Physiology of microcirculation,
venous and lymphatic vessels
Blood flow in veins
Blood flows through the blood
vessels, including the veins, primarily,
because of the pumping action of the
heart, although venous flow is aided
by the heartbeat, the increase in the
negative intrathoracic pressure during
each inspiration, and contractions of
skeletal muscles that compress the
veins (muscle pump).
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.
Mechanism of regulation
Difference of pressure in venous
system is a cause of blood moving.
From the place of high pressure blood
moving to the place of low pressure.
Negative pressure in chest is a cause
of blood moving. Contraction of
skeletal muscles, diaphragm pump,
peristaltic movement of veins walls
are the causes of moving.
Venous pressure
Venous pressure is pressure of blood,
which are circulated in veins. Venous
pressure in healthy person is from 50
to 100 mm H2O. Increase of venous
pressure in physiological condition
may be in the action of physical
activity. Determine of venous
pressure is called phlebotonometry
and give for doctors information about
activity of right atrium.
Phlebography
а – atria wave –contraction of
right atrium
с – passing of carotid artery
pulse on vein
х – systole of ventricles
v – ventricular – filling of
atrium by blood
y – passing of blood in right
atria
Speed of blood stream
Speed of vein blood stream depend
on diameter of vessels. In venules
speed of blood moving is lower. In
veins of middle diameter it 7-14 cm/s,
in big veins the speed is near 20
cm/s. In big veins speed of blood
moving depend on breathing and
heartbeat.
Venous pulse
Venous pulse is a moving of walls of
big veins, which are depend on
heartbeat. The cause of it stop of
blood flow from vein to heart during
atrium systole. At these time pressure
in it increase. Methods of
investigation of venous pulse are
phlebography.
Transport of substances through
capillary membrane
Substances are transported through
capillary membrane are lipid soluble
as O2 or CO2 and water-soluble as
ions or glucose.
At arterial end of capillary pressure is
higher than interstitial fluid pressure,
which causes filtration. At venous end
of capillary plasma colloid osmotic
pressure is lower than interstitial
pressure, which cause reabsorbtion.
Types of capillary
1. Somatic.
2. Visceral
3. Sinusoidal
Lymph and lymphatic circulation
Lymph vessels are present in all
tissues, except bones, nervous and
superficial layers of skin.
Lymphatic capillaries
Lymphatic capillaries begin as one
side closed capacities, which are
drained by smallest lymphatic
vessels. Pressure of lymph inside the
capillary is lower than in intracellular
space, which helps to lymph flow.
Capillary wall has basal membrane
and one layer of endotheliocytes.
Morpho-functional properties of
lymphatic system
Lymph system has capillaries, vessels, where
present valves, lymphatic nodes. In lymphatic
nodes are lymphopoiesis, depo of lymph, their
function is barrier-filter. 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.
Composition and properties of lymph
Lymph is tissue fluid that enters the
lymphatic vessels. It contains clotting
factors and clots on standing in vitro.
There are 3 kinds of lymph: peripheral,
transport, central.
Production of lymph
Fluid efflux normally exceeds influx
across the capillary walls, but the
extra fluid enters the lymph and
drains through them back into the
blood. This keeps the interstitial fluid
pressure from rising and promotes the
turnover of tissue fluid. The normal
24-hour lymph flow is 2-4 L.
Mechanism of lymph flow
Lymph flow is due to movements of
skeletal muscle, the negative intrathoracic
pressure during inspiration, the suction
effect of high velocity flow of blood in the
veins in which the lymphatic vessels
terminate, and rhythmic contractions of the
walls of the large lymph ducts. Since lymph
vessels have valves that prevent backflow,
skeletal muscle contractions push the
lymph toward the heart. Pulsations of
arteries near lymphatic vessels may have a
similar effect.
Basal tone of vessels.
When arterial pressure suddenly increases
local blood flow tends to increase. Than
local blood flow decreases to normal level.
Vessel walls are capable to prolonged tonic
contraction without tiredness even at rest.
Such a condition is supported by
spontaneous myogenic activity of smooth
muscles and efferent impulsation from
autonomic nerve centers, which control
arterial pressure. Partial state of
contraction in blood vessels caused by
continual slow firing of vasoconstrictor area
is called vasculomotor tone.
Blood supply of the spleen
There are 1,5-2 % of volume
circulation in the human spleen. In our
organism spleen has a small amount
of smooth muscle in the capsule and
in pulpe. Activity in the sympathetic
nerves caused vasocontriction.
Histamine, adenosine caused
vasodilatation, adrenaline, serotonine,
prostaglandine – vasocontriction.
Lympathatic system
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 fatsoluble 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.
The lymphatic system consists of a
fluid (lymph), vessels that transport
the lymph, and organs that contain
lymphoid tissue.
The microscopic lymph capillaries merge to form
lymphatic vessels. Small lymphatic vessels join to
form larger tributaries, called lymphatic trunks,
which drain large regions. Lymphatic trunks merge
until the lymph enters the two lymphatic ducts. The
right lymphatic duct drains lymph from the upper
right quadrant of the body. The thoracic duct
drains all the rest.
Like veins, the lymphatic tributaries have thin walls
and have valves to prevent backflow of blood.
There is no pump in the lymphatic system like the
heart in the cardiovascular system. The pressure
gradients to move lymph through the vessels
come from the skeletal muscle action, respiratory
movement, and contraction of smooth muscle in
vessel walls.
Lymphatic Organs
Lymphatic organs are characterized by clusters of
lymphocytes and other cells, such as
macrophages, enmeshed in a framework of short,
branching connective tissue fibers. The
lymphocytes originate in the red bone marrow with
other types of blood cells and are carried in the
blood from the bone marrow to the lymphatic
organs. When the body is exposed to
microorganisms and other foreign substances, the
lymphocytes proliferate within the lymphatic
organs and are sent in the blood to the site of the
invasion. This is part of the immune response that
attempts to destroy the invading agent. The four
types of lymphatic organs are described below.
Tonsils
Tonsils are clusters of lymphatic tissue just under
the mucous membranes that line the nose, mouth,
and throat (pharynx). There are three groups of
tonsils. The pharyngeal tonsils are located near
the opening of the nasal cavity into the pharynx.
When these tonsils become enlarged they may
interfere with breathing and are called adenoids.
The palatine tonsils are the ones that are located
near the opening of the oral cavity into the
pharynx. Lingual tonsils are located on the
posterior surface of the tongue, which also places
them near the opening of the oral cavity into the
pharynx. Lymphocytes and macrophages in the
tonsils provide protection against harmful
substances and pathogens that may enter the
body through the nose or mouth.
Spleen
The spleen is located in the upper left
abdominal cavity, just beneath the
diaphragm, and posterior to the
stomach. It is similar to a lymph node
in shape and structure but it is much
larger. The spleen is the largest
lymphatic organ in the body.
Thymus
The thymus is a soft organ with two lobes that is
located anterior to the ascending aorta and
posterior to the sternum. It is relatively large in
infants and children but after puberty it begins to
decrease in size so that in older adults it is quite
small.
The primary function of the thymus is the
processing and maturation of special lymphocytes
called T-lymphocytes or T-cells. While in the
thymus, the lymphocytes do not respond to
pathogens and foreign agents. After the
lymphocytes have matured, they enter the blood
and go to other lymphatic organs where they help
provide defense against disease. The thymus also
produces a hormone, thymosin, which stimulates
the maturation of lymphocytes in other lymphatic
organs.
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