Beating approximately 60 to 70 times per minute throughout our lives, the human heart plays a vital role in survival, pumping life sustaining blood throughout our bodies. The heart's pumping action occurs in two distinct steps. First, blood returning from the veins enters the receiving chambers and is pumped, through valves, into the ventricles. The ventricles then contract and pump blood through a second set of valves into the arteries for distribution throughout the body.
Role of the Heart
Our bodies consist of approximately 75 trillion living cells, each of which must be nourished, have access to oxygen and be purged of toxic waste products. The circulation of blood accomplishes all of these tasks carrying oxygen from the lungs, nutrients from the liver and digestive tract, and waste to the kidneys. The maintenance of normal blood flow is provided by the heart, which through its cycle of beating provides the pressure that drives life-sustaining blood through our blood vessels.
Normal Heart Rate
Each minute, the human heart pumps about 1.3 gallons of blood throughout the body. Blood enters the heart through large veins and is received into chambers called atria. When filled, the atria contracts, forcing blood into the larger pumping chambers called ventricles. As the blood passes from the atria to ventricles, it flows through a set of valves called A-V valves. When the ventricles are filled, they then contract, forcing blood out into large arteries and to all of the body's tissues and organs. Blood leaving the ventricles passes through a second set of valves called semilunar valves. The normal resting heart rate for an adult is about 70 beats per minute (bpm), which declines while we're sleeping and increases during periods of activity, such as exercise.
Heart Sounds and Valve Function
The beating heart produces characteristic sounds that can be heard through a stethoscope or by placing your ear against a person's chest. Physicians describe this heart sound as a "lubb-dupp," because, as you speak, it appears as a low-pitched rumbling sound followed by a short crisp sound. These heart sounds are caused by the respective closing of the A-V valves (lubb) followed by the closing of the semilunar valves (dupp). Abnormal heart sounds, known as murmurs, are caused by damaged or defective valves.
The Heart's Electrical Conducting System
The regular pattern of heart activity in which the atria contraction is followed by contraction of the ventricles is precisely timed by an electrical conducting system within the heart. This pattern of the heart's electrical activity can be recorded from the surface of the body in the form of the electrocardiogram (EKG or ECG). The electrical pattern of a normal heart beat is shown in the first image, above.
Regulation of Heart Rate
The changing rate of our heart beat as we move from sleep to normal activity to vigorous exercise is regulated by the brain in response to signals from sensors throughout the body. These various sensors constantly monitor body temperature; blood oxygen and carbon dioxide levels; blood pH; and the movement of our joints. The sensors can increase or decrease the normal heart beat as our activity level changes.
References
- "Exercise Science: Understanding and Evaluating Physical Fitness and Health"; Warren Rosenberg, Ph.D. and Ciaran Cullen, D.C.; 2008
- "Heart Rate Variability: Origins, Methods and Interpretive Caveats"; Journal of Psychophysiology; 1997
