12 Circulatory Systems II PPT

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.


Law of LaPlace: T = aPr


Taking into account wall thickness:

σ = Pr/w

thickness stress on wall


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

Double-Circuit Circulatory Systems

Tetrapods:

◦ amphibians, reptiles, birds, & mammals


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


Mammals & Birds:

◦ Completely separated pulmonary & systemic systems.

Amphibians & Most Reptiles

◦ Incompletely separated pulmonary & systemic systems.

Different advantages for both

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

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


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.


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.

12 Circulatory Systems II PPT

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