Blood Pressure and Ohms Law PDF

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These notes talk about Ohms Law and Blood Pressure in the body. ...

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Blood Pressure and Ohms Law Blood Pressure: hydrostatic force exerted by the blood on the vessel wall Determined by 2 factors: - Cardiac output: volume of blood each ventricle pumps every minute o Influenced by heart rate (#beats/min) AND stroke volume (amount of blood pumped per contraction) o Normal: 5L/min (volume of basketball) -

Resistance: factors blood has to overcome to push through the circulatory system o Aka: total peripheral resistance Blood pressure = Cardiac Output X Resistance Blood Pressure = (Heart Rate x Stroke Volume) x Resistance

Ohm’s Law: I =

-

Pressure = flow x resistance

Arterioles

V/R are mainly resistors

Blood Flow rate: vol/time always same in closed system, fixed diameter - If you pinch, same flow rate - If you close it completely, flow rate is 0 Pressure: moves from high to low Resistance: Adding resistance would increase pressure before the resistance and decrease pressure after resistance - Resistance is highest in vessels where blood pressure decreases the most, curve is steepest - Resistance usually higher in arterioles (contraction of smooth muscle) Q: opening a faucet: directly lowers resistance (opening a faucet increases the radius of the tube through which water can flow) and indirectly increases flow

Q: if arteriole resistance increases from 1 to 3, but pressure does not change, then flow to a downstream capillary bed will_____________________. Pressure = flow x resistance 1=1x1 1=?x3 ? = 1/3

Decrease to 1/3 - This can be happening in your gut, liver, intestine as you are exercising - Because flow should increase in skeletal muscle and decrease in rest Systemic circuit: Heart  oxygenated blood  target tissues in arteries  arterioles  capillaries  gas and nutrients exchanged in capillary beds  venules  veins deoxygenated blood  heart Blood Flow at rest: 5L/mon - Digestive system (gut and liver): 20 -25% - Skeletal Muscle: 15-20% - Kidneys: 20% - Brain: 15% - Heart: 4-5% - Skin: 4-5% - Bones: 3-5% Body’s organ systems in the systemic circuit are arranged in parallel: blood flows from arteries to either the digestive system or the kidneys or the skeletal muscle, then back to heart - Allows the body to increase blood flow to one system, while reducing blood flow to another system How to change and adjust the distribution of blood flow to meet body’s need? - Vasoconstriction: when vessels leading to one tissue constrict, resistance in those vessels increase and blood flow through those vessels decrease. This allows blood to be diverted to lower resistance vessels which will receive higher blood flow as a result. - When person exercises: cardiac input increases from 5L/min to about 25 L/min. Share of blood to digestive system, kidneys, and brain decrease and share of blood to skeletal muscles increase o What is happening to blood vessels to make that happen?  Squeeze tube, flow goes down. Smooth muscle are controlling the diameter of the vessels going to different tissues (works because they are in parallel) Small change in radius can have large impact on resistance and blood flow Resistance ∝ 1 / Radius4 Flow ∝ Radius4 Ex: blood vessel that is twice the diameter of another vessel has 1/16 times the resistance and 16 times the blood flow Blood Pressure Problem Normal: below 120/80...