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

2. 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)

3. 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!!
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4. 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

5. (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

6. 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

7. 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

8. 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 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

9. 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

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

11. 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 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

12. 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 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

13. 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

14. 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

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

16. 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

17.   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

18. 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

19. 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