Welcome back to the systems blogs! The respiratory system has the major function of gas exchange, the uptake of oxygen from the environment and the release of carbon dioxide into the environment. Organs imporant in this system are blood vessels, lungs, diaphragm, heart, and the nose. Alveoli are functional units in this system located in the lungs. For mammals, the lungs are the respiratory surface, specifically the alveoli. The respiratory medium is the source of oxygen, which is usually the atmosphere. Lungs have many capillaries under their respiratory surface called the epithilum. Lungs are present in spiders, land snails, and animals with vertebrates. Size of lungs are proportional to the animals metabolic rates.
Lungs in mammals are spongy in texture and has a left and right lung. Branching duets bring air inhaled from the nasal cavity into the lungs, but air first must pass the larynx and pharynx. When food is being swallowed the larynx opens up the esophagus, but for air it closes to open up the trachea, also called the windpipe. The trachea branches into 2 bronchi, 1 for each lung, and these branch into a bronchus. Bronchioles branch from the bronchus. All the ducts have an epithelium lining covered in cilia to trap dust, mucus, pollen, and other contaminants that are pushed back up to be exhaled. Alveoli are present at the tips of the bronchioles, and they are air sacs where gas exchange occurs.
Oxygen that enters the alveoli chambers dissolves and diffuses across their epithelium into capillaries surrounding the alveoli. CO2 diffuses from the capillaries into the alveolus chambers. The oxygen in the capillaries enters the bloodstream and makes blood in the oxygen poor pulmonary artery, rich with oxygen into the pulmonary vein.
Breathing is the process that ventilates the lungs, and this has two pressures: positive and negative. Mammals use negative pressure breathing. this works by pulling air rather than pushing it into the lungs. Lung volume increases when rib muscles and the diaphragm contract which expands the rib-cage by pushing the ribs upward. This pulls in air by allowing and opening up space. As the muscles and diaphragm relax the air is pushed out like a pump. The volume of the air inhaled and exhaled is called the tidal volume. Vital capacity is the maximum tidal volume. residual volume of air remains in lungs after exhaling because the aleveoli cannot exchange all air at once.
Transport of oxygen is dependent on respiratory pigments that circulate in blood. Henocyanin is a pigment in hemoglobin that allows iron to band with oxygen so that oxygen from the lungs is loaded into the hemoglobin and unloaded at tissue cells. Each hemoglobin has four subunits called heme groups and thus each can only carry four oxygen molecules. PH controls hemoglobin affinity. A drop in pH lowers its affinity for oxygen, and this is called the Bohr shift. Hemoglobin also transfers carbon dioxide. 7% of CO2 by tissue cells is transferred by blood plasma, 23% by amino groups of hemoglobin, and 70% in blood as bicarbonate ions. Water enters red blood cells to react with CO2 to form carbonic acid and some CO2 is picked up by hemoglobin. Carbonic acid breaks down into bicarbonate and H+ ions, that are also picked up by hemoglobin. Once the cell reaches the capillaries in the lungs, Hemoglobin releases H+ and CO2, where H+ and bicarbonate react to form H2CO3, which loses water to form CO2. CO2 enters the alveolar chambers in the lungs, and then is exhaled out of the system and body.
Written By: Neil 7/4/2019
Campbell Reese 7th Edition Biology Textbook