MICROCIRCULATION. VENOUS BLOOD FLOW.

Microcirculatory bed

• Arterioli & pre-capillaries• Capillaries• Arterio-venous anastomoses• Post-capillaries

Functional state of capillaries

blood

plasma

Medium capillaries parameters

• Radius – 3-6 μm• Length 750 μm• Cross section square 30 μm2

• Square of exchange – 14 000 μm2 • Linea velocity of blood flow 0,3 mm/seс• Time of erythrocyte staying in the

capillary – 2-3 seс

TYPES OF CAPILLARIES• CONTINUUS – pores of 4-5 nm

• FENESTRAED – «fenestra» in the endothelium of 0,1 μm

• SINUSOIDAL

A. Capillary endothelium in relaxed muscleB. Capillary endothelium in contracted muscle

TRANSCAPILLARY EXCHANGE

АC

V

Рh/bl=30

Рh/t=-6

РО/t=4

РО/pl=27

Рf

13

Рh/pl=10 РО/pl=28

Рh/t=-6РО/t=4

РА

8

Filtration-absorption mechanism

•Net hydrostatic pressure

•Рh/n=Рh/pl –Рh/t=30-(-6)=36

•Net oncotic pressure

•Ро/n=Ро/pl-Ро/t=27-4=23

Filtration-absorption mechanism

• Filtration pressure• Рf=Рh/n-Ро/n=36-23=13

Absorption pressureРh/n=10-(-6)=16Ро/n=28-4=24

Рab=Ро/n-Рh/n=24-16=8

LYMPHATIC SYSTEM

• DRENAGE SYSTEM – excretes from extracellular fluid proteins & high molecular substances, which can’t be reabsorbed into blood capillaries.

• 2L of lymph are produced per day

Lymphatic vessel

лимфокапилляр клапаны

Muscle elements

Лимф-ангион

Lymphatic capillary valves

Lympho-angion

VENAE ARE BLOOD DEPOTS

КАПИЛЯРЫ5%

ЛЁГКИЕ12%

Б.ВЕНЫ25%

М.ВЕНЫ

34%

Б.АРТЕРИИ8%

СЕРДЦЕ9%

М.АРТЕРИИ7%

HEARTBIG ARTERIES

SMALL VEINS

CAPILLARIES

LUNGSBIG VIENS

SMALL ARTERIES

Factors enabling blood flow in veins

1. Pressure difference (12mm Hg – 0 mm Hg )

2. Recoil force of heart & thorasic cavity3. Valves in veins4. Skeletal muscles contraction

VASCULAR TONE REGULATION

VASCULAR TONE

• BASILAR MIOGENIC TONE – TONE, PROVIDED BY SMOOTH MUSCLES AUTOMATICITY.

AORTHA VEIN ARTERIOLA

Factors, influencing vascular tone

• Myogenic• Vasoactive tissue methabolites• Humoral factors, circulating in

blood• Tonic nervous impulses

Local regulatory mechanisms

• Mechanical stretching of vessel wall with blood

• Oxygen deficit• Methabolites• Biologically active substances which

act paracrine• Regulating factors of endothelial

cells of the vessels

Influence of blood pressure on the myogenic vascular tone

Р

Tone increase

Tone decrease

Vasodilating methabolites

• Decreased pressure of О2

• Lactic acid• Pyruvic acid• Adenosin• Increased pressure of СО2

РН decrease, Н+ concentrationincrease

Biologically active substances

• Vasodilators• Kinins (bradikinins)• Prostaglandines (Е1,Е2,В1,А1, А2,

F2)• Hystamine • Vasoconstrictor - serotonin

Endothelium regulating factors

• Arachidonic acid methabolites (prostacyclin PGI2)

• Factor of vessel relaxation– (NO)• Factor of vessel contraction (ECF-

endothelin)• Free radicals

Humoral factors, circulating in blood

Hormones, causing vasoconstriction

• Epinephrin, norepinephrin• Vasopressin• Renin-angiotensin-aldosteron

system

Epinephrin & norepinephrin

• Epinephrin in high concentration constricts the vessels via α-adrenoreceptors

• α-adrenoreceptors are sensitive to norepinephrine in physiological concentrations

Vasopressin

• Is released from posterior pituitary – ADH– causes vessels constriction

• Receptors V1 & V2

• Employs intracellular messengers

Renin-angiotensinogen-aldosterone system

kidney JGA Renin

angiotensinogen angiotensinI

lungs angiotensin II

Adrenal cortexaldosterone

vessels

Sensitivity to epinephrine

constriction

+

Hormones, causing vasodilation

• Epinephrine in physiological concentrations via β-adrenoreceptors.

• β- adrenoreceptors are located in coronary vessels, brain & kidney vessels

Nervous influences

Sympathetic nervous system

Adrenergic fibers Cholinergic fibers

Epinephrine &norepinephrine

α-аdrenoreceptors

constriction

β-аdrenoreceptors

dilation

achetylcholine

M-cholinoreceptors

Sympathetic nervous system

• M-cholinoreceptors are in the vessels of skeletal muscles.

Parasympathetic nervous system

• Salivatory glands vessels • Pelvic organs vessels• Pia mater vessels

• Acetylcholine

• m-cholinoreceptors• dilation

vasoconstrictors

Nervous:• Sympathetic nervous system via α-

adrenoreceptors (all vessels)Hymoral:• Epinephrine, norepinephrine• Vasopressin• Renin-angiotensin-aldosterone system

Vasoconstrictors

Local:

• Serotonin• Endothelial factor of vessel

constriction (endothelin)

vasodilators

Nervous:1. Sympathetic NS via β-

аdrenoreceptors;2. Sympathetic NS via cholinergic fibers3. Parasympathetic fibersкие волокна4. Аxon-reflex

Axon-reflex

CNS

Mechanical, thermal or chemical skin irritation

Local vessel dilation

vasodilatorsHumoral:• Epinephrine via β-adrenoreceptors;• HystamineLocal:• Methabolites• Biologically active substances

(prostaglandines, kinins)• Endothelial factors• Mechanical stretching of vascular wall

Tonic influence of sympathetic NS

• Claude Bernard experiment