Circulatory Systems II
Physics of Circulatory Systems
Fluids flow down pressure gradients
Law of bulk flow: Q = P / R Q = Flow (Rate) P = pressure gradient R = resistance
Flow rate = volume of fluid that moves
past a given point per unit time (L/min)
Radius & Resistance
Poiseuille’s Equation:
Q = P π r4 / 8 L ή
Resistance is inversely proportional to
radius to the forth power.
Small changes in radius result in
large changes in resistance.
Controlling Flow
Vasoconstriction: r R Q
Vasodilation: r R Q
Small changes in r result in large
changes in resistance and flow.
Total Flow
Law of conservation of mass:
The flow through each segment of the
circulatory system must be equal.
Total flow is constant across all parts of
the circulatory system.
Total Flow
Total Flow
Series :
◦ RT = R1 + R2 + R3
Parallel :
◦ 1/RT = 1/R1 + 1/R2 +1/R3
Circulatory systems have both series and
parallel arrangements of blood vessels.
Total Flow
Velocity of Flow
Velocity of blood flow in a given blood
vessel is inversely related to the cross-
sectional area of the blood vessel.
Blood velocity = Q/A
A= summed cross-sectional
area of channels.
Velocity of Flow
Regions of the circulatory system
that are involved in the exchange of
materials have very high total cross-
sectional areas, so they have very
low velocities, which aids diffusion.
Pressure & Blood Vessels
Pressure within walled chambers exerts a force on those walls.
Blood pressure within walled chambers (heart or blood vessels) exerts a force.
Force can be quantified using the
law of LaPlace.
Pressure & Blood Vessels
Law of LaPlace: T = aPr
Pressure & Blood Vessels
Taking into account wall thickness:
σ = Pr/w
thickness stress on wall
Pressure & Blood Vessels
Organisms are reasonably build
As thickness increases, stress in the wall
decreases, therefore:
◦ BVs such as the aorta, which must withstand
very high pressures, are thicker and stronger.
◦ Arterioles which are subject to lower
pressure are thinner.
Circulatory Systems
Vertebrate circulatory systems contain
one or more pumps in a series:
Single-Circuit Circulatory System:
◦ Water breathing fish
Double-Circuit Circulatory System:
◦ Mammals and birds
Single-Circuit Circulatory Systems
Water breathing fish
Single-Circuit Circulatory Systems
Single-Circuit Circulatory Systems
Double-Circuit Circulatory Systems
Tetrapods:
◦ amphibians, reptiles, birds, & mammals
Double-Circuit Circulatory Systems
Systemic system:
◦ Oxygenated blood from heart to tissues.
◦ Deoxygenated blood from tissues to heart.
Pulmonary system:
◦ Deoxygenated blood from heart into lungs
◦ Oxygenated blood from lungs back to heart
Double-Circuit Circulatory Systems
Mammals & Birds:
◦ Completely separated pulmonary & systemic systems.
Amphibians & Most Reptiles
◦ Incompletely separated pulmonary & systemic systems.
Different advantages for both
Double-Circuit Circulatory Systems
Vertebrate Hearts
Main Function:
◦ Pump blood throughout body
Complex walls with 4 main parts:
1. Pericardium
2. Epicardium
3. Myocardium
4. Endocardium
Myocardium
Compact Myocardium
◦ Tightly packed cells arranged in a regular
pattern.
◦ Vascularized
Spongy Myocardium
◦ Meshwork of loosely connected cells.
◦ Not vascularized
◦ Often arranged into trabeculae
Fish Hearts 4 chambers arranged in series
Bony Fish:
Bulbous Arteriosus
Non-Contractile
Elasmobranchs:
Conus Arteriousus
Contractile
Heart rate in fish is temperature dependent
Antarctic cod swim in 0-3°C water
Have antifreeze protein in their blood
Have a low heart rate
Stroke volume 6-15x predicted for their size
Typical fish heart = 0.2% body mass
Atlantic cod heart = 0.6% body mass
Amphibian Hearts
3 chambered heart
2 atria supply blood to a single ventricle
◦ Mixing of oxygenated & deoxygenated blood
Spiral fold helps direct oxygenated &
deoxygenated blood to correct systems
Amphibian Hearts
Amphibian Hearts
Reptile Hearts (non-crocodilian)
Most reptiles (non-crocodilian) have 5 chambered hearts:
2 Atria
Single ventricle divided (by septa) into 3 interconnected compartments:
1. Cavum venosum
2. Cavum pulomnale
3. Cavum arteriosum
Reptile Hearts (non-crocodilian)
Reptile Hearts (non-crocodilian)
R-L shunt =
direct blood to
systemic system
L-R shunt =
direct blood to
pulmonary system
Reptile Hearts (crocodilian)
Crocodilian reptiles:
◦ crocs, alligators, & caimen
Completely divided ventricles:
◦ 4 chambered heart
Pulmonary and systemic circuits are still connected and can shunt blood between them.
Reptile Hearts (crocodilian)
Foramen of Panizza: small opening
located at the base of aortas
Allows for R-L shunt:
bypass pulmonary system
Allows them to remain submerged for
several hours without perfusing their lungs.
Reptile Hearts (crocodilian)
Reptile Hearts (crocodilian)
Top Related