Human Body Systems and Nutrition

The Cardiovascular and Respiratory Systems

The cardiovascular and respiratory systems work in close harmony to supply every cell in your body with oxygen and clear away waste products. At the center of this delivery network is the human heart, which contains four distinct chambers: the right atrium, left atrium, right ventricle, and left ventricle. Blood moves through these chambers in a precise sequence. The right ventricle pumps deoxygenated blood to the lungs through the pulmonary arteries. After picking up oxygen in the lungs, blood enters the left side of the heart. The left ventricle has the thickest muscular wall of all four chambers because it must generate enough force to pump oxygenated blood throughout the entire body via the aorta.

Blood travels through three primary types of blood vessels: arteries, veins, and capillaries. As a rule, arteries carry blood away from the heart, and veins carry blood toward the heart. Most arteries carry oxygen-rich blood, but the pulmonary arteries are an important exception because they carry oxygen-poor blood away from the heart to the lungs. Similarly, most veins carry oxygen-poor blood, but the pulmonary veins carry oxygen-rich blood from the lungs back to the heart. Capillaries are microscopic blood vessels with walls only one cell thick. This razor-thin barrier allows oxygen, nutrients, and wastes to pass easily between the circulating blood and surrounding tissues.

Blood itself consists of specialized cellular components suspended in fluid. Red blood cells contain hemoglobin, an iron-rich protein that binds and transports oxygen throughout the body. White blood cells defend the body against infections, viruses, and foreign invaders. Platelets are cell fragments in the blood that are essential for blood clotting and wound healing, preventing excessive blood loss when an injury occurs.

The respiratory system provides the oxygen that hemoglobin carries and eliminates gaseous waste. The trachea is the main airway leading to the lungs, reinforced by sturdy rings of cartilage to prevent collapse when you breathe. The diaphragm is the primary breathing muscle, contracting downward to draw air into the lungs. Air travels down to microscopic air sacs called alveoli, which are surrounded by adjacent capillaries. During external respiration, oxygen diffuses from the alveoli into the blood, while carbon dioxide diffuses from the blood into the alveoli to be exhaled.