The Heart

Explain why you did this exercise. Where there any safety precautions you needed to follow? If so, what were they?

The safety precautions in this exercise were to wear goggles and gloves due to being exposed to chemicals and dissection of the sheep and cat heart. Appropriate work space was also required.

Exercise 1: Microscopic Anatomy of Cardiac Muscle

Sketch and label your slide in the space provided. Include a description of the structures you observed on the slide.

See attached picture labeled cardiac muscle


A. What are some unique structural features of cardiac muscle?

Cardiac muscle is essentially limited to the heart, though it extends slightly into the nearby blood vessels. It too, is striated, but it differs from skeletal muscle. As far as the features, the cells are much shorter, so they are called myocytes rather than fibers. Cardiac muscle is considered involuntary because it is not usually under conscious control; it contracts even if all nerve connections to it are severed.

B. What are intercalated discs and what do they do?

Intercalated disks are cross-bands that separate the opposing ends of cardiac muscle cells. These bands are the result of elaborate junctions of membranes at the cell’s boundary. They help to hold adjacent cells together and transmit the force of contraction from cell to cell. Intercellular junctions between the fused membranes of the intercalated disks allow diffusion of ions between the cells. This makes it possible for muscle impulses to travel rapidly from cell to cell.

C. Why does cardiac muscle have to be both elastic and strong? Cardiac muscle has to both elastic and strong to provide physical support for the cardiac muscle fibers, blood vessels, and nerves of the myocardium, help distribute the forces of contraction, add strength and prevent overexpansion of the heart and provide elasticity that helps return the heart to its original size and shape after a contraction.

D. Which of the three layers of the heart did the tissue used to make your slide originate from?

The myocardium consists of concentric layers of the cardiac muscle tissue.

Exercise 2: The Pulmonary and Systemic Circuits Questions A. Trace the flow of blood through the pulmonary and systemic circuits. Begin in the right atrium and end in the superior/inferior vena cava. Be sure to list every vessel, heart chamber, and heart valve the blood flows through.

Blood returns to the heart from the body via two large blood vessels, called the superior vena cava and the inferior vena cava. This blood carries little oxygen, as it is returning from the body where oxygen is used. The blood first enters the right atrium. It then flows through the tricuspid valve into the right ventricle. When the heart beats, the ventricle pushes the blood through the pulmonary valve into the pulmonary artery.

The pulmonary artery carries blood to the lungs where it “picks up” oxygen, and leaves the lungs and returns to the heart through the pulmonary vein. The blood enters the left atrium, and then descends through the mitral valve into the left ventricle. The left ventricle then pumps blood through the aortic valve, and into the aorta, the blood vessel that leads to the rest of the body.

B. Explain what you learned from the online human heart dissection. I
learned that the heart is not perfectly symmetrical as it looks in the pictures. It is cone shaped, more hollow and about the size of an adult fist.

Dissection and Comparison

A. Compare the structure of the cat heart and sheep heart. How are they similar? How are they different? The anatomical structure of the sheep heart is much larger in size making it easier to see the internal structure of the heart. Due to the small size of the cat heart it is challenging to dissect and observe the internal structures. The sheep heart has thicker walls and layers in the right and ventricle. Most of the internal structures are similar in both cat and sheep heart except for ligaments connecting the pulmonary artery to the aorta that is observed in the cat heart only.

B. Why is the heart referred to as a double pump?

It is referred as a double pump because it has two separate circuits, the pulmonary circuit pumping deoxygenated blood to the lungs and back to the heart and the systemic circuit pumping oxygenated blood around the body.

C. There are four valves in the heart. Name each valve, list its location and give its function. Tricuspid valve – located between the right atrium and the right ventricle. Pulmonary valve – located between the right ventricle and the pulmonary artery. Mitral valve – located between the left atrium and the left ventricle. Aortic valve – located between the left ventricle and the aorta. The valves prevent the backward flow of blood. Valves have flaps that act as one-way for blood coming into a ventricle and one-way for blood leaving a ventricle.

Each valve has three flaps, except the mitral valve, which only has two flaps. As the heart muscle contracts and relaxes, the valves open and shut, letting blood flow into the ventricles and atria at alternate times. When the left ventricle relaxes, the aortic valve closes and the mitral valve opens, to allow blood to flow from the left atrium into the left ventricle. The left atrium contracts, allowing even more blood to flow into the left ventricle. When the left ventricle contracts again, the mitral valve closes and the aortic valve opens, so blood flows into the aorta. |

D. Compare the left and right sides of the dissected heart. What differences do you see?

The wall of the right ventricle is relatively thin. When it contracts, the right ventricle acts like a bellows, squeezing the blood against the thick wall of the left ventricle. The left ventricle uses six to seven times as much force to exert blood around the systemic circuit as around the pulmonary circuit. The left ventricle has an extremely thick muscular wall and is round in cross section E. Compare and contrast the functions of the atria and the ventricles.

The atriums are smaller than the ventricles, have thinner muscle tissue, only have to pump blood to the ventricles. The ventricles are larger in size, have larger muscle tissue and have to pump blood to either the lungs or around to the rest of the body.

F.List and describe the functions of the three layers of the heart wall Pericardium is the sac that holds the heart and blood vessels outside of the heart and includes a thin layer called the epicardium (Visceral layer of serous pericardium). The pericardium protects the heart and holds it in place. It also keeps the heart lubricated, so it can pump efficiently and smoothly, without it or the different layers of the pericardial sac catching on one another. Additionally, it limits the amount of space that the heart has to expand in, which keeps the heart from getting too big when it fills with blood.

Myocardium is the cardiac muscle layer and bulk of the heart. This is the thick layer of cardiac muscle which is responsible for the contraction and relaxation of the ventricles and atria. Endocardium is the inner lining of the heart (lines chambers and valves). The endocardium consists of the same tissue as the insides of arteries and veins. Its main function is to allow the smooth flow of blood through the heart. It is composed mostly of epithelial tissue.

G. Trace the blood flow through the Coronary Circulation. Begin with the right and left coronary arteries and end in the coronary sinus.

The left and right coronary arteries and their branches lie on the surface of the heart and distribute blood flow to different regions of the heart muscle. The left coronary artery supplies blood to the left ventricle, left atrium, and interventricular septum. As it reaches the anterior surface of the heart, it gives rise to a circumflex branch and an anterior interventricular branch. The circumflex artery curves to the left around the coronary sulcus, eventually meeting and fusing with small branches of the right coronary artery.

The right coronary artery, which follows the coronary sulcus around the heart, supplies blood to the right atrium, portions of both ventricles, and portions the sinoatrial (SA) and atrioventricular (AV) nodes. The great cardiac vein begins on the anterior surface of the ventricles, along the interventricular sulcus. This vein drains blood from the region supplied by the anterior interventricular artery, a branch of the left coronary artery. The great cardiac vein reaches the level of the atria and then curves around the left side of the heart within the coronary sulcus. The vein empties into the coronary sinus.

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Receives deoxygenated blood returning to the heart from the vena cava and pumps it to the right ventricle. Left atrium: Receives oxygenated blood returning to the heart from the pulmonary veins and pumps it to the left ventricle. Ventricles thicker …

I am writing on the human heart. I will be explaining the functions and uses of the heart throughout this paper. The main focus will be on how important the heart is to our entire body’s running like a well-oiled …

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