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3. Blood.pdf

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PHGY 209
Erik Cook

Naveen Sooknanan McGill Fall 2011 Blood: Blood is the medium though which exchanges between the external environment and the milieu interieur can be made It is considered a tissue because it contains both cells and an external fluid (the ISF) In ancient cultures such as Greek and Indian, it used to be though that bleeding an individual was a treatment for disease It compromises both the ECF (plasma) and the ICF (within blood cells) It may be studied in vivo (inside an individual) and in vitro (on a petri dish) It accounts for approximately 7% of total body mass, around 5L in a standard physiological male A person with normal blood volume is called normovolemic. Lower blood volume is called hypovolemia and higher blood volume is called hypervolemia. Blood has many functions in the body It can be used in transport o Nutritive transport o Respiratory transport of oxygen o Excretion of waste o Hormone transport in order to regulate activities in the body o Temperature regulation Acid-Base equilibrium o Maintain a normal pH range of 7.30-7.45 Protective o Against microorganisms entering the body from the external environment in order to maintain integrity in the body Blood is composed of formed elements, meaning cells and cell fragments which are all suspended in plasma. Also located within plasma are nutrient, proteins and metabolic products which are transported between cells. 99% of these cells are erythrocytes, or red blood cells which carry oxygen The other 1% is divided among leukocytes, platelets and other cells involved with the immune system The hematocrit, as discussed before, is the percentage of plasma which is occupies by red blood cells, and should be around 45% in a normal individual o The volume of red blood cells, therefore, is 45% of blood volume, which is 2.25L o The plasma volume, therefore, is 55% of 5L, or 2.75L The composition of plasma is similar to that of the ISF More than 90% water, although its viscosity is 5 times more than water because of materials +uspended-within the plasma - - Mainly Na and Cl , but also potassium, calcium, magnesium, HCO and P3 in much 4 smaller concentrations o This is why plasma can be approximated by a 0.9g/dL NaCl solution, which is physiological saline 1 Naveen Sooknanan McGill Fall 2011 Glucose, amino acids, lipids, oxygen and carbon dioxide o Although present in small concentrations, they reflect enormous turnover as there is a constant flow of these materials between capillaries and the ISF Proteins (colloids) make up 7g%, or 7g/dL of plasma, and are the main reason for the high viscosity of plasma o The plasma mainly contains albumins, globulins and fibrinogens Plasma proteins are separable by 4 main characteristics: Differential precipitation by salts o (NH ) S4 2s 4sed to precipitate all of the proteins in the plasma which can form different layers of sediment Sedimentation by ultracentrifugation o Proteins can be physically separated into different layers Electrophoretic mobility o Movement based on size and charge Immunological characteristics o Very accurate, and allows for identification of specific molecules Electrophoresis is a fractional method based on the movement of charges particles through a matrix along a voltage gradient Proteins dissociate in acidic material, and tend to migrate towards a positive electrode due to their net negative charge Rate of migration is influenced by the number and distribution of charges as well as the molecular weight of each protein o Heavier molecules will not move as far across the matrix o Each protein has its own characteristic migration rate A gel electrophoresis of plasma shows the presence of albumin, the lightest plasma proteins, multiple globulins, each which their own characteristics, as well as fibrinogens, which are one of the heaviest plasma proteins. The scan of the plasma proteins can test for the proportion of the different colloids. The higher the peak, the more of that protein present within the plasma sample o Albumin is the most abundant plasma protein Serum is a sample of plasma that has been treated with an anticoagulant. This removes all of the clotting factors in the blood which allows it to stay longer and is usually used in medical tests. Since fibrinogen is used in the clotting process, it is absent in the serum. Electrophoresis can also be used in the diagnosis of some diseases involved with colloids Renal disease involves an unusually permeable kidney which allows the leaking of proteins. This causes a noticeable decrease in albumin concentration in individuals carrying this disease In bacterial infection, there is an increased concentration of globulins which contain antibodies 2 Naveen Sooknanan McGill Fall 2011 While albumin, fibrinogen, and 1 2nd globulins are produces mainly in the liver, globulins are produced mainly in lymphoid tissue. As seen by this table, albumin are the smallest proteins present in plasma but are in the highest concentration Globulins are a very heterogeneous mixture can vary greatly in size, and have the second highest concentration in plasma Fibrinogens are large, elongated plasma proteins involved in clotting and are the lowest concentration in plasma, but are the main contributors to the viscosity of plasma The primary role of plasma proteins is determining the distribution of fluid between the plasma and the ISF by controlling transcapillary dynamics through the colloidal osmotic pressure. The normal ratio of volumes of ISF and plasma is 3:1, but these fluids are always in a dynamic equilibrium Although the ion concentrations between the plasma and the ISF are very similar, the plasma contains a noticeably higher protein concentration which drives transcapillary dynamics As we saw before, diffusion is responsible for the exchange of nutrients and gases across the CW and the Starling Forces are responsible for the volume distribution between plasma and the ISF o The COP is determines by the number of particles of protein per unit volume It is therefore directly related to concentration in the plasma and inversely related to molecular weight I.e. which has more particles, 10kg of bricks or 10kg of feathers? o As seen in the following table, albumin contributes the most to the COP of plasma while fibrinogen does not contribute much A second function of plasma proteins is contributing to the high viscosity of plasma which is 5-6 times higher than water. This contribution is mainly made by fibrinogen, which are among the largest of plasma proteins A third function of plasma proteins is to contribute to the buffering power of plasma, which allows the blood to maintain a constant pH of around 7.4 Proteins are very good pH buffers Some more specific plasma protein functions include Fibrinogen and some globulins are essential in blood clotting Globulins (immunoglobulins) have specific resistance to infection Albumin and some globulins act as carriers for certain molecules such as lipids, hormones and minerals which are not readily soluble in plasma o Iron is an example which must be bound to proteins because they are toxic when flowing freely in plasma 3 Naveen Sooknanan McGill Fall 2011 There are many types of cells which are suspended in plasma, but the most common are red blood cells (erythrocytes), platelets and white blood cells (leukocytes) RBCs are the most abundant cell found in plasma. There are around 5x10 cells per L and measure 7.2m in diameter o They have a shorter lifespan of around 120 days because they contain no nucleus Platelets, or thrombocytes, are cell fragments 2-3m in diameter which have a very short life span of only 7-8 days o There are only 250000-400000 platelets per L of blood WBCs are even less abundant in blood, only 8000-10000 cells per L, but are larger than RBCs and platelets, around 10-18m. Their size can vary greatly as there are many different types o They can live anywhere from a few hours to a few years, depending on the type A general term, hematopoiesis, is sued to describe the production of blood cells. Erythropoiesis described the production of RBCs Thrombopoiesis describes the production of platelets Leukopoiesis describes the production of WBCs Hematopoiesis begins from a self-replication pluripotent stem cell which, when induced by an inducer, can either replicate or differentiate into committed stem cells
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