Structure and Function of Blood Vessels Flashcards
What are the 2 types of circulation that form the 2 pumps of the heart
Pulmonary circulation - the first pump properly the blood through the vessels in the lungs
Systemic circulation - the second pump propels blood through the vessels in other tissues of the body
What are the roles of the arterioles, capillaries and venules
Arterioles - regulates blood flow and pressure
Capillaries - nutrient and waste exchange
Venule - allow deoxygenated blood to return to from capillaries to the veins
What is the function of the CVS
- Rapid supply of oxygen and nutrients
- Rapid waste removal
- Control system of body temperature and hormone distribution
What drives blood flow
- Pressure gradient (DeltaP)
- heart raises blood pressure in arteries and vein blood pressure is lower
What is darcy’s law
Flow (dotted Q) = Delta P/Resistance
What causes flow resistance
Resistance is due to friction between blood and the internal surface of the vessel and between blood constituents
What is resistance inversely proportional to
The fourth power of the vessel radius
How would a small increase in vessel radius affects flow resistance
Large decrease in resistance
How would a small decrease in vessel radius affect flow resistance
Large increase
What are the units of BP
Force per unit area
Where does the main pressure drop come from in the blood vessels
The arterioles - the highest resistance vessels
Describe laminar blood flow
All particles in the fluid are flowing parallel to the wall of the tube, particles at centre flowing fastest, particles at the edge have almost no velocity
Describe turbulent blood flow
Particles follow an irregular pattern and may develop whirlpools in the blood vessels.
Sets up vibrations in the blood vessel wall and makes noises which are called murmurs
What is the critical velocity relating to blood flow
This is the blood flow velocity at which there is a transition from laminar to turbulent flow
What factors can increase the likelihood of turbulent flow
Increased flow velocity
Increased vessel radius
Increased blood density
Decreased blood viscosity
What is reynolds number and what is its equation
This number shows the tendency towards turbulence
Re = (v x L x p(density))/n (viscosity)
What is the main thing that determines the viscosity of the blood
The haematocrit, which is the percentage of blood volume that is occupied by the red blood cells
How can viscosity be expressed
As relative viscosity, relative to water
What is the relative viscosity of blood plasma and normal blood
Plasma = 1.3 Blood = 2.4
What are the 3 layers of the blood vessel walls, except capillaries
Tunica Intima (inner layer) Tunica Media (middle layer) Tunica Adventitia (outer layer)
Describe the structure and function of the Tunica Intima
Structure - consists of endothelial cells
Function - provides a barrier between blood and the rest of the vessel, filtration controls the passage of white blood cells
What is the structure and function of the Tunica Media
Structure - Two layers of elastic tissue, the internal and external elastic laminae that sandwich a layer of smooth muscle
Function - source of mechanical strength and the smooth muscle is a means of altering the vessel diameter
What is the structure and function of the Tunica Adventitia
Structure - layer of connective tissue containing fibrous tissue
Function - holds the blood vessel in place, provides mechanical strength, prevents over-expansion
What is the vasa vasorum and where is it found
the small blood vessels that supply the walls of the larger blood vessels with nutrients and this runs through the connective tissue
What are the tissues that make up large arteries and what is their use
Made of both fibrous (collagen) and elastic tissue.
Elastic tissue so the arteries can expand and contract during the cardiac cycle.
What are the tissues that make up the small arteries and what are these arteries involved in
Less fibrous tissue but has more smooth muscle than large arteries.
More involved in circulatory control mechanisms.
What is the main component of arterioles and what are they used for
smooth muscle is a major component so that contraction and blood flow can be regulated
What are capillaries made up of
Single layer of endothelial cells, no tunica media or tunica adventitia
What is the role of capillaries
Site of exchange of nutrients and waste products between the circulation and interstitial fluid that surrounds the cells
What are venules made up of and what is their role
Have an endothelial lining together with a small amount of fibrous tissue
They are an important site of movement and water (lymphatic drainage)
What tissues main up the veins
Elastic and fibrous tissues and also smooth muscle but in small amounts compared to arteries.
What is the critical closing pressure
If the pressure gradient across the wall of a blood vessel falls below a certain limiting value then the vessel will collapse.
The transmural pressure at which flow ceases is the critical closing pressure.
In other words there has to be a certain pressure inside the vessel in order to keep it inflated
In healthy individuals why are vessels constricted and dilated
This can be done to divert blood flow to match metabolic needs
