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Temperature, Osmotic Regulation
and the Urinary System
Chapter 50
Regulating Body Temperature
The rate of any chemical reaction is affected
by temperature
-The Q10 is the ratio of reaction rates at two
temperatures that differ by 10oC
-For most enzymes, Q10 is around 2
Most organisms have a Q10 for metabolic rate
around 2 or 3
-Thus, the effect of temperature is mainly
on the enzymes involved in metabolism 2
Regulating Body Temperature
Body temperature is determined by internal
factors, such as metabolism, external
factors that affect heat transfer, as well as
behavior
Body heat = heat produced + heat transferred
-Note that the heat transferred can be either
positive or negative
-Can be used for both heating and
cooling
3
Regulating Body Temperature
Four mechanisms of heat transfer are
relevant to biological systems
-Radiation = By electromagnetic radiation
-Conduction = Directly between two
objects
-Convection = By the movement of a gas
or liquid
-Evaporation = Conversion of water to gas
4
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Reflected sunlight
Direct sunlight
Infrared thermal
radiation from
Dust and particles
atmosphere
Scattered
sunlight
Infrared thermal
radiation
from vegetation
Infrared thermal
radiation from animal
Evaporation
Convection
wind
Infrared thermal
radiation from ground
Reflected sunlight
5
Regulating Body Temperature
Heat transfer also depends on other factors,
that influence these four physical processes
-Surface area to mass ratio
-Difference between ambient and body
temperature
-Specific heat conduction
6
Classification of Organisms
For many years, animals were classified
according to whether they maintained a
constant body temperature
-Homeotherms = Regulate their body
temperature about a set point
-Also called “warm-blooded”
-Poikilotherms = Allow their body
temperature to conform to the environment
-Also called “cold-blooded”
7
Classification of Organisms
Limitations to this dichotomy led to another
view based on how body heat is generated
-Endotherms = Use metabolism to
generate body heat and maintain
temperature above ambient temperature
-Ectotherms = Do not use metabolism to
produce heat and have body temperature
that conforms to ambient temperature
Heterotherms fall between these extremes
8
Ectotherms
Ectotherms regulate temperature using
behavior
-Insects, such as
moths, use a
shivering reflex
to warm thoracic
muscles for flight
9
Ectotherms
Many marine animals, such as killer whales,
limit heat loss in cold water using
countercurrent heat exchange
-Warm blood pumped from within the body
in arteries warms the cooler blood returning
from the skin within veins
10
Ectotherms
Core body
temperature
36°C
5°C
Temperature
of environment
Cold
blood
Capillary
bed
Warm
blood
Cold
blood
Veins
Artery
11
Ectotherms
Reptiles place themselves in varying locations
of sunlight and shade
-Some can maximize the effect of behavioral
regulation by also controlling blood flow
In general, ectotherms have low metabolic
rates, which have the advantage of low
energy intake
-However, they are not capable of sustained
high-energy activity
12
Endotherms
A high metabolic rate can be used to warm
the endotherm if it is cold
The simplest way to regulate body
temperature is by the control of blood flow
to the surface of the animal
-Vasodilation increases blood flow, thereby
increasing heat dissipation
-Vasoconstriction decreases blood flow,
thus limiting heat loss
13
Endotherms
When ambient temperatures rise, many
endotherms take advantage of evaporative
cooling in the form of sweating or panting
The advantage of endothermy is that it
allows sustained high-energy activity
-The tradeoff is that the high metabolic rate
requires constant and high energy intake
(food)
14
Endotherms
In animal physiology, size does matter!
-Smaller animals have much higher
metabolic rates per unit body mass relative
to larger animals
-Small endotherms in cold environments
require significant insulation to maintain
their body temperature
-Large endotherms in hot environments
usually have little insulation
15
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8
Mass-specific metabolic rate
(mL O2 x g–1 x h–1)
7
Shrew
6
5
4
3
Harvest mouse
2
1
Kangaroo mouse
Cactus mouse
Mouse
Flying squirrel
Cat
Rat
Dog Sheep
Rabbit
0
0.01
0.1
1
10
log Mass (kg)
Human Horse Elephant
100
1000
16
Endotherms
When temperatures fall below a threshold,
animals resort to thermogenesis, or use of
normal energy metabolism to produce heat
-Shivering thermogenesis uses muscles to
generate heat, without producing useful
work
-Nonshivering thermogenesis alters fat
metabolism to produce heat instead of ATP
-Brown fat is utilized
17
Control of Body Temperature
Mammalian thermoregulation is controlled by
the hypothalamus
-A rise in body temperature is detected by
neurons, which stimulate the heat-losing
center in the hypothalamus
-Sympathetic nerves cause dilation of
peripheral blood vessels, and production
of sweat from sweat glands
18
Control of Body Temperature
-A drop in body temperature is detected by
neurons, which stimulate the heatpromoting center in the hypothalamus
-Sympathetic nerves cause constriction
of peripheral blood vessels, and inhibit
sweating to prevent evaporative cooling
-Hypothalamus releases hormones that
stimulate the thyroid to produce
thyroxin, which stimulates metabolism
19
Control of Body Temperature
Perturbing factor
Negative
feedback
Sun
Response
Body temperature
falls
Effector
Stimulus
Body temperature
rises
Stimulus
Body temperature
drops
• Blood vessels dilate
• Glands release sweat
(–)
Sensor
Integrating Center
Thermoreceptors
Hypothalamus
Effector
• Blood vessels constrict
• Skeletal muscles
contract, shiver
(–)
Response
Perturbing factor
Snow and ice
Negative
feedback
Body temperature
rises
20
Control of Body Temperature
Pyrogens are substances that cause a rise
in temperature
-Act on the hypothalamus to increase the
normal set point to a higher temperature
-Produce the state we call fever
-A normal response to infection
21
Control of Body Temperature
Torpor is a state of dormancy produced by a
reduction in both metabolic rate and body
temperature
-Allows an animal to reduce the need for
food intake
Hibernation is an extreme state in which
torpor lasts for weeks or months
-Practiced usually by mid-sized animals
22
Osmolarity and Osmotic Balance
To maintain osmotic balance, the extracellular
compartment of an animal’s body must be
able to take water from and excrete excess
water into the environment
-Inorganic ions must also be exchanged to
maintain homeostasis
-These exchanges occur across
specialized epithelial cells, and, in most
vertebrates, through the kidney
23
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External environment
Animal body
H2O
(Sweat)
Solutes
and H2O
Extracellular compartment
(including blood)
CO2 and H2O
O2
Solutes Intracellular
and H2O compartments
CO2 and H2O
Solutes
and H2O
Solutes
and H2O
O2
Food
and
H2O
Solutes
and H2O
Urine (excess H2O)
Solutes
and H2O
Waste
24
Osmolarity and Osmotic Balance
Osmotic pressure is the measure of a
solution’s tendency to take in water by
osmosis
Osmolarity is the number of osmotically
active moles of solute per liter of solution
Tonicity is the measure of a solution’s ability
to change the volume of a cell by osmosis
-Solutions may be hypertonic, hypotonic,
or isotonic
25
Osmolarity and Osmotic Balance
Osmoconformers are organisms that are in
osmotic equilibrium with their environment
-Include most marine invertebrates, and
cartilaginous fish (sharks and relatives)
All other vertebrates are osmoregulators
-Maintain a relatively constant blood
osmolarity despite different concentrations
in their environment
26
Osmolarity and Osmotic Balance
Freshwater vertebrates are hypertonic to
their environment
-Have adapted to prevent water from
entering their bodies, and to actively
transport ions back into their bodies
Marine vertebrates are hypotonic to their
environment
-Have adapted to retain water by drinking
seawater and eliminating the excess ions
through kidneys and gills
27
Osmoregulatory Organs
In many animals, removal of water or salts is
coupled with removal of metabolic wastes
through the excretory system
A variety of mechanisms have evolved to
accomplish this
-Single-celled protists use contractile
vacuoles
28
Osmoregulatory Organs
Invertebrates use specialized cells & tubules
-Flatworms use protonephridia which
branch into bulblike flame cells
-Open to the outside of the body, but not
to the inside
-Earthworms use nephridia
-Open both to the inside and outside of
the body
29
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Fluid
Flame cell
Cilia
Collecting
tubule
Excretory
pore
30
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Nephridium Capillary
network
Nephrostome
Coelomic fluid
Bladder
Pore for
urine excretion
31
Osmoregulatory Organs
Insects use Malpighian tubules, which are
extensions of the digestive tract
-Waste molecules and K+ are secreted into
tubules by active transport
-Create an osmotic gradient that draws
water into the tubules by osmosis
-Most of the water and K+ is then
reabsorbed into the open circulatory
system through hindgut epithelium
32
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Rectum
Malpighian
tubules
Waste
(active transport)
K+
H2O
(osmosis)
Anus
(active
transport)
Rectum
Ions and H2O
Hindgut
Midgut
33
Osmoregulatory Organs
The kidneys of vertebrates consist of
thousands of repeating units, nephrons
-Create a tubular fluid by filtering the blood
under pressure through the glomerulus
-Filtrate contains many small molecules, in
addition to water and waste products
-Most of these molecules and water are
reabsorbed into the blood
-Waste products are eliminated from
the body in the form of urine
34
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Proximal arm
Distal arm
Glomerulus
H2O
Glucose
H2O
Amino acids
H2O
Divalent ions
H2O
Na+ and
Cl–
Na+ and
Cl–
Collecting duct
H2O
Intermediate
segment
(loop of Henle)
35
Evolution of the Vertebrate Kidney
Kidneys are thought to have evolved among
the freshwater teleosts, or bony fishes
-Body fluids are hypertonic with respect to
surrounding water, causing two problems
1. Water enters body from environment
-Fishes do not drink water and
excrete large amounts of dilute urine
2. Solutes tend to leave the body
-Reabsorb ions across nephrons 36
Evolution of the Vertebrate Kidney
In contrast, marine bony fishes have body
fluids that are hypotonic to seawater
-Water tends to leave their bodies by
osmosis across their gills
-Drink large amounts of seawater
-Actively transport monovalent ions out
of the blood across the gill surfaces
-Excrete urine isotonic to body fluids
-Contains divalent cations
37
Evolution of the Vertebrate Kidney
Freshwater Fish
Large glomerulus
Marine Fish
Na+
and Cl–
Kidney tubule
Kidney: Excretion
of dilute urine
Mg2+ and
SO42–
Active tubular
secretion of
Mg2+ and
SO42–
Stomach:
Passive reabsorption
of water,
Na+ and Cl–
Food,
seawater
Food
Gills:
Active absorption
of Na+ and Cl–, water
enters osmotically
Glomerulus
reduced or
absent
Active tubular
reabsorption
of Na+ and Cl–
Intestinal
wastes
Urine
Gills:
Active secretion
Intestinal wastes:
of Na+ and Cl–,
Mg2+ and SO42–
water loss
voided with feces
Kidney:
Excretion of urea,
little water,
Mg2+ and SO42–
38
Evolution of the Vertebrate Kidney
Cartilaginous fish, including sharks and rays,
reabsorb urea from the nephron tubules
-Maintain a blood urea concentration that is
100 times higher than that of mammals
-Blood is isotonic to surrounding sea
-These fishes do not need to drink
seawater or remove large amounts of
ions from their bodies
39
Evolution of the Vertebrate Kidney
The amphibian kidney is identical to that of
freshwater fish
The kidneys of reptiles are very diverse
-Marine reptiles drink seawater and excrete
an isotonic urine
-Eliminate excess salt via salt glands
-Terrestrial reptiles reabsorb much of the
salt and water in their nephron tubules
-Don’t excrete urine, but empty it into
cloaca
40
Evolution of the Vertebrate Kidney
Mammals and birds are the only vertebrates
that can produce urine that is hypertonic to
body fluids
-Accomplished by the loop of Henle
Birds have relatively few or no nephrons with
long loops, and so cannot produce urine as
concentrated as that of mammals
-Marine birds excrete excess salt from salt
glands near the eyes
41
Evolution of the Vertebrate Kidney
Salt gland
Salt secretion
42
Nitrogenous Wastes
When amino acids and nucleic acids are
catabolized, they produce nitrogenous
wastes that must be eliminated from the
body
-First step is the removal of the amino
(-NH2) group, and its combination with H+
to form ammonia (NH3) in the liver
-Toxic to cells, and thus it is only safe
in dilute concentrations
43
Nitrogenous Wastes
Bony fishes and amphibian tadpoles eliminate
most of the ammonia by diffusion via gills
Elasmobranchs, adult amphibians, and
mammals convert ammonia into urea,
which is soluble in water
Birds, terrestrial reptiles, and insects convert
ammonia into the water-insoluble uric acid
-Costs most energy, but saves most water
44
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Amino acids and nucleic acids
Catabolism
Ammonia
by-product
Costs energy, saves water
Eliminated
Directly
Converted
to Urea
Converted
to Uric Acid
Ammonia
Urea
Uric acid
O
NH3
NH2
O
NH
C
NH2
O
Most bony fish
and aquatic
invertebrates
Mammals, amphibians,
and cartilagenous fish
H
N
O
N
H
N
H
Reptiles, birds,
and insects
45
Nitrogenous Wastes
Mammals also produce uric acid, but from
degradation of purines, not amino acids
-Most have an enzyme called uricase,
which convert uric acid into a more soluble
derivative called allantoin
-Humans lack this enzyme
-Excessive accumulation of uric acid
in joints causes gout
46
The Mammalian Kidney
Each kidney receives blood from a renal
artery, and produces urine
-Urine drains from each kidney through a
ureter into a urinary bladder
Within the kidney, the mouth of the ureter
flares open to form the renal pelvis
-Receives urine from the renal tissue
-Divided into an outer renal cortex and
inner renal medulla
47
The Mammalian Kidney
Inferior
vena cava
Adrenal gland
Renal artery
and vein
Aorta
Ureter
Urinary
bladder
Renal
cortex
Nephron
tubule
Juxtamedullary Cortical
nephron
nephron
Renal
cortex
Ureter
Renal Renal
pelvis medulla
b.
Collecting
duct
Renal
medulla
Urethra
a.
c.
48
The Mammalian Kidney
The kidney has three basic functions
-Filtration = Fluid in the blood is filtered out
of the glomerulus into the tubule system
-Reabsorption = Selective movement of
solutes out of the filtrate back into the blood
via peritubular capillaries
-Secretion = Movement of substances from
the blood into the extracellular fluid, then
into the filtrate in the tubular system
49
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Excretion
Secretion
from blood
Glomerulus
Filtration
Bowman's
capsule
Afferent
arteriole
Reabsorption Renal
tubule
to blood
Efferent
arteriole
50
The Mammalian Kidney
Each kidney is made up of about 1 million
functioning nephrons
-Juxtamedullary nephrons = Have long
loops that dip deeply into the medulla
-Cortical nephrons = Have shorter loops
Blood is carried by an afferent arteriole to a
tuft of capillaries in cortex, the glomerulus
-Blood is filtered as it is forced through
porous capillary walls
51
The Mammalian Kidney
Blood components that are not filtered drain
into an efferent arteriole, which empties
into peritubular capillaries
Glomerular filtrate enters the first region of the
nephron tubules, Bowman’s capsule
-Goes into the proximal convoluted tubule
-Then moves down the medulla and
back up into cortex in the loop of Henle
52
The Mammalian Kidney
After leaving the loop, the fluid is delivered to
a distal convoluted tubule in the cortex
-Drains into a collecting duct
-Merges with other collecting ducts to
empty its contents, now called urine,
into the renal pelvis
53
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Proximal
convoluted tubule
Distal
convoluted tubule
Peritubular
capillaries
Glomerulus
Bowman's
capsule
Descending
limb of loop
of Henle
Ascending
limb of loop
of Henle
Renal
artery
Collecting duct
Loop of Henle
Renal
vein Vasa recta
To ureter
54
Reabsorption and Secretion
Most of the water and dissolved solutes that
enter the glomerular filtrate must be
returned to the blood by reabsorption
-Water is reabsorbed by the proximal
convoluted tubule
-Reabsorption of glucose and amino acids is
driven by active transport carriers
Secretion of waste products involves transport
across capillary membranes and kidney
tubules into the filtrate
55
Excretion
A major function of the kidney is elimination of
a variety of potentially harmful substances
that animals eat and drink
-In addition, urine contains nitrogenous
wastes, and may contain excess K+, H+ and
other ions that are removed from blood
Kidneys are critically involved in maintaining
homeostasis
56
Transport in the Nephron
A mechanism is needed to create an osmotic
gradient between the glomerular filtrate and
the blood, to allow reabsorption of water
-Virtually all nutrient molecules in the filtrate,
and two-thirds of the NaCl and water, are
reabsorbed by proximal convoluted tubule
-Active transport of Na+ out of proximal
tubule is followed by passive movement
of K+ and water
57
Transport in the Nephron
The function of the loop of Henle is to create
a gradient of increasing osmolarity from the
cortex to the medulla
-Active extrusion of NaCl from the
ascending loop creates an osmotic gradient
-Allows reabsorption of water from
descending loop and collecting duct
-The two limbs of the loop form a
countercurrent multiplier system, that
creates a hypertonic renal medulla
58
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Bowman's Proximal tubule
capsule
+
Distal tubule
Na
Cl–
Total solute concentration (mOsm)
H2O
300
Cortex
Glomerulus
Collecting
duct
600
H2O
Na+
Cl–
H2O
Outer medulla
Urea
H2O
loop of
Henle
1200
Inner medulla
H2O
59
Transport in the Nephron
Filtrate that reaches distal convoluted tubule
and enters the collecting duct is hypotonic
-The hypertonic interstitial fluid of the renal
medulla pulls water out of the collecting duct
and into the surrounding blood vessels
Kidneys also regulate electrolyte balance in
the blood by reabsorption and secretion
-K+, H+, and HCO3–
60
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Reabsorbed
HCO3–
Filtered
H+
K+
Secreted Secreted
Reabsorbed H+
K+
+
K
K+
H+
Distal
convoluted
tubule
HCO3–
61
Hormones Control Osmoregulation
Kidneys maintain relatively constant levels of
blood volume, pressure, and osmolarity
-Also regulate the plasma K+ and Na+
concentrations and blood pH within narrow
limits
-These homeostatic functions of kidneys
are coordinated primarily by hormones
62
Hormones Control Osmoregulation
Antidiuretic hormone (ADH) is produced by
the hypothalamus and secreted by the
posterior pituitary gland
-Stimulated by an increase in the osmolarity
of blood
-Causes walls of distal tubule and
collecting ducts to become more
permeable to water
-Increases reabsorption of water
63
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Stimulus
Dehydration
Stimulus
Negative feedback
Increased osmolality
of plasma
(–)
Sensor
Osmoreceptors
in hypothalamus
Effector
Posterior
pituitary gland
Increased
ADH secretion
(–)
Thirst
Response
Increased reabsorption
of water
Response
Increased
water intake
64
Hormones Control Osmoregulation
Aldosterone is secreted by the adrenal cortex
-Stimulated by low levels of Na+ the blood
-Causes distal tubule and collecting
ducts to reabsorb Na+
-Reabsorption of Cl– and water follows
Low levels of Na+ the blood are accompanied
by a decrease in blood volume
-Renin-angiotensin-aldosterone system is
activated
65
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Stimulus
Low blood
pressure
Stimulus
1
Low blood
flow
Effector
2
Angiotensinogen
3
(–)
Effector
Sensor
Renin
Juxtaglomerular
apparatus
Negative
feedback
Response
Constrict blood
vessels
4
5
Effector
Angiotensin II
6
Effector
Response
Aldosterone
Increased
blood
volume
Adrenal
cortex
8
Effector
Response
Increased Na+ and
Cl–, and H2O
reabsorption
7
Kidney
66
Hormones Control Osmoregulation
Atrial natriuretic hormone opposes the
action of aldosterone in promoting salt and
water retention
-Secreted by the right atrium of the heart in
response to an increased blood volume
-Promotes the excretion of salt and water
in the urine and lowering blood volume
67