Download Circulatory Systems II

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 crosssectional 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 crosssectional 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.
2.
3.
4.
Pericardium
Epicardium
Myocardium
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)