Gas+Exchange+&+Homeostasis

Diffusion is the only way respiratory gases can be exchanged between an animal and the environment. (No active transport mechanisms) Gas exchange systems are diverse because of the many physical and environmental factors influence that rates of diffusion... and probably many more reasons
 * 37.1** Respiratory gases that animals must exchange are oxygen and carbon dioxide (cellular respiration, the formation of ATP and all that jazz)

Diffusion is driven by concentration differences -areas of high concentration to low -partial pressures: the pressure of each different gas contributing to the total atmospheric pressure

Fick's law applies to all system of gas exchange Q=DA((Psub1-Psub2)/L)

Air is a better respiratory medium than water (oxygen can be obtained more easily from air than from water) -the oxygen content of air is much higher than the oxygen content of water -oxygen diffuses about 8,000 times more rapidly in air than in water -more energy is required to move water over an animal's specialized gas exchange surfaces than air because water is more dense and viscous Large animals need specialized respiratory systems with large surface areas because the diffusion of oxygen in water is so slow that only small bodies with large surface area (to volume ratios) can survive without internal systems for distributing the oxygen.

Osub2 (oxygen) availability is limited in many environments Something really cool: the reason why fish cannot survive in water that is too warm is because when water gets warmer, it holds less oxygen per liter, but fish are ectotherms- as the water heats up, so does the fish, and when fish get warmer, their metabolic rate increases (they need more oxygen). Eventually, the lack of oxygen in the water cannot sustain the metabolic rate of the fish and the fish dies. Another example of limited oxygen supply is for air-breathers when altitude increases

COsub2 (carbon dioxide) is easily lost by diffusion -carbon dioxide diffuses out of the body as oxygen diffuses in -the amount of carbon dioxide in the atmosphere is extremely low (large concentration gradient for diffusion of carbon dioxide from an organism's body) -carbon dioxide is much more soluble in water than oxygen


 * 37.2** Respiratory systems have evolved to maximize partial pressure gradients


 * function of respiratory system
 * transport oxygen in and carbon dioxide out
 * __environment => inside body__ (lungs, gills, etc.) => bloodstream => cells
 * gas exchange focuses on environment => inside body
 * cellular respiration
 * methods for gas exchange
 * organisms evolved different methods for gas exchange depending on __environment__ (and phylogeny)
 * aquatic organisms
 * external system
 * ex: gills
 * countercurrent exchange
 * surrounding water and blood inside gills flow in opposite directions
 * maximize oxygen diffusion from water to the blood
 * this is why fish must always keep swimming!
 * terrestrial organisms
 * moist internal respiratory tissue
 * ex: lungs
 * advantages
 * air is better than water (for gas exchange)
 * high concentration of oxygen
 * gases diffuse faster
 * lighter = easier to pump through the body
 * disadvantages
 * use more water to maintain moisture of respiratory organs


 * =====The process of simple diffusion is only effective over short distances. The distance an O₂ molecule travels as it diffuses through cell membrane (lipid bilayer) is roughly .01 μm. Because this distance is so short, the rate of diffusion is very quick. =====
 * =====Prokaryotes, single-celled eukaryotes, and some animals are able to meet there O₂ demands through simple diffusion. =====
 *  Flatworms and sponges are examples of animals without specialized breathing organs (respiration occurs through simple diffusion).

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Insects and spiders have a tracheal breathing system. Invigilated tubules (or tracheae) branch throughout the body. These tubules are gas filled and are come close enough to every cell that O₂ can diffuse directly to the cells. =====
 * =====In small to mid-sized insects (0.5 cm long), simple diffusion though the tracheae system is sufficient to meet gas exchange needs. =====
 * Larger insects have evolved various methods to create bulk flow though their tracheae.

**bulk flow:** mass movement of a fluid driven by a difference of pressure, from a region of high pressure to a region of low pressure

 * =====For distances greater than 0.5 millimeters, simple diffusion occurs too slowly to meet the respiratory demands of an organism. Larger organisms, in which the majority of cells are not directly in contact with the environment, must have a respiratory/circulatory system to distribute O₂ in bulk throughout the body. =====

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**gill:** a breathing organ that is evaginated (folded outward from the body) and surrounded by the environmental medium; the type of breathing organ found most commonly in water-breathers. =====

**Countercurrent:** blood and water flow in opposite direction along the gas exchange membrane

 * =====Most aquatic animals use a countercurrent system of gas exchange. =====

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**lung:** a breathing organ that is invaginated (folded inward) into the body and contains the environmental medium; the most common type of breathing organ in terrestrial animals. =====
 * =====Air typically enters and leaves the lungs by the same route. This method of ventilation is referred to as tidal ventilation. =====
 * =====Amphibians and air-breathing fish use positive pressure to move fresh air into their lungs. Such animals fill their mouth with air and then contract the muscles in their mouth. This creates an area of high pressure and pushes the air into their lungs. =====
 * =====Mammals and most non-bird reptiles expand their lungs during inhalation, creating an area of low pressure and drawing in fresh air from the environment. =====

Gas exchange in birds occurs in the parabronchi, a system of long, tiny tubes.

 * =====<span style="font-family: Arial,Helvetica,sans-serif;">In contrast to the lungs of other animals – which expand and contract with each breath –bird lungs change only slightly in volume (often described as ridged). =====
 * =====<span style="font-family: Arial,Helvetica,sans-serif;">Air is pumped though the lungs by a series of air sacs; these sacs inflate and deflate with each breath but do not participate in gas exchange. =====


 * <span style="font-family: Arial,Helvetica,sans-serif;">Stoma: **<span style="font-family: Arial,Helvetica,sans-serif;"> opening in the plants epidermis that permits gas exchange; bounded by a pair of guard cells whose osmotic status regulates the size of the opening.
 * plants have no specialized organs for gas exchange
 * gas exchange occurs through simple diffusion
 * All living cells of the plant lie close enough to the external environment (the interior of the stem consists of dead cells which provide structural support for the plant).
 * The respiration rate of plants is much lower than that of animals

cardiovascular system- gas is transported through the blood stream as it is circulated throughout the body muscular system- oxygen provision and carbon dioxide removal is necessary for muscle contraction nervous system- lungs provide oxygen and remove carbon dioxide in neurons


 * Specifically mammals: **

Diagram an alveolus and label the diagram to show how it functions in gas exchange. Create an original image.

Explain why oxygen moves into the blood, and why carbon dioxide moves out of the blood at the alveolus. Once inspiration has occurred, the alveoli have a higher concentration of oxygen than the blood entering the lungs does. Therefore, oxygen diffuses from the alveoli into the blood. The reverse is true of carbon dioxide. The alveoli have a lower concentration of carbon dioxide than does the blood entering the lungs. Therefore, carbon dioxide diffuses out of the blood into the alveoli.

Explain how oxygen and carbon dioxide are transported in the blood. Oxygen: Oxygen is transported in the blood by entering the red blood cells and binding with the iron portion of the hemoglobin. Carbon Dioxide: Carbon dioxide diffuses into the blood at the tissues and from there can be transported in one of three ways: 1. About 10% is transported as a dissolved gas in blood plasma and in the cytoplasm of red blood cells. 2. Approximately 30% of carbon dioxide molecules formed are taken up by the protein (globin) portion of hemoglobin, forming a compound called carbaminohemoblobin. 3. A majority (about 60%) combines with water, forming carbonic acid. The carbonic acid then dissociates to hydrogen ions and biocarbonate ions.

Explain how the respiratory system depends upon other body systems to accomplish the process of gas exchange. Provide three specific examples. Cardiovascular System: The heart pumps blood to the tissues in the body and to the lungs. This is necessary for gas exchange because gas exchange occurs in both the tissues and the lungs. The heart pumping oxygen poor blood to the lungs and oxygen rich blood from the lungs is necessary for oxygen and carbon dioxide exchange. Muscular System: The muscles aid in breathing which means oxygen is brought into the lungs and then exchanged and diffused into the blood, and carbon dioxide which is diffused or exchanged into the alveoli is dispelled. Endocrine System: The endocrine system has growth factors which control production of red blood cells, one of the main components in gas exchange and transport, which carry oxygen.

Describe an example of a regulatory feedback loop that involves the respiratory system (it can involve other systems as well). Explain how changes in the system affect this feedback loop. Identify the system as exemplifying positive or negative feedback, and justify your identification. Strenuous activity occurs, blood oxygen levels decrease and carbon dioxide levels increase, breathing rate increases, blood oxygen levels rise and carbon dioxide levels decrease, breathing decreases to normal rate. This is an example of a negative feedback loop because there was a surplus imbalance and there was an act that corrected it by stopping the process that brought about the surplus.

Describe two examples of disruptions to the respiratory system (a “disease”). Address the cause, symptoms, and treatment of the conditions. Pneumonia: This is a viral or bacterial infection in the lungs, where the bronchi and alveoli become clogged with fluid. Symptoms include chest pain, difficulty breathing, fever, productive cough, and headache. People with pneumonia must be treated with antibiotics. Pulmonary Fibrosis: A condition in which fibrous connective tissue builds up in the lungs, leading to the lungs being unable to inflate properly and always tending towards deflation. Inhaling particles such as silica (sand), coal dust, asbestos, clay, cement, flour, and fiberglass can lead to pulmonary fibrosis. Symptoms include shortness of breath, a (dry) hacking cough, (fast) shallow breathing, gradual unintended weight loss, and tiredness, aching joints and muscles. The only treatment option that is therapeutic is lung transplantation, however this is usually reserved for advanced cases. There are medications available that can slow the scarring process but responses to such treatment are variable.