Respiratory System

• Unicellular eukaryotes generally rely on their cell membrane for gas exchange, as they lack specialized respiratory organs.
• Oxygen and carbon dioxide diffuse directly through the cell membrane.
• Insects typically have a system of tubes called tracheae, which branch throughout the body, allowing air to reach individual cells directly.
• Air enters the tracheae through small openings called spiracles, and then it diffuses into cells.
• In some insects, oxygen is delivered directly to tissues without the need for a circulatory system.
• Gills are common respiratory organs in mollusks, and in snails, a lung-like structure called the mantle cavity is present.
• Oxygen is extracted from water as it flows over the gills in some snails, and a lung extracts oxygen from the air.
• Earthworms breathe through their moist skin, and oxygen and carbon dioxide diffuse directly through the skin.
• Fish use gills for respiration, and water is pumped over gills, allowing oxygen to diffuse from the water into the bloodstream while carbon dioxide diffuses out.
• Amphibians breathe through both lungs and their moist skin, and lungs are used for breathing air, while the skin aids in respiration when submerged.
• Reptiles primarily use lungs for respiration, and air is drawn into the lungs, where gas exchange occurs in lung tissues.
• Birds have air sacs and lungs, and air flows through the respiratory system in a unidirectional manner, allowing for continuous oxygen exchange during both inhalation and exhalation.
• Mammals have lungs for respiration, and air is drawn into the lungs during inhalation, where oxygen is exchanged for carbon dioxide in the alveoli.
• The circulatory system then transports oxygenated blood throughout the body.
• Cilia and mucus play important roles in lung health.
• The respiratory system allows animals to move oxygen into body tissues and remove carbon dioxide from cells.
• Some animals simply allow gases to diffuse through their skins, these animals have a low metabolic rate.
• Structures specialized for gas exchange include gills (aquatic animals), spiracles (terrestrial insects), and lungs (most terrestrial vertebrates).
• In a concurrent system, exchange is inefficient as equilibrium is reached at one end.
• In a countercurrent system, equilibrium is not reached, so gas exchange continues, increasing efficiency.
• Fish increase gas exchange efficiency using countercurrent exchange, running blood through the system in the opposite direction to water keeps a diffusion gradient throughout the entire exchange.
• The site of gas exchange in mammals is the alveoli.
• Gills are widely seen in aquatic animals but not in land animals because one group of land animals that have gills is the Isopods (“pill bugs” and “sow bugs”).
• Parts of the respiratory system include the trachea, bronchi, bronchioles, and alveoli.
• During inspiration, the diaphragm and intercostal muscles contract, during exhalation, these muscles relax.
• The alveoli are moist, thin-walled pockets which are the site of gas exchange, a slightly oily surfactant prevents the alveolar walls from collapsing and sticking together.
• Gas exchange at the lungs and in the body cells moves oxygen into cells and carbon dioxide out.
• When you breathe in, the rib muscles relax, the diaphragm contracts, air leaves the alveoli, and air moves between the chest wall and the lung.
• Premature infants sometimes die of lung collapse and other lung problems, these infants may be missing surfactant.
• The respiratory surface is made up of the alveoli and capillary walls.
• When people quit smoking, if the lungs are not damaged they can often clean themselves because the cilia are no longer paralyzed, but people with cystic fibrosis have trouble with lung infections because their lung mucus is thick and sticky.
• A normal CFTR protein regulates the amount of chloride ions across the cell membrane of lung cells, and if the interior of the cell is too salty, water is drawn from lung mucus by osmosis, causing the mucus to become thick and sticky.
• Smoking can lead to emphysema, where alveoli become dry and brittle, and eventually rupture.
• The walls of the capillaries and the alveoli may share the same membrane for gas exchange.
• Cystic fibrosis is one of the most common inherited disorders in the Caucasian population in the U.S, caused by a mutation of a single gene, the CFTR gene, which controls salt balance in the lungs.
• Cells use up oxygen quickly for cellular respiration, creating carbon dioxide during cellular respiration, so CO2 levels in the cell are higher than in the blood coming to them, aiding in the uptake of oxygen.
• Carbon dioxide can dissolve in plasma, and about 70% forms bicarbonate ions, allowing some carbon dioxide to bind to hemoglobin for transport.
• Gene therapy may one day insert “good” CFTR genes into lung cells to make them operate normally.
• Cigarette smoke cures colds because it kills bacteria in the lungs, but nicotine is one of the most potent neurotoxins on earth, and “passive” smoking is less harmful than “regular” smoking.
• Inhaled smoke contains CO2, carcinogenic chemicals that can trigger tumors, and toxic nicotine, which paralyzes cilia that normally clean the lungs, affecting the CO2 diffusion gradient.