Chapter 44 Overview: A balancing act Osmoregulation and
Transcript of Chapter 44 Overview: A balancing act Osmoregulation and
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PowerPoint Lectures for Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Chapter 44
Osmoregulation and Excretion
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• Overview: A balancing act
• The physiological systems of animals
– Operate in a fluid environment
• The relative concentrations of water and solutes in this environment
– Must be maintained within fairly narrow limits
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• Freshwater animals – Show adaptations that reduce water uptake and
conserve solutes
• Desert and marine animals face desiccating environments – With the potential to quickly deplete the body water
Figure 44.1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Osmoregulation
– Regulates solute concentrations and balances the gain and loss of water
• Excretion
– Gets rid of metabolic wastes
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• Concept 44.1: Osmoregulation balances the uptake and loss of water and solutes
• Osmoregulation is based largely on controlled movement of solutes
– Between internal fluids and the external environment
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Osmosis
• Cells require a balance
– Between osmotic gain and loss of water
• Water uptake and loss
– Are balanced by various mechanisms of osmoregulation in different environments
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Osmotic Challenges
• Osmoconformers, which are only 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
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• Most animals are said to be stenohaline
– And cannot tolerate substantial changes in external osmolarity
• Euryhaline animals
– Can survive large fluctuations in external osmolarity
Figure 44.2
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Marine Animals
• Most marine invertebrates are osmoconformers
• Most marine vertebrates and some invertebrates are osmoregulators
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• Marine bony fishes are hypoosmotic to sea water
– And lose water by osmosis and gain salt by both diffusion and from food they eat
• These fishes balance water loss
– By drinking seawater
Figure 44.3a
Gain of water and salt ions from food and by drinking seawater
Osmotic water loss through gills and other parts of body surface
Excretion of salt ions from gills
Excretion of salt ions and small amounts of water in scanty urine from kidneys
(a) Osmoregulation in a saltwater fish
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Freshwater Animals
• Freshwater animals
– Constantly take in water from their hypoosmotic environment
– Lose salts by diffusion
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• Freshwater animals maintain water balance
– By excreting large amounts of dilute urine
• Salts lost by diffusion
– Are replaced by foods and uptake across the gills
Figure 44.3b
Uptake of water and some ions in food
Osmotic water gain through gills and other parts of body surface
Uptake of salt ions by gills
Excretion of large amounts of water in dilute urine from kidneys
(b) Osmoregulation in a freshwater fish
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Animals That Live in Temporary Waters
• Some aquatic invertebrates living in temporary ponds
– Can lose almost all their body water and survive in a dormant state
• This adaptation is called anhydrobiosis
Figure 44.4a, b (a) Hydrated tardigrade (b) Dehydrated tardigrade
100 µm
100 µm
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Land Animals
• Land animals manage their water budgets
– By drinking and eating moist foods and by using metabolic water
Figure 44.5
Water balance in a human
(2,500 mL/day = 100%)
Water balance in a kangaroo rat
(2 mL/day = 100%)
Ingested in food (0.2)
Ingested in food (750)
Ingested in liquid (1,500)
Derived from metabolism (250)
Derived from metabolism (1.8)
Water gain
Feces (0.9)
Urine (0.45)
Evaporation (1.46)
Feces (100)
Urine (1,500)
Evaporation (900)
Water loss
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• Desert animals
– Get major water savings from simple anatomical features
Figure 44.6
Control group (Unclipped fur)
Experimental group (Clipped fur)
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3
2
1
0
Wat
er lo
st p
er d
ay
(L/1
00 k
g bo
dy m
ass)
Knut and Bodil Schmidt-Nielsen and their colleagues from Duke University observed that the fur of camels exposed to full sun in the Sahara Desert could reach temperatures of over 70°C, while the animals’ skin remained more than 30°C cooler. The Schmidt-Nielsens reasoned that insulation of the skin by fur may substantially reduce the need for evaporative cooling by sweating. To test this hypothesis, they compared the water loss rates of unclipped and clipped camels.
EXPERIMENT
RESULTS Removing the fur of a camel increased the rate of water loss through sweating by up to 50%.
The fur of camels plays a critical role in their conserving water in the hot desert environments where they live.
CONCLUSION
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Transport Epithelia
• Transport epithelia
– Are specialized cells that regulate solute movement
– Are essential components of osmotic regulation and metabolic waste disposal
– Are arranged into complex tubular networks
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• An example of transport epithelia is found in the salt glands of marine birds
– Which remove excess sodium chloride from the blood
Figure 44.7a, b
Nasal salt gland
Nostril with salt secretions
Lumen of secretory tubule
NaCl
Blood flow
Secretory cell of transport epithelium
Central duct
Direction of salt movement
Transport epithelium
Secretory tubule
Capillary
Vein
Artery
(a) An albatross’s salt glands empty via a duct into the nostrils, and the salty solution either drips off the tip of the beak or is exhaled in a fine mist.
(b) One of several thousand secretory tubules in a salt- excreting gland. Each tubule is lined by a transport epithelium surrounded by capillaries, and drains into a central duct.
(c) The secretory cells actively transport salt from the blood into the tubules. Blood flows counter to the flow of salt secretion. By maintaining a concentration gradient of salt in the tubule (aqua), this countercurrent system enhances salt transfer from the blood to the lumen of the tubule.
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• Concept 44.2: An animal’s nitrogenous wastes reflect its phylogeny and habitat
• The type and quantity of an animal’s waste products
– May have a large impact on its water balance
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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
Ammonia Urea Uric acid
NH3 NH2
NH2 O C
C
C N
C O N
H H
C O N C
HN
O H
• Among the most important wastes
– Are the nitrogenous breakdown products of proteins and nucleic acids
Figure 44.8 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Forms of Nitrogenous Wastes
• Different animals
– Excrete nitrogenous wastes in different forms
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Ammonia
• Animals that excrete nitrogenous wastes as ammonia
– Need access to lots of water
– Release it across the whole body surface or through the gills
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Urea
• The liver of mammals and most adult amphibians
– Converts ammonia to less toxic urea
• Urea is carried to the kidneys, concentrated
– And excreted with a minimal loss of water
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Uric Acid
• Insects, land snails, and many reptiles, including birds
– Excrete uric acid as their major nitrogenous waste
• Uric acid is largely insoluble in water
– And can be secreted as a paste with little water loss
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The Influence of Evolution and Environment on Nitrogenous Wastes
• The kinds of nitrogenous wastes excreted
– Depend on an animal’s evolutionary history and habitat
• The amount of nitrogenous waste produced
– Is coupled to the animal’s energy budget
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• Concept 44.3: Diverse excretory systems are variations on a tubular theme
• Excretory systems
– Regulate solute movement between internal fluids and the external environment
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Excretory Processes
• Most excretory systems
– Produce urine by refining a filtrate derived from body fluids
Figure 44.9
Filtration. The excretory tubule collects a filtrate from the blood. Water and solutes are forced by blood pressure across the selectively permeable membranes of a cluster of capillaries and into the excretory tubule.
Reabsorption. The transport epithelium reclaims valuable substances from the filtrate and returns them to the body fluids.
Secretion. Other substances, such as toxins and excess ions, are extracted from body fluids and added to the contents of the excretory tubule.
Excretion. The filtrate leaves the system and the body.
Capillary
Excretory tubule
Filtrate U
rine
1
2
3
4
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• Key functions of most excretory systems are
– Filtration, pressure-filtering of body fluids producing a filtrate
– Reabsorption, reclaiming valuable solutes from the filtrate
– Secretion, addition of toxins and other solutes from the body fluids to the filtrate
– Excretion, the filtrate leaves the system
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Survey of Excretory Systems
• The systems that perform basic excretory functions
– Vary widely among animal groups
– Are generally built on a complex network of tubules
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Nucleus of cap cell
Cilia
Interstitial fluid filters through membrane where cap cell and tubule cell interdigitate (interlock)
Tubule cell
Flame bulb
Nephridiopore in body wall
Tubule Protonephridia (tubules)
Protonephridia: Flame-Bulb Systems
• A protonephridium
– Is a network of dead-end tubules lacking internal openings
Figure 44.10 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The tubules branch throughout the body
– And the smallest branches are capped by a cellular unit called a flame bulb
• These tubules excrete a dilute fluid
– And function in osmoregulation
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Metanephridia
• Each segment of an earthworm
– Has a pair of open-ended metanephridia
Figure 44.11 Nephrostome Metanephridia
Nephridio- pore
Collecting tubule
Bladder
Capillary network
Coelom
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• Metanephridia consist of tubules
– That collect coelomic fluid and produce dilute urine for excretion
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Digestive tract
Midgut (stomach)
Malpighian tubules
Rectum Intestine Hindgut
Salt, water, and nitrogenous
wastes
Feces and urine Anus
Malpighian tubule
Rectum
Reabsorption of H2O, ions, and valuable organic molecules
HEMOLYMPH
Malpighian Tubules
• In insects and other terrestrial arthropods, malpighian tubules
– Remove nitrogenous wastes from hemolymph and function in osmoregulation
Figure 44.12 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Insects produce a relatively dry waste matter
– An important adaptation to terrestrial life
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Vertebrate Kidneys
• Kidneys, the excretory organs of vertebrates
– Function in both excretion and osmoregulation
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• Concept 44.4: Nephrons and associated blood vessels are the functional unit of the mammalian kidney
• The mammalian excretory system centers on paired kidneys
– Which are also the principal site of water balance and salt regulation
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• Each kidney
– Is supplied with blood by a renal artery and drained by a renal vein
Figure 44.13a
Posterior vena cava
Renal artery and vein
Aorta
Ureter
Urinary bladder
Urethra
(a) Excretory organs and major associated blood vessels
Kidney
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• Urine exits each kidney
– Through a duct called the ureter
• Both ureters
– Drain into a common urinary bladder
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(b) Kidney structure
Ureter Section of kidney from a rat
Renal medulla
Renal cortex
Renal pelvis
Figure 44.13b
Structure and Function of the Nephron and Associated Structures
• The mammalian kidney has two distinct regions
– An outer renal cortex and an inner renal medulla
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• The nephron, the functional unit of the vertebrate kidney
– Consists of a single long tubule and a ball of capillaries called the glomerulus
Figure 44.13c, d
Juxta- medullary nephron
Cortical nephron
Collecting duct
To renal pelvis
Renal cortex
Renal medulla
20 µm
Afferent arteriole from renal artery Glomerulus
Bowman’s capsule Proximal tubule
Peritubular capillaries
SEM
Efferent arteriole from glomerulus
Branch of renal vein
Descending limb Ascending limb
Loop of
Henle
Distal tubule
Collecting duct
(c) Nephron
Vasa recta (d) Filtrate and
blood flow
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Filtration of the Blood
• Filtration occurs as blood pressure
– Forces fluid from the blood in the glomerulus into the lumen of Bowman’s capsule
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• Filtration of small molecules is nonselective
– And the filtrate in Bowman’s capsule is a mixture that mirrors the concentration of various solutes in the blood plasma
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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
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Blood Vessels Associated with the Nephrons • Each nephron is supplied with blood by an afferent
arteriole
– A branch of the renal artery that subdivides into the capillaries
• The capillaries converge as they leave the glomerulus
– Forming an efferent arteriole
• The vessels subdivide again
– Forming the peritubular capillaries, which surround the proximal and distal tubules
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Proximal tubule
Filtrate H2O Salts (NaCl and others) HCO3
– H+ Urea Glucose; amino acids Some drugs
Key
Active transport Passive transport
CORTEX
OUTER MEDULLA
INNER MEDULLA
Descending limb of loop of Henle
Thick segment of ascending limb
Thin segment of ascending limb
Collecting duct
NaCl
NaCl
NaCl
Distal tubule
NaCl Nutrients
Urea
H2O
NaCl H2O
H2O HCO3- K+
H+ NH3
HCO3-
K+ H+
H2O
1 4
3 2
3 5
From Blood Filtrate to Urine: A Closer Look
• Filtrate becomes urine
– As it flows through the mammalian nephron and collecting duct
Figure 44.14 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Secretion and reabsorption in the proximal tubule
– Substantially alter the volume and composition of filtrate
• Reabsorption of water continues
– As the filtrate moves into the descending limb of the loop of Henle
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• As filtrate travels through the ascending limb of the loop of Henle
– Salt diffuses out of the permeable tubule into the interstitial fluid
• The distal tubule
– Plays a key role in regulating the K+ and NaCl concentration of body fluids
• The collecting duct
– Carries the filtrate through the medulla to the renal pelvis and reabsorbs NaCl
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• Concept 44.5: The mammalian kidney’s ability to conserve water is a key terrestrial adaptation
• The mammalian kidney
– Can produce urine much more concentrated than body fluids, thus conserving water
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Solute Gradients and Water Conservation
• In a mammalian kidney, the cooperative action and precise arrangement of the loops of Henle and the collecting ducts
– Are largely responsible for the osmotic gradient that concentrates the urine
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• Two solutes, NaCl and urea, contribute to the osmolarity of the interstitial fluid
– Which causes the reabsorption of water in the kidney and concentrates the urine
Figure 44.15
H2O
H2O
H2O
H2O
H2O
H2O
H2O
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
300 300 100
400
600
900
1200
700
400
200
100
Active transport Passive transport
OUTER MEDULLA
INNER MEDULLA
CORTEX
H2O Urea
H2O Urea
H2O Urea
H2O
H2O
H2O
H2O
1200 1200
900
600
400
300
600
400
300
Osmolarity of interstitial
fluid (mosm/L)
300
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• The countercurrent multiplier system involving the loop of Henle
– Maintains a high salt concentration in the interior of the kidney, which enables the kidney to form concentrated urine
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• The collecting duct, permeable to water but not salt
– Conducts the filtrate through the kidney’s osmolarity gradient, and more water exits the filtrate by osmosis
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• 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
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Regulation of Kidney Function
• The osmolarity of the urine
– Is regulated by nervous and hormonal control of water and salt reabsorption in the kidneys
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• Antidiuretic hormone (ADH)
– Increases water reabsorption in the distal tubules and collecting ducts of the kidney
Figure 44.16a
Osmoreceptors in hypothalamus
Drinking reduces blood osmolarity
to set point
H2O reab- sorption helps prevent further
osmolarity increase
STIMULUS: The release of ADH is triggered when osmo- receptor cells in the
hypothalamus detect an increase in the osmolarity
of the blood
Homeostasis: Blood osmolarity
Hypothalamus
ADH
Pituitary gland
Increased permeability
Thirst
Collecting duct
Distal tubule
(a) Antidiuretic hormone (ADH) enhances fluid retention by making the kidneys reclaim more water.
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• The renin-angiotensin-aldosterone system (RAAS)
– Is part of a complex feedback circuit that functions in homeostasis
Figure 44.16b
Increased Na+ and H2O reab-
sorption in distal tubules
Homeostasis: Blood pressure,
volume
STIMULUS: The juxtaglomerular
apparatus (JGA) responds to low blood volume or
blood pressure (such as due to dehydration or loss of
blood)
Aldosterone
Adrenal gland
Angiotensin II
Angiotensinogen
Renin production
Renin
Arteriole constriction
Distal tubule
JGA
(b) The renin-angiotensin-aldosterone system (RAAS) leads to an increase in blood volume and pressure.
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• Another hormone, atrial natriuretic factor (ANF)
– Opposes the RAAS
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• The South American vampire bat, which feeds on blood
– Has a unique excretory system in which its kidneys offload much of the water absorbed from a meal by excreting large amounts of dilute urine
Figure 44.17
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• Concept 44.6: Diverse adaptations of the vertebrate kidney have evolved in different environments
• The form and function of nephrons in various vertebrate classes
– Are related primarily to the requirements for osmoregulation in the animal’s habitat
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• Exploring environmental adaptations of the vertebrate kidney
Figure 44.18
MAMMALS
Bannertail Kangaroo rat (Dipodomys spectabilis)
Beaver (Castor canadensis)
FRESHWATER FISHES AND AMPHIBIANS
Rainbow trout (Oncorrhynchus mykiss)
Frog (Rana temporaria)
BIRDS AND OTHER REPTILES
Roadrunner (Geococcyx californianus)
Desert iguana (Dipsosaurus dorsalis)
MARINE BONY FISHES
Northern bluefin tuna (Thunnus thynnus)