Continuous and Intermittent Flow Flashcards
What are the elastic arteries?
the aorta and branches of the aorta
What type of protein allows arteries to stretch?
elastin
Why is collagen important in elastic arteries?
prevents the arteries from distending too far
what happens when the blood enters the aorta in systole?
the elastic fibres stretch to accomodate the stroke volume
When there isn’t a contraction (in diastole) what propels the blood in the aorta?
the recoil of the elastic fibres which provides the blood with kinetic energy and acts as a second pump
What are the roles of the elastic arteries?
distribution of blood, dampening of pressure changes, conversion of intermittent pumping of the heart to continuous flow
Mid-systole, what is energy used for?
- to stretch elastin
- to propel blood forward
What happens at end systole in terms of energy?
elastic energy is stored in elastin
What happens mid-diastole?
elastin recoils and energy is transferred to the blood
What happens at the end of diastole?
elastin returns to its original shape
What is the pulse pressure?
difference between diastolic pressure and systolic pressure
How do you work out the mean diastolic pressure (MAP)?
MAP= DP + (SP-DP)/3
What three factors influence SP and DP and therefore MAP?
- elastin content
- stroke volume ejected into aorta
- total peripheral resistance
What is systolic pressure determined by?
- stroke volume
- aortic/arterial distensibility
- ejection velocity
- diastolic pressure of previous beat
What can you increase to increase SP?
- EDV (preload) leading to increased SV (increased venous return)
- contractility leading to increased SV (exercise, circulating catecholamines)
What are the factors affecting diastolic pressure?
- arteriolar resistance (how easy it is for blood to run away from the aorta)
- vasoconstriction (increase TPR and increase DP)
- atherosclerosis (increases DP) - Aortic/arterial distensibility (reduction in distensibility leads to decrease in DP)
- Heart rate (v high HR increases DP-less time for blood to run off into peripheral circulation and for blood pressure to fall before the next heart beat)
What happens to systolic/dystolic pressure as you age?
- less elastin when you get older
- aorta can not stretch when blood enters so SP increases
- not as much potential energy to keep pressure high so DP decreases
- increased pulse pressure
- MAP stays the same
What happens when you exercise?
- increased SV (increased SP)
- decreased TPR (DP decreased)
- pulse pressure increased
- MAP stays the same
Breathing is an intermittent pump so how is there constant gases in the alveolar space?
- each breath only adds a small volume (0.35L) to the FRC (2.5L)
- as long as the O2 coming into the alveolar space equals the O2 leaving in the blood in the pulmonary capillary and amount of CO2 coming back in the blood to the amount that leaves the lungs. It remains constant
What are the different types of capillary?
- continuous capillaries (in skeletal muscle, tight junctions between cells so substances travel by facilitated transport or simple diffusion)
- fenestrated capillaries (holey) (larger pores) (usually in glomerular capillaries or liver)
What happens to velocity as the cross sectional area of vessels gets larger?
as cross sectional area increases, velocity decreases (overall flow stays the same`)
What types of exchange can capillaries be involved in?
- diffusion
- filtration
What is flow equal to?
flow= velocity x cross-sectional area
What is oncotic pressure?
the hydrostatic pressure you would have to apply to stop fluid moving across a membrane to an area of protein which is stuck there
What are the forces that favour filtration?
- capillary hydrostatic pressure
- interstitial oncotic pressure (under normal circumstances there should be no protein in the interstitial space)
What are the forces that favour reabsorption?
- interstitial hydrostatic pressure (usually low, fluid normally filtered away)
- plasma oncotic pressure
How do you calculate net filtration?
net filtration= Kf x (forces favour filtration)-(forces favouring reabsorption)
Kf= reflection constant (leakiness of capillary)
How doe the plasma oncotic pressure change through the capillary?
it doesn’t, it stays pretty much the same (conc of plasma proteins stays the same)
What happens to the hydrostatic pressure as you move along the capillary?
-hydrostatic pressure decreases due to resistance
What happens t the interstitial hydrostatic pressure and interstitial oncotic pressure?
they are very low
What is the difference between the arteriole end of the capillary and the venue end of the capillary?
- at arteriole end, net filtration is favouring filtration o fluid out of the capillary
- at the venous end net filtration is favouring reabsorption of fluff into the capillary
Why is at said that there is no net filtration at a capillary?
filtration= reabsorption
What is the effect of pre-capillary vasoconstriction on net filtration?
- decrease radius
- increase R
- blood pressure falls before it enters the capillary
- downstream capillary pressure is lower
- pressure still falls throughout capillary due to resistance
- overall reabsorption is greater than filtration so there is net reabsorption of fluid
- overall because this increases TPR, blood pressure needs to be higher to maintain the same flow
What is the effect of pre-capillary vasodilation on net filtration?
- dilate arteriole
- increased r
- decreased R
- capillary hydrostatic pressure increases
- pressure decreases throughout capillary due to resistance
- filtration greater than reabsorption so overall there is a net filtration of fluid
- upstream this causes decreased TPR so blood pressure doesn’t have to be large to maintain flow
When there is net filtration, what happens to the excess fluid filtered out of the capillaries?
- taken up by lymphatic vessels
- moves fluid to subclavian veins in the chest where the fluid returns to the systemic circulation
