Transcript 29 Physiology of microcirculation

Physiology of microcirculation
Microcirculation
● The microcirculation is the blood flow
through blood vessels smaller than 100 µm
(i.e. arterioles, capillaries, and venules).
● Function:
1. Transport of cells, oxygen and
other substances to/from the tissues
2. Regulation of body temperature
Microcirculation consists of 3
components:
1. Haemomycrocyrculation (arterioles,
precapillares, capillares, postcapillares venules,
venules, arterioles-venules anastomosis)
 2. Substance’ transport to intercticium, where
some hydrostatic and oncotic pressure creates
 3. Limphatic vessels – their walls more thin than
in arteriales and don’t contain basal membrane.
Intercellular cracks – they are the main way of
penetration of tissue fluid into the lumen of
lymphatic vessels
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Arterioles
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An arteriole is a small
diameter (<20 μm, up to 5-9
μm) blood vessel that extends
and branches out from an
artery and leads to capillaries.
Arterioles have thin muscular
walls (usually only one to two
layers of smooth muscle) and
are the primary site of
vascular resistance.
In a healthy vascular system
the endothelium, inner lining
of arterioles and other blood
vessels, is smooth and
relaxed. This healthy
condition is promoted by the
ample production of nitric
oxide in the endothelium.
Arteriola
Metharteriola
Shunt
Arterial
capillares
Precapillary
sphincter
Venous
capillares
Postcapillary
sphincter
Venula
Total peripheral resistance
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Total peripheral resistance refers to the cumulative
resistance of the thousands of arterioles with precapillares in
the body.
 It is approximately equal to the resistance of the arterioles,
since the arterioles are the chief resistance vessels in the
body.
 Total Peripheral Resistance =
Mean
Pressure // Cardiac
CardiacOutput.
Output.
MeanArterial
Arterial Pressure

The total peripheral resistance of healthy lung arterioles is
typically about 0.15 to 0.20 that of the body, so pulmonary
artery mean blood pressures are typically about 0.15 to 0.20
of aortic mean blood pressures.
Capillary
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Capillaries, are the smallest of a body's blood vessels,
measuring 5-10 μm.
They connect arteries and veins, and most closely interact
with tissues.
Capillaries have walls composed of a single layer of cells,
the endothelium.
This layer is so thin that molecules such as oxygen, water
and lipids can pass through them by diffusion and enter the
tissues.
Waste products such as carbon dioxide and urea can
diffuse back into the blood to be carried away for removal
from the body.
Capillary permeability can be increased by the release of
certain cytokines.
The Organization of a Capillary Bed
Figure 21.5a, b
Types of Capillaries
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There are three structural types of
capillaries:
1.Continuous
2.Fenestrated
3.Sinusoids
Type of Capillaries: Continuous
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Continuous capillaries most
abundant in the skin & muscles
– Least permeable, lack pores
– Endothelial cells provide an
uninterrupted lining
– Adjacent cells are connected with
tight junctions
– Intercellular clefts allow the
passage of fluids
Continuous capillaries of the brain
– Have tight junctions completely
around the endothelium
– Constitute the blood-brain barrier
Type of Capillaries: Fenestrated
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Fenestrated Capillaries
– They have pores
(fenestrations)
– Found wherever active
capillary absorption or
filtrate occurs
 Example: intestinal villi,
ciliary process of eye,
endocrine glands,
glomeruli of kidney
Characterized by:
– Greater permeability than
continuous capillaries
Type of Capillaries: Sinusoidal
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Sinusoidal capillaries
are modified, very
permeable (leaky)
capillaries.
 They have a large
lumens with large
fenestrae.
– Found only in the
liver, bone marrow,
lymphoid tissue and
in some endocrine
organs.
TYPES OF CAPILLARY
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1. Somatic.
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2. Visceral
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3. Sinusoidal
Capillary Beds: Microcirculation
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Vascular shunts – metarteriole
– thoroughfare channel
True capillaries – 10 to 100 per capillary bed
– branch off the metarteriole
Precapillary sphincter
– Cuff of smooth muscle that surrounds each true capillary
– Regulates blood flow into the capillary
Blood flow regulated by vasomotor nerves & chemical conditions
Oxygen, CO2,
small solutes,
nutrients move
across capillaries
primarily through
diffusion.
Concentration
gradient
Electrochemical
Hydrostatic
and Osmotic
pressure
Fig 14.9
14-22
Morpho-functional properties of venous system
 Veins
are the vessels, which are carry out
blood from organs, tissues to heart in
right atrium. Only pulmonary vein carry
out blood from lungs in left atrium. There
are superficial (skin) and deep veins.
They are very stretching and have a low
elasticity. Valves are present in veins.
Plexus venosus are storage of blood.
Blood moving in veins under gravity.
Lymphatic system
 The
lymphatic system is a complex network
of lymphoid organs, lymph nodes, lymph
ducts, and lymph vessels that produce and
transport lymph fluid from tissues to the
circulatory system.
 The
lymphatic system is a major component of
the immune system.
Morpho-functional properties of lymphatic system
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Lymph system has capillaries, vessels, where present
valves, lymphatic nodes. In lymphatic nodes are
lymphopoiesis, depo of lymph, their function is barrierfilter. Lymph flow in vein system through the chest
lymph ductus.
Functions of lymph:
1. support of constant level of volume and components
of tissue fluid;
2. transport of nutritive substances from digestive tract in
venous system;
3. barrier-filter function.
4. take place in immunology reactions.
Lympathatic system
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The lymphatic system has three primary functions.
First of all, it returns excess interstitial fluid to the
blood.
 The second function of the lymphatic system is the
absorption of fats and fat-soluble vitamins from
the digestive system and the subsequent transport
of these substances to the venous circulation.
 The third and probably most well known function
of the lymphatic system is defense against
invading microorganisms and disease.
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