Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exchange of materials with the environment Overview: Trading with the Environment.

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

Exchange of materials with the environment

• 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 the exchange of materials occurs directly with the environment

• However, for most of the cells making up multicellular organisms direct exchange with the environment is not possible as they are not in direct contact with the environment.

• Multicellular animals thus need structures specialized for exchange with the outside and a means of transporting materials from these structures to all of the body’s cells.


Salmon gills

• The feathery gills projecting from a salmon are an example of a specialized exchange system found in animals.

Figure 42.1


Internal transport systems

• 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 substances with the outside environment.


Invertebrate Circulation

• The wide range of invertebrate body size and form is paralleled by a great diversity in circulatory systems.

• Simple animals, such as cnidarians (corals and jellyfish) 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.


Cnidarian gastrovascular cavity

• Some cnidarians, such as jellyfish have elaborate gastrovascular cavities that funnel substances throughout the body.

Figure 42.2

Circularcanal

Radial canal

5 cmMouth


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)


Open circulatory system

• In insects, other arthropods, and most molluscs blood bathes the organs directly in an open circulatory system.

Heart

Hemolymph in sinusessurrounding ograns

Anterior vessel

Tubular heart

Lateral vessels

Ostia

(a) An open circulatory systemFigure 42.3a


Closed circulatory system

• In a closed circulatory system blood is confined to vessels and is distinct from the interstitial fluid (the fluid that surrounds the cells).

Figure 42.3b

Interstitialfluid

Heart

Small branch vessels in each organ

Dorsal vessel(main heart)

Ventral vesselsAuxiliary hearts

(b) A closed circulatory system


Survey of Vertebrate Circulation

• Closed systems are more efficient at transporting circulatory fluids to tissues and cells because pressure can be maintained more easily.

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

• Blood flows in a closed cardiovascular system consisting of blood vessels and a two- to four-chambered heart.


• Arteries carry blood to capillaries the sites of chemical exchange between the blood and interstitial fluid.

• Capillaries are extremely thin-walled blood vessels.

• Veins return blood from capillaries to the heart.


Fishes

• A fish heart has two main chambers

– One ventricle (the chamber from which blood flows out of the heart) and one atrium (the chamber in the heart blood enters into)

• 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 (lung and skin) circuit and the systemic (rest of the body) circuit.

• Because there is only one ventricle a mix of oxygenated and deoxygenated blood is pumped to the tissues.


FISHES AMPHIBIANS REPTILES (EXCEPT BIRDS) MAMMALS AND BIRDS

Systemic capillaries Systemic capillaries Systemic capillaries Systemic capillaries

Lung capillaries Lung capillariesLung and skin capillariesGill capillaries

Right Left Right Left Right Left Systemic

circuitSystemic

circuit

Pulmocutaneouscircuit

Pulmonarycircuit

Pulmonarycircuit

SystemiccirculationVein

Atrium (A)

Heart:ventricle (V)

Artery Gillcirculation

A

V VV VV

A A A AALeft Systemicaorta

Right systemicaorta

Figure 42.4

• Vertebrate circulatory systems


Reptiles (Except Birds)

• Reptiles have double circulation with a pulmonary circuit (lungs) and a systemic circuit, but there is still only a single ventricle although it is partially divided reducing mixing of oxygenated and deoxygenated blood.

• 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


Four-chambered heart

• A powerful four-chambered heart was an essential adaptation of the endothermic way of life characteristic of mammals and birds.

• Keeping oxygen rich and oxygen depleted blood separated enables oxygen to be delivered to the tissues more efficiently.


FISHES AMPHIBIANS REPTILES (EXCEPT BIRDS) MAMMALS AND BIRDS

Systemic capillaries Systemic capillaries Systemic capillaries Systemic capillaries

Lung capillaries Lung capillariesLung and skin capillariesGill capillaries

Right Left Right Left Right Left Systemic

circuitSystemic

circuit

Pulmocutaneouscircuit

Pulmonarycircuit

Pulmonarycircuit

SystemiccirculationVein

Atrium (A)

Heart:ventricle (V)

Artery Gillcirculation

A

V VV VV

A A A AALeft Systemicaorta

Right systemicaorta

Figure 42.4

• Vertebrate circulatory systems


Mammalian Circulation: The Pathway

• Heart valves dictate a one-way flow of blood through the heart by preventing blood flowing backwards.

• Blood begins its flow with the right ventricle pumping blood to the lungs via the pulmonary artery.

• In the lungs the blood loads O2 and unloads CO2


Mammalian Circulation: The Pathway

• Oxygen-rich blood from the lungs travels through through the pulmonary vein and enters the heart at the left atrium. It then is pumped by the left ventricle via the aorta to the body tissues.

• Blood returns to the heart from the body via the anterior and posterior venae cavae (singular vena cava) through the right atrium.


• The mammalian cardiovascular system

Pulmonary vein

Right atrium

Right ventricle

Posteriorvena cava Capillaries of

abdominal organsand hind limbs

Aorta

Left ventricle

Left atriumPulmonary vein

Pulmonaryartery

Capillariesof left lung

Capillaries ofhead and forelimbs

Anteriorvena cava

Pulmonaryartery

Capillariesof right lung

Aorta

Figure 42.5

1

10

11

5

4

6

2

9

33

7

8


The Mammalian Heart: A Closer Look

• A closer look at the mammalian heart

– Provides a better understanding of how double circulation works

Figure 42.6

Aorta

Pulmonaryveins

Semilunarvalve

Atrioventricularvalve

Left ventricleRight ventricle

Anterior vena cava

Pulmonary artery

Semilunarvalve

Atrioventricularvalve

Posterior vena cava

Pulmonaryveins

Right atrium

Pulmonaryartery

Leftatrium


Cardiac Cycle

• 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


Cardiac Cycle

• Two sets of valves in the heart are important in controlling blood flow within the heart.

• The semilunar valves control the flow of blood from the ventricles into the aorta and the pulmonary arteries.

• The atrioventricular (or AV) valves control the flow of blood from the atria to the ventricles.


• During the cardiac cycle first both atria and ventricles relax and blood flows into the atria and from the atria into the ventricles. The AV valves are open and semilunar valves are closed.

• Then the atria contract and the ventricles remain relaxed so the blood from the atria flows into the ventricles.

• Finally, the semilunar valves open and the AV valves close. The atria relax and the ventricles contract forcing blood out of the ventricles into the arteries.


• The cardiac 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


Maintaining the Heart’s Rhythmic Beat

• Some cardiac muscle cells are self-excitable meaning they contract without any signal from the nervous system.

• A region of the heart called the sinoatrial (SA) node, or pacemaker sets the rate and timing at which all cardiac muscle cells contract

• Impulses from the SA node travel to the atrioventricular (AV) node

• At the AV node, the impulses are delayed and then travel to the Purkinje fibers that make the ventricles contract


• The impulses that travel during the cardiac cycle can be recorded as an electrocardiogram (ECG or EKG).

• The pacemaker is influenced by nerves, hormones, body temperature, and exercise


• The control of heart rhythm

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


Blood Vessel Structure and Function

• The “infrastructure” of the circulatory system is its network of blood vessels: arteries, capillaries and veins.

• Structural differences in arteries, veins, and capillaries are related to their different functions.


• Arteries have thick muscular walls because they must withstand the high pressure of blood pumped from the heart.

• Veins have thinner walls that can be squeezed by surrounding muscles and also valves that prevent blood flowing backwards.

• Capillaries have extremely thin walls to facilitate the transfer of materials across them.


• In the thinly walled veins blood flows back to the heart mainly as a result of muscle action

Figure 42.10

Direction of blood flowin vein (toward heart)

Valve (open)

Skeletal muscle

Valve (closed)


• The velocity of blood flow varies in the circulatory system. It is slowest in the capillary beds as a result of the high resistance and large total cross-sectional area

• The critical exchange of substances is between the blood and interstitial fluid. It takes place across the thin endothelial walls of the capillaries.


Blood Composition and Function

• Blood is a connective tissue with 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 and

• Plasma proteins which influence blood pH, osmotic pressure, and viscosity.

• Various types of plasma proteins also function in lipid transport, immunity, and blood clotting.


Cellular Elements

• Suspended in blood plasma are two classes of cells

– Red blood cells, which transport oxygen

– White blood cells, which function in defense

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


Figure 42.15

Cellular elements 45%

Cell type Numberper L (mm3) of blood

Functions

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

and help transportcarbon dioxide

Leukocytes(white blood cells)

5,000–10,000 Defense andimmunity

Eosinophil

Basophil

Platelets

NeutrophilMonocyte

Lymphocyte

250,000400,000

Blood clotting

• The cellular elements of mammalian blood

Separatedbloodelements


Cellular elements of blood

• Red blood cells, or erythrocytes are by far the most numerous blood cells and transport oxygen throughout the body.

• White blood cells, or leukocytes function in defense by phagocytizing bacteria and debris or by producing antibodies

• Platelets function in blood clotting


Stem Cells and the Replacement of Cellular Elements

• The cellular elements of blood wear out and are replaced constantly throughout a person’s life.

• The spleen is the organ that scrutinizes blood cells and destroys those that have become old and inflexible (and less able to squeeze through capillaries).


• 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.

• Platelets adhere to collagen fibers in the connective tissue and release a substance that makes nearby platelets sticky.

• Platelets form a plug in the opening. In addition, a cascade of complex reactions converts fibrinogen to fibrin. Threads of fibrin form a mesh patch that seals the opening


Respiratory structures

• Animals require large, moist respiratory surfaces for the adequate diffusion of respiratory gases between their cells and the respiratory medium, either air or water.

• Gas exchange can occur across the skin, but specialized structures (lungs and gills) and common.


Gills in Aquatic Animals

• Gills are outfoldings of the body surface specialized for gas exchange.

• 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


• 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


Lungs

• Spiders, land snails, and most terrestrial vertebrates including mammals have internal lungs.


Mammalian Respiratory Systems: A Closer Look

• A system of branching ducts conveys air to the lungs

Branch from the pulmonary vein (oxygen-rich blood) Terminal bronchiole

Branch from thepulmonaryartery(oxygen-poor blood)

Alveoli

Colorized SEMSEM

50 µ

m

50 µ

m

Heart

Left lung

Nasalcavity

Pharynx

Larynx

Diaphragm

Bronchiole

Bronchus

Right lung

Trachea

Esophagus

Figure 42.23


• In mammals, air inhaled through the nostrils passes through the pharynx into the trachea, bronchi, bronchioles, and dead-end alveoli, where gas exchange occurs


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.

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


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


• In birds air passes through the lungs in one direction only

• Every exhalation completely renews the air in the lungs. Air flows in only one direction and a countercurrent blood flow system maximizes oxygen extraction.

• As a result, bird lungs are more efficient than mammalian lungs.


Control of breathing in humans

• The main breathing control centers are located in two regions of the brain, the medulla oblongata and the pons.

• 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.


Control of Breathing in Humans

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


Control of breathing in humans

• Sensors in the aorta and carotid arteries monitor O2 and CO2 concentrations in the blood and exert secondary control over breathing.


O2 and CO2 transport

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

• 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


Respiratory Pigments

• Respiratory pigments are proteins that transport oxygen and they greatly increase the amount of oxygen that blood can carry.

• The respiratory pigment of almost all vertebrates is the protein hemoglobin, contained in the erythrocytes.


Hemoglobin structure

• 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


• Loading and unloading of O2 depend on cooperation between the subunits of the hemoglobin molecule

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


• Cooperative O2 binding and release is evident in the dissociation curve for hemoglobin

• A drop in pH occurs when CO2 reacts with water in red blood cells and forms carbonic acid. The reduced pH lowers the affinity of hemoglobin for O2


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

satu

ratio

n o

f h

em

og

lob

in (

%)

O2

satu

ratio

n o

f h

em

og

lob

in (

%)

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


Carbon Dioxide Transport

• Hemoglobin also helps transport CO2 and assists in buffering.

• Most CO2 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 Exchange of materials with the environment Overview: Trading with the Environment.

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