- Anatomy Lab - 10 pts.

First, read the Bio 113 information on the Heart

The Heart - The pumping action of the Heart starts with the simultaneous contraction of the two atria. This contraction serves to give an added push to get the blood into the ventricles. Shortly after that, the ventricles contract, marking the beginning of "systole." The aortic and pulmonary valves open and blood is forcibly ejected from the arteries, while the mitral (bicuspid) and tricuspid valves close to prevent backflow. At the same time, the atria start to fill with blood again. After a while, the ventricles relax (called "diastole) the aortic and pulmonary valves close, and the mitral and tricuspid valves open and the ventricles start to fill with blood again.

Electrical Activity of the Heart - When vertebrate muscles are excited, an electrical signal (called an "action potential") is produced and spreads to the rest of the muscle cell, causing an increase in the level of ions inside the cell , the end result being a muscle contraction. This electrical activity of the Heart can be measured by an electrocardiogram (ecg).

One thing that distinguishes the heart from other muscles is that the heart muscle is a "syncytium," meaning a meshwork of interconnected cells. Thus, an electrical excitation occurring in one cell can spread to neighboring cells. Another defining characteristic of the Heart is the presence of pacemaker cells. These are specialized muscle cells that can generate action potentials rhythmically. Under normal circumstances, a wave of electrical excitation originates in the pacemaker cells in the sinoatrial (S-A) node, located on top of the right atrium. Specialized muscle fibers transmit this excitation throughout the atria and initiate a coordinated contraction of the atrial walls. Meanwhile, some of these fibers excite a group of cells located at the border of the left atrium and ventricle known as the atrioventricular (A-V) node. The A-V node is responsible for spreading the excitation throughout the two ventricles and causing a coordinated ventricular contraction.

There are two important vital statistics that doctors use to assess the immediate health of your heart: blood pressure and pulse. These "numbers" fluctuate as your heart's condition changes.

1. Pulse Your pulse is taken by touching one of several "pulse points" located on your body. These spots are areas where the arteries are near enough to the surface of the skin that the movement of blood through them can be felt. You can actually feel your artery expand and contract. Since the artery keeps pace with the heart, doctors can measure heart rate by counting the contractions of the artery.

To find find your pulse: Your pulse is taken by touching one of several "pulse points" located on your body. These spots are areas where the arteries are near enough to the surface of the skin that the movement of blood through them can be felt. You can actually feel your artery expand and contract. Since the artery keeps pace with the heart, doctors can measure heart rate by counting the contractions of the artery.

For some people, neck pulse points are stronger and more accessible. Your carotid artery is located just below your jaw in the groove where your head and neck meet, on either side of your windpipe. Use your index and middle fingertips to feel around in the groove for a tangible pulsation. Hold your fingers in place for a few seconds to make sure you've got it. On the wrist or neck, are the most common spots where people take their pulses.

Click on the clock on your computer, take a count of how many pulse beats you feel for 30 seconds. Multiply the amount of beats by two to calculate your pulse rate per minute. Your pulse will be the same regardless from which point you measure it. Then, keep your fingers on your pulse for another 30 seconds. Is your pulse steady and unwavering? Or is it irregular in any way? Irregularities to note include beats that come closer to the preceding beats than the following ones or anomalous pauses in between beats.

Take your resting pulse (beats/minute) and write it down.

2. Blood pressure - Blood pressure is taken using an instrument called a sphygmomanometer which consists of a cuff that can be filled with air, a hollow rubber bulb that pumps the air, and a glass tube containing a column of mercury. After placing the cuff around the upper arm, the doctor holds a stethoscope over the artery just below the cuff. The pulse can be heard. Next, air is pumped into the cuff, stopping the flow of blood through the artery. Then, air is slowly let out of the cuff, letting the blood flow again. The pressure with which the blood begins to flow represents the pressure of the heart's contraction (known as the systolic phase). More air is let out of the cuff, muffling the sound, and representing the pressure of the heart's relaxation (known as the diastolic phase).

These two phases are measured using two numbers which stand for millimeters. The column of mercury in the glass tube rises and falls with the flow of the blood. The height of the column is measured in millimeters. The first number, which is higher, is taken when the heart beats during the systolic phase. The second number is taken when the heart relaxes during the diastolic phase. Normal blood pressure ranges from 110 to 150 millimeters (as the heart beats) over 60 to 80 millimeters (as the heart relaxes). Patients with readings that exceed either of these ranges are treated for hypertension (high blood pressure). Readings below either of these ranges indicate hypotension (low blood pressure) which does not usually require treatment.

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