Introduction to the CVS L5

Question 1

what are the 3 main functions of the CVS

Answer 1

1. controlled and continuous flow of blood
2. homeostasis
   - Transport of nutrients
   - Transport of metabolic products
   - Heat distribution
   - Defence (immunological)
   - Regulation of pH and osmolality
3. transport of hormones

Question 2

how many pumps are there in the CVS

Answer 2

2

Question 3

what are the two circulation systems
- describe

Answer 3

1. systemic
   - high pressure, blood transports around body
2. pulmonary
   - low pressure, blood transport to lungs

Question 4

how is the flow of CVS describes

Answer 4

unidirectional
- ensured by heart valves

Question 5

is there a difference in the volume of blood each system receives

Answer 5

no
- each system receives same amount blood
- organ circulations are generally in parallel

Question 6

describe the structure of the heart

Answer 6

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

Question 7

describe the vessels of the heart

Answer 7

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)

Question 8

describe AV valves

Answer 8

between atria and ventricle
in right side they are tricuspid
in left side they are bicuspid/ mitral

Question 9

describe SL valves

Answer 9

in right side they are pulmonary
in left side they are aortic

Question 10

describe the valves when heart is relaxed

Answer 10

AV open, SL closed
blood empties atria and ventricles

Question 11

describe valves when heart contracts

Answer 11

AV closed, SL open
blood empties ventricle via artery

Question 12

define
1. stoke volume
2. cardiac output
3. venous return

Answer 12

1. volume of blood pumped by ventricle
   - average is 75mL at rest
2. total volume of blood pumped out per ventricle per minute
   - dependant on heart rate
3. amount of blood returning to the heart
   - under steady conditions, VR = CO

Question 13

what is the equation for cardiac output

Answer 13

cardiac output= stroke volume X heart rate

Question 14

describe the systemic vascular system

Answer 14

1. arteries
   - high pressure elastic vessel
   - used for distribution
2. arterioles
   - high resistant vessel which controls blood flow to tissues
   - have a lot of smooth muscle
3. capillaries
   - thin walled vessels arranged in parallel used for exchange
   - no smooth wall
4. veins
   - low pressure capacitance vessels with one way valves
   - used for collection and storage

Question 15

what drives blood flow through each circulation

Answer 15

a blood pressure gradient

Question 16

what is the equation for pressure gradient

Answer 16

pressure gradient/ ΔP = P1(high pressure value) - P2 (low pressure value)

Question 17

what is the measure used for gradient pressure

Answer 17

mm/Hg

Question 18

what is the relationship between blood pressure and blood flow

Answer 18

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

Question 19

describe the mean pressure in the systematic circulation

Answer 19

highest pressure in aorta, lowest in vena cava
- Blood flows out of the heart (highest pressure) into a closed loop of vessels (lower pressure)

Question 20

what happens to the pressure of blood in motion

Answer 20

The pressure of a fluid in motion decreases with distance, due to friction, as blood travels through the vessels - pressure gradient

Question 21

what is pressure in large arteries like in systemic circulation
what does SP and DP stand for

Answer 21

pulsatile
SP: max systolic pressure
DP: min diastolic pressure

Question 22

what is pulse pressure

Answer 22

difference between SP and DP

Question 23

what happens to the pulses in veins

Answer 23

they decrease

Question 24

what is mean arterial pressure

Answer 24

pressure averaged over time

Question 25

give Darcey’s law

Answer 25

blood flow= ΔP/ resistance

Question 26

what parameters determine resistance

Answer 26

1. length of blood vessel (relatively constant)
2. radius of blood vessel
3. viscosity of blood (relatively constant) (eta: η)

Question 27

give Poiseuille’s Law
(for a single tube)

Answer 27

flow= (ΔP)pie r4/ 8 η L
r: radius of blood vessel
η: viscosity of blood
L: length of blood vessel

Question 28

what is the most important factor short term regulation of Resistance and why

Answer 28

radius due to 4th power effect
- the other values tend to be constants or change very little

Question 29

what happens to resistance and flow if radius doubles at constant pressure gradient

Answer 29

resistance (R) decreases 16 fold and flow increases 16 fold

Question 30

what is blood velocity

Answer 30

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

Question 31

what is the equation for blood velocity

Answer 31

Velocity = Blood Flow/ X-SA (X-SA= πr2)
-Therefore the narrower the vessel the greater is the velocity

Question 32

why is blood velocity lowest in capillaries when they are the most narrow

Answer 32

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

Question 33

why is it functionally good that capillaries have low velocity

Answer 33

slow down for efficient gas exchange