Chapter 42 – Animal Circulation - · PDF fileChapter 42 Circulation and Gas Exchange ......

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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 42

Circulation and Gas Exchange


•  Overview: Trading with the Environment

•  Every organism must exchange materials with its environment

–  And this exchange ultimately occurs at the cellular level


•  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


•  The feathery gills projecting from a salmon

–  Are an example of a specialized exchange system found in animals

Figure 42.1


•  Concept 42.1: Circulatory systems reflect phylogeny

•  Transport systems

–  Functionally connect the organs of exchange with the body cells


•  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

2


Invertebrate Circulation

•  The wide range of invertebrate body size and form

–  Is paralleled by a great diversity in circulatory systems


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


•  Some cnidarians, such as jellies

–  Have elaborate gastrovascular cavities

Figure 42.2

Circular canal

Radial canal 5 cm

Mouth


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)


•  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

Tubular heart

Lateral vessels

Ostia

(a) An open circulatory system Figure 42.3a


•  In a closed circulatory system

–  Blood is confined to vessels and is distinct from the interstitial fluid

Figure 42.3b

Interstitial fluid

Heart

Small branch vessels in each organ

Dorsal vessel (main heart)

Ventral vessels Auxiliary hearts

(b) A closed circulatory system

3


•  Closed systems

–  Are more efficient at transporting circulatory fluids to tissues and cells


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 four-chambered heart


•  Arteries carry blood to capillaries

–  The sites of chemical exchange between the blood and interstitial fluid

•  Veins

–  Return blood from capillaries to the heart


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


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


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

4


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


•  A powerful four-chambered heart

–  Was an essential adaptation of the endothermic way of life characteristic of mammals and birds


FISHES AMPHIBIANS REPTILES (EXCEPT BIRDS) MAMMALS AND BIRDS

Systemic capillaries Systemic capillaries Systemic capillaries Systemic capillaries

Lung capillaries Lung capillaries Lung and skin capillaries Gill capillaries

Right Left Right Left Right Left Systemic

circuit Systemic

circuit

Pulmocutaneous circuit

Pulmonary circuit

Pulmonary circuit

Systemic circulation Vein

Atrium (A)

Heart: ventricle (V)

Artery Gill circulation

A V V V V V

A A A A A Left Systemic aorta

Right systemic aorta

Figure 42.4

•  Vertebrate circulatory systems


•  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


Mammalian Circulation: The Pathway

•  Heart valves

–  Dictate a one-way flow of blood through the heart


•  Blood begins its flow

–  With the right ventricle pumping blood to the lungs

•  In the lungs

–  The blood loads O2 and unloads CO2

5


•  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


•  The mammalian cardiovascular system

Pulmonary vein

Right atrium

Right ventricle

Posterior vena cava Capillaries of

abdominal organs and hind limbs

Aorta

Left ventricle

Left atrium Pulmonary vein

Pulmonary artery

Capillaries of left lung

Capillaries of head and forelimbs

Anterior vena cava

Pulmonary artery

Capillaries of right lung

Aorta

Figure 42.5

1

10

11

5

4

6

2

9

3 3

7

8


The Mammalian Heart: A Closer Look

•  A closer look at the mammalian heart

–  Provides a better understanding of how double circulation works

Figure 42.6

Aorta

Pulmonary veins

Semilunar valve

Atrioventricular valve

Left ventricle Right ventricle

Anterior vena cava

Pulmonary artery

Semilunar valve

Atrioventricular valve

Posterior vena cava

Pulmonary veins

Right atrium

Pulmonary artery

Left atrium


•  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 cardiac cycle

Figure 42.7

Semilunar valves closed

AV valves open

AV valves closed

Semilunar valves open

Atrial and ventricular diastole

1

Atrial systole; ventricular diastole

2

Ventricular systole; atrial diastole

3

0.1 sec

0.3 sec 0.4 sec


•  The heart rate, also called the pulse

–  Is the number of beats per minute

•  The cardiac output

–  Is the volume of blood pumped into the systemic circulation per minute

6


Maintaining the Heart’s Rhythmic Beat

•  Some cardiac muscle cells are self-excitable

–  Meaning they contract without any signal from the nervous system


•  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

–  And then travel to the Purkinje fibers that make the ventricles contract


•  The impulses that travel during the cardiac cycle

–  Can be recorded as an electrocardiogram (ECG or EKG)


•  The control of heart rhythm

Figure 42.8

SA node (pacemaker)

AV node Bundle branches

Heart apex

Purkinje fibers

2 Signals are delayed at AV node.

1 Pacemaker generates wave of signals to contract.

3 Signals pass to heart apex.

4 Signals spread Throughout ventricles.

ECG


•  The pacemaker is influenced by

–  Nerves, hormones, body temperature, and exercise


•  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

7


Blood Vessel Structure and Function

•  The “infrastructure” of the circulatory system

–  Is its network of blood vessels


•  All blood vessels

–  Are built of similar tissues

–  Have three similar layers

Figure 42.9

Artery Vein

100 µm

Artery Vein

Arteriole Venule

Connective tissue

Smooth muscle

Endothelium

Connective tissue

Smooth muscle

Endothelium Valve

Endothelium

Basement membrane

Capillary


•  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


•  In the thinner-walled veins

–  Blood flows back to the heart mainly as a result of muscle action

Figure 42.10

Direction of blood flow in vein (toward heart)

Valve (open)

Skeletal muscle

Valve (closed)


Blood Flow Velocity

•  Physical laws governing the movement of fluids through pipes

–  Influence blood flow and blood pressure


•  The velocity of blood flow varies in the circulatory system

–  And is slowest in the capillary beds as a result of the high resistance and large total cross-sectional area

Figure 42.11

5,000 4,000 3,000 2,000 1,000

0

Aor

ta

Arte

ries

Arte

riole

s

Cap

illar

ies

Venu

les

Vein

s

Vena

e ca

vae P

ress

ure

(mm

Hg)

Ve

loci

ty (c

m/s

ec)

Are

a (c

m2 )

Systolic pressure

Diastolic pressure

50 40 30 20 10

0

120 100

80 60 40 20

0

8


Blood Pressure

•  Blood pressure

–  Is the hydrostatic pressure that blood exerts against the wall of a vessel


•  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


•  Blood pressure

–  Can be easily measured in humans

Figure 42.12

Artery

Rubber cuff inflated with air

Artery closed

120 120

Pressure in cuff above 120

Pressure in cuff below 120

Pressure in cuff below 70

Sounds audible in stethoscope

Sounds stop

Blood pressure reading: 120/70

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.

1

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.

2 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.

3

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.

4

70


•  Blood pressure is determined partly by cardiac output

–  And partly by peripheral resistance due to variable constriction of the arterioles


Capillary Function

•  Capillaries in major organs are usually filled to capacity

–  But in many other sites, the blood supply varies


•  Two mechanisms

–  Regulate the distribution of blood in capillary beds

•  In one mechanism

–  Contraction of the smooth muscle layer in the wall of an arteriole constricts the vessel

9


•  In a second mechanism

–  Precapillary sphincters control the flow of blood between arterioles and venules

Figure 42.13 a–c

Precapillary sphincters Thoroughfare channel

Arteriole Capillaries

Venule (a) Sphincters relaxed

(b) Sphincters contracted Venule Arteriole

(c) Capillaries and larger vessels (SEM)

20 µm


•  The critical exchange of substances between the blood and interstitial fluid

–  Takes place across the thin endothelial walls of the capillaries


•  The difference between blood pressure and osmotic pressure

–  Drives fluids out of capillaries at the arteriole end and into capillaries at the venule end

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.

Capillary Red blood cell

15 µm

Tissue cell INTERSTITIAL FLUID

Capillary Net fluid movement out

Net fluid movement in

Direction of blood flow

Blood pressure Osmotic pressure

Inward flow

Outward flow

Pre

ssur

e

Arterial end of capillary 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.

Figure 42.14 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Fluid Return by the Lymphatic System

•  The lymphatic system

–  Returns fluid to the body from the capillary beds

–  Aids in body defense


•  Fluid reenters the circulation

–  Directly at the venous end of the capillary bed and indirectly through the lymphatic system


•  Concept 42.4: Blood is a connective tissue with cells suspended in plasma

•  Blood in the circulatory systems of vertebrates

–  Is a specialized connective tissue

10


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


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


•  The composition of mammalian plasma Plasma 55%

Constituent Major functions

Water Solvent for carrying other substances

Sodium Potassium Calcium Magnesium Chloride Bicarbonate

Osmotic balance pH buffering, and regulation of membrane permeability

Albumin

Fibringen

Immunoglobulins (antibodies)

Plasma proteins

Icons (blood electrolytes

Osmotic balance, pH buffering

Substances transported by blood Nutrients (such as glucose, fatty acids, vitamins) Waste products of metabolism Respiratory gases (O2 and CO2) Hormones

Defense

Figure 42.15

Separated blood elements

Clotting


•  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


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


Figure 42.15

Cellular elements 45%

Cell type Number per µL (mm3) of blood

Functions

Erythrocytes (red blood cells) 5–6 million Transport oxygen

and help transport carbon dioxide

Leukocytes (white blood cells)

5,000–10,000 Defense and immunity

Eosinophil

Basophil

Platelets

Neutrophil Monocyte

Lymphocyte

250,000- 400,000

Blood clotting

•  The cellular elements of mammalian blood

Separated blood elements

11


Erythrocytes

•  Red blood cells, or erythrocytes

–  Are by far the most numerous blood cells

–  Transport oxygen throughout the body


Leukocytes

•  The blood contains five major types of white blood cells, or leukocytes

–  Monocytes, neutrophils, basophils, eosinophils, and lymphocytes, which function in defense by phagocytizing bacteria and debris or by producing antibodies


Platelets

•  Platelets function in blood clotting


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, leukocytes, and platelets all develop from a common source

–  A single population of cells called pluripotent stem cells in the red marrow of bones

B cells T cells

Lymphoid stem cells

Pluripotent stem cells (in bone marrow)

Myeloid stem cells

Erythrocytes

Platelets Monocytes

Neutrophils

Eosinophils

Basophils

Lymphocytes


Blood Clotting

•  When the endothelium of a blood vessel is damaged

–  The clotting mechanism begins

12


•  A cascade of complex reactions

–  Converts fibrinogen to fibrin, forming a clot

Platelet plug

Collagen fibers

Platelet releases chemicals that make nearby platelets sticky

Clotting factors from: Platelets Damaged cells Plasma (factors include calcium, vitamin K)

Prothrombin Thrombin

Fibrinogen Fibrin 5 µm

Fibrin clot Red blood cell

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.

1 The platelets form a plug that provides emergency protection against blood loss.

2 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).

3


Cardiovascular Disease

•  Cardiovascular diseases

–  Are disorders of the heart and the blood vessels

–  Account for more than half the deaths in the United States


•  One type of cardiovascular disease, atherosclerosis

–  Is caused by the buildup of cholesterol within arteries

Figure 42.18a, b

(a) Normal artery (b) Partly clogged artery 50 µm 250 µm

Smooth muscle Connective tissue Endothelium Plaque


•  Hypertension, or high blood pressure

–  Promotes atherosclerosis and increases the risk of heart attack and stroke

•  A heart attack

–  Is the death of cardiac muscle tissue resulting from blockage of one or more coronary arteries

•  A stroke

–  Is the death of nervous tissue in the brain, usually resulting from rupture or blockage of arteries in the head


•  Concept 42.5: Gas exchange occurs across specialized respiratory surfaces

•  Gas exchange

–  Supplies oxygen for cellular respiration and disposes of carbon dioxide

Figure 42.19

Organismal level

Cellular level

Circulatory system

Cellular respiration ATP Energy-rich molecules from food

Respiratory surface

Respiratory medium (air of water)

O2 CO2


•  Animals require large, moist respiratory surfaces for the adequate diffusion of respiratory gases

–  Between their cells and the respiratory medium, either air or water

13


Gills in Aquatic Animals

•  Gills are outfoldings of the body surface

–  Specialized for gas exchange


•  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

Tube foot

Coelom

Figure 42.20a


•  Many segmented worms have flaplike gills

–  That extend from each segment of their body

Figure 42.20b

(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.

Gill

Parapodia


•  The gills of clams, crayfish, and many other animals

–  Are restricted to a local body region

Figure 42.20c, d

(d) Crayfish. Crayfish and other crustaceans have long, feathery gills covered by the exoskeleton. Specialized body appendages drive water over the gill surfaces.

(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.

Gills

Gills


•  The effectiveness of gas exchange in some gills, including those of fishes

–  Is increased by ventilation and countercurrent flow of blood and water

Countercurrent exchange

Figure 42.21

Gill arch

Water flow Operculum

Gill arch

Blood vessel

Gill filaments

Oxygen-poor blood

Oxygen-rich blood

Water flow over lamellae showing % O2

Blood flow through capillaries in lamellae showing % O2

Lamella

100%

40%

70%

15%

90%

60% 30

% 5%

O2


Figure 42.22a

Tracheae

Air sacs

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.

Tracheal Systems in Insects

•  The tracheal system of insects

–  Consists of tiny branching tubes that penetrate the body

14


•  The tracheal tubes

–  Supply O2 directly to body cells Air sac

Body cell

Trachea

Tracheole

Tracheoles Mitochondria Myofibrils

Body wall

(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 2.5 µm

Air


Lungs

•  Spiders, land snails, and most terrestrial vertebrates

–  Have internal lungs


Mammalian Respiratory Systems: A Closer Look

•  A system of branching ducts

–  Conveys air to the lungs Branch from the pulmonary vein (oxygen-rich blood) Terminal bronchiole

Branch from the pulmonary artery (oxygen-poor blood)

Alveoli

Colorized SEM SEM

50 µ

m

50 µ

m

Heart

Left lung

Nasal cavity

Pharynx

Larynx

Diaphragm

Bronchiole

Bronchus

Right lung

Trachea Esophagus


•  In mammals, air inhaled through the nostrils

–  Passes through the pharynx into the trachea, bronchi, bronchioles, and dead-end alveoli, where gas exchange occurs


•  Concept 42.6: Breathing ventilates the lungs

•  The process that ventilates the lungs is breathing

–  The alternate inhalation and exhalation of air


How an Amphibian Breathes

•  An amphibian such as a frog

–  Ventilates its lungs by positive pressure breathing, which forces air down the trachea

15


How a Mammal Breathes

•  Mammals ventilate their lungs

–  By negative pressure breathing, which pulls air into the lungs

Air inhaled Air exhaled

INHALATION Diaphragm contracts

(moves down)

EXHALATION Diaphragm relaxes

(moves up)

Diaphragm

Lung

Rib cage expands as rib muscles contract

Rib cage gets smaller as rib muscles relax


•  Lung volume increases

–  As the rib muscles and diaphragm contract


How a Bird Breathes

•  Besides lungs, bird have eight or nine air sacs

–  That function as bellows that keep air flowing through the lungs

INHALATION Air sacs fill

EXHALATION Air sacs empty; lungs fill

Anterior air sacs

Trachea

Lungs Lungs Posterior air sacs

Air Air

1 mm Air tubes (parabronchi) in lung


•  Air passes through the lungs

–  In one direction only

•  Every exhalation

–  Completely renews the air in the lungs


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

Pons Breathing control centers Medulla

oblongata

Diaphragm

Carotid arteries

Aorta

Cerebrospinal fluid

Rib muscles

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.

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.

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 decreasing both if CO2 levels are depressed.

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.

1

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

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.

6

5

3

4


•  The centers in the medulla

–  Regulate the rate and depth of breathing in response to pH changes in the cerebrospinal fluid

•  The medulla adjusts breathing rate and depth

–  To match metabolic demands

16


•  Sensors in the aorta and carotid arteries

–  Monitor O2 and CO2 concentrations in the blood

–  Exert secondary control over breathing


•  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


The Role of Partial Pressure Gradients

•  Gases diffuse down pressure gradients

–  In the lungs and other organs

•  Diffusion of a gas

–  Depends on differences in a quantity called partial pressure


•  A gas always diffuses from a region of higher partial pressure

–  To a region of lower partial pressure


•  In the lungs and in the tissues

–  O2 and CO2 diffuse from where their partial pressures are higher to where they are lower


Inhaled air Exhaled air

160 0.2 O2 CO2

O2 CO2

O2 CO2

O2 CO2 O2 CO2

O2 CO2 O2 CO2

O2 CO2

40 45

40 45

100 40

104 40

104 40

120 27

CO2 O2

Alveolar epithelial cells

Pulmonary arteries

Blood entering alveolar

capillaries

Blood leaving tissue

capillaries

Blood entering tissue

capillaries

Blood leaving

alveolar capillaries

CO2 O2

Tissue capillaries

Heart

Alveolar capillaries

of lung

<40 >45

Tissue cells

Pulmonary veins

Systemic arteries Systemic

veins O2 CO2

O2

CO2

Alveolar spaces

1 2

4 3

Figure 42.27

17


Respiratory Pigments

•  Respiratory pigments

–  Are proteins that transport oxygen

–  Greatly increase the amount of oxygen that blood can carry


Oxygen Transport

•  The respiratory pigment of almost all vertebrates

–  Is the protein hemoglobin, contained in the erythrocytes


•  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

Polypeptide chain

O2

O2

Figure 42.28


•  Loading and unloading of O2

–  Depend on cooperation between the subunits of the hemoglobin molecule

•  The binding of O2 to one subunit induces the other subunits to bind O2 with more affinity


•  Cooperative O2 binding and release

–  Is evident in the dissociation curve for hemoglobin

•  A drop in pH

–  Lowers the affinity of hemoglobin for O2


O2 unloaded from hemoglobin during normal metabolism

O2 reserve that can be unloaded from hemoglobin to tissues with high metabolism

Tissues during exercise

Tissues at rest

100

80

60

40

20

0

100

80

60

40

20

0

100 80 60 40 20 0

100 80 60 40 20 0

Lungs

PO2 (mm Hg)

PO2 (mm Hg)

O2 s

atur

atio

n of

hem

oglo

bin

(%)

O2 s

atur

atio

n of

hem

oglo

bin

(%)

Bohr shift: Additional O2 released from hemoglobin at lower pH (higher CO2 concentration)

pH 7.4

pH 7.2

(a) PO2 and Hemoglobin Dissociation at 37°C and pH 7.4

(b) pH and Hemoglobin Dissociation

Figure 42.29a, b

18


Carbon Dioxide Transport

•  Hemoglobin also helps transport CO2

–  And assists in buffering


•  Carbon from respiring cells

–  Diffuses into the blood plasma and then into erythrocytes and is ultimately released in the lungs


Figure 42.30

Tissue cell

CO2 Interstitial fluid

CO2 produced CO2 transport from tissues

CO2

CO2

Blood plasma within capillary Capillary

wall

H2O

Red blood cell

Hb Carbonic acid H2CO3

HCO3– H+

+ Bicarbonate

HCO3–

Hemoglobin picks up

CO2 and H+

HCO3–

HCO3– H+

+

H2CO3 Hb

Hemoglobin releases

CO2 and H+

CO2 transport to lungs

H2O CO2

CO2

CO2

CO2

Alveolar space in lung

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To lungs

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.

Some CO2 is picked up and transported by hemoglobin.

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.

Carbonic acid dissociates into a biocarbonate ion (HCO3

–) and a hydrogen ion (H+).

Hemoglobin binds most of the H+ from H2CO3 preventing the H+ from acidifying the blood and thus preventing the Bohr shift.

CO2 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).

Most of the HCO3– diffuse

into the plasma where it is carried in the bloodstream to the lungs.

In the HCO3– diffuse

from the plasma red blood cells, combining with H+ released from hemoglobin and forming H2CO3.

Carbonic acid is converted back into CO2 and water.

CO2 formed from H2CO3 is unloaded from hemoglobin and diffuses into the interstitial fluid.

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Elite Animal Athletes

•  Migratory and diving mammals

–  Have evolutionary adaptations that allow them to perform extraordinary feats


The Ultimate Endurance Runner

•  The extreme O2 consumption of the antelope-like pronghorn

–  Underlies its ability to run at high speed over long distances

Figure 42.31


Diving Mammals

•  Deep-diving air breathers

–  Stockpile O2 and deplete it slowly

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