Fig. 9.1

Circulatory systems

Open circulatory systemhemolymphlarge volumelow pressuremost invertebrates

Closed circulatory systembloodsmall volumehigh pressurevertebratessome invertebrates

Gastrovascular cavity thin body walls flagella stir fluid

Circulatory systems cardiovascular components (pump + tubes)

valves, muscles

Fig. 9.2

a) External pump

•blood pushed by compression of

surrounding muscles

•direction of flow determined by valves

e.g. human leg veins, arthropod limbs

b) Peristaltic contractions•blood vessels or peristaltic heartscontract•waves of contractions push blood

c) Contractile chamberclosed chambers, valves(e.g. vertberate heart)

Types of circulatory systems

1.OPEN CIRCULATORY SYSTEM(most invertebrates) Low pressure (< 1.5 kPa)

High volume (30% body vol.)Slow velocity

Fig. « 9.7 »

Electrical conduction in the mammalian heartdepolarization (contraction) repolarization (relaxation)

Fig. 9.23

Normal pacemaker is the SINOATRIAL NODE Heart beat: begins at SA node

spreads through atriadelayed at AV nodespreads through ventricles

Fig. 9.10

2. CLOSED CIRCULATORY SYSTEM (cephalopods, vertebrates)

High pressure (>12 kPa)

Low volume (5-10%)

High velocity

Distribution regulationUltrafiltrationLymphatic system

Circulation in fish (water breathing)respiratory and systemic circulations in series

sinus venosus – precursor of SA node in mammals

Circulation in birds and mammalsrespiratory and systemic circulations in parallel

Four chambered heart

Two completely separate circuitspulmonary circuit(low pressure)

systemic circuit(high pressure)

Anatomy of the mammalian heart

adult heartfour chamberscomplete separation of left and right heart

fetal heartforamen ovaleductus arteriosuspulmonary circuit not

functional

CARDIAC VALVES •thin flaps of fibrous tissue

•move passively in response to

differential pressures

•prevent flow of blood

Atrioventricular valves

RA → RV

LA → LV

Semilunar valves

RV PA Pulmonary SL valve

LV DA Aortic SL valve (larger & stronger)

Heart MurmursValve deformities abnormal blood flow murmurs

CORONARY CIRCULATION•heart receives 4-5% of blood pumped•coronary arteries arise at base of aorta•blood enters only during ventricular relaxation due to force of elastic recoil of aorta•blockage of coronary arteries causes heart failure •coronary bypass

Electrical conduction in the mammalian heartdepolarization (contraction) repolarization (relaxation)

Fig. 9.23

Normal pacemaker is the SINOATRIAL NODE Heart beat: begins at SA node

spreads through atriadelayed at AV nodespreads through ventricles

Fig. 4.2 The structure of gap junctions

GAP JUNCTIONScells coupled metabolically and electrically via hydrophilic channels

Passage of:-     inorganic ions-     small water-soluble molecules:

amino acidssugarsnucleotides

-     electrical signals

P wave depolarization of atrium

QRS depolarization of ventricle

T wave repolarization of ventricle(repolarization of atrium masked by QRS)

Fig. 9.25 Electrocardiogram (ECG) tracings

CARDIAC CYCLEcardiac contraction (systole, 0.3 sec in human)cardiac relaxation (diastole, 0.5 sec in human)

Fig. 9.19

Pressure changes in the heart and arteries of mammals•greater pressure in left heart (supplies systemic circuit)•lower pressure in right heart (supplies pulmonary circuit)

right side of heart left side of heart

Fig. 9.26

N.B. same volume changes at different pressures

STROKE VOLUME (SV)= (end diastolic vol. - end systolic vol.) in healthy humans at rest

stroke volume ~ (140 - 60) ml = 80 ml

both ventricles eject same volume of blood (total blood volume in humans 5-6 L)

SV regulated by: end diastolic volume SV EDV

mean arterial pressure SV 1/MAP

contractility SV C

End-diastolic volume determined by:

venous filling pressurevenoconstriction, skeletal muscle pumpatrial pressureventricular distensibility

filling time

Blood Pressures in human circulation

usually reported as mm Hg ( = torr)

normal range 120-130/80-85 mm Hg (systolic/diastolic pressure)

CARDIAC OUTPUT (CO)= stroke volume x heart rate

in healthy humans at rest, heart rate ~70 beats/min

cardiac output = 80 ml x 70 = 5.6 L/min

Frank-Starling Law of the Heart

Contractility EDV

Increase in EDV causes:

• in myocardial stretch

• in contractile tension

• in ventricular systolic pressure

ventricular filling during diastole,

ejection during systole

heart receives & ejects given volume of blood each cardiac cycle. Fig. 9.28

CIRCULATION How do velocity and pressure change as blood flows from heart through various blood vessels:

Geometry of Blood Vessels (dog)Type D(mm) Number Total area (cm2) Total volume (mL)Aorta 10 1 0.8 30Arteries 3 40 3 60Arterioles 0.02 40000000 125 25Capillaries 0.008 1200000000600 60Venules 0.03 80000000 570 110Veins 6 40 11 220Vena Cava 12.5 1 1.2 50

Laminar and turbulent flowin vessels

Poiseuille's equationrelationship between pressure and flow in small terminal arteries, capillaries, and veins

Q (flow rate) = (P1- P2) r4

8 L η

(P1- P2) pressure differencer radius of vesselL length of vesselη viscosity of fluid

flow pressure difference

r4

flow 1/ distance

1/ viscosity

resistance = (P1 - P2) = 8Lη

Q r4

Flow & resistance most influenced by vessel diameter

Fig. 9.29

COMPLIANCEincreased P stretch increased volumeincreased r decreased resistance increased flow

Compliance = volume/pressure

Venous system:very compliant volume reservoirlarge volume changes result in small pressure changes

Arterial system:less compliant pressure reservoirmaintain capillary flow

Compliance of veins 24x greater than arteries:

(except elastic aortae which dampen pressure oscillations)

Fig.9.31

tunica intima:endothelium

tunica media:smooth muscleelastin

tunica externa:collagen

Blood flow in vertebrate circulatory systems

•high and variable pressure in ventricle

•low pressure, steady flow in capillaries, venules, veins

•velocity increase in venoussystem

FUNCTIONS OF ARTERIAL SYSTEM1. Deliver blood to capillaries2. Pressure reservoir3. Dampen oscillations in pressure and flow4. Selectively control blood distribution

Arterial volume & pressure depend on:-cardiac output (filling)-capillary flow (emptying)-capillary flow depends on ∆ P (Parterial - Pvenous)

Aorta is a pressure reservoirArterial blood pressure

systolic (max)diastolic (min)

Fig. 9.34

Functions of Venous System1. return blood to heart (skeletal muscle pump)2. blood storage reservoir (large volume, low pressure)3. maintain arterial pressure and capillary flowVenous compliance related to large volume

ARTERIOLES

•control blood distribution to tissues

•surrounded by smooth muscle

•vasoconstriction, vasodilation

nutritional flowwaste disposal

regulation of cell activities

Q (flow rate) = (P1- P2) r4

8 L

Capillaries· thin-walled (<0.5 mm)· small diameter (7 mm)· extensively branched; no cell > 0.1 mm from capillary· large surface area· low blood velocity

minimum diffusion differencemaximum surface area and time for

exchange

except for capillaries in brain, no carrier-mediated transport

exchange by diffusion

through endothelial cell membrane or through capillary pores

Fig. 9.32

Capillary structure

discontinuous capillarybone marrow, liver, spleen,

kidney, intestine

muscle, lung, adipose tissue

Regulation of circulation

Priorities: maintain continuous perfusion of brain & heart

then supply other organs as needed

maintain ECF volume & composition

hyperemia increased capillary flow

ischemia cessation of capillary flow

tissue metabolism vessel dilation flow

brain and heart continuously perfused, last to be deprived of capillary flow

Supplying O2 during exercise in human

increase O2 delivery via:increased Hb saturationincrease O2 extractionincreased cardiac output

Distribution of cardiac output during exercise

Medullary cardiovascular center

receives inputs from

Baroreceptorscarotid sinusaortic archsubclaviancommon carotidpulmonary artery

Mechanoreceptorsatrialventricular

Chemoreceptorsarterialventricular

Skeletal muscle afferent fibres

BaroreceptorsMonitor blood pressuree.g. carotid sinus baroreceptors

spontaneous resting AP rate blood pressure = stretch vessel wall AP rate

decrease CO via bradycardia and

decrease peripheral vascular resistance

blood pressure (negative feedback)

Mechanoreceptors

Monitor stretch e.g. atrial myelinated B-fibres

spontaneous resting AP rate sensitive to atrial filling rate&volume blood volume venous volume = venous P atrial filling AP rate

increase heart rate and increase diuresis blood volume (negative feedback feedback)

Peripheral Chemoreceptors

Monitor O2, CO2, pH in arterial blood

primary effect on regulation of ventilation

During normal breathing:

decrease O2, increase CO2 = decrease pH

hyperventilation

peripheral vasodilation (except lungs)

increased cardiac output

During apnea (e.g. diving)

decreased O2

peripheral vasoconstriction (except brain and heart)

bradycardia

decreased cardiac output

Fig. 9.41

Baroreceptorreflex

Capillary Filtration

Fig.9.36

Blood P>Oncotic P Oncotic P> P BloodOncotic P = colloid osmotic P due to [protein] plasma> [protein] interstitial fluid

Consequences of capillary filtrationbulk fluid flow in interstitial spaces a v

carrying small organic molecules & ions

~85% of filtered fluid is uptaken (except in kidney) but 15% not recovered

gradual net loss of fluid from blood and edema

SOLUTION?

LYMPHATIC SYSTEM- parallels veins in structure, function, and topography- no connection with arterial system- low pressure

Fig. 9.37

FUNCTION

·return lymph to circulatory system (3 L/day in humans)

·filter lymph at lymph nodes·lymphocytes secrete antibodies and destroy cells·carry chylomicrons from intestine to circulatory system·carry albumin from liver to circulatory system

Causes of Edema

Increased blood pressure

increases filtration pressure at arterial end of capillaries

more fluid is filtered

Increased tissue proteinincreases solutes in tissue interstitial fluid

less fluid reabsorbed at venous end of capillaries

usually localized edema due to leakage of plasma protein

Decreased plasma proteindecreases solutes in plasma

less fluid reabsorbed at venous end of capillaries caused by:

liver disease (decreased protein production)kidney disease (leakage into urine)protein malnutrition

Obstruction of lymph vesselslymph accumulatese.g. infections of filaria round worm

Hb Saturation

arterial (fully saturated) ~97%

venous at rest 75%mild exercise 58%heavy exercise 27%

Increased cardiac output (= stroke vol x heart rate)

via: stroke volume

heart rate

In human:

CO (L) SV (ml) HR (bpm)

at rest 5.6 80 70heavy exercise 18 80 220trained athlete 5 100 50