Circulation

Question 1

What is the difference between convection and diffusion?

Answer 1

Convection - long distance at a high speed

Diffusion - slowly across barriers (short distance)

Question 2

Explain open and closed circulations. What are they found in?

Answer 2

Open

• extracellular fluid (hemolymph) circulates
• Found in insects, crustaceans, molluscs

Closed

• blood is separate from ECF and circulates in closed tubes
• found in vertebrates, squid and annelids

Question 3

What are the two main overall designs of cardiovascular systems? What are the differences?

Answer 3

Single - heart pumps blood and it travels to all other tissues and back to the heart

Double - Travels through the heart twice in one circuit. From heart to lungs, back to heart and then through circulation to tissues

Question 4

What is the general design of a circulation system?

Answer 4

Heart pumps to generate pressure and blood flow by contraction - valves cause unidirectional flow

Distribution and collection by vessels - control of vessel size permits control of distribution

Exchange areas for diffusion - capillary beds in closed circulation

Question 5

What is different about the design of circulation in crustaceans?

Answer 5

There are many different example types in crustaceans that mostly depend on activity level and metabolic rate.

Some have elaborate circulations if they are active with blood vessels that branch to direct flow

But smaller crustaceans mostly use diffusion

Question 6

What type of animal are the exception to the higher metabolism leads to high complexity rule? Why?

Answer 6

Insects - very high metabolism but very basic circulation

They do not use it to transport oxygen

Question 7

What are the steps of the heart cycle? Relate them to valve position and pressure changes

Answer 7

Filling - pressure in veins is higher than pressure in ventricle, input valve opens

Isovolumetric contraction - pressure rises above venous pressure but below arterial pressure. Both valves closed

Ejection - pressure from contraction higher than arterial, blood ejected into artery causing decrease in ventricle volume

Isovolumetric relaxation - ventricle relaxes and pressure drops below arterial to stop output. Both valves closed because pressure still greater than venous

Ventricle relaxes till pressure is lower than venous and starts to fill again

Question 8

What is a pacemaker cell? What drives them?

Answer 8

Cells that have intrinsically oscillating membrane potential - with no external input

Oscillation caused by time-dependent changes in membrane permeability

Question 9

What is the equation for membrane potential and permeability of Na+ and K+

Answer 9

Vm = 58 log10 (Pk x {Kout} + Pna x {Na+out})/(Pk x {K+in} + Pna x {Na+in})

Question 10

How long are action potentials generated by pacemaker cells compared to muscle cells? What helps maintain them? How are they stopped?

Answer 10

The action potentials of the heart are much longer than in skeletal muscle cells because calcium channels are opened to maintain it.

They are stopped and potential goes back to normal by closing Na and Ca channels and opening K+ channels

Question 11

What controls the spread of an action potential across the heart?

Answer 11

SA - start of action potential, spreads over atria first

AV node - delays action potential across atrium. AP is prevented from spreading to the ventricle by dense connective tissue and only connection is AV node.

Purkinje fibers - ventricular muscle fibers that spread action potentials

Question 12

What is the equation for cardiac output? What factors increase it?

Answer 12

Cardiac output = heart rate x stroke volume

Heart rate doesn’t increase output because heart doesn’t have time to fill

Increasing venous return will increase stroke volume and effect output regardless of heart rate

Question 13

What are things that can affect the relationship between pressure and volume in ventricle contraction if heart rate and venous return are constant?

Answer 13

Increased blood pressure shifts the cycle to the right of the graph, with the heart doing more work moving the same volume at a higher pressure

Things like epinephrine can increase the contractility of the heart by increasing Ca release - shifts the curve to the left with less blood left after contraction

Question 14

What is the effect on the pressure/volume relationship in contraction when heart rate is increased? When venous return is increased?

Answer 14

If heart rate is increased, stroke volume would be decreased proportionately without proper time to fill

Increasing the venous return increases the volume proportionately

Question 15

What is the effect of exercise on the pressure/volume relationship in contraction?

Answer 15

Venous return is greatly increased, heart rate increases, inotropic state of the heart is increased by sympathetic stimulation

Question 16

What is the equation for central pressure (blood pressure)? Local pressure?

Answer 16

deltaP = Q x Rtpr

(total flow or cardiac output times total peripheral resistance)

Flow(local) = deltaP/local R

Question 17

How do you calculate resistance for resistors in series? For resistors in parallel?

Answer 17

In series:
R(T) = R1 + R2 + …

In parallel:
1/R(T) = (1/R1) + (1/R2) + …

Question 18

What is the relationship between resistance and vessel radius?

Answer 18

R is inversely proportional to radius to the fourth power

R = K x 1/r^4

K = (8 x L x viscosity)/π

Question 19

Where is the main resistance of flow found?

Answer 19

In the small arteries and arterioles

Question 20

What are the regional functions of different vessels?

Answer 20

Large arteries - low resistance, elastic walls

Small arteries - high resistance, determine distribution of flow

Capillaries - slow flow, high exchange

Veins - low pressure, low resistance