Chapter 51: Salt and Water Balance and Nitrogen Excretion Chapter 51 Salt and Water Balance and Nitrogen Excretion

Chapter 51: Salt and Water Balance and Nitrogen Excretion Tissue Fluids and Water Balance Tissue Fluids and Water Balance Distinguishing Environments and Animals in Terms of Salt and Water Distinguishing Environments and Animals in Terms of Salt and Water Excreting Nitrogen Excreting Nitrogen The Diverse Excretory Systems of Invertebrates The Diverse Excretory Systems of Invertebrates

Chapter 51: Salt and Water Balance and Nitrogen Excretion Vertebrate Excretory Systems Are Built of Nephrons Vertebrate Excretory Systems Are Built of Nephrons The Mammalian Excretory System The Mammalian Excretory System Control and Regulation of Kidney Functions Control and Regulation of Kidney Functions

Chapter 51: Salt and Water Balance and Nitrogen Excretion Tissue Fluids and Water Balance The problems of salt and water balance and nitrogen excretion that animals face depend on their environments,The problems of salt and water balance and nitrogen excretion that animals face depend on their environments, In all animal excretory systems, there is no active transport of water.In all animal excretory systems, there is no active transport of water.4

Chapter 51: Salt and Water Balance and Nitrogen Excretion Tissue Fluids and Water Balance All adaptations for maintaining salt and water balance and for excreting nitrogen wastes employ filtration of body fluids and active secretion and resorption of specific ions.All adaptations for maintaining salt and water balance and for excreting nitrogen wastes employ filtration of body fluids and active secretion and resorption of specific ions.5

Chapter 51: Salt and Water Balance and Nitrogen Excretion Distinguishing Environments and Animals in Terms of Salt and Water Marine animals can be osmoconformers or osmoregulators.Marine animals can be osmoconformers or osmoregulators. Freshwater animals must be osmoregulators and continually excrete water and conserve salts.Freshwater animals must be osmoregulators and continually excrete water and conserve salts. All animals are ionic regulators to some degree.All animals are ionic regulators to some degree. Review Figure

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Chapter 51: Salt and Water Balance and Nitrogen Excretion Distinguishing Environments and Animals in Terms of Salt and Water On land, water conservation is essential, and diet determines whether salts must be conserved or excreted.On land, water conservation is essential, and diet determines whether salts must be conserved or excreted. Marine birds excrete excess salt through nasal salt glands.Marine birds excrete excess salt through nasal salt glands. Review Figure

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Chapter 51: Salt and Water Balance and Nitrogen Excretion Excreting Nitrogen Aquatic animals can eliminate nitrogenous wastes such as ammonia by diffusion across their gill membranes.Aquatic animals can eliminate nitrogenous wastes such as ammonia by diffusion across their gill membranes. Terrestrial animals must detoxify it by converting it to urea or uric acid.Terrestrial animals must detoxify it by converting it to urea or uric acid. Review Figure

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Chapter 51: Salt and Water Balance and Nitrogen Excretion Excreting Nitrogen Depending on the form in which they excrete their nitrogenous waste products, animals are classified asDepending on the form in which they excrete their nitrogenous waste products, animals are classified as ammonotelic ureotelic uricotelic13

Chapter 51: Salt and Water Balance and Nitrogen Excretion The Diverse Excretory Systems of Invertebrates The protonephridia of flatworms consist of flame cells and excretory tubules.The protonephridia of flatworms consist of flame cells and excretory tubules. Tissue fluid is filtered into the tubules, which process the filtrate to produce a dilute urine.Tissue fluid is filtered into the tubules, which process the filtrate to produce a dilute urine. Review Figure

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Chapter 51: Salt and Water Balance and Nitrogen Excretion The Diverse Excretory Systems of Invertebrates In annelid worms, blood pressure causes blood filtration across capillary walls.In annelid worms, blood pressure causes blood filtration across capillary walls. The filtrate enters the coelomic cavity, and is taken up by metanephridia.The filtrate enters the coelomic cavity, and is taken up by metanephridia. As it passes through the tubules to the outside, its composition is changed by active transport mechanisms.As it passes through the tubules to the outside, its composition is changed by active transport mechanisms. Review Figure

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Chapter 51: Salt and Water Balance and Nitrogen Excretion The Diverse Excretory Systems of Invertebrates The Malpighian tubules of insects receive ions and nitrogenous wastes by active transport across the tubule cells.The Malpighian tubules of insects receive ions and nitrogenous wastes by active transport across the tubule cells. Water follows by osmosis. Ions and water are resorbed from the rectum, so the insect excretes semisolid wastes.Water follows by osmosis. Ions and water are resorbed from the rectum, so the insect excretes semisolid wastes. Review Figure

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Chapter 51: Salt and Water Balance and Nitrogen Excretion Vertebrate Excretory Systems Are Built of Nephrons The nephron is the functional unit of the vertebrate kidneyThe nephron is the functional unit of the vertebrate kidney It consists of a glomerulus, in which blood is filtered across the walls of a knot of capillaries, andIt consists of a glomerulus, in which blood is filtered across the walls of a knot of capillaries, and A renal tubule, which processes the filtrate into urine.A renal tubule, which processes the filtrate into urine. A system of peritubular capillaries serves the tubule.A system of peritubular capillaries serves the tubule. Review Figure

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Chapter 51: Salt and Water Balance and Nitrogen Excretion Vertebrate Excretory Systems Are Built of Nephrons Adaptations of marine fishes and terrestrial animals to conserve water are diverse.Adaptations of marine fishes and terrestrial animals to conserve water are diverse. Bony fishes have few glomeruli and produce little urine.Bony fishes have few glomeruli and produce little urine. Cartilaginous fishes retain urea so the osmotic concentration of their body fluids remains above that of seawater.Cartilaginous fishes retain urea so the osmotic concentration of their body fluids remains above that of seawater. Amphibians remain near water or have waxy skin coverings.Amphibians remain near water or have waxy skin coverings. Reptiles have scaly skin, lay shelled eggs, and excrete nitrogenous wastes as uric acid.Reptiles have scaly skin, lay shelled eggs, and excrete nitrogenous wastes as uric acid.22

Chapter 51: Salt and Water Balance and Nitrogen Excretion Vertebrate Excretory Systems Are Built of Nephrons Birds share the adaptations of reptiles.Birds share the adaptations of reptiles. They also can produce urine more concentrated than their tissue fluids.They also can produce urine more concentrated than their tissue fluids. Only birds and mammals can produce such urine.Only birds and mammals can produce such urine.23

Chapter 51: Salt and Water Balance and Nitrogen Excretion The Mammalian Excretory System The concentrating ability of the mammalian kidney depends on its anatomy.The concentrating ability of the mammalian kidney depends on its anatomy. Review Figure

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Chapter 51: Salt and Water Balance and Nitrogen Excretion The Mammalian Excretory System The glomeruli and the proximal and distal convoluted tubules are located in the cortex of the kidney.The glomeruli and the proximal and distal convoluted tubules are located in the cortex of the kidney. Certain molecules, salts, and water are resorbed in bulk, and other molecules are secreted in the convoluted tubules without the urine becoming more concentrated.Certain molecules, salts, and water are resorbed in bulk, and other molecules are secreted in the convoluted tubules without the urine becoming more concentrated. Straight sections of renal tubules (loops of Henle) and collecting ducts are arranged in parallel in the medulla of the kidney.Straight sections of renal tubules (loops of Henle) and collecting ducts are arranged in parallel in the medulla of the kidney. Review Figure

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Chapter 51: Salt and Water Balance and Nitrogen Excretion The Mammalian Excretory System The loops of Henle create a concentration gradient in the extracellular fluids of the renal medulla by a countercurrent multiplier mechanism.The loops of Henle create a concentration gradient in the extracellular fluids of the renal medulla by a countercurrent multiplier mechanism. Urine flowing down collecting ducts to the ureter is concentrated by osmotic loss of water caused by the concentration gradient in surrounding tissue fluid.Urine flowing down collecting ducts to the ureter is concentrated by osmotic loss of water caused by the concentration gradient in surrounding tissue fluid. Review Figure

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Chapter 51: Salt and Water Balance and Nitrogen Excretion Control and Regulation of Kidney Functions Kidney function in mammals is controlled by autoregulatory mechanisms that maintain a constant high glomerular filtration rate even if blood pressure varies.Kidney function in mammals is controlled by autoregulatory mechanisms that maintain a constant high glomerular filtration rate even if blood pressure varies. Review Figure

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Chapter 51: Salt and Water Balance and Nitrogen Excretion Control and Regulation of Kidney Functions An important autoregulatory mechanism is renin release by the kidney when blood pressure falls.An important autoregulatory mechanism is renin release by the kidney when blood pressure falls. Renin activates angiotensin, which causes constriction of peripheral blood vessels, causes release of aldosterone (which enhances water resorption), and stimulates thirst.Renin activates angiotensin, which causes constriction of peripheral blood vessels, causes release of aldosterone (which enhances water resorption), and stimulates thirst.32

Chapter 51: Salt and Water Balance and Nitrogen Excretion Control and Regulation of Kidney Functions Kidney function in mammals is also controlled by mechanisms responsive to blood pressure and osmolarity.Kidney function in mammals is also controlled by mechanisms responsive to blood pressure and osmolarity. Changes in these influence release of antidiuretic hormone, which controls the permeability of the collecting duct to water, thus amount of water resorbed from urine.Changes in these influence release of antidiuretic hormone, which controls the permeability of the collecting duct to water, thus amount of water resorbed from urine. ADH stimulates expression of proteins called aquaporins that serve as water channels in the collecting duct cell membranes.ADH stimulates expression of proteins called aquaporins that serve as water channels in the collecting duct cell membranes. Review Figure

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Chapter 51: Salt and Water Balance and Nitrogen Excretion Control and Regulation of Kidney Functions Hydrogen ions secreted by renal tubules are buffered in the urine by bicarbonate and other buffering systems.Hydrogen ions secreted by renal tubules are buffered in the urine by bicarbonate and other buffering systems. Review Figure

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