Starter Compare the structures of arteries, veins and capillaries with reference to structure and function

Transport in Animals Transport Systems Blood Vessels This lesson Transport in Animals Transport Systems Blood Vessels Exchange in the Capillaries The Structure of the Heart The Cardiac Cycle Coordination of the Cardiac Cycle Transport of Oxygen Transport of Carbon Dioxide

Exchange in the Capillaries Learning outcomes Exchange in the Capillaries Who? Outcomes Some Describe the formation of tissue fluid from plasma Most Apply knowledge of the formation of tissue fluid from plasma

Composition of the blood What do these two electron microscope images show? Why are these cells important in the blood? Red blood cells (erythrocytes) White blood cells (leucocytes) Fragments called platelets

Composition of the blood Blood consists of a liquid called plasma containing many blood cells and dissolved substances inc. oxygen, carbon dioxide, minerals, glucose, amino acids, hormones and plasma proteins

Composition of the blood

Tissue Fluid Similar to blood plasma minus plasma proteins and most the blood cells Formed by plasma leaking from the capillaries Surrounds and supplies the cells in the tissue As blood plasma leaks from the capillary, it carries dissolved substances into the tissue fluid by mass flow down a pressure gradient (not diffusion) Waste products from cell metabolism are carried back to the capillary with the returning fluid

Formation of Tissue Fluid Blood flowing into an organ or tissue is contained in the capillaries At the arterial end of the capillary, blood is at a relatively high hydrostatic pressure (pressure exerted by fluid pushing against the sides of the vessel) > blood fluid is pushed out through the capillary wall > fluid (plasma with dissolved nutrients and oxygen) can leave through the tiny gaps between the cells in the capillary wall> exchange of gases and nutrients can occur by diffusion, facilitated diffusion and active transport

Returning to the Blood At the venous end of the capillary, blood is at a relatively low hydrostatic pressure > some tissue fluid returns to the capillary, carrying carbon dioxide and other waste substances Some tissue fluid is directed into another tubule system (the lymph/ lymphatic system), which drains excess tissue fluid and returns it to the blood system in the subclavian vein in the chest. Tissue in this system is called lymph and is like tissue fluid but contains more lymphocytes (produced in the lymph nodes – swellings along the lymphatic system which have an important role in immune response)

Lymphatic System

Oncotic pressure Alongside the hydrostatic pressure of both the blood and the tissue fluid, oncotic pressure as an influence = ‘pressure created by the osmotic effects of the solutes’ Hydrostatic pressure pushes fluid out of the capillaries into the blood at the arterial end and back in at the venous end Oncotic pressure of the blood pulls water back into the blood, oncotic pressure of the tissue fluid pulls blood into the tissue fluid Together these forces create a pressure to push fluid out of the capillary at the arterial end and into it at the venous end.

Oncotic pressure A single capillary showing the relative hydrostatic and osmotic (water potential) forces

Copy and Complete Feature Blood Plasma Tissue Fluid Lymph Hydrostatic pressure High Low Oncotic pressure (created by the osmotic effects of solutes) More negative Less negative Cells Red blood cells, neutrophils, lymphocytes Some neutrophils, especially in infected areas Lymphocytes Proteins Plasma proteins Few proteins Fats Transported in lipoproteins Few fats More fats, especially near the digestive system

Complete the exam questions Summarise the similarities and differences between plasma, tissue fluid and lymph Explain how hydrostatic and oncotic pressure affect the movement of fluids into and out of capillaries Describe the main functions of the blood

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Exchange in the Capillaries Learning outcomes Exchange in the Capillaries Who? Outcomes Some Describe the formation of tissue fluid from plasma Most Apply knowledge of the formation of tissue fluid from plasma