Transcript video slide

Chapter 42
Circulation and Gas
Exchange
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
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The Mammalian Heart: A Closer Look
• A closer look at the mammalian heart provides a better
understanding of how double circulation works
Pulmonary artery
Aorta
Pulmonary
artery
Left
atrium
Anterior vena cava
Right atrium
Pulmonary
veins
Pulmonary
veins
Semilunar
valve
Atrioventricular
valve
Semilunar
valve
Atrioventricular
valve
Posterior
Figure 42.6 vena cava
Right ventricle
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Left ventricle
The human heart
•
Cone shaped organ located beneath the sternum
and has a size of a clinched fist (a hand that is
tightly closed).
•
Surrounded by a sac with a two-layered wall.
•
Comprised mostly of cardiac muscle tissue.
•
The two atria have thin walls and function as
collection chambers for blood returning to the heart,
and pumping only the short distances to the
ventricles
•
The two ventricles have thick, powerful walls that
pump blood to the organs. The left ventricle pumps
blood to all the body organs.
•
The heart chambers alternately; contract → pump
blood or relax → fill with blood.
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• The heart contracts and relaxes
– In a rhythmic cycle called the cardiac cycle
• The contraction, or pumping, phase of the cycle
– Is called systole
• The relaxation, or filling, phase of the cycle
– Is called diastole
• The heart rate, also called the pulse
– Is the number of beats per minute
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The cardiac cycle
2 Atrial systole;
Semilunar
valves
closed
ventricular
diastole
0.1 sec
0.4 sec
Semilunar
valves
open
0.3 sec
AV valves
open
1 Atrial and
ventricular
diastole
Figure 42.7
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AV valves
closed
3 Ventricular systole;
atrial diastole
• The volume of blood per minute that the left ventricle
pumps into the systemic circuit is called the cardiac
output (5.25 liter per minute= the whole blood
volume).
• The volume of pumped blood depends on;
– Heart rate: The number of heart beats per minute.
It is 60 beats in humans but also depends on the
individual’s activity. Elephants hearts beat 25 per
minute while shrew ( one type of mice) beats 600
per minute.
– Stroke volume: The amount of blood pumped by
the left ventricle each time it contracts (75 ml per
beat).
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•
Cardiac output can increase up to five fold
during heavy exercise , this is equivalent to
pumping amount of blood equal to 2-3 body
weight in 2-3 minutes.
There are four valves (flap of connective tissue) in
the heart to prevent back flow of blood during
systole (dictate a one way flow through the
heart):
•
Atrioventicular valves: found between each
atrium and ventricle and keep blood from
flowing back to the atria during ventricle
contraction.
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• Semilunar valves: located where the aorta leaves
the left ventricle and where the pulmonary artery
leaves the right ventricle. They prevent flow of
blood back into ventricles when they relax
(diastole)
• A heart murmur is a defect in ore or more valves
that allows back flow of blood. In serious cases, a
surgery involves replacing the valves is a must.
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Maintaining the Heart’s Rhythmic Beat
• Some cardiac muscle cells are self-excitable
– Meaning they contract without any signal from
the nervous system
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• A region of the heart called the sinoatrial (SA)
node, or pacemaker
– Sets the rate and timing at which all cardiac
muscle cells contract
• Impulses from the SA node
– Travel to the atrioventricular (AV) node
• At the AV node, the impulses are delayed (0.1
sec).
– And then travel to the Purkinje fibers that make
the ventricles contract
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The impulses that travel during the cardiac cycle
produce electrical currents as they pass through
cardiac muscle.
Can be recorded as an electrocardiogram (ECG
or EKG).
Because the SA node of the human heart is made
up of specialized cells and located within the
heart itself, it is called myogenic heart. In
contrast, pacemaker of most arthropod
hearts originated in motor nerves arising from
the outside, it is referred to as a neurogenic
heart.
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• The control of heart rhythm
1 Pacemaker generates
wave of signals
to contract.
SA node
(pacemaker)
2 Signals are delayed
3 Signals pass
at AV node.
4 Signals spread
to heart apex.
Throughout
ventricles.
Heart
apex
Purkinje
fibers
Bundle
branches
AV node
ECG
Figure 42.8
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SA node is influenced by variety of physiological
cues; two sets of nerves affect the heart rate;
– one set speeds up the pacemaker
– the other set slows it down
SA is also affected by some hormones such as
epinephrine (fight–or-flight hormone) which
increases the heart rate
body temperature is another factor that affect the
pacemaker as an increase of 1C in the body
temperature increases the heart rate of 10
beats/min.
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• Concept 42.3: Physical principles govern blood
circulation
• The same physical principles that govern the
movement of water in plumbing systems
– Also influence the functioning of animal
circulatory systems
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Blood Vessel Structure and Function
•
The “infrastructure” of the circulatory system
–
•
Is its network of blood vessels
The walls of arteries and veins have three similar
layers:
–
An outer layer of connective tissue with elastic fibers
that permits stretching and recoil of the vessel.
–
A middle layer of smooth muscles and elastic fibers.
–
An inner endothelium of simple squamous epithelium
i.e the lining of the vessels.
–
The middle and outer walls of arteries are thicker
than that of veins.
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All blood vessels
• Are built of similar tissues
– Have three similar layers
Artery
Vein
Basement
membrane
Endothelium 100 µm
Valve
Endothelium
Endothelium
Smooth
muscle
Smooth
muscle
Connective
tissue
Capillary
Connective
tissue
Vein
Artery
Venule
Figure 42.9
Arteriole
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• Structural differences in arteries, veins, and
capillaries
– Correlate with their different functions
• Arteries have thicker walls
– To accommodate the high pressure of blood
pumped from the heart
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• In the thinner-walled veins
– Blood flows back to the heart mainly as a
result of muscle action
Direction of blood flow
in vein (toward heart)
Valve (open)
Skeletal muscle
Valve (closed)
Figure 42.10
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Blood Flow Velocity
•
Physical laws governing the movement of fluids
through pipes influence blood flow and blood
pressure
–
Blood flows about 30 cm/second in the aorta and
about 0.026 cm/second in the capillaries. i.e
approximately 1000 time faster.
–
The velocity decreases in accordance with the Law
of Continuity: Fluid will flow faster through narrow
portions of a pipe than wider portions if the volume of
flow remains constant.
–
An artery give rise to so many arterioles and then
capillaries that the total diameter of vessels is much
greater in capillary beds than in the artery, thus blood
flow slower.
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50
40
30
20
10
0
Systolic
pressure
Venae cavae
Veins
Capillaries
Venules
Diastolic
pressure
Arteries
120
100
80
60
40
20
0
Arterioles
Figure 42.11
5,000
4,000
3,000
2,000
1,000
0
Aorta
Pressure (mm Hg)
Velocity (cm/sec) Area (cm2)
• The velocity of blood flow varies in the circulatory
system
Blood Pressure
Is the hydrostatic pressure that blood exerts against
the wall of a vessel
•
Pressure is greater in arteries than in veins and is greater during
systole.
•
Peripheral resistance: results from impedance by arterioles;
blood enters arteries faster than it can leave. As a consequence
of the elasticity of the arteries working against peripheral
resistance there is a substantial blood pressure even at
diastole.
•
In veins, pressure is nearly zero. Blood return to the heart by the
action of skeletal muscles around the veins.
•
Veins have valves that allow blood to flow only towards the
heart.
•
The blood pressure of a healthy resting human oscillates
between 120 Hg at systole and 70 mm Hg at diastole.
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• Systolic pressure
– Is the pressure in the arteries during
ventricular systole
– Is the highest pressure in the arteries
• Diastolic pressure
– Is the pressure in the arteries during diastole
– Is lower than systolic pressure
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Blood pressure
• Can be easily measured in humans
1 A typical blood pressure reading for a 20-year-old
is 120/70. The units for these numbers are mm of
mercury (Hg); a blood pressure of 120 is a force that
can support a column of mercury 120 mm high.
4 The cuff is loosened further until the blood flows freely
through the artery and the sounds below the cuff
disappear. The pressure at this point is the diastolic
pressure remaining in the artery when the heart is relaxed.
Blood pressure
reading: 120/70
Pressure
in cuff
above 120
Rubber cuff
inflated
with air
120
Pressure
in cuff
below 120
Pressure
in cuff
below 70
120
70
Sounds
audible in
stethoscope
Artery
Sounds
stop
Artery
closed
2 A sphygmomanometer, an inflatable cuff attached to a
pressure gauge, measures blood pressure in an artery.
The cuff is wrapped around the upper arm and inflated
until the pressure closes the artery, so that no blood
flows past the cuff. When this occurs, the pressure
exerted by the cuff exceeds the pressure in the artery.
Figure 42.12
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3 A stethoscope is used to listen for sounds of blood flow
below the cuff. If the artery is closed, there is no pulse
below the cuff. The cuff is gradually deflated until blood
begins to flow into the forearm, and sounds from blood
pulsing into the artery below the cuff can be heard with
the stethoscope. This occurs when the blood pressure
is greater than the pressure exerted by the cuff. The
pressure at this point is the systolic pressure.
• Blood pressure is determined partly by cardiac
output
– And partly by peripheral resistance due to
variable constriction of the arterioles
– Nerve impulses, hormones and other signals
(stress) can raise the blood pressure by
constricting blood vessels
– Cardiac output is adjusted in coordination with
changes in peripheral resistance
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Capillary Function
•
All tissues and organs receive a sufficient
supply of blood even though only 5-10% of
the capillaries are carrying blood at any
given time.
•
Capillaries in the brain, heart, kidneys and
liver usually carry a full load of blood.
•
During exercise blood is drew from the
digestive tract to the skeletal muscles and
skin that is why indigestion might occur if
some one had a big meal and went directly
to play or swim
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Mechanism of blood distribution in capillaries
•
In one mechanism
–
involves the contraction and relaxation of the
smooth muscle layer of the arterioles.
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In a second mechanism
– Precapillary sphincters control the flow of
blood between arterioles and venules
Precapillary sphincters
(a)
Thoroughfare
channel
Sphincters relaxed increase blood flow
Arteriole
(b) Sphincters contracted
Reduce blood flow
Arteriole
Venule
Capillaries
Venule
(c) Capillaries and larger vessels (SEM)
Figure 42.13 a–c
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20 m
• The critical exchange of substances between
the blood and interstitial fluid
– Takes place across the thin endothelial walls of
the capillaries
– About 85% of fluid that leaves the blood at the
arterial end of the capillary returns from the
interstitial fluid at the venous end while the
other 15% returned to the blood through the
lymphatic system.
– Fluid reenters the circulation directly at the venous
end of the capillary bed and indirectly through the
lymphatic system
–
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• The difference between blood pressure and
osmotic pressure
– Drives fluids out of capillaries at the arteriole
end and into capillaries at the venule end
Red
15 m
blood
cell
At the arterial end of a
capillary, blood pressure is
greater than osmotic pressure,
and fluid flows out of the
capillary into the interstitial fluid.
Tissue cell
INTERSTITIAL FLUID
Capillary
Net fluid
movement out
Net fluid
movement in
Capillary
Figure 42.14
Pressure
Direction of
blood flow
Blood pressure
Osmotic pressure
Inward flow
Outward flow
Arterial end of capillary
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Venule end
At the venule end of
a capillary, blood
pressure is less than
osmotic pressure,
and fluid flows from
the interstitial fluid
into the capillary.
Fluid Return by the Lymphatic System
•
capillary walls leak fluid about 4 L/day and
some blood proteins which return to the blood
via the Lymphatic System. Once inside the
lymphatic system this fluid (blood and proteins)
is called lymph
•
The lymphatic system returns fluid to the body
from the capillary beds
•
Lymph is a fluid similar in composition to
interstitial fluid.
•
The lymphatic system drains into the circulatory
system at two locations near the shoulders.
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•
Lymph nodes are specialized swellings
along the system that filter the lymph and
attack viruses and bacteria thus participate
in the defense system.
•
Lymph capillaries penetrate small intestine
villi and absorb fats, thus transporting it from
the digestive system to the circulatory
system.
•
Inside the lymph nodes there is connective
tissue filled with white blood cells specialized
for defense.
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•
Concept 42.4: Blood is a connective tissue
with cells suspended in plasma
•
Blood has a pH of 7.4
•
Humans have 4-6 liters of whole blood
(plasma+ cellular elements).
•
Cellular elements represent about 45% of
the blood.
•
Cellular elements can be separated form
plasma by centrifugation
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Blood Composition and Function
• Blood consists of several kinds of cells
– Suspended in a liquid matrix called plasma
• The cellular elements
– Occupy about 45% of the volume of blood
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Plasma
• Blood plasma is about 90% water
• Among its many solutes are
– Inorganic salts in the form of dissolved ions,
sometimes referred to as electrolytes
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The composition of mammalian plasma
Plasma 55%
Constituent
Water
Ions (blood electrolytes)
Sodium
Potassium
Calcium
Magnesium
Chloride
Bicarbonate
Major functions
Solvent for
carrying other
substances
Osmotic balance
pH buffering, and
regulation of
membrane
permeability
Separated
blood
elements
Plasma proteins
Albumin
Fibringen
Immunoglobulins
(antibodies)
Osmotic balance,
pH buffering
Clotting
Defense
Substances transported by blood
Nutrients (such as glucose, fatty acids, vitamins)
Waste products of metabolism
Respiratory gases (O2 and CO2)
Hormones
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Figure 42.15
• Another important class of solutes is the
plasma proteins
– Which influence; blood pH, osmotic pressure,
and viscosity
• Various types of plasma proteins
– Function in lipid transport, immunity, and blood
clotting
• Serum: is the blood plasma that has the
clotting factors removed and normally contain
the antibodies
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Cellular Elements
• Suspended in blood plasma are two classes of
cells
– Red blood cells, which transport oxygen
– White blood cells, which function in defense
• A third cellular element, platelets
– Are fragments of cells that are involved in
clotting
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The cellular elements of mammalian blood
Cellular elements 45%
Cell type
Number
per L (mm3) of blood
Erythrocytes
(red blood cells)
Separated
blood
elements
5–6 million
Leukocytes
5,000–10,000
(white blood cells)
Functions
Transport oxygen
and help transport
carbon dioxide
Defense and
immunity
Lymphocyte
Basophil
Eosinophil
Neutrophil
Monocyte
Platelets
Figure 42.15
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250,000
400,000
Blood clotting
Erythrocytes
•
Each ml of human blood contains 5-6 million RBC and there are
about trillion of these cells in the body’s 5 L of blood.
•
Their main function is the transport of O2 which depends on rapid
diffusion of O2 through plasma membrane
•
Lack nuclei and mitochondria thus keeps all the space for larger
amount of the hemoglobin
•
generates ATP by anaerobic respiration therefore, they do not
consume any of the oxygen they carry
•
Contain hemoglobin, iron-containing trans protein.
•
There are 250 million molecules of hemoglobin in each RBC, thus an
RBC can carry about a billion oxygen molecules.
•
Erythropoietin is a protein produced in kidneys in response to
shortage of O2 in tissues. This protein stimulates the production of
RBC.
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Leukocytes; Blood contains five types of WBC
•
function in defense and immunity.
•
There are 5 types of leukocytes: basophils,
eosinophils, neutrophils, lymphocytes and
monocytes.
•
Monocytes and neutrophils are phagocytes
•
There are usually 5000-10000 WBC in each ml of blood
but this number increase temporarily during infection.
•
Spend most of their time outside the circulatory system
in the interstitial fluid and lymphatic system.
•
Lymphocytes become specialized during an infection
and produce the body’s immune response.
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Platelets
•
Fragments of cells, 2-3 um in diameter.
•
Lack nuclei
•
Inters blood and function in blood clotting.
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Stem Cells and the Replacement of Cellular Elements
•
The cellular elements of blood wear out and are
replaced constantly throughout a person’s life
•
Erythrocytes circulate the blood for 3-4 months
before being destroyed by phagocytic cells.
•
The Pluripotent Stem Cells give rise to all three
types of cellular elements.
•
These cells are self renewable,found in the red
bone marrow and arise in the early embryonic
stage.
•
They produce a number of new blood cells
equivalent to the number of dying cells.
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Differentiation of blood cells from pluripotent stem cells
Pluripotent stem cells
(in bone marrow)
Lymphoid
stem cells
Myeloid
stem cells
Basophils
B cells
T cells
Lymphocytes
Eosinophils
Neutrophils
Erythrocytes
Figure 42.16
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Platelets
Monocytes
Stem cells and replacement of cellular elements
• Erythrocyte production is controlled by a negative feed
back mechanism.
• If tissue do not receive enough O2, the kidneys
synthesis and secrete a hormone called erythropoietin
(EPO) that stimulates production of RBC. The reveres
happens if tissues receive more O2 than what they are
suppose to have.
• EPO is used to treat anemia however, some athletes
injects themselves with EPO to increase their RBC
levels
• This practice is called blood doping and is banned by
Olympic committee
• Pluripotent cells are used for regenerating the bone
marrow after destroying it as a cancer treatment.
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Blood Clotting
•
Blood clotting happened after an injury happens to
the endothelium of vessels
•
After the injury the connective tissue become
exposed and the platelets adheres to the fibers
•
A substance that makes nearby platelets sticky is
released
•
Platelets clump together to for a temporary plug
and release clotting factors (12 clotting factors are
known).
•
Clotting factors result in conversion of inactive
fibrinogen to active fibrin by the help of thrombin.
•
Fibrin aggregates into threads that form the clot.
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A cascade of complex reactions
• Converts fibrinogen to fibrin, forming a clot
1
The clotting process begins
when the endothelium of a
vessel is damaged, exposing
connective tissue in the
vessel wall to blood. Platelets
adhere to collagen fibers in
the connective tissue and
release a substance that
makes nearby platelets sticky.
2
The platelets form a
plug that provides
emergency protection
against blood loss.
Collagen fibers
Platelet releases chemicals
that make nearby platelets sticky
Platelet
plug
3
This seal is reinforced by a clot of fibrin when
vessel damage is severe. Fibrin is formed via a
multistep process: Clotting factors released from
the clumped platelets or damaged cells mix with
clotting factors in the plasma, forming an
activation cascade that converts a plasma protein
called prothrombin to its active form, thrombin.
Thrombin itself is an enzyme that catalyzes the
final step of the clotting process, the conversion of
fibrinogen to fibrin. The threads of fibrin become
interwoven into a patch (see colorized SEM).
Fibrin clot
Clotting factors from:
Platelets
Damaged cells
Plasma (factors include calcium, vitamin K)
Prothrombin
Figure 42.17
Thrombin
Fibrinogen
Fibrin
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5 µm
Red blood cell
•
Hemophilia is a genetic disorder caused by
mutations that affect blood clotting and is
characterized by excessive bleeding from even
minor cuts.
•
Spontaneous clotting in the body without injury
is inhibited by anti-clotting factors in blood.
•
Some times platelets clump and fibrin
coagulates within blood vessel making what is
known as thrombus.
•
These potentially dangerous clots are likely to
form in individuals with cardiovascular diseases.
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Cardiovascular Disease
– Are disorders of the heart and the blood
vessels
– Account for more than half the deaths in the
United States
– Tendency to have cardiovascular disease
might be inherited however, life style plays a
major role, such as smoking, eating habits,
lack of exercise, high concentration of
cholesterol in the blood.
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Cholesterol
•
Normally high concentration of LDLs (low density
lipoproteins, bad cholesterol) in the blood correlate with
atherosclerosis.
•
HDLs (high density lipoproteins, good cholesterol)
reduce deposition of cholesterol in arterial plaques.
•
Ratio of LDLs to HDLs is more reliable than total
plasma cholesterol as indicator of impending
cardiovascular disease
•
Exercise increase HDLs. Diet also increases HDL
example of such diet is the consumption of olive oil
which is rich of monounsaturated fatty acids that was
found to decrease LDL and increase HDL.
•
Smoking increase LDL; HDL ratio therefore, increases
the risk of cardiovascular disease.
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• One type of cardiovascular disease,
atherosclerosis
– Is caused by the buildup of cholesterol within arteries
Connective
tissue
Smooth muscle
Plaque
Endothelium
(a) Normal artery
50 µm
(b) Partly clogged artery
Figure 42.18a, b
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250 µm
Atherosclerosis
•
commonly known as hardening of arteries. Figure 4.18
•
Chronic cardiovascular disease characterized by plaques that
develop in the inner walls of arteries and narrow the bore of the
vessel
•
Form at sites where smooth muscle layer of artery thickens
abnormally and inner walls become rough
•
Site become infiltrated with fibrus connective tissue and lipids
such as cholesterol thus encouges thrombus formation.
•
embolus more likely trapped in narrow vessels.
Sings of Atherosclerosis;
•
Angina pectoris: chest pain that occur when heart receives
insufficient oxygen due to plaques in the arteries.
•
Hypertension: High blood pressure, increase the risk of
atheroseclerosis, heart attack and stroke.
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Hypertension
•
Promotes atherosclerosis by damaging
endothelium layer of the blood vessels
•
Increase risk of heart attack and stroke
•
Atherosclerosis increase blood pressure by
narrowing and reducing their elasticity.
•
High blood pressure can be controlled by
medication, diet, exercise or combination
•
A diastolic pressure above 90 is a cause for
concern
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A heart attack Is the death of cardiac muscle tissue
resulting from blockage of one or more coronary
arteries thus decreasing O2 supply to the cardiac
muscle.
A thrombus that causes heart attack/stroke may form;
•
–
In a coronary artery
–
Artery in the brain
–
Elsewhere in the circulatory system and reaches the
heart.
The thrombus occurs due to the accumulation of
LDL in arteries triggering an inflammatory reaction
similar to that caused by bacterial infection.
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• Embolus is a moving clot from one place to another.
– Cardiac or brain tissue downstream from obstruction may
die
– If damage in the heart interrupts conduction of electrical
impulses through cardiac muscle, heart rate may
change dramatically or the heart may stop beating
– If cardiopulmonary resuscitation (CPR) within few
minutes, person may survive.
• A stroke
– Is the death of nervous tissue in the brain, usually
resulting from rupture or blockage of arteries in the head.
Once happened survival depends on damage extent.
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Mammalian Respiratory Systems: A Closer Look
• A system of branching ducts
– Conveys air to the lungs
Branch
from the
pulmonary
artery
(oxygen-poor
blood)
Branch
from the
pulmonary
vein
(oxygen-rich
blood)
Terminal
bronchiole
Nasal
cavity
Pharynx
Left
lung
Alveoli
50 µm
50 µm
Larynx
Esophagus
Trachea
Right lung
Bronchus
Bronchiole
Diaphragm
SEM
Heart
Figure 42.23
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Colorized SEM
• The lungs of mammals have a spongy texture and are
honeycombed with a moist epithelium that functions as
the respiratory surface
• Air inters through the nostrils and get filtered by hair,
warmed, humidified and sampled for odor then flow
through to pharynx then to larynx which works as a
voice box that contains the vocal cords which
produces the sound by vibrating.
• From the larynx air pass through the trachea (windpipe)
which branches in two bronchi one leading to each
lung. Each bronchus branches into finer tubes called
bronchioles. At the air tips the bronchioles dead ends
are called alveoli (singular alveolus)
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Concept 42.6: Breathing ventilates the lungs
• The process that ventilates the lugs is called
breathing, a frog ventilates its lungs by positive
pressure while mammals ventilate their lungs by
negative pressure (which forces air down the
trachea).
• Negative pressure works like a suction pump
pulling air instead of pushing it into the lungs in a
process called inhalation.
• The alternate inhalation and exhalation of air
ventilates the lungs.
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How a Mammal Breathes
• Mammals ventilate their lungs
– By negative pressure breathing, which pulls air
into the lungs
Rib cage
expands as
rib muscles
contract
Air inhaled
Rib cage gets
smaller as
rib muscles
relax
Air exhaled
Lung
Diaphragm
INHALATION
Diaphragm contracts
(moves down)
Figure 42.24
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EXHALATION
Diaphragm relaxes
(moves up)
Lung volume
•
Vertebrates ventilate their lungs by Breathing
•
Maintain a maximumO2 concentration and minimum
CO2 concentration in the alveoli.
•
When a mammal is at rest, most of the shallow
inhalation results from contraction of the diaphragm.
•
When the diaphragm contracts, it pushes down
towards the abdomen, enlarging the thoracic cavity.
•
Contraction of the rib muscles expands the rib cage
by pulling the ribs upward and the breastbone
upward. This change increase the lung volume
and as a result the air pressure in the alveoli
become lower than the atmospheric pressure.
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•
Because gas flow from region of higher pressure
to the region of lower pressure, air pushes
through and inhalation occurs.
•
During exhalation, the rib muscles and diaphragm
relax, lung volume is reduced and the air
pressure is increased in the alveoli forcing air up
to breathing tubes and out of the trachea to
nostrils producing the exhalation. During exercise
, contraction of the rib muscles increases lung
volume
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• Tidal Volume: the amount of air an animal inhales
and exhales with each breath during normal breathing.
(500 ml in humans).
• Vital Capacity: the maximum air volume that can be
inhaled and exhaled during forced breathing. (4800 ml
in young males, 3400 ml in females.)
• Residual Volume: is the amount of air that remains in
the lungs even after forced breathing after exhalation.
• As lungs lose their resilience (strength) as a result of
aging or disease the residual volume increases on the
expense of the vital capacity which limits the
effectiveness of gas exchange.
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Control of Breathing in Humans
• The main breathing control centers
– Are located in two regions of the brain, the
medulla oblongata and the pons. Figure 42.26.
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Control of Breathing in Humans
Figure 42.26
Cerebrospinal
fluid
1
The control center in the
medulla sets the basic
rhythm, and a control center
in the pons moderates it,
smoothing out the
transitions between
inhalations and exhalations.
4 The medulla’s control center
also helps regulate blood CO2 level.
Sensors in the medulla detect changes
in the pH (reflecting CO2 concentration)
of the blood and cerebrospinal fluid
bathing the surface of the brain.
5
Pons
Nerve impulses trigger
muscle contraction. Nerves
from a breathing control center
in the medulla oblongata of the
brain send impulses to the
diaphragm and rib muscles,
stimulating them to contract
and causing inhalation.
2
Breathing
control
centers
Medulla
oblongata
Nerve impulses relay changes in
CO2 and O2 concentrations. Other
sensors in the walls of the aorta
and carotid arteries in the neck
detect changes in blood pH and
send nerve impulses to the medulla.
In response, the medulla’s breathing
control center alters the rate and
depth of breathing, increasing both
to dispose of excess CO2 or decreasin
both if CO2 levels are depressed.
Carotid
arteries
In a person at rest, these
nerve impulses result in
about 10 to 14 inhalations
per minute. Between
inhalations, the muscles
relax and the person exhales.
Aorta
3
6
Diaphragm
Rib muscles
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The sensors in the aorta and
carotid arteries also detect changes
in O2 levels in the blood and signal
the medulla to increase the breathing
rate when levels become very low.
The Control of Breathing
•
Breathing is an automatic action. We inhale
when nerves in the breathing control centers of
the medulla oblonga and pons send impulses to
the rib muscles or diaphragm, stimulating the
muscles to contract.
•
This occurs every 10-14 time per minute.
•
The medulla’s control center also monitors
blood and cerebrospinal fluid pH, which drops
as blood CO2 concentration increase.
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The Control of Breathing … cont.
• When pH is dropped (increase of CO2), the tempo
and depth of breathing are increased and the
excess CO2 is removed in exhaled air.
• O2 concentration in the blood only effects the
breathing control centers when it becomes
extremely low.
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• Sensors in the aorta and carotid arteries
– Monitor O2 and CO2 concentrations in the
blood
– Exert secondary control over breathing by
signaling the medulla to increase breathing
rate.
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• Concept 42.7: Respiratory pigments bind and
transport gases
• The metabolic demands of many organisms
– Require that the blood transport large quantities
of O2 and CO2
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The Role of Partial Pressure Gradients
•
The diffusion of gases , whether in air or water
depends on partial pressure.
•
The partial pressure of gas is the proportion of the
total atmospheric pressure (760 mm Hg)
contributed by the gas.
•
Oxygen comprises 21% of the atmosphere: its
partial pressure (PO2)= 160 mm, (0.21 x 760).
•
CO2 comprises about 0.03% of the atmosphere,
(PCO2 = 0.23 mm Hg).
•
Gases diffuse always from areas of high partial
pressure to those of low partial pressures.
•
Blood arriving at the lungs from systemic circulation
has a lower PO2 and a higher PCO2 than air in the
alveoli.
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•
Thus the blood exchange gases with air in the
alveoli and the PO2 of the blood increases while
the PCO2 decreases.
•
In systemic capillaries gradients of partial
pressure favor diffusion of O2 out of the blood
and diffusion of CO2 into it, since cellular
respiration rapidly depletes interstitial fluid of O2
and adds CO2.
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• In the lungs and in the tissues
– O2 and CO2 diffuse from where their partial
pressures are higher to where they are lower
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Inhaled air
Exhaled air
1600.2
Alveolar
epithelial
cells
Blood
entering
alveolar
capillaries
120 27
O2CO2
Alveolar spaces
O2 CO2
104
40
O2CO2
1
Alveolar
capillaries
of lung
Pulmonary
arteries
Blood
4
leaving
tissue
capillaries
40 45
O2 CO2
Heart
Tissue
O
COcapillaries
2
CO2
Tissue
cells
Figure 42.27
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2
O2
40 45
O2 CO2
Systemic
veins
O2
CO2
<40 >45
O2 CO2
O2
Blood
leaving
alveolar
capillaries
104 40
O2 CO2
Pulmonary
veins
Systemic
arteries
2
3
Blood
entering
tissue
capillaries
100 40
O2 CO2
• Like all respiratory pigments
– Hemoglobin must reversibly bind O2, loading
O2 in the lungs and unloading it in other parts
of the body
Heme group Iron atom
O2 loaded
in lungs
O2 unloaded
In tissues
Figure 42.28
Polypeptide chain
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O2
O2
Oxygen Transport
•
oxygen is carried by respiratory pigments in the
blood of most animals since oxygen is not very
soluble in water.
•
Hemoglobin is the oxygen transporting pigment in
almost all vertebrates.
•
Binding of oxygen to hemoglobin is reversible:
binding occur in the lungs, release occurs in the
tissues.
•
Binding and release of oxygen depends on
cooperation between subunits of hemoglobin in which
the binding of O2 to one subunit induces the other
subunits to bind O2 with more affinity.
•
.
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• Cooperative O2 binding and release
– Is evident in the dissociation curve for hemoglobin
• A drop in pH
– Lowers the affinity of hemoglobin for O2 thus
releases O2 to the tissues
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• Bohr’s shift is the lowering of hemoglobin’s
affinity for oxygen upon a drop in pH.
• This occur in active tissues due to the entrance
of CO2 into the blood
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O2 saturation of hemoglobin (%)
(a) PO2 and Hemoglobin Dissociation at 37°C and pH 7.4
100 O2 unloaded from
hemoglobin
during normal
metabolism
80
O2 reserve that can
be unloaded from
hemoglobin to
tissues with high
metabolism
60
40
20
0
0
20
40
60
80 100
Tissues during Tissues
exercise
at rest
Lungs
(b) pH and Hemoglobin Dissociation
Figure 42.29a, b
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O2 saturation of hemoglobin (%)
PO2 (mm Hg)
100
pH 7.4
80
Bohr shift:
Additional O2
released from
pH 7.2 hemoglobin at
lower pH
(higher CO2
concentration)
60
40
20
0
0
20
40 60 80 100
PO2 (mm Hg)
Carbon Dioxide Transport
•
Carbon dioxide is transported by the blood in three forms:
–
dissolved CO2 in the plasma (7%).
–
Bound to the amino groups of hemoglobin (23%).
–
As biocarbonate ions in the plasma (70%).
•
CO2 from cells diffuses into the blood plasma and then into
RBC. In the RBCs, CO2 is converted into bicarbonate.
•
The CO2 reacts with water to form carbonic acid.
•
Carbonic acid quickly disassociate to bicarbonate and hydrogen
ions
•
Bicarbonate then diffuse out of RBCs to the blood plasma.
•
The hydrogen ions attach to the hemoglobin and other proteins.
•
This process is reversed in the lungs.
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• Carbon dioxide from respiring cells
– Diffuses into the blood plasma and then into
erythrocytes and is ultimately released in the
lungs
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1
2
Carbon dioxide produced by
body tissues diffuses into the
interstitial fluid and the plasma.
Over 90% of the CO2 diffuses
into red blood cells, leaving only 7%
in the plasma as dissolved CO2.
Tissue cell
CO2 produced
Some CO2 is picked up and
transported by hemoglobin.
7
Most of the HCO3– diffuse
into the plasma where it is
carried in the bloodstream to
the lungs.
8
In the HCO3– diffuse
from the plasma red blood cells,
combining with H+ released from
hemoglobin and forming H2CO3.
9
Carbonic acid is converted back
into CO2 and water.
10
CO2 formed from H2CO3 is unloaded
from hemoglobin and diffuses into the
interstitial fluid.
InterstitialCO
2
fluid
1
Blood plasma CO
2
within capillary
Capillary
wall
2
CO2
H2O
3
CO2 transport
from tissues
3
4
Hemoglobin
Red
H2CO3
blood Carbonic acid Hb picks up
cell
CO and H+
2
5
HCO3– + H+
Bicarbonate
4
However, most CO2 reacts with water
in red blood cells, forming carbonic
acid (H2CO3), a reaction catalyzed by
carbonic anhydrase contained. Within
red blood cells.
HCO3–
7
6
To lungs
CO2 transport
to lungs
HCO3–
8
HCO3– + H+
5
Carbonic acid dissociates into a
biocarbonate ion (HCO3–) and a
hydrogen ion (H+).
H2CO3
Hb
9
11 CO2
Hemoglobin
releases
CO2 and H+
H2O
CO2
6
Hemoglobin binds most of the
H+ from H2CO3 preventing the H+
from acidifying the blood and thus
preventing the Bohr shift.
Figure 42.30
CO2
CO2 10
CO2 11
Alveolar space in lung
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diffuses into the alveolar
space, from which it is expelled
during exhalation. The reduction
of CO2 concentration in the plasma
drives the breakdown of H2CO3
Into CO2 and water in the red blood
cells (see step 9), a reversal of the
reaction that occurs in the tissues
(see step 4).
End of material requested
from this chapter
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• Overview: Trading with the Environment
• Every organism must exchange materials with
its environment
– And this exchange ultimately occurs at the
cellular level
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• In unicellular organisms
– These exchanges occur directly with the
environment
• For most of the cells making up multicellular
organisms
– Direct exchange with the environment is not
possible
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• The feathery gills projecting from a salmon
– Are an example of a specialized exchange
system found in animals
Figure 42.1
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• Concept 42.1: Circulatory systems reflect
phylogeny
• Transport systems
– Functionally connect the organs of exchange
with the body cells
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• Most complex animals have internal transport
systems
– That circulate fluid, providing a lifeline between
the aqueous environment of living cells and the
exchange organs, such as lungs, that exchange
chemicals with the outside environment
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Invertebrate Circulation
• The wide range of invertebrate body size and
form
– Is paralleled by a great diversity in circulatory
systems
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Gastrovascular Cavities
• Simple animals, such as cnidarians
– Have a body wall only two cells thick that
encloses a gastrovascular cavity
• The gastrovascular cavity
– Functions in both digestion and distribution of
substances throughout the body
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• Some cnidarians, such as jellies
– Have elaborate gastrovascular cavities
Circular
canal
Mouth
Radial canal
5 cm
Figure 42.2
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Open and Closed Circulatory Systems
• More complex animals
– Have one of two types of circulatory systems:
open or closed
• Both of these types of systems have three
basic components
– A circulatory fluid (blood)
– A set of tubes (blood vessels)
– A muscular pump (the heart)
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• In insects, other arthropods, and most molluscs
– Blood bathes the organs directly in an open
circulatory system
Heart
Hemolymph in sinuses
surrounding ograns
Anterior
vessel
Figure 42.3a
Lateral
vessels
Ostia
Tubular heart
(a) An open circulatory system
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• In a closed circulatory system
– Blood is confined to vessels and is distinct
from the interstitial fluid
Heart
Interstitial
fluid
Small branch vessels
in each organ
Dorsal vessel
(main heart)
Auxiliary hearts
Figure 42.3b
Ventral vessels
(b) A closed circulatory system
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• Closed systems
– Are more efficient at transporting circulatory
fluids to tissues and cells
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Survey of Vertebrate Circulation
• Humans and other vertebrates have a closed
circulatory system
– Often called the cardiovascular system
• Blood flows in a closed cardiovascular system
– Consisting of blood vessels and a two- to fourchambered heart
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• Arteries carry blood to capillaries
– The sites of chemical exchange between the
blood and interstitial fluid
• Veins
– Return blood from capillaries to the heart
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Fishes
• A fish heart has two main chambers
– One ventricle and one atrium
• Blood pumped from the ventricle
– Travels to the gills, where it picks up O2 and
disposes of CO2
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Amphibians
• Frogs and other amphibians
– Have a three-chambered heart, with two atria
and one ventricle
• The ventricle pumps blood into a forked artery
– That splits the ventricle’s output into the
pulmocutaneous circuit and the systemic
circuit
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Reptiles (Except Birds)
• Reptiles have double circulation
– With a pulmonary circuit (lungs) and a
systemic circuit
• Turtles, snakes, and lizards
– Have a three-chambered heart
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Mammals and Birds
• In all mammals and birds
– The ventricle is completely divided into
separate right and left chambers
• The left side of the heart pumps and receives
only oxygen-rich blood
– While the right side receives and pumps only
oxygen-poor blood
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• A powerful four-chambered heart
– Was an essential adaptation of the
endothermic way of life characteristic of
mammals and birds
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• Vertebrate circulatory systems
AMPHIBIANS
REPTILES (EXCEPT BIRDS)
MAMMALS AND BIRDS
Lung and skin capillaries
Lung capillaries
Lung capillaries
FISHES
Gill capillaries
Artery
Pulmocutaneous
circuit
Gill
circulation
Heart:
ventricle (V)
A
Atrium (A)
Systemic
Vein circulation
Systemic capillaries
Right
systemic
aorta
Pulmonary
circuit
A
A
V
Right
V
Left
Right
Systemic
circuit
Systemic capillaries
Figure 42.4
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Pulmonary
circuit
Left
Systemic
V aorta
Left
A
Systemic capillaries
A
V
Right
A
V
Left
Systemic
circuit
Systemic capillaries
• Concept 42.2: Double circulation in mammals
depends on the anatomy and pumping cycle of
the heart
• The structure and function of the human
circulatory system
– Can serve as a model for exploring
mammalian circulation in general
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Mammalian Circulation: The Pathway
• Heart valves
– Dictate a one-way flow of blood through the
heart
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• Blood begins its flow
– With the right ventricle pumping blood to the
lungs
• In the lungs
– The blood loads O2 and unloads CO2
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• Oxygen-rich blood from the lungs
– Enters the heart at the left atrium and is
pumped to the body tissues by the left ventricle
• Blood returns to the heart
– Through the right atrium
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• The mammalian cardiovascular system
7
Capillaries of
head and
forelimbs
Anterior
vena cava
Pulmonary
artery
Aorta
Pulmonary
artery
9
6
Capillaries
of right lung
Capillaries
of left lung
2
4
3
Pulmonary
vein
5
1
Right atrium
3
11
Left atrium
Pulmonary
vein
10
Left ventricle
Right ventricle
Aorta
Posterior
vena cava
8
Figure 42.5
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Capillaries of
abdominal organs
and hind limbs
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How a Bird Breathes
• Besides lungs, bird have eight or nine air sacs
– That function as bellows that keep air flowing
through the lungs
Air
Air
Anterior
air sacs
Trachea
Posterior
air sacs
Lungs
Lungs
Air tubes
(parabronchi)
in lung
EXHALATION
Air sacs empty; lungs fill
INHALATION
Air sacs fill
Figure 42.25
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1 mm
Elite Animal Athletes
• Migratory and diving mammals
– Have evolutionary adaptations that allow them
to perform extraordinary feats
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The Ultimate Endurance Runner
• The extreme O2 consumption of the antelopelike pronghorn
– Underlies its ability to run at high speed over
long distances
Figure 42.31
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Diving Mammals
• Deep-diving air breathers
– Stockpile O2 and deplete it slowly
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• Concept 42.5: Gas exchange occurs across
specialized respiratory surfaces
• Gas exchange
– Supplies oxygen for cellular respiration and
disposes of carbon dioxide
Respiratory
medium
(air of water)
O2
CO2
Respiratory
surface
Organismal
level
Circulatory system
Cellular level
Energy-rich
molecules
from food
Cellular respiration
Figure 42.19
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ATP
• Animals require large, moist respiratory
surfaces for the adequate diffusion of
respiratory gases
– Between their cells and the respiratory
medium, either air or water
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Gills in Aquatic Animals
• Gills are outfoldings of the body surface
– Specialized for gas exchange
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• In some invertebrates
– The gills have a simple shape and are
distributed over much of the body
(a) Sea star. The gills of a sea
star are simple tubular
projections of the skin.
The hollow core of each gill
is an extension of the coelom
(body cavity). Gas exchange
occurs by diffusion across the
gill surfaces, and fluid in the
coelom circulates in and out of
the gills, aiding gas transport.
The surfaces of a sea star’s
tube feet also function in
gas exchange.
Gills
Coelom
Figure 42.20a
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Tube foot
• Many segmented worms have flaplike gills
– That extend from each segment of their body
(b) Marine worm. Many
polychaetes (marine
worms of the phylum
Annelida) have a pair
of flattened appendages
called parapodia on
each body segment. The
parapodia serve as gills
and also function in
crawling and swimming.
Parapodia
Figure 42.20b
Gill
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• The gills of clams, crayfish, and many other
animals
– Are restricted to a local body region
(c) Scallop. The gills of a
scallop are long,
flattened plates
that project from the
main body mass
inside the hard shell.
Cilia on the gills
circulate water around
the gill surfaces.
(d) Crayfish. Crayfish and
other crustaceans
have long, feathery
gills covered by the
exoskeleton. Specialized
body appendages
drive water over
the gill surfaces.
Gills
Gills
Figure 42.20c, d
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• The effectiveness of gas exchange in some
gills, including those of fishes
– Is increased by ventilation and countercurrent
flow of blood and water
Oxygen-poor
blood
Gill arch
Gill
arch
Water
flow
Blood
vessel
Oxygen-rich
blood
Lamella
Operculum
O2
Figure 42.21
Water flow
over lamellae
showing % O2
Gill
filaments
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Blood flow
through capillaries
in lamellae
showing % O2
Countercurrent exchange
Tracheal Systems in Insects
• The tracheal system of insects
– Consists of tiny branching tubes that penetrate
the body
Air sacs
Tracheae
Spiracle
(a) The respiratory system of an insect consists of branched internal
tubes that deliver air directly to body cells. Rings of chitin reinforce
the largest tubes, called tracheae, keeping them from collapsing.
Enlarged portions of tracheae form air sacs near organs that require
a large supply of oxygen. Air enters the tracheae through openings
called spiracles on the insect’s body surface and passes into smaller
tubes called tracheoles. The tracheoles are closed and contain fluid
(blue-gray). When the animal is active and is using more O2, most of
the fluid is withdrawn into the body. This increases the surface area
of air in contact with cells.
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Figure 42.22a
• The tracheal tubes
– Supply O2 directly to body cells
Body
cell
Air
sac
Tracheole
Trachea
Air
Tracheoles
Mitochondria
Body wall
Myofibrils
(b) This micrograph shows cross
sections of tracheoles in a tiny
piece of insect flight muscle (TEM).
Each of the numerous mitochondria
in the muscle cells lies within about
5 µm of a tracheole.
Figure 42.22b
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2.5 µm
Lungs
• Spiders, land snails, and most terrestrial
vertebrates
– Have internal lungs
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