Feb 29 ,2012 Lecture Notes
Composition of Arterioles
The SEM of arterioles
Endothelial cells are in direct contact with the blood (thin layer of cells)
Smooth muscle cells form layers around the endothelial cells
Arteriole is a nice long tube, endothelial cells run lengthwise along the surface , smooth
muscle cells are circumferentially around it. Wrapping around allows the smooth muscle
to control the diameter of the arteriole. The smooth muscle cells can change capacity,
contract and relax. If they are fully contracted, they are going to squeeze the arteriole to
smaller diameter which will create A HIGH RESISTANCE FLOW PATHWAY (more
difficult for blood to enter and pass through this arteriole).
If Smooth Muscle small relax then arteriole can take a larger circumference , and a lot
more blood can pass through it. That is whats going on in order to mainupulate blood
flow through arteriole
Endothelial cells, they are the inner lining of all the blood vessels, cardiac chambers, &
Endothelial cells were recognized to play major role in preventing blood cells and
platelets from globing on to the sides. Endothelial cells keep the blood cells & platelets
from adhering to the surface, which prevents the clots from occurring at random
locations throughout the blood vessels.
Thrombus that can form on the inner side of atherscelotic plaque, because it can
fill up blood vessel with the clot, IT HAPPENS IF THE ENDOTHELIAL CELLS
GET DAMAGED. The endothelial cells are not creating smooth layer therefore a
LARGE CLOT is formed.
Endothelial cells structure is imp in controlling exchanging fluids and nutrients
from within the plasma compartment to Extracellular compartment and other
Important substances are produced by endothelial cells, and have direct effect on
smooth muscle cells, .. Nitric oxide is a vasodilator(dilation to enlarge) vasodilator
increases the diameter of blood vessel, meaning it increases flow.
Endothelin (produced in large quantities, for people that have high blood pressure) very powerful vasoconstrictor and causes the smooth muscles to
contract and reduce the diameter of the arteriole.
Endothelial cells within the capailiers through the process of angiogenesis. They
also have effect on smooth muscle cells,
Also effect if cells will be proliferate (multiply) NORMALLY YOU DON’T WANT
SMOOTH MUSCLE CELLS TO MULTIPLY YOU WANT IT TO CONTINUE, iTS
BAD, but it happens in atherscelorsis.
Endothelial cells regulate inflammatory responses because they are the cell layer
that immune cells have to interact with in order for immune cells to exit the blood
and get to the side of infection, .. There are specific interactions that need to
occur…Endothelial cells make sure they occur.
Function of Smooth Muscle cells.
Wrapping around the exterior
Provide statbility and strength to the arteriole,
Arteriole cells are very thin and can’t support and on their own they cannot
support a lot of pressure, so smooth muscle cells make them stable.
Smooth muscle cells main job is setting the blood vessel diameter in doing so
they regulate blood flow. They can contract and relax, but they are normally
operating at a level of partial contraction (unlike striated muscle all or none
response). Smooth muscle will be partial contracted in NORMAL conditions this
is called vascular tone . Because the smooth muscle cells can hold this for
hours and hours, and they can do this because they have diff structure of actin
and myosin inside them and different myosin ATPases.
Major point is that they can hold partial contraction for a LONG time, (under
By operating at partial contraction, they have max felxibaility to whatever signals
they recived, it’s the vascular tone, that is set by arterioles, THAT DETERMINES
WHAT YOUR MEAN ARTERIAL PRESSURE IS.
Smooth muscle cells it helps regulate blood flow and establish mean arterial
Smooth muscle cells can also be a big player in hypertension ( high blood pressure).Smooth muscle cells will spend more time in constricted state so there
is more resistance.
Nitric Oxide (NO) POSTED ON MOODLE
Nitric oxide is major VASODILATOR in endothelial cells. Nerves can also make it
This process involves using an amino acid, called L-Arginine which is the
substrate for the enzyme that makes nitric oxide which is called nitric oxide
Nitric oxide is a gas, (NO)
Nitrous gas ( laughing gas)
Nitric oxide is lipid soluable which means that its not going to just stay in
endothelial cells , its freely diffusible so it can diffuse across the endothelial cell
membrane, across the space that seperates endotheliam and smooth muscle
cells, and right into the smooth muscle cells. Does not require receptor because
it just moves freely through lipid memembrane. Once its inside the smooth
muscle will cause activation of an enzyme Guanlate cyclase (responsible for
producing secondary messenger called cGMP) ---increases in the cGMP causes
the relaxation of the smooth muscle cells, coz the myosin and actin cross bridges
break apart allowing the cell to relax. When the smooth muscle cell relaxes and
dimater of the arteriole increases and more blood flow is coming through the
2 step process.
(i) the cell that makes the nitric oxide (endothelial cells)
(ii) the cell that actually have to react to the nitric oxide respond to it
Endothelial cells have no capacity to change the diameter on their own, OR
cause the blood vessel to change the shape on its own, we need to have
smooth muscle cell reacting to a stimulus in order to get change in blood flow.
But the endothelial provides this signal to the smooth muscle cells. Endothelial
cells constantly produce low level of nitric oxide, and so you always have smooth
muscle cells having nitrix oxide coming to them which maintains a healthy
(VASCULAR SYSTEM) Nitric oxide gas is very unstable, doesn’t last it gets broken into nitrates. So you
cant get it to go very far, since it breaks down fast.
Nitric Oxide (PRACTICAL APPLICATIONS)
nitric oxide production is enhanced in the body , taken the pill prior to workout so
you since more blood will be rushing to muscle so you get much stronger muscle
pumpe will be able to work out more extremely and develop more muscle mass
and work out more extremely.
Pill is L-arginine that will help you produce more nitric oxide will active gynalate
cyclase wwhich will activate cGMP which will get hyper activation of nitric oxide
OR relaxation of smooth muscle so there is more blood flowing.
There are NO SCIENTIFIC studies that show that in healthy individuals that
taking in more L-arginine will produce more nitric oxide. Since L-arginine is not a
limiting factor of Nitric Oxide so taking in more L-arginine will not produce Nitric
The limiting factor in this process is