Lecture 15 - Pressure Gradients And Blood Flow Flashcards
What is the resistance like within arteries
Low
What do arteries act as in relation to pressure
Pressure reservoirs
What allows for the arteries to hold extra blood after contraction
Elasticity
What explains why arterial blood pressure doesn’t return to zero during diastole
Elastic recoil
What are the major sites of resistance
Arterioles
What are arterioles responsible for
The patten of blood flow distribution and the regulation of the arterial blood pressure
What are capillaries the site of
Gas exchange
What do capillaries determine
The distribution of extracellular fluid between the plasma and interstitial fluid
What is the resistance like in veins
Low
Why is a veins capacity adjusted
To facilitate the flow of blood
What is the outer layer of blood vessels composed of
Collagen and elastin
What do collagen and elastin give blood vessels
Strength and elasticity
Composition of the endothelium blood vessel wall
5% elastic artery, 10% arteriole, 95% capillary and 20% venule
Composition of smooth muscle blood vessel wall
25% elastic artery, 60% arteriole and 20% venule
Composition of elastic tissue blood vessel walls
40% elastic artery and 10% arteriole
Composition of connective tissue blood wall
30% elastic tissue, 20% arteriole, 5% capillary and 60% venule
What is the interaction between pressure, flow and resistance of blood known as
Haemodynamics
In the vascular system how does blood flow in relation to pressure
Blood always flows from a region of high pressure to one of a lower pressure
What is the pressure exerted by a fluid known as
Hydrostatic pressure
What are the units of flow
Volume per unit time
What are the units of pressure difference
mmHg
What is needed to calculate the flow
The pressure between two points and the resistance
What is resistance
A measure of how difficult it is for blood to flow between two points at any given pressure difference
What is known as the measurement of the friction impeding flow
Resistance
What is the driving force of blood
The pressure generated by contractions of the heart
What are the factors that affect the resistance of blood
The viscosity of blood, the vessel length and the vessel radius
What does an increase in viscosity of blood cause
A decrease in flow
What is the main factor that influences resistance of blood
The vessel diameter
What equation states that a two-fold change in radius will produce a 16-fold change in flow
The poiseuille equation
What is Laplace’s law for blood vessels
The pressure within a vessel is equal to the tension in its walls divided by the radius of the vasculature
What does thickness increase in proportion to
Diameter
What is the average internal pressure of capillaries
4kPa
What is the average internal pressure of the aorta
13kPa
What is the radius and wall thickness of the capillaries
4 um and 1um
What is the radius and wall thickness of the aorta
13mm and 20 mm
What does the higher arteriolar resistance cause
A marked drop in mean pressure as blood flows through the arterioles
Why is the drop in pressure in arterioles physiologically important
The pressure gradient helps to drive the blood from the heart to the tissue capillary beds
What do arterioles convert pulsatilla arterial pressure into
Non-fluctuating capillary pressure
What do the walls of arterioles include
A thick layer of smooth muscle
What innervates the thick layer of smooth muscle in arterioles
The sympathetic nervous system
What is the smooth muscular layer sensitive to
Local chemical changes and certain circulating hormones
What is vasoconstriction
Contraction causes a decrease in radius which increases the resistance which causes a decrease in local blood flow
What is vasodilation
During relaxation the radius is increased which decreases resistance which causes an increase in local blood flow
What is the rate of partial contraction in arteriolar smooth muscle known as
Vascular tone
What are the two factors responsible for vascular tone
Myogenic activity and sympathetic activity
Why is vascular tone important
As it makes it possible to either decrease or increase contractile activity
What does a change in contractility of arteriolar smooth muscle cause
A substantial change in resistance to flow in these vessels
