Lab 11 Heart

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Santa Monica College *

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Biology

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May 7, 2024

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LAB 11: HEART TOPICS:  Structure of the heart  Path of blood flow  Heart rate  ECG  Blood pressure BACKGROUND: The general function of the heart was not understood until the early 1600s, when William Harvey demonstrated the pathway of circulation. Harvey showed, in a series of very elegant experiments, that our hearts drive the blood in a figure-eight pattern between the lungs and the body tissue, with the heart at the center. As you can see, a complete journey through the circulation in a mammal involves two passages through the heart. The right side of the heart drives blood through the lungs to load oxygen, making the blood red in color. This is the pulmonary circulation . The left side of the heart supplies blood to all the other tissues, where oxygen is delivered, turning the blood bluish/purple in color. This is the systemic circulation . Both of these circuits have arteries, veins, and capillary beds. Because mammals, birds, and many crocodiles have separate pulmonary and systemic circuits, we are said to have double circulation . Fish, however, have a single circulation, so they must drive the blood through two capillary beds in sequence. This isn't very efficient, compared to our system, but is perfectly adequate for fish. Amphibians and reptiles present a nice evolutionary intermediate with their double circulation and three-chambered hearts (two atria and one incompletely divided ventricle). Each side of the mammalian heart has two chambers. The receiving chamber on each side of the heart is called the atrium , and the chamber that pumps blood out to the arteries is called the ventricle . In order to keep blood flowing in one direction, there are valves at the entrance and exit of each ventricle. The valves between the atria and ventricles are called the atrioventricular valves . The right atrioventricular valve is also called the tricuspid valve , and the left atrioventricular valve is also called the bicuspid , or mitral valve . The valves between the ventricles and the arteries are called the semilunar valves . The valve on the right side (guarding the entrance to the pulmonary artery) is the pulmonary semilunar valve and the valve on the left side (guarding the entrance to the largest systemic artery, the aorta) is the aortic semilunar valve .

Everyone knows that a beating heart produces sound: "lubb-dup, lubb-dup, lubb- dup..etc." The lubb is the simultaneous slamming shut of both atrioventricular valves, and the dup is the shutting of the semilunar valves. If someone is born with a valve defect or if one of these valves is damaged by disease, blood leaks backwards or regurgitates . This produces the lisping or sloshy noises we refer to as a heart murmur . DIAGRAM OF THE MAMMALIAN HEART: The beating of the heart is stimulated by rhythmic impulses generated within the sinoatrial node of the right atrium. There is a tiny electrical current generated in this process at a certain rate, which is called your heart rate . This current spreads first to the right and left atria, causing them to contract and push blood to the ventricles. It then spreads to the right and left ventricles, causing them to contract and push blood to the arteries. Chamber contraction is called systole , and chamber relaxation is called diastole . The electrical current that moves through the heart is also transmitted to the surface of the body by the conductivity of our tissue fluids and can therefore be detected with electrodes placed on the skin. The resultant spikes are the normal electrocardiogram ( EKG or ECG ). Each "heartbeat" is recorded as three peaks. The first (and smallest) peak is the P-wave , arising from contraction of the atria. The second (and tallest) peak is the QRS-complex . This is produced by both relaxation of the atria and contraction of the ventricles. The third peak is the T-wave , representing the relaxation of the ventricles.

Arteries are relatively thick-walled vessels that always carry blood away from the heart. Large arteries close to the heart tend to be elastic (see blood pressure), whereas the smaller arteries more distant from the heart tend to be muscular. Veins have relatively thinner walls and a larger passage ( lumen ) for the blood within. Operating at much lower pressures, veins always carry blood toward the heart. Capillaries are not much larger than the diameter of a single red blood cell, very thin-walled, and located in voluminous beds in or near all of the body's tissues. The blood flow slows down in the capillaries to facilitate the exchange of respiratory gases and other metabolites. In order for blood to flow through any circuit, there must be a difference in pressure between the arteries and veins, with the pressure in arteries being higher than the pressure in veins. Blood pressure in arteries can be measured. This pressure is not a constant number, but rather rises and falls between a peak value (called systolic pressure ) and a low value (called diastolic pressure ). The reason for this rise and fall of pressure is because the ventricles are pumping blood into the arteries in spurts, and the elastic walls of the arteries are stretched by the force of the incoming blood and then recoil to push the blood onwards. It is important to routinely assess blood pressure because if it falls too low, there won’t be adequate blood flow, and if it rises too high, it can damage vessels and the heart. When measuring blood pressure, a sphygmomanometer (aka. blood pressure cuff) is used to temporarily constrict the vessel and halt blood flow. You can listen to blood flow through a stethoscope over an artery. Whenever the pressure in the cuff is higher than the pressure in the artery, blood won’t be able to flow through the artery, which is silent. When the pressure in the cuff is lower than the pressure in the artery, blood is able to flow. If the pressure in the cuff is in between systolic and diastolic pressure, blood enters the artery in spurts, which makes sounds called Korotkoff sounds . The first and last Korotkoff sounds indicate the pressures that are systolic and diastolic, respectively.

PROCEDURES : Heart structure and flow of blood: Complete these sections of the worksheet. Heart rate: As the heart pushes blood through arteries, the arteries expand with the flow of the blood. This can be felt in certain arteries that are close to the skin. The normal pulse for healthy adults ranges from 60-100 beats per minute. Pulse can be checked in several arteries, including the carotid, brachial, femoral, popliteal, dorsalis pedis, and radial arteries. Today you will measure your pulse either at the radial artery on your wrist or the carotid artery in your neck. Measure for 30 seconds and multiplying by 2. Record your heart rate in your worksheet. ECG: All students will record their own ECG and label it. 1. Turn on the machine. Clean both wrists and both ankles with an alcohol swab. Attach an electrode sticker to each area, tab pointing down. Then apply the following leads to these stickers: White – right wrist; Green – right ankle; Black – left wrist; Red – left ankle. Make sure that the snap tips are not touching the sticky part of the electrode. 2. Select the ‘(I, II, III)’ lead channel using the blue up and down arrows. To start the ECG recording, press the ‘MANUAL PRINT’ button. Press the red ‘STOP’ button to stop. You only need a few inches of recording. 3. Obtain your ECG strip. Label p, qrs, and t on the Lead II section of your ECG strip. Also indicate what causes each wave (contraction and relaxation of the atria and ventricles). Then paste the strip into your lab, or insert a photo of it on your submission. Blood pressure: 1. Wrap the cuff around your partner's bare upper arm. Make it snug, but not tight. Blood flow should not be restricted. 2. Clean the earpieces of the stethoscope with an alcohol swab. 3. Place the disk of the stethoscope over the joint of the arm (inside the elbow). Two large arteries run below this point. 4. Twist the small knob at the bulb clockwise, squeeze the bulb, and inflate the cuff to about 140. The cuff can begin to hurt by 150-160, so be careful. Watch the cuff. It

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