PHYSIOLOGY - Circulatory System Flashcards
What % of total blood volume is in the systemic circulation when at rest?
84%
What % of total blood volume is in the heart and lung circulation when at rest?
16%
What is micro circulation ?
Arterioles, capillaries and venues
What are conduits?
Elastic arteries - i.e aorta and other large arteries
What are resistance vessels?
Muscular arteries i.e arterioles
Arterioles are not very well innervate t/f?
False. They are well innervated
What are exchange vessels?
Capillaries
Is the pressure higher in the arterial system or the venous system ?
Arterial system
Which contains most of the blood in the circulatory system, the veins or the arteries?
Veins - they act as a blood reservoir
What are capitance vessels?
The veins. They act as blood reservoirs
How is venous return to the heart assisted?
- Skeletal muscle pump
- Contraction of diaphragm
Which have a wider diameter, veins or arteries?
Veins
How many capillaries are there in an average human?
3 billion
Veins are highly distensible t/f?
True.
What allows blood to be stored in the venous system?
The highly distensible veins
Define blood pressure
The pressure of blood in the heart/circulatory system exerted outwards onto a unit are of the vessel wall
What are the 2 physical laws of blood flow and pressure?
- Blood flows from a region of high pressure to a region of low pressure ( P1-P2 = ΔP )
- The rate of blood flow is directly proportional to ΔP
What is the normal blood pressure in the veins which are emptying into the heart?
0mmHg
What is normal aortic pressure?
90mmHg
What is ΔP for the systemic circulation and how is it calculated?
ΔP = 90mmHg
Calculated by subtracting vena cava pressure from aortic pressure
What is normal ΔP for the pulmonary circulation?
20mmHg
What does resistance to blood flow depend on?
- Length of blood vessels
- Radius of blood vessels
- Viscosity of blood
What is blood viscosity ?
The resistance to blood flow caused by blood cells rubbing against each other
Describe the relationship between rate of blood flow (F) and resistance
F is inversely proportional to resistance
F = ΔP/R (Ohm’s Law)
What symbol denotes resistance? (poiseuille’s law)
R
What symbol denotes length of blood vessels? (poiseuille’s law)
L
What symbol denotes viscosity of blood? (poiseuille’s law)
η ( greek letter ‘eta’ )
What are the major regulators of blood flow?
- mean arterial pressure
- vascular blood vessel diameter
- blood viscosity
Where does most resistance to flow originate and what % ?
65% in small arterioles
Explain the fourth power law.
Small changes in diameter of a blood vessel can result in large changes in resistance (r^4 where r is radius of the blood vessel )
What component of blood highly affects the viscosity of blood?
Haemocrit
Who normally has a higher haemocrit, males or females?
Males
What is the viscosity of normal blood?
Roughly 3 times that of water
What can happen to viscosity, and blood flow in someon with polycythaemia?
- blood viscosity can dramatically increase
- this increases resistance and blood flow can be compromised
- heart has to pump harder to overcome the resistance
- this means that blood flow to some tissues may be compromised
What can happen to blood viscosity in somebody with sever anaemia ?
It can drop to 1.5 times the viscosity of water
What happens to the blood flow of someone with severe anaemia and what are the effects?
- blood flows far faster than normal due to decreased resistance
- increased venous return and cardiac output
- hypoxia causes blood vessels to dilate, further increasing cardiac output
- there is a sustained increase in the pumping workload of the heart.
How can you increase ΔP?
- increase in flow
- increase in resistance
What is the definition of compliance/capitance?
The volume of blood which can be stored in a blood vessel for each mmHg pressure rise
What is the equation for compliance ?
Compliance = distensibility x volume
Ca = ΔV/ΔP
What determines distensibilty and thus compliance ?
- Quantity of elastin fibers in the vessel wall
- Wall thickness
How do large arteries act as pressure reservoirs?
- during systole, ejected blood causes the elastic walls of the aorta to expand
- during diastole, the walls recoil, maintaining blood flow through vasculature
Blood flow is pulsation t/f?
False. It is continous due to the hydraulic filter created by aorta
Does the elastin content of your arteries stay the same throughout your life?
No. Elastin replaced with collagen as you age
What happens when the walls of arteries become rigid?
The walls cannot distend
Pressure increases during systole
This increases the afterload
Do compliant artieries increase/reducer the workloads of the heart?
Reduce
Do rigid artieries increase/reducer the workloads of the heart?
Increase
How are b.p measurements quoted?
Systolic pressure / diastolic pressure
Why is the mean arterial pressure calculated ?
Because arterial pressure is pulsatile
How do you calculate MAP?
MAP = diastolic p + 1/3(systolic-diastolic)
Why is the value of MAP closer to diastolic pressure?
Diastole lasts twice as long as systole
What is hypertension?
elevated b.p
What % of adults have hypertension?
20%
What are the two types of hypertension?
- Essential hypertension
- Secondary hypertension
What is the cause of essential hypertension?
Mainly unclear- could be diet, genetics etc.
What % of hypertension cases are essential hypertension?
95%
What causes secondary hypertension?
It results from another condition e.g renal disease
- chronically elevated salt and water reabsorption in the nephron increases blood volume , therefore raising b.p
Why is hypertension bad for health?
- causes long term damage to heart, kidneys, blood vessels
- risk factor for heart attack and stroke
Why does hypertension cause damage to the heart?
The heart must contract stronger in order to overcome teh increased afterload
Why does hypertension put someone at risk for a stroke/heart attack ?
- promotes formation of atherosclerotic plaques
How do you calculate pulse pressure?
Systolic pressure - diastolic pressure = pulse pressure
When is the dicrotic wave visible on the blood pressure wave?
During the diastolic phase of a young healthy person
What causes the dicrotic wave?
- recoil of blood from closed aortic valve
- reflection of systolic pressure wave back from small arteries in the lower body
What causes pulse pressure ?
- LV contraction creates a pulse of systolic pressure as blood isi pushed into arteries.
- the pulse is transmitted through the elastic walls of large arteries
- velocity of pulse transmission is 15x the velocity of blood flow
- the pressure changes the diameter of the artery so it can be felt by palpitation
At rest what % of blood is stored in the veins?
64%
What is the term used to describe the fact that aorta maintains blood flow by recoiling?
Hydraulic filter
Why does hypertension increase risk of atherosclerotic plaques?
It damages the endothelial lining of the blood vessels which causes and increased tendency fro atherosclerosis
