Osmoregulation and Excretion 滲透調節作用與排泄作用

Osmoregulation and Excretion 滲透調節作用與排泄作用
Chapter 44 Osmoregulation and Excretion 滲透調節作用與排泄作用

Overview: A Balancing Act
Physiological systems of animals operate in a fluid environment Relative concentrations of water and solutes must be maintained within fairly narrow limits Osmoregulation滲透壓調節作用 regulates solute concentrations and balances the gain and loss of water © 2011 Pearson Education, Inc.

Freshwater animals show adaptations that reduce water uptake and conserve solutes
Desert and marine animals face desiccating environments that can quickly deplete body water Excretion排泄作用 gets rid of nitrogenous metabolites and other waste products © 2011 Pearson Education, Inc.

Figure 44.1 Figure 44.1 How does an albatross drink salt water without ill effect?

Concept 44.1: Osmoregulation balances the uptake and loss of water and solutes
Osmoregulationis based largely on controlled movement of solutes between internal fluids and the external environment © 2011 Pearson Education, Inc.

Osmosis and Osmolarity
Cells require a balance between uptake and loss of water Osmolarity滲透壓 (溶質濃度),, the solute concentration of a solution, determines the movement of water across a selectively permeable membrane If two solutions are isoosmotic, the movement of water is equal in both directions If two solutions differ in osmolarity, the net flow of water is from the hypoosmotic to the hyperosmotic solution © 2011 Pearson Education, Inc.

Selectively permeable membrane
Figure 44.2 Selectively permeable membrane Solutes Water Hyperosmotic side: Hypoosmotic side: Higher solute concentration • Lower solute concentration • Lower free H2O concentration • Higher free H2O concentration • Figure 44.2 Solute concentration and osmosis. Net water flow

Osmotic Challenges Osmoconformers滲透壓適應者, consisting only of some marine animals, are isoosmotic with their surroundings and do not regulate their osmolarity Osmoregulators滲透壓調節者 expend energy to control water uptake and loss in a hyperosmotic or hypoosmotic environment © 2011 Pearson Education, Inc.

Most animals are stenohaline狹鹽性; they cannot tolerate substantial changes in external osmolarity
Euryhaline廣鹽性 animals can survive large fluctuations in external osmolarity © 2011 Pearson Education, Inc.

Marine Animals Most marine invertebrates are osmoconformers
Most marine vertebrates and some invertebrates are osmoregulators Marine bony fishes are hypoosmotic to sea water They lose water by osmosis and gain salt by diffusion and from food They balance water loss by drinking seawater and excreting salts © 2011 Pearson Education, Inc.

(a) Osmoregulation in a marine fish
Figure 44.3 (a) Osmoregulation in a marine fish (b) Osmoregulation in a freshwater fish Gain of water and salt ions from food Excretion of salt ions from gills Osmotic water loss through gills and other parts of body surface Gain of water and some ions in food Uptake of salt ions by gills Osmotic water gain through gills and other parts of body surface Figure 44.3 Osmoregulation in marine and freshwater bony fishes: a comparison. Gain of water and salt ions from drinking seawater Excretion of salt ions and small amounts of water in scanty urine from kidneys Key Excretion of salt ions and large amounts of water in dilute urine from kidneys Water Salt

Cl-, Na+ Ca2+ , Mg2+ ,SO42- (a) Osmoregulation in a marine fish
Figure 44.3a (a) Osmoregulation in a marine fish Gain of water and salt ions from food Excretion of salt ions from gills Osmotic water loss through gills and other parts of body surface Cl-, Na+ Figure 44.3 Osmoregulation in marine and freshwater bony fishes: a comparison. Ca2+ , Mg2+ ,SO42- Gain of water and salt ions from drinking seawater Excretion of salt ions and small amounts of water in scanty urine from kidneys Key Water Salt

Freshwater Animals 淡水魚生活於低張環境中，容易經由擴散作用流失鹽分，惟將由食物獲得補充或由鰓吸收
Freshwater animals constantly take in water by osmosis from their hypoosmotic environment They lose salts by diffusion and maintain water balance by excreting large amounts of dilute urine Salts lost by diffusion are replaced in foods and by uptake across the gills 淡水魚生活於低張環境中，容易經由擴散作用流失鹽分，惟將由食物獲得補充或由鰓吸收 © 2011 Pearson Education, Inc.

(b) Osmoregulation in a freshwater fish
Figure 44.3b (b) Osmoregulation in a freshwater fish Gain of water and some ions in food Uptake of salt ions by gills Osmotic water gain through gills and other parts of body surface Figure 44.3 Osmoregulation in marine and freshwater bony fishes: a comparison. Key Excretion of salt ions and large amounts of water in dilute urine from kidneys Water Salt

Figure 44.4 Figure 44.4 Sockeye salmon (Oncorhynchus nerka), euryhaline osmoregulators.

Animals That Live in Temporary Waters
Some aquatic invertebrates in temporary ponds lose almost all their body water and survive in a dormant state This adaptation is called anhydrobiosis脫水殘存作用；無水存活 cryptobiosis隱生 © 2011 Pearson Education, Inc.

(a) Hydrated tardigrade (b) Dehydrated tardigrade
Figure 44.5 50 m 50 m Figure 44.5 Anhydrobiosis. (a) Hydrated tardigrade (b) Dehydrated tardigrade

(a) Hydrated tardigrade
Figure 44.5a 50 m Figure 44.5 Anhydrobiosis. (a) Hydrated tardigrade

在隱生的情況下，一般可以在高溫（151 °C）、接近絕對零度（-272.8 °C）、高輻射、真空或高壓的環境下生存數分鐘至
Figure 44.5b 水熊蟲(緩步動物門)具有全部四種隱生（Cryptobiosis）性低濕隱生 (Anhydrobiosis）低溫隱生（Cryobiosis）變滲隱生（Osmobiosis）缺氧隱生（Anoxybiosis）能夠在惡劣環境下停止所有新陳代謝。被認為是生命力最強的動物。在隱生的情況下，一般可以在高溫（151 °C）、接近絕對零度（ °C）、高輻射、真空或高壓的環境下生存數分鐘至數日不等。曾經有緩步動物隱生超過120年的記錄。 50 m (b) Dehydrated tardigrade Figure 44.5 Anhydrobiosis.

Land Animals Adaptations to reduce water loss are key to survival on land Body coverings of most terrestrial animals help prevent dehydration Desert animals get major water savings from simple anatomical features and behaviors such as a nocturnal life style Land animals maintain water balance by eating moist food and producing water metabolically through cellular respiration © 2011 Pearson Education, Inc.

Water balance in a kangaroo rat (2 mL/day)
Figure 44.6 Water balance in a kangaroo rat (2 mL/day) Water balance in a human (2,500 mL/day) Ingested in food (0.2) Ingested in food (750) Ingested in liquid (1,500) Water gain (mL) Derived from metabolism (1.8) Derived from metabolism (250) Figure 44.6 Water balance in two terrestrial mammals. Feces (0.09) Feces (100) Water loss (mL) Urine (0.45) Urine (1,500) Evaporation (1.46) Evaporation (900)

Energetics of Osmoregulation
Osmoregulators must expend energy to maintain osmotic gradients The amount of energy differs based on How different the animal’s osmolarity is from its surroundings How easily water and solutes move across the animal’s surface The work required to pump solutes across the membrane © 2011 Pearson Education, Inc.

Transport Epithelia in Osmoregulation
Animals regulate the solute content of body fluid that bathes their cells Transport epithelia are epithelial cells that are specialized for moving solutes in specific directions They are typically arranged in complex tubular networks An example is in nasal glands of marine birds, which remove excess sodium chloride from the blood © 2011 Pearson Education, Inc.

Secretory cell of transport epithelium Lumen of secretory tubule Vein
Figure 44.7 Secretory cell of transport epithelium Lumen of secretory tubule Vein Artery Nasal salt gland Ducts Nasal gland Salt ions Capillary Secretory tubule Transport epithelium Nostril with salt secretions (a) Location of nasal glands in a marine bird (b) Secretory tubules Blood flow Salt secretion Figure 44.7 Countercurrent exchange in salt-excreting nasal glands. Key (c) Countercurrent exchange Salt movement Blood flow Central duct

Nostril with salt secretions
Figure 44.7a Nasal salt gland Ducts Nasal gland Nostril with salt secretions Figure 44.7 Countercurrent exchange in salt-excreting nasal glands. (a) Location of nasal glands in a marine bird

Vein Artery Nasal gland Capillary Secretory tubule
Figure 44.7b Vein Artery Nasal gland Capillary Secretory tubule Transport epithelium Figure 44.7 Countercurrent exchange in salt-excreting nasal glands. Key Salt movement Blood flow Central duct (b) Secretory tubules

Secretory cell of transport epithelium Lumen of secretory tubule
Figure 44.7c Secretory cell of transport epithelium Lumen of secretory tubule Salt ions Figure 44.7 Countercurrent exchange in salt-excreting nasal glands. Blood flow Salt secretion (c) Countercurrent exchange

Concept 44.2: An animal’s nitrogenous wastes reflect its phylogeny and habitat
The type and quantity of an animal’s waste products may greatly affect its water balance Among the most significant wastes are nitrogenous breakdown products of proteins and nucleic acids Some animals convert toxic ammonia (NH3) to less toxic compounds prior to excretion © 2011 Pearson Education, Inc.

Most aquatic animals, including most bony fishes
Figure 44.8 Proteins Nucleic acids Amino acids Nitrogenous bases —NH2 Amino groups Most aquatic animals, including most bony fishes Mammals, most amphibians, sharks, some bony fishes Many reptiles (including birds), insects, land snails Figure 44.8 Forms of nitrogenous waste. Ammonia Urea Uric acid

Most aquatic animals, including most bony fishes
Figure 44.8a Most aquatic animals, including most bony fishes Mammals, most amphibians, sharks, some bony fishes Many reptiles (including birds), insects, land snails Figure 44.8 Forms of nitrogenous waste. Ammonia Urea Uric acid

Forms of Nitrogenous Wastes
Animals excrete nitrogenous wastes in different forms: ammonia, urea, or uric acid These differ in toxicity and the energy costs of producing them © 2011 Pearson Education, Inc.

Urea The liver of mammals and most adult amphibians converts ammonia to the less toxic urea The circulatory system carries urea to the kidneys, where it is excreted Conversion of ammonia to urea is energetically expensive; excretion of urea requires less water than ammonia © 2011 Pearson Education, Inc.

Uric Acid Insects, land snails, and many reptiles, including birds, mainly excrete uric acid Uric acid is relatively nontoxic and does not dissolve readily in water It can be secreted as a paste with little water loss Uric acid is more energetically expensive to produce than urea © 2011 Pearson Education, Inc.

Figure 44.9 Figure 44.9 Recycling nitrogenous waste.

The Influence of Evolution and Environment on Nitrogenous Wastes
The kinds of nitrogenous wastes excreted depend on an animal’s evolutionary history and habitat, especially water availability Another factor is the immediate environment of the animal egg The amount of nitrogenous waste is coupled to the animal’s energy budget © 2011 Pearson Education, Inc.

Concept 44.3: Diverse excretory systems are variations on a tubular theme
Excretory systems regulate solute movement between internal fluids and the external environment © 2011 Pearson Education, Inc.

Excretory Processes Most excretory systems produce urine by refining a filtrate derived from body fluids Key functions of most excretory systems Filtration: Filtering of body fluids Reabsorption: Reclaiming valuable solutes Secretion: Adding nonessential solutes and wastes from the body fluids to the filtrate Excretion: Processed filtrate containing nitrogenous wastes, released from the body © 2011 Pearson Education, Inc.

1 Filtration Capillary Filtrate Excretory tubule 2 Reabsorption 3
Figure 44.10 1 Filtration Capillary Filtrate Excretory tubule 2 Reabsorption Figure Key steps of excretory system function: an overview. 3 Secretion Urine 4 Excretion

Survey of Excretory Systems
Systems that perform basic excretory functions vary widely among animal groups They usually involve a complex network of tubules © 2011 Pearson Education, Inc.

Protonephridia A protonephridium is a network of dead-end tubules connected to external openings The smallest branches of the network are capped by a cellular unit called a flame bulb These tubules excrete a dilute fluid and function in osmoregulation © 2011 Pearson Education, Inc.

Interstitial fluid flow Tubule
Figure 44.11 Nucleus of cap cell Flame bulb Cilia Interstitial fluid flow Tubule Tubules of protonephridia Opening in body wall Figure Protonephridia: the flame bulb system of a planarian. Tubule cell

Metanephridia Each segment of an earthworm has a pair of open-ended metanephridia Metanephridia consist of tubules that collect coelomic fluid and produce dilute urine for excretion © 2011 Pearson Education, Inc.

Components of a metanephridium:
Figure 44.12 Coelom Capillary network Components of a metanephridium: Collecting tubule Figure Metanephridia of an earthworm. Internal opening Bladder External opening

Malpighian Tubules In insects and other terrestrial arthropods, Malpighian tubules remove nitrogenous wastes from hemolymph and function in osmoregulation Insects produce a relatively dry waste matter, mainly uric acid, an important adaptation to terrestrial life Some terrestrial insects can also take up water from the air © 2011 Pearson Education, Inc.

Salt, water, and nitrogenous wastes
Figure 44.13 Digestive tract Rectum Hindgut Intestine Midgut (stomach) Malpighian tubules Salt, water, and nitrogenous wastes Feces and urine To anus Malpighian tubule Figure Malpighian tubules of insects. Rectum Reabsorption HEMOLYMPH

Excretory Organs Kidney Structure Nephron Types Cortical nephron
Figure a Excretory Organs Kidney Structure Nephron Types Cortical nephron Juxtamedullary nephron Renal cortex Posterior vena cava Renal medulla Renal artery Renal artery and vein Kidney Renal vein Renal cortex Aorta Ureter Figure Exploring: the Mammalian Excretory System Ureter Renal medulla Urinary bladder Urethra Renal pelvis

Nephron Organization Afferent arteriole from renal artery Glomerulus
Figure b Nephron Organization Afferent arteriole from renal artery Glomerulus Bowman’s capsule Proximal tubule Peritubular capillaries Distal tubule Efferent arteriole from glomerulus Branch of renal vein Figure Exploring: the Mammalian Excretory System Descending limb Loop of Henle Vasa recta Collecting duct 200 m Ascending limb Blood vessels from a human kidney. Arterioles and peritubular capillaries appear pink; glomeruli appear yellow.

Excretory Organs Posterior vena cava Renal artery and vein Kidney
Figure 44.14a Excretory Organs Posterior vena cava Renal artery and vein Kidney Figure Exploring: the Mammalian Excretory System Aorta Ureter Urinary bladder Urethra

Kidney Structure Renal cortex Renal medulla Renal artery Renal vein
Figure 44.14b Kidney Structure Renal cortex Renal medulla Renal artery Renal vein Figure Exploring: the Mammalian Excretory System Ureter Renal pelvis

Nephron Types Juxtamedullary Cortical nephron Nephron 進髓質腎元
Figure 44.14c Nephron Types Juxtamedullary Nephron 進髓質腎元 Cortical nephron Renal cortex Figure Exploring: the Mammalian Excretory System Renal medulla

Nephron Organization Afferent arteriole from renal artery Glomerulus
Figure 44.14d Nephron Organization Afferent arteriole from renal artery Glomerulus Bowman’s capsule Proximal tubule Peritubular capillaries Distal tubule Efferent arteriole from glomerulus Branch of renal vein Figure Exploring: the Mammalian Excretory System Descending limb Loop of Henle Vasa recta Collecting duct Ascending limb

Figure 44.14e Figure Exploring: the Mammalian Excretory System 200 m Blood vessels from a human kidney. Arterioles and peritubular capillaries appear pink; glomeruli appear yellow.

Concept 44.4: The nephron is organized for stepwise processing of blood filtrate
The filtrate produced in Bowman’s capsule contains salts, glucose, amino acids, vitamins, nitrogenous wastes, and other small molecules © 2011 Pearson Education, Inc.

From Blood Filtrate to Urine: A Closer Look
Proximal Tubule 近曲小管 Reabsorption of ions, water, and nutrients takes place in the proximal tubule Molecules are transported actively and passively from the filtrate into the interstitial fluid and then capillaries Some toxic materials are actively secreted into the filtrate As the filtrate passes through the proximal tubule, materials to be excreted become concentrated © 2011 Pearson Education, Inc.

Animation: Bowman’s Capsule and Proximal Tubule
Right-click slide / select “Play” © 2011 Pearson Education, Inc.

Proximal tubule Distal tubule Filtrate CORTEX Loop of Henle
Figure 44.15 Proximal tubule Distal tubule NaCl Nutrients H2O HCO3 H2O K NaCl HCO3 H NH3 K H Filtrate CORTEX Loop of Henle NaCl H2O OUTER MEDULLA NaCl Collecting duct Figure The nephron and collecting duct: regional functions of the transport epithelium. Key Urea Active transport NaCl H2O Passive transport INNER MEDULLA

Descending Limb of the Loop of Henle
Reabsorption of water continues through channels formed by aquaporin proteins Movement is driven by the high osmolarity of the interstitial fluid, which is hyperosmotic to the filtrate The filtrate becomes increasingly concentrated © 2011 Pearson Education, Inc.

Ascending Limb of the Loop of Henle
In the ascending limb of the loop of Henle, salt but not water is able to diffuse from the tubule into the interstitial fluid The filtrate becomes increasingly dilute © 2011 Pearson Education, Inc.

Animation: Loop of Henle and Distal Tubule

Collecting Duct 集尿管 The collecting duct carries filtrate through the medulla腎髓質 to the renal pelvis 腎盂 One of the most important tasks is reabsorption of solutes and water Urine is hyperosmotic to body fluids © 2011 Pearson Education, Inc.

Animation: Collecting Duct

Solute Gradients and Water Conservation
The mammalian kidney’s ability to conserve water is a key terrestrial adaptation Hyperosmotic urine can be produced only because considerable energy is expended to transport solutes against concentration gradients The two primary solutes affecting osmolarity are NaCl and urea © 2011 Pearson Education, Inc.

The Two-Solute Model In the proximal tubule, filtrate volume decreases, but its osmolarity remains the same The countercurrent multiplier system involving the loop of Henle maintains a high salt concentration in the kidney This system allows the vasa recta直血管 to supply the kidney with nutrients, without interfering with the osmolarity gradient Considerable energy is expended to maintain the osmotic gradient between the medulla and cortex © 2011 Pearson Education, Inc.

The collecting duct conducts filtrate through the osmolarity gradient, and more water exits the filtrate by osmosis Urea diffuses out of the collecting duct as it traverses the inner medulla Urea and NaCl form the osmotic gradient that enables the kidney to produce urine that is hyperosmotic to the blood © 2011 Pearson Education, Inc.

Osmolarity of interstitial fluid (mOsm/L)
Figure Osmolarity of interstitial fluid (mOsm/L) 300 300 300 300 H2O CORTEX 400 400 H2O H2O OUTER MEDULLA H2O 600 600 Figure How the human kidney concentrates urine: the two-solute model. H2O H2O 900 900 Key H2O INNER MEDULLA Active transport 1,200 1,200 Passive transport

Figure Osmolarity of interstitial fluid (mOsm/L) 300 300 300 100 100 300 H2O NaCl CORTEX 400 200 400 H2O NaCl H2O NaCl OUTER MEDULLA H2O NaCl 600 400 600 Figure How the human kidney concentrates urine: the two-solute model. H2O NaCl H2O NaCl 900 700 900 Key H2O NaCl INNER MEDULLA Active transport 1,200 1,200 Passive transport

Figure Osmolarity of interstitial fluid (mOsm/L) 300 300 300 100 100 300 300 H2O NaCl H2O CORTEX 400 200 400 400 H2O NaCl H2O NaCl H2O NaCl H2O NaCl OUTER MEDULLA H2O NaCl H2O 600 400 600 600 Figure How the human kidney concentrates urine: the two-solute model. H2O NaCl H2O Urea H2O NaCl H2O 900 700 900 Urea Key H2O NaCl H2O INNER MEDULLA Urea Active transport 1,200 1,200 1,200 Passive transport

Adaptations of the Vertebrate Kidney to Diverse Environments
The form and function of nephrons in various vertebrate classes are related to requirements for osmoregulation in the animal’s habitat © 2011 Pearson Education, Inc.

Mammals The juxtamedullary nephron is key to water conservation in terrestrial animals Mammals that inhabit dry environments have long loops of Henle, while those in fresh water have relatively short loops © 2011 Pearson Education, Inc.

Birds and Other Reptiles
Birds have shorter loops of Henle but conserve water by excreting uric acid instead of urea Other reptiles have only cortical nephrons but also excrete nitrogenous waste as uric acid © 2011 Pearson Education, Inc.

Figure 44.17 Figure The roadrunner (Geococcyx californianus), an animal well adapted to its dry environment.

Freshwater Fishes and Amphibians
Freshwater fishes conserve salt in their distal tubules and excrete large volumes of dilute urine Kidney function in amphibians is similar to freshwater fishes Amphibians conserve water on land by reabsorbing water from the urinary bladder © 2011 Pearson Education, Inc.

Marine Bony Fishes Marine bony fishes are hypoosmotic compared with their environment Their kidneys have small glomeruli and some lack glomeruli entirely Filtration rates are low, and very little urine is excreted © 2011 Pearson Education, Inc.

Concept 44.5: Hormonal circuits link kidney function, water balance, and blood pressure
Mammals control the volume and osmolarity of urine The kidneys of the South American vampire bat吸血蝙蝠 can produce either very dilute or very concentrated urine This allows the bats to reduce their body weight rapidly or digest large amounts of protein while conserving water © 2011 Pearson Education, Inc.

Figure 44.18 Figure A vampire bat (Desmodus rotundas), a mammal with a unique excretory situation.

Antidiuretic Hormone The osmolarity of the urine is regulated by nervous and hormonal control Antidiuretic hormone (ADH) makes the collecting duct epithelium more permeable to water An increase in osmolarity triggers the release of ADH, which helps to conserve water © 2011 Pearson Education, Inc.

Animation: Effect of ADH

Osmoreceptors in hypothalamus trigger release of ADH.
Figure Osmoreceptors in hypothalamus trigger release of ADH. Thirst Hypothalamus ADH Pituitary gland STIMULUS: Increase in blood osmolarity (for instance, after sweating profusely) Figure Regulation of fluid retention in the kidney by antidiuretic hormone (ADH). Homeostasis: Blood osmolarity (300 mOsm/L)

Osmoreceptors in hypothalamus trigger release of ADH.
Figure Osmoreceptors in hypothalamus trigger release of ADH. Thirst Hypothalamus Drinking reduces blood osmolarity to set point. ADH Increased permeability Pituitary gland Distal tubule STIMULUS: Increase in blood osmolarity (for instance, after sweating profusely) Figure Regulation of fluid retention in the kidney by antidiuretic hormone (ADH). H2O reabsorption helps prevent further osmolarity increase. Collecting duct Homeostasis: Blood osmolarity (300 mOsm/L)

Second-messenger signaling molecule
Figure 44.20 ADH receptor LUMEN Collecting duct COLLECTING DUCT CELL ADH cAMP Second-messenger signaling molecule Storage vesicle Exocytosis Figure ADH response pathway in the collecting duct. Aquaporin water channel H2O H2O

Alcohol is a diuretic as it inhibits the release of ADH
Mutation in ADH production causes severe dehydration and results in diabetes insipidus尿崩症 Alcohol is a diuretic as it inhibits the release of ADH © 2011 Pearson Education, Inc.

Aquaporin gene H2O (control)
Figure 44.21 EXPERIMENT 1 Prepare copies of human aquaporin genes: two mutants plus wild type. Aquaporin gene Promoter Mutant 1 Mutant 2 Wild type 2 Synthesize mRNA. H2O (control) 3 Inject mRNA into frog oocytes. 4 Transfer to 10-mOsm solution and observe results. Aquaporin proteins Figure Inquiry: Can aquaporin mutations cause diabetes insipidus? RESULTS Injected RNA Permeability (m/sec) Wild-type aquaporin 196 None 20 Aquaporin mutant 1 17 Aquaporin mutant 2 18

Aquaporin gene H2O (control)
Figure 44.21a EXPERIMENT 1 Aquaporin gene Prepare copies of human aquaporin genes: two mutants plus wild type. Promoter Mutant 1 Mutant 2 Wild type 2 Synthesize mRNA. H2O (control) 3 Inject mRNA into frog oocytes. Figure Inquiry: Can aquaporin mutations cause diabetes insipidus? 4 Transfer to 10-mOsm solution and observe results. Aquaporin proteins

Permeability (m/sec)
Figure 44.21b RESULTS Injected RNA Permeability (m/sec) Wild-type aquaporin 196 None 20 Aquaporin mutant 1 17 Figure Inquiry: Can aquaporin mutations cause diabetes insipidus? Aquaporin mutant 2 18

The Renin-Angiotensin-Aldosterone System
The renin-angiotensin-aldosterone system (RAAS) is part of a complex feedback circuit that functions in homeostasis A drop in blood pressure near the glomerulus causes the juxtaglomerular apparatus (JGA) to release the enzyme renin Renin triggers the formation of the peptide angiotensin II © 2011 Pearson Education, Inc.

Homeostasis: Blood pressure, volume
Figure JGA releases renin. Distal tubule Renin Juxtaglomerular apparatus (JGA) STIMULUS: Low blood volume or blood pressure (for example, due to dehydration or blood loss) Figure Regulation of blood volume and blood pressure by the renin-angiotensin-aldosterone system (RAAS). Homeostasis: Blood pressure, volume

Homeostasis: Blood pressure, volume
Figure Liver Angiotensinogen JGA releases renin. Distal tubule Renin Angiotensin I ACE Angiotensin II Juxtaglomerular apparatus (JGA) STIMULUS: Low blood volume or blood pressure (for example, due to dehydration or blood loss) Figure Regulation of blood volume and blood pressure by the renin-angiotensin-aldosterone system (RAAS). Homeostasis: Blood pressure, volume

Juxtaglomerular apparatus (JGA)
Figure Liver Angiotensinogen JGA releases renin. Distal tubule Renin Angiotensin I ACE Angiotensin II Juxtaglomerular apparatus (JGA) STIMULUS: Low blood volume or blood pressure (for example, due to dehydration or blood loss) Adrenal gland Figure Regulation of blood volume and blood pressure by the renin-angiotensin-aldosterone system (RAAS). Aldosterone Arterioles constrict, increasing blood pressure. More Na and H2O are reabsorbed in distal tubules, increasing blood volume. Homeostasis: Blood pressure, volume

Homeostatic Regulation of the Kidney
ADH and RAAS both increase water reabsorption, but only RAAS will respond to a decrease in blood volume Another hormone, atrial natriuretic peptide (ANP), opposes the RAAS ANP is released in response to an increase in blood volume and pressure and inhibits the release of renin © 2011 Pearson Education, Inc.

Figure 44.UN01 Animal Inflow/Outflow Urine Freshwater fish. Lives in water less concentrated than body fluids; fish tends to gain water, lose salt Does not drink water Large volume of urine Salt in (active transport by gills) H2O in Urine is less concentrated than body fluids Salt out Marine bony fish. Lives in water more concentrated than body fluids; fish tends to lose water, gain salt Drinks water Small volume of urine Salt in H2O out Urine is slightly less concentrated than body fluids Salt out (active transport by gills) Figure 44.UN01 Summary figure, Concept 44.1 Terrestrial vertebrate. Terrestrial environment; tends to lose body water to air Drinks water Moderate volume of urine Salt in (by mouth) Urine is more concentrated than body fluids H2O and salt out

Salt in (active transport by gills) H2O in
Figure 44.UN01a Animal Inflow/Outflow Urine Freshwater fish. Lives in water less concentrated than body fluids; fish tends to gain water, lose salt Does not drink water Large volume of urine Salt in (active transport by gills) H2O in Urine is less concentrated than body fluids Figure 44.UN01 Summary figure, Concept 44.1 Salt out

Urine is slightly less concentrated than body fluids
Figure 44.UN01b Animal Inflow/Outflow Urine Marine bony fish. Lives in water more concentrated than body fluids; fish tends to lose water, gain salt Drinks water Small volume of urine Salt in H2O out Urine is slightly less concentrated than body fluids Figure 44.UN01 Summary figure, Concept 44.1 Salt out (active transport by gills)

Moderate volume of urine Salt in (by mouth)
Figure 44.UN01c Animal Inflow/Outflow Urine Terrestrial vertebrate. Terrestrial environment; tends to lose body water to air Drinks water Moderate volume of urine Salt in (by mouth) Urine is more concentrated than body fluids Figure 44.UN01 Summary figure, Concept 44.1 H2O and salt out

Figure 44.UN02 Figure 44.UN02 Appendix A: answer to Test Your Understanding, question 7

Osmoregulation and Excretion 滲透調節作用與排泄作用

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