Plasma, Tissue Fluid and Lymph
Circulatory system
• The structure of arteries, arterioles and veins in
relation to their function.
• The structure of capillaries and their importance in
metabolic exchange.
• The formation of tissue fluid and its return to the
circulatory system.
Over large distances, efficient
supply of materials is provided by
mass transport.
• Mass transport is the bulk movement of a fluid such as
blood through a body with the purpose of transporting
materials such as nutrients (glucose) waste and gases.
• The system also collects and distributes/delivers these
materials to cells or body systems for removal.
The structure of arteries, arterioles
and veins in relation to their function.
Arterioles can
control the flow
rate of blood by
smooth muscle
contraction.
Vasodilation or
vasoconstriction
Note the
valves in
the vein
only.
Capillaries
are the
only blood
vessels that
allow
exchange.
Wall of an artery or a vein
Capillaries numerous with enormous
total surface area.
Systemic circulation
Heart
Aorta
Venules
Veins
Arteries
Capillaries
Vena Cava
Arterioles
Heart
Pressure changes in the circulatory
system. Blood pressure
Structure
Blood Plasma
Blood is composed of cells floating in pale
yellow liquid called plasma.
Blood plasma is mostly water with a variety
substances dissolved in it.
Components of blood
Things within blood plasma?
•
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Oxygen
Carbon dioxide
Amino acids
Fatty acids as lipoproteins.
Glucose
Vitamins
Urea
Hormones
Antibodies
Salts such as sodium chloride
Also there are plasma proteins such as Albumin.
Erythrocytes (rbc) and leucocytes (neutrophils, macrophages, B
and T lymphocytes).
Tissue Fluid
• Tissue fluid is formed from the plasma of the
blood. It is a watery fluid that contains
glucose, amino acids, fatty acids, salts and
oxygen, all of which it supplies to the tissues.
In return it receives carbon dioxide and other
waste materials from the tissues. Tissue fluid
is the means by which things are exchanged
between blood and the cells of the tissues and
as such it bathes all of the cells of the body.
Interstitial fluid = Tissue fluid
Formation of Tissue Fluid:
pressure differences along a capillary
• Blood pumped by the heart passes along the
arteries then the narrower arterioles and
finally into the capillaries. This creates a
pressure, called hydrostatic pressure of
around 3.7 kPa at the arterial end of the
capillaries. This pressure forces liquid out of
the capillaries. This pressure is opposed by
two forces
Forces resisting the OUTWARD
movement of fluid.
• Hydrostatic Pressure of the tissue fluid outside
the capillaries that prevents the outward
movement of fluid.
• Water Potential that is due to plasma proteins,
which tend to pull water back into the capillaries.
Tissue fluid formation results whereby the overall
pressure of 1.7kPa forces fluid out of the blood
however the larger proteins and cells are held
back within the capillary and remain in the blood.
_________ _________ ____________ ____________
Arterial end of Capillary bed
Hydrostatic
Pressure of
Blood
3.7KPa
Hydrostatic
Pressure of
Tissue fluid +
Water potential of
Plasma. 2.0KPa
______ _______ _________ _______ ___ ___
Net pressure causes fluid to leave capillary
1.7 KPa
Pressure change in the capillary.
• The loss of tissue fluid reduces the pressure in
the capillaries, so that by the time the blood
has reached the venous end of the network,
its hydrostatic pressure is less than that of the
tissue fluid outside it. Along with the osmotic
forces due to the proteins in the blood that
pull water back into the capillary there is also
an overall negative pressure (Water Potential)
of -2.0kPa drawing tissue fluid back into the
capillaries.
_________ _________ ____________ ____________
Venous end of Capillary bed
Hydrostatic
Pressure of
Blood
Hydrostatic
Pressure of
Tissue fluid +
Water potential of
Plasma. 2.0KPa
______ _______ _________ _______ ___ ___
Net pressure causes fluid to enter capillary
• This fluid has lost most of its oxygen and
nutrients by diffusion to the cells it has
bathed. The returning fluid has picked up
carbon dioxide and excretory products from
cells.
• About 90% of the fluid returns into the venous
end of the capillary bed the remainder drains
into the lymphatic system.
Pressure, Velocity and Surface Area.
Permeability of the capillary
epithelium
Substance
Water
Relative molecular Permeability
mass
18
1.00
Sodium ions
23
0.96
Urea
60
0.8
glucose
180
0.6
Haemoglobin
68,000
0.01
Albumin
69,000
0.000 01
• Lymphatic system
Lymph vessels or LYMPHATICS are tiny blunt
ended vessels which are found in most of the
body tissues.
Lymphatic system
Tissue fluid can flow into the end of the
lymphatic through tiny valves which allow it to
flow in but not out.
• Lymph is a milky liquid made up of material
from three sources.
• Tissue Fluid that has not been reabsorbed at
the venous end of the capillaries (about 10%).
• Fatty substances absorbed by lacteals in the
villi of the ileum.
• Lymphocytes which have either been
produced by bone marrow and moved to
lymph nodes or have migrated from capillaries
to fight infection.
• Lymph is carried in the lymphatic system which is made
up of capillaries resembling blood capillaries. Closed
ended lymphatic capillaries lie in spaces between cells.
They unite to form larger and larger vessels eventually
to join the great veins in the neck dripping their
contents into the blood. The lymph fluid will have to
pass through lymph nodes that contain lymphocytes
and macrophages. These cells screen the lymph and
will remove foreign materials. Lymph nodes may swell
with dead cells causing swelling in the groin, armpits
and neck during infection (swollen glands).
Lymphatic system
The spleen is a
reservoir for blood
and also
contributes to the
breakdown of old
red blood cells and
is a rich source of
lymphocytes.
Lymph moves by three methods:
• HYDROSTATIC PRESSURE due to plasma
leaving the capillaries to form tissue fluid.
• CONTRACTION OF striated body muscle
squeezes lymph capillaries forcing the lymph
forward. Valves prevent backflow.
• Enlargement of the thorax during BREATHING
IN.
Lymphatic System (Lacteals)
• What happens when a parasitic worm infects
and blocks the lymphatic system?