4F- Blood Pressure

what is blood pressure

• pressure exerted by blood on the inside walls of a vessel

  • caused by contraction of the ventricles

  • highest in aorta (because its close to the heart)

    • during rest- 120mmHg during systole/ 80 during diastole

• pressure falls steadily in systemic circulation with distance from left ventricle

  • 35 mmHg entering the capillaries

  • 0 mmHg entering the right atrium

what affects venous pressure, and does it increase or decrease it

1. inspiratory movements - increases

2. skeletal muscle pump - increases

3. blood volume - increases

4. activity of sympathetic nerves of veins - increases

what affects venous return and how does it affect it

venous pressure - increases

what increases atrial pressure and how does it affect it, also where does this happen

venous return - increases - right atrium

what affects end-diastolic ventricular volume and how does it affect it, also what is another name for it

atrial pressure - increases - preload

what affects stroke volume and how does it affect it

1. afterload - decreases

2. end-diastolic ventricular volume - increases

3. plasma epinephrine - increases

4. activity of sympathetic nerves to heart - increases

what affects heart rate and how does it affect it

1. activity of sympathetic nerves to heart - increases

2. plasma epinephrine - increases

3. activity of parasympathetic nerves to heart - increases

what affects cardiac output and does does it affect it

1. stroke volume

2. heart rate

SV * HR = cardiac output

what is afterload

• the pressure that must be overcome before a semilunar valve opens and blood can be sent to pulmonary and systemic circulation

what is preload

• the degree of stretch of the heart before contraction (frank-starling law)

• is proportional to EDV

  • more stretch = more blood comes out

what is contractility

the forcefulness of contraction of the ventricle fibers, depends on the calcium kinetics and agents that increase or decrease the availability of calcium on sarcolemma

what is the way that venous return affects stroke volume

• volume of blood flowing back to the heart form the systemic veins

  • depends on pressure difference from venules (16 mmHg) to right atrium (0 mmHg)

  • pressure difference between venous side to the right heart normally is enough to drive blood back to the right heart

• two extra mechanisms

  • muscle pump

  • respiratory pump

what is the muscle pump action

the skeletal muscle contracts which helps to drive blood back to the RH through a milking action

• why when you suddenly stop after running for a long time you fall down bc you take away the pump

what is the respiratory pump

during inhalation the diaphragm is pushed down and there is a pressure difference between the abdominal (high) to the thoracic cavity (low)

• this drives blood back to the RH

how is the velocity of blood flow and the CSA of blood vessels related

inversely

ex. capillaries have the greatest CSA but the lowest blood velocity

what is the cross sectional area of blood

the amount of space it takes up

what affects arteriolar radius and how does it affect it

1. sympathetic vasoconstrictor nerves - decreases

2. plasma epinephrine and angiotensin - decreases

what affects blood viscosity and how does it affect it

hematocrit - increases

what affects total peripheral resistance and how does it affect it

1. arteriolar radius - decreases

2. total blood vessel length - increases

3. blood viscosity - increases

what affects mean arterial pressure and how

1. cardiac output

2. total peripheral resistance

cardiac output * total peripheral resistance

what does not have a direct relationship with BP

1. activity of parasympathetic nerves to heart

2. sympathetic vasoconstrictor nerves

3. arteriolar radius

4. plasma epinephrine and angiotensin

what is systemic vascular resistance (SVR) / total peripheral resistance (TPR), and what are they influenced by

• sum of all friction between blood and the walls of vessels

• influenced by;

  • size of lumen (diameter, VC, VD)

    • most influential

  • blood viscosity

  • total blood vessel length

what causes an increase in blood vessel length

growing or gaining a lot of weight

how does this change in the diameter of the lumen affect flow

the smaller the diameter the greater the resistance the less the blood flow the greater the BP

how would a decrease in muscle pump activity influence MAP and when would this happen

• this would decrease venous pressure, venous return, arterial pressure, EDV, SV, Q, and MAP

• this would happen if you were exercising and stopped thus taking away the muscle pump

how would an increase in blood volume influence MAP and how might this happen

• an increase in BV would increase venous pressure, venous return, arterial pressure, EDV, SV, Q, and MAP

• this might happen if a person injected plasma into their blood or if they were over-hydrated

how would a decrease in hematocrit influence MAP, how would this happen

• a decrease in hematocrit means that the blood is less viscous, this would decrease TPR and MAP

• One way to decrease your hematocrit is to lose RBC’s

how would epinephrine influence MAP, what is an example

• epi increase MAP through increasing HR and SV which increase Q and MAP, it also decreases arteriolar radius with increases TPR and MAP

• an example is a stressful event which increases epi