Respiratory System PDF

# Respiratory System ## Introduction - O2 and CO2 travel in and out of cells by passive transport (diffusion). - Does not occur over large (>1mm) distances... respiratory/circulatory systems are needed... to maintain O2 and CO2 partial pressures. - What helps diffusion... - A large surface...

# Respiratory System ## Introduction - O2 and CO2 travel in and out of cells by passive transport (diffusion). - Does not occur over large (>1mm) distances... respiratory/circulatory systems are needed... to maintain O2 and CO2 partial pressures. - What helps diffusion... - A large surface area. - Minimal distance for diffusion. - Tissue permeability (amphibian vs. reptile skin). - Fluid circulation inside/outside body. - Fish and tetrapods BOTH doing SAME thing; i.e., breathing a respiratory medium (air, water) in order to extract oxygen from the medium and load it into blood for distribution to the tissues for aerobic cellular respiration. - The organ (gill, lung) has a respiratory surface (e.g., secondary gill lamellae, alveoli) where the exchange of gas (oxygen or carbon dioxide) takes place by the transport mechanism of simple diffusion. This the movement of gas from a region of high concentration to low concentration. - Diffusion needs "help" in order to work effectively. Various adaptations do this: - Large surface area: secondary gill lamellae are huge increase in surface area for more efficient diffusion, alveoli also huge increase too. - Mimimal distance: respiratory surface of respiratory organ is simple, squamous epithelium so diffusion distance is small, all cells within 1 or 2 cells distance from nearest capillary. - Tissue permeability: in amphibians the thin epidermis allows for oxygen diffusion to blood vessels below and makes a significant contribution overall oxygen uptake. Not possible in the fully-terrestrial amniotes. - Fluid circulation: a circulatory system with a pump (heart) to move the blood is necessary to get oxygen-rich blood to the tissues. ## Organs of Respiration ### 1. Gills - Oxygen will dissolve in water - can be extracted using gills ("Breathing" water). - **Internal Gills** - Capillaries "hang" from branchial arches. - Kept inside body, lining the pharyngeal slits. - Protected by: operculum (bony fish) or interbranchial septum (cartilaginous fish) - **External Gills** - Gills hang outside body. - Amphibian larvae (metamorphosis: switch = gill to lungs). - Gills contain very dense capillary beds (heavily vascularized). Because the site of gas exchange (oxygen or carbon dioxide) is always the capillaries, NOT the arteries, arterioles, veins, or venules). - Gills are the respiratory organ for fish and fish use them to breathe water. Gills work in water but not air. (Lungs are respiratory organ for tetrapods and lungs work in air but not water). - Two type of gills: - Internal: protected by operculum, interbranchial septum, one type in Agnathans with no outer covering to protect the gill chamber. - External: gills protrude into the water, seen in amphibian larvae who switch to lungs during metamorphosis to adult ## Agnathans: Gills are simply frills lining the inside of branchial pouches. - In parasitic lamprey, the water can go in and out of the pharyngeal slits (tidal ventilation). - Elasmobranchs: Greater organization of gill supports... - Interbranchial septum - Branchial arch - Gill ray - Hemibranch/Holobranch - Primary/Secondary lamellae - Agnathan (lamprey). No outer covering to protect gill chamber. SEE 11.15 (adult) - In free-living lamprey it's one-way flow of water through mouth and out gill slits, moving across gill surface in process. - In parasitic lamprey the mouth is blocked (attached to host) so water goes in and out of gill slits = TIDAL VENTILATION (a ventilation mechanism). This is unlike most fish. - Branchial muscles pump water in and out. - Elasmobranchs. SEE FIGURE 11.17 - Interbranchial septum: covered by soft skin forms a "flap valve" at its tip. It extends all the way to branchial arch with gill rays for internal support. - Gill Ray: like ribs of a fan, internal support for gill, inside the interbranchial septum. - Hemibranch only half of the gill has lamellae; i.e., on one side of gill arch, on one side of interbranchial septum. - Holobranch: lamella on both sides of septum, both sides of gill arch. - Primary lamellae is support/base for the secondary lamellae. Water flows across sides of the secondary lamellae (site of respiratory surface) ## Teleost fish have a more complex V-shaped gill: - Operculum - Branchial arch - Primary/Secondary lamellae - Adductor muscles can control the amount of space between gills. - Spaces between operculum and other side of gills (buccal cavity) are key to movement of water across gills (i.e., the ventilation mechanism). This forms a "dual pump"... - SEE FIGURE 11.40 - Broad base is primary lamellae - The perpendicular lines are secondary lamellae. ## In virtually all fish, blood flow in gills demonstrates countercurrent exchange: - Direction of water flow - Capillaries - Efferent blood - Afferent blood - Secondary lamellae - Primary lamellae - Countercurrent exchange is more efficient than concurrent exchange (greater transfer of oxygen). - Countercurrent GAS-EXCHANGE MECHANISM. See handout. - SEE Chapter 4, FIGURE 4.43. - FIGURE 11.38 - E, Ex out of, away from. A, AD to, towards something. - Very efficient exchange of oxygen between water and blood. - Respiratory surface is secondary lamellae with capillary beds. - Water and blood flow in opposite directions, "counter". - Mechanism maintains high partial pressure of gas (oxygen) (also high concentration gradient) along entire length of contact. - 90% of oxygen in water is transferred by diffusion to blood. - A greater proportion than concurrent (flow in same direction) which is about 50-60% of oxygen is transferred from water to blood. - Blood in capillaries always flow through water with higher concentration of oxygen than in blood...a constant gradient and the difference is always relatively high. In concurrent blood oxygen concentration could at best reach oxygen concentration of outflowing water. ## Ventilation of gills brought about by a dual-pump mechanism in most fish... - Gills - Operculum - Mouth - Buccal cavity - Opercular cavity - Suction Phase - Force Phase - Some fish simply ram water through the gills. - SEE FIGURE 11.10 - Ventilation Mechanisms (see h/o) are muscular mechansims for moving the respiratory medium across the respiratory surface of the respiratory organ. - The "dual" means the buccal cavity is pump 1 and the opercular cavity is pump 2. - During suction phase, muscles of the buccal and opercular cavities expand the size of these spaces. The mouth is open and operculum is closed. When these expand it creates a vacuum or area of low pressure relative to the outside. The water then moves from high pressure zone to low pressure. The lowest is the opercular cavity - see arrows indicating water flow across the gill curtain. - Force phase the muscles squeeze the chambers putting them under high pressure relative to the outside. So now water goes from high to low (as always), but with the mouth now closed and the operculum open it continues on its way to the outside again. - One-way flow of water. - In Elasmobranch its same but the valves covering the gill chambers open and close and its called "parabranchial ventilation mechanism" but also a dual pump. FIGURE 11.18. - Ram ventilation during fast swimming just open mouth and forward movement provides power to "ram" the water from mouth, across gill curtain, and out gill slits. E.g., Tuna, sharks (sharks can switch between parabranchial and ram ventilation.