Physiology of microcirculation,
venous and lymph system.
Regulation of blood flow
Functional element of
microcirculation
Microcirculatory part of vascular system performs
all blood functions. There are such types of
vessels: arterioles, metarterioles, capillaries and
venuls. Mean diameter of these vessels is less
than 100 mcm. Arterioles, capillary bed venuls and
lymphatic capillaries compose functional element
of microcirculation. Main processes as bloodtissue exchange or lymph production are
performed there. Mean diameter of capillaries is 36 mcm. The length of capillary vessel is near 750
mcm. Capillaries perform exchange in surface
near 14000 mkm2. Blood flow velocity in
capillaries consists near 0.3 mm/s, which permits
passing erythrocytes through capillary in 2-3 s.
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 depo 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.
Speed of blood stream
Speed of vein blood stream depend
on diameter of vessels. In venuls
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. Substances of
molecule size more than 6-7 nm cannot diffuse
through intra-endothelial pores. The greater the
concentration difference of a given substance on
two sides of capillary membrane, the greater will bi
net rate of diffusion. Forces that determine fluid
movement through capillary membrane are
capillary pressure, interstitial fluid pressure,
plasma colloid osmotic pressure and interstitial
fluid colloid osmotic pressure. 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.
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. Lymphatic capillaries have
valves, which prevent opposite movement of
lymph. Connective tissue fibers fix outer surface of
lymphatic capillary to surrounding intracellular
substance and keep it voluminous shape.
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 drains into the venous blood via the
thoracic and right lymphatic ducts. It contains clotting
factors and clots on standing in vitro. Its protein
content is generally lower than that of plasma but
varies with the region from which the lymph drains. It
should be noted that, in most locations, interstitial
fluid is not protein-free; it contains proteins that
traverse capillary walls and return to the blood via
lymph. Water-insoluble fats are absorbed from the
intestine into the lymphatic vessels, and the lymph in
the thoracic duct after a meal is milky because of its
high fat content Lymphocytes enter the circulation
principally through the lymphatic vessels, and there
are appreciable numbers of lymphocytes in thoracic
duct lymph. Time of clotting – 10-15 minutes. There
are 3 kinds of lymph: peripheral, transport, central.
The difference between them in cell quantity level.
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. Appreciable quantities
of protein enter the interstitial fluid in the
liver and intestine, and smaller quantities
enter from the blood in other tissues. The
walls of the lymphatic are permeable to
macromolecules, and the proteins are
returned to the bloodstream via the
lymphatic.
The amount of protein returned in this fashion in 1
day is equal to 25-50 % of the total circulating
plasma protein. In the kidneys, formation of a
maximally concentrated urine depends upon an
intact lymphatic circulation; removal of reabsorbed
water from the medullar pyramids is essential for
the efficient operation of the countercurrent
mechanism and water enters the vasa recta only if
an appreciable osmotic gradient is maintained
between the medullar interstitial and the vasa
recta blood by drainage of protein-containing
interstitial fluid into the renal lymphatic. Some
large enzymes – notably histaminases and lipase
– may reach the circulation largely or even
exclusively via the lymphatic vessels after their
secretion from cells into the interstitial fluid. The
transport of absorbed long-chain fatty, for
example, cholesterol from the intestine via the
lymphatic vessels.
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.
However, the contractions of the walls of the
lymphatic ducts are important, and the rate of
these contractions increases in direct proportion to
the volume of lymph in the vessels. There is
evidence that the contractions are the principal
factor propelling the lymph.
Basal tone of vessels.
When arterial pressure suddenly increases local
blood flow tends to increase. It leads to sudden
stretch of arterioles cause smooth muscles in their
wall to contract. 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. Due to regulatory nerve
and humoral influences this basal ton changes
according to functional needs of curtain organ.
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. Of the fluid that leaves the capillary, about
90 percent is returned. The 10 percent that does
not return becomes part of the interstitial fluid that
surrounds the tissue cells. Small protein molecules
may "leak" through the capillary wall and increase
the osmotic pressure of the interstitial fluid. This
further inhibits the return of fluid into the
capillaries, and fluid tends to accumulate in the
tissue spaces. If this continues, blood volume and
blood pressure decrease significantly and the
volume of tissue fluid increases, which results in
edema (swelling). Lymph capillaries pick up the
excess interstitial fluid and proteins and return
them to the venous blood. After the fluid enters the
lymph capillaries, it is called lymph.
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 mucosa that lines the small
intestine is covered with fingerlike projections called villi.
There are blood capillaries and special lymph capillaries,
called lacteals, in the center of each villus. The blood
capillaries absorb most nutrients, but the fats and fat-soluble
vitamins are absorbed by the lacteals. The lymph in the
lacteals has a milky appearance due to its high fat content
and is called chyle.
The third and probably most well known function of the
lymphatic system is defense against invading
microorganisms and disease. Lymph nodes and other
lymphatic organs filter the lymph to remove microorganisms
and other foreign particles. Lymphatic organs contain
lymphocytes that destroy invading organisms.
The lymphatic system consists of a
fluid (lymph), vessels that transport
the lymph, and organs that contain
lymphoid tissue.
Lymph
Lymph is a fluid similar in composition to
blood plasma. It is derived from blood
plasma as fluids pass through capillary
walls at the arterial end. As the interstitial
fluid begins to accumulate, it is picked up
and removed by tiny lymphatic vessels and
returned to the blood. As soon as the
interstitial fluid enters the lymph capillaries,
it is called lymph. Returning the fluid to the
blood prevents edema and helps to
maintain normal blood volume and
pressure.
Lymphatic Vessels
Lymphatic vessels, unlike blood vessels, only
carry fluid away from the tissues. The smallest
lymphatic vessels are the lymph capillaries, which
begin in the tissue spaces as blind-ended sacs.
Lymph capillaries are found in all regions of the
body except the bone marrow, central nervous
system, and tissues, such as the epidermis, that
lack blood vessels. The wall of the lymph capillary
is composed of endothelium in which the simple
squamous cells overlap to form a simple one-way
valve. This arrangement permits fluid to enter the
capillary but prevents lymph from leaving the
vessel.
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.
Lymph Nodes
Lymph nodes are small bean-shaped structures that are
usually less than 2.5 cm in length. They are widely
distributed throughout the body along the lymphatic
pathways where they filter the lymph before it is returned to
the blood. Lymph nodes are not present in the central
nervous system. There are three superficial regions on each
side of the body where lymph nodes tend to cluster. These
areas are the inguinal nodes in the groin, the axillary nodes
in the armpit, and the cervical nodes in the neck.
The typical lymph node is surrounded by a connective tissue
capsule and divided into compartments called lymph
nodules. The lymph nodules are dense masses of
lymphocytes and macrophages and are separated by spaces
called lymph sinuses. Several afferent lymphatic vessels,
which carry lymph into the node, enter the node on the
convex side. The lymph moves through the lymph sinuses
and enters an efferent lymphatic vessel, which carries the
lymph away from the node. Because there are more afferent
vessels than efferent vessels, the passage of lymph through
the sinuses is slowed down, which allow time for the
cleansing process. The efferent vessel leaves the node at an
indented region called the hilum.
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.
Surrounded by a connective tissue capsule, which
extends inward to divide the organ into lobules,
the spleen consists of two types of tissue called
white pulp and red pulp. The white pulp is
lymphatic tissue consisting mainly of lymphocytes
around arteries. The red pulp consists of venous
sinuses filled with blood and cords of lymphatic
cells, such as lymphocytes and macrophages.
Blood enters the spleen through the splenic artery,
moves through the sinuses where it is filtered,
then leaves through the splenic vein.
The spleen filters blood in much the way that the
lymph nodes filter lymph. Lymphocytes in the
spleen react to pathogens in the blood and
attempt to destroy them. Macrophages then engulf
the resulting debris, the damaged cells, and the
other
large particles. The spleen, along with the liver,
removes old and damaged erythrocytes from the
circulating blood. Like other lymphatic tissue, it
produces lymphocytes, especially in response to
invading pathogens. The sinuses in the spleen are
a reservoir for blood. In emergencies such as
hemorrhage, smooth muscle in the vessel walls
and in the capsule o
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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