microcirculation, exchange of substances, venus circulation Flashcards
what is Microcirculation
The microcirculation is the circulation of the blood in the smallest blood vessels, the microvessels of the microvasculature present within organ tissues.
exchange of materials is possible between blood and ECF is made by…
by permeable capillaries
what is Diffusion
Diffusion is defined as the movement of individual molecules of a substance through a semipermeable barrier from an area of higher concentration to an area of lower concentration
what affect the rate of diffusion?
The rate of diffusion depends on the concentration
gradient, permeability, and the surface area.
what are the Two types of transport by diffusion:
Flow limited:
Diffusion limited:
what is flow limited in diffusion:
Flow limited: For small molecules ot is only the rate of blood flow that limits the transport.
what is diffusion limited in diffusion:
Diffusion limited: For large molecules (e.g. polypeptides) it is the rate of diffusion that limits the transport.
explain diffusion of gases
Partial pressure of the gas drops in both directions:
towards the end of the capillary, and towards distant cells. The higher the actual oxygen consumption of the tissue, the higher will be the gradient for oxygen.
local autoregulation in diffusion of gases
Cells getting less oxygen release more regulatory signals, and these open more capillaries in the vicinity of these cells.
determine the pressure gradient for the fluids
Hydrostatic pressure and oncotic pressure of the blood
and of the tissue
Phcap
hydrostatic pressure in the capillary
Point
oncotic pressure in the interstitium
Pocap
oncotic pressure in the capillary
Phint
hydrostatic pressure in interstitium
Effective pressures are the differences of the blood and tissue pressures eq
Pheffective = Phcap - Phint Poeffective = Pocap - Point
The final effective filtration is the difference of he effective hydrostativ and effective oncotic pressures EQ
Peffective = Pheffective - Poeffective
what does effective filtration show
The effective filtration pressure shows towards the tissue at the arterial side of the capillary
The flow of fluid depends on
the effective pressure
and on the permeability
Formation of ISF:
Water, electrolytes and anelectrolites with small molecular weight can permeate the capillary wall without restriction.
Pathes of transport:
o Through fenestration
o Through interendothelial ways o In a transcellular way
o By cytosis (endo-, exo-, pyno)
Forces determining transport:
Diffusion
Osmotic forces:
Electric forces:
1) Electroneutrality
2) Thermodynamic rule:
Hydrostatic pressure:
Forces determining transport:Diffusion:
It is the most important factor to insure transport of substances. The greatest part of
substances crossing the capillary membrane is transported in this way.
Forces determining transport:Osmotic forces
: The osmotic effect of the
proteins in the solution makes water to move. The water content inside will increase. This so- called oncotic pressure continuously gets the water to move into the intravasal compartments from the ISF.
Forces determining transport:Electric forces
: If the movement of some components is restricted between two compartments, the concentration of the diffusible ions will be different in the two compartments after the balance develops:
Forces determining transport: Electric forces: Electroneutrality and Thermodynamic rule
▪ Electroneutrality: The total amount of anions and cations have to be equal in certain compartments
▪ Thermodynamic rule: The product of the concentrations of diffusible ions must be equal on both sides of the membrane.
Forces determining transport: Hydrostatic pressure:
The hydrostatic pressure coming from blood is not the same at the arterial
and the venous “end” of the capillary, that is why the net fluid flow is different.
The venus circulation: function determined by:
Function is determined by: structure of the wall and venous valves.
The venus circulation: characteristics
Characteristics of Venous System: capacitance-system (reservoir), 55 – 75 % of circulating blood reside in the veins.
Factors Maintaining Venous Circulation
the work of the heart
Gravitation
Venous valves
Skeletal muscle pump
Changing pressure in chest and in abdomen
