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10 29 07 - Respiratory System II

10 29 07 - Respiratory System II - Respiratory System II...

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Respiratory System II Air Respiration in fishes A variety of structures exist that bring a “respiratory membrane” in contact with air: - a specialized, vascular skin (analogous to amphibians) - vascularized pharynx and esophagus - outpocketings in the caudal pharynx that are vascularized - vascularized intestines (air is actually swallowed, and passes through the GI tract) - lungs Lungs Most Actinopterygians have lungs or a swim bladder. The most primitive and many later groups have lungs implying that this was the primitive condition. Various groups within actinopterygii have swim bladders or neither swim bladders nor lungs. Provides buoyancy Carp The lungs or swim bladder form as a ventral evagination of the foregut in some fish and dorsal in others. Some researchers think that the lungs are serial homologs to pharyngeal pouches. Surface area is increased in many groups by the folding of the epithelial wall. Air is “gulped from the surface and is forced into the lungs via pharyngeal constriction. The air is then expelled by contraction of the lungs. Swim Bladders The swim bladder allows the fish to regulate it’s buoyancy by increasing or decreasing the volume of air in the bladder through the movement of O2 gas. Provide buoyancy Dorsal side of coelom Close relation with circulatory system Blood comes in and contacts the gas gland Gas gland takes oxygen from the blood and brings it into swim bladder Increasing volume: In acidic environments, O2 is released more readily by hemoglobin. The gas gland , is in the wall of the bladder and secretes acids. When arterial blood passes by, it unloads an unusually high percentage of it’s O2. The excess O2 diffuses into the bladder, increasing it’s volume. More acid = more volume. The volume of the fish increases and the mass remains constant, lowering the overall density of the fish This helps for buoyancy Walls impermeable to O 2 use secondary chamber to increase density A sphincter is present to regulate airflow to secondary chamber
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