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Dissection of the heart

AIM:  

To observe the parts of a mammalian heart

HOW DOES IT WORK?                                                                

Time allocation: 45 Min

The heart can be described as the biological pump of the body, pumping blood from the lungs to the rest of the body and back. Blood carries oxygen and other nutrients to tissues through arteries where it is filtered out to tissues through capillaries, is de-oxygenated and reabsorbed. It is then transported back to the heart through the veins where it is pumped back to the lungs. Understanding the various anatomical structures of the heart is crucial for understanding the circulatory system.

The heart externally is covered by the pericardium (protective sac) that is filled with liquid to help reduce mechanical damage. Externally the heart is divided into the apex and body of the heart. It is fed blood separately from the rest of the body through the Coronary artery and vein. The heart lies with the apex of the heart pointing towards the sternum. The heart is important for blood circulation.

MATERIALS:

  • Dissecting needles
  • Tweezer Stainless steel Straight Fine Point 110/115mm
  • Scalpel Handle Size 4
  • Scalpel Blade No. 4 Size 21
  • Dissection scissor
  • Needle of metal probe
  • Dissecting tray or dissecting board to cut on
  • Pins
Supplied by Educator
  • Fresh sheep’s/cow’s/pig’s heart specimen
  • Labels or flags

METHOD:

  1. Obtain a fresh specimen of a sheep heart
  2. Put on safety glasses or goggles, gloves, and lab apron
  3. Place the heart in a dissecting tray or board
  4. Study Figures 1 and 2 and familiarize yourself with the mammalian heart internal anatomy.

  1. Notice the fat that covers the upper part of the heart and blood vessels. Remove as much of this fat as possible, using forceps to either pick or scrape it away. Work carefully and do not damage any of the heart structures as you remove the fat.
  2. The fat is light colored, soft, and without structure. Heart muscle is dark and fibrous. The walls of blood vessels are thin, tough, and usually smooth on the inside. Make an effort to distinguish between these 3 tissue types.
  3. Once you remove the fat, locate the structures shown in Figures 1 and 2. In some cases, the blood vessels may be cut so close to the heart that little more than holes remain to show where they once attached.
  4. The hearts anterior must face you.

  1. Cut open the left atrium and locate the bicuspid valve between the left atrium and ventricle.
  2. Beginning at a point below the middle of the left ventricle, make an incision through the left ventricle wall as shown in the figure below. Remove the lower-front portion of the wall.

  1. Look through the hole you have produced and locate the chordae tendinous and the papillary muscles as shown in Figure 5.
  2. Trim away the front and side of the left ventricular wall, leaving part of the papillary muscles and all of the bicuspid valve in place. Make an incision to the side of the bicuspid valve as shown at A in Figure 5.
  3. Spread the left side of the heart and identify the structures labelled in Figure 5.

  1. The right side is dissected similarly; begin by opening the top of the right atrium and locating the tricuspid valve between the right atrium and ventricle.
  2. Remove the lower-front portion of the ventricular wall just as you removed that of the left ventricle.
  3. Cut high across the front of the heart to locate the pulmonary semi lunar valves.

  1. Identify the structures labelled in Figure 6.
  2. Observe the thick septum that divides the right and left sides of the heart
  3. Use forceps or tweezers to pull part of the membrane, called the pericardium, away from the heart muscle.
  4. Identify the two atria and feel the thickness of their walls.
  5. Squeeze the left and right ventricles and describe what you feel.
  6. Identify the blood vessels to and from the heart. Find the vena cava, large veins that enter the right atrium, blood vessels
  7. Push a dissecting needle or probe down these vessels to help you find out from which part of the heart they are coming
  8. Compare the wall thickness of the pulmonary artery and aorta with those of vena cava and pulmonary vein.
  9. Use the label tags or label flags to identify the different blood vessels, chambers, valves, muscles on the label flags

PRECAUTIONS:

  • Ensure all participants wear latex gloves and aprons or laboratory coats
  • All tissues must be disposed of afterward , none of the by-products of dissection are consumable
  • Sterilize surface before and after dissection
  • In Case of cut do the following first aid measures:
  • Do not treat students without latex gloves on
  • Rinse wound to clear away any contaminated substances
  • Wipe wound using sterile swab gauze and a topical sterilization cream , e.g. Savlon
  • Apply first degree compression (compression to wound directly) using a sterile swab and compression bandage to stop bleeding
  • If bleeding still continues:
  • Place wound so that it is above the heart
  • Apply cold source, e.g. ice, on top of bandages
  • Apply secondary compression, compression on the artery that feeds the area : Arms : brachial artery(under arm) and wrist Legs: Ankle and femoral artery
  • A person requires stitches when the 2 edges of the skin along the cut are pulled apart and the layer of flesh can be seen under it.