performing the dissection. Review pertinent portions of any Safety Data Sheets (SDS) before beginning the activity. Keep pets and children away from lab materials and equipment.

Dissections require special attention to safety. Please follow these additional precautions:

•    Clean the counter or workspace thoroughly before and after the dissection, using isopropyl alcohol (or other non-bleach disinfectant).

Isopropyl alcohol (rubbing alcohol) is flammable. Keep away from open  flame if using alcohol as disinfectant.

•    Wash your hands thoroughly with soap and water before and after the dissection.

•    Only perform the dissection on the dissecting tray. This will contain both the specimen and any excess fluids.

•    Spread the absorbent pad blue-side down underneath the tray to capture any spilled fluid. 

•    Scalpels are used infrequently in most dissection labs and require special handling and disposal:

- Never cut toward your holding hand and fingers.

- Cut in a downward motion using a steady, even pressure.

- Always use a sharp blade. - Do not use a scalpel that is nicked, bent, or

damaged. - Do not use a scalpel to cut through bone or

heavy cartilage. - Never use a scalpel for anything other than

dissection.

Using a Scalpel http://players.brightcove.

net/17907428001/HJ2y9UNi_default/index. html?videoId=5170128655001

Carolina’s Perfect Solution® Independent, certified laboratory analyses of  specimens fixed in Carolina’s Perfect Solution® have found that it is nontoxic and does not give off dangerous fumes. This means that, for safety  purposes, use of Carolina’s Perfect Solution® specimens does not require specialized ventilation. Carolina does recommend performing the dissection in a well-ventilated room with some active ventilation when working with any preserved specimens. For a home setting, this may include opening windows and turning on a ceiling fan. The safe nature of Carolina’s Perfect Solution® also means that in most localities there are no mandated disposal requirements.

Carolina’s Perfect Solution® causes mild skin irritation if suitable PPE is not worn. Avoid contact with skin and

eyes. Do not ingest specimen, especially if you are or may become pregnant.

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Storage of Specimens If it is necessary to store the specimen between work periods, you may choose to place it in the plastic storage bag with as much of the original solution as possible. Establishing an airtight seal is the best way to retain specimen integrity and prevent drying out of the specimen. First, squeeze as much air out of the specimen bag as possible before securing the opening with a rubber band, tape, or a binder clip. After closing the bag, the specimen can be stored in a larger, airtight box or bag at room temperature.

Preparation 1. Review the dissection instructions and the

glossary at the end of this investigation. 2. Print out the dissection procedure to avoid

getting fluid from the specimen on your  computer or mobile device.

3. Clean the work area. Put on your PPE: safety glasses, gloves, and lab apron, and keep them on during the dissection and cleanup.

4. Lay the pad on the work area with the white, absorbent side facing up.

5. Lay the scalpel, forceps, probe, and hand lens (if available) on the pad.

6. Inspect the scalpel. Do not use the scalpel if it is bent, nicked, or damaged.

7. Place the dissecting tray in the middle of the pad to absorb any fluid that might spill onto  the work area.

8. Position the dissection mat so it is easily viewed.

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ACTIVITY

ACTIVITY 1 A Dissection of a Mammalian Heart

Click to view a video showing major features of the heart

http://players.brightcove.net/17907428001/ HJ2y9UNi_default/index. html?videoId=4886990696001

1. The most important step in the heart dissection is placing the heart in the correct anatomical position. When the heart is in the anatomical position, it will be anterior (ventral) side up (facing you), and posterior (dorsal) side down (against the absorbent pad). The left side of the heart will be on your right, and the right side of the heart will be on your left. Use the dissection mat for reference.

Note: In many drawings and photographs of correctly-positioned mammalian hearts, you will notice that the apex points to the left (your right). The apex may not be as easy to locate on your specimen because the preservation and packing processes often cause distortion. You can find the anterior side by looking for the T-shaped pulmonary trunk extending up and branching into the pulmonary arteries. You can confirm that you are looking at the anterior side of the heart by locating the atrial appendages. They will be oriented anteriorly, much like forward- pointing dog’s ears.

2. Locate and identify as many externally-visible structures as

possible, using the dissection mat as a guide. Numbers in parentheses correspond to numbered structures on the heart dissection mat. In the following steps you are asked

to identify and photograph a number of structures. Each photograph may have multiple structures pinned or presented. Take notes to keep track of which structures are presented in each picture. a. Use the forceps to grasp the tough, superficial epicardial layer that adheres  tightly to the heart.

b. Approximate the locations of the right (20) and left (12) atria and right (21) and left (15) ventricles, using the coronary sulcus (8) and interventricular sulcus (11) as guides.

c. Note the atrial appendages (4) and the heart apex (3).

d. Gently insert the blunt end of the probe into each of the following vessels: pulmonary artery (17) and pulmonary trunk (18), pulmonary vein, superior vena cava (22), inferior vena cava (9), and aorta (1).

3. Now you will open the heart along its frontal plane in preparation for examining its internal structures. a. Position the heart for a longitudinal cut as

shown on the front of the dissection mat. You will be looking down on the left atrium, and the apex will be pointing toward you.

b. Using the scalpel, start your incision just below the left atrium. Make a deep incision, cutting all the way to the interventricular septum (10).

c. Continue the incision, slicing through the left ventricle until you have reached the apex.

d. Cut through the left atrium until you have reached the start of the original incision.

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e. To complete the section, turn the heart over and cut from the apex through the right ventricle and right atrium. Now the heart should be cut completely in two along the frontal plane as shown on the back of the dissection mat.

4. Identify and photograph the internal structures of the heart, using the

dissection mat as a reference. Take notes of which structures appear in each photograph so that you may label them later. a. Locate both atria, both ventricles, and all large blood vessels (previously identified  in step 2d above). Photograph them again to show what they look like from the interior of the heart. As you examine the inner ventricular walls, notice the trabeculae carneae (23). Note the very thin, transparent layer of endocardium lining the heart chambers.

b. Identify the aortic valve (2). Also locate the pulmonary valve, which is not labeled on the mat but lies between the right ventricle and the base of the pulmonary trunk.

c. Identify the biscupid (5) and tricuspid (24) valves, as well as the chordae tendinae (7) and papillary muscles (16) attached to them. Inspect the valves and chordae tendinae, using a the hand lens if available, and compare their surfaces with those of the trabeculae carneae and the sectioned walls of the heart chambers. The trabeculae carneae, chamber walls, and papillary muscles are composed of cardiac muscle tissue, whereas the valves and chordae tendinae are made up of connective tissue and endocardium.

Disposal and Cleanup 1.  Dispose of any excess fluids down the drain 

with the water running. Allow the faucet to run for about 30 seconds to dilute the fluids.

2. Place the specimen in its storage bag and seal tightly. If you are finished working with  your specimen, put the bag into an opaque trash bag for disposal in the household garbage.

3. Rinse and carefully air dry the dissection tools, and return the materials to your equipment kit.

4. Sanitize the workspace with isopropyl alcohol (or other non-bleach disinfectant) and paper towels. If this is insufficient for removing  grease during cleanup, use soap and water, followed by more alcohol/disinfectant.

ACTIVITY 1 continued

ACTIVITY

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Glossary Anatomists and health care providers use a very specific terminology that enables them to  precisely communicate their work. Directional anatomical terms are used for describing the

relative positions of different body structures or  to provide instructions for incisions. Directional anatomical terms (Table 1 and Figure 3) are used in this and most other dissection guides to describe the relative positions of body struc- tures. Therefore, learning these terms is essen- tial for the understanding and study of anatomy.

Table 1.

Direction or Plane Definition

Anterior Toward the front of the body; synonymous with ventral Posterior Toward the back of the body; synonymous with dorsal Superior Above, over Inferior Below, under Dorsal Toward the back or spine; synonymous with posterior Ventral Toward the belly or abdomen; synonymous with anterior Superficial Toward or along the surface Deep A significant distance below the surface Sagittal plane Divides the body into longitudinal left and right portions Midsagittal plane Divides the body into equal left and right halves Transverse plane Perpendicular to the long axis; produces cross-sections Frontal plane Divides the body into dorsal and ventral portions

Figure 3. Midsagittal plane

Frontal plane

Transverse planeMidsagittal

plane

Frontal plane

Transverse plane

BipedQuadruped

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The terms listed in Table 2 are used in this dissection and are important parts of the mammalian heart.

Table 2.

Structure Short Definition

Aorta Large artery that emerges from the left ventricle; carries blood to the systemic circulation

Apex Pointed, lower end of the heart consisting of muscle from the left ventricle Artery Blood vessel that carries blood away from the heart

Atrium One of the two upper chambers of the heart that receive blood; the plural form is atria

Atrial appendage Ear-like flap made up of muscle from the atrium; also termed an auricular appendage or auricle

Base Point of attachment for blood vessels entering and exiting the heart

Bicuspid valve Heart valve between the left atrium and ventricle; also called the left atrioventricular (AV) valve or mitral valve

Chordae tendineae Fibrous cords that connect atrioventricular valves with papillary muscles; also referred to as the “heart strings”

Coronary artery Artery leading from the aorta that supplies blood to the heart muscle

Coronary sulcus Groove that passes around the heart and separates the ventricles below from the atria above and is also known as the atrioventricular groove; runs perpendicular to the interventricular groove

Inferior vena cava Large vein that returns blood from the lower body regions to the right atrium Interatrial septum Muscular wall between the right and left atria

Interventricular groove

Groove that runs perpendicular to the coronary sulcus and indicates the position of the interventricular septum

Interventricular septum Muscular wall between the right and left ventricles

Papillary muscles Muscles anchoring the chordae tendineae to the atrioventricular valves

Pulmonary circulation Pathway of blood that flows through the lungs and then returns the oxygen-rich blood to the heart

ACTIVITY 1 continued

ACTIVITY

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Table 2 continued.

Structure Short Definition

Semilunar valves Valve between the aorta and left ventricle, and between the pulmonary trunk and right ventricle; often called the aortic valve and pulmonary valve, respectively

Superior vena cava Large vein that returns blood from the anterior regions of the body to the right atrium

Systemic circulation The pathway of blood to arteries that branch to transport the oxygen-rich blood through the body and veins that convey deoxygenated blood back to the heart

Trabeculae carneae Ridges and folds on the walls of the ventricles

Tricuspid valve Heart valve between the right atrium and right ventricle; also called the right atrioventricular (AV) valve Vein Blood vessel that returns blood to the heart

Ventricle One of the two lower chambers of the heart that force blood into either the aorta or the right and left pulmonary arteries, formed by branching of the pulmonary trunk

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NOTES

CB781101701

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ANATOMY & PHYSIOLOGY Mammalian Heart Dissection

Investigation Manual

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