L.8 - continuity principle Flashcards
What does blood consist of?
- plasma and different types of blood cells
Describe plasma and what it contains. How much of the blood bilge does it make up?
- almost clear liquid which makes up approx. 55% of the blood volume.
- It contains many dissolved materials such as proteins, carbs, lipids, ions (electrolytes), etc.
What are the 3 types of blood cells?
- erythrocytes (main cellular component of blood)
- leukocytes
- platelets (thrombocytes)
For erythrocytes - What is the function, diameter, lifetime, and how much of the blood does it make up?
- function: transport of O2 and CO2
- diameter: ~7 um
- lifetime: ~120 days
- volume of erythrocytes in blood:
5 x 10^6 cells/mm^3 of blood
For leukocytes - what is the diameter, volume of it in blood, function, and lifetime?
Diameter: ~9-15 um
Volume in blood: 8000 cells per mm^3
Function: to protect against infection.
Lifetime: 20 day cycle
For platelets (thrombocytes) - what is the diameter, volume of it in blood, function, and lifespan?
Diameter: ~3 um
Volume of it in blood: ~200,009 per mm^3 of blood
Function: to allow clotting
Lifespan: 7-10 day lifespan
How can blood components be separated?
- by centrifugation
Define haematocrit ratio.
- the ratio of RBC volume to the total blood volume (ie- %RBC volume)
What does haematocrit determine?
- the effective viscosity of the blood
haematocrit varies from what?
- from tissue to tissue and also with body condition
In %, how much does blood represent in the total body mass? Give example.
- 7%
Example - how much litres of blood is in a 70 kg male?
0.07 x 70 = 4.9
Approx. 5 litres of blood
How much blood does the heart pump per contraction & how long does it take for an average blood cell to make one full cycle of the body?
- 1 minute since the heart pumps about 80 ml of blood per contraction
Closed pumping system consists of 2 synchronous force pumps which are…?
- left ventricle (veins) and right ventricle (artery)
What does the muscles around the heart walls do?
- contracts and relaxes to form the pumping action (boyle’s law)
- heart contracts in systolic phase
- heart relaxes in diastolic phase
What is the contraction of both atria (atrial systole) is followed by…?
- by a contraction of ventricles (ventricular systole)
- which is then followed by a relaxation phase (diastole)
What stimulates the mechanical contractions of the heart?
- stimulated by electrical pulses (action potentials) generated in the sinoatrial node
What does left ventricle and right ventricle supply respectively?
L.V - provides systemic blood
R.V - supplies the lung
The 2 synchronous pumps work on the basis of what law?
- boyle’s law which states that for a gas at constant temperature, pressure x volume = constant
PV= constant
What is boyle’s law?
P•V = constant
What happens to the volume and pressure in the heart when the heart chambers relax and expand?
- volume increases
- pressure inside the chambers decreases (drawing blood into the chamber)
What happens to the volume and pressure in the heart when the heart chambers contracts?
- volume decreases
- pressure increases (forces blood out of chamber)
What happens as the blood circulates through the systemic system?
- pressure is lost
- pressure drops from 120 mmHg in the aorta to ~4-5 mmHg when entering the right atria.
What happens to the pressure when the right atria and ventricle contracts?
- pressure is increased to around 25-40 mmHg before entering the lungs where it decreases again to around 7-8 mmHg
What is the continuity principle (aka equation of continuity EOC state)?
- consider a channel through which a fluid can flow (e.g. artery)
- the EOC states that for an incompressible fluid, the rate of flow of fluid into one end of the channel must be equal to the rate of flow of fluid leaving the other end.
What is the ‘rate of flow of a fluid’? What is its equation?
- ‘Q’ - symbol of rate of flow of fluid
- is the volume of fluid (🔺V) passing a fixed point within some time interval (🔺t)
Q = 🔺V/🔺t (m^3 s^-1)
How to find the volume flow rate? What is the equation we use?
Q = (x-sectional area (A)) • (velocity of fluid (v))
Simply:
Q = A•v [ flow rate in m^3 s^-1 ]
Consider the image on slide 20. How would we find the volume flow rate of these 2 ends?
Q1 = Q2
A1v1 = A2v2
Ie - the product of the cross-sectional area and the velocity is constant
What happens to the flow velocity if the cross-sectional area is reduced?
- flow velocity is increased
What happens to the flow velocity if the cross-sectional area is increased?
- flow velocity is reduced
Would the blood flow much faster in the capillaries than in the aorta?
- NO!!!
- We would expect the blood to flow much faster in the cabinet he’s been in the aorta since the ex cross-sectional area of 1 cal very much less than X Sentinel area of the aorta.
- However, this is NOT the case since the aorta feeds into millions of capillaries via the arteriols.
- In fact, typical aorta has a X sectional area of about 3 cm^2 compared to the total X sectional area of the capillary network which is approximately 900 cm³^3
What is the x-sectional area of a typical aorta VS the total x sectional area of the capillary network?
Typical aorta has a X sectional area of about 3 cm^2 compared to the total X sectional area of the capillary network which is approximately 900 cm³^3
What is the blood flow speed in the aorta Vs capillaries?
- aorta = approx 30 cm s^-1
- capillaries = approx 1 mm s^-1
- this increases as the blood movies into the veins and reaches ~5 cm s^-1 in the vena cava
What is streamline or laminar flow?
- a well ordered flow of fluid such that which flows in a smooth walled, straight section of clean blood vessel
- such flow results in a minimum loss of energy in the flow and is ‘silent’ (aka cannot be heart with a stethoscope placed over an artery)
What is turbulent flow?
- where the fluid contains eddies and swirls etc.
- This usually happens when the flow velocity exceed some threshold or critical flow speed, ie. caused by an obstruction or buildup of plaque on the wall of a blood vessel
What happens to the x-sectional area and flow speed when an artery is narrowed by plaque build up?
- x-sectional area is reduced
- flow speed increases (continuity principle)
What can build up of plaque on the inner wall of a blood vessel result in?
- results in turbulence which may be detected using a stethoscope
What is the equation used to find the critical flow (V crit) speed?
V crit = (constant)•(viscosity) / (density)•(vessel radius)
What is the constant called in V crit equation? What are the values of viscosity of blood and density of blood?
- The constant is called reynold’s number
- for blood, has a billie of ~1000
-viscosity of blood= 4 x 10^-3 Pa s
- density of blood= 1059 kg m^-3
What is the radius of a typical aorta? What is the Vcrit of a typical aorta
- radius = 1 dm
- Vcrit = ~ 0.4 m s^-1
What happens to the flow speed in the aorta during the cardiac cycle? What does this mean?
- flow speed increases and decreases during systole and diastole and the velocity varies between ~0 m s^-1 and 0.5 m s^-1
- this means that blood flow will be turbulent during some parts of the cardiac cycle
