Regulation of Arteriolar Resistance + pressure and flow Flashcards
How is arterial pressure measured
auscultation of korotkoff (blood flow) sounds using Sphygmomanometer (cuff) and stethoscope
Describe what you should hear in a healthy person
at rest - you should not hear anything as should be smooth laminar flow pressure above systolic pressure - silence as blood flow is cut off pressure just below systolic pressure - tapping sound - large obstruction to blood flow pressure below systolic pressure - more blood moving through arteries - more turbulent so longer thumping sounds (less constriction) pressure = diastolic pressure - muffled sounds as the cuff is still constricting the artery a little as pressure decreases below diastolic - normal smooth laminar flow again so should be silence again
What is systolic pressure?
pressure of the blood in the arteries when the heart pumps/contracts. It is the higher of the two numbers in the blood pressure.
What is diastolic pressure?
pressure in your blood vessels when your heart rests between beats
Describe pressure and flow in arteries
elastic arteries act as pressure reservoir as ventricular relaxation occurs, the energy being stored in the walls of the aorta is released and this pushes blood out through the arterioles
why would it be hard to push blood through arterioles?
if the arterioles are constricted - increased total peripheral resistance
what on average is normal blood pressure values?
120/80 however now looking a bit higher in our current ageing population ie 130/80
arterial pressure increases with what?
age and individually
describe the variety in pressure within the vascular tree
pressure falls throughout the vascular tree aorta - pressure stays high due to elastic walls retaining it capillaries - very low pressure - thin walled and fragile
value for the drop in pressure through arteries
95-90 mmHg
value for the drop in pressure through arterioles
90-40 mmHg
value for the pressure difference pushing blood back through the veins to the heart?
20 to 5 mmHg
what does blood flow depend on?
total cross-sectional area ie aorta has the highest velocity of blood flow but there is only one in the body so it has the lowest cross sectional area along with venae cavae. However there are loads of capillaries in the body so these have the highest total cross-sectional area but lowest velocity of flow - allows time for exchange of gases and nutrients
Describe pressure and flow in veins
pressure is low. There is a small decrease in pressure required to push blood back through the veins to the heart. Veins are susceptible to being compressed by pressure but can also expand easily and carry a lot of blood.
what external influences can affect blood flow in veins (5)
- gravity
- skeletal muscle pump
- respiratory pump
- venomotor tone
- systemic filling pressure
How does gravity affect blood flow in veins?
when you stand up blood is pushed down to your feet due to gravity which increases the pressure there. Blood is sucked out of the brain so blood pressure decreases there. Standing up leads to a decrease in EDV, preload, SV, CO and MAP Gravity causes venous distension (dilatation) in legs and venous collapse in the neck (less blood flows through it - jugular vein shouldn’t be visible)
what does gravity not affect?
the driving pressure from arteries to veins
what is orthostatic hypotension
low blood pressure that continues after standing up common in the elderly
what can the height of jugular vein collapse be used to estimate?
central venous pressure
describe pressure and jugular vein
pressure in the vein gets smaller as you go up as gravity is pulling blood down pressure outside the vein is always about 0 so at some point the pressure outside will be higher than inside and this constricts the vein in a healthy person it will collapse below the clavicle
why might you see a healthy person’s jugular vein? for example in a footballer celebrating after scoring a goal
higher BP means higher central venous pressure and a higher point of colla[se in the neck so the JV is visible.
What is the skeletal muscle pump
mechanism that alters venous blood flow Every time you contract the muscle in your leg it pushes blood out of the vein and this blood gets pushed back towards the heart even though it wouldn’t normally. Increased venous return, preload, EDV
in what type of exercise does skeletal muscle pump occur
in rhythmic exercise in static exercise the muscle length doesn’t change - wight lifting
why might a person faint?
if blood is sent to periphery as your EDV gets smaller and smaller.
What is the respiratory pump
when you inhale you draw more blood back to your heart as your diaphragm contracts and pressure decreases in the thorax. This causes an increase in the pressure gradient that is pushing blood back to the heart.
what is venomotor tone?
state of contraction of the smooth muscle surrounding the venules and veins alters blood flow by mobilising capacitance of vessels
what is systemic filling pressure?
pressure created by ventricles and transmitted through vascular tree to the veins changes during exercise
It is an indicator of how full the circulatory system is (i.e. the volume of blood in the system compared to the capacity of the system)
influenced by the vol of circulating blood and the smooth muscle tone in the walls of the venous system (which determines the capacity of the system)
describe the anti-clotting mechanisms of the endothelium of vessels.
blood flows so slowly through capillaries that it is in danger of clotting so your endothelium has to work hard to prevent inappropriate clotting:-
- It stops blood contacting collagen - no platelet aggregation
- produces prostacyclin and NO which both inhibit platelet aggregation and are vasodilators
- Produces tissue factor pathway inhibitor TFPI which stops thrombin production so will stop fibrin from being produced
- Expresses heparin - also inactivates thrombin - natural anticoagulant
- secretes tissue plasminogen activator (t-PA) - plasminogen turns to plasmin and digests clot
define dicrotic notch
a secondary upstroke in the descending part of a pulse tracing corresponding to the transient increase in aortic pressure upon closure of the aortic valve
what are the anacrotic and catacrotic limbs?
the ascending and decending parts of pressure wave
