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2. Increased metabolic heat production occurs
when
a. hormonal changes boost the metabolic
rate in birds and mammals,
b. birds and mammals shiver,
c. organisms increase their physical activity, and
d. honeybees cluster and shiver.
3. Insulation is provided by
a. hair,
b. feathers, and
c. fat layers.
4. Circulatory adaptations include
a. increased or decreased blood flow to
skin and
b. countercurrent heat exchange, with
warm and cold blood flowing in opposite
directions.
5. Evaporative cooling may involve
a. sweating,
b. panting, or
c. spreading saliva on body surfaces.
6. Behavioral responses
a. are used by endotherms and ectotherms
and
b. include
i. moving to the sun or shade,
ii. migrating, and
iii. bathing.
25
Control of Body
Temperature and Water Balance
CHAPTER
Lecture Outline
I. Introduction (Bears Essay)
A. During cold winters, bears are often dormant.
B. Physiological processes aid homeostasis,
keeping the body temperature about 5ºC below normal.
1. Body fat and dense fur provide insulation.
2. Blood flow to extremities is reduced.
3. Nitrogen-containing wastes are metabolized
differently.
C. Homeostasis is the maintenance of steady internal conditions despite fluctuations in the external environment.
D. Examples of homeostasis include
1. thermoregulation—the maintenance of internal temperature within narrow limits,
2. osmoregulation—the control of the gain and
loss of water and solutes, and
3. excretion—the disposal of nitrogencontaining wastes.
II. Thermoregulation
A. 25.1 An animal’s regulation of body temperature helps maintain homeostasis
1. Thermoregulation is
a. the process by which animals maintain
an internal temperature within a tolerable
range and
b. a form of homeostasis.
2. Ectothermic animals
a. gain most of their heat from external
sources and
b. include many fish, most amphibians, lizards, and most invertebrates.
3. Endothermic animals
a. derive body heat mainly from their metabolism and
b. include birds, mammals, a few reptiles
and fish, and many insects.
B. 25.2 Heat is gained or lost in four ways
1. Heat exchange with the environment may
occur by
a. conduction—the transfer of heat by direct contact,
b. convection—the transfer of heat by
movement of air or liquid past a surface,
c. radiation—the emission of electromagnetic waves, or
d. evaporation—the loss of heat from the
surface of a liquid that is losing some of
its molecules as a gas.
C. 25.3 Thermoregulation involves adaptations
that balance heat gain and loss
1. Five general categories of adaptations help
animals thermoregulate.
III.
Osmoregulation and Excretion
A. 25.4 Animals balance the level of water and
solutes through osmoregulation
1. Osmoregulation is the homeostatic control
of the uptake and loss of water and solutes
such as salt and other ions.
2. Osmosis is one process whereby animals
regulate their uptake and loss of fluids.
3. Osmoconformers
a. have body fluids with a solute concentration equal to that of seawater,
b. face no substantial challenges in water
balance, and
c. include many marine invertebrates.
4. Osmoregulators
a. have body fluids whose solute concentrations differ from that of their environment,
b. must actively regulate water movement,
and
c. include
i. many land animals,
ii. freshwater animals such as trout, and
iii. marine vertebrates such as sharks.
5. Freshwater fish
a. gain water by osmosis (mainly through
gills),
b. lose salt by diffusion to the more dilute
environment,
c. take in salt through their gills and in food,
and
d. excrete excess water in dilute urine.
6. Saltwater fish
a. lose water by osmosis from the gills and
body surface,
b. drink seawater, and
c. use their gills and kidneys to excrete excess salt.
7. Land animals
a. face the risk of dehydration,
b. lose water by evaporation and waste
disposal,
c. gain water by drinking and eating, and
d. conserve water by
i. reproductive adaptations,
ii. behavior adaptations,
iii. waterproof skin, and
iv. efficient kidneys.
B. 25.5 EVOLUTION CONNECTION: A variety of
ways to dispose of nitrogenous wastes has
evolved in animals
1. Metabolism produces toxic by-products.
2. Nitrogenous wastes are toxic breakdown
products of proteins and nucleic acids.
3. Animals dispose of nitrogenous wastes in
different ways.
4. Ammonia (NH3) is
a. poisonous,
b. too toxic to be stored in the body,
c. soluble in water, and
d. easily disposed of by aquatic animals.
5. Urea is
a. produced in the vertebrate liver by combining ammonia and carbon dioxide,
b. less toxic,
c. easier to store, and
d. highly soluble in water.
6. Uric acid is
a. excreted by some land animals (insects,
land snails, and many reptiles),
b. relatively nontoxic,
c. largely insoluble in water,
d. excreted as a semisolid paste, conserving water, but
e. more energy expensive to produce.
C. 25.6 The urinary system plays several major
roles in homeostasis
1. The urinary system
a. forms and excretes urine and
b. regulates water and solutes in body fluids.
2. In humans, the kidneys are the main processing centers of the urinary system.
3. Nephrons
a. are the functional units of the kidneys,
b. extract a fluid filtrate from the blood, and
c. refine the filtrate to produce urine.
4. Urine is
a. drained from the kidneys by ureters,
b. stored in the urinary bladder, and
c. expelled through the urethra.
D. 25.7 Overview: The key processes of the urinary system are filtration, reabsorption, secretion, and excretion.
1. Filtration
a. Blood pressure forces water and many
small molecules through a capillary wall
into the start of the kidney tubule.
2. Reabsorption
a. refines the filtrate,
b. reclaims valuable solutes (such as glucose, salt, and amino acids) from the filtrate, and
c. returns these to the blood.
3. Substances in the blood are transported into the filtrate by the process of secretion.
4. By excretion the final product, urine, is excreted via the ureters, urinary bladder, and
urethra.
E. 25.8 Blood filtrate is refined to urine through
reabsorption and secretion
1. Reabsorption in the proximal and distal tubules removes
a. nutrients,
b. salt, and
c. water.
2. pH is regulated by
a. reabsorption of HCO3– and
b. secretion of H+.
3. High NaCl concentration in the medulla
promotes reabsorption of water.
F. 25.9 Hormones regulate the urinary system
1. Antidiuretic hormone (ADH) regulates the
amount of water excreted by the kidneys by
a. signaling nephrons to reabsorb water
from the filtrate, returning it to the blood,
and
b. decreasing the amount of water excreted.
2. Diuretics
a. inhibit the release of ADH and
b. include alcohol and caffeine.
G. 25.10 CONNECTION: Kidney dialysis can be
lifesaving
1. Kidney failure can result from
a. hypertension,
b. diabetes, and
c. prolonged use of common drugs, including alcohol.
2. A dialysis machine
a. removes wastes from the blood and
b. maintains its solute concentration.
Vocabulary to Know
ammonia
filtrate
renal medulla
antidiuretic hormone
filtration
secretion
(ADH)
glomerulus (plural, glomeruli)
thermoregulation
Bowman’s capsule
loop of Henle
urea
collecting duct
nephron
ureter
countercurrent heat exchange
osmoconformer
urethra
dialysis
osmoregulation
uric acid
distal tubule
osmoregulator
urinary bladder
ectotherm
proximal tubule
urinary system
endotherm
reabsorption
urine
excretion
renal cortex
Word Roots
anti- = against; -diure = urinate (antidiuretic hormone: a hormone made by the hypothalamus and secreted by
the posterior pituitary that promotes water retention by the kidneys)
counter- = opposite (countercurrent heat exchange: parallel blood vessels that convey warm and cold blood in
opposite directions, maximizing heat transfer to the cold blood)
dia- = through; -lyso = loosen (dialysis: the separation and disposal of metabolic wastes from the blood by mechanical means; an artificial method of performing the functions of the kidneys)
ecto- = outside; -therm = heat (ectotherm: an animal that warms itself mainly by absorbing heat from its surroundings)
endo- = within; -therm = heat (endotherm: an animal that derives most of its body heat from its own metabolism)
glomer- = a ball (glomerulus: the ball of capillaries in the nephron of the vertebrate kidney surrounded by Bowman’s capsule; together, the glomerulus and Bowman’s capsule produce filtrate from blood)
osmo- = pushing; -conform = the same (osmoconformer: an organism whose body fluids have a solute concentration equal to that of its surroundings); -regula = regular (osmoregulation: the control of the gain and loss
of water and dissolved solutes in an organism; osmoregulator: an organism whose body fluids have a solute
concentration different from that of its environment and that must use energy to control water loss or gain)
reni- = a kidney; cortex- = shell (renal cortex: the outer portion of the vertebrate kidney; renal medulla: the inner portion of the vertebrate kidney)
thermo- = heat; -regula = regular (thermoregulation: the maintenance of internal temperature within a range
that allows cells to function efficiently)
Name
Date
Class
Ch. 25 Study Guide: On a separate sheet of paper- Use the Chapter 25 Outline to construct a summary
for each of the following objectives by converting the appropriate information into paragraph form.
Opening Essay
Explain how bear physiology adjusts during a period of dormancy.
Thermoregulation
25.1 Distinguish between endotherms and ectotherms, providing examples of each.
25.2
Describe the four ways that heat is gained or lost by an animal.
25.3
Describe the five general categories of adaptations that help animals thermoregulate.
Provide specific examples of each.
Osmoregulation and Excretion
25.4 Describe the osmoregulatory challenges and associated adaptations of freshwater and saltwater fish, terrestrial arthropods, and terrestrial vertebrates.
25.5
Describe the three ways that animals eliminate nitrogenous wastes, and the
advantages and disadvantages of each method.
25.6
Describe the general and specific structure of the human kidney. Explain how this organ
promotes homeostasis.
25.7
Describe the four major processes by which the human excretory system
produces and disposes of urine.
25.8
Describe the key events in the process of converting filtrate into urine in the kidneys.
25.9
Explain how antidiuretic hormone contributes to homeostasis.
25.10 Explain how a dialysis machine functions.