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systemic blood pressure
- when fluid flows through closed system it is under pressure
- closer to the pum has the greatest pressure
- blood flow move along the pressure gradient from nhigh to low pressure
- result is that blood pressure is highest leaving the heart and lowest returing (near zero) dut to length of the cardiovasular system and diameter of vessels
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arteriole pressure depends on
- how much elastic arteries cn be strecthed
- volume of blood forced through them
- the pressure is not constant due to heart beat
- as ventricles contract and eject blood the arteries stretch
- this causes an increase in pressure (sytole pressure)
- blood flow away from heart because of difference of pressure
- during ventricular distole similunar valves shut to prevent the back flow into the heart
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elastic recoil in the aorta propels
- blood forward
- the kinetic energy used to stretch aorta temporarily stored as potential
- this energy is conveted back into kinetic (blood moving)as aorta relaxes
- the energy maintains blood flow through arteries during ventricular diastole
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capillary pressure
- large pressure gradient from aorta to arteriols
- blood pressure drops to 35- 40 mmhg before entering capillaries
- at the end of capillaries pressure drops to 20 mmhg
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why is low pressure required in capillaries
- capillaries are very thin walled and cant handle high pressure and will burst if pressure is to high
- capillaries are premeable to fluid even at low pressure
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edema
swelling of tissue due to excess fluid in hands, feet, etc swells up
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venous pressure
- pressure is steady not palstitle
- pressure gradient is low
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factors aiding venous return
- respiratory pump
- muscular pump
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muscular pump
- squeaze veins and pushes blood to the next area and backflow is prevented by valves(acts as elevators)
- skeletal muscles relax and conctract forcing blood along (milking)
- blood cannot flow backwards due to valves
- most important of the two mechanism(respiratory pump and muscular)
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3 factors of maintaining blood pressure
- cardiac output
- peripheral resistance
- blood volume
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cardiac output
- change in heart rate
- change in stroke volume
- change in both
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blood volume
- change due to anything you drink or eat
- under kidney control
- can remove access fluid if volume is to great
- cannot add fluid back if there has been loss, but can onlyu prevent further loss
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body loses water by
- sweat
- breathing
- urine- the only one body can prevent from losing
- defication
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peripheral resistance
most important means of controlling blood pressure
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peripheral resistance is altered by
- changing in diameter of blood vessels(vasocontriction or vasodiliation)
- distribution of blood between organs
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what pathways are used for distribution of blood between organs in the peripheral reisitance
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vasomoter center
- located in cardiovasular center of medulla oblongata
- trasmits nervous impulse along motor nerves to smooth muscles linning blood vessels
- muscles are always slightly constricted (vessel tone)
- increase in firing rate causing (vasconctriction)
- decreae in firing rate causes muscles to relax (vasodialation)
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barorecptor initiated reflex
- pressure receptors located in cartotids, aorta, and large elastic arteries of throat and thorax
- increase in pressure causes receptors to signal to vasomtor center resulting in vasodilation (bp decrease)
- also sends message to cardiac center to cause reduction in heart rate
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baroreceptor reflex
- decrease in bp causes oppposite reaction
- receptor sends singals to vasomotor to cause vasocontriction
- this cause an increase in bp
- system helps protect body from rapid change in bp such as occur during standing
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chemoreceptor initiated reflex
- respond to change in o2, co2, and ph levels
- receptors are located in the carotids and aortic arch
- low o2, high co2, or low ph sends signlas to vasomoter center to cause vasoconstriction
- increase in bp speeds blood to heart and lungs
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chemical control
epihephrine and norepinephrine
- secreated by adrenal medulla
- part of sympathetic nervous system
- affects heart by increasing cardiac output
- causes vasoconstriction of arteriols and blood vessels suppluing digestive organs
- causes vasodialtion in skeletal and cardiac muscle
- cause an over all increase in bp
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renin- angiotensin- aldosterone (raas)
- involved in maintaine bp and blood volume
- response to decrease in blood volume
- vasoconstriction of aretioles
- increase water and salt reabsorption
- functions to increase overall bp
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total length of the blood vessels
- as length increases so do resistance
- stays relatively constant
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characteristic of blood vessels diameter
- not constant
- most important factor in determing resistacne
- smaller in diameter, the greater the resistance
- ristance is proportional to the 1/radius to the 4th power
- more fluid in contact with the walls of the blood vessels
- capiliaries have the greates resistance(smallest) and large vessels have low resistance (aorta)
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how is blood flow directly related to the blood pressure
the higher the pressure the higher the flow
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how is flow negativly related to resistance
- flow go down whe resistance increases
- flow increases whe resistance decreases
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