The document discusses microcirculation, specifically focusing on the smallest blood vessels and the mechanisms of capillary exchange, which include diffusion, transcytosis, and bulk flow. It explains how oncotonic and hydrostatic pressures influence fluid movement in and out of capillaries, with a balance maintained by plasma proteins. Additionally, the document highlights the key functions of microcirculation in regulating body temperature and transporting vital substances like oxygen and nutrients.

1. MICROCIRCULATION
AND
CAPILLARY EXCHANGE
SUBMITTED BY:
*EVELIN GEORGE
*19BCU006
* 2ND B.Sc. BIOCHEMISTRY
SUBMITTED BY:
*EVELIN GEORGE
*19BCU006
* 2ND B.Sc. BIOCHEMISTRY

2. MICROCIRCULATION
The microcirculation refers to the smallest blood vessels in the body: the
smallest arterioles, the metarterioles, the precapillary sphincters, the
capillaries,the small venules.
Capillary exchange refers to the exchange of material between the blood and
tissues in the capillaries.
There are three mechanisms that facilitate capillary exchange:
*diffusion,
*transcytosis
*and bulk flow.

3. DIFFUSION VS TRANSCYTOSIS VS BULK
FLOW

4. CAPILLARY EXCHANGE MECHANISM
Diffusion, the most widely-used mechanism, allows the flow of small molecules across
capillaries such as glucose and oxygen from the blood into the tissues and carbon dioxide
from the tissue into the blood. The process depends on the difference of gradients
between the interstitium and blood, with molecules moving to low-concentrated spaces
from high-concentrated ones.
Transcytosis is the mechanism whereby large, lipid-insoluble substances cross the
capillary membranes. The substance to be transported is endocytosed by the endothelial
cell into a lipid vesicle which moves through the cell and is then exocytosed to the other
side.
Bulk flow is used by small, lipid-insoluble solutes in water to cross the the capillary wall.
The movement of materials across the wall is dependent on pressure and is bi-directional
depending on the net filtration pressure derived from the four Starling forces that
modulate capillary dynamics.

6. FORCES AND PRESSURES INVOLVED
The four Starling forces modulate capillary dynamics.
Oncotic or colloid osmotic pressure is a form of osmotic pressure exerted by
proteins in the blood plasma or interstitial fluid.
Hydrostatic pressure is the force generated by the pressure of fluid within or
outside of capillary on the capillary wall.
The net filtration pressure derived from the sum of the four forces described
above determines the fluid flow into or out of the capillary. Movement from the
bloodstream into the interstitium is favored by blood hydrostatic pressure and
interstitial fluid oncotic pressure.
Alternatively, movement from the interstitium into the bloodstream is favored by
blood oncotic pressure and interstitial fluid hydrostatic pressure.

7. CAPILLARY MICROCIRCULATION

8. CAPILLARY DYNAMICS
Oncotic pressure exerted by proteins in blood plasma tends to pull water into the
circulatory system.
Due to the pressure of the blood in the capillaries, blood hydrostatic pressure is
greater than interstitial fluid hydrostatic pressure, promoting a net flow of fluid
from the blood vessels into the interstitium.
However, because large plasma proteins, especially albumin, cannot easily cross
through the capillary walls, their effect on the osmotic pressure of the capillary
interiors will to some extent balance the tendency for fluid to leak from the
capillaries.
In conditions where plasma proteins are reduced (e.g. from being lost in the urine
or from malnutrition), or blood pressure is significantly increased, a change in
net filtration pressure and an increase in fluid movement across the capillary
result in excess fluid build-up in the tissues (edema).

10. FUNCTIONS OF MICROCIRCULATION
The principal function of the microcirculation are:
 Regulation of body temperature
Transport of cell, oxygen, and other crucial substances.
Substances involved include- * water,
* electrolytes,
*gases (O2, CO2),
*nitrogenous wastes,
*glucose,
*lipids and
*drugs.