Functions of the kidney
The kidney regulates fluid and electrolyte balance by filtration, excretion and reabsorption. It activates both erythropoeitin (for production of red blood cells) & vitamin-D which regulates calcium metabolism. It also produces renin (in the afferent arte
Structures of the Kidney
Renal cortex: (external) receives most of the blood flow, and is mostly concerned with reabsorbing filtered material.
Renal medulla: (internal) is a highly metabolically active area, which serves to concentrate the urine.
Renal pelvis: collects urine for
Nephrons
2 types: ones in the cortex, ones in the medulla
1. The glomerulus: the blood kidney interface, plasma is filtered from capillaries into the Bowman's capsule.
2. Proximal convoluted tubule: reabsorbs most of the filtered load, including nutrients and elec
Nephron Function
Glomerular filtration
Net filtration pressure (NFP): increases when the glomerular membrane is inflamed due to increase presence of proteins in the glomerular filtrate.
Glomerular hydrostatic pressure: A narrowed proximal convoluted tubule results in incr
Preinuria and Hematuria
Proteinuria (protein loss in urine) commonly occurs after long-distance events because the glomerular cells have been injured by prolonged hypoxia (low oxygen levels). If the damage is substantial, hematuria (blood loss in urine) will occur. Painless hema
Autoregulation of RBF/GFR
through baroreceptors (measuring renal bp through the glomerulus) and NaCl levels monitored by the macula densa.
Neural regulation
Neurol regulation of RBF/GFR
Sympathetic nervous system: It produces a powerful vasoconstriction of the afferent arterioles, decreasing the GFR and slowing the production of filtrate (b1 stimulation).
Vasoconstriction (diminishes GFR)
Autonomic Regulation of the GFR Most of the auto
Hormonal regulation of RBF/GFR
The major mechanism for hormonal regulation is the renin-angiotensin-aldosterone system, which can increase systemic arterial pressure and change renal blood flow.
Release of renin can be inhibited by atrial natriuretic peptide, resulting in decreased blo
Five major functions of the PCT (proximal convoluted tubule)
-Reabsorption of Organic Nutrients: PCT reabsorbs > 99 % of glucose, amino acids, and other nutrients.
-Active Reabsorption of Ions: PCT actively transport ions; Na, K, Mg, HCO3, Phosphate, and sulfate ions. Bicarbonate is important in stabilizing blood p
Concentration and Dilution of Urine
Countercurrent exchange system
-Contributes to production of concentrated urine
-Fluid flows in opposite direction through parallel tubes
-Fluid moves up and down the parallel limbs of the loop of Henle
-The longer the loop, the greater the concentration
How the Countercurrent multiplication operates
A. Na & Cl are pumped out of the thick ascending limb and into the peritubular fluid.
B. The result is an osmotic flow of water out of the thin descending limb & into the peritubular fluid, increasing the solute concentration in the thin descending limb.
Benefits of Countercurrent Multiplication
1. It efficiently reabsorbs solutes and water before the tubular fluid reaches the DCT and collecting system.
2. It establishes a concentration gradient that permits the passive reabsorption of water from the tubular fluid in the collecting system. This r
Water and Solute regulation
The normal amount of water and solute loss in the collecting system is regulated in two ways:
1. By aldosterone, which controls sodium ion pumps along most of the DCT and the proximal portion of the collecting system.
2. By ADH, which controls the permeab
The Effects of ADH on the DCT and Collecting Duct
In the absence of ADH, water is not reabsorbed in these segments, so all the fluid reaching the DCT is lost in the urine.
As ADH levels rise, the DCT and collecting system become more permeable to water, the amount of water reabsorbed increases, and the u
Reabsorption
Sodium Ion Reabsorption: The collecting system contains aldosterone-sensitive ion pumps that exchange in tubular fluid for in peritubular fluid.
Bicarbonate Reabsorption: Bicarbonate ions are reabsorbed in exchange for chloride ions in the peritubular flu
Secretion
The collecting system is an important site for the control of body fluid pH by means of the secretion of hydrogen or bicarbonate ions.
Control of Urine Volume & Osmotic Concentration
Urine volume and osmotic concentration are regulated by controlling the reabsorption of water. Water is reabsorbed by osmosis in the PCT and the loop of Henle. The ascending limb of the loop of Henle is impermeable to water, but 1-2 % of the volume of wat
Diuresis
Diuresis is the elimination of urine. Diuretics are drugs that promote the loss of water in urine. The usual goal in diuretic therapy is a reduction in blood volume, blood pressure, extracellular fluid volume, or all three.
Renal "Clearance
The ability of the kidneys to filter a substance and excrete it in the urine is a reflection of the GFR, tubular secretion, and tubular reabsorption (thus also RBF and functioning of nephrons)
Concentration and Dilution of Urine
Urea
Catecholamines
Antidiuretic hormone (ADH)
Natriuretic peptide
Diuretics
Aging and Renal Function
Decrease in kidney size
Decrease in renal blood flow and GFR
Number of nephrons decrease due to renal vascular and perfusion changes
Glomerular capillaries atrophy
Tubular transport response decreases
Increased bladder symptoms
Urgency, frequency, and noc
Urinary Tract Obstruction
Blockage of urine flow within the urinary tract due to an obstruction that can be caused by an anatomic or functional defect
Hydroureter: distention of the ureter with urine or watery fluid, due to obstruction.
Hydronephrosis : distention of the renal cal
Urolithiasis: Kidney Stones
Factors affecting stone formation: Crystal growth-inhibiting substances and particle retention.
Stones: Most common; Ca oxalate or Ca phosphate.
Kidney Stone Diagnosis and Prognosis
Manifestation: Renal colic
Evaluation: Stone analysis, Kidney-ureter-bladder (KUB), Intravenous pyelogram, and Spiral abdominal computed tomography (CT)
Treatment: Stone removal
Kidney Stones: Calculi
Masses of crystals, protein, or other substances that form within and may obstruct urinary tract.
Risk factors: Male, Age 20-40 years, Inadequate fluid intake (biggest contributor), Living in desert or tropical region (temperature, humidity, fluid, and di
Urinary Tract Infection (UTI)
Inflammation of the urinary epithelium following invasion and colonization by some pathogen within the urinary tract
Cystitis: An inflammation of the bladder
Most common pathogens: Escherichia coli,
Staphylococcus saprophyticus
Pyelonephritis
Acute infection of the ureter, renal pelvis, and/or renal parenchyma
Contributing factors: Cystitis, Urinary tract obstruction with reflux infection
Clinical manifestations: flank pain, fever, chills, costobertebral tenderness, puss in urine
Glomerular Disorders
Glomerular disease has sudden or insidious onset of hypertension, edema, and an elevated blood urea nitrogen (BUN)
Characterized by: Decreased glomerular filtration rate, increased glomerulur capillary permeability, elevated plasma creatinine, urea, and r
Glomerulonephritis
Inflammation of the glomerulus
Most commonly cause by immunologic abnormalities. Decreased glomerular perfusion (glomerular blood flow) due to inflammation, Glomerular sclerosis (scarring), and Thickening of the glomerular basement membrane (but increased
Nephrotic Syndrome
Excretion of 3.5 g or more of protein in the urine per day. Protein excretion is due to glomerular injury
Findings: Hypoalbuminemia, edema, hyperlipidemia, and lipiduria
Causes of Nephrotic Syndrome
Glomerulonephritis, Genetic defects that alter the glomerular membrane, Systemic diseases (diabetes, SLE), Drug/toxin injury, Infections (especially chronic and/or recurrent)
Renal Dysfunction
Renal insufficiency, Renal failure, End-stage renal failure (ESRD - need transplant), Uremia, Azotemia
Renal Failure
Acute: Sudden and rapidly progressive within hours (often reversible); abrupt reduction in renal function
Chronic: slowly progressing to end-stage renal failure over months or years
Azotemia: increased urea and frequently creatinine levels
Uremia: elevate
Prerenal Acute Renal Failure (ARF)
Caused by impaired renal blood flow (sudden reduction of perfusion to the kidneys)
GFR declines due to the decrease in filtration pressure (results in oliguria)
Ischemia leads to hypoxic injury and acute tubular necrosis (ATN)
Intrarenal ARF
Damage to the renal parenchyma: acute tubular necrosis (most common cause)
Postrenal ARF
Occurs with urinary tract obstructions that affect the kidneys bilaterally and increase the intraluminal pressure upstream (decrease in GFR)
-Prostatic hypertrophy, Bladder outlet obstruction, Bilateral ureteral obstruction
Clinical Manifestations of ARF
Oliguria/anuria
Elevated BUN and creatinine
Hyperkalemia
Metabolic acidosis
Hypertension (volume overload)
Chronic Renal Failure
The irreversible loss of renal function that affects nearly all organ systems
Progression: Reduced renal reserve, Renal insufficiency, Renal failure, End-stage renal disease
Multiorgan/Multisystem Failures
Neurologic: Neuropathies, Encephalopathy
Gastrointestinal: Nausea, vomiting, anorexia
Endocrine: Insulin resistance, Decreased sex hormones
Metabolic: Altered protein, lipid, carbohydrate metabolism
Integumentary, bone, mineral: Hyperphosphatemia, Hypocal
Ms. Cornwall is admitted with pyelonephritis. She has chills and her temperature is 101� F. She is complaining of flank pain, frequency, and dysuria. Her urine has white blood cell casts, and her urine culture is growing Escherichia coli. Why does she hav
Ms. Cornwall has a focal bacterial infection of her renal pelvis, calyces, and medulla. The bacterial invasion triggers an inflammatory reaction with white blood cell response causing edema and release of inflammatory mediators.
What is the difference among prerenal acute renal failure, intrarenal acute renal failure, and postrenal acute renal failure? Give examples of each.
Prerenal acute renal failure is decreased renal function with elevated blood urea nitrogen (BUN) and plasma creatinine caused by impaired blood flow to the kidney.
Intrarenal acute renal failure is caused by impaired blood flow within the kidney. It is th
How can a person with chronic renal failure become anemic? How are they related?
normochromic (normal hemoglobin that gives the red color of the blood) anemia is a companion to chronic renal failure because of the insufficient production and release of erythropoietin, blood loss, and decreased red blood cell life span.
Physicians frequently request a clean-catch midstream urine sample. Why?
a physician is trying to get the best representative sample of a person's urine.
What causes renal stones to form?
Kidney stones consist of large amounts of crystal, protein, or other kinds of substances.
What are the goals in treating renal calculi?
The goals for treating kidney stones are acute pain management, stone passage promotion, stone size reduction, and prevention of new stone formation.
What is a urethral stricture and what causes it?
A urethral stricture occurs when the lumen is narrowed as a result of infection, trauma, or surgical manipulation, which leaves a scar and then reduces the size of the urethra.
What causes acute cystitis (infection of the urinary bladder)?
The most common microorganisms are strains of Escherichia coli and Staphylococcus saprophyticus.
How does acute unilateral renal obstruction predispose people to hypertension?
The reduced perfusion of the affected kidney activates the renin-angiotensin-aldosterone system, which causes constriction of peripheral arterioles.
The most common type of renal stone is comprised of:
calcium oxalate
Hypercalciuria is usually attributable to:
hyperthyroidism, intestinal hyperabsorption of dietary calcium, and bone demineralization caused by prolonged immobilization.
Which statements are true about struvite stones?
They grow large and branch into a staghorn configuration in renal pelvis and calyces, they are more common in women than men, and they are closely associated with urinary tract infections caused by urease-producing bacteria, such as Pseudomonas.
The most common causes of uncomplicated urinary tract infections are:
Escherichia coli
Which clinical manifestation of pyelonephritis is different from those of cystitis?
Flank pain
Considering host defense mechanisms, which element in the urine is bacteriostatic (prevents the growth of bacteria), if any?
High urea
Clinical manifestations of a urinary tract infection in an 85 year old may include:
confusion and poorly localized abdominal discomfort
Pyelonephritis is usually caused by antibody-coated:
bacteria
Which abnormal lab value is found in glomerular disorders?
Elevated creatinine clearance
A patient has hematuria with casts and proteinuria exceeding 3 to 5 g/day with albumin as the major protein. This data suggest the presence of which disorder?
Glomerulonephritis
The kidney disorder characterized by hypoalbuminemia, edema, hyperlipidemia and lipiduria is:
nephrotic syndrome
Which antibiotics are considered "major culprits" in causing nephrotoxic acute tubular necrosis (ATN)?
Neomycin, gentamicin, and tobramycin
How are glucose and insulin used to treat hyperkalemia associated with acute renal failure?
When insulin transports glucose into the cell, it also carries potassium with it.
Creatinine is constantly released from _____ tissue and excreted primarily by glomerular filtration.
muscle
Anemia of chronic renal failure can be successfully treated with:
erythropoietin
Match the causes of acute renal failure with examples of specific disorders
Acute tubular necrosis: Intrarenal
Hypovolemia: Prerenal
Prostatic Hypertrophy: Postrenal