chap 40 animal structure and function. epithelia are classified by the number of cell layers and the...
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Chap 40
Animal Structure and Function
• Epithelia are classified by the number of cell layers and the shape of the cells on the free surface.
• A simple epithelium has a single layer of cells, and a stratified epithelium has multiple tiers of cells.
• The shapes of cells may be cuboidal (like dice), columnar (like bricks on end), or squamous (flat like floor tiles).
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Fig. 40.1
• There are three kinds of connective tissue fibers, which are all proteins: collagenous fibers, elastic fibers, and reticular fibers.
1. Collagenous fibers are made of collagen.– Collagenous fibers are nonelastic and do not tear
easily when pulled lengthwise.
2. Elastic fibers are long threads of elastin.– Elastin fiber provide a rubbery quality.
3. Reticular fibers are very thin and branched.– Composed of collagen and continuous with
collagenous fibers, they form a tightly woven fabric that joins connective tissue to adjacent tissues.
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CoREl
Six major types of connective tissues in vertebrates are:
1. loose connective tissue, 2. adipose tissue, 3. fibrous connective tissue, 4. cartilage, 5. bone, and 6. blood.
– Each has a structure correlated with its specialized function.
Fig. 40.2Laura finds computers at Best Buy.
Binds epithelia to underlying tisssue
Binds epithelia to underlying tisssue
Pads, insulates, stores fuel
Pads, insulates, stores fuel
Tendons and ligaments
Tendons and ligaments
1
2
3
4
5
6
• Loose connective tissue binds epithelia to underlying tissues and functions as packing materials, holding organs in place.– Loose connective tissue has all three fiber
types.
• Two cell types predominated in the fibrous mesh of loose connective tissue.– Fibroblasts secrete the protein
ingredients of the extracellular fibers.– Macrophages are amoeboid cells that
roam the maze of fibers, engulfing bacteria and the debris of dead cells by phagocytosis.Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Blood functions differently from other connective tissues, but it does have an extensive extracellular matrix.– The matrix is a liquid called plasma, consisting of
water, salts, and a variety of dissolved proteins.– Suspended in the plasma are erythrocytes (red blood
cells), leukocytes (white blood cells) and cell fragments called platelets.• Red cells carry oxygen.
• White cells function in defense against viruses, bacteria, and other invaders.
• Platelets aid in blood clotting.
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• Cartilage has an abundance of collagenous fibers embedded in a rubbery matrix made of a substance called chondroitin sulfate, a protein-carbohydrate complex.– Chondrocytes secrete collagen and chondroitin sulfate.
– The composite of collagenous fibers and chondroitin sulfate makes cartilage a strong yet somewhat flexible support material.
– The skeleton of a shark is made of cartilage and the embryonic skeletons of many vertebrates are cartilaginous.
– We retain cartilage as flexible supports in certain locations, such as the nose, ears, and vertebral disks.
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• The skeleton supporting most vertebrates is made of bone, a mineralized connective tissue.– Osteoblasts deposit a matrix of collagen.
– Then, calcium, magnesium, and phosphate ions combine and harden within the matrix into the mineral hydroxyapatite.
– The osteoblast becomes an osteocyte in the Lacuna.
– The combination of hard mineral and flexible collagen makes bone harder than cartilage without being brittle.
– The microscopic structure of hard mammalian bones consists of repeating units called osteons (or Haversian systems)..• Each osteon has concentric layers of
mineralized matrix deposited around a
central canal containing blood vessels
and nerves that service the bone.
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osteon
–The osteoblast becomes an osteocyte in the Lacuna.
• Nervous tissue senses stimuli and transmits signals from one part of the animal to another.– The functional unit of nervous tissue is the neuron,
or nerve cell.– It consists of a cell body and two or more
extensions, called dendrites and axons.– Dendrites transmit nerve impulses from their tips
toward the rest of the neuron.– Axons transmit impulses toward
another neuron or toward an effector, such as a muscle cell.
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Fig. 40.3
• There are three types of muscle tissue in the vertebrate body: skeletal muscle, cardiac muscle, and smooth muscle.
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Fig. 40.4
One cell
• Attached to bones by tendons, skeletal muscle is responsible for voluntary movements.– Skeletal muscle is also called striated muscle
because the overlapping filaments give the cells a striped (striated) appearance under the microscope.
• Cardiac muscle forms the contractile wall of the heart.– It is striated like cardiac muscle, but cardiac cells
are branched.– The ends of the cells are joined by intercalated
disks, which relay signals from cell to cell during a heartbeat.
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Animals w/o a circulatory system must keep a large SA/Volume ratio
Multi-celled Animals are two layered thick so each cell is in contact with the environment.
• Organisms with more complex body plans– Have highly folded internal surfaces specialized for
exchanging materials
External environment
Food CO2 O2Mouth
Animalbody
Respiratorysystem
Circulatorysystem
Nutrients
Excretorysystem
Digestivesystem
Heart
Blood
Cells
Interstitialfluid
Anus
Unabsorbedmatter (feces)
Metabolic wasteproducts (urine)
The lining of the small intestine, a diges-tive organ, is elaborated with fingerlikeprojections that expand the surface areafor nutrient absorption (cross-section, SEM).
A microscopic view of the lung reveals that it is much more spongelike than balloonlike. This construction provides an expansive wet surface for gas exchange with the environment (SEM).
Inside a kidney is a mass of microscopic tubules that exhange chemicals with blood flowing through a web of tiny vessels called capillaries (SEM).
0.5 cm
10 µm
50 µ
m
Figure 40.4
• The amount of energy an animal uses in a unit of time is called its metabolic rate - the sum of all the energy-requiring biochemical reactions occurring over a given time interval.– Energy is measured in calories (cal) or kilocalories
(kcal).• A kilocalorie is 1,000 calories.
• The term Calorie, with a capital C, as used by many nutritionists, is actually a kilocalorie.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Metabolic rate provides clues to an animal’s bioenergetic “strategy”
• There are two basic bioenergetic “strategies” used by animals.– Birds and mammals are mainly endothermic,
maintaining their body temperature at a certain level with heat generated by metabolism.• Endothermy is a high-energy strategy that permits
intense, long-duration activity of a wide range of environmental temperatures.
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– Most fishes, amphibians, reptiles, and invertebrates are ectothermic, meaning they do not produce enough metabolic heat to have much effect on body temperature.• The ectothermic strategy requires much less energy than
is needed by endotherms, because of the energy cost of heating (or cooling) an endothermic body.
• However, ectotherms are generally incapable of intense activity over long periods.
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• One of animal biology’s most intriguing, but largely unanswered questions has to do with the relationship between body size and metabolic rate.– Physiologists have shown that the amount of energy it
takes to maintain each gram of body weight is inversely related to body size.
– For example, each gram of a mouse consumes about 20 times more calories than a gram of an elephant.
3. Metabolic rate per gram is inversely related to body size
among similar animals
• One hypothesis for the inverse relationship between metabolic rate and size is that the smaller the size of an endotherm, the greater the energy cost of maintaining a stable body temperature.– The smaller the animal, the greater its surface to
volume ratio, and thus the greater loss of heat to (or gain from) the surroundings.
• However, this hypothesis fails to explain the inverse relationship between metabolism and size in ectotherms.
• Nor is it supported by experimental tests.• Researchers continue to search for causes
underlying this inverse relationship.Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• The basal metabolic rate (BMR)– Is the metabolic rate of an endotherm at rest
• The standard metabolic rate (SMR)– Is the metabolic rate of an ectotherm at rest
• For both endotherms and ectotherms– Activity has a large effect on metabolic rate
Activity and Metabolic Rate
Size and Metabolic Rate
• Metabolic rate per gram– Is inversely related to body size among similar
animals
• In general, an animal’s maximum possible metabolic rate– Is inversely related
to the duration of the activity
Figure 40.9
Max
imum
met
abol
ic r
ate
(kca
l/min
; log
sca
le)
500
100
50
10
5
1
0.5
0.1
A H
AH
A
A
A
H
H
H
A = 60-kg alligator
H = 60-kg human
1second
1minute
1hour
Time interval
1day
1week
Key
Existing intracellular ATP
ATP from glycolysis
ATP from aerobic respiration
• The BMR of a human is much higher than the SMR of an alligator.
• Both can reach high levels of maximum potential metabolicrates for short periods, but metabolic rate drops as the duration of the activityincreases and the source of energy shifts toward aerobic respiration.
Fig. 40.12
• Sustained activity depends on the aerobic process of cellular respiration for ATP supply.– An endotherm’s respiration rate is about 10 times
greater than an ectotherm’s.– Only endotherms are capable of long-duration
activities such as distance running.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• An animal’s use of energy– Is partitioned to BMR (or SMR), activity,
homeostasis, growth, and reproductionEndotherms Ectotherm
Ann
ual e
nerg
y ex
pend
iture
(kc
al/y
r)
800,000Basalmetabolicrate
ReproductionTemperatureregulation costs
Growth
Activitycosts
60-kg female humanfrom temperate climate
Total annual energy expenditures (a)
340,000
4-kg male Adélie penguinfrom Antarctica (brooding)
4,000
0.025-kg female deer mousefrom temperateNorth America
8,000
4-kg female pythonfrom Australia
Ene
rgy
expe
nditu
re p
er u
nit
mas
s (k
cal/k
g•da
y)
438
Deer mouse
233
Adélie penguin
36.5
Human
5.5
Python
Energy expenditures per unit mass (kcal/kg•day)(b)
Figure 40.10a, b
• Concept 40.4: Animals regulate their internal environment within relatively narrow limits
• The internal environment of vertebrates– Is called the interstitial fluid, and is very different
from the external environment
• Homeostasis is a balance between external changes– And the animal’s internal control mechanisms that
oppose the changes
• Regulating and conforming– Are two extremes in how animals cope with
environmental fluctuations
Regulating and Conforming
• An animal is said to be a regulator– If it uses internal control mechanisms to moderate
internal change in the face of external, environmental fluctuation
• An animal is said to be a conformer– If it allows its internal condition to vary with certain
external changes
• Mechanisms of homeostasis– Moderate changes in the internal environment
Mechanisms of Homeostasis
• A homeostatic control system has three functional components– A receptor, a control center, and an effector
Figure 40.11
Response
No heatproduced
Roomtemperaturedecreases
Heaterturnedoff
Set point
Toohot
Setpoint
Control center:thermostat
Roomtemperatureincreases
Heaterturnedon
Toocold
Response
Heatproduced
Setpoint
• Most homeostatic control systems function by negative feedback– Where buildup of the end product of the
system shuts the system off
• A second type of homeostatic control system is positive feedback– Which involves a change in some variable that
triggers mechanisms that amplify the change
• Concept 40.5: Thermoregulation contributes to homeostasis and involves anatomy, physiology, and behavior
• Thermoregulation– Is the process by which animals maintain an
internal temperature within a tolerable range
• Ectotherms– Include most invertebrates, fishes, amphibians, and
non-bird reptiles
• Endotherms– Include birds and mammals
Ectotherms and Endotherms
• In general, ectotherms– Tolerate greater
variation in internal temperature than endotherms
Figure 40.12
River otter (endotherm)
Largemouth bass (ectotherm)
Ambient (environmental) temperature (°C)
Bod
y te
mpe
ratu
re (
°C)
40
30
20
10
10 20 30 400
• Endothermy is more energetically expensive than ectothermy– But buffers animals’ internal temperatures
against external fluctuations– And enables the animals to maintain a high
level of aerobic metabolism
Modes of Heat Exchange• Organisms exchange heat by four physical
processesRadiation is the emission of electromagnetic waves by all objects warmer than absolute zero. Radiation can transfer heat between objects that are not in direct contact, as when a lizard absorbs heat radiating from the sun.
Evaporation is the removal of heat from the surface of aliquid that is losing some of its molecules as gas. Evaporation of water from a lizard’s moist surfaces that are exposed to the environment has a strong cooling effect.
Convection is the transfer of heat by the movement of air or liquid past a surface, as when a breeze contributes to heat loss from a lizard’s dry skin, or blood moves heat from the body core to the extremities.
Conduction is the direct transfer of thermal motion (heat) between molecules of objects in direct contact with each other, as when a lizard sits on a hot rock.
Figure 40.13
Balancing Heat Loss and Gain
• Thermoregulation involves physiological and behavioral adjustments– That balance heat gain and loss
Insulation
• Insulation, which is a major thermoregulatory adaptation in mammals and birds– Reduces the flow of heat between an animal
and its environment– May include feathers, fur, or blubber
Hair
Sweatpore
Muscle
Nerve
Sweatgland
Oil glandHair follicle
Blood vessels
Adipose tissue
Hypodermis
Dermis
Epidermis
• In mammals, the integumentary system– Acts as insulating material
Figure 40.14
• Many endotherms and some ectotherms– Can alter the amount of blood flowing between
the body core and the skin
Circulatory Adaptations
• In vasodilation– Blood flow in the skin increases, facilitating heat
loss
• In vasoconstriction– Blood flow in the skin decreases, lowering heat loss
• Many marine mammals and birds– Have
arrangements of blood vessels called countercurrent heat exchangers that are important for reducing heat loss
In the flippers of a dolphin, each artery issurrounded by several veins in acountercurrent arrangement, allowingefficient heat exchange between arterialand venous blood.
Canadagoose
Artery Vein
35°C
Blood flow
VeinArtery
30º
20º
10º
33°
27º
18º
9º
Pacific bottlenose dolphin
2
1
3
2
3
Arteries carrying warm blood down thelegs of a goose or the flippers of a dolphinare in close contact with veins conveyingcool blood in the opposite direction, backtoward the trunk of the body. Thisarrangement facilitates heat transferfrom arteries to veins (blackarrows) along the entire lengthof the blood vessels.
1
Near the end of the leg or flipper, wherearterial blood has been cooled to far below the animal’s core temperature, the artery can still transfer heat to the even colderblood of an adjacent vein. The venous bloodcontinues to absorb heat as it passes warmer and warmer arterial blood traveling in the opposite direction.
2
As the venous blood approaches the center of the body, it is almost as warm as the body core, minimizing the heat lost as a result of supplying blood to body partsimmersed in cold water.
3
Figure 40.15
1 3
• Some specialized bony fishes and sharks– Also possess countercurrent heat exchangers
Figure 40.16a, b
21º25º 23º
27º
29º31º
Body cavity
SkinArtery
Vein
Capillarynetwork withinmuscle
Dorsal aortaArtery andvein underthe skin
Heart
Bloodvesselsin gills
(a) Bluefin tuna. Unlike most fishes, the bluefin tuna maintainstemperatures in its main swimming muscles that are much higherthan the surrounding water (colors indicate swimming muscles cutin transverse section). These temperatures were recorded for a tunain 19°C water.
(b) Great white shark. Like the bluefin tuna, the great white sharkhas a countercurrent heat exchanger in its swimming muscles thatreduces the loss of metabolic heat. All bony fishes and sharks loseheat to the surrounding water when their blood passes through thegills. However, endothermic sharks have a small dorsal aorta, and as a result, relatively little cold blood from the gills goes directly to the core of the body. Instead, most of the blood leaving the gillsis conveyed via large arteries just under the skin, keeping cool bloodaway from the body core. As shown in the enlargement, smallarteries carrying cool blood inward from the large arteries under theskin are paralleled by small veins carrying warm blood outward fromthe inner body. This countercurrent flow retains heat in the muscles.
• Many endothermic insects– Have countercurrent
heat exchangers that help maintain a high temperature in the thorax
Figure 40.17
Cooling by Evaporative Heat Loss
• Many types of animals– Lose heat through the evaporation of water in
sweat– Use panting to cool their bodies
• Bathing moistens the skin– Which helps to cool an animal down
Figure 40.18
• Both endotherms and ectotherms– Use a variety of behavioral responses to control
body temperature
Behavioral Responses
• Some terrestrial invertebrates– Have certain
postures that enable them to minimize or maximize their absorption of heat from the sun
Figure 40.19
Adjusting Metabolic Heat Production
• Some animals can regulate body temperature– By adjusting their rate of metabolic heat
production
• Many species of flying insects– Use shivering
to warm up before taking flight
Figure 40.20
PREFLIGHT PREFLIGHTWARMUP
FLIGHT
Thorax
Abdomen
Tem
per
atur
e (°
C)
Time from onset of warmup (min)
40
35
30
25
0 2 4
• Mammals regulate their body temperature– By a complex negative feedback system that
involves several organ systems
Feedback Mechanisms in Thermoregulation
• In humans, a specific part of the brain, the hypothalamus– Contains a group of
nerve cells that function as a thermostat
Thermostat inhypothalamusactivates coolingmechanisms.
Sweat glands secrete sweat that evaporates, cooling the body.
Blood vesselsin skin dilate:capillaries fillwith warm blood;heat radiates fromskin surface.
Body temperaturedecreases;thermostat
shuts off coolingmechanisms.
Increased bodytemperature (suchas when exercising
or in hotsurroundings)
Homeostasis:Internal body temperatureof approximately 36–38C
Body temperatureincreases;thermostat
shuts off warmingmechanisms.
Decreased bodytemperature
(such as whenin cold
surroundings)
Blood vessels in skinconstrict, diverting bloodfrom skin to deeper tissuesand reducing heat lossfrom skin surface.
Skeletal muscles rapidlycontract, causing shivering,which generates heat.
Thermostat inhypothalamusactivateswarmingmechanisms.
Figure 40.21
HOT
COLD
Adjustment to Changing Temperatures
• In a process known as acclimatization– Many animals can adjust to a new range of
environmental temperatures over a period of days or weeks
• Acclimatization may involve cellular adjustments– Or in the case of birds and mammals,
adjustments of insulation and metabolic heat production
Torpor and Energy Conservation
• Torpor– Is an adaptation that enables animals to save
energy while avoiding difficult and dangerous conditions
– Is a physiological state in which activity is low and metabolism decreases
• Hibernation is long-term torpor– That is an adaptation to winter cold and food scarcity
during which the animal’s body temperature declines
Additional metabolism that would benecessary to stay active in winter
Actualmetabolism
Bodytemperature
Arousals
Outsidetemperature Burrow
temperature
June August October December February April
Tem
pera
ture
(°C
)M
etab
olic
rat
e(k
cal p
er d
ay)
200
100
0
35
30
25
20
15
10
5
0
-5
-10
-15
Figure 40.22
• Estivation, or summer torpor– Enables animals to survive long periods of high
temperatures and scarce water supplies
• Daily torpor– Is exhibited by many small mammals and birds and
seems to be adapted to their feeding patterns