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Regulating the Internal Environment
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Animals need to regulate:1. Water/solute concentration of body fluids
– Body fluids-total amount of fluids in the body
• Intracellular-amount of fluids found inside the cells, blood cells, and other tissue
• Extracellular-amount of fluids found outside of the cells
– Plasma-extracellular fluids found in the circulatory system
– Interstitial fluid-fluids found between the cells outside the circulatory system
2. pH
3. temperature
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• The excretory system is a regulatory system that helps to maintain homeostasis within the body
• Homeostasis is the dynamic constancy of the internal environment
• The excretory system eliminates wastes and functions in osmoregulation.
• Osmoregulation is the control of salt and water balance
• Osmoconformers– Do not actively adjust their internal osmolarity
• Osmoregulators– Animals whose body fluids are not isotonic with
the external environment must manipulate solute concentrations in their body fluids
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Osmoregulation involves:
1.Osmosis-diffusion of H2O across a membrane due to a concentration gradient
• remember, hyper/hypo/isotonic
2. Excretion- process of an organism ridding their bodies of metabolic wastes. This process also helps regulate Salt Balance.
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Animals have to get rid of nitrogen
• The metabolism of proteins and nucleic acids produces toxic by-products ammonia
• Ammonia:– a small and very toxic molecule– can be transported and excreted only in a very
dilute solution• Many animals convert ammonia to urea (mammals
and amphibians) or uric acid (birds and reptiles), which are much less toxic, but require ATP to produce
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Maintaining Extracellular Fluid• Urinary/Excretory system:
– keeps volume and composition of extracellular
fluid within tolerable ranges
– regulates solute movement between internal
fluids and the external environment
• interacts with the digestive, respiratory, and
circulatory systems to fulfill these tasks
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Urinary System Interactionsfood, water intake oxygen intake
DIGESTIVE SYSTEM
RESPIRATORY SYSTEM
elimination of carbon dioxide
CIRCULATORY SYSTEM
URINARY SYSTEM
oxygen carbon dioxide
water, solutes
nutrients, water, salts
elimination of food residues
rapid transport to and from all living cells
elimination of excess water, salts, wastes
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Aquatic animals: -excrete ammonia which can readily cross membranes and then be flushed from the body
1. Many Marine invertebrates - lack a specialized excretory system, most waste diffuses across a membrane. The sea is an isotonic solution so salt balance is no problem EXCEPT if the organism is put in fresh water or a hypotonic solution. The animal most likely will lose salts and fluids and die
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2. Marine fish - their body fluids are diluted (or hypotonic) in comparison to their environment (sea water)
-Marine fish tend to lose water to their environment
-Compensation
1. Marine fish drink water to replace H2O loss
2. Gills secrete ammonia not urine
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Gain of water andsalt ions from foodand by drinkingseawater
Osmotic water lossthrough gills and other partsof body surface
Excretion ofsalt ionsfrom gills
Osmoregulation in a saltwater fish
Excretion of salt ions and small amountsof water in scantyurine from kidneys
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3. Fresh water fish – their body fluids are concentrated (or hypertonic) in comparison to their environment
- Fresh water fish tend to gain water from their environment
- Compensation
- almost never drink H2O
- Fish excrete a dilute urine, therefore keeping more salts in the body
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Excretion oflarge amounts ofwater in diluteurine from kidneys
Osmotic water gainthrough gills and other partsof body surface
Osmoregulation in a freshwater fish
Uptake ofsalt ionsby gills
Uptake ofwater and someions in food
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Terrestrial animals:
**must fight desiccation (drying out)
-compensation
1. drinking H2O
2. food with H2O
3. H2O is a by product respiration
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-Mammal and amphibians form Urea and finally urine
-Birds and reptile form uric acid which is insoluble and less H2O is needed for excretion. Also will not toxify embyos in eggs.
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Nitrogenous bases
Nucleic acids
Amino acids
Proteins
—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
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Ammonia• Animals that excrete nitrogenous wastes as
ammonia need lots of water
• They release ammonia across the whole body surface or through gills
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Urea• The liver of mammals and most adult amphibians
converts ammonia to less toxic urea
• The circulatory system carries urea to the kidneys, where it is excreted
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Uric Acid• Insects, land snails, and many reptiles,
including birds, mainly excrete uric acid • Uric acid is largely insoluble in water and can
be secreted as a paste with little water loss
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Excretory Processes
• Most excretory systems produce urine by refining a filtrate derived from body fluids
• Key functions of most excretory systems:– Filtration: pressure-filtering of body fluids– Reabsorption: reclaiming valuable solutes– Secretion: adding toxins and other solutes from
the body fluids to the filtrate– Excretion: removing the filtrate from the system
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Protonephridia: Flame-Cell Systems - flatworms
• A protonephridium is a network of dead-end tubules lacking internal 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
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LE 44-10
Protonephridia(tubules)
Tubule
Nephridioporein body wall
Flamebulb
Interstitial fluidfilters throughmembrane wherecap cell and tubulecell interdigitate(interlock)
Tubule cell
Cilia
Nucleusof cap cell
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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
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LE 44-11
Collectingtubule
Nephridio-pore
Capillarynetwork
Coelom
Bladder
MetanephridiumNephrostome
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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, an important adaptation to terrestrial life
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LE 44-12
Salt, water, andnitrogenous
wastes
Digestive tract
Midgut(stomach)
Malpighiantubules
RectumIntestine Hindgut
Reabsorption of H2O,ions, and valuableorganic molecules
Malpighiantubule
HEMOLYMPH
Anus
Rectum
Feces and urine
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The Vertebrate Excretory System
• Kidneys (function in both excretion and osmoregulation), ureters, urinary bladder, urethra, renal artery, renal vein
• Also…– Lungs: excrete carbon dioxide– Skin: excretes water, salts, and a small
amount of urea (in sweat)
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Water Gains and Losses
Water Gains
• Absorption from
gut
• Metabolism
Water Losses
• Urination
• Cell secretions
• Sweating
• Water in feces
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Solute Gains and Losses
Solute Gains
• Absorption from
gut
• Cell secretions
• Respiration
• Metabolism
Solute Losses
• Urinary
excretion
• Respiration
• Sweating
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Controlling Water Gain & Loss
• Urinary excretion provides the
most control over water loss
• Concentration of urine can be
varied
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Components of Urinary System
• Pair of kidneys
• Pair of ureters
• Urinary bladder
• Urethra
• Anytime you see the terms “nephr” or renal it has something to do with the kidneys
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Urinary Excretion
• Urine flows from each kidney to a ureter
• Ureters deliver urine to bladder
• Contraction of the smooth muscle of the bladder forces urine out of the body into the urethra
• Skeletal muscle surrounds urethra; allows voluntary control of urination
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Function of Kidneys
• Filter water, mineral ions, wastes from
the blood
• Adjust filtrate concentration and return
most to blood
• Remaining water and solutes in filtrate
constitute urine
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Structure of Kidney
• Renal capsule surrounds kidney
• Two regions – Outer renal cortex– Inner renal medulla
• Renal pelvis collects urine and funnels it to ureter
Figure 42.4aPage 747
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Excretory organs and major associated blood vessels
RenalmedullaRenalcortex
Renalpelvis
Section of kidney from a ratKidney structure
Ureter
Kidney
Glomerulus
Bowman’s capsule
Proximal tubule
Peritubular capillaries
Afferentarteriolefrom renalartery
Efferentarteriole from glomerulus
Distaltubule
Collectingduct
SEM20 µm
Branch ofrenal vein
Filtrate and blood flow
Vasarecta
Descendinglimb
Ascendinglimb
LoopofHenle
Renalmedulla
Nephron
Torenalpelvis
Renalcortex
Collectingduct
Juxta-medullarynephron
Corticalnephron
Posterior vena cava
Renal artery and vein
Aorta
Ureter
Urinary bladder
Urethra
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Nephron
• Functional unit of
the kidney
• Each consists of
a renal tubule and
associated
capillaries
Bowman’s capsule (red)
proximal tubule
distal tubule
loop of Henle
collecting duct
Figure 42.4cPage 747
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Humans - There are over 1,000,000 nephrons in each kidney. 1,100-1,200 L of blood flows through the kidneys each day.
-blood is delivered via an efferent arteriole to a capillary bed called the glomerulus.
-The blood leaves the glomerulus via the afferent arteriole forming a second capillary bed called the peritubular capillaries that surrounds the nephron. --The blood then leaves the nephron via the a venule.
-
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Urine Formation
Filtration
Tubular reabsorption
Tubular secretion
Hormone action
Excretion
Figure 42.5 Page 748
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Leaky Glomerular Capillaries
• Glomerular capillaries
have large pores
• Fluid leaks from
glomerular capillaries
into kidney tubules
Figure 42.5Page 748
Renal corpuscle (Bowman’s capsule + glomerular capillaries)
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Filtration Rate Varies
• Increased blood pressure increases
glomerular filtration
• Flow volume to kidneys changes in
response to neural, endocrine, and local
changes
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Most Filtrate Is Reabsorbed
• Each day, about 180
liters of filtrate flows out
of glomerulus into
tubules
• 1 to 2 liters excreted
• Most filtrate is
reabsorbed into blood
peritubular capillaries
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Tubular Reabsorption
• Ions move from the filtrate in tubule lumen into the interstitial fluid
• Sodium ions are actively pumped out of the proximal tubule into the interstitial fluid
• Chloride ions follow; they are passively transported
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Tubular Reabsorption
• Ion flow creates an osmotic gradient; it is saltier outside the tubule than inside
• Water flows down the osmotic gradient, from the tubule lumen into the interstitial fluid
• Peritubular capillaries pick up the water and ions from the interstitial fluid
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Amino acids, vitamins, proteins, and glucose are reabsorbed in the PCT.
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Tubular Reabsorption
peritubular capillary
sodium pump
Na+
Na+
Na+
Na+
Cl-
H2O
interstitial fluid filtrate in tubule
Na+
Na+
Figure 42.6Page 749
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Tubular Secretion
• The opposite of reabsorption
• Molecules are transported out of the
peritubular capillaries, through tubule
cells, and into the filtrate
• Eliminates H+ ions, metabolites, and
toxins
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Filtrate
H2O
Salts (NaCl and others)
HCO3–
H+
Urea
Glucose; amino acids
Some drugs
Key
Active transport
Passive transportINNERMEDULLA
OUTERMEDULLA
NaCl
H2O
CORTEX
Descending limbof loop ofHenle
Proximal tubule
NaCl Nutrients
HCO3–
H+
K+
NH3
H2O
Distal tubule
NaCl HCO3–
H+K+
H2O
Thick segmentof ascendinglimb
NaCl
NaCl
Thin segmentof ascendinglimb
Collectingduct
Urea
H2O
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INNERMEDULLA
OUTERMEDULLA
CORTEX
Osmolarity ofinterstitial
fluid(mosm/L)
NaCl
Urea
H2O
Activetransport
Passivetransport
300300
300 100
100
400 200H2O
H2O
H2O
H2O
H2O
H2O
600 400
900 700
1200
300
400
H2O
600
12001200
600
900
300
400NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
UreaH2O
UreaH2O
H2O
H2O
H2O
H2O
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Urine Formation
Filtration
Tubular reabsorption
Tubular secretion
Hormone action
Excretion
Figure 42.5 Page 748
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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
Hormones:
1.Antidiuretic hormone (ADH) increases water reabsorption in the distal tubules and collecting ducts of the kidney making urine more concentrated and conserving water– Acts on collecting ducts; makes walls more
permeable to water
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Osmoreceptorsin hypothalamus
Hypothalamus
ADH
Pituitarygland
Increasedpermeability
Distaltubule
Thirst
Drinking reducesblood osmolarity
to set point
Collecting duct
H2O reab-sorption helpsprevent further
osmolarityincrease
Homeostasis:Blood osmolarity
STIMULUSThe release of ADH istriggered when osmo-receptor cells in the
hypothalamus detect anincrease in the osmolarity
of the blood
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2. The renin-angiotensin-aldosterone system (RAAS) is part of a complex feedback circuit that functions in homeostasis controlling blood pressure and volume
• If low blood volume or low blood pressure:
a) Aldosterone - Stimulates reabsorption of sodium (H2O follows) in the Distal Convoluted Tubule , increasing blood volume and therefore pressure
b) Kidneys can also secrete an enzyme (resin) which is converted to Angiotensin which helps control blood pressure by causing arterioles to constrict
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Distaltubule
Aldosterone
Homeostasis:Blood pressure,
volume
STIMULUS:The juxtaglomerular
apparatus (JGA) respondsto low blood volume or
blood pressure (such as due to dehydration or
loss of blood)
Increased Na+
and H2O reab-sorption in
distal tubules
Reninproduction
Arterioleconstriction
Adrenal gland
Angiotensin II
Angiotensinogen
JGA
Renin
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Thirst
• Osmoreceptors detect changes
• Activate thirst center in hypothalamus
and ADH-secreting cells
• Angiotensin II acts on brain to promote
thirst and ADH secretion
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3. Another hormone, atrial natriuretic factor (ANF), opposes the RAAS
• The walls of the atria of the heart release ANF in response to increase in blood volume and pressure.
• ANF inhibits the release of rennin from the JGA and inhibits NaCl reabsorption by the collecting ducts
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Variation in Urinary Systems
• Structure of vertebrate urinary systems varies in details
• Adapted to particular habitats
• Freshwater fish must deal with continuous influx of water by osmosis
• Marine fish must deal with continuous loss of water
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Length of Loop of Henle
• Longer loop of Henle allows an organism to
produce a very steep osmotic gradient and the
more water that is conserved or retained by the
body
• Kangaroo rats have very long loops of Henle.
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Kidney Disorders
• Glomerulonephritis
– Infection of glomeruli leads to chronic
inflammation that damages kidney
• Kidney stones
– Uric acid and calcium salts settle out of
urine, form hard deposits that can lodge in
ureter or urethra
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Renal Failure
• Both kidneys are damaged to the point where they are nonfunctional
• Fatal if not treated
• Dialysis is used to restore normal solute balances temporarily
• Transplant is only way to fully restore function
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Acid-Base Balance
• Kidneys work in concert with
buffering systems to keep pH in
normal range
• Normal range is 7.37 to 7.43
• Normal metabolism produces an
excess of H+
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Buffer Systems
• Weak acid and weak base that can
reversibly bind and release ions
• Bicarbonate-carbon dioxide buffer
system can neutralize excess H+
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Regulating Blood pH (1)
• Involves secretion of H+ and reabsorption
of HCO3- (bicarbonate)
• HCO3- in filtrate combines with H+ to form
carbonic acid (H2CO3)
• H2CO3 becomes CO2 and H2O, which are
reabsorbed into blood from filtrate
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Regulating Blood pH (2)
• In blood, HCO3 dissociates to form
HCO3- and H+
• The H+ can be secreted into proximal tubule, while the HCO3
- remains in
blood, thus increasing blood pH
• H+ can also combine with K+ or ammonia and leave body in urine
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Core Temperature
• Internal temperature of an animal’s body
• Must be maintained within a narrow range for
normal enzyme function
– Human body temp is 37C or 98.6F on average
• Heat gains and losses must be kept in
balance
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THERMOREGULATION• Thermoregulation – homeostatic process
where body temperature is maintained
• VASOCONSTRICTION & VASODILATION – making blood vessels smaller or larger to shunt blood to areas of the body
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ENDOTHERM METHODS• Shivering – involuntary muscle contraction
that generates heat
• Goose bumps – muscles at base of hairs raise hairs off of skin creating a pocket of warmer air near skin
• Sweating – water evaporating removes heat energy from the skin
• Panting – loss of body heat as water evaporates from moist surfaces of resp. tract (birds, dogs, bears)
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Maintaining Temperature
• Peripheral thermoreceptors in skin
• Thermoreceptors deeper in body
• Feed input to hypothalamus
• Hypothalamus sends messages to
effectors by way of nervous system
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Response to Heat Stress
• Peripheral vasodilation
• Sweating
• Panting
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Response to Cold
• Peripheral vasoconstriction
• Pilomotor response –moving the hairs
• Shivering response
• Nonshivering heat response
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Fever
• Part of response to tissue damage
• Hypothalamus resets body thermostat
at higher temperature
• Moderate fever can promote healing
and need not be suppressed
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ECTOTHERM METHODS• CONDUCTION – direct transfer of heat
between molecules of objects in contact (lizard on a hot rock)
• CONVECTION – transfer of heat by movement of air or liquid past a surface – blood moving heat from extremities to the core
• RADIATION – sun
• EVAPORATION – cooling effect
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