Circulation and Gas Exchange

Chapter 42

A.P. Biology

Mr. Knowles

Liberty Senior High

It’s all because of cellular respiration!

C6H12O6 + 6O2 --> 6CO2 + 6H2O +

(ATP)

We Need This! To Make This!

And Eliminate

This!

• 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 ATPEnergy-richmoleculesfrom food

Respiratorysurface

Respiratorymedium(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.

• 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.

• 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

External Respiration• Uptake of O2 and the release of CO2 into the

environment- external respiration.

• Dry Air = 78 % N2, 21 % O2 , 0.93% argon and other inert gases, and 0.03 % CO2 .

• Amount of air changes at altitude, but not composition.

• Each gas exerts a fraction of total atmospheric pressure- partial pressure (PN2

, PO2, PCO2

…)

Remember the Plasma Membrane?

• Like H2O, O2 and CO2 diffuse through the phospholipid bilayer.

• Membrane must have H2O on both sides for its integrity (hydrophobic).

• All terrestrial organisms obtain gas diffusion across a moist membrane, never dry. Dissolved gases (O2 and CO2 ) diffuse through.

Intracellular Diffusion of Gases is Passive

Aerobically Respiring Cell

[O2] is lower

[CO2] is higher

[O2] is higher

[CO2] is lower

Dissolved Oxygen in Water• Factors that affect O2 solubility in H2O:

1. PO2 in air, decreases with altitude. Less

PO2 , less dissolved O2 in the H2O.

2. Temperature of the H2O. Inversely related.

3. Concentration of other solutes in H2O. Inversely related.

What happens to the oxygen level when tides

go out?

The Story of the Tarpon

Discovery: Blue Planet- Tidal Seas

Problems in External Respiration• Simple diffusion- limited to a

distance of 0.5 mm. • As organisms become larger, their

surface area to volume ratio decreases.

• Keep Intracellular [O2] < Extracellular [O2]. If not, there is no net movement of O2 by diffusion.

Invertebrate Circulation

• The wide range of invertebrate body size and form:

–Is paralleled by a great diversity in circulatory systems

Evolution of External Respiration• Unicellular bacteria and protists –

simple diffusion. Problem: Limits size of organism. • Jellyfish (Phylum Cnidaria)– have

no respiratory system. Very thin and slow down metabolism to allow diffusion of gases. (an unusual case)

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

Circularcanal

Radial canal

5 cmMouth

The Jellyfish Life!

Discover: Blue Planet- Seasonal Seas

Cyanea capillata – 7 ft. bell, 120 ft tentacles

Creating a Water Current

• Sponges (Phylum Porifera) – diffusion directly from surrounding water; set up a current using cilia. Beating cilia replace water over the diffusion surface.

Sponges (Porifera)

Sponges (Porifera)

Sponges and Corals

Discovery: Blue Planet- Coral Seas

Creating a Water Current

• Problem: Limited to aquatic environments; not efficient for really large organisms.

But sponges are aquatic! What about terrestrial

organisms?

Enter Cutaneous Respiration!

Cutaneous Respiration

• Cutaneous Respiration – gas exchange occurs directly across an animal’s body surface.

• Problem: Must stay moist for gas diffusion; must increase body surface area; limits size.

The Worms!• Flatworms (Phylum Platyhelminthes)

– very thin to permit direct diffusion from surrounding fluid (tapeworms-host fluid).

• Roundworms (Phylum Nematoda) and Earthworms (Phylum Annelida) - direct diffusion; requires a moist cuticle; often secret mucous to keep skin wet.

• 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 gillsand also function incrawling and swimming.

Gill

Parapodia

So why do earthworms die on your driveway

after a rain?

They dry out and, therefore, suffocate!

Mouth-to-skin, anyone?

What are the down sides to cutaneous respiration?

The World’s Largest Earthworm

Video: Nigel Marvin’s Giant Creepy Crawlies

Scolex

Proglottids

Cutaneous Respiration in a Tapeworm

Video: The Body Snatchers

Increasing the Diffusion Surface Area

• Advanced Invertebrates (Phylum Echinodermata, Mollusca, Arthropoda) – increase surface area and bring external fluid close to internal fluid.

• Use a primitive gill - increases diffusion surface area.

• 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

Primitive Gill • Phylum Echinodermata – use a

primitive gill called papulae.

Body Cavity

Epidermis

O2 CO2papula

• 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 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

Axolotl- permanent salamander larvae

External Gills

O2CO2

The External Gills• Some, like the axolotl (aquatic

salamander) physically moves its external gills through the water for improved gas exchange.

• A problem with external gills: Difficult to circulate water past surfaces constantly.

• Problem: external gills are fragile and offer resistance in water.

Brachial Chambers• Brachial chambers – a muscular,

internal pouch used to pump water over the gills.

• Phylum Mollusca – use an internal mantle cavity that pumps water over gills. Ex. Squid and octopi.

Internal Gills• Cartilaginous Fishes (Sharks and

Rays) – force water through mouth over internal gills by constant swimming. Water flows out gill slits.

• Swim with mouth open to force water over gills – ram ventilation.

• Problem: Must stay in motion or suffocate.

Filament

• The feathery gills projecting from a salmon– Are an example of a specialized exchange

system found in animals.

Figure 42.1

The Best Brachial Chamber• Bony Fishes – have opercular cavities. Gills

are between mouth and opercular cavities.• Opercula (Gill Covers) – are flexible and

they pull water through cavity, like a bellows.

• Each gill – two rows of gill filaments and each filament has rows of lamellae parallel to direction of water movement (see Fig. 46.6).

• 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

Gillfilaments

Oxygen-poorblood

Oxygen-richblood

Water flowover lamellaeshowing % O2

Blood flowthrough capillariesin lamellaeshowing % O2

Lamella

100%

40%

70%

15%

90%

60%

30% 5%

O2

The Gill Filament• In each lamella, blood flows in a

direction opposite the direction of water movement – countercurrent flow.

• Maximizes the differences in O2 between the water and blood (see Fig. 46.7).

• Most efficient respiratory organ known – 85% available oxygen is removed.

Countercurrent Flow in Gills

What if you’re not aquatic?

Why do fish die out of water?

They suffocate.

The Problem of Terrestrial Respiration

• Water – 5-10 ml of O2 per liter• Air – 210 ml O2 per liter (rich in O2)• Gills don’t work in air :

– Air is less buoyant than water, fragile lamellae collapse and reduce surface area and not enough gas diffusion.

– Water diffuses into air by evaporation. Gills provide too much surface area for water loss.

Terrestrial Organisms• Use two types of internal passage ways for

gas diffusion; sacrifice efficiency for reduced evaporation.

• Terrestrial Insects use tracheae – air-filled passages connecting the surface of the insect to all potions of its body. Diffusion directly with internal cells and no circulatory system.

• Use openings called spiracles along the abdomen that can be controlled. Effective for small animals.

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• The tracheal system of insects

– Consists of tiny branching tubes that penetrate the body

• The tracheal tubes– Supply O2 directly to body cells.

Airsac

Body cell

Trachea

Tracheole

Tracheoles Mitochondria MyofibrilsBody 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

How large can an insect become?

Video: Nigel Marvin’s Giant Creepy Crawlies

First Terrestrial Organism

• Problem: Tracheal breathing limits the size of the organism. Ventilation is by movement of organism.

Lungs

• Spiders, land snails, and most terrestrial vertebrates:

– Have internal lungs (simple sacs).

Other Terrestrial Organ• Lung – moves air through a moist,

internal, tubular passage and back out same passage.

• Benefit – minimizes evaporation.• Problem: lower efficiency than gill,

but O2 more abundant in air.• Four variations of the terrestrial,

vertebrate lung.

The First Terrestrial Animals?

Class Amphibia• Amphibian Lung – simple sac with a

folded membrane; has trachea with a valve – glottis.

• Can breathe through nose and mouth.

• Perform positive pressure breathing – create a positive pressure outside and forces air into lungs (throat breathing in frogs).

I supplement by lung

breathing with

cutaneous respiration,

too!

Problems with the Amphibian System

• Lung is not very efficient; poor surface area.

• Cutaneous Respiration – requires moist skin. Limited to moist environments and/or secrete mucous covering. Dependent on water.

• Cannot be very active; slower metabolism.

Class Reptilia• Living completely on land, no

connection to water. Made water-tight skin (scales) to prevent evaporation.

• Little or no cutaneous respiration.• Reptile Lung – contains many

small air chambers; increase surface area.

Class Reptilia• Reptiles use negative pressure

breathing – intercostal muscles and diaphragm to expand thoracic cavity and create a negative pressure in lungs.

• Air is pulled into lungs rather than pushed.

• Also called body cavity breathing or chest breathing.

Class Mammalia• Must maintain constant body temperature –

need more efficient lung.

• Use millions of sacs, clustered like grapes – alveoli (alveolus = sing.)

• Each cluster connected to a short, branching passageway – bronchiole.

• Bronchioles connect into left and right bronchi (bronchus = sing.)

• Bronchi are connected to superior trachea.

How a Mammal Breathes• Mammals ventilate their lungs

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

Air inhaled Air exhaled

INHALATIONDiaphragm contracts

(moves down)

EXHALATIONDiaphragm relaxes

(moves up)

Diaphragm

Lung

Rib cage expands asrib muscles contract

Rib cage gets smaller asrib muscles relax

Figure 42.24

BronchiBronchioles

(No Cartilage)

Deoxygenated Blood

Oxygenated Blood

About 1 µm

80 m2 of Surface Area!

Mechanics of Human Breathing• Trachea and Bronchi have hyaline cartilage,

but not bronchioles.• Bronchioles are surrounded by smooth

muscle.• Bronchoconstriction – nervous system or

hormones (histamine) signal smooth muscle to contract and narrow bronchioles (asthma).

• Bronchodilation - nervous system or hormones (epinephrine) signal smooth muscle to relax and open bronchioles.

Mechanics of Human Breathing

• Visceral Pleural Membrane – surrounds outside of lung.

• Parietal Pleural Membrane – lines thoracic cavity.

• Pleural Cavity – is fluid-filled space between; connects lung to wall of cavity.

Mechanics of Human Breathing• One-cycle pump.• Inspiration: intercostal muscles and

diaphragm contract = increase volume of thoracic cavity.

• Pleural membranes are coupled, lungs expand.

• Air pressure in lungs is decreased and air is pulled in – negative pressure breathing.

Mechanics of Human Breathing• One-cycle pump.

• Expiration: Intercostal muscles and diaphragm relax, elastic recoil of thoracic cavity = decrease volume of cavity and lungs.

• Air pressure in lungs is increased, forces air out.

Mechanics of Human Breathing• Tidal Volume = amount of air

moved into and out of lungs at rest (500 ml).

• Functional Residual Capacity = amount of air left in lungs after normal expiration at rest.

• Residual Volume = amount of air left after forceful, maximum expiration.

Mechanics of Human Breathing• Anatomical Dead Space = constant

amount of air trapped in trachea, bronchi, bronchioles (150 ml).

• Vital Capacity = max. amount of air exhaled after a forceful, maximum inhalation (VC = TV + IRV + ERV).

• Total Lung Capacity = TV + IRV + ERV + RV

Class Aves

• Flight requires more ATP.

• Avian lung is a two-cycle pump (Fig. 46-9).

• Uses a system of anterior and posterior air sacs and a lung.

• Gas exchange occurs in lung only.

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

LungsLungsPosterior

air sacs

Air Air

1 mm

Air tubes(parabronchi)in lung

Figure 42.25

1

2

34

5

Two-Cycle Breathing• 1st Inspiration – air travels down

trachea to posterior air sacs.• 1st Expiration – air flows from sacs to

lung.• Lung – gas exchange.• 2nd Inspiration – air flows from lung to

anterior air sacs.• 2nd Exhalation – air flows from sacs out

through trachea.

Benefits to Avian Breathing• Unidirectional flow of air through lung

– no “dead volume” of air left in lung. Always fully oxygenated air.

• Flow of blood is perpendicular to air flow – cross-current flow.

• Very efficient at extracting oxygen from air.

• Most efficient terrestrial respiration.

Gas Transport and Exchange

• If transport were by simple diffusion, then O2 would require three years to travel from lung to toe.

• Use a circulatory system; but plasma could only carry 3 ml O2 per l.

• Use RBC with hemoglobin to carry 200 ml O2 per l.

Erythrocyte

Hemoglobin (Hb)• Accounts for 95% of proteins

inside the RBC.

• 280 million Hbs in each RBC.

• Hb binds to and transports O2 and CO2.

Hb Molecule• Each Hb molecule = four protein chains

= 2 alpha chains + 2 beta chains of polypeptides.

• Each chain is a globular subunit and has a heme group.

• Heme – a porphyrin which is a ring compound with an iron in the center.

• Iron has a + charge and can bind to O2

(negative).

• 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 loadedin lungs

O2 unloadedIn tissues

Polypeptide chain

O2

O2

Figure 42.28

Quaternary Structure of Hemoglobin

Hb Molecule• When hemoglobin binds to O2 – it

becomes oxyhemoglobin (bright red).

• Very weak interaction; easy to separate.

• At the tissues, some oxyhemoglobin releases its O2 becomes- deoxyhemoglobin (dark red).

Deoxygenated Blood

Oxygenated Blood

PO2 = 105 mm Hg

PO2 = 100 mm Hg

Oxygen Transport• Lungs are efficient; 97 % of hemoglobin

in RBC’s is fully saturated.

• At capillaries, extracellular fluid has lower PO2

and O2 diffuses into tissues.

• Venous blood leaving tissues has PO2 = 40

mm Hg.

• Only about 22% of oxyhemoglobin has releases O2 into tissues.

Body Tissues

[O2] is higher

[O2] is 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

veinsO2CO2

O2

CO 2

Alveolar spaces

12

43

Figure 42.27

Why so little O2 released into tissues?

• Blood can supply oxygen needs during exercise.

• Blood has enough oxygen to maintain life 4 or 5 minutes without breathing.

How does Hb “know” when to let go?

• In RBC, CO2 + H2O H2CO3 , lowers pH.• Hb’s affinity for O2 decreases with lower

pH. Releases oxygen into tissue.• Hb’s affinity for O2 inversely related to

temperature. Metabolically active tissues are warmer. Cause release of O2 into tissues.

Figure 42.30

Tissue cell

CO2Interstitialfluid

CO2 producedCO2 transportfrom tissues

CO2

CO2

Blood plasmawithin capillary Capillary

wall

H2O

Redbloodcell

HbCarbonic acid

H2CO3

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

56

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

What about the CO2?

• As Hb releases O2, a binding site on protein absorbs CO2. CO2 does not bind to heme group (20%).

• 8% dissolved in the blood plasma. • 72 % diffuses from plasma RBC

cytoplasm and converted by enzyme into H2CO3 HCO3

- + H+ ions.

O2 unloaded fromhemoglobinduring normalmetabolism

O2 reserve that canbe unloaded fromhemoglobin totissues with highmetabolism

Tissues duringexercise

Tissuesat rest

100

80

60

40

20

0

100

80

60

40

20

0

100806040200

100806040200

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

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

PonsBreathing control centers Medulla

oblongata

Diaphragm

Carotidarteries

Aorta

Cerebrospinalfluid

Rib muscles

In a person at rest, these nerve impulses result in

about 10 to 14 inhalationsper minute. Between

inhalations, the musclesrelax 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 aortaand carotid arteries in the neck detect changes in blood pH andsend nerve impulses to the medulla. In response, the medulla’s breathingcontrol center alters the rate anddepth of breathing, increasing bothto dispose of excess CO2 or decreasingboth if CO2 levels are depressed.

The control center in themedulla sets the basic

rhythm, and a control centerin the pons moderates it,

smoothing out thetransitions between

inhalations and exhalations.

1

Nerve impulses trigger muscle contraction. Nerves

from a breathing control centerin the medulla oblongata of the

brain send impulses to thediaphragm and rib muscles, stimulating them to contract

and causing inhalation.

2

The sensors in the aorta andcarotid arteries also detect changesin O2 levels in the blood and signal the medulla to increase the breathing rate when levels become very low.

6

5

3

4

Controlling Breathing• Respiratory Control Center – Medulla

Oblongata in brain.

• Impulses sent to diaphragm and intercostal muscles contraction and expand thoracic cavity (inhalation).

• No impulse, muscles relax and cavity becomes smaller (exhalation).

• Part of ANS but can be voluntary.

Controlling Breathing• If breathing stops, the PCO2 of plasma

rises.• Causes pH to drop (increase in [H+]).• Peripheral chemoreceptors in walls of

aorta and coratid arteries detect increase in [H+].

• Send signals to respiratory control center.• Initiates breathing.

What does exercise do?

• Working tissue causes ↑ PCO2 in

plasma and ↓in pH.

• As [H+] ↑, chemoreceptors cause an ↑ in respiratory rate.

• Can you indefinitely hyperventilate?

• Why can people hold their breath longer if they hyperventilate first?

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