51 terms

Flow of Blood (physiology)

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Arteries
Elastic and stiff muscular vessels carrying blood away from heart
Arterioles
Able to contract and dilate, main determinant of peripheral resistance
Capillaries
One cell later thick vessels where all exchange between blood and cells occurs
Venules
Like capillaries, but larger.
Veins
Very compliant vessels that carry low O2 blood to the heart
Smooth muscle controls the
Diameter of the blood vessels
Smooth muscle is always
Partially contracted
Norepinephrine
Binds to alpha receptors, causes vasoconstriction
Binds to beta receptors, causes vasodilation
Myogenic (local)
Muscle cell stretch
Paracrines (local)
Metabolic agent
Metarterioles
Short vessels that link arterioles and capillaries, allow passage of larger cells to circulation
Naropinephrine binding to beta receptors
Causes vasodilation
Elastic arteries maintain
Pressure
Elastic arteries:
Aorta and its major branches
Norepinephrine binding to alpha receptors
Causes vasoconstriction
1. When left ventricle contracts...
It forces the walls of the aorta and other elastic arteries to bulge out
2. Kinetic energy of blood flowing is transferred to
Walls of artery and stored in walls as potential energy
3. When left ventricle relaxes, the potential energy in artery walls is
Released and that kinetic energy allows blood to keep flowing at high pressure (diastolic)
Pressure in fluids
Force on container
hydrostatic pressure
Blood should be hydraulic pressure
Hydrostatic pressure is
the pressure exerted by fluid in an enclosed space
What determines resistance
Radius of tube, length of tube, viscosity of fluid
How is velocity of flow different from flow rate?
Velocity is the distance a fixed volume will travel in a given period of time: Rate is volume of blood that passes one point in the system per unit of time
How is velocity of blood flow related to the radius of a blood vessel?
Smaller radius means higher velocity
What does cross sectional area of vessels do to blood flow?
blood flow is decreased
Why is velocity of blood vessels lowest in capillaries?
The total cross section of all capillaries is much bigger than other vessels
What is MAP (mean arterial pressure)?
Indirect measure of ventricular contraction pressure (driving force)
systolic pressure
During contraction ~120mmHg
diastolic pressure
During relaxation ~80mmHg
Poiseuille's Law
Radius of blood vessels determine blood flow
Flow rate =
Amount of blood travelled per minute (mL/min)
Resistance
Any force that opposes flow
Velocity =
Distance travelled per minute (cm/min)
V =
Q/cross sectional area of a tube (A)
vasoconstriction
Decrease flow rate or increase velocity
Vasolidation
Increase flow rate or decrease velocity
Hypotension:
<90/50 mmHg
Hypertension
>140/90 mmHg
Rarterioles
Peripheral resistance
parallel circuit
A circuit that contains more than one path for current flow.
capillary density in tissue
Dependent on metabolic demands of tissue
Types of capillary exchange
Continuous, fenestrated, sinusoid
bulk flow (filtration)
Movement due to hydrostatic/osmotic gradients
Hydrostatic
Blood pushing on capillary wall
Osmotic
Solutes in solution
colloid osmotic pressure
Proteins in plasma
Filtration
From blood to ECF
Absorption
From ECF to blood
ECF
extracellular fluid
Arterial end
Filtration
Venous end
Absorption
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