WEEK 8 (Hemodynamics) Flashcards
Describe the velocity of ideal, non-viscous liquid particles
Ideal, non-viscous liquid particles are moving with the same velocity
Describe the velocity of real, viscous liquid
In Real, viscous liquid the velocity of the fluid is zero near the pipe wall and maximal in the centre of the pipe
What do falling ball viscosimeters measure?
They measure the movement of particles (spheres of known dimensions ion a liquid by its weight)
What is Stocke’s law?
Stoke’s Law is a mathematical equation that expresses the settling velocities of the small spherical particles in a fluid medium. The law is derived considering the forces acting on a particular particle as it sinks through the liquid column under the influence of gravity. The force that retards a sphere moving through a viscous fluid is directly proportional to the velocity and the radius of the sphere, and the fluid’s viscosity.
F = 6 π η r v
η – viscosity, r – radius of a sphere, v - velocity
Which law does viscosity of the liquid follow?
Stocke’s law
What are Capillary viscosimeters based on?
Measurement of time (t) necessary for the fluid volume (v) to flow through the capillary at constant pressure
What is Poiseuille’s law and what can be extracted from it?
the law that the velocity of a liquid flowing through a capillary is directly proportional to the pressure of the liquid and the fourth power of the radius of the capillary and is inversely proportional to the viscosity of the liquid and the length of the capillary.
In Poiseuille’s law, as the radius of the tube increases, the resistance decreases significantly since r is to the power of four
What is Reynold’s number for most fluids?
2000-3000
What are the key components of viscosity?
- Viscosity of liquid rapidly drops with increasing of temperature
- Viscosity of blood depends on the number of red blood cells
What is the normal value of blood viscosity?
0.4-0.45 Pa
What are the levels of viscosity in terms of children, women and men?
Children - lowest
Women - higher
Men - highest
Given an example of a complex fluid
Blood is a “complex fluid”
What are the different segmentations of blood?
- PLASMA (55%)
- BUFFY COAT (LEUKOCYTES & PLATELETS) <1%
- ERYTHROCYTES (45%)
What are the different segmentations of plasma?
- WATER (92%)
- PROTEIN (7%)
- ORGANIC & INORGANIC MOLECULES
- DISSOLVED GASES
What are the key properties of blood?
- behaves as a Newtonian vicious fluid with a viscosity about 20% higher than that of water
- leukocytes come in five varieties
What are platelets?
Small cells that are involved in blood clotting and are produced in bone marrow
What are the statistics of blood?
- Human blood is 1/13 of total body mass
- Average male adult is 5-6L
- 50% red blood cells
What is the relationship between Hematocrit and Viscosity of blood?
As Hematocrit % increases so does the velocity of blood
[Hematocrit = the ratio of the volume of red blood cells to the total volume of blood]
Describe the fahraeus-lindqvist effect
The decrease in apparent viscosity that occurs when a suspension, such as blood, is made to flow through a tube of small diameter (observed with blood in tubes less than about 0.3 mm in diameter).
After 0.3mm, the relative viscosity plateaus
Describe what happens in capillary microcirculation
1) At the arterial end of the capillary blood is under high pressure since it has just come from the heart. Hydrostatic (blood) pressure is higher than osmotic pressure of the blood therefore fluid is forced out leaving solutes behind which increases solute concentration of the blood.
[HYDROSTATIC PRESSURE > OSMOTIC PRESSURE]
2) At the capillary end, blood pressure is very low since blood has been diverted to many capillaries. Osmotic pressure is relatively high as well as solute concentration.
3) Since OSMOTIC PRESSURE > HYDROSTATIC PRESSURE at the venule end fluid moves back into capillaries and blood become dilute once again (around 90%) due to osmotic pressure. The other 10% enters the lymphatic vessels which eventually merges with the circulatory system
4) Midway along the capillary, where blood pressure is lower, hydrostatic and osmotic pressure cancel each other out & there’s no net movement of water so solutes diffuse according to their concentration gradients (H2O, C6H12O6, O2 diffuse out & waste substances diffuse in)
What parts of the body are involved in the circulation of blood?
- Aorta & Pulmonary artery
- Arteries
- Aterioles
- Capillary
- Venules
- Veins
- Vena cava
What are some statistics of the heart?
- Size of fist
- 80 cm3 in each heart beat
- 70 beats per second
- 5.5 liter/minute in rest
- 25 liter/minute during intense activity
- 26.5 cm/sec (VELOCITY IN AORTA)
- 0.07 cm/sec (VELOCITY IN CAPILLARIES)
What has a larger vessel diameter, Arteries or Capillaries?
Arteries
What has a larger total cross-sectional area of vessels, Arteries or Capillaries?
Capillaries
What has a higher average blood pressure, Arteries or Veins?
Arteries
What has a higher velocity of blood flow, Arteries or Capillaries?
Arteries
Average blood pressure varies in limits between of:
0-100 torr
Bernoulli’s principle applies to both _________ and _________
liquids & gases
What is blood moved through the vascular system by?
Pressure gradients created by the heart
What does Farhaeus-Lindqvist describe?
Blood viscosity decreases with decrease of diameter of vessels
What does friction between the blood and vessel walls cause?
Peripheral resistance
