pressure and flow in arteries and veins

Question 1

How to measure pressure in the arteries

Answer 1

Use a stethoscope to measure Koroktoff sounds
Systole= tapping sound
Diastole= muffling sound
MAP= 120/80 mmhg

Question 2

what does the MAP depend on?

Answer 2

• stroke volume: greater volume of blood into aorta
• nature of arteries: elastic fibres- prevents the systole and diastolic pressure getting too high/low
• TPR: effects fall
• velocity of ejection; if you push blood out faster you will increase the pressure

Question 3

Changes in pressure across the vessels

Answer 3

1- aorta maintains a high pressure due to elasticity (95-90 mmhg)
2- arteries maintain high pressure to get blood out to tissues (90-40 mmhg)
3- by capillaries the pressure is low which is required as they are thin walled and would explode otherwise
4- blood is returned to the heart via the veins and venues by the systemic filling pressure ( 20-5 mmhg)

N.B the pulmonary circulation pressure is 1/5 of the systemic as the right side of the heart is 1/5th left

Question 4

what does velocity of the blood depend on and where is it highest?

Answer 4

depends on cross sectional area
cross section is highest In capillaries and lowest in aorta.
velocity of blood is highest in capillaries and lowest in aorta
higher in veins than arteries

Question 5

what affects blood flow back to the heart in the veins

Answer 5

veins are elastic and distensible so can strongly be effected by external factors

• gravity: adds 80mmg to lower legs making pressure in feet 100mmg and subtracts 40mmhg to head- making pressure in head -20mmg.
• systemic filling pressure
• respiratory pump: when inhalation occurs- pressure in thorax becomes negative- pressure in abdomen increases. pressure gradient helps return blood to the heart
• skeletal muscle pump: skeletal muscle contracting helps squeeze blood from veins- valves stops blood flowing back- can lead to build up of blood
• venomotor pump: smooth muscle around veins contracting increases capacitance

Question 6

what happens when you inhale deeper and faster?

Answer 6

blood returned to the heart faster
Decrease Stroke volume- stroke volume is dependant on EDV
When heart rate is increased then the rapid filling time is cut into so EDV decreases

Question 7

what effect can gravity have on pressure in the vessels?

Answer 7

original pressure in head and feet = 20mmhg

• venous distension - pooling of blood in legs can lead to varicose veins and thrombosis when static exercise is carried out
• Collapse of jugular vein- pressure in blood column lower than atmospheric pressure so collapses- can help detect central venous pressure i.e. when bulging veins then pressure is high