Blood vessels + circulation Flashcards
Describe the tunica interna of the artery wall
- smooth squamous endothelium
- has basement membrane
- contains internal elastic lamina
Describe the tunica media of the artery wall
- thickest layer
- elastic fibres
- smooth muscle
Describe the tunica externa of artery walls
- elastic + collagen fibres
List the functions of elastic (conducting) arteries
- largest diameter arteries
- carry blood away from the heart
- store elastic energy which helps move blood during diastole
- pressure reservoir
List the functions of muscular (distributing) arteries
Medium sized arteries
- distribute + regulate blood flow to muscles + internal organs (constrict + dilate)
- superficial muscular arteries form pressure points (eg. control bleeding/measure pulse) -> carotid, brachial, femoral
Describe the functions of arterioles
- deliver blood to capillaries
- regulate systemic vascular resistance through vasoconstriction + vasodilation
- resistance vessels
Describe the function + structure of meta arterioles
- supply capillary beds
- distal end has no smooth muscle -> thoroughfare channel
Describe the structure + function of capillaries
- walls consist of only endothelium + basement membrane
- exchange of nutrients + waste via interstitial fluids (exchange vessels)
Describe true capillaries + what their flow is regulated by
- emerge from arterioles + meta arterioles
- flow regulated by pre capillary sphincter
-> intermittent flow caused by alternating contraction/relaxation of meta arterioles + pre capillary sphincters
-> RBCs move single file through capillary
List the 3 types of capillaries + their characteristics
continuous capillaries
- uninterrupted lining
- most common
fenestrated capillaries
- many fenestrations/pores
- found in kidney
sinusoidal capillaries
- large fenestrations + intercellular clefts
- incomplete basement membrane
- found in liver, spleen + bone marrow
-> enable drugs to be metabolised
Describe what venules are formed from
small veins formed from merging of several capillaries -> merge to form veins
Describe the 3 tunics of veins + their characteristics
- tunica interna thinner
- tunica media thinner -> less smooth muscle + elastic fibres
- tunica externa -> collagen = elastic fibres / lack elastic lamina of arteries
What are the functions of veins
- hold 60% of blood volume
- capacitance vessels (volume reservoir)
Define blood flow
volume of blood that flows through a tissue per unit time
-> determined by blood pressure + resistance
Describe the conditions required for blood flow
circulatory pressure must be greater than total peripheral resistance (where TPR is determined by vascular resistance, blood viscosity + turbulence)
What factor determines blood viscosity
ratio of RBC to plasma
Define turbulence + the factors which affect it
- the slowing of blood flow
- high flow rates, irregular surfaces eg. plaque build up, + sudden changes in vessel diameter -> all increase turbulence
What is the relationship b/t velocity of blood flow + CSA + how does this change through the vessels
- velocity inversely related to CSA
-> velocity decreases as blood flows from aorta to capillaries
-> velocity increases as blood flows from capillary to heart
Why is velocity of blood flow slowest in capillaries
allows increased time for exchange
Define blood pressure
Pressure exerted on walls of a blood vessel
-> decreases as moves further away from the heart
What is venous return maintained by
- pressure gradient est. by heart
- skeletal muscle pumped
- respiratory pump
- valves
List 3 things that occur if blood pressure is too low
- vessels collapse
- blood flow stops
- tissues die
list 2 things that happen if blood pressure is too high
- vessel walls stiffen
- capillary beds rupture
List the 3 methods substances can enter + leave the capillaries by
- diffusion (most important)
- transcytosis (vesicular transport) -> lipid soluble across membrane
- bulk flow (filtration + absorption)
Why is capillary exchange important + what drives it
- regulates relative volumes of blood + interstitial fluid
- driven by balance b/t hydrostatic + osmotic pressures (net filtration pressure)
List the 3 mechanisms controlling cardiovascular regulation
- autoregulation
- neural mechanisms
- hormonal mechanisms
Describe how autoregulation occurs through local factors + what is affected by this
local factors = alter pattern of blood flow through capillaries via local vasoconstrictors or local vasodilators
-> act on pre capillary sphincters to control blood flow through a single capillary bed
List 4 local vasodilators
- increased tissue CO2 or decreased O2
- lactic/other acid from tissue cells
- chemicals released during inflammation eg. histamines
- elevated local temp
what is an example of a local vasocontrictor
prostaglandins from activated platelets
explain the negative feedback loop that occurs that has vasodilation as the effect
- homeostasis disturbed by physical stress (increased temp), chem. changes or increased tissue activity
- causes inadequate local blood flow/BP
- results in local decrease in resistance + increase in blood flow
- homeostasis restored
state where neural control happens from + what it changes
- neural control via cardiac centres + vasomotor centres in medulla oblongata
-> changes HR, contractility + resistance of blood vessels (affects CO)
List the 4 areas the cardiovascular system receives input from
- higher brain regions eg. hypothalamus
- proprioceptors
- baroreceptors (monitor BP)
- chemoreceptors (monitor blood acidity)
what 2 mechanisms does the cardiovascular centre send outputs via
sympathetic impulses :
- cardio accelerator nerves (increase HR and contractility)
- vasomotor nerves (cause vasoconstriction + vasodilation)
parasympathetic impulses:
- vagus nerve decreases HR
Explain the function + location of baroreceptors
function = monitors degree of stretch of blood vessels
-> BP falls when stretched less therefore send impulse to CV centre
location = carotid sinus + aorta
Explain the response to increased baroreceptor stimulation when BP increases
- homeostasis disturbed by increased BP
- baroreceptors stimulated
- cardio inhibitory centre stimulated = decrease CO
- cardio accelatory + vasomotor centres inhibited = vasodilation occurs
-> homeostasis restored + BP decreases
opposite for decreased BP
list the 4 hormones produced by the endocrine system to regulate the CV system + describe their functions
E + NE from adrenal medulla = increase CO + peripheral vasoconstriction
ADH from posterior pituitary= increase peripheral vasoconstriction -> increase BP
Angiotensin 2 = causes vasoconstriction -> increases BP
Erythropoietin from kidneys = stimulates RBC production in bone marrow
list the 3 CV responses to exercise
- extensive vasodilation
- increased venous return
- increased CO via increased venous return + increased sympathetic activity
