Renal system

Renal System

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Objectives

Anatomy. Function and Physiology. Laboratory Findings. Cardinal features of kidney and urinary tract disease.
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Adult kidneys are 11-14 cm. The right kidney is usually a few centimeters lower because the liver lies above it. Each kidney contains approximately 1 million functional units, or 'nephrons'. The kidney has an extensive vasculature that accommodates 20 to 25% of the cardiac output. Of the daily filtrate of over 150 L, typically 99% is reabsorbed in the tubules.
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urine

blood
filtration
tubular reabsorption and secretion
General Functioning of the Kidney
“refreshed” blood *

Glomeruli: Autoregulation maintains a constant glomerular filtration rate(GFR) by altering arteriolar tone over a wide range of systemic blood pressure and renal perfusion pressure.Proximal Tubule: The proximal tubule is responsible for reabsorbing ~60% of filtered NaCl and water, as well as ~90% of filtered bicarbonate and most critical nutrients such as glucose and amino acids.Loop of Henle: The loop of Henle consists of three major segments: descending thin limb, ascending thin limb, and ascending thick limb. Approximately 15–25% of filtered NaCl is reabsorbed in the loop of Henle, mainly by the thick ascending limb. Distal Convoluted Tubule: The DCT reabsorbs ~5% of the filtered NaCl. Is the site of action of SpironolactoneCollecting Duct: The collecting duct regulates the final composition of the urine, contribute to reabsorbing ~4–5% of filtered Na+ and are important for hormonal regulation of salt and water balance. *


Ureter, Bladder and Prostate
Ureter deliver urine from renal pelvis to bladder which store urine. Sympathetic innervation cause detrusor muscle relaxation and bladder neck contraction. While parasympathetic stimulate detrusor muscle contraction and micturition. Prostate: it surround the proximal urethra, produce 20% of ejaculatory fluid.
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Functions of Kidney

Regulating the volume and composition of body fluids. This is achieved by making large volumes of an ultrafiltrate of plasma (120 mL/min, 170 L/day). The kidney is primarily responsible for excretion of many metabolic breakdown products (including ammonia, urea and creatinine from protein, and uric acid from nucleic acids), drugs and toxins. Hormonal functions Erythropoietin is production Hydroxylation of 25-hydroxycholecalciferol to the active form, 1,25-dihydroxycholecalciferol. Renin is secretion in response to reduced afferent arteriolar pressure, stimulation of sympathetic nerves, and changes in sodium content of fluid in the distal convoluted tubule at the macula densa.
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Laboratory Findings

Twenty-four Hour Urine Collection for Protein Excretion Proteinuria (as albuminuria) of greater than 3.5 g in 24 hours indicates glomerular disease. Occasionally, overflow proteinuria of a small-molecular-weight protein, such as light chains in Bence Jones proteinuria, can be greater than 3.5 g/day without any of the manifestations or implications of the nephrotic syndrome. A urine protein electrophoresis study is important in making the distinction. Protein-to-Creatinine Ratio : The 24-hour urine collection for protein excretion is subject to inaccuracies. A spot urine sample for protein and creatinine can be used to estimate the amount of protein excreted. A protein-to-creatinine ratio of 3 estimates that the 24-hour protein excretion is about 3 g. The ratio may be inaccurate in patients with orthostatic proteinuria.
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Urine for Microalbumin : The excretion of abnormal quantities of albumin below the level detectable by the urine dipstick is called microalbuminuria. Normal albumin excretion is less than 30 mg/day. Microalbuminuria is the earliest clinically detectable stage of diabetic nephropathy. Twenty-four Hour Urine Collection for Calcium, Uric Acid, Oxalate, Citrate, Sodium, and Creatinine :These studies are performed in the evaluation of the patient with recurrent kidney stones. Fractional Excretion of Sodium: The excretion of sodium in the setting of oliguria and acute renal failure often gives insight into the appropriateness of tubular function. The fractional excretion of sodium (FeNa) is calculated as follows: Fe=(U Na/P Na)(Ucr/P Cr)*100
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Urinalysis

Appearance and Color :The normal color of the urine is derived from urochromes. Certain appearances give clue to the underlying renal disease like; foamy urine=proteinuria, yellow= Conjugated bilirubin, Smoky pink= Hematuria. Urine pH is often 5. Glucose threshold is 180mg/dl. Glycosuria is seen in diabetes mellitus, when pregnancy causes the tubular threshold for glucose reabsorption to change, and in tubular diseases. The dipstick is most sensitive to the presence of albumin and is much less sensitive to other proteins, such as the light chains of Bence Jones protein. In normal urine, RBC and WBC are rare (RBC 0-1 / HP , WBC < 5 / HP ) . Leukocytes present in infections and in inflammatory conditions. Eosinophiluria (>5% of urine leukocytes) is a common finding (~90%) in antibiotic-induced allergic interstitial nephritis
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Urine Sediment: RBCs may originate from intrarenal vessels, glomeruli, tubules, or anywhere in the urogenital tract. Dysmorphic RBCs are cells that have been deformed by transit through glomeruli. Hyaline casts are casts of Tamm-Horsfall proteins that are formed normally and are seen in increased numbers after exercise. Granular casts are degenerated tubular cell casts. Pigmented granular casts are seen in rhabdomyolysis with myoglobinuria or, rarely, hemoglobinuria. RBC casts are diagnostic of glomerulonephritis. WBC casts are seen commonly in pyelonephritis and in acute and chronic nonbacterial infections
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Urine specific gravity ~ 1.001 to 1.030 Pyelonephritis- urine has high specific gravity. Diabetes insipidus- urine has low specific gravity, drinks excessive water; injury or tumor in pituitary
Specific Gravity
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Crystals

Crystals often can be a normal finding in the urine or serve as clues to pathophysiologic processes. Hexagonal crystals seen with cystinuria, are always abnormal Triple phosphate crystals are composed of ammonium magnesium phosphate and are coffin shaped. Other dynamic tests of tubular function, including concentrating ability, ability to excrete a water load and ability to excrete acid, are valuable in some circumstances.
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Blood tests and biochemistry A normochromic normocytic anemia is coomon in chronic kidney disease is due to iron and erythropoeitin deficiency and bone suppression because of retained toxins. There is low serum calcium and high phosphate associated with high parathyroid hormone in chronic kidney disease.
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Causes of increased plasma urea concentrationPhysiological: high protein diet.Pathological: Renal Failure (Acute. Chronic), acidosis, postsurgery, moderate or heavy bleeding in the upper gastrointestinal tractCauses of decreased plasma urea concentration:Non-pathological: low –protein, high carbohydrate diet, pregnancy.Pathological: hepatic failure, inappropriate ADH secretion, decrease of blood flow to the kidney (as seen in Heart failure or dehydration).Iatrogenic: prolonged intravenous fluid treatment, steroid use, patients on total parenteral nutrition *

Measurement of Renal Function

Glomerular filtration rate is the rate of plasma filtration by glomeruli/minute and it's calculated by Cockcroft-Gault formula: The more cumbersome and more accurate MDRD (modification of diet in renal disease) uses plasma creatinine, sex, race, and age. Creatinine clearance is calculated often using a 24-hour urine collection for measurement of the creatinine concentration. Inulin is an ideal marker for the measurement of GFR because it is not reabsorbed, secreted, synthesized, or metabolized.
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Complement levels: are usually low in active SLE, poststreptococcal glomerulonephritis, endocarditis, membranoproliferative glomerulonephritis, cryoglobulinemia, shunt nephritis, and glomerulonephritis associated with visceral abscesses. Imaging Plain radiography of kidney, ureter, and bladder (KUB): estimation of renal size and in the evaluation of calcium stones. Intravenous pyelography (IVP) involves direct injection of contrast medium into the collecting system from above or below. Intravenous urography.
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Renal ultrasonography: has become the most commonly used imaging study. The study has only 90% sensitivity for the detection of hydronephrosis. Doppler imaging permits evaluation of the renal vessels and resistive index. MRI with MR angiography has revolutionized the evaluation of renovascular disease. MRI also can be used to evaluate renal masses. Its main advantages are that it is a noninvasive test and does not require the use of iodinated contrast material. Renal arteriography is the gold standard in the evaluation of renal artery stenosis.
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Renal Biopsy
The current indications for renal biopsy include the following: Unexplained renal failure of any cause. RPGN without a serologic diagnosis. Nephrotic syndrome without an obvious cause. Proteinuria, below the nephrotic range. SLE with renal involvement. Renal transplantation with acute and chronic renal failure, in which the biopsy information can be crucial in guiding diagnosis and treatment. Chronic kidney disease with normal-sized kidneys Isolated haematuria or proteinuria with renal characteristics or associated abnormalities.
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Lower urinary tract symptoms

Upper urinary tract symptoms

Abnormal urine volume

Abnormal urinary constituents

Hypertension

Acute or chronic parenchymal disease or renovascular disease.
Uraemia
A group of symptoms and signs of advanced kidney disease
Cardinal features of kidney and urinary tract disease
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