RENAL PHYSIOLOGY Zekeriyya ALANOGLU, MD, DESA. Ahmet Onat Bermede, MD. Ankara University School of Medicine Dept. Anesthesiology and ICM
Kidneys Stabilize the composition of the ECF (electrolyte, H + concentration) Excrete end-products of protein metabolism (urea) Retain essential body nutrients (amino acids, glucose) Secrete hormones Regulation of sistemic blood pressure (angiotensin II, PG, kinins) Production of erythrocytes (erythropoietin)
Anatomy 115 160 g Located retroperitoneally, beneath the diaphragm Cortical (outer) and medullary (inner) portion Level of L2 Receives 20% of the CO
Nephron
Nephron Glomerulus Only in renal cortex Invaginate into dilated blind end of renal tubule as Bowman s capsule Afferent arteriol Efferent arteriol Afferent Arteriole Efferent Arteriole Proximal Tubule 10
Nephron Renal tubule Proximal con. tubule Loop of Henle Distal con. tubule Cortical ve Juxtamedullary nephrons Collecting duct delivers fluid into the renal pelvis Water and solutes are reabsorbed Other solutes are secreted by epithelial cells
Renal Blood Flow Receives 20-25% of cardiac output 400 ml/100 g/min (Heart and liver 70 ml/100 g/min) 90-95% of blood flow delivered to the renal cortex High oxygen consumption Renal cortex PO 2 50mmHg; 10 mmhg in medulla
Influence of Anesthesia and Surgery Anesthetic drugs Potential to alter renal function (systemic blood pressure, CO) Redistribution of blood flow Renal cortex Inner renal medulla Sodium and water conservation Anesthetic-induced Decreases in CO Release of arginine vasopressin (AVP) (ADH) Increased activity of sympathetic nervous system Renin angiotensin aldosterone system
Influence of Anesthesia and Surgery Hypovolemia + sympathethic nervous system Renal vascular resistance Shunt to non renal sites!!! Intraoperative urine output does not correlate with postoperative renal function.
Prostaglandins Renal response to ischemia NSAID Inhibits COX No effect in healthy subjects RBF and GF if renal circulation compromised PGE 2, Na + reabsorption O2 consump.
Glomerular capillaries Afferent arteriole Efferent arteriole Resistance to blood flow Glomerular capillaries High pressure system Fluid moving into Bowman s capsule
Peritubular capillaries Renal cortex blood flow Efferent arteriole Peritubular capillaries Low pressure system Fluid from renal tubules is absorbed 180 L/day filtered from glomerular capillaries 1.5-2 L stays in the renal tubules
Vasa Recta Renal medulla blood flow Maintain a high osmolarity Solute transport out of the ascending limb of Henle Allow tubular fluid to be concentrated Countercurrent arrangement of a specialized portion of the peritubular capillaries: Vasa recta
Autoregulation of Renal Blood Flow MAP 60,80-160, 180 mmhg Myogenic response Tubuloglomerular feedback
Juxtaglomerular Apparatus
Juxtaglomerular Apparatus Distal renal tubule passes in the angle between afferent and efferent arteriole Renin
Glomerular Filtrate Great permeability of glomerular capillaries Presence pores in the endothelial cells Rapid filtration of fluid and small molecular weight substance (<8nm) Glomerular filtrate: Plasma without proteins
Glomerular filtration rate The amount of glomerular filtrate (GF) formed each minute by all the nephrons. 125 ml/min, 180 L/day Reabsorption %99 of GF during passage through renal tubule Urinary sodium ion excretion parallels GFR
Glomerular Filtrate Normal GFR 12.5 ml/min/mmhg of filtration pressure resulting in a GFR of 125 ml/min Net filtration pressure 10 mmhg
Glomerular Filtrate Mean arterial pressure Blunted by autoregulation Tubuloglomerular feedback Cardiac output Sempathetic nervous system T 4 -T 12 Preferential constriction of afferent arteriole Glomerular blood flow
Renal Tubular Function Reabsorption is more important than secretion 2/3 of reabsorption and secretion is in proximal renal tubules Aldosteron AVP Renal prostaglandins ANF
Renal Tubular Function Active transport against concentration gradient Na-K ATPase system Cotransport (glucose, amino acid, organic acid) Proximal convoluted renal tubules 80% O 2 consumption Aldosteron Reabsorbtion of Na, secretion of H and K in the distal tubule
Renal Tubular Function 99% of water reabsorbed Distal renal tubules impermeable to water AVP determines permeability of epithelial cells in collecting ducts
Renal Tubular Function Aquaporins Simple diffusion protein water channel Aquaporin 1, 2, 3 in kidney A-4 in brain A-5 in salivary glands and respiratory tract Countercurrent system Blood inflow runs parallel and opposite direction to outflow Eliminate soluts with minimal excretion of water
Regulation of Body Fluid Blood volume Extracellular fluid volume Osmolarity of body fluids Plasma concentration of ions
Blood Volume
Extracellular Fluid Volume Same as blood volume Reservoir for excess fluid that may be administered intravenously during perioperative period
Osmolarity of Body Fluids Administered by sodium in extracellular fluid Osmoreceptor-AVP mechanism Thirst reflex Aldosterone effect is limited!!!
Osmolarity of Body Fluids Osmoreceptor-AVP mechanism Supraoptic nuclei of hypothalamus AVP release from posterior pituitary Retention of water Thirst reflex Increased Na concentration in ECF causes Angiotensin II production Sensation of dry mouth Na 2mEq/L or plasma osm 4 mosm/l
Plasma Concentration of Ions Potassium Aldosteron effects on renal tubules Increased secretion of K + ions H + ions compete for secretion Na + intake may influence potassium
Plasma Concentration of Ions Sodium Active transport of Na into peritubular capillaries 2/3 of Na reabsorbed from proximal tubules Aldosterone Influences Na reabsorption from distal tubules and collecting ducts
Plasma Concentration of Ions Hydrogen Secrete H + by exchanging Na + Acidify the urine Ammonium formation Calcium Parathyroid hormone Magnesium Reabsorbed by renal tubules
Plasma Concentration of Ions Urea Most abundant of the metabolic waste products Determining the rate of urea excretion Blood urea nitrogen (BUN) GFR 50% of urea enters the renal tubules appears in urine
Atrial Renal Natriuretic Factors ANP; Synthesize by cardiac atria Related to atrial pressure and atrial diameter Cardiovascular regulator Vasodilator, systemic blood pressure İnhibition of ANP, urine output, NA excretion and renin PEEP, ANP RNP (urodilatin); Synthesize by cortical nephrons İntrarenal regulation of Na excretion
Acute Renal Failure Abrupt deterioration of renal function with a decrease in glomerular filtration rate occuring over a period of hours to days, resulting in the failure of kidneys to excrete nitrogenous waste products (urea/cre) and to maintain fluid and electrolyte homeostasis
Acute Renal Failure
Prerenal Azotemia Renal hypoperfusion Hypovolemia and renal artery atherosclerosis in elderly patients NSAID in prostaglandin dependent patient for renal vasodilatation Congestive heart failure, septic shock, radiocontrast media
Intrinsic Renal Failure Renal tubular necrosis due to ischemia or nephrotoxins Destruction of epithelial cells lining the renal tubules Imbalance of the oxygen supply and demand of renal medullary ascending limb tubular cells Ischemia of renal medullary ascending tubular cells in the perioperative period
Postrenal Nephropathy Obstructive renal failure Renal stones Prostatic hypertrophy Mechanical kinking of catheters Sudden acute oliguria in perioperative period Mechanical obstruction of drainage devices
Acute Renal Failure Oliguric Urine output < 400 ml/day Nonoliguric Urine output > 400 ml/day Better prognosis 20-60% of patients require dialysis
Acute Renal Failure Diagnosis
Acute Renal Failure Treatment Reverse underlying cause Correct fluid and electrolyte imbalances Dopamine if needed Mannitol and furosemid? Dialysis Volume overload Hyperkalemia Metabolic acidosis Severe uremia
Chronic Renal Failure Progressive loss of nephron function and decline in GFR
Chronic Renal Failure Manifestations of chronic renal failure Accumulation of metabolic waste products in blood Excretion of fixed specific gravity urine Metabolic acidosis Hyperkalemia Anemia Platelet dysfunction Fluid overload and systemic hypertension Nervous system dysfunction Osteomalacia
Chronic Renal Failure Dialytic Therapy Indications Hyperkalemia Acidosis Fluid overload BUN 80-100 mg/dl İnfection remains main cause of death İntermittent,continuous and peritoneal
Chronic Renal Failure Complications of Dialytic Therapy Infection Activation of complement system Hypotension Arterial hypoxemia Skeletal muscle cramping Protein depletion Anticoagulation Access failure