Control of Body Temperature and Water Balance Chapter 25 Control of Body Temperature and Water Balance

Functions of the Excretory System All organisms must eliminate waste products!! EXTERNAL ENVIRONMENT CO2 Food O2 respiratory system Eliminates CO2 and excess H+. Mouth ANIMAL Functions of the Excretory System -- Maintains salt/water balance -- Eliminates metabolic wastes, drugs, toxins -- Indirect regulation of blood pressure and pH digestive system eliminates solid wastes B l o d Respiratory system Digestive system Interstitial fluid Heart Nutrients Circulatory system Body cells Urinary system Intestine Anus Unabsorbed matter (feces) Metabolic waste products (urine)

Osmoregulation = The Balance of water and solute levels in body fluids. Osmoconformers (marine invertebrates) have body fluids with a [solute] = to [seawater] Osmoregulators (land animals, freshwater animals, saltwater fish) have body fluids with [solute] that differ from environment must actively regulate water movement Student Misconceptions and Concerns The idea that a freshwater fish never drinks can be conceptually challenging, especially for students who have heard the old saying “drinks like a fish”! Consider introducing your discussion of osmoregulation with this remarkable and seemingly counterintuitive fact to generate interest. Teaching Tips Students may better understand the challenges of osmoregulation in freshwater fish if they are reminded of what occurs when humans soak their hands in water. Students will likely recall that this causes the skin on their hands to wrinkle, and some may have noticed that their skin wrinkles even faster in soapy water. Skin absorbs water by osmosis (just as a freshwater fish gains water). Oils on our skin reduce the influx of water. Soapy water, which washes away these oils, speeds up the process. The wrinkling occurs because the skin can expand only in certain areas, creating puckers. Osmoregulation strategy depends on animal’s habitat!! © 2012 Pearson Education, Inc. 3

Osmoregulation = Balance of solutes and water Freshwater fish gain water by osmosis (mainly through gills), take in salt by active transport through their gills and in food excrete excess water in dilute urine. Passive water gain through gills Salts actively Taken up by gills Student Misconceptions and Concerns The idea that a freshwater fish never drinks can be conceptually challenging, especially for students who have heard the old saying “drinks like a fish”! Consider introducing your discussion of osmoregulation with this remarkable and seemingly counterintuitive fact to generate interest. Teaching Tips Students may better understand the challenges of osmoregulation in freshwater fish if they are reminded of what occurs when humans soak their hands in water. Students will likely recall that this causes the skin on their hands to wrinkle, and some may have noticed that their skin wrinkles even faster in soapy water. Skin absorbs water by osmosis (just as a freshwater fish gains water). Oils on our skin reduce the influx of water. Soapy water, which washes away these oils, speeds up the process. The wrinkling occurs because the skin can expand only in certain areas, creating puckers. Excretion of dilute urine from kidneys FRESH WATER (hypotonic environment) Osmoregulation strategy depends on animal’s habitat!! © 2012 Pearson Education, Inc. 4

(hypertonic environment) Osmoregulation = Balance of solutes and water Saltwater fish lose water by osmosis from the gills and body surface, drink seawater, and use their gills and kidneys to excrete excess salt. Passive loss of water through gills Drinks seawater Student Misconceptions and Concerns The idea that a freshwater fish never drinks can be conceptually challenging, especially for students who have heard the old saying “drinks like a fish”! Consider introducing your discussion of osmoregulation with this remarkable and seemingly counterintuitive fact to generate interest. Teaching Tips Students may better understand the challenges of osmoregulation in freshwater fish if they are reminded of what occurs when humans soak their hands in water. Students will likely recall that this causes the skin on their hands to wrinkle, and some may have noticed that their skin wrinkles even faster in soapy water. Skin absorbs water by osmosis (just as a freshwater fish gains water). Oils on our skin reduce the influx of water. Soapy water, which washes away these oils, speeds up the process. The wrinkling occurs because the skin can expand only in certain areas, creating puckers. SALT WATER (hypertonic environment) Excretion of concentrated urine Salts actively excreted by gills © 2012 Pearson Education, Inc. 5

Osmoregulation = Balance of solutes and water Land animals risk of dehydration lose water by evaporation and waste disposal gain water by drinking and eating conserve water by efficient kidneys. Student Misconceptions and Concerns The idea that a freshwater fish never drinks can be conceptually challenging, especially for students who have heard the old saying “drinks like a fish”! Consider introducing your discussion of osmoregulation with this remarkable and seemingly counterintuitive fact to generate interest. Teaching Tips Students may better understand the challenges of osmoregulation in freshwater fish if they are reminded of what occurs when humans soak their hands in water. Students will likely recall that this causes the skin on their hands to wrinkle, and some may have noticed that their skin wrinkles even faster in soapy water. Skin absorbs water by osmosis (just as a freshwater fish gains water). Oils on our skin reduce the influx of water. Soapy water, which washes away these oils, speeds up the process. The wrinkling occurs because the skin can expand only in certain areas, creating puckers. © 2012 Pearson Education, Inc. 6

Disposal of Nitrogenous and metabolic wastes Metabolism produces toxic by-products. Nitrogenous wastes = breakdown products of proteins and nucleic acids. Animals dispose of nitrogenous wastes in different ways. Student Misconceptions and Concerns The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store. Teaching Tips Student experience with osmoregulation not pertaining to their bodies may be quite limited. However, many students are familiar with the pasty white color of bird droppings. Consider beginning your discussion of nitrogenous wastes by asking your class to explain why bird droppings are white. © 2012 Pearson Education, Inc. 7

The Human Urinary System The urinary system forms and excretes urine and regulates water and solutes in body fluids. Student Misconceptions and Concerns 1. The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store. 2. Before addressing the human urinary system, challenge each student in your class to explain how a drink of water may end up as urine. Consider having students write out their answers on a 3  5 card in class. This quick survey will likely reveal misunderstandings that would otherwise be concealed by quiet students’ reluctance to speak up. Students might suggest that some sort of tube transports fluid from the digestive tract to the kidneys or urinary bladder. Such surveys provide a useful means of gauging the initial assumptions of your students as they approach a new subject. Teaching Tips 1. A moderately full human urinary bladder holds about 500 ml (or 1 pint) of fluid. The bladder’s maximum capacity may be up to double that volume, although if overdistended, it may burst! 2. Students must understand that blood consists of two main components, cells and plasma. If your course has not covered Chapter 23, consider assigning Module 23.12 to ensure that they have this important background knowledge. 3. During the production of urine, blood cells remain within blood vessels, and components of the plasma are filtered out and selectively reabsorbed. Students may appreciate your making this important distinction early on in the discussion of renal functions. 8

Animation: Nephron Introduction Nephrons = functional units of kidneys extract a fluid filtrate from the blood, and refine the filtrate to produce urine. Animation: Nephron Introduction

DETAILED STRUCTURE OF A NEPHRON Figure 25.6_4 Anatomy of the human excretory system: nephron structure (part 4) 10

Processing of Urine in 4 Stages Filtration Blood enters kidney via renal artery --> various capillary beds (GLOMERULUS) Each capillary bed wraps around nephron Blood filtered through capillary bed by force of blood pressure Proteins and RBCs remain in blood Filtrate contains: Water, salts, glucose, amino acids, urea collected by Bowman’s capsule Reabsorption Secretion Excretion Urine To renal vein Filtration Nephron tubule Capillary Interstitial fluid H2O, other small molecules Bowman’s capsule From renal artery Student Misconceptions and Concerns The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store. Teaching Tips 1. Students must understand that blood consists of two main components, cells and plasma. If your course has not covered Chapter 23, consider assigning Module 23.12 to ensure that they have this important background knowledge. 2. During the production of urine, blood cells remain within blood vessels, and components of the plasma are filtered out and selectively reabsorbed. Students may appreciate your making this important distinction early on in the discussion of renal functions. 3. Some drugs are excreted in urine. This is the basis of drug testing using samples of a person’s urine. Making this simple connection can help generate interest and improve comprehension in your students. 4. Many students do not know about interstitial fluid or its functions. They may think that blood delivers nutrients directly to cells, perhaps through direct contact between capillaries and cells. Instead, interstitial fluids typically act as an intermediate and promote homeostasis in many ways. Interstitial fluid is discussed in detail in Module 23.7, which may not have been addressed previously in your class. © 2012 Pearson Education, Inc. 11

Processing of Urine in 4 Stages Reabsorption proximal and distal tubules return Glucose, salt, and amino acids to blood by active transport Water follows by osmosis Secretion Substances in the blood are transported into the urine by active transport at PCT and DCT Excretion Student Misconceptions and Concerns The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store. Teaching Tips 1. Students must understand that blood consists of two main components, cells and plasma. If your course has not covered Chapter 23, consider assigning Module 23.12 to ensure that they have this important background knowledge. 2. During the production of urine, blood cells remain within blood vessels, and components of the plasma are filtered out and selectively reabsorbed. Students may appreciate your making this important distinction early on in the discussion of renal functions. 3. Some drugs are excreted in urine. This is the basis of drug testing using samples of a person’s urine. Making this simple connection can help generate interest and improve comprehension in your students. 4. Many students do not know about interstitial fluid or its functions. They may think that blood delivers nutrients directly to cells, perhaps through direct contact between capillaries and cells. Instead, interstitial fluids typically act as an intermediate and promote homeostasis in many ways. Interstitial fluid is discussed in detail in Module 23.7, which may not have been addressed previously in your class. Reabsorption Secretion Excretion Urine To renal vein Filtration Nephron tubule Capillary Interstitial fluid H2O, other small molecules Bowman’s capsule From renal artery © 2012 Pearson Education, Inc. 12

Processing of Urine Glomerulus PCT and DCT Loop of Henle Filters Urine by force of blood pressure Filtrate captured by Bowman’s Capsule PCT and DCT Active transport or secretion of substances to and from blood Loop of Henle Concentration of urine and reabsorption of water Active transport of Na out Water follows by osmosis Collecting Duct Further concentration of urine and reabsorption of water Responds to ADH Student Misconceptions and Concerns The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store. Teaching Tips Many students do not know about interstitial fluid or its functions. They may think that blood delivers nutrients directly to cells, perhaps through direct contact between capillaries and cells. Instead, interstitial fluids typically act as an intermediate and promote homeostasis in many ways. Interstitial fluid is discussed in detail in Module 23.7, which may not have been addressed previously in your class. © 2012 Pearson Education, Inc. 13

PROXIMAL TUBULE DISTAL TUBULE NaCl Nutrients H2O HCO3– H2O K+ NaCl NH3 K+ H+ CORTEX DESCENDING LIMB OF LOOP OF HENLE ASCENDING LIMB OF LOOP OF HENLE Filtrate Contains: H2O Salts (NaCl and others) HCO3– H+ Urea Glucose; amino acids Some drugs NaCl H2O OUTER MEDULLA NaCl COLLECTING DUCT Key Urea Active transport Passive transport NaCl H2O INNER MEDULLA

Animation: Bowman’s Capsule and Proximal Tubule Animation: Collecting Duct Animation: Effect of ADH Animation: Loop of Henle and Distal Tubule

Bowman’s capsule Proximal tubule Nutrients H2O HCO3 NaCl Blood Figure 25.8_1 Bowman’s capsule Proximal tubule Nutrients H2O NaCl HCO3 Blood Some drugs and poisons H Cortex Filtrate composition Medulla H2O Salts (NaCl and others) HCO3 H Urea Glucose Amino acids Some drugs Figure 25.8_1 Reabsorption and secretion in a nephron (part 1) Reabsorption Secretion Filtrate movement 16

  Proximal tubule Distal tubule Nutrients H2O H2O NaCl HCO3 NaCl Figure 25.8_2 Proximal tubule Distal tubule Nutrients H2O 1 H2O NaCl HCO3 NaCl HCO3 Some drugs and poisons H K  H  3 Collecting duct Cortex Medulla Interstitial fluid Loop of Henle 2 NaCl NaCl H2O Figure 25.8_2 Reabsorption and secretion in a nephron (part 2) Reabsorption Urea NaCl Secretion H2O Filtrate movement Urine (to renal pelvis) 17

Hormonal Control of Kidneys Osmoreceptors in hypothalamus Hypothalamus ADH Pituitary gland Thirst Drinking reduces blood osmolarity to set point Collecting duct H2O reab- sorption helps prevent further osmolarity increase Homeostasis: Proper blood pressure Solute levels STIMULUS Increase in solute concentration In blood; decrease blood Volume; Decreased blood pressure Antidiuretic hormone (ADH) Produced by pituitary gland Released in response to decreased blood volume Regulates the permeability of collecting duct to water High ADH; nephrons reabsorb water from the urine, returning it to the blood Leads to increased blood volume and blood pressure Student Misconceptions and Concerns The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store. Teaching Tips Students may be particularly interested in the diuretic effects of alcohol and caffeine. The text notes that the diuretic effects of alcohol may contribute to some of the symptoms of a hangover. However, the concentration of alcohol and caffeine are important factors. Higher urine output resulting from the high consumption of low-alcohol (1–5%) beer may largely be the consequence of increased water consumption. Drinks with higher alcohol levels, such as shots of hard liquor (gin, vodka, whiskey) or higher caffeine levels (espresso) and low fluid volume would be expected to better reveal the diuretic effects. © 2012 Pearson Education, Inc. 18

Kidneys and Acid-Base Balance pH is regulated by Secretion of acidic and basic organic compounds reabsorption of HCO3– and secretion of H+. Student Misconceptions and Concerns The kidney’s role in filtration and selective reabsorption may initially be confusing to many students. The process is a bit like cleaning up a closet by removing all the contents and then selectively returning to it what you wish to store. Teaching Tips Students may be particularly interested in the diuretic effects of alcohol and caffeine. The text notes that the diuretic effects of alcohol may contribute to some of the symptoms of a hangover. However, the concentration of alcohol and caffeine are important factors. Higher urine output resulting from the high consumption of low-alcohol (1–5%) beer may largely be the consequence of increased water consumption. Drinks with higher alcohol levels, such as shots of hard liquor (gin, vodka, whiskey) or higher caffeine levels (espresso) and low fluid volume would be expected to better reveal the diuretic effects. © 2012 Pearson Education, Inc. 19