FunctionProduction of urine which is the fluid thatfacilitates the elimination of metabolic wastematerials from the body.Helps maintain homeostasis by manipulatingthe composition of blood plasma.Regulation of the acid-base balance and fluidelectrolyte balance.Blood filtration, reabsorption, and secretion.
Function…Fluid Balance Regulation- The amount of urine produced helps ensure that the body contains the right amount of water. If the body has excess water and needs to get rid of it, more urine is formed (diuresis). If the body needs to conserve water, less urine will be produced. Much of this function is under the control of antidiuretic hormone (ADH) and aldosterone.
Function…Acid-Base Balance Regulation- Enabled by the ability to remove hydrogen and bicarbonate ions from the blood and excrete them in the urine.Hormone Production- The kidneys have a close association with the endocrine system. They can influence the rate of release of ADH and aldosterone. They also produce erythropoietin and some prostaglandins.
Gross AnatomyBean shaped andcovered by a fibrouscapsule.The indented area iscalled a hilus.Renal pelvis- a urinecollection chamber thatforms the beginning ofthe ureter
Gross AnatomyRenal cortex- outerportion.Renal medulla-surrounds the renalpelvis and has a smoothappearance.
Microscopic AnatomyThe Nephron- The basic functional unit of the kidney. Each nephron is composed of a: Renal corpuscle Proximal Convoluted Tubule (PCT) Loop of Henle Distal Convoluted Tubule (DCT)
Terms to Remember…Osmosis- the passage of water across a semi-permeable membrane from a weaker to a strongersolution.Diffusion- the passage of a substance from an areaof high concentration to an area of low concentration.Reabsorption- the passage of chemical substancesfrom the lumen of the renal tubules into the renalcapillaries, back into the body.Secretion- the passage of chemical substances fromthe renal capillaries into the lumen of the renaltubules, out of the body, into the urine.
Microscopic Anatomy…Renal corpuscle- located in the cortex ofthe kidney. Made up of the glomerulus (a tuft of capillaries) and Bowman’s capsule. The function is to filter blood in the first stage of urine production. The blood pressure within each glomerulus is high because the blood comes directly from the renal artery and the aorta. The walls of the efferent arteriole of the glomerulus are able to constrict under the influence of renin.
Microscopic Anatomy…High pressure forces fluid and smallmolecules out through the pores and into thelumen of the glomerular capsule.This process of ultrafiltration results in theformation of glomerular filtrate.It is very dilute and consists of 99% water and1% chemical solutes and is isotonic withplasma.
Microscopic Anatomy…PCT- a continuation of Bowman’s capsule. The longest part of the nephron. Functions- Reabsorption of glucose, water, and sodium from the filtrate. Secretion of toxins and certain drugs (penicillin). Concentration of nitrogenous waste- mainly urea produced as a result of protein metabolism.
Microscopic Anatomy…Loop of Henle- Function: to concentrate or dilute the filtrate according to the status of the blood plasma and the rest of the extracellular fluid. Occurs in 2 stages: Descending loop- water is drawn out of the filtrate by sodium ions and is reabsorbed by the capillaries. Ascending loop- sodium is pumped out of the filtrate into the medullary tissue.
Microscopic Anatomy…Loop of Henle… Na+ and Cl- are pumped out of the ascending loop into the tissue of the surrounding medulla. Normally, water would follow Na+ by osmosis but the walls of the ascending loop are impermeable to water so this does not occur. The walls of the descending loop are permeable to water, so water is drawn out by osmosis.
Microscopic Anatomy…The resulting filtrate, now referred to as urine,is more concentrated and is reduced involume.
MicroscopicDCT- Anatomy… Function: to make final adjustments to the chemical make- up of urine in response to the status of blood plasma. Under the control of aldosterone. Reabsorption of sodium ions. Excretion of potassium ions. Regulation of the acid-base balance (pH) of the blood by the excretion of hydrogen ions. In this part of the tubule, water is not reabsorbed in any great quantity.
Microscopic Anatomy…Collecting Ducts- Carry tubular filtrate through the medulla and eventually empty into the renal pelvis. Function: make final adjustments to the water content of urine. This change occurs by altering the permeability of the duct walls. Under the control of antidiuretic hormone (ADH).
Physiology…Reabsorption- Sodium The glomerular filtrate Potassium contains the waste products that need to be Calcium removed from the body. Chloride That filtrate also contains Magnesium substances found in plasma that need to be Glucose reabsorbed to maintain Amino acids homeostasis. Bicarbonate Water
Physiology…Reabsorption- Some substances make this movement passively through osmosis or diffusion. Others have to be actively transported across cell membranes. About 65% of all tubular reabsorption takes place in the PCT. About 80% of the water, sodium, chloride, & bicarbonate are reabsorbed. 100% of the glucose and amino acids are reabsorbed.
Glucose Threshold (p . 3 1 2 )The limit of the amount of glucose that can bereabsorbedDogs: 180 mg/dlCats: 240 mg/ml
Physiology…Secretion- Many waste products are not filtered from the blood in sufficient amounts from the glomerular capillaries. The “left over” substances are removed by tubular secretion. Most tubular secretion occurs in the DCT. Hydrogen, potassium, & ammonia are some of the substances eliminated by secretion.
Urine Volume RegulationADH & aldosterone are responsible for themajority of urine volume regulation.
Urine Volume RegulationADH acts on the DCT & collecting ducts topromote water reabsorption.Aldosterone increases the reabsorption of sodiuminto the bloodstream.This causes an osmotic imbalance thatencourages water to follow sodium.Water cannot move out of the DCT unlesssufficient ADH control is present.
UretersThe tubes that exit the kidney at the hilus andconnect to the bladder.They continuously move urine from thekidneys to the bladder.The smooth muscle layer propels the urinethrough the ureter by peristaltic contractions.
BladderStores urine as it is produced and releases itfrom the body.Lined with transitional epithelium thatstretches as the bladder fills.The wall contains smooth muscle. When it contracts, urine is expelled.
UrethraA continuation of the neck of the bladder thatruns through the pelvic canal.Carries urine from the bladder to the externalenvironment.
Acute Renal FailureAn abrupt decrease in glomerular filtration.Usually the result of hypoperfusion ornephrotoxic injury to the kidney, whichcauses damage to the nephron. Nephrotoxins- ethylene glycol, gentamicin, sulfonamides…Azotemia- a build-up of toxins within thebody.
Chronic Renal Failure“CRF”A common disease of older pets.An irreversible and progressive decline in renalfunction caused by destruction of the nephron units.Main coon, Abyssinian, Russian Blue, and Burmesebreeds seem to be predisposed.Irreversible destruction of the nephron results inuremia.BUN, Creatinine, & isothenuria specificgravity=water
Ethylene Glycol ToxicityMost dangerous form of antifreeze.Most commercial antifreeze products containbetween 95-97% ethylene glycol.Minimum lethal dose of undiluted ethylene glycolantifreeze is 4.4-6.6ml/kg in dogs and 1.4ml/kg incats.Causes metabolic acidosis and acute renal tubularnecrosis.Peak levels of ethylene glycol are reached within 1-4hours post ingestion.
Ethylene Glycol Toxicity…Clinical Signs:Vomiting is seen within the first few hoursprogressing to depression, ataxia, weakness,tachypnea, polyuria, and polydipsia (1-6hours)18-36 hours acute renal failure occurs.
Diabetes Insipidus (p . 3 1 2 )Insipid means tasteless***A decrease in the pituitary release of ADH(antidiuretic hormone)ADH is responsible for regulating urinevolumeThe collecting ducts do not reabsorbadequate amounts of water which causesPU/PD
FLUTD/FUS & Urolithiasis Colville p. 317“Feline Lower Urinary Tract Disease” or “Feline UrologicSyndrome”Presence of mineral precipitatesUrolith’s are the most common causeCalcium oxylate is the most common mineral found (urine is tooacidic)Signs- hematuria, dysuriaDetected by urinalysis, radiographs or ultrasound.Urolith’s that remain in the bladder can damage the bladderlining, resulting in secondary bacterial infections and hematuria.
Physical PropertiesInclude all observations that can be madewithout the aid of a microscope or chemicalreagents.
ColorNormal is light yellow to amber and is a resultof pigments called urochromes.The magnitude of color depends on thedegree of urine concentration or dilution.
Color…Colorless- Low specific gravity. Associated with polyuria.Dark yellow- High specific gravity. Associated with oliguria.(less urine than norm)Yellow-brown or green- is likely to containbile pigments.
Color…Red or reddish-brown- indicates thepresence of red cells (hematuria) orhemoglobin (hemoglobinuria).Brown- may contain myoglobin, which isexcreted during conditions that cause musclecell lysis, such as rhabdomyolysis.
Clarity (Transparency)Normal is clear/transparent.Urine may become cloudy while standingbecause of bacterial multiplication or crystalformation.
OdorSamples standing at room temperature maydevelop an ammonia odor as a result ofbacterial growth.Sweet or fruity odor indicates the presence ofketones.
Urine Specific Gravity (USG)Defined as the weight (density) of a liquid comparedto that of distilled water.May be determined before or after centrifugation.USG yields information on the hydration status andthe ability of the kidney to concentrate or dilute urine.Only the refractometer should be used to determineUSG.
Urine Specific Gravity (USG)…Causes of USG- water intake fluid loss Acute renal failure Dehydration Shock
Urine Specific Gravity (USG)…Causes of USG- Water re-absorption problems fluid intake Excessive fluid administration Pyometra Diabetes insipidus Diuretic therapy
Urine Specific Gravity (USG)…Isothenuria “Fixed USG”- 1.008-1.012 Occurs when the USG approaches that of glomerular filtrate. Urine in this range has not been concentrated or diluted by the kidneys. The closer the USG is to isothenuric, the greater the amount of kidney function has been lost (~75%).
pHExpresses the hydrogen ion (H+) concentration.A measure of the degree of acidity or alkalinity ofurine.A pH >7.0 is alkaline, <7.0 is acidic.Urine left standing open at room temperaturetends to increase in pH resulting from a lossof carbon dioxide.The pH of urine is largely dependant on diet.
pH…Decreased pH- Fever, starvation, high protein diet, acidosis, excessive muscular activity.Increased pH- Alkalosis, high fiber diets, urethral obstruction, bladder paralysis (urine retention).An abnormal pH can result in crystal or urolithformation.The pH can be corrected by manipulating the diet tohelp dissolve the solids or prevent uroliths fromforming.
ProteinUsually absent or present in trace amounts ofnormal urine.Urine dip sticks allow semi-quantitativemeasurements by progressive color changeson the reagent pad. Reagent strips commonly detect albumin and are not very sensitive to globulins (proteins insoluble in water).
Protein…Urine Protein : Creatinine Ratio- This test is used to confirm significant amounts of protein in the urine. Used to determine the degree of protein loss in chronic renal disease. See page 161
Protein…Protein interpretation- Very dilute urine may yield a false negative because the protein concentration may be below the sensitivity of the testing method. Transient Proteinuria- may result from a temporary increase in glomerular permiability. This condition is caused by increased pressure in the glomerular capillaries and may be found in muscle exertion, emotional stress, or convulsions.
Protein…Protein interpretation- Proteinuria indicates disease of the urinary tract, especially the kidneys. Both acute and chronic renal disease lead to proteinuria. Acute nephritis is characterized by marked proteinuria with WBC’s and casts in the urine.
GlucoseThe presence of glucose in the urine is known asglucosuria.Glucose is filtered through the glomerulus andreabsorbed by the tubules.Glucosuria usually does not occur unless the bloodglucose level exceeds the renal threshold.At this concentration, tubular reabsorption cannotkeep up with the glomerular filtration of glucose, andglucose passes into the urine.
Glucose…Glucosuria occurs in diabetes mellitus as aresult of a deficiency of insulin or an inabilityof insulin to function.Transient glucosuria- a release ofepinepherine causes glucose levels to rise forenergy. Causes: fear, excitement, restraint.
KetonesIncludes: acetone, acetoacetic acid, and β-hydroxybutyric acid.Ketone bodies are formed during incompletecatabolism of fatty acids.When fatty acid metabolism is notaccompanied by sufficient carbohydratemetabolism, excess ketones are present inthe urine. A condition known as ketonuria.
Ketones…Ketonuria frequently occurs in animals with diabetesmellitus.Because the animal lacks the insulin necessary forcarbohydrate metabolism, fat is broken down to meetthe animal’s energy needs and excess ketones areexcreted in the urine.Ketones are toxic, causing CNS depression andacidosis. Hence- ketoacidosis or acidosis resulting from ketonuria.
Ketones…Transient ketonuria- can occur with starvationor prolonged anorexia. ketones can suggest diabetes mellitus.
Bile PigmentsBilirubin and urobilinogen.Only conjugated (water soluble) bilirubin isfound in urine.Bilirubinuria can be seen with bile ductobstructions, liver disease, and hemolyticanemia.
Bile Pigments… Bilirubin (bilirubinuria) suggests: Excessive hemolysis of RBC’s. Hepatobiliary obstruction Liver disease
BloodTests for blood in the urine detect: Hematuria- usually a sign of disease causing bleeding somewhere in the urogenital tract. Hemoglobinuria- usually the result of intravascular hemolysis. Myoglobinuria- Myoglobin is a protein found in muscle. Severe muscle damage causes myoglobin to leak from muscle cells into the blood.
Blood…Causes of hematuria- Inflammation (cystitis) Urolithiasis Bladder tumors- transitional cell carcinoma Iatrogenic trauma- catheter placement, cystocentesis.Causes of hemoglobinuria- Excessive lysis of RBC’s (hemoglobinemia) IMHA Mismatched blood transfusion RBC parasites
LeukocytesYou can believe a positive reaction but neverbelieve a negative reaction.Always examine the sediment forconfirmation.Presence usually indicates a bacterialinfection in the urogenital tract.A positive nitrate reaction occurs with alarge quantity of bacteria in the urine.
Microscopic Examination of Urine The 5 “C’s” Cells, Casts, Crystals, Critters, & Crap
CellsErythrocytes- may haveseveral differentappearances depending onthe urine concentration, pH,and time elapsed betweencollection and examination.May be confused with fatglobules or yeast.Indicates bleedingsomewhere in the urogenitaltract.
Cells…Leukocytes- Larger than RBC’s. Finding more than 2-3/hpf indicates an inflammatory process in the urogenital tract. Pyuria is indicative of nephritis, cystitis, or urethritis. Urine with pyuria should always be cultured for bacteria.
Cells…Squamous EpithelialCells- Their presence usually is not considered significant. They often have straight edges and distinct corners which sometimes curl or fold. They contain a small, round nucleus.
Cells…Transitional Cells- Come from the bladder, ureters, renal pelvis, and proximal urethra. Usually round, may be pear-shaped or caudate. Small nucleus. Increased numbers suggest cystitis or pyelonepheritis.
Cells…Renal Epithelial Cells- The smallest epithelial cells observed in urine. Originate in the renal tubules. Often confused with WBC’s. Generally round with a large nucleus. Increased numbers occur in diseases of the renal parenchyma.
CastsFormed in the lumen of the distal and collectingtubules of the kidney. Where the concentration and acidity of urine is the greatest.In the renal tubules, secreted protein precipitates inacidic conditions and forms casts shaped like thetubules.All casts are cylindrical structures, with parallel sides.Their ends may be tapered or round.Casts dissolve in alkaline urine.Larger numbers may indicate a lesion in the renaltubules.
Casts…Hyaline Casts- Clear, colorless, and somewhat transparent structures. Composed only of protein. Usually only identified in dim light. Numbers are increased with renal irritation, fever, poor renal profusion, or general anesthesia.
Casts…Granular Casts- Hyaline casts containing granules. Most common type of cast. May be coarse or fine. Seen with acute nepheritis.
Casts…Leukocyte Casts- The presence of leukocyte casts indicates inflammation in the renal tubules.
Casts…Waxy Casts- Usually wider, with square ends. Highly refractile. Indicates chronic, severe degeneration of the renal tubules.
Casts…Fatty Casts- Contain many small droplets of fat that appears as refractile bodies. Frequently seen in cats with renal disease because they have lipid in their renal parenchyma. Suggestive of degeneration of the renal tubules.
Crystals“Crystalluria”Some crystals form as a consequence ofmetabolic diseases.Conditions that lead to crystal formation (diet)may also cause formation of urinary calculi.The type of crystal depends on the urine pH,concentration, and temperature.
Serum Chemistries (Review)BUN- evaluates the kidneys ability to removeurea from the blood.Creatinine- formed from creatine, found inskeletal muscle, also evaluates the kidneysfiltering ability.Glucose- useful to evaluate the renalthreshold and diabetes.
Electrolyte Assays (Review)Sodium- evaluates filtration andreabsorption.Chloride- evaluates water distribution andosmotic pressure.CO2/Bicarbonate- evaluates excretion andreabsorption.
Send Out Tests (Usually)Urine Culture and Sensitivity (C&S)Creatinine : Cortisol RatioProtein : Creatinine Ratio