Circulation and Gas Exchange Chapter 42 (all)

4-17-06

• Overview: Trading with the Environment

• Every organism must exchange materials with its environment (whether it be nutrients or gases (oxygen and carbon dioxide)– And this exchange ultimately occurs at the

cellular level

• In unicellular organisms– These exchanges occur directly with the environment

across the cell membrane. Diffusion is adequate for necessary rapid exchange.

• For most of the cells making up multicellular organisms direct exchange with the environment is not possible because diffusion distances are too great! Therefore specialized exchange and transport systems have evolved!

Gills as exchange sites in aquatic animals!

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

found in animals

Figure 42.1

Gill arch with filaments which have lamellae on both sides!Surface area of gill equal body skin surface area!

• Transport systems– Functionally connect the organs of exchange

with the body cells where nutrients and oxygen required!

• Most complex animals have internal transport systems providing a conduit between the evironment and the cell cytoplasm!

Invertebrate Circulation

• The wide range of invertebrate body size and form is paralleled by a great diversity in circulatory systems. Water vascular system in star fish, open circulatory systems in insects and closed circulatory systems in earth worms and squids.

Gastrovascular Cavities

• Simple animals, such as cnidarians– Have a body wall only two cells thick that

encloses a gastrovascular cavity (recall sea anemone sac with a mouth!)

• The gastrovascular cavity– Functions in both digestion and distribution of

substances throughout the body. Also gas exchange for cells lining the cavity.

• Some cnidarians, such as jellies– Have elaborate gastrovascular cavities with

canals radiating off the central sac!

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 systems• In insects, other arthropods, and most molluscs

– Blood bathes the organs and tissues 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

Valves in heart so blood flow is unidirectional

No interstitial space or fluid!

Closed Circulatory System • In a closed circulatory system

– Blood is confined to vessels and is distinct from the interstitial fluid

Figure 42.3b

Interstitialfluid

Heart

Small branch vessels in each organ

Dorsal vessel(main heart)

Ventral vesselsAuxiliary hearts

(b) A closed circulatory system

Closed systemsare more efficient at transporting circulatory fluids to tissues and cells.

Earthworm an annelid is the first time we see a closed circulatory system!

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.

• Arteries carry blood from heart to capillaries– The capillaries are the sites of chemical exchange

between the blood and interstitial fluid

• Veins collect blood from capillaries and return blood to the heart.– Types of hearts!

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

Fishes- two chambered heart!

• A fish heart has two main chambers– One ventricle and one atrium and blood

pumped from the ventricle through the gills

where it is loaded with oxygen and unloadsf CO2. It then travels through the dorsal aorta to the organs and tissues thru capillary beds and is returned to the heart as venous blood. Where does heart get its oxygen? Enough remains in the venous blood. In some active species (Tuna fishes) a branch off the ventral aorta supplies oxygenated blood to the heart.

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 (lung and skin) and the systemic circuit. Thus a certain amount of mixing of oxygenated and oxygen poor blood occures.

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

• A powerful four-chambered heart– Was an essential adaptation of the

endothermic way of life characteristic of mammals and birds. Reason is because of metabolism being almost 10 times greater than the ectotherms!

• A powerful four-chambered heart was an essential adaptation of the endothermic way of life characteristic of mammals and birds. Reason is because of metabolism being almost 10 times greater than the ectotherms!

• Double circulation in mammals depends on the anatomy and pumping cycle of the heart (Good model).

• Heart valves dictate a one-way flow of blood through the heart.

• Blood begins its flow– With the right ventricle pumping blood to the lungs

• In the lungs– The blood loads O2 and unloads CO2

• Oxygen-rich blood from the lungs– Enters the heart at the left atrium and is

pumped to the body tissues by the left ventricle

• Blood returns to the heart– Through the right atrium

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

See text for description of

sequential events

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

In fetus ductus artieriosus shunts blood from pulmonary artery into the aorta. Closes off at birth when the lungs inflate!

• 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

• The cardiac cycle: filling of chambers longest!

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

• 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 and depends on the rate of contraction and the stroke volume (how much blood is “loaded” into the ventricle during diastole).

Maintaining the Heart’s Rhythmic Beat

• Some cardiac muscle cells are self-excitable (myogenic)– Meaning they contract without any signal from the

nervous system (heart transplant).• 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 spread across the atria to the atrioventricular (AV) node

• At the AV node, the impulses are delayed and then travel down bundle fiber to the 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 control of heart rhythm • The impulses that travel during the cardiac cycle can be

recorded as an electrocardiogram (EKG)

Figure 42.8

SA node(pacemaker)

AV node Bundlebranches

Heartapex

Purkinjefibers

2 Signals are delayedat AV node.

1 Pacemaker generates wave of signals in the atriato contract.

3 Signals passto heart apex.

4 Signals spreadthroughoutventricles.

ECG

• The pacemaker is influenced by– Nerves, hormones, body temperature, and

exercise

Blood Circulation

• The same physical principles that govern the movement of water in plumbing systems– Also influence the functioning of animal

circulatory systems.– Structure of circulatory system is a network of

vessels that are differ in structure to accommodate function.

• The velocity of blood flow varies in the circulatory system– And is slowest in the capillary beds as a result of the

high resistance and large total cross-sectional area

Figure 42.11

5,0004,0003,0002,0001,000

0

Aor

ta

Art

erie

s

Art

erio

les

Cap

illar

ies

Ven

ules

Vei

ns

Ven

ae c

avae

Pre

ssur

e (m

m H

g)V

eloc

ity (

cm/s

ec)

Are

a (c

m2)

Systolicpressure

Diastolicpressure

50403020100

120100806040200

• All blood vessels– Are built of similar tissues– Have three similar layers

Figure 42.9

Artery Vein

100 µm

Artery Vein

ArterioleVenule

Connectivetissue

Smoothmuscle

Endothelium

Connectivetissue

Smoothmuscle

EndotheliumValve

Endothelium

Basementmembrane

Capillary

Arteries have thicker walls to accommodate the high pressure of blood pumped from the heart. Veins thinner walls.

Basement membrane composed of mucopolysaccharides and collagen fibers. Not a barrier to diffusion of molecules.

• In the thinner-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)

Blood Flow Velocity

• Physical laws governing the movement of fluids through pipes– Influence blood flow and blood pressure

• Blood pressure– Is 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– Can be easily measured in humans

Figure 42.12

Artery

Rubber cuffinflatedwith air

Arteryclosed

120 120

Pressurein cuff above 120

Pressurein cuff below 120

Pressurein cuff below 70

Sounds audible instethoscope

Sounds stop

Blood pressurereading: 120/70

A typical blood pressure reading for a 20-year-oldis 120/70. The units for these numbers are mm of mercury (Hg); a blood pressure of 120 is a force that can support a column of mercury 120 mm high.

1

A sphygmomanometer, an inflatable cuff attached to apressure gauge, measures blood pressure in an artery.The cuff is wrapped around the upper arm and inflated until the pressure closes the artery, so that no blood flows past the cuff. When this occurs, the pressure exerted by the cuff exceeds the pressure in the artery.

2 A stethoscope is used to listen for sounds of blood flow below the cuff. If the artery is closed, there is no pulse below the cuff. The cuff is gradually deflated until blood begins to flow into the forearm, and sounds from blood pulsing into the artery below the cuff can be heard with the stethoscope. This occurs when the blood pressure is greater than the pressure exerted by the cuff. The pressure at this point is the systolic pressure.

3

The cuff is loosened further until the blood flows freely through the artery and the sounds below the cuff disappear. The pressure at this point is the diastolic pressure remaining in the artery when the heart is relaxed.

4

70

• Blood pressure is determined partly by cardiac output– And partly by peripheral resistance due to variable

constriction of the arterioles (anaphylactic shock). – For high blood pressure try and reduce peripheral

resistance using smooth muscle relaxants!

Capillary Function

• Capillaries in major organs are usually filled to capacity– But in many other sites, the blood supply

varies. Homeostatic mechanisms involved to keep blood pressure constant!

Control of Blood Flow Through Capillaries

• Two mechanisms– Regulate the distribution of blood in capillary

beds

• In one mechanism– Contraction of the smooth muscle layer in the

wall of an arteriole constricts the vessel

• In a second mechanism– Precapillary sphincters control the flow of

blood between arterioles and venules

Figure 42.13 a–c

Precapillary sphincters Thoroughfarechannel

ArterioleCapillaries

Venule(a) Sphincters relaxed

(b) Sphincters contractedVenuleArteriole

(c) Capillaries and larger vessels (SEM)

20 m

• The critical exchange of substances between the blood and interstitial fluid– Takes place across the thin endothelial walls

of the capillaries

• The difference between blood pressure and osmotic pressure– Drives fluids out of capillaries at the arteriole

end and into capillaries at the venule end

At the arterial end of acapillary, blood pressure is

greater than osmotic pressure,and fluid flows out of the

capillary into the interstitial fluid.

Capillary Redbloodcell

15 m

Tissue cell INTERSTITIAL FLUID

CapillaryNet fluidmovement out

Net fluidmovement in

Direction of blood flow

Blood pressureOsmotic pressure

Inward flow

Outward flow

Pre

ssur

e

Arterial end of capillary Venule end

At the venule end of a capillary, blood pressure is less than osmotic pressure, and fluid flows from the interstitial fluid into the capillary.

Figure 42.14

Osmotic pressure in capillary due to plasma proteins!

Fluid Return by the Lymphatic System

• The lymphatic system– Returns fluid to the body from the capillary beds– Aids in body defense because it passes through

lymph nodes where white blood cells take out any pathogens or foreign material!

• Fluid reenters the circulation– Directly at the venous end of the capillary bed and

indirectly through the lymphatic system

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

Blood• The cellular elements of mammalian blood

Separatedbloodelements

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

• The composition of mammalian plasma

Plasma 55%

Constituent Major functions

Water Solvent forcarrying othersubstances

SodiumPotassiumCalciumMagnesiumChlorideBicarbonate

Osmotic balancepH buffering, andregulation of membranepermeability

Albumin

Fibringen

Immunoglobulins(antibodies)

Plasma proteins

(blood electrolytes)

Osmotic balance,pH buffering

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

Defense

Figure 42.15

Separatedbloodelements

Clotting

Erythrocytes

• Red blood cells, or erythrocytes– Are by far the most numerous blood cells– Transport oxygen throughout the body– Platelets function in blood clotting

Blood Clotting• A cascade of complex reactions

– Converts fibrinogen to fibrin, forming a clot

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 clotRed 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.

2 This 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

A baby aspirin per day makes the platelets lazy!

Hemophiliacs