Circulatory and Respiratory Systems
What are they and how do they work?
Circulatory System:
The circulatory system is a vast network of organs and vessels that is responsible for the flow of blood, nutrients, hormones, oxygen and other gases to and from cells. Without the circulatory system, the body would not be able to fight disease or maintain a stable internal environment - such as proper temperature and pH - known as homeostasis.
Description of the circulatory system
While many view the circulatory system, also known as the cardiovascular system, as simply a highway for blood, it is made up of three independent systems that work together: the heart (cardiovascular); lungs (pulmonary); and arteries, veins, coronary and portal vessels (systemic), according to the U.S National Library of Medicine (NLM).
In the average human, about 2,000 gallons (7,572 liters) of blood travel daily through about 60,000 miles (96,560 kilometers) of blood vessels, according to the Arkansas Heart Hospital. An average adult has 5 to 6 quarts (4.7 to 5.6 liters) of blood, which is made up of plasma, red blood cells, white blood cells and platelets. In addition to blood, the circulatory system moves lymph, which is a clear fluid that helps rid the body of unwanted material.
The heart, blood, and blood vessels make up the cardiovascular component of the circulatory system. It includes the pulmonary circulation, a "loop" through the lungs where blood is oxygenated. It also incorporates the systemic circulation, which runs through the rest of the body to provide oxygenated blood, according to NLM.
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The pulmonary circulatory system sends oxygen-depleted blood away from the heart through the pulmonary artery to the lungs and returns oxygenated blood to the heart through the pulmonary veins, according to the Mayo Clinic.
Oxygen-deprived blood enters the right atrium of the heart and flows through the tricuspid valve (right atrioventricular valve) into the right ventricle. From there it is pumped through the pulmonary semilunar valve into the pulmonary artery on its way to the lungs. When it gets to the lungs, carbon dioxide is released from the blood and oxygen is absorbed. The pulmonary vein sends the oxygen-rich blood back to the heart, according to NLM.
The systemic circulation is the portion of the circulatory system is the network of veins, arteries and blood vessels that transports blood from heart, services the body's cells and then re-enters the heart, the Mayo Clinic noted.
Milestones
Some milestones in the history and study of the circulatory system include:
- 16th century B.C.: The Ebers Papyrus, an ancient Egyptian medical document, provides some of the earliest writing on the circulatory. It describes the connection of the heart to the arteries.
- 6th century B.C.: Ayurvedic physician Sushruta in ancient India describes how vital fluids circulate through the body.
- 2nd century A.D.: the Greek physician Galen documents how blood vessels carry blood, identifies venous (dark red) and arterial (brighter and thinner) blood and notes that each has a separate functions.
- 1628: William Harvey, an English physician, first describes blood circulation.
- 1706: Raymond de Vieussens, a French anatomy professor, first describes the structure of the heart's chambers and vessels.
- 1733: Stephen Hales, an English clergyman and scientist, measures blood pressure for the first time.
- 1816: Rene T.H. Laennec, a French physician, invents the stethoscope.
- 1902: American physician James B. Herrick first documents heart disease resulting from hardening of the arteries.
- 1903: Dutch physiologist Willem Einthoven invents the electrocardiograph.
- 1952: The first successful open heart surgery takes place by F. John Lewis, an American surgeon.
- 1967: South African surgeon Christiaan Barnard performs the first transplant of a whole heart from one person to another.
- 1982: American physician Robert Jarvik designs the first artificial heart and American surgeon Willem DeVries implants it.
Respiratory System:
The human respiratory system is a series of organs responsible for taking in oxygen and expelling carbon dioxide. The primary organs of the respiratory system are lungs, which carry out this exchange of gases as we breathe.
Red blood cells collect the oxygen from the lungs and carry it to the parts of the body where it is needed, according to the American Lung Association. During the process, the red blood cells collect the carbon dioxide and transport it back to the lungs, where it leaves the body when we exhale.
The human body needs oxygen to sustain itself. A decrease in oxygen is known as hypoxia and a complete lack of oxygen is known as anoxia and, according to MedLine Plus. These conditions can be fatal; after about four minutes without oxygen, brain cells begin dying, according to NYU Langone Medical Center, which can lead to brain damage and ultimately death.
In humans, the average rate of breathing is dependent upon age. A newborn's normal breathing rate is about 40 times each minute and may slow to 20 to 40 times per minute when the baby is sleeping, according to the Children's Hospital of Philadelphia.
For adults, the average resting respiratory rate for adults is 12 to 16 breaths per minute, according to Johns Hopkins Medicine. Physical exertion also has an effect on respiratory rate, and healthy adults can average 45 breaths per minute during strenuous exercise.
Parts of the respiratory system
As we breathe, oxygen enters the nose or mouth and passes the sinuses, which are hollow spaces in the skull. Sinuses help regulate the temperature and humidity of the air we breathe.
The trachea, also called the windpipe, filters the air that is inhaled, according to the American Lung Association. It branches into the bronchi, which are two tubes that carry air into each lung. The bronchial tubes are lined with tiny hairs called cilia. Cilia move back and forth, carrying mucus up and out. Mucus, a sticky fluid, collects dust, germs and other matter that has invaded the lungs. We expel mucus when we sneeze, cough, spit or swallow.
The bronchial tubes lead to the lobes of the lungs. The right lung has three lobes; the left lung has two, according to the American Lung Association. The left lung is smaller to allow room for the heart, according to the National Heart, Lung and Blood Institute (NHLBI). Lobes are filled with small, spongy sacs called alveoli, and this is where the exchange of oxygen and carbon dioxide occurs.
The alveolar walls are extremely thin (about 0.2 micrometers). These walls are composed of a single layer of tissues called epithelial cells and tiny blood vessels called pulmonary capillaries.
Blood passes through the capillaries. The pulmonary artery carries blood containing carbon dioxide to the air sacs, where the gas moves from the blood to the air, according to the NHLBI. Oxygenated blood goes to the heart through the pulmonary vein, and the heart pumps it throughout the body.
The diaphragm, a dome-shaped muscle at the bottom of the lungs, controls breathing and separates the chest cavity from the abdominal cavity, the American Lung Association noted. When a breath it taken, it flattens out and pulls forward, making more space for the lungs. During exhalation, the diaphragm expands and forces air out.
Milestones
Some milestones in the study of the respiratory system.
- 13th century: Anatomist and physiologist Ibn Al-Nafis advances his theory that the blood must have passed through the pulmonary artery, through the lungs, and back into the heart to be pumped around the body. This is believed by many to be the first scientific description of pulmonary circulation.
- 1897: Gustav Killian uses a rigid esophagoscope to extract a pork bone from a farmer's bronchus.
- 1898: A. Coolidge performs the first bronchoscopy in the United States at the Massachusetts General Hospital.
- 1905: Looking to improve the care of tuberculosis patients by sharing their experiences and discoveries, a small group of physicians form what becomes the American Thoracic Society.
- 1907: In Philadelphia, Chevalier Jackson develops and improves the instruments for bronchoscopy and esophagoscopy.
- 1963: James Hardy of the University of Mississippi performs the first human lung transplant. The patient lives for 18 days.
- 1964: Shigeto Ikeda develops a prototype of what was to be the first flexible bronchoscope.
- 1983: Joel D. Cooper, a thoracic surgeon, performs the first successful lung transplant in Toronto.
- 1986: Cooper performs the first successful double lung transplant.