Blood

• Blood


  Fluid connective tissue
• Blood


  • Average adult has about 4-6 liters, approx 8% of body weight
  • Constantly circulates around the body, propelled by the pumping action of the heart
  • Transports oxygen, nutrients (glucose), hormones, heat, antibodies (immunoglobulins), immune cells, clotting factors, and waste materials

  
• Whole blood


  Specimen obtained by medical technologist or phlebotomist; components are not yet separated

  
• Centrifugation of whole blood

  Different layers/components can be seen based on their molecular weight: heaviest at the bottom

  
• Main components of blood


  • Plasma (55%)
  • Cells or formed elements (45%)

  
• Buffy coat


  Junction between plasma & cells; contains platelets and white blood cells

  
• Formed elements or different cellular components


  • Platelets
  • White blood cells (neutrophils, lymphocytes, monocytes, eosinophils, basophils)
  • Red blood cells

  
• Plasma


  Largest part of our blood (55%); liquid (yellow) portion of the blood

  
• Plasma


  • Main constituent is water (90-92%)
  • Other components (dissolved in the plasma): proteins, inorganic salts/ions (electrolytes), nutrients, waste products, regulatory substances (e.g. hormones), gases
• Plasma proteins


  Normally retained within the blood because of their size; mainly responsible for creating the osmotic pressure of our blood, which keeps the plasma fluid within the circulation; the viscosity of the plasma is because of these proteins (mainly albumin and fibrinogen)

  
• Three types of dissolved proteins in the plasma

  • Albumins
  • Globulins
  • Clotting Factors
• Albumins


  Most abundant plasma proteins (about 60% of total); maintain normal plasma osmotic pressure; act as carrier molecules; formed in the liver; main function: protein transport
• Globulins


  Antibodies (immunoglobulins) - detection of antigen and trigger; transport some hormones and mineral salts (e.g. thyroglobulin); spherical proteins; defense or immunity; inhibition of some proteolytic enzymes (e.g. ⍺2-macroglobulin)
• Clotting Factors


  Responsible for blood coagulation; fibrinogen (most abundant clotting factor) - clotting protein dissolved in the plasma; formed in the liver; serum - refers to the plasma with the fibrinogen or clotting factors removed
• Other plasma components


  • Electrolytes
  • Nutrients
  • Waste Products
  • Hormones
  • Gases
• Electrolytes


  Have wide range of functions; ex: Ca2+, K+, Na+, PO43-; blood pH is maintained between 7.35-7.45 - slightly alkaline; the buffer systems in our body contains these electrolytes to help maintain acid-base balance
• Nutrients


  Substances essential for cellular growth and metabolism; necessary substances for our body to perform bodily functions normally; ex: glucose, amino acids, and vitamins; absorbed into the blood through our digestive system
• Waste Products


  By-products of some physiological processes; secreted into the blood to facilitate its removal; ex: waste products of protein metabolism (nitrogenous waste) removed from the blood by the kidneys: urea, creatinine, uric acid; waste product of tissue metabolism which is transported to the lungs for its excretion: carbon dioxide; waste product from the breakdown of worn out red blood cells: bilirubin
• Hormones


  Chemical messengers; regulatory substances; synthesized by the endocrine glands
• Gases


  Dissolved gases; oxygen (less than 2%) - most oxygen are found in the RBCs; enter or leave the body through the lungs; needed by the body for chemical reactions to occur; can also be produced by different cellular reactions as a waste product (ex: oxygen)
• Cellular content of blood


  Also known as formed elements; three types of blood cells: erythrocytes (red blood cells/RBCs), leukocytes (white blood cells/WBCs), thrombocytes (platelets)

  
• Blood cell synthesis


  Most blood cells are synthesized in red bone marrow; all blood cells originate from pluripotent stem cells - aka HEMOCYTOBLAST (hematopoietic stem cells); except the lymphocytes, all blood cells is formed in the red bone marrow; some lymphocytes are produced in lymphoid tissue
• Hemopoiesis/Hematopoiesis


  Process of blood cell formation
• Types of hemopoiesis


  • Erythropoiesis (production of RBCs)
  • Thrombopoiesis (production of platelets)
  • Leukopoiesis (production of WBCs)
• Erythrocytes (RBCs)


  • Most abundant type of blood cell (about 99% of all blood cells); biconcave discs; no nucleus; diameter: about 7 μm; main function is to transport gas mainly oxygen; flexible; no intracellular organelles (more room for hemoglobin); flattened shape allows them to stack like dinner plates in the bloodstream, reducing turbulence; lifespan in the circulation: ~120 days; RBCs in the average human body: ~30 trillion 10!"

  
• Erythropoiesis


  Erythrocyte development from stem cells (about 7 days); immature cells are released into the bloodstream as reticulocytes, and mature into erythrocytes over a few days within the circulation; both vitamin B12 and folic acid are required for red blood cell synthesis, in addition to iron, vitamin C, and copper
• Hemoglobin


  A large, complex molecule containing a globular protein (globin) and a pigmented iron-containing complex called heme/haem; each hemoglobin molecule contains four globin chains and four heme units, each with one atom or iron; each atom of iron can combine with an oxygen molecule; a single hemoglobin molecule can carry up to four molecules of oxygen
• Iron


  Carried in the bloodstream bound to its transport protein, transferrin, and stored in the liver; normal RBC production requires a steady supply of iron; absorption of iron from the alimentary canal is very slow, even if the diet is rich in iron, meaning that iron deficiency can readily occur if losses exceed intake
• Oxygen transport


  When all four oxygen-binding sites on a hemoglobin molecule are full, it is described as saturated; hemoglobin binds reversibly to oxygen to form oxyhemoglobin
• Oxyhemoglobin


  Oxygen-rich blood (usually arterial blood) - bright red
• Deoxyhemoglobin


  Oxygen-deficient blood (usually venous blood) - dark red
• Low pH


  Metabolically active tissues release acid waste products, causing oxyhemoglobin to readily break down and give up additional oxygen for tissue use
• Low oxygen levels in tissue (hypoxia)


  In metabolically active tissues, oxygen levels are always low; as tissue oxygen demand rises, so does the supply to match it; ↓ O2 levels = oxyhemoglobin breaks down to release oxygen
• Increased temperature


  Increases oxygen release
• Control of erythropoiesis


  Rate of RBC production = rate of RBC destruction; numbers remain fairly constant; homeostatic negative feedback mechanism; the primary stimulus for increased erythropoiesis is hypoxia; erythropoietin (produced mainly by the kidney) hormone that regulates red blood cell production
• Hypoxemia


  Low oxygen levels in your blood; may lead to hypoxia; possible causes: high elevation/altitudes, increased exercise, carbon monoxide exposure: erythrocytes favor carrying carbon monoxide than oxygen, resulting to a nonfunctional for oxygen transport RBC
• Hypoxia


  Low oxygen levels in your tissues
• Hemolysis


  Breakdown or destruction of RBCs carried out by macrophages in the spleen, bone marrow and liver; as erythrocytes age, their cell membranes become more fragile and so more susceptible to hemolysis; iron released by hemolysis is returned to the bone marrow to form new hemoglobin molecules; biliverdin is formed from the heme of the hemoglobin, reduced to the yellow pigment bilirubin, and excreted in bile
• Blood typing


  Based on the presence of ABO and Rhesus (Rh) antigens (inherited) on the surface of cells; antibodies are dissolved proteins in plasma that react to react to foreign antigens in a process called agglutination; antibodies for the ABO group are acquired as a child; antibodies for Rh antigens are acquired only through an exposure to the antigen
• Blood groups


  • AB - universal recipient; compatible with all groups as it makes no antibodies
  • O - universal donor; compatible with all groups since it has no antigens