chapter 42 – animal circulation - · pdf filechapter 42 circulation and gas exchange ......
TRANSCRIPT
1
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Overview: Trading with the Environment
• Every organism must exchange materials with its environment
– And this exchange ultimately occurs at the cellular level
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The feathery gills projecting from a salmon
– Are an example of a specialized exchange system found in animals
Figure 42.1
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Concept 42.1: Circulatory systems reflect phylogeny
• Transport systems
– Functionally connect the organs of exchange with the body cells
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Invertebrate Circulation
• The wide range of invertebrate body size and form
– Is paralleled by a great diversity in circulatory systems
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Some cnidarians, such as jellies
– Have elaborate gastrovascular cavities
Figure 42.2
Circular canal
Radial canal 5 cm
Mouth
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Closed systems
– Are more efficient at transporting circulatory fluids to tissues and cells
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Arteries carry blood to capillaries
– The sites of chemical exchange between the blood and interstitial fluid
• Veins
– Return blood from capillaries to the heart
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• A powerful four-chambered heart
– Was an essential adaptation of the endothermic way of life characteristic of mammals and birds
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Mammalian Circulation: The Pathway
• Heart valves
– Dictate a one-way flow of blood through the heart
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Blood begins its flow
– With the right ventricle pumping blood to the lungs
• In the lungs
– The blood loads O2 and unloads CO2
5
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Maintaining the Heart’s Rhythmic Beat
• Some cardiac muscle cells are self-excitable
– Meaning they contract without any signal from the nervous system
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The impulses that travel during the cardiac cycle
– Can be recorded as an electrocardiogram (ECG or EKG)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The pacemaker is influenced by
– Nerves, hormones, body temperature, and exercise
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Blood Vessel Structure and Function
• The “infrastructure” of the circulatory system
– Is its network of blood vessels
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Blood Flow Velocity
• Physical laws governing the movement of fluids through pipes
– Influence blood flow and blood pressure
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Blood Pressure
• Blood pressure
– Is the hydrostatic pressure that blood exerts against the wall of a vessel
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Blood pressure is determined partly by cardiac output
– And partly by peripheral resistance due to variable constriction of the arterioles
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Capillary Function
• Capillaries in major organs are usually filled to capacity
– But in many other sites, the blood supply varies
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The critical exchange of substances between the blood and interstitial fluid
– Takes place across the thin endothelial walls of the capillaries
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Fluid reenters the circulation
– Directly at the venous end of the capillary bed and indirectly through the lymphatic system
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Erythrocytes
• Red blood cells, or erythrocytes
– Are by far the most numerous blood cells
– Transport oxygen throughout the body
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Platelets
• Platelets function in blood clotting
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Stem Cells and the Replacement of Cellular Elements
• The cellular elements of blood wear out
– And are replaced constantly throughout a person’s life
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Figure 42.16 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Blood Clotting
• When the endothelium of a blood vessel is damaged
– The clotting mechanism begins
12
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Figure 42.17 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Cardiovascular Disease
• Cardiovascular diseases
– Are disorders of the heart and the blood vessels
– Account for more than half the deaths in the United States
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Gills in Aquatic Animals
• Gills are outfoldings of the body surface
– Specialized for gas exchange
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Lungs
• Spiders, land snails, and most terrestrial vertebrates
– Have internal lungs
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Figure 42.23 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• In mammals, air inhaled through the nostrils
– Passes through the pharynx into the trachea, bronchi, bronchioles, and dead-end alveoli, where gas exchange occurs
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Concept 42.6: Breathing ventilates the lungs
• The process that ventilates the lungs is breathing
– The alternate inhalation and exhalation of air
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
How an Amphibian Breathes
• An amphibian such as a frog
– Ventilates its lungs by positive pressure breathing, which forces air down the trachea
15
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Figure 42.24 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Lung volume increases
– As the rib muscles and diaphragm contract
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Figure 42.25 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Air passes through the lungs
– In one direction only
• Every exhalation
– Completely renews the air in the lungs
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Sensors in the aorta and carotid arteries
– Monitor O2 and CO2 concentrations in the blood
– Exert secondary control over breathing
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• A gas always diffuses from a region of higher partial pressure
– To a region of lower partial pressure
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• In the lungs and in the tissues
– O2 and CO2 diffuse from where their partial pressures are higher to where they are lower
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Respiratory Pigments
• Respiratory pigments
– Are proteins that transport oxygen
– Greatly increase the amount of oxygen that blood can carry
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Oxygen Transport
• The respiratory pigment of almost all vertebrates
– Is the protein hemoglobin, contained in the erythrocytes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Cooperative O2 binding and release
– Is evident in the dissociation curve for hemoglobin
• A drop in pH
– Lowers the affinity of hemoglobin for O2
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Carbon Dioxide Transport
• Hemoglobin also helps transport CO2
– And assists in buffering
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Carbon from respiring cells
– Diffuses into the blood plasma and then into erythrocytes and is ultimately released in the lungs
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
2
1
3 4
5 6
7
8
9
10
11
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.
1
2
3
4
5
6
7
8
9
10
11
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Elite Animal Athletes
• Migratory and diving mammals
– Have evolutionary adaptations that allow them to perform extraordinary feats
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Diving Mammals
• Deep-diving air breathers
– Stockpile O2 and deplete it slowly