gas exchange unit circulation and urry • cain • …6.3.pdf · urry • cain • wasserman •...

CAMPBELL BIOLOGY IN FOCUS

© 2014 Pearson Education, Inc.

Urry • Cain • Wasserman • Minorsky • Jackson • Reece

Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge

Unit 6.3

Circulation and Gas Exchange


Overview: Trading Places

▪ The resources that animal cells require, such as nutrients and O2, enter the cytoplasm by crossing the plasma membrane

▪ In unicellular organisms, these exchanges occur directly with the environment

▪ Most multicellular organisms rely on specialized systems that carry out exchange with the environment and transport materials through the body


▪ Gills are an example of a specialized exchange system in animals

▪ O2 diffuses from the water into blood vessels▪ CO2 diffuses from blood into the water

▪ Internal transport and gas exchange are functionally related in most animals


Figure 34.1


Concept 34.1: Circulatory systems link exchange surfaces with cells throughout the body

▪ Small, nonpolar molecules such as O2 and CO2 move between cells and their immediate surroundings by diffusion

▪ Diffusion time is proportional to the square of the distance travelled

▪ Diffusion is only efficient over small distances


▪ In small or thin animals, cells can exchange materials directly with the surrounding medium

▪ In most animals, cells exchange materials with the environment via a fluid-filled circulatory system


Gastrovascular Cavities

▪ Some animals lack a circulatory system▪ Some cnidarians, such as jellies, have elaborate

gastrovascular cavities▪ A gastrovascular cavity functions in both digestion

and distribution of substances throughout the body▪ The body wall that encloses the gastrovascular

cavity is only two cells thick▪ Flatworms have a gastrovascular cavity and a flat

body shape to optimize diffusional exchange with the environment


Figure 34.2

Gastrovascularcavity

Mouth

1 mm


Open and Closed Circulatory Systems

▪ A circulatory system has a circulatory fluid, a set of interconnecting vessels, and a muscular pump, the heart

▪ Several basic types of circulatory systems have arisen during evolution, each representing adaptations to constraints of anatomy and environment


▪ All circulatory systems are either open or closed▪ In insects, other arthropods, and some molluscs,

circulatory fluid bathes the organs directly in an open circulatory system

▪ In an open circulatory system, there is no distinction between circulatory fluid and interstitial fluid, and this general body fluid is called hemolymph


Figure 34.3

Branch vesselsin each organ

Tubular heart

Pores

Hemolymph in sinuses

(a) An open circulatory system

Heart

(b) A closed circulatory system

HeartBlood

Dorsal vessel(main heart)

Auxiliaryhearts

Ventral vessels

Interstitialfluid


Figure 34.3a

Tubular heart

Pores

Hemolymph in sinuses

(a) An open circulatory system

Heart


▪ In closed circulatory systems the circulatory fluid called blood is confined to vessels and is distinct from interstitial fluid

▪ These systems are found in annelids, most cephalopods, and all vertebrates

▪ One or more hearts pump blood through the vessels▪ Chemical exchange occurs between blood and

interstitial fluid and between interstitial fluid and body cells


Figure 34.3b

Branch vesselsin each organ

(b) A closed circulatory system

HeartBlood

Dorsal vessel(main heart)

Auxiliaryhearts

Ventral vessels

Interstitialfluid


Organization of Vertebrate Circulatory Systems

▪ Humans and other vertebrates have a closed circulatory system called the cardiovascular system

▪ The three main types of blood vessels are arteries, veins, and capillaries

▪ Blood flow is one-way in these vessels


▪ Arteries branch into arterioles and carry blood away from the heart to capillaries

▪ Networks of capillaries called capillary beds are the sites of chemical exchange between the blood and interstitial fluid

▪ Venules converge into veins and return blood from capillaries to the heart


▪ Arteries and veins are distinguished by the direction of blood flow, not by O2 content

▪ Vertebrate hearts contain two or more chambers▪ Blood enters through an atrium and is pumped out

through a ventricle


Single Circulation

▪ Bony fishes, rays, and sharks have single circulation with a two-chambered heart

▪ In single circulation, blood leaving the heart passes through two capillary beds before returning


Figure 34.4

Lungand skincapillaries

Body capillaries

Vein

Gill capillaries

(a) Single circulation: fish

Heart:

(b) Double circulation:amphibian

Key

Systemiccapillaries

Pulmocutaneous circuit

Artery

Ventricle (V)Atrium (A)

Oxygen-rich bloodOxygen-poor blood

Right Left

A A

V

Systemic circuit

Lungcapillaries

(c) Double circulation:mammal

Systemiccapillaries

Pulmonary

circuit

Right Left

A AV

Systemic circuit

V


Figure 34.4a

Body capillaries

Vein

Gill capillaries

(a) Single circulation: fish

Heart:

Key

Artery

Ventricle (V)Atrium (A)



Double Circulation

▪ Amphibians, reptiles, and mammals have double circulation

▪ Oxygen-poor and oxygen-rich blood is pumped separately from the right and left sides of the heart

▪ Having both pumps within a heart simplifies coordination of the pumping cycle


Figure 34.4b

Lungand skincapillaries

(b) Double circulation:amphibian

Key

Systemiccapillaries

Pulmocutaneous

circuit


Right

Left

A A

V

Systemic circuit


Figure 34.4c

Key Oxygen-rich blood

Oxygen-poor blood

Lungcapillaries

(c) Double circulation:mammal

Systemiccapillaries

Pulmonary

circuit

Right Left

A AV

Systemic circuit

V


▪ In reptiles and mammals, oxygen-poor blood flows through the pulmonary circuit to pick up oxygen through the lungs

▪ In amphibians, oxygen-poor blood flows through a pulmocutaneous circuit to pick up oxygen through the lungs and skin

▪ Oxygen-rich blood delivers oxygen through the systemic circuit

▪ Double circulation maintains higher blood pressure in the organs than does single circulation


Evolutionary Variation in Double Circulation

▪ Some vertebrates with double circulation are intermittent breathers

▪ These animals have adaptations that enable the circulatory system temporarily to bypass the lungs


▪ Frogs and other amphibians have a three-chambered heart: 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

▪ When underwater, blood flow to the lungs is nearly shut off


▪ Turtles, snakes, and lizards have a three-chambered heart: two atria and one ventricle

▪ Their circulatory system allows control of relative amounts of blood flowing to the lungs and body

▪ In alligators, caimans, and other crocodilians a septum divides the ventricle

▪ A connection to atrial valves can temporarily shunt blood away from the lungs, as needed


▪ Mammals and birds have a four-chambered heart with two atria and two ventricles

▪ The left side of the heart pumps and receives only oxygen-rich blood, while the right side receives and pumps only oxygen-poor blood

▪ There is no mechanism to vary relative blood flow to the lungs and body

▪ Mammals and birds are endotherms and require more O2 than ectotherms


Concept 34.2: Coordinated cycles of heart contraction drive double circulation in mammals

▪ The mammalian cardiovascular system meets the body’s continuous demand for O2


Mammalian Circulation

▪ Blood begins its flow with the right ventricle pumping blood to the lungs via the pulmonary arteries

▪ The blood loads O2 and unloads CO2 in the capillary beds of the lungs

▪ Oxygen-rich blood from the lungs enters the heart at the left atrium via the pulmonary veins and is pumped through the aorta to the body tissues by the left ventricle


▪ The aorta provides blood to the heart through the coronary arteries

▪ Diffusion of O2 and CO2 takes place in the capillary beds throughout the body

▪ Blood returns to the heart through the superior vena cava (blood from head, neck, and forelimbs) and inferior vena cava (blood from trunk and hind limbs)

▪ The superior vena cava and inferior vena cava flow into the right atrium


Figure 34.5

Capillaries ofabdominal organsand hind limbs

Aorta

Capillariesof right lung

Superiorvena cava

Pulmonaryartery

PulmonaryveinRight atriumRight ventricleInferior vena cava

Capillariesof left lung

Pulmonary artery

Pulmonaryvein

Left atriumLeft ventricle

Capillaries ofhead andforelimbs

Aorta

9

7

6

42

11

3

5

8

101

3


The Mammalian Heart: A Closer Look

▪ A closer look at the mammalian heart provides a better understanding of double circulation

▪ When the heart contracts, it pumps blood; when it relaxes, its chambers fill with blood

▪ One complete sequence of pumping and filling is called the cardiac cycle


▪ Atria have relatively thin walls and serve as collection chambers for blood returning to the heart

▪ The ventricles are more muscular and contract much more forcefully than the atria

▪ The volume of blood each ventricle pumps per minute is called the cardiac output


Figure 34.6

Aorta

Atrioventricular(AV) valve

Semilunarvalve

Pulmonary artery

Rightatrium

Right ventricle

Pulmonary artery

Left atrium

Left ventricle

Atrioventricular(AV) valve

Semilunarvalve


Figure 34.7-3

Atrial andventriculardiastole

Atrial systole andventricular diastole

Ventricular systole and atrial diastole

0.4sec

0.3 sec

0.1sec

1

2

3


▪ The heart rate, also called the pulse, is the number of beats per minute

▪ The stroke volume is the amount of blood pumped in a single contraction

▪ Cardiac output depends on both the heart rate and stroke volume


▪ Four valves prevent backflow of blood in the heart▪ The atrioventricular (AV) valves separate each

atrium and ventricle▪ The semilunar valves control blood flow to the

aorta and the pulmonary artery


▪ The “lub-dup” sound of a heart beat is caused by the recoil of blood against the AV valves (lub) then against the semilunar (dup) valves

▪ Backflow of blood through a defective valve causes a heart murmur


Maintaining the Heart’s Rhythmic Beat

▪ Some cardiac muscle cells are autorhythmic, meaning they contract without any signal from the nervous system

▪ The sinoatrial (SA) node, or pacemaker, sets the rate and timing at which all other cardiac muscle cells contract

▪ The SA node produces electrical impulses that spread rapidly through the heart and can be recorded as an electrocardiogram (ECG or EKG)


Figure 34.8-4

Signals (yellow)from SA nodespreadthrough atria.

SA node(pacemaker)

1 Signals aredelayedat AV node.

Bundlebranchespass signalsto heart apex.

Signalsspreadthroughoutventricles.

AV node

Bundlebranches Heart

apex

Purkinjefibers

ECG

2 3 4


▪ 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 pacemaker is regulated by two portions of the nervous system: the sympathetic and parasympathetic divisions

▪ The sympathetic division speeds up the pacemaker▪ The parasympathetic division slows down the

pacemaker▪ The pacemaker is also regulated by hormones and

temperature


Concept 34.3: Patterns of blood pressure and flow reflect the structure and arrangement of blood vessels

▪ The physical principles that govern movement of water in plumbing systems also apply to the functioning of animal circulatory systems


Blood Vessel Structure and Function

▪ A vessel’s cavity is called the central lumen▪ The epithelial layer that lines blood vessels is called

the endothelium▪ The endothelium is smooth and minimizes resistance

to blood flow


▪ Capillaries have thin walls, the endothelium and its basal lamina, to facilitate the exchange of substances

▪ Arteries and veins have an endothelium, smooth muscle, and connective tissue

▪ Arteries have thicker walls than veins to accommodate the high pressure of blood pumped from the heart


Figure 34.9

Connectivetissue

Smoothmuscle Connective

tissue

Smoothmuscle

Endothelium Endothelium

Artery Vein

Artery Vein

Red bloodcells

Basal lamina

Capillary

Red blood cell

Capillary

ArterioleVenule

Valve100 μm

15 μ

m

LMLM


Blood Flow Velocity

▪ Blood vessel diameter influences blood flow▪ Velocity of blood flow is slowest in the capillary

beds, as a result of the high resistance and large total cross-sectional area

▪ Blood flow in capillaries is necessarily slow for exchange of materials


Figure 34.10

Systolicpressure

Diastolicpressure

4,000

2,000

120

20

40

8040

0

0

0

Pres

sure

(mm

Hg)

Velo

city

(cm

/sec

)A

rea

(cm

2 )

Aor

ta

Art

erie

s

Vena

eca

vae

Vein

s

Cap

illar

ies

Venu

les

Art

erio

les


Blood Pressure

▪ Blood flows from areas of higher pressure to areas of lower pressure

▪ Blood pressure exerts a force in all directions


Changes in Blood Pressure During the Cardiac Cycle

▪ Systole is the contraction phase of the cardiac cycle▪ Pressure at the time of ventricle contraction is called

systolic pressure▪ Diastole is the the relaxation phase of the cardiac

cycle; diastolic pressure is lower than systolic


Maintenance of Blood Pressure

▪ Blood pressure is determined by cardiac output and peripheral resistance due to constriction of arterioles

▪ Vasoconstriction is the contraction of smooth muscle in arteriole walls; it increases blood pressure

▪ Vasodilation is the relaxation of smooth muscles in the arterioles; it causes blood pressure to fall


▪ Vasoconstriction and vasodilation help maintain adequate blood flow as the body’s demands change

▪ Nitric oxide is a major inducer of vasodilation▪ The peptide endothelin is an important inducer of

vasoconstriction


▪ Fainting is caused by inadequate blood flow to the head

▪ Animals with long necks require a higher systolic pressure to pump blood against gravity

▪ Gravity is a consideration for blood flow in veins, particularly in the legs

▪ One-way valves in veins prevent backflow of blood ▪ Blood returns to the heart through contraction of

smooth muscle in the walls of veins and venules and by contraction of skeletal muscles


Figure 34.11

Direction of bloodflow in vein(toward heart)

Valve (open)

Valve (closed)

Skeletal muscle


Capillary Function

▪ Blood flows through only 5–10% of the body’s capillaries at a time

▪ Capillaries in major organs are usually filled to capacity

▪ Blood supply varies in many other sites


▪ Two mechanisms alter blood flow in capillary beds▪ Vasoconstriction or vasodilation of the arteriole that

supplies a capillary bed▪ Precapillary sphincters, rings of smooth muscle at the

capillary bed entrance, open and close to regulate passage of blood

▪ Critical exchange of substances takes place across the thin walls of the capillaries


▪ Blood pressure tends to drive fluid out of the capillaries

▪ The difference in solute concentration between blood and interstitial fluid (the blood’s osmotic pressure) opposes fluid movement from the capillaries

▪ Blood pressure is usually greater than osmotic pressure

▪ Net loss of fluid from capillaries occurs in regions where blood pressure is highest


Fluid Return by the Lymphatic System

▪ The lymphatic system returns fluid, called lymph, that leaks out from the capillary beds

▪ Lymph has a very similar composition to interstitial fluid

▪ The lymphatic system drains into veins in the neck▪ Valves in lymph vessels prevent the backflow of

fluid


Figure 34.12

Interstitialfluid

Lymphaticvessel

Lymphaticvessel

Bloodcapillary

Tissue cells

Lymph node

Masses ofdefensivecells

Lymphaticvessels

Lymph nodes

Peyer’s patches(small intestine)

Appendix(cecum)

Thymus(immunesystem)

AdenoidTonsils

Spleen


▪ Lymph vessels have valves to prevent backflow▪ Lymph nodes are organs that filter lymph and play

an important role in the body’s defense▪ Edema is swelling caused by disruptions in the flow

of lymph▪ The lymphatic system also plays a role in harmful

immune responses, such as those responsible for asthma


Concept 34.4: Blood components function in exchange, transport, and defense▪ With open circulation, the fluid that is pumped

comes into direct contact with all cells and has the same composition as interstitial fluid

▪ The closed circulatory systems of vertebrates contain blood, which can be much more highly specialized


Blood Composition and Function

▪ Blood is a connective tissue consisting of cells suspended in a liquid matrix called plasma

▪ The cellular elements occupy about 45% of the volume of blood


Figure 34.13

Separatedbloodelements

Solvent forcarrying othersubstances

Plasma 55% Cellular elements 45%

Constituent Major functions

Osmotic balance,pH buffering,and regulationof membranepermeability

Water

Ions (bloodelectrolytes)SodiumPotassiumCalciumMagnesiumChlorideBicarbonate

Osmotic balance,pH buffering

Clotting

Defense

Fibrinogen

Plasma proteinsAlbumin

Immunoglobulins(antibodies)

Substances transported by bloodNutrients (such as glucose, fattyacids, vitamins)Waste products of metabolismRespiratory gases (O2 and CO2)Hormones

Functions

Leukocytes (white blood cells)

Transportof O2 and some CO2

Cell typeNumber

per μL (mm3)of blood

Basophils Lymphocytes

Eosinophils

Neutrophils Monocytes

Platelets

Erythrocytes (red blood cells)

250,000–400,000

5,000,000– 6,000,000

Bloodclotting

5,000–10,000 Defenseandimmunity


Plasma

▪ Blood plasma is about 90% water▪ Among its solutes are inorganic salts in the form of

dissolved ions, sometimes called electrolytes▪ Plasma proteins influence blood pH, osmotic

pressure, and viscosity▪ Particular plasma proteins function in lipid transport,

immunity, and blood clotting


Cellular Elements

▪ Blood contains two classes of cells▪ Red blood cells (erythrocytes) transport O2

▪ White blood cells (leukocytes) function in defense

▪ Platelets, a third cellular element, are fragments of cells that are involved in clotting


Figure 34.14

Stem cells(in bone marrow)

Basophils

Lymphocytes

Eosinophils

Neutrophils

MonocytesPlatelets

Erythrocytes

Myeloidstem cells

Lymphoidstem cells

B cells T cells


Erythrocytes▪ Red blood cells, or erythrocytes, are by far the most

numerous blood cells▪ They contain hemoglobin, the iron-containing

protein that transports O2

▪ Each molecule of hemoglobin binds up to four molecules of O2

▪ In mammals, mature erythrocytes lack nuclei


▪ Sickle-cell disease is caused by abnormal hemoglobin that polymerizes into aggregates

▪ The aggregates can distort an erythrocyte into a sickle shape


▪ Through a person’s life, multipotent stem cells replace the worn-out cellular elements of blood

▪ Erythrocytes circulate for about 120 days before they are replaced

▪ Stem cells that produce red blood cells and platelets are located in red marrow of bones like the ribs, vertebrae, sternum, and pelvis


Leukocytes▪ There are five major types of white blood cells, or

leukocytes▪ They function in defense by engulfing bacteria and

debris or by mounting immune responses against foreign substances

▪ They are found both in and outside of the circulatory system


Platelets▪ Platelets are fragments of cells and function in

blood clotting


Blood Clotting

▪ Coagulation is the formation of a solid clot from liquid blood

▪ A cascade of complex reactions converts inactive fibrinogen to fibrin, which forms the framework of a clot

▪ A blood clot formed within a blood vessel is called a thrombus and can block blood flow


Figure 34.15

PlateletPlateletplug

Collagenfibers

PlateletsClotting factors from:

Damaged cellsPlasma (factors include calcium, vitamin K)

Fibrin

Thrombin

Fibrinogen

Prothrombin

Enzymatic cascade

Fibrin clot

Fibrin clotformation

Red blood cell 5 μm

1 2 3


Cardiovascular Disease

▪ Cardiovascular diseases are disorders of the heart and the blood vessels

▪ Cardiovascular diseases account for more than half the deaths in the United States

▪ Cholesterol, a steroid, helps maintain normal membrane fluidity


▪ Low-density lipoprotein (LDL) delivers cholesterol to cells for membrane production

▪ High-density lipoprotein (HDL) scavenges excess cholesterol for return to the liver

▪ Risk for heart disease increases with a high LDL to HDL ratio

▪ Inflammation is also a factor in cardiovascular disease


Atherosclerosis, Heart Attacks, and Stroke

▪ One type of cardiovascular disease, atherosclerosis, is caused by the buildup of fatty deposits within arteries

▪ A fatty deposit is called a plaque; as it grows, the artery walls become thick and stiff and the obstruction of the artery increases


Figure 34.16

Endothelium

Lumen

Plaque

Blood clot


▪ A heart attack, or myocardial infarction, is the death of cardiac muscle tissue resulting from blockage of one or more coronary arteries

▪ Coronary arteries supply oxygen-rich blood to the heart muscle

▪ A stroke is the death of nervous tissue in the brain, usually resulting from rupture or blockage of arteries in the head

▪ Angina pectoris is caused by partial blockage of the coronary arteries and may cause chest pain


Risk Factors and Treatment of Cardiovascular Disease

▪ A high LDL to HDL ratio increases the risk of cardiovascular disease

▪ The proportion of LDL relative to HDL is increased by smoking and consumption of trans fats and decreased by exercise

▪ Drugs called statins reduce LDL levels and risk of heart attacks


▪ Inflammation plays a role in atherosclerosis and thrombus formation

▪ Aspirin inhibits inflammation and reduces the risk of heart attacks and stroke

▪ Hypertension (high blood pressure) contributes to the risk of heart attack and stroke

▪ Hypertension can be reduced by dietary changes, exercise, medication, or some combination of these


Concept 34.5: Gas exchange occurs across specialized respiratory surfaces

▪ Gas exchange is the uptake of molecular O2 from the environment and the discharge of CO2 to the environment


Partial Pressure Gradients in Gas Exchange

▪ Partial pressure is the pressure exerted by a particular gas in a mixture of gases

▪ For example, the atmosphere is 21% O2, by volume, so the partial pressure of O2 (PO2) is 0.21 × the atmospheric pressure


▪ Partial pressures also apply to gases dissolved in liquid, such as water

▪ When water is exposed to air, an equilibrium is reached in which the partial pressure of each gas is the same in the water and the air

▪ A gas always undergoes net diffusion from a region of higher partial pressure to a region of lower partial pressure


Respiratory Media

▪ O2 is plentiful in air, and breathing air is relatively easy

▪ In a given volume, there is less O2 available in water than in air

▪ Obtaining O2 from water requires greater energy expenditure than air breathing

▪ Aquatic animals have a variety of adaptations to improve efficiency in gas exchange


Figure 34.17

Coelom

Tube foot

Gills

(b) Sea star(a) Marine worm

Parapodium (functions as gill)


Respiratory Surfaces

▪ Gas exchange across respiratory surfaces takes place by diffusion

▪ Respiratory surfaces tend to be large and thin and are always moist

▪ Respiratory surfaces vary by animal and can include the skin, gills, tracheae, and lungs


Gills in Aquatic Animals

▪ Gills are outfoldings of the body that create a large surface area for gas exchange

▪ Ventilation is the movement of the respiratory medium over the respiratory surface

▪ Ventilation maintains the necessary partial pressure gradients of O2 and CO2 across the gills


▪ Aquatic animals move through water or move water over their gills for ventilation

▪ Fish gills use a countercurrent exchange system, where blood flows in the opposite direction to water passing over the gills

▪ Blood is always less saturated with O2 than the water it meets

▪ Countercurrent exchange mechanisms are remarkably efficient


Figure 34.18

Lamella

Water flow

Countercurrent exchange

O2-poor blood

Gill filaments

Operculum

Gillarch

Waterflow

Gill arch

Bloodvessels

O2-rich blood

Blood flow

PO2 (mm Hg) in blood

PO2 (mm Hg) in water

Netdiffusionof O2

140 110 80 50 30

150 120 90 60 30


Tracheal Systems in Insects

▪ The tracheal system of insects consists of a network of air tubes that branch throughout the body

▪ The tracheal system can transport O2 and CO2 without the participation of the animal’s open circulatory system

▪ Larger insects must ventilate their tracheal system to meet O2 demands


Figure 34.19Tracheoles

Muscle fiberMitochondria

Tracheae

Air sacs

External opening

Airsac Tracheole

Trachea

Air2.

5 μm

Body

cell


Lungs

▪ Lungs are an infolding of the body surface, usually divided into numerous pockets

▪ The circulatory system (open and closed) transports gases between the lungs and the rest of the body

▪ The use of lungs for gas exchange varies among vertebrates that lack gills


Mammalian Respiratory Systems: A Closer Look

▪ A system of branching ducts conveys air to the lungs▪ Air inhaled through the nostrils is warmed,

humidified, and sampled for odors▪ The pharynx directs air to the lungs and food to the

stomach▪ Swallowing tips the epiglottis over the glottis in the

pharynx to prevent food from entering the trachea


▪ Air passes through the pharynx, larynx, trachea, bronchi, and bronchioles to the alveoli, where gas exchange occurs

▪ Exhaled air passes over the vocal cords in the larynx to create sounds

▪ Cilia and mucus line the epithelium of the air ducts and move particles up to the pharynx

▪ This “mucus escalator” cleans the respiratory system and allows particles to be swallowed into the esophagus


▪ Gas exchange takes place in alveoli, air sacs at the tips of bronchioles

▪ Oxygen diffuses through the moist film of the epithelium and into capillaries

▪ Carbon dioxide diffuses from the capillaries across the epithelium and into the air space


Figure 34.20

Bronchiole

Bronchus

Right lungTrachea(Esophagus)Larynx

Pharynx

(Heart)

Terminalbronchiole

Leftlung

Nasalcavity

Capillaries

Alveoli

Dense capillary bedenveloping alveoli(SEM)

Branch ofpulmonary vein(oxygen-richblood)

Branch of pulmonary artery (oxygen-poorblood)

50 μm

Diaphragm


▪ Alveoli lack cilia and are susceptible to contamination▪ Secretions called surfactants coat the surface of

the alveoli▪ Preterm babies lack surfactant and are vulnerable to

respiratory distress syndrome; treatment is provided by artificial surfactants


Figure 34.21

Deaths fromother causes

RDS deaths

Body mass of infant<1,200 g >1,200 g

(n = 9) (n = 0) (n = 29)

(n = 9)

Surf

ace

tens

ion

(dyn

es/c

m)

Results

10

20

30

40

0

What causes respiratory distress syndrome?


Concept 34.6: Breathing ventilates the lungs

▪ The process that ventilates the lungs is breathing, the alternate inhalation and exhalation of air


▪ An amphibian such as a frog ventilates its lungs by positive pressure breathing, which forces air down the trachea

▪ Birds have eight or nine air sacs that function as bellows that keep air flowing through the lungs

▪ Air passes through the lungs of birds in one direction only

▪ Passage of air through the entire system—lungs and air sacs—requires two cycles in inhalation and exhalation


How a Mammal Breathes

▪ Mammals ventilate their lungs by negative pressure breathing, which pulls air into the lungs

▪ Lung volume increases as the rib muscles and diaphragm contract

▪ The tidal volume is the volume of air inhaled with each breath


Figure 34.22

Inhalation:Diaphragm contracts

(moves down).

Diaphragm

Exhalation:Diaphragm relaxes

(moves up).

Lung

Airinhaled.

Airexhaled.

Rib cageexpands asrib musclescontract.

Rib cage getssmaller asrib musclesrelax.

1 2


▪ The maximum tidal volume is the vital capacity▪ After exhalation, a residual volume of air remains

in the lungs▪ Each inhalation mixes fresh air with oxygen-depleted

residual air▪ As a result, the maximum PO2 in alveoli is

considerably less than in the atmosphere


Control of Breathing in Humans

▪ In humans, the main breathing control center consists of neural circuits in the medulla oblongata, near the base of the brain

▪ The medulla regulates 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


Figure 34.23-4

Carotidarteries

Response:Signals frommedulla to ribmuscles anddiaphragmincrease rateand depth ofventilation.

Homeostasis:Blood pH of about 7.4

CO2 leveldecreases. Stimulus:

Rising level of CO2in tissues lowers

blood pH.

Sensor/controlcenter:

Aorta

Cerebro-spinalfluid

Medullaoblongata


▪ Sensors in the aorta and carotid arteries monitor O2 and CO2 concentrations in the blood

▪ These sensors exert secondary control over breathing


Concept 34.7: Adaptations for gas exchange include pigments that bind and transport gases

▪ The metabolic demands of many organisms require that the blood transport large quantities of O2 and CO2


Coordination of Circulation and Gas Exchange

▪ Blood arriving in the lungs has a low PO2 and a high PCO2 relative to air in the alveoli

▪ In the alveoli, O2 diffuses into the blood and CO2 diffuses into the air

▪ In tissue capillaries, partial pressure gradients favor diffusion of O2 into the interstitial fluids and CO2 into the blood

▪ Specialized carrier proteins play a vital role in this process


Figure 34.24

Alveolarepithelialcells

Alveolarspaces

Alveolarcapillaries

Inhaled airExhaled air

Pulmonaryveins

Systemicarteries

Pulmonaryarteries

Systemicveins

Systemiccapillaries

Heart

CO2 O2

Body tissuecells

O2 CO2

120 27

O2 CO2

40 45

O2 CO2

160 0.2

O2 CO2

104 40

O2 CO2

<40 >45

O2CO2


Respiratory Pigments

▪ Respiratory pigments circulate in blood or hemolymph and greatly increase the amount of oxygen that is transported

▪ A variety of respiratory pigments have evolved among animals

▪ These mainly consist of a metal bound to a protein


▪ The respiratory pigment of almost all vertebrates and many invertebrates is hemoglobin

▪ A single hemoglobin molecule can carry four molecules of O2, one molecule for each iron- containing heme group

▪ Hemoglobin binds oxygen reversibly, loading it in the gills or lungs and releasing it in other parts of the body


Figure 34.UN01

Hemoglobin

Heme

Iron


▪ Hemoglobin binds O2 cooperatively▪ When O2 binds one subunit, the others change shape

slightly, resulting in their increased affinity for oxygen▪ When one subunit releases O2, the others release

their bound O2 more readily▪ Cooperativity can be demonstrated by the dissociation

curve for hemoglobin


Figure 34.25

pH 7.4

PO2 (mm Hg)

pH 7.2

Hemoglobinretains lessO2 at lower pH(higher CO2concentration

Tissuesat restPO2 (mm Hg)

Tissues duringexercise

Lungs

O2 unloadedto tissues

during exercise

O2 unloadedto tissuesat rest

(b) pH and hemoglobin dissociation(a) PO2 and hemoglobin dissociationat pH 7.4

O2

satu

ratio

n of

hem

oglo

bin

(%)

O2

satu

ratio

n of

hem

oglo

bin

(%) 100

80

60

40

20

0

100

80

60

40

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0100806040200 100806040200


Figure 34.25a

Tissuesat restPO2 (mm Hg)

Tissues duringexercise

Lungs

O2 unloadedto tissues

during exercise

O2 unloadedto tissuesat rest

(a) PO2 and hemoglobin dissociationat pH 7.4

O2

satu

ratio

n of

hem

oglo

bin

(%)

100

8060

4020

01008

0604

0200


▪ CO2 produced during cellular respiration lowers blood pH and decreases the affinity of hemoglobin for O2; this is called the Bohr shift

▪ Hemoglobin also assists in preventing harmful changes in blood pH and plays a minor role in CO2 transport


Figure 34.25b

pH 7.4

PO2 (mm Hg)

pH 7.2

Hemoglobinretains lessO2 at lower pH(higher CO2concentration

(b) pH and hemoglobin dissociation

O2

satu

ratio

n of

hem

oglo

bin

(%)

100

8060

4020

01008

0604

0200


Carbon Dioxide Transport

▪ Most of the CO2 from respiring cells diffuses into the blood and is transported in blood plasma, bound to hemoglobin or as bicarbonate ions (HCO3

–)


Respiratory Adaptations of Diving Mammals

▪ Diving mammals have evolutionary adaptations that allow them to perform extraordinary feats

▪ For example, Weddell seals in Antarctica can remain underwater for 20 minutes to an hour

▪ For example, elephant seals can dive to 1,500 m and remain underwater for 2 hours

▪ These animals have a high blood to body volume ratio


▪ Deep-diving air breathers can store large amounts of O2

▪ Oxygen can be stored in their muscles in myoglobin proteins

▪ Diving mammals also conserve oxygen by▪ Changing their buoyancy to glide passively▪ Decreasing blood supply to muscles▪ Deriving ATP in muscles from fermentation once

oxygen is depleted

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