CVS: introduction Flashcards
Why do we need a CVS?
- Pump blood through lungs and carry oxygen
- Regulate the body temperature
- Transports nutrients to the muscles and organs
- Circulates hormones and immune mediators
- Connection to the lymphatic system
- Human reproduction
What is passive diffusion?
Passive diffusion is the random undirected thermal movement of molecules
Explain how distance affects the rate of diffusion
The time needed to diffuse given distance is proportional to the square of the distance
T ∝ D^2
Where:
T= time
D= distance
Diffusion is mostly efficient is micrometers (um) but NOT in >1mm; therefore it is not suitable for transport throughout the body
What causes blood to flow in the body?
The PRESSURE DIFFERENCE between the aorta (HIGH) and the large veins (LOW)
Output of blood at high pressure creates a pressure difference with distant blood vessels
What is meant by systole?
Systole = contraction
What is meant by diastole?
Diastole = relaxation
die=rest=relax
What is meant by cardiac output?
Volume of blood ejected from the heart per minute
usually 5litres/min
Where does cardiac output go?
- Liver
- GI
- Muscle
- Brain
- Myocardium
- Kidney
and other places
describe why blood flow to the brain and myocardium are important
The brain and myocardium are under perfused; meaning a small drop in perfusion could mean risk of:
→ Angina
→ MI (myocardial infarction)
and Stroke
Name the 3 things that control cardiac output
- Filling pressure (sterling’s law)
- Sympathetic and parasympathetic autonomic nerves
- Chemical factors and hormones (eg- adrenaline)
What is the equation used to calculate cardiac output?
Cardiac output = heart rate x stroke volume
Units: litres/min
Why are blood flow and blood pressure important?
Blood flow and blood pressure are critical for correct bodily functioning. This is because they are linked in the proper distribution of blood.
What is the equation for calculating blood flow?
(Pa - Pv)
Blood flow = ————–
Resistance
Pa= arterial pressure Pv= venule pressure
· This means the higher resistance = less blood flow
· Blood flow is proportional to pressure across blood vessel
- Blood flow is inversely proportional to resistance of blood vessel
Give an example of where blood flow slows down and explain why this happens
Blood flow slows down in capillaries (pulmonary circulation) to allow for gaseous/nutrient exchange to occur
Why is the blood flow slower in the capillaries?
The velocity of blood is much slower in the capillaries to allow for gaseous/nutrient exchange to occur
describe the cross sectional area of capillaries compared to aorta and describe the impact this has on the blood velocity
Capillaries are made up of LOADS of small vessels = large cross-sectional area
Aorta is ONE large vessels = low cross-sectional area
Smaller cross sectional area = blood speed up
Larger cross sectional area = blood slows down
describe the type of circulation used to supply the body organs
Most organs are supplied with blood in parallel dual circulation
what is systemic circulation
Systemic: oxygenated blood from the lungs enter the left side of the heart via the pulmonary veins. This blood can then travel round the body, delivering oxygen to tissues and organs
what is pulmonary circulation
Pulmonary: deoxygenated blood travels from the right atrium to the lungs via the pulmonary arteries
What are the differences between the venous and arterial walls?
Arteries have a THICKER elastic wall to maintain blood pressure
Veins has THINNER elastic walls
Describe the role of the arteries and veins in the flow of blood
Arteries: have a high pressure that ensures blood flows in one direction
Veins: have valves that ensure blood flows in one direction
what is the endothelium in a blood vessel and what is it’s purpose
Endothelium- inner lining of the artery
Produces NO which relaxes the vessel
what is the tunica media in a blood vessel and what is its purpose
Tunica media- smooth muscle walls (circular layers)
Contraction = narrow
In the tunica media, stimulation of alpha-1 adrenoreceptors by NA = vasoconstriction
What happens if the body wants to increase blood flow?
Endothelium NO overpowers the ANS = vasodilation = more blood flow
What happens if the body wants to decrease blood flow?
ANS overpowers NO, and releases NA to stimulate the A-1 adrenoreceptors = vasoconstriction = less blood flow
what is the main function of the arteries
Elastic vessels: ARTERIES
Large arties that accommodate stroke volume AND convert intermittent ejection into continuous flow
what is the main function of the arterioles
Resistance vessels: ARTERIOLES
Control arterial blood pressure and regulates local blood flow
what is the main function of the capillaries
Exchange vessels: CAPILLARIES
Nutrient delivery to cells and tissues for water and lymph formation
Removal of metabolic waste
what is the main function of the venues and veins
Capacitance vessels: VENULES + VEINS
Control the filling pressure and provide a reservoir of blood, so the veins can constrict and send blood to the heart if needed
