Blood cells, clotting and blood diseases

• The main functions of the blood

  -transport of important blood components

  -protection from infection and blood loss

  -homeostasis
• Blood is composed of plasma and cellular element.
• Plasma contains water, ions, organic molecules, trace elements and nutrients and gases.
• The plasma proteins in the blood are albumins, globulins and fibrinogen.
• The white blood cells include: lymphocytes, monocyte, neutrophil, eosinophil and basophils.
• Red blood cells have a 4 month lifespan.
• Red blood cells are also called erythrocyte.
• Albumins are produced by the liver and provide the osmotic pressure needed to maintain blood volume and pressure, by drawing water from the tissues into the capillaries.
• Alpha and beta globulin’s transport lipids and fat-soluble vitamin.
• Gamma globulins are the antibodies produced by activated B lymphocytes.
• Fibrinogen is an important clotting factor produced by the liver that gets converted into fibrin during the clotting process to reduce blood loss.
• Red blood cells transport oxygen and carbon dioxide between the lungs and the body. They are biconcave disc(7.5 micrometer in diameter) and have no nucleus.
• Dead cells are removed by macrophages in the liver, spleen and bone marrow. New cells are made in the bone marrow under hormonal control (erythropoietin)
• The cells are packed with haemoglobin.
• Tissues with extensive ECM present include epithelial, neural and muscle.
• Insoluble protein fibres such as collagen, fibronectin and laminin provide strength and anchor cells in the tissue (particularly in cartilage and bone)
• Desmosomes, like adherens junctions in previous slide, also use cadherin proteins (grey) to link adjacent cells together but via intermediate filaments in the cytoskeleton, not actin. 

  •Strongest of the cell/cell junctions
• Hemidesmosomes use cell surface integrin proteins to link keratin of the cell to the laminin protein found in the extracellular matrix 

  •(cell/ECM interaction)
• Focal Adhesions:

  •Also use integrin proteins to link cellular actin cytoskeleton fibres to mainly fibronectin proteins in the extracellular matrix

  •(cell/ECM interaction)
• The cell membranes of adjacent cells partially fuse together using proteins called Claudins, Occludins and JAM proteins (junction adhesion proteins).
• Tight junctions are found for example in the gastrointestinal (GI) tract, and the kidney (transport epithelia).
• The blood-brain barrier is created by tight junctions.
• Tight Junctions (cell/cell)

  Form a barrier that restricts movement of material between cells (also called occluding junctions)
• Gap Junctions

  Allow rapid, direct communication between adjacent cells = communicating junctions
• Connexins- Cylindrical proteins that form intercellular channels (cytoplasmic bridges) that span the two cell adjoining cell membranes
• Each channel (pale blue in diagram) is composed of 12 connexin proteins
• Clusters of many channels form a Gap junctionwhich can open and close to allow chemical or electrical signals to flow between cells
• Gap junctions regulate the passage of ions and small molecules between cells
• Gap junctions are the simplest form of junction between cells
• Secretory epithelial cells (such as the cells of the pancreas) make and release products.

  Exocrine secretions, such as mucus or digestive enzymes are secreted out of the cell into tissues and organs.

  Endocrine secretions (e.g. Hormones such as insulin) are released into the blood.
• 1. Transport epithelium

  Selectively move substances between the lumen (inside space of a tubular structure. (e.g. small intestine) and the extracellular fluid (e.g. blood)