pressure gradients, blood flow and peripheral resistance Flashcards
what are arteries
low resistance vessels conducting blood to the various organs with little loss in pressure
act as pressure resevoirs for maintaining blood flow between ventricular contractions
what are arterioles (basic)
major sites of resistance to blood flow
responsible for the pattern of blood flow distribution
participate in the regulation of arterial blood pressure
what are capillaries
site of exchange between blood and tissues
what are veins
low resistance vessels for blood to flow back to the heart
their capacity for blood is adjusted to facilitate flow
what are the components of vessels
adventitial layer - connective tissue
medial layer - smooth muscle cells
intimal layer - endothelial cells
what is the composition of the elastic artery wall
5% endothelium
25% smooth muscle
40% elastic tissue
30% connective tissue
what is the composition of the arteriole wall
10% endothelium
60% smooth muscle
10% elastic tissue
20% connective tissue
what is the composition of the capillary wall
95% endothelium
5% connective tissue
what is the composition of the venule wall
20% endothelium
20% smooth muscle
60% connective tissue
measurements of the aorta
internal radius = 12mm
wall thickness = 2mm
measurements of medium artery
internal radius = 2mm
wall thickness = 1mm
measurements of arteriole
internal radius = 15µm
wall thickness = 20µm
measurements of true capillary
internal radius = 3µm
wall thickness = 1µm
measurement of vein
internal radius = 2.5mm
wall thickness = 0.5mm
measurement of venule
internal radius = 10µm
wall thickness = 2µm
measurement of vena cava
internal radius = 15mm
wall thickness = 1.5mm
features of arteries
several hundred
thick, highly elastic walls
large radii
passageway from heart to organs
serve as pressure resevoirs
features of arterioles
half a million
highly muscular, well-innervated walls
small radii
primary resistance vessels
determine distribution of cardiac output
features of capillaries
ten billion
thin walled
large total cross-sectional area
site of exchange
determine distribution of extracellular fluid between plasma and interstitial fluid
features of veins
several hundred
thin walled
highly distensible
large radii
passageway to heart from organs
serve as blood resevoir
what is haemodynamics; pressure, flow and resistance
throughout the vascular system blood flow (F) is always from a region of higher pressure to one of lower pressure
what is hydrostatic pressure
the pressure exerted by a fluid
what is the units of flow
volume per unit time
L/min or ml/min
what is the units of pressure difference
ΔP
drives the floe
mmHg
what is flow rate
to work out;
the pressure difference between two points (ΔP) and the resistance (R) to flow
what is resistance (basic)
a measure of how difficult it is for blood to flow between two points at any given pressure difference
a measure of the friction impeding flow
what is blood flow
blood flow through vessels depends upon the pressure gradient and vascular resistance
blood flows through ‘tubes’
the driving force is the pressure generated by contractions of the heart
F = ΔP/R
flow is directly proportional to ΔP
flow rate depends on the pressure difference NOT the absolute pressure
what is resistance
a measure of the friction impeding flow
depends upon 3 factors;
1. viscosity of the blood
2. vessel length
3. vessel radius - major determinant of resistance to flow, a slight change in radius brings about a notable change in flow > resistance is directly proportional to 1/r^4, flow is directly proportional to r^4
what is the poiseuille equation
INSERT IMAGE
what is arterial pressure
fluctuates in relation to ventricular systole and diastole
mean arterial pressure = diastolic pressure + 1/3pulse pressure
what are arterioles
the major resistance vessels
the small radius of arterioles offers considerable resistance to blood flow
this high arteriolar resistance causes a marked drop in mean pressure as blood flows through arterioles
this pressure gradient helps drive blood from the heart to the tissue capillary beds
arteriolar resistance also converts pulsatile arterial pressure into non-fluctuating capillary pressure
what is smooth muscle in the vasculature
arteriolar walls include a thick layer of smooth muscle that is richly innervated by nerves of the sympathetic nervous system
- this smooth muscle is also sensitive to many local chemical changes and certain circulating hormones
the smooth muscle runs circularly around the arteriole
what is smooth muscle contraction of arterioles
⬇️ radius, ⬆️ resistance
⬇️ local blood flow
vasoconstriction
what is smooth muscle relaxation of arterioles
⬆️ radius, ⬇️ resistance
⬆️ local blood flow
vasodilation
what is vasoconstriction
increase contraction of smooth muscle
increase resistance
decrease of flow through the vessel
what is vasodilation
decrease contraction of smooth muscle
decrease resistance
increase flow through the vessel
hat a
