Transcript Interstitial fluid and the lymph

Interstitial fluid and the lymph
Definition
• The fluid found in the intercellular spaces composed
of:
• water,
• amino acids,
• sugars,
• fatty acids,
• coenzymes,
• hormones,
• neurotransmitters,
• salts,
• and cellular products.
• It bathes and surrounds the cells of the body
• Provides a means of delivering materials to
the cells
• intercellular communication,
• and removal of metabolic waste
Plasma and interstitial fluid
• Plasma and interstitial fluid are very similar.
Plasma, the major component in blood,
communicates freely with interstitial fluid
through pores and intercellular clefts in
capillary endothelium
• Capillaries are composed of a single layer of
epithelium surrounded by a thin basement
membrane.
• Most capillaries have pores (spaces) between the
individual cells that make up the capillary wall.
Plasma fluid and small nutrient molecules leave the
capillary and enter the interstitial fluid through these
pores, in a process called bulk flow.
• Bulk flow facilitates the efficient transfer of nutrient
out of the blood and into the tissues. However, blood
cells and plasma proteins, which are too large to fit
through the pores, do not filter out of the capillaries
by bulk flow.
Blood and interstitial fluid
• Red blood cells, platelets and plasma proteins
cannot pass through the walls of the
capillaries.
• The resulting mixture that does pass through
is essentially blood plasma without the plasma
proteins. Tissue fluid also contains some types
of white blood cell, which help combat
infection.
•Together, blood plasma and interstitial fluid
make up the extracellular fluid (ECF). Plasma
constitutes 20%, while interstitial fluid
constitutes 80% of the ECF.
•The distribution of extracellular fluid between
these two compartments is determined by the
balance between two opposing forces:
hydrostatic pressure and osmotic pressure
The lymph
Definition
• Lymph is considered a part of the interstitial
fluid.
• The lymphatic system returns protein and
excess interstitial fluid to the circulation.
The beating of the heart generates
hydrostatic pressure, which causes
bulk flow of fluid from plasma to
interstitial fluid through walls of the
capillaries.
The pressure in the system forces
plasma to filter out into the
interstitial compartment. The
composition of the interstitial fluid
and the plasma is essentially the
same except that plasma also
contains plasma proteins not found
in the interstitial fluid. plasma has a
higher solute concentration than
does the interstitial fluid.
Consequently, osmotic pressure
causes interstitial fluid to be
absorbed into the plasma
compartment. In other words, the
plasma proteins drive the
reabsorption of water back into the
capillaries via osmosis.
The magnitudes of filtration and
absorption are not equal. The net
filtration of fluid out of the capillaries
into the interstitial compartment is
greater than the net absorption of fluid
back into the capillaries. The excess
filtered fluid is returned to the blood
stream via the lymphatic system. In
addition to its roles in digestion and
immunity, the lymphatic system
functions to return filtered plasma back
to the circulatory system. The smallest
vessels of the lymphatic system are the
lymphatic capillaries (shown in yellow).
These porous, blind-ended ducts form
a large network of vessels that infiltrate
the capillary beds of most organs.
Excess interstitial fluid enters the
lymphatic capillaries to become lymph
fluid
How does the lymphatic system works?
• The clear, watery blood plasma -- containing
the oxygen, proteins, glucose and white
blood cells -- "leaks" out through the capillary
walls and flows around all the cells.
• The pores in the capillaries are too small to let
red blood cells through, however All of the
cells in your body are therefore bathed in
lymph, and they receive their nutrients and
oxygen from the lymph.
• Somehow, all of this lymph has to end up
somewhere, so it is recirculated.
• The lymph capillaries and vessels pick up the lymph
fluid and start pumping it away from the cells.
• Lymph vessels do not have an active pump like the
heart. Instead, lymph vessels have muscle motion
that pumps the lymph.
•You have just as many lymph vessels and capillaries
as you have blood vessels and capillaries!
• Lymph in the lymph vessels eventually reaches a
lymph node -- there are about 100 nodes
scattered throughout the body.
• Lymph nodes filter the lymph and also contain
large numbers of white blood cells (a big part of
the immune system), which remove foreign cells
and debris from the lymph.
• When you get certain infections, the lymph nodes
swell with billions of white blood cells working to
clear the foreign cells causing the infection.
• The filtered lymph then flows back into the blood
stream at certain points.
Functions of the lymphatic system:
1) To maintain the pressure and volume of the
extracellular fluid by returning excess water
and dissolved substances from the interstitial
fluid to the circulation.
2) lymph nodes and other lymphoid tissues are
the site of clonal production of immuno
competent lymphocytes and macrophages in
the specific immune response.
Filtration forces water and dissolved substances
from the capillaries into the interstitial fluid. Not all
of this water is returned to the blood by osmosis,
and excess fluid is picked up by lymph capillaries
to become lymph.
From lymph capillaries fluid flows into lymph
veins (lymphatic vessels) which virtually parallel
the circulatory veins and are structurally very
similar to them.
Lymph nodes
• Lymph nodes lie along the lymph veins
successively filtering lymph. Afferent lymph veins
enter each node, efferent veins lead to the next
node becoming afferent veins upon reaching it.
• Lympho kinetic motion (flow of the lymph) due
to:
• 1) Lymph flows down the pressure gradient.
• 2) Muscular and respiratory pumps push lymph
forward due to function of the semilunar valves.
• Lymph nodes: are small encapsulated organs
located along the pathway of lymphatic vessels.
• They vary from about 1 mm to 1 to 2 cm in
diameter and are widely distributed throughout
the body, with large concentrations occurring in
the areas of convergence of lymph vessels.
• They serve as filters through which lymph
percolates on its way to the blood.