157
Structure and Function
Learning Tip With a study group or a study partner, use side-
Box 6-1 The Pulse Oximeter The device used to monitor heart rate and to measure the saturation of peripheral oxygen (SpO 2 ) in the blood is called a pulse oximeter. It can differentiate between oxygenated and deoxygenated blood by passing two beams of light, infrared and red, through the finger to a light detector. The oxygenated hemoglobin in blood is a bright red color and absorbs more of the infrared light. The deoxygenated hemoglobin is a dark red color and absorbs more of the red light. The absorption difference is calculated, and a measurement of oxygenated blood appears on the screen as a percentage. This measure helps determine if enough oxygen is being supplied to the body. The normal SpO 2 for healthy individuals is 96% to 99%. An SpO 2 of lower than 90% may indicate respiratory distress. Pulse oximeters are used in a variety of settings, including outpatient physician offices and home health care. Physical therapists use portable units (see the accompanying photo) to monitor changes in the patient’s SpO 2 during exercise.
walk chalk to draw a giant illustration of the heart on cement or pavement out- doors. Make it as colorful and as accurate as you can. Label and verbally identify all the heart structures. Draw arrows to indicate the direc- tion of blood flow. When the drawing is complete, take turns walking along the circulatory route through the right side of the heart, to the lungs, back through the left side of the heart, out to the body, and then back to where you started. While you follow this route, iden- tify whether you are simulat- ing the path of oxygen-rich or oxygen-poor blood and why. If you have young fam- ily members, they may enjoy doing the drawing while you direct them in what to draw.
Blood Vessels When oxygen-rich blood is pumped from the heart, it travels to all parts of the body through an intricate network of arteries (Figure 6-2). The arteries vary in size, from the very large aorta to very tiny arterioles . From the arterioles, blood enters numerous microscopic-sized capillaries with walls that are just one cell thick. This allows O 2 and nutrients to easily leave the capillaries and enter the tissues and cells. It also allows waste products and CO 2 to easily move from the cells and tissues back into the capillaries. Blood that is now low in O 2 and high in CO 2 and waste leaves the capillaries and enters microscopic-sized venules (tiny veins). While it continues its return journey, the blood travels through increasingly larger veins until it reaches the heart. Blood is drained from the head and upper body via the superior vena cava and from the lower body via the inferior vena cava. Venous blood travels under much less pressure than arterial blood. Consequently, it cannot easily flow against gravity to ascend the legs and return to the heart. Fortunately, veins contain one-way valves that facilitate cir- culation by preventing the backflow of blood. The pumping action created by the contraction and relaxation of leg muscles also helps to propel the blood upward. Occasionally, arteriosclerosis develops; the vessels become narrowed and hardened due to several factors, including hypertension (high blood pressure). In addition, a fatty, plaque-like substance composed of cholesterol may build up on the inside surfaces of the coronary vessels, causing further narrowing or even
Powered by FlippingBook