What The Bronchial Tree Is All About

The bronchial tree consists of the airways through which we breathe. It is called the bronchial tree because, from an anatomical viewpoint, it consists of a trunk, and branches which continuously subdivide into smaller and smaller branches. In truth, it would be more accurate to compare the bronchial tree to the root system of a tree, as when we are standing, the trunk is at the top, in our throat, and the tiny rootlets are at the bottom, in our lungs.

The Trachea -The trunk, or main stem of the bronchial tree is the trachea, usually referred to as the windpipe. The trachea starts at the back of our throat and extends downward approximately 5 inches (in an adult), into what is called the thoracic cavity, the thorax being the part of our abdomen we call the chest. The thoracic cavity lies within the rib cage and contains the heart, lungs and most of the bronchial tree.

The trachea, or windpipe is about an inch in diameter, and is made up of rings of cartilage which keep it from collapsing. If it were not for these rings, our windpipe would have a tendency to collapse between breaths. Fortunately it rarely does, unless injured. Problems associated with the trachea are more often those associated with blockage or partial blockage of one type or another.

The Bronchi - Once entering the thoracic cavity, the trachea splits in two, forming the right and left bronchi which enter the right and left lung, respectively. This would be the first branching of the bronchial tree. The two bronchi are not the same size, in part due to the location of the heart, which also determines the relative size of our two lungs. Because of the physical shape and location of the heart, our left lung is smaller than the right. The left bronchus is correspondingly smaller than is the right bronchus. Being narrower, it is often the left bronchus where we are most apt to a problem if we inhale an object, or swallow something that goes into the windpipe. Like the trachea, the two bronchi have rings of cartilage in their walls keeping them stable and open.

The Bronchioles – It is at the far end of the two bronchi that our bronchial tree really begins to take shape and deserve its name. Each bronchus divides into a number of smaller tubes or branches called bronchioles. These tubes do not have walls consisting of rings of cartilage, but rather of smooth muscle. Rather than being firm and somewhat inflexible, as is the case with the bronchi and the trachea, the bronchioles, tend to flex, contracting and expanding as we breathe, an action which helps the transfer of oxygen and carbon dioxide into and out of the lungs.

The Alveoli - The bronchioles in turn, branch still further into what are called alveolar ducts, tiny tubes, each of which feed the alveoli, the air sacs which make up the functioning part of our lungs. We could draw a parallel to the alveoli with clusters of berries at the end of the branch of a tree, each berry held in place by its individual stem. An adult human has on the order of 300 million alveoli in his or her two lungs.

The alveoli have very thin walls. In fact the walls of the alveoli are only two cells in thickness. This allows for easy transport of gases into and out of the blood stream. Oxygen, inhaled into the bronchial tree, will pass through the alveoli into the bloodstream, while waste products, in this case carbon dioxide, will pass from the blood stream and into the alveoli, to be exhaled up and out through the bronchial tree.

The tiny alveoli, with each one doing its job, keeps us alive. The bronchial tree, simply acts as an airway, supplying oxygen to the alveoli and carrying carbon dioxide away. The bronchial tree is every bit as vital to our existence of course. Without one we'd have to learn to breathe through our skin, as some other forms of animal life can do.




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