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Red represents a higher value (e.g. of temperature or the partial pressure of a gas) than blue so the property being transported in the channels flows from red to blue. In fish a countercurrent flow (lower diagram) of blood and water in the gills is used to extract oxygen from the environment. [6] [7] [8] All basal vertebrates breathe with gills.
The blood from the heart is then pumped to the gills to be oxygenated, and is then circulated through the rest of the body. [47] The four compartments are arranged sequentially: Sinus venosus: A thin-walled sac or reservoir with some cardiac muscle that collects deoxygenated blood through the incoming hepatic and cardinal veins.
The lateral line system consists of canals that run along a fish's body, connecting rows of openings (pores) through the skin and scales to the water outside the body. Small sense organs, neuromasts (inset), are positioned both at intervals along the canals, and on the surface of the body. Each hair cell contains a bundle of sensory hairs.
Fish exchange gases by pulling oxygen-rich water through their mouths and pumping it over their gills. Within the gill filaments, capillary blood flows in the opposite direction to the water, causing counter-current exchange. The gills push the oxygen-poor water out through openings in the sides of the pharynx.
Countercurrent flow occurs when deoxygenated blood moves through the gill in one direction while oxygenated water moves through the gill in the opposite direction. This mechanism maintains the concentration gradient thus increasing the efficiency of the respiration process as well and prevents the oxygen levels from reaching an equilibrium .
The blood carries oxygen to other parts of the body. Carbon dioxide passes from the blood through the thin gill tissue into the water. Gills or gill-like organs, located in different parts of the body, are found in various groups of aquatic animals, including mollusks, crustaceans, insects, fish, and amphibians.
The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled organ in bony fish (but not cartilaginous fish [1]) that functions to modulate buoyancy, and thus allowing the fish to stay at desired water depth without having to maintain lift via swimming, which expends more energy. [2]
Madreporite of Asterias. In sea stars, water enters the system through a sieve-like structure on the upper surface of the animal, called the madreporite.This overlies a small sac, or ampulla, connected to a duct termed the stone canal, which is, as its name implies, commonly lined with calcareous material.