blood, tissue fluid and lymph

• Blood


  A tissue which functions mainly as a transport medium
• Functions of blood


  • Transport plasma
  • Transport yellow components
  • Transport all cellular components
  • Transport gases like oxygen and carbon dioxide
  • Transport heat
• Blood components


  • Plasma
  • Red blood cells
  • White blood cells
  • Platelets
• Plasma


  A pale (straw coloured) watery liquid containing about 90% water plus 10% dissolved substances, including plasma proteins, inorganic salts, organic nutrients, hormones, urea, lactic acid, carbon dioxide
• Plasma proteins


  Include albumin, globulin, lipoproteins (HDLs & LDLs)
• Red blood cells/Erythrocytes


  Small biconcave disc-shaped cells with a diameter of 7-8μm, continuously made in the bone marrow (about 5 million cells/ml of blood), specially adapted for carrying oxygen, lifespan of approx. 120 days after which they are broken down in the liver, contain haemoglobin (approx. 300 million molecules of Hb occur in each erythrocyte and each molecule of Hb can bind a maximum of FOUR molecules of oxygen), biconcave shape gives a large surface area to volume ratio for maximum absorption of oxygen, flexible plasma membrane enables them to squeeze through narrow capillaries
• Leucocytes


  Irregular in shape with a diameter of between 6-20μm, involved in defence against disease, do not have any role in blood flow, fewer white blood cells in the blood (approx. 7000/ml of blood) but this increases dramatically when there is an infection
• Types of leucocytes


  • Phagocytes (neutrophils and macrophages)
  • Lymphocytes (T cells and B cells)
  • Eosinophils
  • Basophils
  • Mast cells
  • NK cells
• Phagocytes


  Phagocytose and destroy pathogens e.g. bacteria, viruses and protozoa, phagocytose damaged body cells and help in the clean-up and repair process, can change shape and squeeze out of capillaries, detect chemical signals called chemokines and move towards foreign particles or microbes by chemotaxis
• Neutrophils


  Most abundant white blood cell in the blood stream, make up 70% of all leucocytes, have multi-lobed nucleus and granular cytoplasm, non-dividing, short-lived (less than a day)
• Macrophages


  Largest of all leucocytes and long lived, found initially in the blood as monocytes, migrate to the tissues and become tissue macrophages which are long-lived cells found in the lungs, brain, kidney, bone, spleen and lymph nodes
• Lymphocytes


  Spherical cells from 7-12μm in diameter, large round nucleus which almost fills the cell, motile (not as much as phagocytes), main cells in lymphoid tissue, main cells in the specific immune response
• Types of lymphocytes


  • T lymphocytes (helper T cells, killer/cytotoxic T cells, regulatory T cells)
  • B lymphocytes
• Platelets/Thrombocytes


  Small non-nucleated fragments, of larger cells found in the bone marrow, important role in the clotting of blood
• Blood clotting


  1. Platelets surrounding the damaged region release an enzyme which converts the soluble blood plasma protein fibrinogen to the insoluble threads of fibrin

  2. Erythrocytes and leucocytes then get trapped in this tangled network of fibres and form a clot

  3. The clot eventually dries out and forms a scab
• Tissue fluid


  The fluid immediately surrounding the body cells, very similar to plasma but with fewer proteins
• Exchange of materials between blood and tissues


  1. As blood flows through the capillaries it slows down

  2. The capillary walls are thin and permeable and the high hydrostatic pressure forces plasma out through the capillary walls and into the spaces between the body cells; it is now known as tissue fluid

  3. When plasma leaves the blood, dissolved nutrients and oxygen go with it and these diffuse into the body cells from the tissue fluid

  4. Most tissue fluid returns to the capillaries carrying waste materials such as CO2 which it has picked up from the body cells

  5. Some tissue fluid passes into the lymph vessels and becomes lymph
• Lymph


  Fluid found in lymphatic system and consists mainly of 95% water + protein, glucose, salts, lymphocytes, and macrophages similar to plasma but fewer proteins and lipoproteins (HDLs/LDLs)
• Lymph vessels


  As numerous as capillaries, begin as blind-ending tubes in the capillary beds, the small lymph vessels join to form larger vessels which unite to form two main branches which eventually drain their contents into the subclavian vein in the upper thorax, under low pressure, have valves which ensure lymph flows in only one direction, situated between skeletal muscles so that muscle contraction squeezes the lymph along the vessels
• Lymph nodes


  Small organs made up mainly of lymphocytes, together with macrophages and other cells involved in the immune response, located in pairs on either side of the neck, in both armpits and in the groin area
• Plasma membranes are composed mainly of phospholipids with some cholesterol and proteins embedded within them.
• Phospholipid molecules have hydrophilic (water-loving) heads and hydrophobic (water-hating) tails.