Unit 4D notes.docx - Responses to Dehydration Dehydration...

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Responses to Dehydration - Dehydration causes decrease in blood volume/pressure & increase in osmolarity o Decrease blood volume – sensed by atrial volume receptors Carotid & aortic baroreceptors signal cardiovascular control center to raise blood pressure Sympathetic output increases while parasympathetic output decreases o Causes sympathetic vasoconstriction in kidneys = decrease GFR = conserves fluid o Causes activity of granular cells increasing renin secretion o Decrease blood pressure directly decreases GFR Low GFR = conserves more fluid = decrease fluid flow down macula densa and triggers paracrine factors/renin release o Increase osmolarity triggers hypothalamus osmoreceptors to release vasopressin to increase H20 reabsorption - Summary o Restoration of volume by water conservation & fluid intake (vasopressin & thirst) o Maintenance of blood pressure through increased blood volume, increased cardiac output & vasoconstriction (sympathetic output to decrease GFR) o Restoration of all normal osmolarity by decreased Na+ reabsorption and increased water reabsorption Acid- Base Balance – Why it Matters - H+ concentration is closely monitored because it affects tertiary structure of proteins (enzyme function) - Abnormal pH can affect the nervous system o Acidosis o Alkalosis - pH disturbances are associated with K+ disturbances o Due to renal transporters (H+/K+ ATPase) Acidosis – secretes H+, reabsorbs K+ Alkalosis – reabsorbs H+, secretes K+ pH Balance in the Body - H+ input o Fatty Acids & Amino Acids (diet) o Co2/Ketoacid/Lacticacid (metabolism) - Buffers o HCO3- in extracellular fluid o Proteins/hemoglobin & phosphates in cells o Phosphates/ammonia in urine - H+ output o CO2 – ventilation o H+ renal
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Sources of H+ - CO2 during aerobic respiration is the main source of acid in the body - Reaction takes place in all cells in the plasma but slowly o High levels of carbonic anhydrase can increase speed - Hypoventilate (accumulate CO2) = shifts reaction to the right more H+ acidosis - Hyperventilate = shifts reaction to left, lower H+ alkalosis Components of pH Homeostasis - Buffers o First line of defence - Ventilation o Blowing off CO2 o Fast response o Second line of defence (corrects 75% of disturbances but can also cause) - Renal Regulation o Slower, but highly effective o Directly by excreting or reabsorbing H+ o Indirectly by changing the rate at which HCO3- is reabsorbed or excreted When is Which components used? - If plasma pH moves out of normal range and buffer has been overwhelmed, it is up to ventilation & renal regulation - If primary cause is respiratory than only renal mechanism will remain - If primary cause is metabolic, then both respiratory & renal mechanisms can be used Respiratory Compensation for Acidosis (Hypoventilation)
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