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.

Note the valves in the vein only.

Capillaries are the only blood vessels that allow exchange.

Arterioles can control the flow rate of blood by smooth muscle contraction. Vasodilation or vasoconstriction

Wall of an artery or a vein

Capillaries numerous with enormous total surface area.

Systemic circulation

Heart Aorta Arteries

Venules Capillaries Arterioles Veins Vena Cava Heart

Pressure changes in the circulatory system. Blood pressure

Structure

Blood PlasmaBlood 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?• 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 Hydrostatic Blood Pressure of 3.7KPa 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 Hydrostatic Pressure of Pressure of Blood 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 Relative molecular mass

Permeability

Water 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 systemLymph 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?