Renal and Urinary System
Structures and Functions
The renal or urinary system consists of the kidneys, ureters, bladder, and urethra.
The primary function of this system is to filter blood, remove waste products, regulate fluid and electrolyte balance, and maintain homeostasis within the body.
The kidneys are the main organs of the urinary system.
They are located in the flank area between the T12 and L3 vertebrae and receive a large portion of cardiac output.
Their function is to regulate blood composition, fluid balance, and blood pressure, while also removing metabolic waste.
The functional unit of the kidney is the nephron.
Each kidney contains over one million nephrons.
The nephron is responsible for forming urine through filtration, reabsorption, secretion, and excretion.
The glomerulus filters blood, allowing water and small solutes to pass into the nephron, while retaining larger components such as proteins and blood cells.
If proteins or blood are found in the urine, it indicates a problem with filtration.
After filtration, reabsorption occurs in the renal tubules, where essential substances such as glucose, amino acids, sodium, water, calcium, and bicarbonate are returned to the bloodstream.
Approximately 99 percent of water is reabsorbed, which helps maintain fluid balance.
Secretion is the process of transferring substances such as hydrogen ions, potassium, creatinine, and ammonia from the blood into the nephron. This helps regulate acid-base balance and eliminate excess substances.
Excretion is the final process where urine is eliminated from the body through the ureters, bladder, and urethra.
The kidneys also have endocrine functions. They produce renin, which helps regulate blood pressure through the renin-angiotensin-aldosterone system. They produce erythropoietin, which stimulates red blood cell production. They also activate vitamin D, which is necessary for calcium absorption and bone health.
The ureters are tubes that carry urine from the kidneys to the bladder using smooth muscle contractions. Narrow points, such as the ureterovesical junction, are common areas where kidney stones may become lodged.
The bladder is a muscular, stretchable organ that stores urine until it is eliminated. The detrusor muscle allows the bladder to expand and contract. The urge to urinate typically occurs when the bladder contains about 150 mL of urine, and normal adult urine output is approximately 30 mL per hour.
The urethra is the tube that allows urine to exit the body. Females have a shorter urethra, which increases the risk of urinary tract infections.
Continence refers to the ability to control urination. This is maintained by the nervous system and pelvic floor muscles. Kegel exercises can strengthen the perineal muscles and improve continence.
Age-Related Changes
As individuals age, kidney function declines. There is a decrease in the number of nephrons and reduced blood flow to the kidneys. Older adults have a decreased ability to concentrate urine, which increases the risk of dehydration.
Bladder capacity may decrease, and muscle tone can weaken, leading to urinary retention or incontinence. Older adults are also at increased risk for urinary tract infections due to incomplete bladder emptying and other physiological changes.
These changes also affect medication use, as drugs may accumulate in the body due to decreased renal clearance.
Assessment and Diagnostics
A thorough assessment includes both subjective and objective data. Subjective data includes symptoms such as dysuria, frequency, urgency, nocturia, flank pain, and changes in urine appearance.
Objective assessment includes monitoring urine output, color, clarity, and odor. Normal urine is pale yellow and clear. Abnormal findings include hematuria, cloudy urine, or strong odor.
Important laboratory tests include blood urea nitrogen (BUN), creatinine, and glomerular filtration rate (GFR). Creatinine is the most specific indicator of kidney function. Elevated BUN and creatinine levels indicate impaired kidney function, while a decreased GFR indicates worsening kidney performance.
Urinalysis is used to detect abnormalities such as bacteria, blood, protein, glucose, and white blood cells. A clean-catch midstream sample is used to reduce contamination. A 24-hour urine collection may be used to assess kidney function more accurately.
Urine culture and sensitivity testing identifies the specific organism causing infection and determines the appropriate antibiotic treatment.
Diagnostic imaging includes X-rays, ultrasounds, and CT scans to visualize structures and identify obstructions, stones, or abnormalities.
Urinary Tract Infections (UTIs)
UTIs are classified as either lower or upper urinary tract infections. Lower UTIs include cystitis, while upper UTIs include pyelonephritis.
Cystitis is inflammation of the bladder and presents with dysuria, frequency, urgency, and suprapubic discomfort. Pyelonephritis involves the kidneys and presents with more severe symptoms, including flank pain, fever, and systemic illness.
Common causative agents include Escherichia coli. Predisposing factors include female anatomy, urinary retention, catheter use, and poor hygiene.
Urinalysis findings in UTIs include the presence of bacteria, white blood cells, and sometimes blood.
Treatment includes antibiotics, increased fluid intake, and proper hygiene. Patient education focuses on wiping front to back, staying hydrated, and avoiding irritants.
Urethritis is inflammation of the urethra and presents with localized burning and irritation.
Urinary Tract Calculi (Kidney Stones)
Urinary calculi are stones formed from crystallized substances in the urine. Risk factors include dehydration, high calcium levels, dietary factors, and metabolic conditions.
Types of stones include calcium, uric acid, struvite, and cystine stones. Stones often lodge in narrow areas such as the ureterovesical junction.
When a stone moves, it causes renal colic, which is severe, sharp flank pain that may radiate to the abdomen or groin. Other symptoms include nausea, vomiting, and hematuria.
Treatment focuses on pain management, hydration, and facilitating stone passage. Severe cases may require lithotripsy or surgical removal.
Patients are instructed to strain their urine to collect stones for analysis.
Diet plays a role in prevention. Depending on the type of stone, patients may need to limit calcium, oxalate, sodium, or purine intake.
Benign Prostatic Hyperplasia (BPH)
BPH is the enlargement of the prostate gland due to hyperplasia, which is an increase in the number of cells. This enlargement compresses the urethra and interferes with urine flow.
Symptoms include urinary retention, weak stream, hesitancy, dribbling, and nocturia.
Treatment includes medications such as alpha-blockers and 5-alpha reductase inhibitors. Surgical treatment may include a Transurethral Resection of the Prostate.
Post-TURP Complications
After a TURP, patients are at risk for bleeding, clot formation, and obstruction of urine flow. Continuous bladder irrigation is often used to prevent clot formation.
Complications include hemorrhage, infection, and TURP syndrome, which is caused by fluid absorption leading to fluid overload and electrolyte imbalances.
Nursing interventions include monitoring urine color, output, and signs of complications, as well as ensuring catheter patency.
Key Vocabulary (Your Worksheet Terms Integrated)
Bladder is the muscular organ that stores urine.
Nephron is the functional unit of the kidney.
Cystoscopy is an endoscopic procedure to visualize the bladder.
Ureters carry urine from the kidneys to the bladder.
Hematuria is blood in the urine.
Frequency is urinating often in small amounts.
Ureterovesical junction is where the ureter enters the bladder.
Retention is the inability to empty the bladder.
Hyperplasia is an increase in cell number causing enlargement.
Lithotripsy is a procedure to break up kidney stones.
Renal colic is severe pain caused by kidney stones.
Catheterization is insertion of a tube to drain urine.
Urgency is a sudden need to urinate.
Urinalysis is a test of urine.
Cystitis is inflammation of the bladder.
Urethritis is inflammation of the urethra.
Continence is control of urination.
Nocturia is urinating at night.
Calculi are kidney stones.
Dysuria is painful urination.
If kidneys fail:
waste builds up
fluid overload occurs
electrolytes become imbalanced
blood pressure increases
anemia can develop
If there is obstruction:
urine backs up
hydronephrosis can occur
kidney damage can happen