Andrew’s Note:  Today we’re providing a lesson from FM 4-25.11 First Aid (Approved For Public Release) on understanding vital body functions for first aid.

Understanding Vital Body Functions for First Aid

In order for the service member to learn to perform first aid procedures, he must have a basic understanding of what the vital body functions are and what the result will be if they are damaged or not functioning.

a.  Breathing Process.  All humans must have oxygen to live.  Through the breathing process, the lungs draw oxygen from the air and put it into the blood. The heart pumps the blood through the body to be used by the cells that require a constant supply of oxygen.  Some cells are more dependent on a constant supply of oxygen than others. For example, cells of the brain may die within 4 to 6 minutes without oxygen. Once these cells die, they are lost forever since they do not regenerate. This could result in permanent brain damage, paralysis, or death.

b.  Respiration.  Respiration occurs when a person inhales (oxygen is taken into the body) and then exhales (carbon dioxide [CO2] is expelled from the body). Respiration involves the—

• Airway.  The airway consists of the nose, mouth, throat, voice box, and windpipe. It is the canal through which air passes to and from the lungs.
• Lungs.  The lungs are two elastic organs made up of thousands of tiny air spaces and covered by an airtight membrane.     The bronchial tree is a part of the lungs.
• Rib cage.  The rib cage is formed by the muscle- connected ribs, which join the spine in back, and the breastbone in front.

The top part of the rib cage is closed by the structure of the neck, and the bottom part is separated from the abdominal cavity by a large dome-shaped muscle called the diaphragm (Figure 1-1). The diaphragm and rib muscles, which are under the control of the respiratory center in the brain, automatically contract and relax. Contraction increases and relaxation decreases the size of the rib cage. When the rib cage increases and then decreases, the air pressure in the lungs is first less and then more than the atmospheric pressure, thus causing the air to rush into and out of the lungs to equalize the pressure. This cycle of inhaling and exhaling is repeated about 12 to 18 times per minute.

Figure 1-1 Airway, lungs, and rib cage

c.  Blood Circulation.  The heart and the blood vessels (arteries, veins, and capillaries) circulate blood through the body tissues. The heart is divided into two separate halves, each acting as a pump. The left side pumps oxygenated blood (bright red) through the arteries into the capillaries; nutrients and oxygen pass from the blood through the walls of the capillaries into the cells. At the same time waste products and CO2 enter the capillaries.  From the capillaries the oxygen poor blood is carried through the veins to the right side of the heart and then into the lungs where it expels the CO2 and picks up oxygen. Blood in the veins is dark red because of its low oxygen content. Blood does not flow through the veins in spurts as it does through the arteries. The entire system of the heart, blood vessels, and lymphatics is called the circulatory system.

(1)  Heartbeat. The heart functions as a pump to circulate the blood continuously through the blood vessels to all parts of the body. It contracts, forcing the blood from its chambers; then it relaxes, permitting its chambers to refill with blood.  The rhythmical cycle of contraction and relaxation is called the heartbeat. The normal heartbeat is from 60 to 80 beats per minute.

(2)  Pulse. The heartbeat causes a rhythmical expansion and contraction of the arteries as it forces blood through them.  This cycle of expansion and contraction can be felt (monitored) at various points in the body and is called the pulse. The common points for checking the pulse are at the—

• Side of the neck (carotid).
• Groin (femoral).
• Wrist (radial).
• Ankle (posterior tibial).

Figure 1-2. Carotid pulse

(a)  Carotid pulse. To check the carotid pulse, feel for a pulse on the side of the casualty’s neck closest to you. This is done by placing the tips of your first two fingers beside his Adam’s apple (Figure 1-2).

Figure 1-4. Radial pulse

(c)  Radial pulse. To check the radial pulse, place your first two fingers on the thumb side of the casualty’s wrist (Figure 1-4).

(d)  Posterior tibial pulse. To check the posterior tibial pulse, place your first two fingers on the inside of the ankle (Figure 1-5).

Figure 1-5. Posterior tibial pulse