Circulation and Gas Exchange

Chapter 42

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

Circulatory System

Internal transport systemDistributes nutrientsRemoves wastesRepairs tissuesHelps fight infections

In circulation… What needs to be transported

nutritive nutrients fuels from digestive system

respiratory O2 & CO2 from & to gas exchange systems: lungs, gills

excretory waste products from cells

water, salts, nitrogenous wastes (urea) protection

blood clotting immune defenses

white blood cells & others patrolling body regulation

hormones

Invertebrate Circulation Simple Diffusion

Body cavity 2-cell layers think all cells within easy reach of fluid use gastrovascular cavity for exchange

Cnidarians

Hydra

Circulatory systemsAll animals have:

circulatory fluid = bloodtubes = blood vesselsmuscular pump = heart

Open or Closed Systems

Open circulatory system Taxonomy

invertebrates insects,

arthropods, mollusks

Structure no distinction

between blood & extracellular (interstitial) fluid hemolymph

Closed circulatory system Taxonomy

invertebrates earthworms, squid,

octopusesvertebrates

Structureblood confined to vessels

& separate from interstitial fluid

1 or more hearts large vessels to smaller

vessels material diffuses

between vessels & interstitial fluid

Vertebrate Circulatory System Closed system

number of heart chambers differs

What’s the adaptive value of a 4 chamber heart?4 chamber heart is double pump =

separates oxygen-rich & oxygen-poor blood

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 A powerful four-chambered heart

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

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

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

Evolution of vertebrate circulatory system

fish amphibian reptiles birds & mammals

A A

VV V VV

A AAAA

V

2 chamber 3 chamber 3 chamber 4 chamber

heart structure & increasing body size

Driving evolution of CV systems

Metabolic rateendothermy = higher

metabolic rate greater need for energy,

fuels, O2, waste removal more complex circulatory

system more powerful hearts

The Cardiac Cycle

A rhythmic cycle the heart contracts and relaxes

Systole contraction, or pumping, phase of the cycle

Diastole relaxation, or filling, phase of the cycle

Figure 42.7

Semilunarvalvesclosed

AV valvesopen

AV valvesclosed

Semilunarvalvesopen

Atrial and ventricular diastole

1

Atrial systole; ventricular diastole

2

Ventricular systole; atrial diastole

3

0.1 sec

0.3 sec0.4 sec

Pulse and Cardiac Output

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

Maintaining the Heart’s Rhythmic Beat

Some cardiac muscle cells are self-excitable 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

Electrocardiograms(ECG or EKG) Recorded impulses that travel during

the cardiac cycle

Figure 42.8

SA node(pacemaker)

AV node Bundlebranches

Heartapex

Purkinjefibers

2 Signals are delayedat AV node.

1 Pacemaker generates wave of signals to contract.

3 Signals passto heart apex.

4 Signals spreadThroughoutventricles.

ECG

The control of heart rhythm

Blood Vessel Structure and Function

The “infrastructure” of the circulatory system Is its network of blood vessels

Blood Vessels The “infrastructure” of the circulatory

system Is its network of blood vessels

Arteries carry blood to capillaries The sites of chemical exchange between

the blood and interstitial fluid Veins

Return blood from capillaries to the heart

Blood Vessels

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

Blood Pressure 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

Figure 42.13 The movement of fluid between capillaries and the interstitial fluid

Figure 43.4 The human lymphatic system

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

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,

most numerous White blood cells, which function in defense

A third cellular element, platelets Are fragments of cells that are involved in

clotting

Figure 42.14 The composition of mammalian blood

Figure 42.15 Differentiation of blood cells

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

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

Lymphoidstem cells

Pluripotent stem cells(in bone marrow)

Myeloidstem cells

Erythrocytes

Platelets Monocytes

Neutrophils

Eosinophils

Basophils

Lymphocytes

Figure 42.16

Blood Clotting When the endothelium of a blood vessel is

damaged The clotting mechanism begins

Plateletplug

Collagen fibers

Platelet releases chemicalsthat make nearby platelets sticky

Clotting factors from:PlateletsDamaged cellsPlasma (factors include calcium, vitamin K)

Prothrombin Thrombin

Fibrinogen Fibrin5 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. Plateletsadhere to collagen fibers in the connective tissue and release a substance thatmakes nearby platelets sticky.

1 The platelets form a plug that providesemergency protectionagainst blood loss.

2This seal is reinforced by a clot of fibrin when vessel damage is severe. Fibrin is formed via amultistep process: Clotting factors released fromthe clumped platelets or damaged cells mix withclotting factors in the plasma, forming an activation cascade that converts a plasma proteincalled 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

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 artery50 µm 250 µm

Smooth muscleConnective 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

Gas Exchange Supplies oxygen for cellular respiration

and disposes of carbon dioxide

Figure 42.19

Organismal level

Cellular level

Circulatory system

Cellular respiration ATPEnergy-richmoleculesfrom food

Respiratorysurface

Respiratorymedium(air of water)

O2 CO2

Gills in Aquatic Animals

Animals require large, moist respiratory surfaces for the adequate diffusion of respiratory gases Between their cells and the respiratory

medium, either air or water

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 gillis an extension of the coelom(body cavity). Gas exchangeoccurs by diffusion across thegill surfaces, and fluid in thecoelom circulates in and out ofthe 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

Segmented Worms Have flaplike gills 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 gillsand also function incrawling and swimming.

Gill

Parapodia

Gills of clams, crayfish, and many other animals

Are restricted to a local body region

Figure 42.20c, d

(d) Crayfish. Crayfish and other crustaceanshave long, feathery gills covered by the exoskeleton. Specialized body appendagesdrive water over the gill surfaces.

(c) Scallop. The gills of a scallop are long, flattened plates that project from themain body mass inside the hard shell.Cilia on the gills circulate water around the gill surfaces.

Gills

Gills

Fish Gills

Countercurrent exchange

Figure 42.21

Gill arch

Water flow Operculum

Gill arch

Blood vessel

Gillfilaments

Oxygen-poorblood

Oxygen-richblood

Water flowover lamellaeshowing % O2

Blood flowthrough capillariesin lamellaeshowing % 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 internaltubes that deliver air directly to body cells. Rings of chitin reinforcethe 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 ofthe fluid is withdrawn into the body. This increases the surface area of air in contact with cells.

Tracheal Systems in Insects Consists of tiny branching tubes that

penetrate the body

The tracheal tubes Supply O2 directly to body cells

Airsac

Body cell

Trachea

Tracheole

TracheolesMitochondria

Myofibrils

Body wall

(b) This micrograph shows crosssections of tracheoles in a tinypiece of insect flight muscle (TEM).Each of the numerous mitochondriain the muscle cells lies within about5 µm of a tracheole.

Figure 42.22b 2.5 µm

Air

Lungs Restricted to one location

Human Anatomy

Nares Pharynx Larynx/Epiglottis Glottis Trachea Bronchi Bronchioles Alveoli Lungs Diaphragm

Microscopic Anatomy Bronchioles Alveoli Blood Supply

Pulmonary A/VBronchial A/V

Mechanism of Breathing

When you breathe in . . .

Vagus Nerve

How an Amphibian Breathes

An amphibian such as a frog Ventilates its lungs by positive pressure

breathing, which forces air down the trachea

How a Bird Breathes

Besides lungs, bird have eight or nine air sacs That function as bellows that keep air

flowing through the lungs

INHALATIONAir sacs fill

EXHALATIONAir sacs empty; lungs fill

Anteriorair sacs

Trachea

Lungs LungsPosteriorair sacs

Air Air

1 mm

Air tubes(parabronchi)in lung

Figure 42.25

Autonomic Breathing Control

Vagus Nerve Medulla sets

rhythm

Pons moderates rhythm

Chemoreceptors Baroreceptors

Carotid, aorta

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 0.2O2 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

CO2O2

Alveolarepithelialcells

Pulmonaryarteries

Blood enteringalveolar

capillaries

Blood leavingtissue

capillaries

Blood enteringtissue

capillaries

Blood leaving

alveolar capillaries

CO2O2

Tissue capillaries

Heart

Alveolar capillaries

of lung

<40 >45

Tissue cells

Pulmonaryveins

Systemic arteriesSystemic

veinsO2

CO2

O2

CO 2

Alveolar spaces

12

43

Figure 42.27

Respiratory Pigments

Respiratory pigments Are proteins that transport oxygen Greatly increase the amount of oxygen

that blood can carry

Hemoglobin must reversibly bind O2, loading O2 in the lungs and unloading it in other parts of the body

Transport of Oxygen98.5% bound to hemoglobin

1.5% dissolved in plasma

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

CO2Interstitialfluid

CO2 producedCO2 transportfrom tissues

CO2

CO2

Blood plasmawithin capillary Capillary

wall

H2O

Redbloodcell

HbCarbonic acidH2CO3

HCO3–

H++Bicarbonate

HCO3–

Hemoglobinpicks up

CO2 and H+

HCO3–

HCO3– H++

H2CO3Hb

Hemoglobinreleases

CO2 and H+

CO2 transportto lungs

H2O

CO2

CO2

CO2

CO2

Alveolar space in lung

2

1

34

5 6

7

8

9

10

11

To lungs

Carbon dioxide produced bybody 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 bycarbonic anhydrase contained. Withinred 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 thuspreventing the Bohr shift.

CO2 diffuses into the alveolarspace, from which it is expelledduring exhalation. The reductionof CO2 concentration in the plasmadrives the breakdown of H2CO3 Into CO2 and water in the red bloodcells (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 unloadedfrom hemoglobin and diffuses into the interstitial fluid.

1

2

3

4

5

6

7

8

9

10

11

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