Renal Anatomy, Function, and Urinalysis

Comprehensive practice flashcards covering renal anatomy, physiological functions, urine formation, macroscopic/chemical/microscopic urinalysis, urinary casts, crystals, renal markers (urea, uric acid, creatinine, ammonia), renal diseases, and dialysis.

Approximately how much blood plasma do the kidneys filter daily?

The kidneys filter approximately $180\,L$ of blood plasma daily.

What are the four main steps of urine formation?

1. Glomerular Filtration
2. Tubular Reabsorption
3. Tubular Secretion
4. Excretion

During glomerular filtration, what passes into Bowman's capsule and what remains in circulation?

Water and small molecules pass into Bowman's capsule, while large proteins and blood cells remain in circulation.

Which essential substances are returned to the bloodstream during tubular reabsorption?

Water, glucose, amino acids, and electrolytes.

Through which anatomical structures is final urine excreted?

Through the renal pelvis, ureters, bladder, and urethra.

What triggers the release of renin and what system does it activate?

Renin is released when blood pressure decreases, and it activates the renin-angiotensin-aldosterone system (RAAS) to help regulate blood pressure.

What is the function of erythropoietin (EPO), and what can decreased production cause?

EPO stimulates the production of red blood cells in bone marrow; decreased production may lead to anemia in kidney disease.

What is calcitriol (1,25-dihydroxyvitamin D₃) and what are its primary functions?

Calcitriol is the active form of vitamin D. It increases calcium absorption from the intestines and is essential for bone health.

What are the normal and abnormal colour indications during macroscopic examination of urine?

Normal urine colour is pale yellow to amber. Dark urine may indicate dehydration, and red urine may indicate blood or certain foods/drugs.

What are the clinical implications of cloudy urine and sweet-smelling urine?

Cloudy urine may indicate infection or crystals, while a sweet smell may suggest ketones or diabetes.

What is the normal daily urine volume, and what terms describe increased and decreased volume?

Normal volume is approximately $1\text{-}2\,L/\text{day}$. Increased volume is termed polyuria, and decreased volume is termed oliguria.

What does urine specific gravity (SG) measure, and what is its normal range?

Specific gravity measures urine concentration and indicates hydration and kidney concentrating ability. The normal range is $1.005\text{-}1.030$.

What is the normal reference range for urine pH?

The normal reference range for urine pH is $4.5\text{-}8.0$.

What do the presence of glucose, ketones, and persistent protein in urine indicate?

Glucose suggests diabetes mellitus; ketones are present during starvation, fasting, or uncontrolled diabetes; and persistent proteinuria indicates renal damage.

What do positive nitrite and leukocyte esterase tests indicate in urinalysis?

A positive nitrite test suggests bacterial infection, while leukocyte esterase indicates white blood cells in urine and suggests a urinary tract infection.

What magnification objectives are used during microscopic examination of urine sediment?

$10\times$ is used for scanning casts and crystals, and $40\times$ is used for cells and bacteria.

What are the normal microscopic reference ranges for red blood cells (RBCs) and white blood cells (WBCs) in urine?

Normal RBCs: $\le 2/\text{HPF}$ Normal WBCs: $\le 5/\text{HPF}$

What factors contribute to the formation of urinary casts?

Urinary stasis, increased protein concentration, acidic urine, and Tamm-Horsfall mucoprotein.

Under what non-pathological conditions might hyaline casts occur in small numbers?

Dehydration, fever, exercise, and stress.

What do RBC casts and WBC casts typically indicate in urine sediment?

RBC casts are a strong indicator of glomerular damage (common in acute glomerulonephritis), whereas WBC casts suggest infection within kidney tissue (typical finding in pyelonephritis).

Which crystals are typically found in acidic urine ($\text{pH} < 7$)?

Calcium oxalate, amorphous urates, uric acid, cholesterol, and cystine.

Which crystals are typically found in alkaline urine ($\text{pH} > 7$)?

Amorphous phosphates, calcium carbonate, triple phosphate, and ammonium biurate.

Which urinary crystals are classified as pathological?

Leucine, tyrosine, cystine, sulfonamides, and cholesterol.

Where is urea produced, and what are its clinical uses?

Urea is produced by the liver from protein metabolism and eliminated by the kidneys. It is clinically used to assess renal function, hydration status, and dialysis effectiveness.

What are the prerenal, renal, and postrenal causes of increased urea?

Prerenal: dehydration, congestive heart failure, hemorrhage, shock. Renal: kidney disease causing reduced filtration. Postrenal: urinary tract obstruction, renal calculi.

What are the Urea:Creatinine ratio values for prerenal, renal, and postrenal causes?

Prerenal: $> 80$ Renal: $50\text{-}80$ Postrenal: initially $> 80$

What is the reference range for urea, and how does azotemia differ from uremia?

The reference range is $2.0\text{-}7.0\,\text{mmol/L}$. Azotemia is elevated urea and creatinine in the blood, whereas uremia is severe azotemia accompanied by clinical symptoms (such as nausea, fatigue, confusion, and itching).

What is uric acid derived from, what are its clinical uses, and what is its reference range?

Uric acid is a product of purine metabolism. It is used in diagnosing/monitoring gout, assessing kidney stones, and monitoring tumour lysis syndrome during chemotherapy. Its reference range is $210\text{-}430\,\mu\text{mol/L}$.

Why is creatinine the best routine indicator of renal filtration function, and what is its reference range?

Creatinine is produced from muscle metabolism and released at a relatively constant rate, making it inversely related to GFR. Its reference range is $50\text{-}100\,\mu\text{mol/L}$ (generally lower in females).

What specimens are required to measure Creatinine Clearance (CrCl)?

A 24-hour urine collection and a blood sample collected during the collection period.

What variables are used to calculate estimated glomerular filtration rate (eGFR)?

Serum creatinine, age, and sex.

What are the specimen collection and processing requirements for blood ammonia testing?

Collect on ice immediately using an EDTA or heparin tube, centrifuge cold within $20\,\text{minutes}$, separate plasma promptly, avoid hemolysis, and do not smoke before specimen collection.

What is the normal reference range for ammonia, and what does an elevated level indicate?

The reference range is $11\text{-}35\,\mu\text{mol/L}$. Elevated levels commonly indicate severe liver disease and can contribute to hepatic encephalopathy.

How do the kidneys maintain acid-base balance and blood pH within the range of $7.35\text{-}7.45$?

By reabsorbing bicarbonate ($\text{HCO}_3$), excreting hydrogen ions ($\text{H}$), and excreting ammonia and phosphate buffers.

What infection commonly precedes acute glomerulonephritis, and what are its characteristic laboratory findings?

It often follows Group A beta-hemolytic streptococcal infection. Findings include hematuria, proteinuria ($< 3\,\text{g/day}$), increased urea, increased creatinine, decreased GFR, RBC casts, and increased hyaline and granular casts.

What are the hallmark laboratory findings and complications of Nephrotic Syndrome?

Findings include massive proteinuria ($> 3.5\,\text{g/day}$), edema, hyperlipidemia, hypoalbuminemia, and oval fat bodies in urine. Complications include increased risk of infection and increased blood clot formation.

How can pyelonephritis be distinguished from cystitis based on laboratory and clinical findings?

Pyelonephritis involves kidney tissue, features WBC casts, and commonly causes fever and flank pain. Cystitis is limited to the bladder, has no WBC casts, and typically causes dysuria and urinary frequency.

What is the most common type of urinary calculi (kidney stone)?

Calcium oxalate stones.

How do hemodialysis and peritoneal dialysis differ in their filtering mechanism?

In hemodialysis, blood is filtered externally through a machine (usually multiple times per week). In peritoneal dialysis, the patient's peritoneal membrane acts as the filtering surface with dialysis solution placed into the abdomen.

What are the four clinical indications for dialysis?

Severe uremia, hyperkalemia, severe metabolic acidosis, and fluid overload resistant to treatment.