Introduction to the CVS L5 Flashcards
what are the 3 main functions of the CVS
- controlled and continuous flow of blood
- homeostasis
- Transport of nutrients
- Transport of metabolic products
- Heat distribution
- Defence (immunological)
- Regulation of pH and osmolality - transport of hormones
how many pumps are there in the CVS
2
what are the two circulation systems
- describe
- systemic
- high pressure, blood transports around body - pulmonary
- low pressure, blood transport to lungs
how is the flow of CVS describes
unidirectional
- ensured by heart valves
is there a difference in the volume of blood each system receives
no
- each system receives same amount blood
- organ circulations are generally in parallel
describe the structure of the heart
top of the heart called the base
bottom of the heart called apex
top chambers are atria
bottom chamber are ventricles
atrioventricular valves between atria and ventricle
semi lunar valves between artery and ventricle
describe the vessels of the heart
left side of heart
- pulmonary vein (from lung)
- aorta (to body)
right side of heart
- inferior and superior vena cava (from body)
- pulmonary artery (to lung)
describe AV valves
between atria and ventricle
in right side they are tricuspid
in left side they are bicuspid/ mitral
describe SL valves
in right side they are pulmonary
in left side they are aortic
describe the valves when heart is relaxed
AV open, SL closed
blood empties atria and ventricles
describe valves when heart contracts
AV closed, SL open
blood empties ventricle via artery
define
1. stoke volume
2. cardiac output
3. venous return
- volume of blood pumped by ventricle
- average is 75mL at rest - total volume of blood pumped out per ventricle per minute
- dependant on heart rate - amount of blood returning to the heart
- under steady conditions, VR = CO
what is the equation for cardiac output
cardiac output= stroke volume X heart rate
describe the systemic vascular system
- arteries
- high pressure elastic vessel
- used for distribution - arterioles
- high resistant vessel which controls blood flow to tissues
- have a lot of smooth muscle - capillaries
- thin walled vessels arranged in parallel used for exchange
- no smooth wall - veins
- low pressure capacitance vessels with one way valves
- used for collection and storage
what drives blood flow through each circulation
a blood pressure gradient
what is the equation for pressure gradient
pressure gradient/ ΔP = P1(high pressure value) - P2 (low pressure value)
what is the measure used for gradient pressure
mm/Hg
what is the relationship between blood pressure and blood flow
blood flow is proportional to pressure gradient but is not the absolute pressure themselves
- flow of two different vessels can be the same despite them having different pressures
describe the mean pressure in the systematic circulation
highest pressure in aorta, lowest in vena cava
- Blood flows out of the heart (highest pressure) into a closed loop of vessels (lower pressure)
what happens to the pressure of blood in motion
The pressure of a fluid in motion decreases with distance, due to friction, as blood travels through the vessels - pressure gradient
what is pressure in large arteries like in systemic circulation
what does SP and DP stand for
pulsatile
SP: max systolic pressure
DP: min diastolic pressure
what is pulse pressure
difference between SP and DP
what happens to the pulses in veins
they decrease
what is mean arterial pressure
pressure averaged over time
give Darcey’s law
blood flow= ΔP/ resistance
what parameters determine resistance
- length of blood vessel (relatively constant)
- radius of blood vessel
- viscosity of blood (relatively constant) (eta: η)
give Poiseuille’s Law
(for a single tube)
flow= (ΔP)pie r4/ 8 η L
r: radius of blood vessel
η: viscosity of blood
L: length of blood vessel
what is the most important factor short term regulation of Resistance and why
radius due to 4th power effect
- the other values tend to be constants or change very little
what happens to resistance and flow if radius doubles at constant pressure gradient
resistance (R) decreases 16 fold and flow increases 16 fold
what is blood velocity
Blood flow (rate) is volume per minute (e.g. mL/min = cm3/min)
Blood velocity is distance travelled per minute (e.g. cm/min)
Blood velocity depends on Flow and cross-sectional area of vessel
what is the equation for blood velocity
Velocity = Blood Flow/ X-SA (X-SA= πr2)
-Therefore the narrower the vessel the greater is the velocity
why is blood velocity lowest in capillaries when they are the most narrow
because of the parallel arrangement of capillaries in a tissue, so you have to consider the Total X-CA of all the capillaries in that vascular bed, not just X-SA of one capillary. Total X-SA is greatest in capillaries
- baso imagine lots of capillaries close together make one massive vessel
why is it functionally good that capillaries have low velocity
slow down for efficient gas exchange
