physiology of microcirculation, venous and lymph system

7/29/2019 Physiology of Microcirculation, Venous and Lymph System

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Physiology of microcirculation,

venous and lymph system.Regulation of blood flow


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Functional element of

microcirculation

Microcirculatory part of vascular system performsall blood functions. There are such types ofvessels: arterioles, metarterioles, capillaries andvenuls. Mean diameter of these vessels is lessthan 100 mcm. Arterioles, capillary bed venuls and

lymphatic capillaries compose functional elementof microcirculation. Main processes as blood-tissue exchange or lymph production areperformed there. Mean diameter of capillaries is 3-6 mcm. The length of capillary vessel is near 750

mcm. Capillaries perform exchange in surfacenear 14000 mkm2. Blood flow velocity incapillaries consists near 0.3 mm/s, which permitspassing erythrocytes through capillary in 2-3 s.


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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 aidedby the heartbeat, the increase in the

negative intrathoracic pressure during

each inspiration, and contractions ofskeletal muscles that compress the

veins (muscle pump).


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Morpho-functional properties of

venous system

Veins are the vessels, which are carryout blood from organs, tissues toheart in right atrium. Only pulmonary

vein carry out blood from lungs in leftatrium. There are superficial (skin)and deep veins. They are verystretching and have a low elasticity.

Valves are present in veins. Plexusvenosus are depo of blood. Bloodmoving in veins under gravity.


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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.


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Venous pressure

Venous pressure is pressure of blood,which are circulated in veins. Venouspressure in healthy person is from 50

to 100 mm H2O. Increase of venouspressure in physiological conditionmay be in the action of physicalactivity. Determine of venous

pressure is called phlebotonometryand give for doctors information aboutactivity of right atrium.


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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 andheartbeat.


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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 duringatrium systole. At these time pressure

in it increase. Methods of

investigation of venous pulse arephlebography.


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Transport of substances through

capillary membrane

Substances are transported through capillarymembrane are lipid soluble as O2 or CO2 andwater-soluble as ions or glucose. Substances ofmolecule size more than 6-7 nm cannot diffusethrough intra-endothelial pores. The greater theconcentration difference of a given substance ontwo sides of capillary membrane, the greater will binet rate of diffusion. Forces that determine fluidmovement through capillary membrane arecapillary pressure, interstitial fluid pressure,plasma colloid osmotic pressure and interstitial

fluid colloid osmotic pressure. At arterial end ofcapillary pressure is higher than interstitial fluidpressure, which causes filtration. At venous end ofcapillary plasma colloid osmotic pressure is lowerthan interstitial pressure, which causereabsorbtion.


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Lymph and lymphatic circulation

Lymph vessels are present in all

tissues, except bones, nervous and

superficial layers of skin.


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Lymphatic capillaries

Lymphatic capillaries begin as one side closedcapacities, which are drained by smallestlymphatic vessels. Lymphatic capillaries havevalves, which prevent opposite movement of

lymph. Connective tissue fibers fix outer surface oflymphatic capillary to surrounding intracellularsubstance and keep it voluminous shape.Pressure of lymph inside the capillary is lower thanin intracellular space, which helps to lymph flow.

Capillary wall has basal membrane and one layerof endotheliocytes.


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Morpho-functional properties of

lymphatic system

Lymph system has capillaries, vessels,where present valves, lymphatic nodes. Inlymphatic nodes are lymphopoiesis, depoof lymph, their function is barrier-filter.Lymph flow in vein system through thechest lymph ductus. Functions of lymph: 1.support of constant level of volume andcomponents of tissue fluid; 2. transport of

nutritive substances from digestive tract invenous system; 3. barrier-filter function. 4.take place in immunology reactions.


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Composition and properties of lymphLymph is tissue fluid that enters the lymphatic

vessels. It drains into the venous blood via thethoracic and right lymphatic ducts. It contains clottingfactors and clots on standing in vitro. Its proteincontent is generally lower than that of plasma butvaries with the region from which the lymph drains. Itshould be noted that, in most locations, interstitial

fluid is not protein-free; it contains proteins thattraverse capillary walls and return to the blood vialymph. Water-insoluble fats are absorbed from theintestine into the lymphatic vessels, and the lymph inthe thoracic duct after a meal is milky because of its

high fat content Lymphocytes enter the circulationprincipally through the lymphatic vessels, and thereare appreciable numbers of lymphocytes in thoracicduct lymph. Time of clotting 10-15 minutes. Thereare 3 kinds of lymph: peripheral, transport, central.The difference between them in cell quantity level.


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Production of lymph

Fluid efflux normally exceeds influx across

the capillary walls, but the extra fluid entersthe lymph and drains through them backinto the blood. This keeps the interstitialfluid pressure from rising and promotes theturnover of tissue fluid. The normal 24-hour

lymph flow is 2-4 L. Appreciable quantitiesof protein enter the interstitial fluid in theliver and intestine, and smaller quantitiesenter from the blood in other tissues. Thewalls of the lymphatic are permeable to

macromolecules, and the proteins arereturned to the bloodstream via thelymphatic.


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The amount of protein returned in this fashion in 1day is equal to 25-50 % of the total circulatingplasma protein. In the kidneys, formation of a

maximally concentrated urine depends upon anintact lymphatic circulation; removal of reabsorbedwater from the medullar pyramids is essential forthe efficient operation of the countercurrentmechanism and water enters the vasa recta only ifan appreciable osmotic gradient is maintainedbetween the medullar interstitial and the vasarecta blood by drainage of protein-containinginterstitial fluid into the renal lymphatic. Somelarge enzymes notably histaminases and lipase may reach the circulation largely or even

exclusively via the lymphatic vessels after theirsecretion from cells into the interstitial fluid. Thetransport of absorbed long-chain fatty, forexample, cholesterol from the intestine via thelymphatic vessels.


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Mechanism of lymph flowLymph flow is due to movements of skeletal

muscle, the negative intrathoracic pressure duringinspiration, the suction effect of high velocity flowof blood in the veins in which the lymphaticvessels terminate, and rhythmic contractions ofthe walls of the large lymph ducts. Since lymph

vessels have valves that prevent backflow,skeletal muscle contractions push the lymphtoward the heart. Pulsations of arteries nearlymphatic vessels may have a similar effect.However, the contractions of the walls of the

lymphatic ducts are important, and the rate ofthese contractions increases in direct proportion tothe volume of lymph in the vessels. There isevidence that the contractions are the principalfactor propelling the lymph.


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Basal tone of vessels.When arterial pressure suddenly increases local

blood flow tends to increase. It leads to suddenstretch of arterioles cause smooth muscles in theirwall to contract. Than local blood flow decreasesto normal level. Vessel walls are capable toprolonged tonic contraction without tiredness even

at rest. Such a condition is supported byspontaneous myogenic activity of smooth musclesand efferent impulsation from autonomic nervecenters, which control arterial pressure. Partialstate of contraction in blood vessels caused by

continual slow firing of vasoconstrictor area iscalled vasculomotor tone. Due to regulatory nerveand humoral influences this basal ton changesaccording to functional needs of curtain organ.


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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 andin pulpe. Activity in the sympathetic

nerves caused vasocontriction.

Histamine, adenosine causedvasodilatation, adrenaline, serotonine,

prostaglandine vasocontriction.


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Lympathatic system

The lymphatic system has three primary functions.

First of all, it returns excess interstitial fluid to theblood. Of the fluid that leaves the capillary, about90 percent is returned. The 10 percent that doesnot return becomes part of the interstitial fluid thatsurrounds the tissue cells. Small protein moleculesmay "leak" through the capillary wall and increase

the osmotic pressure of the interstitial fluid. Thisfurther inhibits the return of fluid into thecapillaries, and fluid tends to accumulate in thetissue spaces. If this continues, blood volume andblood pressure decrease significantly and the

volume of tissue fluid increases, which results inedema (swelling). Lymph capillaries pick up theexcess interstitial fluid and proteins and returnthem to the venous blood. After the fluid enters thelymph capillaries, it is called lymph.


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The second function of the lymphatic system is theabsorption of fats and fat-soluble vitamins from the digestivesystem and the subsequent transport of these substances tothe 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 bloodcapillaries absorb most nutrients, but the fats and fat-solublevitamins are absorbed by the lacteals. The lymph in thelacteals has a milky appearance due to its high fat contentand is called chyle.

The third and probably most well known function of thelymphatic system is defense against invadingmicroorganisms and disease. Lymph nodes and otherlymphatic organs filter the lymph to remove microorganismsand other foreign particles. Lymphatic organs containlymphocytes that destroy invading organisms.


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The lymphatic system consists of a

fluid (lymph), vessels that transport

the lymph, and organs that contain

lymphoid tissue.


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Lymph

Lymph is a fluid similar in composition toblood plasma. It is derived from bloodplasma as fluids pass through capillarywalls at the arterial end. As the interstitial

fluid begins to accumulate, it is picked upand removed by tiny lymphatic vessels andreturned to the blood. As soon as theinterstitial fluid enters the lymph capillaries,it is called lymph. Returning the fluid to the

blood prevents edema and helps tomaintain normal blood volume andpressure.


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Lymphatic Vessels

Lymphatic vessels, unlike blood vessels, onlycarry fluid away from the tissues. The smallestlymphatic vessels are the lymph capillaries, whichbegin in the tissue spaces as blind-ended sacs.

Lymph capillaries are found in all regions of thebody except the bone marrow, central nervoussystem, and tissues, such as the epidermis, thatlack blood vessels. The wall of the lymph capillaryis composed of endothelium in which the simple

squamous cells overlap to form a simple one-wayvalve. This arrangement permits fluid to enter thecapillary but prevents lymph from leaving thevessel.


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The microscopic lymph capillaries merge to formlymphatic vessels. Small lymphatic vessels join to

form larger tributaries, called lymphatic trunks,which drain large regions. Lymphatic trunks mergeuntil the lymph enters the two lymphatic ducts. Theright lymphatic duct drains lymph from the upperright quadrant of the body. The thoracic duct

drains all the rest.Like veins, the lymphatic tributaries have thin wallsand have valves to prevent backflow of blood.There is no pump in the lymphatic system like theheart in the cardiovascular system. The pressure

gradients to move lymph through the vesselscome from the skeletal muscle action, respiratorymovement, and contraction of smooth muscle invessel walls.


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Lymphatic Organs

Lymphatic organs are characterized by clusters oflymphocytes and other cells, such asmacrophages, enmeshed in a framework of short,branching connective tissue fibers. Thelymphocytes originate in the red bone marrow with

other types of blood cells and are carried in theblood from the bone marrow to the lymphaticorgans. When the body is exposed tomicroorganisms and other foreign substances, thelymphocytes proliferate within the lymphaticorgans and are sent in the blood to the site of theinvasion. This is part of the immune response thatattempts to destroy the invading agent. The fourtypes of lymphatic organs are described below.


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Lymph NodesLymph nodes are small bean-shaped structures that areusually less than 2.5 cm in length. They are widely

distributed throughout the body along the lymphaticpathways where they filter the lymph before it is returned tothe blood. Lymph nodes are not present in the centralnervous system. There are three superficial regions on eachside of the body where lymph nodes tend to cluster. Theseareas are the inguinal nodes in the groin, the axillary nodesin the armpit, and the cervical nodes in the neck.

The typical lymph node is surrounded by a connective tissuecapsule and divided into compartments called lymphnodules. The lymph nodules are dense masses oflymphocytes and macrophages and are separated by spacescalled 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 sinusesand enters an efferent lymphatic vessel, which carries thelymph away from the node. Because there are more afferentvessels than efferent vessels, the passage of lymph throughthe sinuses is slowed down, which allow time for thecleansing process. The efferent vessel leaves the node at anindented region called the hilum.


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TonsilsTonsils are clusters of lymphatic tissue just under

the mucous membranes that line the nose, mouth,and throat (pharynx). There are three groups oftonsils. The pharyngeal tonsils are located nearthe opening of the nasal cavity into the pharynx.When these tonsils become enlarged they mayinterfere with breathing and are called adenoids.

The palatine tonsils are the ones that are locatednear the opening of the oral cavity into thepharynx. Lingual tonsils are located on theposterior surface of the tongue, which also placesthem near the opening of the oral cavity into the

pharynx. Lymphocytes and macrophages in thetonsils provide protection against harmfulsubstances and pathogens that may enter thebody through the nose or mouth.


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SpleenThe spleen is located in the upper left abdominalcavity, just beneath the diaphragm, and posterior

to the stomach. It is similar to a lymph node inshape and structure but it is much larger. Thespleen is the largest lymphatic organ in the body.Surrounded by a connective tissue capsule, whichextends inward to divide the organ into lobules,the spleen consists of two types of tissue calledwhite pulp and red pulp. The white pulp islymphatic tissue consisting mainly of lymphocytesaround arteries. The red pulp consists of venoussinuses filled with blood and cords of lymphaticcells, 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.


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The spleen filters blood in much the way that thelymph nodes filter lymph. Lymphocytes in thespleen react to pathogens in the blood andattempt to destroy them. Macrophages then engulfthe resulting debris, the damaged cells, and the

otherlarge particles. The spleen, along with the liver,removes old and damaged erythrocytes from thecirculating blood. Like other lymphatic tissue, itproduces lymphocytes, especially in response toinvading pathogens. The sinuses in the spleen area reservoir for blood. In emergencies such ashemorrhage, smooth muscle in the vessel wallsand in the capsule o


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ThymusThe thymus is a soft organ with two lobes that islocated anterior to the ascending aorta and

posterior to the sternum. It is relatively large ininfants and children but after puberty it begins todecrease in size so that in older adults it is quitesmall.

The primary function of the thymus is the

processing and maturation of special lymphocytescalled T-lymphocytes or T-cells. While in thethymus, the lymphocytes do not respond topathogens and foreign agents. After thelymphocytes have matured, they enter the bloodand go to other lymphatic organs where they helpprovide defense against disease. The thymus alsoproduces a hormone, thymosin, which stimulatesthe maturation of lymphocytes in other lymphaticorgans.


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physiology of microcirculation, venous and lymph system

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