Download Tissue Fluid and Lymph

Tissue Fluid and Lymph
Objectives:
• Explain the differences between blood,
tissue fluid and lymph.
• Describe how tissue fluid is formed from
plasma.
Exchange across the Capillaries
Substances leave
(and enter)
capillaries through
the walls
Formation of tissue fluid
• As blood flows through the capillaries some plasma
passes out to bathe the surrounding cells.
• This tissue fluid is very similar to plasma but does not
have large plasma protein molecules in it. They were
too big to pass through the tiny gaps between the
endothelial cells making up the capillary walls.
• The tissue fluid supplies the cells with glucose, amino
acids, fatty acids, salts and oxygen.
• The fluid then returns to the blood in the capillaries
taking any waste products from the cells with it e.g.
CO2 and Urea
Exchange across the capillaries
Arterial End of Capillary
• Here the hydrostatic pressure of the blood is high. This will encourage the
filtration of the fluid content of the blood through small gaps between
the endothelial cells of the walls of the capillary. Blood cells and plasma
proteins are too large to be filtered.
• However, as the blood has a low (negative) water potential at the arterial
end of the capillary, there is a tendency for water to move into the
capillary from the surrounding tissue fluid, due to osmosis.
• As the hydrostatic pressure encouraging fluid out of the capillary is higher
than the osmotic pressure encouraging water into the capillary, the net
result is water (and small molecules dissolved in it) moves out of the blood
and into the surrounding tissue fluid.
Venous End of Capillary
• Here the hydrostatic pressure of the blood is lower, as much of the fluid
content was lost to the surroundings. The hydrostatic pressure will still
encourage filtration of fluid out of the blood into the surrounding tissue
fluid, but the size of this force is low.
• The blood now has a very low (very negative) water potential, as it consists
mainly of blood cells and large plasma proteins with very little fluid. This
encourages movement of water (and any small substances dissolved in it)
from the tissue fluid into the blood.
• As the osmotic pressure encouraging fluid into the capillary is greater than
the hydrostatic pressure encouraging it out, the net result is that fluid reenters the capillary.
Lymph
• Not all the fluid returns
to the blood capillary.
• 10% enters a separate
system of microscopic
tubes called lymph
capillaries. These are
part of the lymph
system.
• The lymph capillaries
join to form lymph
vessels.
• Lymph vessels have
valves that let fluid
enter but not leave them
FLUIDS
•
•
•
•
•
•
Fluid in the blood is called...
Plasma
Fluid surrounding the cells is called...
Tissue fluid
Fluid in the lymphatic system is called...
Lymph
There is very little difference between these three!
Lymph
• Flow of liquid through the lymph system is
very slow
• It depends on movement of our muscles, the
valves in the vessels and the negative
pressure in chest when we breath in.
• Flow is in one direction only, from tissues
towards the heart.
• Most of the lymph re-enters the blood
stream at the subclavian veins under the
collar bones
• Lymph is a milky looking fluid
• Digested fat is absorbed into the lymph
Lymph
• At intervals along the lymph
vessels are structures
called lymph nodes
• These are part of the
immune system
• Lymphocytes are produced
in the lymph nodes
• Lymphocytes are white
blood cells that produce
antibodies.
• The lymph nodes swell up at
times of infection