CCHT Exam

The urinary system consists of two kidneys, two ureters, one urinary bladder, and one urethra. The primary functions of this system include eliminating metabolic waste products, regulating fluid and electrolyte balance, maintaining acid-base homeostasis, and producing hormones essential for various physiological processes.

Each kidney is a bean-shaped organ located in the retroperitoneal space on either side of the vertebral column, between the levels of T12 and L3. The right kidney sits slightly lower than the left due to the position of the liver. An adult kidney measures approximately 11–12 cm in length, 5–6 cm in width, and 3 cm in thickness, weighing between 120–170 grams.

The kidney has three distinct regions. The renal cortex is the outer layer containing the glomeruli and proximal and distal convoluted tubules. The renal medulla is the inner region composed of 8–18 renal pyramids containing the loops of Henle and collecting ducts. The renal pelvis is the funnel-shaped central cavity that collects urine and channels it into the ureter.

The functional unit of the kidney is the nephron. Each kidney contains approximately 1 million nephrons. A nephron consists of the renal corpuscle (glomerulus and Bowman's capsule) and the renal tubule (proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct).

The kidneys receive approximately 20–25% of cardiac output, which translates to about 1,200 mL of blood per minute. Blood enters through the renal artery, which branches into segmental arteries, then interlobar arteries, arcuate arteries, interlobular arteries, and finally afferent arterioles that supply the glomeruli. Blood exits the glomerulus through efferent arterioles, passes through peritubular capillaries (or vasa recta in juxtamedullary nephrons), and eventually drains into the renal vein.

Glomerular filtration is the first step in urine formation. Blood pressure forces water, electrolytes, glucose, amino acids, urea, creatinine, and other small molecules through the glomerular capillary walls into Bowman's capsule, forming the glomerular filtrate. The glomerular filtration rate (GFR) is approximately 125 mL/min or 180 liters per day in healthy adults. Of this filtrate, 99% is reabsorbed, resulting in approximately 1–2 liters of urine output daily.

The glomerular filtration barrier consists of three layers: the fenestrated endothelium of the glomerular capillaries, the glomerular basement membrane, and the podocytes with their filtration slits. This barrier prevents the passage of large proteins and blood cells into the filtrate.

Tubular reabsorption occurs primarily in the proximal convoluted tubule, where approximately 65% of filtered sodium, water, and virtually all glucose and amino acids are reabsorbed. The loop of Henle creates the concentration gradient in the medulla necessary for urine concentration. The distal convoluted tubule and collecting duct fine-tune sodium, potassium, and water reabsorption under hormonal control.

Tubular secretion moves substances from peritubular capillaries into the tubular fluid. This process is important for eliminating drugs, toxins, and excess potassium and hydrogen ions.

Excretory functions include removing metabolic waste products such as urea (from protein metabolism), creatinine (from muscle metabolism), uric acid (from nucleic acid metabolism), and various drugs and toxins.

Regulatory functions encompass maintaining fluid balance by adjusting urine volume, regulating electrolyte concentrations (sodium, potassium, calcium, phosphorus, magnesium), and maintaining acid-base balance by excreting hydrogen ions and reabsorbing bicarbonate.

Endocrine functions involve producing erythropoietin (EPO), which stimulates red blood cell production in bone marrow; activating vitamin D (converting 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D or calcitriol), which regulates calcium and phosphorus absorption; and secreting renin, which initiates the renin-angiotensin-aldosterone system (RAAS) for blood pressure and fluid regulation.

Chronic kidney disease (CKD) is defined as kidney damage or decreased kidney function (GFR less than 60 mL/min/1.73 m²) persisting for three months or longer. CKD is classified into five stages based on GFR.

Stage 1 involves kidney damage with normal or increased GFR (90 mL/min or higher). Stage 2 involves mild reduction in GFR (60–89 mL/min). Stage 3a involves mild to moderate reduction (45–59 mL/min). Stage 3b involves moderate to severe reduction (30–44 mL/min). Stage 4 involves severe reduction (15–29 mL/min). Stage 5 is kidney failure (GFR less than 15 mL/min) or dependence on dialysis.

End-stage renal disease (ESRD), also called end-stage kidney disease (ESKD), occurs when kidney function declines to the point where the kidneys can no longer sustain life without renal replacement therapy. Patients with ESRD require hemodialysis, peritoneal dialysis, or kidney transplantation to survive.

The leading causes of ESRD are diabetes mellitus (approximately 44% of cases) and hypertension (approximately 29% of cases). Other causes include glomerulonephritis, polycystic kidney disease, obstructive uropathy, lupus nephritis, IgA nephropathy, and chronic pyelonephritis.

Uremia is the clinical syndrome resulting from the accumulation of waste products and toxins in the blood when the kidneys fail. Signs and symptoms affect multiple organ systems.

Neurological manifestations include fatigue, difficulty concentrating, peripheral neuropathy, restless legs syndrome, encephalopathy, and seizures.

Cardiovascular manifestations include hypertension, pericarditis, cardiomyopathy, and accelerated atherosclerosis.

Gastrointestinal manifestations include nausea, vomiting, anorexia, metallic taste, and gastrointestinal bleeding.

Hematological manifestations include anemia, platelet dysfunction, and increased bleeding tendency.

Dermatological manifestations include pruritus, uremic frost (rare), and dry skin.

Musculoskeletal manifestations include muscle cramps, bone pain, and renal osteodystrophy.