Heart Dissectin Intrductin Mammals have fur-chambered hearts and duble circulatin. The heart f a bird r mammal has tw atria and tw cmpletely separated ventricles. The dublelp circulatin is similar t amphibians and reptiles, but the xygen-rich bld is cmpletely separated frm xygen-pr bld. The left side f the heart handles nly xygenated bld, and the right side receives and pumps nly dexygenated bld. With n mixing f the tw kinds f bld, and with a duble circulatin that restres pressure after bld has passed thrugh the lung capillaries, delivery f xygen t all parts f the bdy fr cellular respiratin is enhanced. As endtherms, which use heat released frm metablism t warm the bdy, mammals require mre xygen per gram f bdy weight than ther vertebrates f equal size. Birds and mammals descended frm different reptilian ancestrs, and their fur-chambered hearts evlved independently - an example f cnvergent evlutin. Objective Using a pig heart, students will bserve the majr chambers, valves, and vessels f the heart and be able t describe the circulatin f bld thrugh the heart t the lungs and back and ut t the rest f the bdy. (The pig heart is used because it is very similar t the human heart in structure, size, & functin.) Materials Dissecting pan, dissecting kit, safety glasses, lab aprn, pig heart, & glves Prcedure - External Structure When yu have finished dissecting the heart, dispse f the heart as yur teacher advises and clean, dry, and return all dissecting equipment t the lab cart. Wash yur hands thrughly with sap. 1. Place a heart in a dissecting pan & rinse ff the excess preservative with tap water. Pat the heart dry. 2. Examine the heart and lcate the thin membrane r pericardium that still cvers the heart. The pericardium r pericardial sac, is a duble-layered clsed sac that surrunds the heart and anchrs it. The pericardium cnsists f tw tissues layers - the visceral pericardium that cvers the
surface f the heart & the parietal pericardium cvering the inner surface f the parietal sac. These tw tissue layers are cntinuus with each ther where the vessels enter r leave the heart. The slender gap between the parietal & visceral surfaces is the pericardial cavity & is filled with fluid t reduce frictin between the layers as the heart pumps. 3. After examining the pericardium, carefully remve this tissue. Lcated belw the pericardium is the muscle f yur heart called the mycardium. Mst f the mycardium is lcated in the lwer tw chambers f the heart called ventricles. 4. Lcate the tip f the heart r the apex. Only the left ventricle extends all the way t the apex. 5. Place the heart in the dissecting pan s that the frnt r ventral side is twards yu ( the majr bld vessels are n the tp and the apex is dwn). The frnt f the heart is recgnized by a grve that extends frm the right side f the brad end f the heart diagnally t a pint abve & t yur left f the apex. Frnt r Ventral Side f the Heart 6. The heart is nw in the pan in the psitin it wuld be in a bdy as yu face the bdy. Lcate the fllwing chambers f the heart frm this surface: Left atria - upper chamber t yur right Left ventricle - lwer chamber t yur right
Right atria - upper chamber t yur left Right ventricle - lwer chamber t yur left 7. While the heart is still in this psitin in the dissecting pan, lcate these bld vessels at the brad end f the heart: Crnary artery - this bld vessel lies in the grve n the frnt f the heart & it branches ver the frnt & the back side f the heart t supply fresh bld with xygen & nutrients t the heart muscle itself. Pulmnary artery - this bld vessel branches & carries bld t the lungs t receive xygen & can be fund curving ut f the right ventricle (upper chamber t yur left) Arta - majr vessel lcated near the right atria & just behind the pulmnary arteries t the lungs. Lcate the curved part f this vessel knwn as the artic arch. Branching frm the artic arch is a large artery that supplies bld t the upper bdy. Pulmnary veins - these vessels return xygenated bld frm the right & left lungs t the left atrium (upper chamber n yur right)
Inferir & Superir Vena Cava - these tw bld vessels are lcated n yur left f the heart and cnnect t the right atrium (upper chamber n yur left). Dexygenated bld enters the bdy thrugh these vessels int the right receiving chamber. Use yur prbe t feel dwn int the right atrium. These vessels d nt cntain valves t cntrl bld flw. Prcedure - Internal Anatmy: 8. Use scissrs t cut thrugh the side f the pulmnary artery and cntinue cutting dwn int the wall f the right ventricle. Be careful t just cut deep enugh t g thrugh the wall f the heart chamber. (Yur cutting line shuld be abve & parallel t the grve f the crnary artery.) 9. With yur fingers, push pen the heart at the cut t examine the internal structure. If there is dried bld inside the chambers, rinse ut the heart. 10. Lcate the right atrium. Ntice the thinner muscular wall f this receiving chamber. 11. Find where the inferir & superir vena cava enter this chamber & ntice the lack f valves. 12. Lcate the valve that between the right atrium and right ventricle. This is called the tricuspid valve. The valve cnsists f three leaflets & has lng fibers f cnnective tissue called chrdae tendinae that attach it t papillary muscles f the heart. This valve allws bld flw frm the right atrium int the right ventricle during diastle (perid when the heart is relaxed). When the heart begins t cntract (systle phase), ventricular pressure increases until it is greater than the pressure in the atrium causing the tricuspid t snap clsed. Tricuspid Valve 13. Use yur fingers t feel the thickness f the right ventricle and its smth lining. Als nte the netwrk f irregular muscular crds n the inner wall f this chamber.
14. Find the septum n the right side f the right ventricle. This thick muscular wall separates the right & left pumping ventricles frm each ther. 15. Inside the right ventricle, lcate the pulmnary artery that carries bld away frm this chamber. Find the ne-way valve called the pulmnary valve that cntrls bld flw away frm the right ventricle at the entrance t this bld vessel. 16. Using yur scissrs, cntinue t cut pen the heart. Start a cut n the utside f the left atrium dwnward int the left ventricle cutting tward the apex t the septum at the center grve. Push pen the heart at this cut with yur fingers & rinse ut any dried bld with water. 17. Examine the left atrium. Find the penings f the pulmnary veins frm the lungs. Observe the ne-way, semi-lunar valves at the entrance t these veins. 18. Inside this chamber, lk fr the valve that cntrls bld flw between the upper left atrium and lwer left ventricle. This valve is called the bicuspid r mitral valve. This valve cnsists f tw leaflets & bld flws frm the left atrium int the left ventricle during diastle. Bicuspid r Mitral Valve 19. Examine the left ventricle. Ntice the thickness f the ventricular wall. This heart chamber is respnsible fr pumping bld thrughut the bdy. 20. Using yur scissrs, cut acrss the left ventricle tward the arta & cntinue cutting t expse the valve. 21. Cunt the three flaps r leaflets n this valve leading frm the left ventricle int the arta and nte their half-mn shape. This is called the artic valve. 22. Using scissrs, cut thrugh the arta and examine the inside. Find the hle r crnary sinus in the wall f this majr artery. This leads int the crnary artery which carries bld t and nurishes the heart muscle itself.
23. Answer the questins n yur lab reprt.