Download Circulation Circulatory System Function Types of Circulation Types

Circulatory System Function
• Move circulatory fluid (blood) around body
Circulation
Chapter 3
Types of Circulation
• Sponges
– intracellular spaces
– allows water to flow through
• Nematodes, Platyhelminths, etc
– gut cavity, coelomic fluid
• Arthropods, annelids, chordates, etc
– distinct circulatory system
– pumps and channel system
Types of Channel Systems
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Gas Transport
Nutrient Transport
Excretory Product Transport
Cell Signal Transport
Hydraulic Force
Heat Conductance
Immunity
Types of Pumps (Hearts)
• Peristaltic
– waves of muscular contraction along tubes drives
blood flow
• Chamber
– muscular pump divided into chambers which contract
• Pressure
– contraction of muscles external to the circulatory
system drives flow
Invertebrate Circulation:
Annelids
• Closed circulatory systems
– blood carried in tubes (blood vessels)
• arteries, capillaries and veins
– vertebrates, cephalopods, echinoderms, annelids
• Open circulatory systems
– blood (hemolymph) passes from heart through short
arteries into open sinuses surrounding the tissues
• Closed circulatory system
• Dense capillary network at integument
(respiration)
• Peristaltic dorsal blood vessel drives
blood flow
– most mollusks and arthropods
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Invertebrate Circulation:
Bivalves and Gastropods
• Open circulatory system
– (hemolymph) circulated in an open space
(hemocoel) divided into lacunae
• Two- or three-chambered heart
• Hydraulic force used to control movement of
the foot in bivalves
Invertebrate Circulation:
Insects
• Open circulatory system
• Minimal gas transport
• Large dorsal vessel w/peristaltic
heart in posterior segment
– hemolymph runs anteriorly to head,
then ends in hemocoel
– flow directed through hemocoel by
longitudinal membranes
– flows back to posterior dorsal vessel
• Auxillary pumps supply wings
limbs, and antennae
Invertebrate Circulation:
Crustaceans
• Some small or sessile spp.
lack heart or blood vessels
• Larger spp possess open
system similar to insects
• Extensive circulation in gills
– heart receives oxygenated
hemolymph from the gills then
pumps it to the rest of the body
Invertebrate Circulation:
Cephalopods
• Closed circulatory system
– pair of branchial hearts
(drive blood to gills)
– single chambered systemic
heart (ventricle)
– similar to system in higher
vertebrates
• separate pulmonary and
systemic circuits
Invertebrate Circulation:
Arachnids
• Similar to insect design
• Hemolymph contains higher [hemocyanin]
– O2 transport
• More extensive arterial systems in arachnids with
books lungs
• Specific arteries supply hydraulic pressure to legs
for locomotion
– legs of spiders lack extensor muscles
Vertebrate Circulation:
General Patterns
• Single passage through
heart during circuit
(e.g., fish)
– Single circuit
• Double passage through
heart during circuit
(e.g., mammals)
– Separate pulmonary and
systemic circuits
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Vertebrate Circulation:
Cyclostomes
• Partially open system
– large blood sinuses
• Multiple “hearts”
– branchial (regular) heart
• two chambered
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cardinal heart
portal heart
caudal hearts
gills (drive arterial blood)
Vertebrate Circulation:
Dipnoi (Lungfish)
• Three-chambered heart
– Two-chambered atrium
– Partially divided ventricle &
bulbus cordis (conus arteriosis)
• Separates oxygenated (left)
and deoxygenated (right)
blood
• Can shunt blood to lungs or
gill lamellae
Vertebrate Circulation:
Non-Archosaur Reptiles
• Three chambered heart
– Two chambered atrium
– partly divided ventricle
• Ventricle contains three sub-chambers
– divided upon contraction
– “five-chambered” heart
– allows heart to redirect blood flow btw
pulmonary and systemic circuits
– “cardiac shunting”
Vertebrate Circulation:
Teleosts and Elasmobranchs
• Two-chambered heart
– atrium + ventricle
• Atrial contraction (systole) pushes
blood into ventricle
– valves prevent flow into sinus venosus
• Ventricular systole forces blood
into bulbus arteriosus
• Backflow upon relaxation (diastole)
prevented by valves
– elastic recoil of bulbus arteriosus
drives blood through blood vessels
Vertebrate Circulation:
Amphibians
• Three chambered heart
– Two chambered atrium
– Undivided ventricle
– Spiral valve - separates blood flow in conus arteriosus
• Right side (pulmonary)
– Receives blood from tissues and skin
– Pumps to skin and lungs
• Left side (systemic)
– Receives blood from lungs
– Pumps to tissues
Vertebrate Circulation:
Crocodilians
• Four-chambered heart
– Left aortic arch and pulmonary
artery arise from right ventricle
– L and R arches connected by
foramen of Panizza
• Allows cardiac shunting
– blood directed to lungs during
air breathing
– blood directed to tissues during
diving
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Vertebrate Circulation:
Mammals and Birds
• Four-chambered heart
• Complete separation into
right and left halves
• Blood pressure can differ
between pulmonary and
systemic circuits
– systemic BP = 95 mmHg
– pulmonary BP = 14 mmHg
Mammalian/Avian
Cardiac Cycle
• Systole (contraction)
– Muscular walls of the ventricles
contract
– Elevation of blood pressure in
the ventricles
– Closure of atrioventricular valves
– Blood pushes through arterial
valves
– Blood flows into arteries
Cardiac Output
• amount of blood pumped by the heart per
min.
Qh = ƒh * Vh
• ƒh = heart rate
– frequency of contraction
• Vh = stroke volume
Vertebrate Circulation:
Mammals and Birds
• Atria
– Thin walled, support ventricular filling
• Ventricles
– Primary pumps for driving blood
through circulation
• One-way valves
– Atrioventricular valves
– Arterial (semilunar) valves
– ensure unidirectional flow
• veins → atria → ventricles → arteries
Mammalian/Avian
Cardiac Cycle
• Diastole (relaxation)
– Muscular walls of the ventricles
relax
– Blood pressure in the ventricles
falls below arterial pressure
– Closure of arterial valves
– Pressure falls below atrial
pressure
– Blood pushes through
atrioventricular valves
– Ventricular volume increases
Cardiac Output
• Adjusted to meet metabolic demands of
an organism
– ↑ activity, ↑ cardiac output
• Modify cardiac output by changing either
heart rate or stroke volume
– volume of blood pumped by heart per
contraction
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Heart Excitation:
Myogenic (Vertebrates)
• Heart excitation and contraction
can occur in absence of external
stimulation
• Presence of internal
“pacemakers” (modified muscle
cells) form conduction system
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Sinoatrial node
Atrioventricular node
Atrioventricular bundle
Purkinje fibers
Regulation of Cardiac Output
(Mammals)
• Heart rate (modify pacemaker activity):
– The autonomic nervous system:
• Parasympathetic nervous system (vagus nerve)
– acetylcholine slows HR
• Sympathetic nervous system (accelerans nerve)
– norepinephrine increases HR
– Hormones
• Epinephrine (released from adrenal glands)
Heart Excitation:
Neurogenic (Arthropods)
• Signals received from
neurons directly
responsible for muscle
contraction
– Posterior cells act as
pacemakers
– Anterior cells stimulate
muscle contraction
Regulation of Cardiac Output
(Mammals)
• Stroke volume (modify force of contraction):
– neural/hormonal
• epinephrine and norepinephrine
– increases force of muscle contraction
– autoregulation
• Frank-Starling Law
– increased venous return increases stretch on the heart
– increased stretch leads to stronger contractions
– increased HR
Oxygen Delivery During
Exercise
• ↑ activity, ↑O2 requirements and CO2
production
• Three mechanisms of obtaining more O2
– ↑ O2 extraction from the blood
• only 25% of O2 removed from blood at rest
• increase to 80-90% during exercise
– ↑ Heart Rate
– ↑ Stroke Volume
Animal Size and Cardiac Output
• Smaller animals have relatively higher
metabolic rates (b ~ 0.75)
• Smaller animals have relatively higher
cardiac outputs (b ~ 0.75)
• Higher cardiac output due to higher heart
rates, not larger stroke volumes
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Blood Vessels
• Arteries - large, elastic tubes, multiple layers of
muscles
• Arterioles - smaller diameter, less elastic, fewer
muscle layers
• Capillaries - thin diameter, thin walls, low diffusion
resistance
• Venules - larger diameter, thin walled, no muscle
• Veins - large diameter, elastic walls, little muscle,
may possess valves
Blood Flow
• Blood flows from an area of high total fluid
energy to low total fluid energy
• Bernoulli’s Theorem
E = pv + mgh + 1/2mu2
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E = total fluid energy
pv = potential energy of pressure generated by the heart
mgh = gravitational potential energy
1/2mu2 = kinetic energy
Blood Vessels
• Structural Patterns
– ↓ diameter, ↑ number, ↑ cross-sectional area
• Functional Patterns
– Blood volume: largest in veins, smallest in capillaries
– Blood pressure: ↓ with ↑ distance passed
– Blood flow velocity: ↓ with ↓ diameter and ↑ crosssectional area
Overview of Blood Flow
• Reasonable assumptions that will help
simplify things…
– Kinetic Energy varies little from one location to another
within the system being analyzed
– Flow is horizontal (gravitational potential energy is
constant)
Blood Flow:
Poiseuille’s Law
• For the laminar flow of a fluid
through a straight, rigid tube:
Q = (∆pr4π) / (8Lη)
– Q = blood flow (volume per unit time)
– ∆p = difference in pressure between
both ends
– r = radius of the tube
– L = length of the tube
– η= viscosity
Blood Flow:
Poiseuille’s Law
• Q α ∆p
– as pressure gradient increases, flow increases
• Q α r4
– increased radius, large increase in flow
– decreased radius, large decrease in flow
• Q α 1/L
– flow decreases with increased tube length
• Q α 1/ η
– increased viscosity decreases flow
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Gravity Effects
on Blood Pressure
• As height ↓’s, gravitational
potential energy ↓’s, pressure ↑’s
• Venous return
– blood pressure in lower body greater
than upper body due to gravity
• pressure in veins exceeds arterial
pressure
• blood pools in leg veins
• returned by venous pressure pumps
Capillaries
• Enormous number of capillaries
– overall large cross-sectional area
• Extremely thin diameter
– slow blood flow
– high SA/V ratio
• Thin walls (simple squamous endothelium)
Gravity Effects
on Blood Pressure
• Head perfusion
– arterial blood pressure must be high
enough for blood to reach head
– giraffes - long vertical neck
• high arterial BP
• venous values prevent backflow when
head brought to ground level
Ultrafiltration
• Small molecules can diffuse into and out of
capillaries
• Additional amounts of fluid driven out by
hydraulic pressure inside the capillaries =
ultrafiltration.
– Small particles driven out with water
– large molecules (e.g. plasma proteins) remain in blood
– low diffusion distance
Ultrafiltration
• Loss of water with retention of proteins
increases the colloid osmotic pressure of the
blood
– generates tendency for water to flow back into
the blood as pressure in the capillaries
decreases
Lymphatic System
• Generally water loss by ultrafiltration
exceeds water uptake by colloid osmotic
movement of water
– lost fluid enters lymphatic system
– returned to the blood
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