Fluids of the circulatory system name them the fluid derived from blood plasma, that surrounds the cells in a tissue the fluid held in the heart, arteries, veins and capillaries the fluid held in the lymphatic system (lymph nodes and lacteals) Tissue fluid Blood/plasma Lymph

Learning Objectives the formation of tissue fluid from plasma To include reference to hydrostatic pressure, oncotic pressure an explanation of the differences in the composition of blood, tissue fluid and lymph.

Tissue fluid colourless fluid formed from blood plasma by pressure filtration through capillary walls surrounds all the cells of the body Allows exchanges between the blood and cells of eg oxygen, glucose, carbon dioxide Tissue fluid contains: Glucose Amino acids Fatty acids Salts Oxygen So what does the tissue fluid take away? Carbon dioxide Other waste products Supplies all of these to the tissues

Pressures at work Hydrostatic Pressure Oncotic Pressure (-3.3KPa) Pushing fluid out arterial end about 4.6KPa Venous end about 2.3KPa Oncotic Pressure (-3.3KPa) Blood proteins pulling fluid back in

Fluid in or out of the capillary? Both hydrostatic and oncotic pressure are found in the blood vessels and in the tissues. Their relative balance determines whether fluid enters or leaves the capillary What effect could high blood pressure have on tissue fluid formation.

Net outflow? Net inflow? 1.2kPa -1.0kPa see p183 Arterial end: blood is under high pressure (hydrostatic pressure = 4.6kPa) due to contraction of heart muscle tends to push fluid out of capillaries through tiny gaps in their walls (red blood cells, most white blood cells, platelets and plasma proteins are too large to leave) Venous end: blood has lost hydrostatic pressure it is now 2.3 kPa. Osmotic pressure -3.3kPa exceeds hydrostatic pressure so this creates a pull which moves fluid back into capillary Net outflow? Net inflow? 1.2kPa -1.0kPa see p183

Lymph A milky liquid made up of excess tissue fluid not all tissue fluid returns to capillaries about 10% drains away into lymphatic system fatty substances absorbed from intestines 3. Lymphocytes produced in lymph nodes (swellings along lymphatic system which filter bacteria from lymph fluid). phagocytes engulf and destroy bacteria.

Human Lymphatic System Lymphatic system is made up of one way vessels resembling blood capillaries Start at tissues, drain excess fluid into larger vessels Rejoin blood system in chest cavity Lymphatic System

Lymphatic problems Oedema accumulation of tissue fluid can have several causes. Elephantiasis caused by roundworm infection in the lymph nodes Malnutrition Kwashiorkor

Jan 2004 Jan 2002 Past paper questions

Pulling fluid into tissues with a force of 0.2kPa Capillary HP +SP (OP) 4.3kPa +-3.3kPa= 1.0kPa Tissues HP=SP (OP) 1.1kPa + -1.3kPa = -0.2kPa Pulling fluid into tissues with a force of 0.2kPa Add this to the capillary outward force of 1.0kPa = 1.2kPa in total Capillary HP +SP (OP) 1.6kPa +-3.3kPa= -1.7kPa Tissues HP=SP (OP) 1.1kPa + -1.3kPa = -0.2kPa Pulling fluid into tissues with a force of 0.2kPa Add this to the capillary inward pull of -1.7kPa = -1.5kPa in total

NOTE You may not be expected to take the hydrostatic and oncotic effect of the tissues into account but you should be aware of it

Heart

Lymph is moved along the vessels in three ways: Hydrostatic pressure. Contraction of the body muscles. Valves maintain one way flow

Tasks Complete the comparison table for blood, tissue fluid and lymph