ANAT 261 Lecture Notes - Lecture 12: Collagen, Bradykinin, Blood Pressure

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ANAT 261 October 12, 2010
Dr. Mandato Lecture 12
Arterioles
· have 1-2 layers of smooth muscle cells and IELM is not properly defined. The smooth
muscle cells in a longitudinal section appear as if it were a cross section.
· Looks similar to duct of sweat gland in the epidermis so BE CAREFUL. Duct has 2-3
layers of nuclei, but no other layers outside (i.e no adventitia)
· Intima - endothelial cells, Basement membrane, and internal elastica (just elastic
fibers, no membrane which goes in the same direction/axis of arteriole).
· Media - smotth muscle cells, and reticular fibers
· Adventitia - has fibrocytes, collagen Type I and nerve fibers.
oThe fibrocyte nuclei are darker and larger than the smooth muscle cell.
· less than 0.5mm in diameter, and metarterioles are much smaller.
Capillaries
· Hard to distinguish between capillaries and post-capillary venule. Whenever there’s a
tiny structure with ONE red blood cell, then its a capillary since the diameter of
both is 7 micrometers.
· The post-capillary venule has 2-3 red blood cells in it.
· From end of metarteriole to beginning of post-capillary venule - 1 mm.
· Area of capillary network - 6000 m2
· Diameter - when you put together all the capillaries in the body, that diameter will be
800 times larger than that of the aorta
· Flow in aorta - 320 mm/sec; flow in capillaries: 0.3mm/sec.
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ANAT 261 October 12, 2010
Dr. Mandato Lecture 12
· At the level of capillaries - exchange of lipids, proteins, and other nutritional
substances. All the waste products from metabolism goes through the capillary
system, and is excreted at the level of the kidneys and liver.
· At the level of the metarterioles, there’s thermoregulation, and blood pressure
regulation.
oWhen there’s a drop in temperature, the metarteriole sphincter relaxes, thus
increasing blood flow along the capillaries (ex. red cheeks).
oIf there’s an accident, and considerable loss of blood heart doesn’t contract
much and cardiac arrest is a possible outcome. In order to prevent this,
metarteriole senses the decrease in blood perssure and it contracts. This
decreases the blood flow to the capillaries, and this blood is shunted back
to the arteries. In the arterial system, there’s AV anastomosis, where the
venules transport the blood back to the heart so it can pump normally. A
consequence of this is that the extremeties (ex. skin) don’t receive as much
blood flow.
Small Vessels
Pericyte in post capillary venule has a star shape, and can’t be seen under a light
microscope unless a special technique is used.
oThought to be either contractile elements or macrophages.
The endothelial cells in capillaries and post-capillary venules are joined by tight
junctions (zonula occludens)
There are continuous and fenestrated capillaries.
Continuous capillaries
overy selective/impermeable. Allows only small amounts of substances to
the basal compartment.
oThere are endocytic vesicles whose receptors pick up specific molecules
from the capillary lumen. Some vesicles have clathrin around the them.
oOnce the contents are in the vesicle, it detaches and fuses to the basal
plasma membrane (which is where the basement membrane is too) where
the contents are released.
oIn some cases, there are two vesicles at the lumen and basement membrane
side; which temporarily fuse to produce - trans endothelial channels.
oContinuous capillaries present in - NERVOUS TISSUE, SKELETAL,
CARDIAC, SMOOTH MUSCLE, SKIN, LUNG, LYMPHATIC
ORGANS.
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