Open and Closed Circulatory Systems

More complex animals have either open or closed circulatory systems

Both systems have three basic components: A circulatory fluid (blood or hemolymph) A set of tubes (blood vessels) A muscular pump (the heart)

Hemolymph in sinusessurrounding organs

Heart

Anteriorvessel

Ostia

Tubular heart

An open circulatory system.

Lateralvessel

A closed circulatory system.

Auxiliary hearts Ventral vessels

Dorsal vessel(main heart)

Small branch vesselsin each organ

Interstitialfluid

Heart

FISHES

Gill capillaries

AMPHIBIANS

Lung and skin capillaries

REPTILES (EXCEPT BIRDS)

Lung capillaries

MAMMALS AND BIRDS

Lung capillaries

Gillcirculation

Heart:Ventricle (V)

Atrium (A)

Artery

VeinSystemic

circulation

Systemic capillaries Systemic capillaries

Systemiccircuit

Pulmocutaneouscircuit

Right Left

AA

V

A

V

A

V

Systemic capillaries

Right Left

PulmonarycircuitRight

systemic aorta

V

A

V

Systemic capillaries

Right Left

Pulmonarycircuit

A

Systemiccircuit

Leftsystemic aorta

Systemic circuits include all body tissues except lungs. Note that circulatory systems are depicted as if the animal is facing you: with the right side of the heart shown at the left and vice-versa.

Anteriorvena cava

Pulmonaryartery

Capillariesof right lung

Aorta

Pulmonaryvein

Right atrium

Right ventricle

Posteriorvena cava

Capillaries ofabdominal organsand hind limbs

Pulmonaryvein

Left ventricle

Left atrium

Aorta

Pulmonaryartery

Capillaries ofhead andforelimbs

Capillariesof left lung

Semilunarvalvesclosed

AV valvesopen

0.1 sec

0.3 sec

0.4 sec

Atrial andventriculardiastole

AV valvesclosed

Ventricular systole;atrial diastole

Semilunarvalvesopen

Atrial systole;ventriculardiastole

Pacemakergenerates wave ofsignals to contract.

Signals are delayedat AV node.

Signals passto heart apex.

Signals spreadthroughoutventricles.

SA node(pacemaker)

ECG

AV node

Bundlebranches Heart

apex

Purkinjefibers

Artery Arteryclosed

Pressurein cuffabove 120120Rubber cuff

inflatedwith air

Pressurein cuffbelow 120120

Soundsaudible instethoscope

Pressurein cuffbelow 70

70

Blood pressurereading: 120/70

Soundsstop

Physical principles govern blood circulation

The physical principles that govern movement of water in plumbing systems apply to circulatory systems

Second law of Thermodynamics Law of continuity

V1A1 = V2A2

Systolicpressure

Vena

e ca

vae

Vein

s

Venu

les

Capi

llari

es

Arte

riol

es

Arte

ries

Aort

a

Diastolicpressure

Pres

sure

(mm

Hg) 120

10080604020

0

Area

(cm

2 )

5,0004,0003,0002,0001,000

0

Velo

city

(cm

/sec

) 5040302010

0

Precapillary sphincters Thoroughfarechannel

CapillariesVenuleArteriole

Sphincters relaxed

VenuleArteriole

Sphincters contracted

Capillaries and larger vessels (SEM) 20 µm

Valve (open)

Skeletal muscle

Valve (closed)

Direction of blood flowin vein (toward heart)

SodiumPotassiumCalciumMagnesiumChlorideBicarbonate

Osmotic balance,pH buffering, andregulation ofmembranepermeability

Plasma 55%

Constituent Major functions

Water Solvent forcarrying othersubstances

Ions (blood electrolytes)

Albumin Osmotic balance,pH buffering

Plasma proteins

Fibrinogen

Immunoglobulins(antibodies)

Clotting

Defense

Nutrients (such as glucose, fatty acids, vitamins)Waste products of metabolismRespiratory gases (O2 and CO2)Hormones

Substances transported by blood

Cellular elements 45%

Cell type Number Functionsper µL (mm3) of blood

5–6 million Transport oxygenand help transportcarbon dioxide

Leukocytes(white blood cells)

5,000–10,000 Defense andimmunity

Monocyte

Basophil

Eosinophil

Lymphocyte

Neutrophil

PlateletsBlood clotting250,000–

400,000

Erythrocytes(red blood cells)

Separatedbloodelements

Capillary Red bloodcell

15 µm

Tissue cell

CapillaryNet fluidmovement out

INTERSTITIAL FLUID

Net fluidmovement in

Blood pressureOsmotic pressure

Inward flow

Direction ofblood flow

Pres

sure

Outward flow

Venous endArterial end of capillary

Respiratorymedium(air or water)

Organismallevel

Cellular level

Energy-richfuel molecules

from food

Respiratorysurface

Circulatory system

Cellular respiration

CO2O2

ATP

Branchfrompulmonaryvein(oxygen-richblood)

Terminalbronchiole

Branchfrompulmonaryartery(oxygen-poorblood)

Alveoli

50 µ

m

Colorized SEMSEM

Nasalcavity

50 µ

m

Leftlung

Heart

Larynx

Pharynx

EsophagusTrachea

Rightlung

Bronchus

Bronchiole

Diaphragm

Breathingcontrolcenters

Cerebrospinalfluid

Medullaoblongata

Pons

Carotidarteries

Aorta

Diaphragm

Rib muscles

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 partial pressure

Inhaled air

Bloodenteringalveolar

capillaries

Alveolarepithelialcells

Alveolar spaces

Alveolarcapillaries

of lung

Exhaled air

Bloodleavingalveolar

capillaries

Pulmonaryveins

Pulmonaryarteries

Tissuecapillaries

HeartSystemicveins

Systemicarteries

Bloodleavingtissue

capillaries

Bloodentering

tissuecapillaries

Tissuecells

CO2O2

CO2 O2

O2 CO2

CO2O2

< 40 > 45

40 45

CO2O2

100 40

CO2

O 2

CO2O2

40 45

CO2O2

104 40

O2

CO 2

CO2O2

CO2O2

CO2 O2

104 40

120 27160 0.2

Polypeptide chain

O2 unloadedin tissues

O2 loadedin lungs

Iron atomHeme group

O2 unloaded fromhemoglobinduring normalmetabolism

O2 reserve that canbe unloaded fromhemoglobin totissues with highmetabolism

P and hemoglobin dissociation at 37°C and pH 7.4O2

P (mm Hg)O2

Tissues duringexercise

Tissues at rest

Lungs

1008060402000

20

40

60

80

100

O2 s

atur

ation

of h

emog

lobi

n (%

)

Bohr shift:additional O2 released fromhemoglobin atlower pH(higher CO2concentration)

pH and hemoglobin dissociation

P (mm Hg)O2

1008060402000

20

40

60

80

100

O2 s

atur

ation

of h

emog

lobi

n (%

)

pH 7.2

pH 7.4

CO2 transportfrom tissuesCO2 produced

Tissue cell

CO2

CO2

CO2

Interstitialfluid

Blood plasmawithin capillary

Capillarywall

Hemoglobinpicks up

CO2 and H+

To lungs

H2CO3

Carbonic acid

H2O

Hb

HCO3–

Bicarbonate

Redblood

cell

H++

HCO3–

CO2 transportto lungsHCO3

–

Hemoglobinreleases

CO2 and H+

H++HCO3–

CO2

H2CO3

H2O

CO2

CO2

CO2

Hb

Alveolar space in lung