W2 - Blood pressure

blood pressure

differences in BP drive blood flow

• the heart generates pressure in the arteries

• blood flows from high pressure (arteries) to low pressure (veins)

• blood is opposed by resistance

• BP ↓ as it overcomes resistance to drive blood flow

• BP is pulmonary circulation (↓P) is much lower than in the systemic circulation (↑P)

Arterial blood pressure

• BP in elastic arteries is pulsatile due to the action of the heart

• gives rise to two diff. pressures in the arteries

• systolic pressure:

  • peak pressure in the large arteries when ventricles contract

  • normal range 95-140 mmHG (avg. 120 mmHg)

• diastolic pressure:

  • lower presser in the arteries due to ventricular relaxation

  • normal range 60=80mmHg (avg, 80 mmHg)

Pulse pressure

• throbbing sensation associated with a “pulse”

• waker as move away from the heart

• systolic pressure - diastolic pressure

  • 120mmHg = 80mmHg = 40 mmHg

Mean arterial pressure (MAP)

• average pressure in arteries over cardiac cycle

• a better indication of perfusion of tissue

• average between systole and diastole

  • MAP = diastolic + (1/3 x pulse pressure)

  • MAP = 80mmHg + (1/3 × 40) = 93mmHg

Capillary BP

• changes as move through the capillary bed

  • 35mmHg at arterial end

  • 15mmHg at the venous end

• low pressure is required to prevent damages of thin-walled delicate capillaries

venous BP

• relatively constant, doesn’t change significantly with cardiac cycle

• pressure in venules/veins - 15mmHg

• pressure in vena cava = approaching 0mmHg

• small pressure gradient

• how does blood return to the heart

  • muscular pump (skeletal msucle)

  • respiratory pump (pressure changes in thorax and abdomen)

  • valves to prevent backflow