Capillaries and Exchange of Materials

Learning Outcomes Capillaries allow exchange of substances with tissues. Pressure filtration of fluids through capillary walls. Similarity of tissue fluid and blood plasma with the exception of plasma proteins. Tissue fluid supplies cells with glucose, oxygen and other substances. Carbon dioxide and other metabolic wastes diffuse out of the cells and into the tissue fluid to be excreted Much of the tissue fluid returns to the blood. Lymphatic vessels absorb excess tissue fluid and return the lymph fluid to the circulatory system.

Capillaries Blood is transported from arterioles to venules by passing through a dense network of blood vessels called capillaries All exchanges of substances between blood and living tissue takes place through capillary walls Capillary walls are composed of endothelium and are only one cell thick

Artery Tissues To the lungs From the lungs 1.Oxygen 2. Glucose 1. Carbon Dioxide 2. Waste O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 CO 2 Vein Capillary Network

capillaries

Plasma and Tissue fluid Plasma is a watery yellow fluid containing dissolved substances such as glucose, amino acids, blood cells, platelets and plasma proteins Blood arriving at the arteriole end of a capillary bed is at a higher pressure than blood in the capillaries As blood is forced into the narrow capillaries, it undergoes pressure filtration and much of the plasma is squeezed out through the thin walls This liquid is called tissue fluid The only difference between plasma and tissue fluid is that plasma has proteins

every living cell is bathed in tissue fluid... Tissue fluid contains a high concentration of dissolved food, oxygen, useful ions etc. These diffuse, down a concentration gradient, into the surrounding cells Carbon dioxide and other metabolic wastes diffuse out of the cells, down a concentration gradient, into the tissue fluid to be excreted

Tissue fluid Tissue Fluid

Tissue fluid and Lymph Much of the tissue fluid returns to the blood in the capillaries at the venule end of the capillary bed This is brought about by osmosis Tissue fluid lacks plasma proteins so it has a higher water concentration than the blood plasma Some of the tissue fluid does not return to the blood in the capillaries This excess tissue fluid is absorbed by thin-walled lymphatic vessels When the tissue fluid is in the lymphatic vessel it is called lymph

Lymphatic System Tiny lymph vessels unite to form larger vessels Flow of lymph is brought about by the vessels being compressed when muscles contract during breathing, movement etc. Larger lymph vessels have valves to prevent backflow Lymph vessels return their contents to the blood via two lymphatic ducts These enter the veins coming from the arms

Try these questions... 1.What is tissue fluid? 2.Name a substance that passes from body cells into tissue fluid 3.Describe two methods by which tissue fluid returns to the bloodstream 4.Describe the means by which lymph is forced along through the lymphatic system 5.Which structures prevent the backflow of lymph in the lymphatic system? 6.Which structures enable lymph to return to the blood circulatory system?

Answers... 1.It is the liquid consisting of plasma and small, dissolved molecules that is squeezed out of capillaries during pressure filtration 2.Carbon dioxide 3.It is returned to blood capillaries by osmosis and is absorbed into the lymphatic system via thin-walled lymphatic vessels 4.When the vessels are pressed during muscular contraction, the lymph is pushed along the lymph vessels 5.Valves 6.Two lymphatic ducts

1. What is tissue fluid? It is the liquid consisting of plasma and small, dissolved molecules that is squeezed out of capillaries during pressure filtration 2. Name a substance that passes from body cells into tissue fluid Carbon dioxide 3. Describe two methods by which tissue fluid returns to the bloodstream It is returned to blood capillaries by osmosis and is absorbed into the lymphatic system via thin-walled lymphatic vessels 4. Describe the means by which lymph is forced along through the lymphatic system When the vessels are pressed during muscular contraction, the lymph is pushed along the lymph vessels 5. Which structures prevent the backflow of lymph in the lymphatic system? Valves 6. Which structures enable lymph to return to the blood circulatory system? Two lymphatic ducts