Download temp, water balance and the urinary sytem

Temperature, Osmotic Regulation
and the Urinary System
Chapter 50
Regulating Body Temperature
The rate of any chemical reaction is affected
by temperature
-Thus, the effect of temperature is
mainly on the enzymes involved in
metabolism
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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
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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
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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
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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”
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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
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Ectotherms
Ectotherms regulate temperature using
behavior
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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
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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
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high-energy activity
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
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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)
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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
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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
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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
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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
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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
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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,
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or isotonic
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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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