22 Renal Mechanisms

22 Renal Mechanisms - RENAL MECHANISMS page 1 AC Brown A7d...

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RENAL MECHANISMS © AC Brown page 1 A7d INTRODUCTION A. Role of Kidneys: primarily regulation or homeostasis (rather than excretion) 1. Regulation of blood plasma and interstitial fluid composition (homeostasis), especially inorganic ions – electrolyte balance (e.g. Na + , K + , Cl - , Ca 2+ ) and osmolality 2. Regulation of body fluid volume -- fluid balance 3. Regulation of blood plasma and interstitial fluid pH 4. Excretion of (non-volatile) metabolic end products (e.g. urea, uric acid, creatinine, NH 4 + ) and “foreign” solutes (e.g. some drugs) Note: The above are functions are vital; loss of renal function leads to debilitation beginning in about one day and terminating in death in one-two weeks 5. Endocrine organ, secreting a. renin , for regulation of Na + , ECF (extracellular fluid volume), vascular resistance b. erythropoietin , for regulation of erythrocyte production c. calcitriol , related to calcium regulation 6. Metabolic functions: e.g. peptide degradation, synthesis of NH 3 and H + B. General Renal Mechanism of Body Fluid Regulation: Selective withdrawal of substances from the blood plasma flowing through the kidneys and excretion these substances in the urine (main mechanism) Note: When renal function is measured, the values generally refer to both kidneys taken together; e.g. renal blood flow refers to the total blood flow rate through both kidneys, renal sodium excretion rate refers to the total excretion of sodium ion by both kidneys C.. Urine Formation Rate Normal 1 ml/min (1.5 L/day) Normal range 0.4-2 ml/min (0.5-3 L/day) Oliguria < 0.4 ml/min (< 0.5 L/day) Anuria < 0.04 ml/min (< 50 ml/day) Polyuria > 2 ml/min (> 3 L/day)
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RENAL MECHANISMS © AC Brown page 2 A7d INTRODUCTION (continued) D. Typical Composition of Urine (and Blood Plasma) Plasma Urine Na + 145 100 mM/L Cl - 105 100 K + 4.5 90 HCO 3 - 24 1 glucose 90 (5 mM/L) 0 mg/dl (mg%) plasma proteins 7 0 gm/dl (gm%) urea 15 900 mg/dl uric acid 5 45 creatinine 1 120 pH 7.4 6.0 osmolar conc 300 500 mOsm/kg (Note: mg/dl = mg solute per 100 ml fluid; mg/dl = mg%) Plasma has a relatively constant composition Urine composition is variable in order to maintain homeostasis E. Terms renal refers to kidney nephro- refers to kidney or its functional unit (nephron) nephritis inflammation of the kidney nephrology medical specialty dealing with the kidney -uria refers to urine composition or volume glucosuria presence of glucose in the urine albuminuria presence of albumin in urine anuria no urine formation urology surgical specialty dealing with the urinary tract -emia refers to blood uremia high concentration of urea in blood plasma diuresis excretion of a large volume of urine water diuresis excretion of a large volume of dilute urine osmotic diuresis excretion of a large volume of normal or high osmolarity diuretic a substance that causes diuresis diabetes certain diseases characterized by diuresis diabetes mellitus diuresis characterized by glucose containing urine diabetes insipidus
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22 Renal Mechanisms - RENAL MECHANISMS page 1 AC Brown A7d...

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