H2: The Circulation

Question 1

Difference between blue and red circulation?

Affect on pressure and volume?

Answer 1

Red: Systemic Arterial circulation
•High pressure, low volume

Blue: Venus circulation - lead to pulmonary circulation
•Low pressure, high volume (~60%)

Question 2

What are the 2 vessel types?

Answer 2

Capacitance vessels - the veins (holding ~60% of the BV)

Resistance vessels - Arterioles + capillaries (mainly responsible for blood pressure regulation and regulation of flow thru organs) ~7%

Question 3

What are capillaries?

Answer 3

Perfusion beds (made up of much small blood vessels) in individual tissues. 
These are fed by Arterioles

Exchange O2 + CO2 + nutrients

Question 4

Systemic vs Pulmonary

Answer 4

Systemic: occurs between the heart and the entire body

Pulmonary: occurs between the heart and the lungs

Question 5

Diameter and wall thickness of different parts of circulation system

Answer 5

Aorta: diameter = 25mm
            wall thickness = 2mm
Artery: diameter = 4mm
            wall thickness = 1mm
Arteriole: diameter = 30 μm
                wall thickness = 6 μm

Terminal Arteriole: diameter = 10 μm
wall thickness = 2 μm
Capillaries: diameter = 8 μm
wall thickness = 0.5 μm

Venule: diameter = 20 μm
              wall thickness = 1 μm
Vein: diameter = 5mm
           wall thickness =0.5mm
Vena Cava: diameter = 30mm
                     wall thickness = 1.5 μm

Question 6

Darcy’s Law - relation bw flow + pressure

Answer 6

F = ΔP / R
(increased R = decreased F)

MABP = CO * TPR

TPR is controlled by diameter of the small vessels. It has the biggest affect on BP

MABP = DBP + (SBP - DBP)/3

MABP is not 1/2 way bw systolic & diastolic BP, rather it’s 1/3 of the difference

Question 7

Relationship between flow velocity and resistance in the vascular tree

Answer 7

Flow velocity is highest at Arteries, and gets smaller

Most of Vascular resistance is in the Arterioles (flow regulation occurs)

Question 8

Laminar vs Tubular flow

Answer 8

Laminar: smooth surfaced-tube, fluid dynamic gives a phenomena called laminar flow
>flow velocity fastest in the centre
>flow on outside will be slower bc of friction

Turbulent: narrowing in the vessel beyond a certain point/ if flow velocity exceeds parameters under which laminar flow can occur
(BAD)

Question 9

Reynold’s number equation.

How is Turbulent flow prevented?

Answer 9

Re = plv/n

Laminar flow when Re

Question 10

How is stenosis usually formed in the vasuclar tree

Answer 10

Usually atherosclerotic plaques build up at bifurcation sites, due to the turbulent flow.

Changes at these sites partly to do with reflection of waves of the vessel wall.

Eg: plqs in coronary arteries = Heart attack
plqs in corotid arteries = stroke
plqs in peripheral = peripheral vascular disease

Question 11

Laplace’s law?

Answer 11

P = T/r

Important bc a small diameter vessel requires much less tension to contain a given pressure

Question 12

Pressure v Time graph

Answer 12

Diastolic pressure equivalent to the minimum pressure in Aorta during diastole (75mmHg).
This increases during ejection phase

Peaks ~120mmHg (systolic pressure)

The little blip (dicrotic notch) shows closure of aortic valve

Mean pressure is 1/3 of max pressure

Question 13

Rigid v Elastic tube

Answer 13

If Aorts was rigid, change in pressure would be very steep. This can cause damage (during systole + diastole)

Elastic tube decreases height of pressure Δ. An elastic (compliant) Aorta helps smooth out the variation in arterial BP and store energy (WindKessel function)

> Elastic recoiling in diastole helps maintain BF in forward direction, so helps to maintain BP + flow to tissues during relaxation phase