3-12;Pressure/Flow/Pumps/Surface Tension Flashcards
states of matter
solid=internal order and fixed atomic positions
liquids=takes shape of container, no rigidity, atoms have very strong cohesive forces that hold them together
gas=only forces exerted are due to collisions
ideal fluid
fluid is non-viscous=internal friction is negligible) and incompressible (density is constant)
pressure
exertion of force upon a surface by an object/fluid
force/area [N/m^2 or Pa]
what does the penetrating ability of an object depend on
depends on pressure, not only force since a sharper needle will require less force to produce required penetrating pressure
pressure in liquids
at rest pressure caused by liquid is proportional to depth of liquid density
how is pressure exerted in a static liquid
liquid pressure is exerted equally in all directions so that net force is 0
pascal’s principle
any change of pressure in an enclosed fluid is transmitted undiminished to all parts of the fluid
clinical applications of pascal’s principle
chronically ill patients develop decubitus ulcers/bedsores, mainly on elbows due to exertion of largest pressure = prevented by use of water mattress = P evenly distributed against every part of body in contact w/ mattress
cerebrospinal fluid = increase in P = increases P in all part of fluid so if there is a tumour, will cause an increase in P
unborn fetus protected by amniotic sac fluid = distributes forces exerted on abdominal area equally = mother cautioned against tight clothes
Eye contains enclosed fluid = blow to front of eye transmits P to backof eye = Optic nerve/retina/blood vessels injured by XS P
buoyancy
when something is being immersed in fluid appears to be lighter than it does in air
why is buoyancy needed
to provide lifting force required to float a ship on water or balloon in air
how does buoyant forces arise
due to difference in liquid pressure above and below object
Archimedes’ principle
buoyant force on submerged object = to weight of fluid displaced
he found objects weigh less under water: weight of object in air - weight when submerged = weight of water displaced = use this to determine vol of irregular shaped object and weight density by weight/vol
what does pressure in flowing liquid depend on
depends on details of flow process, uniform pressure drop due to smooth flow through uniform tube
why are there drops in pressure during flow
loss in energy due to frictional effects
laminar flow
average flow speed that is 1/2 max speed found at centre, represents min energy loss
turbulent flow
when flow speeds up past a certain critical speed or an obstruction in flow path to form eddies = causes laminar flow to break down into turbulent flow
viscosity
frictional forces that oppose flow w/i fluid
function of a pump
to increase pressure in a fluid to allow fluid to move in a desired manner to overcome system resistance
types of pumps
lift or force pump
lift=lifts liquid rather than forcing it through system, completely mechanical, relies of Patm
force=don’t rely on Patm directly, circulates liquid in a sealed closed liquid circuit
heart as a pump
the action of ventricles is a force pump, achieves XS P by contraction
Heart is 2 synchronous force pumps.
receives blood from Venous system and raises P to push it out into arterial system.
When RV expands, AV valve opens, lets venous blood flow into ventricle whilst SL valve remains closed to prevent backflow of previously pumped blood.
what causes faults in pumping action of heart
valves that have holes or don’t close properly.
if R AV Valve isn’t closed, RV contraction pumps blood back out into venous system
if SL V isn’t closed = blood backflows from Arterial system when ventricle expands
describe pressure in circulatory system
P highest when it leaves LV, lowest when enters RA.
P raised by RV to drop enter LA as low residual pressure
LV main pump = supplies P for systematic circulation through body
why is P drop greater or lesser in arterioles than across capillaries
P drop depends on Vol Flow rate and resistance, since there are more capillaries than arterioles = vol flow rate through each capillary is much smaller
why is it important to control vol flow rate of heart
to supply required oxygen and nutrients to cells
to reduce R of CS to enable body to respond to greater demands for blood during exercise w/o overburdening heart pump
EG. Moderate EX=increase blood flow rate^3 but BP only increases by small % = total R drops less than 1/2
Vigorous EX = larger fraction of blood flows to muscles = vasodilation of muscle tissue
how is VFR controlled
blood pressure and internal radii used for short term control of VFR.
arterioles are surrounded by muscle cells so provide large changes in vessel diameters = known as resistance vessels
applicability of Poiseuille’s law
departures from the law expected in capillaries due to distortion of RBC needed to fit through by 1/2 or smaller
law only applies to laminar flow but during exercise, turbulence may occur in aorta, this increases R = increase in P to increase VFR
what are changes in blood speed during circulation
speed MAX in aorta, drops to MIN in capillaries then accelerates to high speed in major veins leading to heart
speed in capillaries is very large compared to aorta due to reduced diameter, but total area is order of 1000 larger than aorta so flow in caps assumed to be slowed by factor of 1000
laplace law
showed wall tension is required to withstand a given fluid P proportional to vessel radius
so smaller vessel can withstand more pressure w/ a given wall strength, but if artery wall expands = too weak to provide required tension = so expansion places an even greater tension on membrane = classic vicious cycle
what happens when blood flows to feet and upwards, what does this mean
gravitational potential energy reduced, some converted into P and Ke to aid heart
upward= some P and Ke used to overcome gravity = increases Gravitational Potential energy
so BP at head is lower when standing than lying on floor
systolic pressure
peak pressure produced by ventricular contraction
diastolic pressure
min pressure maintained by elastic system
how is arteries adapted for contraction
arteries are comprised of extremely elastic system of tubing = so blood bulges out of walls leaving aorta to store energy as Elastic Potential energy = elastic expansion of wall travels along arteries like a wave = pulse
where is P variation typical in
the arterial system only, it diminishes at arterioles and venous system
absolute P
sum of atmospheric pressure and liquid pressure
hydrostatic pressure
P exerted by fluid at rest due to force of gravity
EG when u dive to bottom of swimming pool
hydrometer
measures specific gravity of liquid
glass tube of standard specific gravity floating in liquid
if specific gravity increases = hydrometer floats
EG urinometer
specific gravity
ratio of density of substance to density of some substance, usually pure water
urinometer
measures specific gravity of urine to identify disease, which alters composition of urine = changes its specific gravity
