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Fig. 44-1 Osmoregulation and Excretion Chapter 44 Osmoregulation is based largely on controlled movement of solutes between internal fluids and the external.

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Presentation on theme: "Fig. 44-1 Osmoregulation and Excretion Chapter 44 Osmoregulation is based largely on controlled movement of solutes between internal fluids and the external."— Presentation transcript:

1 Fig Osmoregulation and Excretion Chapter 44 Osmoregulation is based largely on controlled movement of solutes between internal fluids and the external environment

2 Osmotic Challenges Osmoconformers, consisting only of some marine animals, are isoosmotic with their surroundings and do not regulate their osmolarity Osmoregulators expend energy to control water uptake and loss in a hyperosmotic or hypoosmotic environment Most animals are stenohaline; they cannot tolerate substantial changes in external osmolarity Euryhaline animals can survive large fluctuations in external osmolarity

3 Fig Excretion of salt ions from gills Gain of water and salt ions from food Osmotic water loss through gills and other parts of body surface Uptake of water and some ions in food Uptake of salt ions by gills Osmotic water gain through gills and other parts of body surface Excretion of large amounts of water in dilute urine from kidneys Excretion of salt ions and small amounts of water in scanty urine from kidneys Gain of water and salt ions from drinking seawater (a) Osmoregulation in a saltwater fish(b) Osmoregulation in a freshwater fish

4 Fig (a) Hydrated tardigrade (b) Dehydrated tardigrade 100 µm anhydrobiosis

5 Fig Water gain (mL) Water loss (mL) Urine (0.45) Urine (1,500) Evaporation (1.46) Evaporation (900) Feces (0.09)Feces (100) Derived from metabolism (1.8) Derived from metabolism (250) Ingested in food (750) Ingested in food (0.2) Ingested in liquid (1,500) Water balance in a kangaroo rat (2 mL/day) Water balance in a human (2,500 mL/day) Land Animals

6 Transport Epithelia in Osmoregulation Animals regulate the composition of body fluid that bathes their cells Transport epithelia are specialized epithelial cells that regulate solute movement They are essential components of osmotic regulation and metabolic waste disposal They are arranged in complex tubular networks An example is in salt glands of marine birds, which remove excess sodium chloride from the blood

7 Fig Ducts Nostril with salt secretions Nasal salt gland EXPERIMENT

8 Fig Salt gland Secretory cell Capillary Secretory tubule Transport epithelium Direction of salt movement Central duct (a) Blood flow (b) Secretory tubule ArteryVein NaCl Salt secretion Countercurrent exchange

9 The type and quantity of an animal’s waste products may greatly affect its water balance Among the most important wastes are nitrogenous breakdown products of proteins and nucleic acids Some animals convert toxic ammonia (NH 3 ) to less toxic compounds prior to excretion

10 Fig Many reptiles (including birds), insects, land snails AmmoniaUric acid Urea Most aquatic animals, including most bony fishes Mammals, most amphibians, sharks, some bony fishes Nitrogenous bases Amino acids Proteins Nucleic acids Amino groups Concept 44.2: An animal’s nitrogenous wastes reflect its phylogeny and habitat

11 Fig Capillary Secretion adding toxins and other solutes from the body fluids to the filtrate Reabsorption Excretory tubule Filtration: pressure-filtering of body fluids Filtrate Urine reclaiming valuable solutes Excretion removing the filtrate from the system Key functions of most excretory systems:

12 Fig Tubule Tubules of protonephridia Cilia Interstitial fluid flow Opening in body wall Nucleus of cap cell Flame bulb Tubule cell

13 Fig Capillary network Components of a metanephridium: External opening Coelom Collecting tubule Internal opening Bladder

14 Fig Rectum Digestive tract Hindgut Intestine Malpighian tubules Rectum Feces and urine HEMOLYMPH Reabsorption Midgut (stomach) Salt, water, and nitrogenous wastes

15 Structure of the Mammalian Excretory System The mammalian excretory system centers on paired kidneys, which are also the principal site of water balance and salt regulation Each kidney is supplied with blood by a renal artery and drained by a renal vein Urine exits each kidney through a duct called the ureter Both ureters drain into a common urinary bladder, and urine is expelled through a urethra

16 Fig Posterior vena cava Renal artery and vein Urinary bladder Ureter Aorta Urethra Kidney (a) Excretory organs and major associated blood vessels Cortical nephron Juxtamedullary nephron Collecting duct (c) Nephron types To renal pelvis Renal medulla Renal cortex 10 µm Afferent arteriole from renal artery Efferent arteriole from glomerulus SEM Branch of renal vein Descending limb Ascending limb Loop of Henle ( d) Filtrate and blood flow Vasa recta Collecting duct Distal tubule Peritubular capillaries Proximal tubule Bowman’s capsule Glomerulus Ureter Renal medulla Renal cortex Renal pelvis (b) Kidney structure Section of kidney from a rat 4 mm

17 Fig b (b) Kidney structure Section of kidney from a rat 4 mm Renal cortex Renal medulla Renal pelvis Ureter

18 Fig cd Cortical nephron Juxtamedullary nephron Collecting duct (c) Nephron types To renal pelvis Renal medulla Renal cortex 10 µm Afferent arteriole from renal artery Efferent arteriole from glomerulus SEM Branch of renal vein Descending limb Ascending limb Loop of Henle (d) Filtrate and blood flow Vasa recta Collecting duct Distal tubule Peritubular capillaries Proximal tubule Bowman’s capsule Glomerulus

19 The nephron, the functional unit of the vertebrate kidney, consists of a single long tubule and a ball of capillaries called the glomerulus Bowman’s capsule surrounds and receives filtrate from the glomerulus

20 Fig c Cortical nephron Juxtamedullary nephron Collecting duct (c) Nephron types To renal pelvis Renal medulla Renal cortex

21 Fig d Afferent arteriole from renal artery Efferent arteriole from glomerulus SEM Branch of renal vein Descending limb Ascending limb Loop of Henle (d) Filtrate and blood flow Vasa recta Collecting duct Distal tubule Peritubular capillaries Proximal tubule Bowman’s capsule Glomerulus 10 µm

22 Filtration of the Blood Filtration occurs as blood pressure forces fluid from the blood in the glomerulus into the lumen of Bowman’s capsule Filtration of small molecules is nonselective The filtrate contains salts, glucose, amino acids, vitamins, nitrogenous wastes, and other small molecules

23 Pathway of the Filtrate From Bowman’s capsule, the filtrate passes through three regions of the nephron: the proximal tubule, the loop of Henle, and the distal tubule Fluid from several nephrons flows into a collecting duct, all of which lead to the renal pelvis, which is drained by the ureter Cortical nephrons are confined to the renal cortex, while juxtamedullary nephrons have loops of Henle that descend into the renal medulla

24 Blood Vessels Associated with the Nephrons Each nephron is supplied with blood by an afferent arteriole, a branch of the renal artery that divides into the capillaries The capillaries converge as they leave the glomerulus, forming an efferent arteriole The vessels divide again, forming the peritubular capillaries, which surround the proximal and distal tubules Vasa recta are capillaries that serve the loop of Henle The vasa recta and the loop of Henle function as a countercurrent system

25 Concept 44.4: The nephron is organized for stepwise processing of blood filtrate The mammalian kidney conserves water by producing urine that is much more concentrated than body fluids

26 Fig Key Active transport Passive transport INNER MEDULLA OUTER MEDULLA H2OH2O CORTEX Filtrate Loop of Henle H2OH2OK+K+ HCO 3 – H+H+ NH 3 Proximal tubule NaClNutrients Distal tubule K+K+ H+H+ HCO 3 – H2OH2O H2OH2O NaCl Urea Collecting duct NaCl H2O Salts HCO3- H+ Urea Glucose Amino acid Some drugs

27 From Blood Filtrate to Urine: A Closer Look Proximal Tubule 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 secreted into the filtrate The filtrate volume decreases

28 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 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 The thin segment: NaCl diffuses out to help maintain the osmolarity of the interstitial fluid The thick segment: actively transports NaCl into the interstitial fluid

29 Distal Tubule The distal tubule regulates the K+ and NaCl concentrations of body fluids The controlled movement of ions contributes to pH regulation Collecting Duct The collecting duct carries filtrate through the medulla to the renal pelvis Water is lost as well as some salt and urea, and the filtrate becomes more concentrated Urine is hyperosmotic to body fluids

30 Solute Gradients and Water Conservation Urine is much more concentrated than blood – The osmolarity of blood is about 300 mOsm/L – Urine: 1,200mOsm/L, Australian hopping mice:9,300mOsm/L The cooperative action and precise arrangement of the loops of Henle and collecting ducts are largely responsible for the osmotic gradient that concentrates the urine NaCl (the loop of Henle) and urea (the collecting duct) contribute to the osmolarity of the interstitial fluid, which causes reabsorption of water in the kidney and concentrates the urine

31 Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig Anatomy of gills Gill arch Water flow Operculum Gill arch Gill filament organization Blood vessels Oxygen-poor blood Oxygen-rich blood Fluid flow through gill filament Lamella Blood flow through capillaries in lamella Water flow between lamellae Countercurrent exchange P O 2 (mm Hg) in water P O 2 (mm Hg) in blood Net diffu- sion of O 2 from water to blood Gill filaments To maximize oxygen absorption by fish gills The countercurrent mechanisms involve passive movement

32 Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig Canada gooseBottlenose dolphin Artery Vein Blood flow 33º35ºC 27º 30º 18º 20º 10º9º To reduce heat loss in endotherms The countercurrent mechanisms involve passive movement

33 Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings countercurrent multiplier systems The countercurrent system involvig the loop of Henle expends energy to actively transport NaCl from the filtrate in the upper part of the ascending limb of the loop. To expend energy to create concentration gradients, are called countercurrent multiplier systems.

34 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 – Considerable energy is expended to maintain the osmotic gradient between the medulla and cortex This system allows the vasa recta to supply the kidney with nutrients, without interfering with the osmolarity gradient – Descending vessel conveys blood toward the inner medulla: water lost and NaCl isgained by diffusion. – Ascending vessel: these fluxess are reversed

35 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

36 Fig Key Active transport Passive transport INNER MEDULLA OUTER MEDULLA CORTEX H2OH2O 300 H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O 1,200 H2OH2O 300 Osmolarity of interstitial fluid (mOsm/L) ,200

37 Fig Key Active transport Passive transport INNER MEDULLA OUTER MEDULLA CORTEX H2OH2O 300 H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O 1,200 H2OH2O 300 Osmolarity of interstitial fluid (mOsm/L) , NaCl 100 NaCl

38 Fig Key Active transport Passive transport INNER MEDULLA OUTER MEDULLA CORTEX H2OH2O 300 H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O 1,200 H2OH2O 300 Osmolarity of interstitial fluid (mOsm/L) , NaCl 100 NaCl , H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O NaCl Urea

39 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 The juxtamedullary nephron contributes 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 Mammals

40 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 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

41 Antidiuretic Hormone (vasopressin) The osmolarity of the urine is regulated by nervous and hormonal control of water and salt reabsorption in the kidneys Antidiuretic hormone (ADH) increases water reabsorption in the distal tubules and collecting ducts of the kidney An increase in osmolarity  ADH  increase in the number of aquaporin molecules in the membranes of collecting duct cells. Diabetes insipidus

42 Fig Thirst Drinking reduces blood osmolarity to set point. Osmoreceptors in hypothalamus trigger release of ADH. Increased permeability Pituitary gland ADH Hypothalamus Distal tubule H 2 O reab- sorption helps prevent further osmolarity increase. STIMULUS: Increase in blood osmolarity Collecting duct Homeostasis: Blood osmolarity (300 mOsm/L) (a) Exocytosis (b) Aquaporin water channels H2OH2O H2OH2O Storage vesicle Second messenger signaling molecule cAMP INTERSTITIAL FLUID ADH receptor ADH COLLECTING DUCT LUMEN COLLECTING DUCT CELL

43 Fig a-1 Thirst Osmoreceptors in hypothalamus trigger release of ADH. Pituitary gland ADH Hypothalamus STIMULUS: Increase in blood osmolarity Homeostasis: Blood osmolarity (300 mOsm/L) (a)

44 Fig a-2 Thirst Drinking reduces blood osmolarity to set point. Increased permeability Pituitary gland ADH Hypothalamus Distal tubule H 2 O reab- sorption helps prevent further osmolarity increase. STIMULUS: Increase in blood osmolarity Collecting duct Homeostasis: Blood osmolarity (300 mOsm/L) (a) Osmoreceptors in hypothalamus trigger release of ADH.

45 Fig b Exocytosis (b) Aquaporin water channels H2OH2O H2OH2O Storage vesicle Second messenger signaling molecule cAMP INTERSTITIAL FLUID ADH receptor ADH COLLECTING DUCT LUMEN COLLECTING DUCT CELL 1.Mutation in ADH production causes severe dehydration and results in diabetes insipidus 2.Alcohol is a diuretic as it inhibits the release of ADH

46 Fig Prepare copies of human aqua- porin genes. 196 Transfer to 10 mOsm solution. Synthesize RNA transcripts. EXPERIMENT Mutant 1 Mutant 2 Aquaporin gene Promoter Wild type H 2 O (control) Inject RNA into frog oocytes. Aquaporin protein RESULTS Permeability (µm/s) Injected RNA Wild-type aquaporin None Aquaporin mutant 1 Aquaporin mutant 2

47 Fig a Prepare copies of human aqua- porin genes. Transfer to 10 mOsm solution. Synthesize RNA transcripts. EXPERIMENT Mutant 1 Mutant 2Wild type H 2 O (control) Inject RNA into frog oocytes. Aquaporin protein Promoter Aquaporin gene

48 Fig b 196 RESULTS Permeability (µm/s) Injected RNA Wild-type aquaporin None Aquaporin mutant 1 Aquaporin mutant 2

49 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 Angiotensin II – Raises blood pressure and decreases blood flow to the kidneys – Stimulates the release of the hormone aldosterone, which increases blood volume and pressure

50 Fig Renin Distal tubule Juxtaglomerular apparatus (JGA) STIMULUS: Low blood volume or blood pressure Homeostasis: Blood pressure, volume

51 Fig Renin Distal tubule Juxtaglomerular apparatus (JGA) STIMULUS: Low blood volume or blood pressure Homeostasis: Blood pressure, volume Liver Angiotensinogen Angiotensin I ACE Angiotensin II

52 Fig Renin Distal tubule Juxtaglomerular apparatus (JGA) STIMULUS: Low blood volume or blood pressure (due to dehydration or blood loss) Homeostasis: Blood pressure, volume Liver Angiotensinogen Angiotensin I ACE Angiotensin II Adrenal gland Aldosterone Arteriole constriction Increased Na + and H 2 O reabsorption in distal tubules Angiotensin converting enzyme

53 Homeostatic Regulation of the Kidney ADH and RAAS both increase water reabsorption, but only RAAS will respond to a decrease in blood volume – A situation that causes an excessive loss of both salt and body fluids—a major wound, for example, or severe diarrhea will reduce blood volume without increasing osmolarity.  This will not affect ADH release, but the RAAS will respond to the drop in blood volume and pressure by increasing water and Na+ reabsorption. Another hormone, atrial natriuretic peptide (ANP), opposes the RAAS

54 ANP –ANP is released in response to an increase in blood volume and pressure and the release of renin –ANP( the wall of the atria of the heart)--> inhibits renin from the JGA  Inhibits NaCl reabsorption by the collecting ducts and reduces aldosterone release from the adrenal glands  lower blood volume and pressure –Thus, ADH, the RASS, and ANP are provided to control the osmolarity, salt concentration, volume, and pressure of blood

55 Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Conn’s syndrome? A tumor in the adrenal cortex  high amounts of aldosterone – The major symptom?


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