Lecture 14 Body Fluids

Lecture 14: By the process of centrifugation of blood, we are packing all the cells together which is called PCV (packed cells volume) So the blood is distributed in these percentages: Plasma: 55% Platelets 1% or less Cells 45% What is the composition of plasma? 1. Mostly water 2. Small molecules as electrolytes (2%) 3. Proteins: 60-80 g/L mostly, types of proteins found are: - Albumin (40-50 g/L) about 54% - Globulins (alpha 1 and 2, beta, gama): (20-30 g/L) about 38% Note gama globulins are the antibodies - Fibrinogen: which is hardened to form the final product for blood clotting (fibrin) Ways to separate blood products: 1. Leaving the blood to coagulate first then centrifuging  fibrinogen is consumed with other coagulation factors  here we have serum along with cells 2. Centrifuging the blood without the process of coagulation here we have plasma along with cells So, serum is plasma without fibrinogen How to measure the plasma volume? Using something that can’t leave vessels proteins 1. we actually use iodine radioactive albumin and after half an hour we take samples and use the dilation method 2. we can also use” Evans blue” how to measure the total volume? 1. By labelling the RBCs with Cr-radioactive and by taking a sample and measuring its reactivity we can know the total blood volume 2. We can calculate it by using this equation if we know the plasma volume and the ratio of hematocrit: Total volume = plasma volume/(1-hematocrit) The osmolality is highly regulated By 1. Regulating the sodium concentration (osmolality) Osmoreceptors sense any change in the osmolality sending these changes towards the CNS which sends signals towards other centers in hypothalamic to activate the thirst sensation  drinking water.(increasing the input) In addition, the increase in osmolality leads to an increase in the secretion of ADH (antidiuretic hormone) from the pituitary gland, ADH acts on the kidney causing more reabsorption of water. (decrease the output) 2. Regulating the volume How do we sense the volume changes? - Any decrease in the volume of ECF will reduce the blood flow towards the kidney, activating another endocrine system called renin angiotensin aldosterone system: Renal cells (juxtaglomerular cells) can synthesize an enzyme called renin which converts angiotensinogen to angiotensin I, then ling tissue converts angiotensin I to angiotensin II which activates the release of aldosterone from suprarenal gland, aldosterone increases the absorption of sodium and the retention of sodium changes the osmolality causing osmosis and this changing the volume. - If there is an increase in volume: the right atrium releases the ANP hormone (atrial natriuretic peptide) which effect is to decrease blood pressure but also is has some other effects to reduce water and salt and decrease the angiotensin II (indirect effect) Disorders related to change in volume: 1. Hypervolemia 2. Hypovolemia Disorders related to change in osmolality: 1. Hyponatremia 2. Hypernatremia Some examples the Dr mentioned in the lecture: - Loss of pure water only by decreasing the secretion of ADH  hypovolemia , hypernatremia - Loss of plasma from the body  hypovolemia , isonatremia - Ingesting high amount of pure water  hypervolemia , hyponatremia - Giving someone hypertonic solution  hypervolemia , hypernatremia - Loss of salts by decreasing aldosterone  hypovolemia , hyponatremia - Increasing ADH  hypervolemia , hyponatremia - How can we increase the ECF only with no change in osmolality? by giving normal saline - Increase both ECF and ICF but decrease osmolality? increase ADH - Diabetes insipidus: decrease in ADH leading to high urination (osmolality increases and volume decreases) - Increase osmolality and increase ECF but decrease ICF? taking high amount of salts (increases osmolality and causes shifting of water from ICF to ECF)