Parts of the Respiratory System When you inhale, air enters through your nose or your mouth. Did you know that your nose does more than serve as a passageway for respiration? Ode to the nose! The nose also: -Contains receptors for your sense of smell -Filters inhaled air and screens out some foreign particles -Moistens and warms incoming air -Provides a resonating chamber that helps give your voice its characteristic tone Cool. Thanks, nose! From there, incoming air next enters the pharynx (throat), which connects the mouth and the nasal cavity to the larynx (voice box). The upper pharynx extends from the nasal cavity to the roof of the mouth. Into it open the two auditory tubes that drain the middle ear cavities and equalize air pressure between the middle ear and outside air. The lower pharynx is a common passageway for both food and air. Food passes through on its way to the esophagus, and air flows on its way to the lower respiratory tract. The lower respiratory tract includes the larynx, the trachea, the bronchi and the lungs with their bronchioles and alveoli. The trachea is the "windpipe" that extends from the larynx to the left and right bronchi. Like the nasal cavity, the trachea is lined with cilia-covered epithelial tissue that secretes mucus. The mucus traps foreign particles and the cilia move them upward, away from the lungs. The trachea branches into two airways called the right and left bronchi (singular: bronchus...hehe) as it enters the lung cavity. Like the branches of a tree, the two bronchi divide into a network of smaller and smaller bronchi. The walls of bronchi contain fibrous connective tissue and smooth muscle reinforced with cartilage. As the branching airways get smaller and smaller the amount of cartilage declines. By definition, the smaller airways that lack cartilage are called bronchioles. In addition to air transport, the bronchi and bronchioles have several other functions in addition to air transport. They also clean the air, warm it up to body temperature and lovingly saturate it with water vapor before it reaches the delicate gas-exchange surfaces of the lungs. Most bronchi and bronchioles are lined with ciliated epithelial cells and occasional mucus-secreting cells. These cells trap particles and then sweep them upward toward the pharynx so they can be swallowed. The respiratory bronchioles eventually become alveolar ducts. Basically, the lungs are a system of branching airways that end in 300 million tiny air-filled sacs called alveoli. It is in these sacs where gas exchange takes place. Alveoli are arranged in clusters at the end of every terminal bronchiole, like wild grapes dangling from a stem. A single alveolus is a thin bubble of living squamous epithelial cells only one layer thick YET their combined surface area is nearly 40 times the area of our skin. This tremendous amount of surface area and the thinness of the squamous type of epithelium facilitate gas exchange with nearby capillaries. Within each little alveolus, certain epithelial cells secrete a lipoprotein called surfactant that coats the interior of the alveoli and reduces surface tension. Surface tension happens because of the attraction of water molecules towards each other Without surfactant, the force of surface tension could collapse the alveoli. My friends and I slaughtered a sheep last fall for meat and when I touched the lungs of our recently departed friend I was struck by how soft and frothy they were. It was surprising to me at the time - that lungs are mostly air! The lungs are organs consisting of supportive tissue enclosing the bronchi, bronchioles, blood vessels and the areas where gas exchange occurs. They occupy most of the thoracic cavity. There are two lungs, one on the right side and one of the left side, separated from each other by the heart. Each lung is enclosed in two layers of thin epithelial membranes called the pleural membranes. One of these layers represents the outer lung surface and the other lines the thoracic cavity. The pleural membranes are separated by a small space called the pleural cavity, that contains a very small amount of watery fluid. The fluid reduces friction between the pleural membranes and the lungs and chest wall during breathing. The Process of Breathing Breathing involves getting air into and out of the lungs in a cyclic manner that requires muscular effort. The lungs themselves don't have any skeletal muscle tissue so how does this happen? The lungs expand passively because the surrounding bones and muscles expand the size of the chest cavity. The bones and muscles involved in respiration include the ribs, the intercostal muscles between the ribs, and the main muscle of respiration called the diaphragm, a broad sheet of muscle that separates the thoracic cavity from the abdominal cavity. The intercostal muscles and the diaphragm are skeletal muscles. To understand why air moves into and out of the lungs in a cyclic manner, let's take a look at some general principles of gas pressure and of how gases move: 1. Gas pressure is caused by colliding molecules of gas 2. When the volume of a closed space increases, the molecules of gas in that space are farther away from each other, and the pressure inside the space decreases. Conversely, when the volume in a closed space decreases, the gas pressure increases. 3. Gases flow from areas of higher pressure to areas of lower pressure Overall, the lungs expand and contract only because they are compliant (stretchable) and because they are surrounded by the pleural cavity, which is airtight and sealed. If the volume of the pleural cavity expands, the lungs will expand with it. Inspiration (inhalation) pulls air into the respiratory system as lung volume expands, and expiration (exhalation) pushes air out as lung volume declines again. When the lungs expand, the pressure within them falls relative to the atmospheric pressure and air rushes in. During expiration the lungs become smaller and increasing pressure within them forces air out. During our normal breathing, the act of inspiration is active (requiring energy) and expiration is passive. We normally breathe at about 12 breaths per minute with a tidal volume of 500 ml per breath. Our vital capacity is the maximum amount of air we can exhale after a maximal inhalation. Gas Exchange and Transport Occur Passively Overall, oxygen and carbon dioxide (a waste product of body processes) are exchanged in the tiny air sacs of the alveoli at the end of the bronchial tubes. When a person inhales, oxygen moves from the alveoli to the surrounding capillaries and into the bloodstream. At the same time, carbon dioxide moves from the bloodstream to the capillaries and into the alveoli. The carbon dioxide is removed from the lungs when a person exhales. The lungs are in a constant state of filtering contaminants from the outside air, releasing toxins from the body and balancing the levels of oxygen and carbon dioxide in your body. Interestingly, the bronchial tubes look like an up-side down tree and the respiratory system exists in a dynamic symbiosis with the plant world, using and releasing the opposing gases that keep both alive. It's an exciting connection that we can also use plants to assist us in facing respiratory woes. In our therapeutics class this year, Betzy talked about the following strategies for treating and managing respiratory ailments:
-Open the airways (and improve oxygen utilization) -Reduce histamine and mucus -Soothe irritation and spasms -Rebuild and repair lung tissue -Fight infection -Decrease inflammation -Avoid respiratory irritants Many lung issues, including asthma and bronchitis, involve a constriction and/or spasm of the lungs and bronchi. Many herbs we talked about in class address this but many herbalists consider mullein, elecamane and yerba santa to be the bee's knees in opening the airways. Overreactive immune and histamine response is at the center of many respiratory ailments, including asthma, seasonal allergies, postnasal drip, congestion and others. While an immune-supporting lifestyle can reduce the severity and frequency of an overreactive response, there are herbs that can reduce histamine production and relieve symptoms. Horehound leaf can thin mucus and help clear it from the airways while addressing spasms. Goldenrod contains anti-inflammatory, antihistamine properties and helps thin and drain mucus while toning the mucosal lining. There are a number of demulcent and vulnerary herbs that help counteract dryness, irritation, heat and inflammation while supporting vital tissue and healthy amounts of mucus. Marshmallow root, licorice root and plantain would help here. Wild cherry bark specifically quells dry, irritated, hacking coughs and soothes irritated lungs while reishi and cordyceps have immune-supportive benefits that strengthen respiratory function and structure. Overall, there are many great herbs to help rebuild, repair, fight infection, sooth irritation, open the airways and fight overactive histamine and mucus production.
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AuthorThe adventures, studies, and musings of a student at the Vermont Center for Integrative Herbalism.
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