Chapter 25: Control of Body
Temperature and Water Balance
vocab
1. Thermoregulation: the maintenance of
internal temperature within narrow limits
– Aided by adaptations
2. Osmoregulation: the control of the gain and loss
of water and solutes and the control of excretion
3. Excretion: the disposal of nitrogen containing
wates
Endotherms vs ectotherms
• Endoterms: they are
warmed by heat
generated by their own
metabolism
– Examples: birds and
mammals
• Ectotherms: they gain
most of their heat from
external sources
– Examples: amphibians,
lizards, many fishes and
most invertebrates
How heat is gained or lost
1. conduction: the transfer of
thermal motion (heat)
between molecules of
objects in direct contact
2. Convection: the transfer
of heat by the movement
of air
3. Radiation: the emission of
electromagnetic waves
4. Evaporation: the loss of
heat from the surface of a
liquid that is losing some
of its molecules as a gas
Metabolic Heat Production
• In cold weather,
hormonal changes tend
to boost the metabolic
rate of birds and
mammals, increasing
heat production
• Shivering produces heat
• Honeybees survive
winters by clustering
together and shivering
in their hive
Insulation
• Hair, feathers, or fat
layers
• Most land mammals
and birds react to the
cold by raising their fur
or feathers next to the
warm skin
• Aquatic animals are
insulated by blubber
Circulatory adaptation
• Heat loss can be altered
by blood flow
• In a bird or mammal,
nerve signals surface
blood vessels to constrict
or dilate. When vessels
constrict, less blood flows
from the warm body core
to the body surface
reducing the rate of heat
loss
Countercurrent heat exchange
• Warm and cold blood
flow in opposite
directions in two
adjacent blood vessels
Evaporative cooling and behavioral
responses
Evaporative cooling
• Evaporative cooling can be
increased by panting,
sweating, or spreading
saliva to body surfaces
• Humans sweat
• Dogs lose heat as moisture
evaporates from their
nostrils and mouth during
panting
Behavioral responses
• Migration
• Lizards bask in the sun
• Animals bathe
• Dress for warmth
Nitrogen wastes
• Ammonia:
– aquatic animals
– Most toxic of metabolic byproducts
– Too toxic to be stored in
the body but is highly
soluble in water
– Soft bodied organisms
(planaria) diffuse ammonia
across it body surface
– Fish diffuse it across their
gills
Nitrogen wastes
• Urea
– Mammals, most
amphibians, sharks and
some bony fish
– Highly soluble in water
– Can be disposed of with
relatively little water loss
Nitrogen waste
• Uric acid
– Birds, many reptiles,
insects, land snails and a
few amphibians living in
deserts
– Avoid water loss
problem completely
– Relatively nontoxic
– Largely insoluble in
water
– White material in bird
droppings
Urinary System
• Plays a central role in
homeostasis, forming
and excreting urine
while regulating the
amount of water and
ions in the body fluids
Kidneys
• Human body contains
about 5 L of blood which
repeatedly circulates
through the capillaries in
the kidneys everyday for
about 1100-2000 L per
day
• From this the kidneys
extract about 180 L of
filtrate (water, urea and
valuable solutes)
Kidneys
• Blood to be filtered
enters each kidney by
the renal artery
• Blood gets filtered and
leaves each kidney by
the renal vein
Kidneys continued
• Urine leaves each
kidney through the
ureter and gets stored
in the bladder.
• The bladder then
empties during
urination
• Urine leaves the body
by the urethra
kidneys
• Renal cortex and renal
medulla: 2 main
regions of the kidneys
• Each kidney contains
about a million tiny
units called nephrons
nephrons
• Extracts a tiny amount of
filtrate from the blood and
then refines the filtrate into
a much smaller quantity of
urine
• Each nephron starts and
ends with in the kidney’s
cortex
• The receiving end of the
nephron is the Bowman’s
capsule and the other end is
the collecting duct which
carries urine to the renal
pelvis
nephron
• Bowman’s capsule envelops a
ball of capillaries called the
glomerulus
• Glomerulus + Bowman’s
Capsule=blood filtering unit of
the nephron
• Blood pressure forces water
and solutes from the blood in
the glomerular capillaries
across the wall of the
Bowman’s Capsule and into
the nephron tubule- this
process creates filtrate, leaving
blood cells and large
molecules
Nephrons continued
• Tubule has three sections
– Proximal tubule
– Loop of henle (carries
filtrate toward the medulla
and back toward the cortex
– Distal tubule (drains into a
collect duct which receives
filtrate from many
nephrons)
From the collecting ducts the
processed filtrate or urine
passes into the renal pelvis
and then into the ureter
4 key processes of the Urinary System
1. filtration: water and all other molecules small
enough to be forced through the capillary wall
enter the nephron tubule from the glomeruls
2. Reabsorption: water and valuable solutes are
returned to the blood stream from the filtrate
3. Secretion: substance in the blood are
transported into the filtrate/ eliminates certain
drugs and other toxic substances from the blood
4. Excretion: urine passes from the kidneys to the
outside
Proximal and Distal tubules
• Proximal tubule actively
transports nutrients from the
filtrate into the interstitial fluid to
be reabsorbed into the capillaries
• NaCl is reabsorbed by both the
proximal and distal tubules and
water follows by osmosis
• Secretion of excess hydrogen and
HCO3- occur here helping to
regulate blood pH
• Potassium concentration in the
blood is regulated by secretion of
excess potassium into the distal
tubule
• Drugs and poisons that were
processed in the liver are
secreted into the proximal tubule
Loop of Henle and collecting duct
• Water reabsorption
• Carries the filtrate deep
into the medulla and
then back to the cortex
Collecting duct
• Final refining of the
filtrate
• Determines how much
salt is excreted in the
urine
• The nephron returns
much of the water that
filters into it from the
blood-this water
conservation is one of the
kidneys major funcitons
ADH
• Antidiuretic hormone
• Our kidneys maintain a
balance between water
and solutes in our body
fliuds
• When the solute
concentration rises
above a set point a
control center in the
brain increases the
blood level of ADH