Suffixes

Combining Forms

Pulmonary Circulation

In short, pulmonary circulation goes from the heart to the lungs and then back to the heart. Pulmonary circulation begins with the right side of the heart, sending blood to the lungs to absorb oxygen (O₂) and release carbon dioxide (CO₂). Note in Fig. 10-1 that the vessels that carry blood to the lungs from the heart are blue to show the blood as being deoxygenated (dee OCK sih juh nay tid), or oxygen deficient. Once the oxygen is absorbed, the blood is considered oxygenated, or oxygen rich. Note in Fig. 10-1 that the vessels traveling away from the lungs are red to show oxygenation. The blood then progresses back to the left side of the heart, where it is pumped out to begin its route through the systemic circulatory system.

Systemic Circulation

The systemic circulation carries blood from the heart to the cells of the body, where nutrient and waste exchange takes place; the wastes, such as CO₂, are carried back to the heart on the return trip. This blood is then pumped out of the right side of the heart to the lungs to dispose of its CO₂, absorb O₂, and repeat the cycle. In systemic circulation, the blood traveling away from the heart first passes through the largest artery in the body called the aorta (a ORE tuh). From the aorta, the vessels branch into conducting arteries (AR tur reez), then into smaller arterioles (ar TEER ee olez), and finally to the capillaries (CAP ih lair eez). Arteries are blood vessels that carry blood away from the heart (Fig. 10-2, A). Note in Fig. 10-3 that the color has changed from the red of oxygenated blood to a purple color at the capillaries. This is the site of exchange between the cells’ fluids and the plasma of the circulatory system. Oxygen and other substances are supplied, and carbon dioxide collected, along with a number of other wastes. Once the blood begins its journey back to the heart, it first goes through venules (VEEN yools), then veins (vayns), and finally into one of the two largest veins, either the superior or the inferior vena cava (VEE nuh KAY vuh). Veins are blood vessels that carry blood toward the heart (Fig. 10-2, B). Fig. 10-4 illustrates the muscular, thick nature of arteries; the valvular, thinner nature of veins; and the delicate exchange function of capillaries. Arteries are generally thicker than veins, because they must withstand the force of the heart’s pumping action. Veins do not have the thick muscle coat of the arteries to propel the blood on its journey through the circulatory system but instead rely on one-way valves that prevent the backflow of blood. In addition, skeletal muscle contraction provides pumping action. The capillaries’ diameters are so tiny that only one blood cell at a time can pass through them.

Anatomy of the Heart

The human heart is about the size of a fist. It is located in the mediastinum of the thoracic cavity, slightly left of the midline. Its pointed tip, the apex, rests just above the diaphragm. The area of the chest wall anterior to the heart and lower thorax is referred to as the precordium (pree KORE dee um). The heart muscle has its own dedicated system of blood supply, the coronary (KORE ih nair ee) arteries (Fig. 10-5, A). The two main coronary arteries are called the left and right coronary arteries (LCA, RCA). They supply a constant, uninterrupted blood flow to the heart. The areas of the heart wall that they feed are designated as inferior, lateral, anterior, and posterior.

The heart has four chambers (Fig. 10-5, B). The upper chambers are called atria (A tree uh) (sing. atrium). The lower chambers are called ventricles (VEN trih kuls). Between the atria and ventricles, and between the ventricles and vessels, are valves that allow blood to flow through in one direction. Those values are opened and closed with the assistance of the papillary muscles and their connecting cords, the chordae tendinae. The tissue walls between the chambers are called septa (SEP tuh) (sing. septum). The heart wall is constructed of three layers. The endocardium (en doh KAR dee um) is the thin tissue that acts as a lining of each of the chambers and valves. The myocardium (mye oh KAR dee um) is the cardiac muscle surrounding each of these chambers. The pericardium (pare ee KAR dee um) is the double-folded layer of connective tissue that surrounds the heart. The inner surface of this double fold is called the visceral (VIS uh rul) pericardium, and the outer membrane, closest to the body wall, is the parietal (puh RYE uh tul) pericardium. Another name for the visceral pericardium is the epicardium (eh pee KAR dee um) because it is the structure on top of the heart.

Blood Flow Through the Heart

Using Fig. 10-6 as a guide, follow the route of the blood through the heart. The pictures and words in this diagram are shaded red and blue to represent oxygenated and deoxygenated blood. Blood is squeezed from the right atrium (RA) to the right ventricle (RV) through the tricuspid (try KUSS pid) valve (TV). Valves are considered to be competent if they open and close properly, letting through or holding back an expected amount of blood. Once in the right ventricle, the blood is squeezed out through the pulmonary semilunar valve through the short, wide pulmonary trunk and into the pulmonary arteries (PA), which carry blood to the lungs and are the only arteries that carry deoxygenated blood. In the capillaries of the lungs, the CO₂ is passed out of the blood and O₂ is taken in. The now-oxygenated blood continues its journey back to the left side of the heart through the pulmonary veins. These are the only veins that carry oxygenated blood. The blood then enters the heart through the left atrium (LA) and has to pass the mitral (MYE trul) valve (MV), also termed the bicuspid valve, to enter the left ventricle (LV). When the left ventricle contracts, the blood is finally pushed out through the aortic semilunar valve into the aorta and begins yet another cycle through the body.

The amount of blood expelled from the left ventricle compared with the total volume of blood filling the ventricle is referred to as the stroke volume and is a measure of the ejection fraction of cardiac output. Typically around 65%, this amount is reduced in certain types of heart disease.

If a woman’s heart rate is 80 beats per minute (bpm), then that means her heart contracts almost 5000 times per hour and more than 100,000 beats per day, every day, for a lifetime. Truly an amazing amount of work is accomplished by an individual’s body without a bit of conscious thought!

The Cardiac Cycle

Systemic and pulmonary circulations occur as a result of a series of coordinated, rhythmic pulsations, called contractions and relaxations, of the heart muscle. The normal rate of these pulsations in humans is 60 to 100 beats per minute (BPM) and is noted as a patient’s heart rate. Fig. 10-7 illustrates various pulse points, places where heart rate can be measured in the body. Blood pressure (BP) is the resulting force of blood against the arteries. The contractive phase is systole (SIS toh lee), and the relaxation phase is diastole (dye AS toh lee). Blood pressure is recorded in millimeters of mercury (Hg) as a fraction representing the systolic pressure over the diastolic pressure. Optimum blood pressure is a systolic reading less than 120 and a diastolic reading less than 80. This is written as 120/80. Normal blood pressure is represented by a range. See the table below for blood pressure guidelines.

The cues for the timing of the heartbeat come from the electrical pathways in the muscle tissue of the heart (Fig. 10-8). The heartbeat begins in the right atrium in the tissue referred to as the sinoatrial (sin oh A tree ul) (SA) node, also called the natural pacemaker of the heart. The initial electrical signal causes the atria to undergo electrical changes that signal contraction. This electrical signal is sent to the atrioventricular (a tree oh ven TRICK yoo lur) (AV) node, which is located at the base of the right atrium proximal to the interatrial septum. From the AV node, the signal travels next to the bundle of His (also called the atrioventricular bundle). This bundle, a band of specialized cardiac muscle fibers, is in the interatrial septum, and its right and left bundle branches transmit the impulse to the Purkinje (poor KIN jee) fibers in the right and left ventricles. Once the Purkinje fibers receive stimulation, they cause the ventricles to undergo electrical changes that signal contraction to force blood out to the pulmonary arteries and the aorta. If the electrical activity is normal, it is referred to as a normal sinus rhythm (NSR) or heart rate. Any deviation of this electronic signaling may lead to an arrhythmia (ah RITH mee ah), an abnormal heart rhythm that compromises an individual’s cardiovascular functioning by pumping too much or too little blood during that segment of the cardiac cycle.