## 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 =...
Author: Avice Rose
Circulatory Systems II

Physics of Circulatory Systems 

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)

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.

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)