Circulatory systems
Gastrovascular cavity
thin body walls
flagella stir fluid
Fig. 9.1
Open circulatory system
hemolymph
large volume
low pressure
most invertebrates
Closed circulatory system
blood
small volume
high pressure
vertebrates
some invertebrates
Circulatory systems cardiovascular components (pump + tubes)
valves, muscles
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 hearts
contract
•waves of contractions push blood
c) Contractile chamber
closed chambers, valves
(e.g. vertberate heart)
Fig. 9.2
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 heart
depolarization (contraction)
repolarization (relaxation)
Normal pacemaker is the
SINOATRIAL NODE
Heart beat:
begins at SA node
spreads through atria
delayed at AV node
spreads through ventricles
Fig. 9.23
2. CLOSED CIRCULATORY SYSTEM
(cephalopods, vertebrates)
High pressure (>12 kPa)
Low volume (5-10%)
High velocity
Distribution regulation
Ultrafiltration
Lymphatic system
Fig. 9.10
Circulation in fish (water breathing)
respiratory and systemic circulations in series
sinus venosus – precursor of SA node in mammals
Circulation in birds and mammals
respiratory and systemic circulations
in parallel
Four chambered heart
Two completely separate circuits
pulmonary circuit
(low pressure)
systemic circuit
(high pressure)
Anatomy of the mammalian heart
adult heart
four chambers
complete separation
of left and right heart
fetal heart
foramen ovale
ductus arteriosus
pulmonary 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 Murmurs
Valve 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 heart
depolarization (contraction)
repolarization (relaxation)
Normal pacemaker is the
SINOATRIAL NODE
Heart beat:
begins at SA node
spreads through atria
delayed at AV node
spreads through ventricles
Fig. 9.23
GAP JUNCTIONS
cells coupled metabolically and
electrically via hydrophilic channels
Passage of:
- inorganic ions
- small water-soluble molecules:
amino acids
sugars
nucleotides
- electrical signals
Fig. 4.2 The structure of gap junctions
Fig. 9.25 Electrocardiogram (ECG) tracings
P wave
depolarization of atrium
QRS
depolarization of ventricle
T wave
repolarization of ventricle
(repolarization of atrium masked by QRS)
CARDIAC CYCLE
cardiac contraction (systole, 0.3 sec in human)
cardiac relaxation (diastole, 0.5 sec in human)
right side of heart
left side of heart
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)
N.B. same volume changes at
different pressures
Fig. 9.26
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 pressure
venoconstriction, skeletal muscle pump
atrial pressure
ventricular 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
Aorta
10
1
Arteries
3
40
Arterioles 0.02
40000000
Capillaries 0.008
1200000000 600
Venules
0.03
80000000
Veins
6
40
Vena Cava 12.5
1
Total area (cm2)
0.8
3
125
60
570
11
1.2
Total volume (mL)
30
60
25
110
220
50
Laminar and turbulent flow
in vessels
Poiseuille's equation
relationship between pressure and flow in small terminal arteries,
capillaries, and veins
Q (flow rate) = (P1- P2) pr4
8Lη
(P1- P2) pressure difference
r
radius of vessel
L
length of vessel
η
viscosity of fluid
flow
flow
resistance =

pressure difference

r4
1/
distance
1/
viscosity
(P1 - P2)
Q
= 8Lη
pr4
Flow & resistance most influenced by vessel diameter
Fig. 9.29
COMPLIANCE
increased P  stretch  increased volume
increased r  decreased resistance  increased flow
Compliance = D volume/D pressure
Venous system:
very compliant \volume reservoir
large volume changes result in small pressure changes
Arterial system:
less compliant \ pressure reservoir
maintain capillary flow
Compliance of veins 24x greater than arteries:
(except elastic aortae which dampen pressure oscillations)
tunica
intima:
endothelium
tunica media:
smooth muscle
elastin
tunica externa:
collagen
Fig.9.31
Blood flow in vertebrate circulatory systems
•high and variable pressure
in ventricle
•low pressure, steady flow
in capillaries, venules, veins
•velocity increase in venous
system
FUNCTIONS OF ARTERIAL SYSTEM
1.
2.
3.
4.
Deliver blood to capillaries
Pressure reservoir
Dampen oscillations in pressure and flow
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 reservoir
Arterial blood pressure
systolic (max)
diastolic (min)
Fig. 9.34
Functions of Venous System
1.
return blood to heart (skeletal muscle pump)
2.
blood storage reservoir (large volume, low pressure)
3.
maintain arterial pressure and capillary flow
Venous compliance related to large volume
ARTERIOLES
•control blood distribution to tissues
•surrounded by smooth muscle
•vasoconstriction, vasodilation
Q (flow rate) = (P1- P2) pr4
8Lh
nutritional flow
waste disposal
regulation of cell activities
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 difference
maximum 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
Capillary structure
muscle, lung, adipose tissue
kidney, intestine
discontinuous capillary
bone marrow, liver, spleen,
Fig. 9.32
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
Distribution of cardiac output during exercise
Supplying O2 during exercise
in human
increase O2 delivery via:
increased Hb saturation
increase O2 extraction
increased cardiac output
Medullary cardiovascular center
receives inputs from
Baroreceptors
carotid sinus
aortic arch
subclavian
common carotid
pulmonary artery
Mechanoreceptors
atrial
ventricular
Chemoreceptors
arterial
ventricular
Skeletal muscle afferent fibres
Baroreceptors
Monitor blood pressure
e.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
Baroreceptor
reflex
Fig. 9.41
Capillary Filtration
Fig.9.36
Oncotic P = colloid osmotic P due to
[protein] plasma> [protein] interstitial fluid
Blood P>Oncotic P
Oncotic P> P Blood
Consequences of capillary filtration
bulk 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
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
Fig. 9.37
Causes of Edema
Increased blood pressure
increases filtration pressure at arterial end of capillaries
\ more fluid is filtered
Increased tissue protein
increases solutes in tissue interstitial fluid
\less fluid reabsorbed at venous end of capillaries
usually localized edema due to leakage of plasma protein
Decreased plasma protein
decreases 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 vessels
lymph accumulates
e.g. infections of filaria round worm
Hb Saturation
arterial
(fully saturated)
~97%
venous
at rest
mild exercise
heavy exercise
75%
58%
27%
Increased cardiac output (= stroke vol x heart rate)
via:
 stroke volume
 heart rate
In human:
at rest
heavy exercise
trained athlete
CO (L)
SV (ml)
HR (bpm)
5.6
18
5
80
80
100
70
220
50