Blood Vessels and Tissue Fluid Blood Vessels Arteries

Blood Vessels and Tissue Fluid

Blood Vessels Arteries: Carry blood away from the heart Arterioles: Control blood flow from arteries to capillaries Capillaries: Link arterioles to venules Venules: Link capillaries to veins Veins: Carry blood towards the heart

Guide to blood vessels 3 of 33 © Boardworks Ltd 2008

Structure of Blood Vessels • Tough outer layer – resists pressure • Muscle layer – can contract and control the flow of blood • Elastic layer – can stretch and recoil to maintain blood pressure • Endothelium – smooth layer to prevent friction • Lumen – not a layer – a cavity

Structure of Arteries • Thick muscle layer – control the flow of blood • Thick elastic layer – maintains blood pressure by stretching and recoiling • Narrow lumen

Structure of Veins • • Thin muscle layer Thin elastic layer Wide lumen Valves to prevent backflow of blood

Blood flow in veins 7 of 33 © Boardworks Ltd 2008

Varicose veins If a vein wall becomes weakened, valves may no longer close properly. This allows backflow of blood, causing the vein to become enlarged and bumpy, and become varicose. This usually happens in superficial veins, near the skin surface in the lower legs, as opposed to deep veins, which lie underneath muscles. Varicose veins can be surgically removed without affecting blood flow, as most blood is returned to the heart by deep veins. 8 of 33 © Boardworks Ltd 2008

Structure of Capillaries • No muscle • No elastic • Thin layer of cells only

Capillary Structure and Function • Thin layer of cells – short diffusion distance. • Numerous and highly branched – large SA for diffusion. • Narrow diameter – keep all cells close by. • Narrow lumen – bring red blood cells close to cells = short diffusion distance. • Spaces between cells – allow white blood cells to escape.

Structure of Arterioles Structure of Venules • Thicker muscle layer than arteries • Thinner elastic layer than arteries • Can constrict to control blood flow through capillaries • Muscle and elastic layers • Similar to veins but lumen is smaller • Can constrict to control blood flow through capillaries

Blood Vessels and Tissue Fluid

1 T I N U Key Ideas Diffusion – the movement of a substance from an area of high concentration to an area of lower concentration. Osmosis – the movement of water from a higher to a lower water potential through a semi-permeable membrane.

1 T I N U Water Potential �A measure of the tendency of water molecules to move from one area to another. �Pure water has a water potential of 0 k. Pa. �All other water potentials are negative (i. e. lower values). �The higher the concentration of solute, the more negative the water potential.

Key Terms Osmotic pressure – the ‘physical’ pressure you’d have to apply to stop water moving into a solution by osmosis, i. e. a measure of the likelihood of water moving into/out of a solution. We’re interested in the effect this has on a system.

Key Terms Hydrostatic pressure – the pressure exerted by a fluid at rest, i. e. a measure of the likelihood of water moving into/out of a solution. We’re interested in the effect this has on a system.

Plasma proteins and blood pressure About 8% of blood plasma consists of plasma proteins, of which about half may be albumins. These are a group of small proteins involved in the transport of other substances (e. g. fatty acids, hormones) and which help regulate the osmotic pressure of blood. The balance between the hydrostatic pressure of blood (‘blood pressure’) and the osmotic pressure of blood is important in the formation of tissue fluid. 20 of 33 © Boardworks Ltd 2008

Formation of tissue fluid 21 of 33 © Boardworks Ltd 2008

Lymph Not all tissue fluid returns to the capillaries. The excess drains into the lymphatic system, where it forms lymph. Lymph is a colourless/pale yellow fluid similar to tissue fluid but containing more lipids. lymphatic capillaries The lymphatic system drains into the circulatory system near the vena cavae via the thoracic duct. 22 of 33 © Boardworks Ltd 2008

The lymphatic system is a secondary circulatory system and a major part of the immune system. It consists of: l lymphatic capillaries and vein-like lymph vessels, containing valves l lymph nodes – sac-like organs that trap pathogens and foreign substances, and which contain large numbers of white blood cells l lymphatic tissue in the spleen, thymus and tonsils – these also contain large amounts of white blood cells and are involved in their development. 23 of 33 © Boardworks Ltd 2008

Problems – kwashiorkor • Lack of protein in the diet leads to lower plasma protein concentration • Water potential of blood is higher than normal • More water tends to leave capillaries and less is reabsorbed • Build up of tissue fluid, especially in abdomen. 24 of 33 © Boardworks Ltd 2008

Problems – blockage of the lymph ducts Can lead to lymphedema, elephantiasis or hydrocele. 25 of 33 © Boardworks Ltd 2008

Problems - cancer • Tumour cells multiply out of control • Some may break free from the tumour and travel in the blood/lymphatic system • Can become lodged in other areas • New tumours form - metastasis 26 of 33 © Boardworks Ltd 2008

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