Functions of the Kidneys

Kidney Functions

• Glomerular Filtration: Straining fluid into the nephron.
• Tubular Secretion: Actively removing components from capillaries and depositing into renal tubule.
• Tubular Reabsorption: Removing components from tubule to return them to capillaries and systemic circulation.
• Six Basic Functions:
  • Maintaining water balance.
  • Maintaining acid-base balance.
  • Regulating electrolytes ($Na^+$, $K^+$).
  • Removing metabolic poisons (ammonia, urea, creatinine, drugs).
  • Endocrine functions (renin, activated Vitamin D, erythropoietin).
  • Regulating blood pressure.

Water Balance & Hormones

• Glomerular Filtration Rate (GFR): Normal is $125 ext{ mL/min}$, $124 ext{ mL}$ reabsorbed, $1 ext{ mL}$ urine made.
• Antidiuretic Hormone (ADH):
  • Secreted by posterior pituitary.
  • Promotes water reabsorption in distal convoluted tubules and collecting ducts.
  • Triggered by decreased blood volume, sympathetic stimulation, increased sodium levels.
• Aldosterone:
  • Released from adrenal cortex.
  • Promotes sodium and water reabsorption, potassium excretion.
  • Triggered by high potassium levels, sympathetic stimulation, Angiotensin $II$.
  • Stimulates $Na^+-K^+ ext{ exchange pump}$.
• Atrial Natriuretic Peptide (ANP):
  • Released by atrial distension (increased plasma volume).
  • Prevents renin, ADH, and Angiotensin $II$ effects on adrenal glands (prevents aldosterone secretion).
  • Causes arteriolar dilation, increases GFR.

Acid-Base Balance

• Secrete excess $H^+$ into urine, reabsorb bicarbonate ($HCO_3^-$).
• Acidosis: More bicarbonate reabsorbed, collecting ducts secrete more $H^+$ and generate more bicarbonate, more ammonia buffer formed.
• Alkalosis: Kidney excretes more bicarbonate, reduced $H^+$ secretion, more ammonia excreted.

Renin-Angiotensin-Aldosterone System (RAAS) & Blood Pressure Regulation

• Renin (kidneys) released in response to decreased renal perfusion.
• Renin activates Angiotensin $I$.
• Angiotensin $I$ travels to lungs, Angiotensin Converting Enzyme (ACE) converts it to Angiotensin $II$.
• Angiotensin $II$ causes vasoconstriction (increases BP) and acts on adrenal glands to produce aldosterone.
• Aldosterone increases $Na^+$ and water retention, increasing circulating plasma volume and BP.
• Hypertension Medications:
  • ACE Inhibitors: Block conversion of Angiotensin $I$ to Angiotensin $II$ (e.g., drugs ending in -pril).
  • Angiotensin Receptor Blockers (ARBs): Block Angiotensin $II$ from working on adrenal glands (e.g., drugs ending in -sartan).

Diuretics

• Loop Diuretics: Work in the loop of Henle.
• Thiazide Diuretics: Work in the distal tubule.
• Potassium-Sparing Diuretics: Work at the end of the distal tubule.

Diagnostic Tests

• Urinalysis: Assesses color, odor, protein (renal damage, uncontrolled diabetes), glucose (diabetes), ketones (DKA), bilirubin (liver disorders), specific gravity (concentration).
• Urine Culture & Sensitivity: Sterile specimen, identifies bacteria type/amount, determines effective antibiotic.
• Creatinine Clearance:
  • $24$-hour urine collection.
  • Discard first specimen, keep collected urine on ice/refrigerated.
  • Used to diagnose renal disorders; requires serum creatinine within $24 ext{ hr}$.
  • In renal failure, serum creatinine (>1.3 mg/dL is critical) is higher, urine creatinine is lower.
• KUB (Kidneys, Ureters, Bladder) X-ray: Radiologic exam to diagnose stones or abnormalities.
• IVP (Intravenous Pyelogram):
  • X-ray with IV dye to outline urinary tract structures.
  • Pre-procedure: Assess for shellfish/Betadine allergies, NPO, bowel prep, informed consent.
  • Contraindications: End-stage renal disease (ESRD), dye allergies.
  • Post-procedure: Assess hydration, potential creatinine draw ($IV ext{ dye}$ is nephrotoxic), increase oral fluids to flush dye.
• Cystoscopy:
  • Invasive procedure to visualize bladder and urethra with a scope.
  • Diagnoses tumors, inflammation, BPH, structural anomalies, removes calculi.
  • Pre-procedure: Assess for allergies, signed consent, NPO, hold bladder medications (antispasmodics/cholinergics).
• Cystourethrogram (VCUG/Retrograde CUG):
  • X-ray test of bladder and urethra with contrast while full and during urination (VCUG).
  • Retrograde: contrast injected against urine flow.
• Renal Biopsy:
  • Needle inserted through skin into kidney for tissue sample.
  • Pre-procedure: Signed consent, check PT/APTT, NPO, prone position, local anesthetic.
  • Post-procedure: Increase PO fluid intake, assess for breakthrough bleeding/hematuria/flank pain, bed rest, avoid strenuous activity.

Aging Client

• Kidneys decrease in size; 30-50 ext{%} glomeruli non-functional by age $70$.
• Decreased ADH, aldosterone, ANP production leads to decreased ability to concentrate urine.
• Stressors (illness, infection, decreased blood volume) can precipitate acute renal failure.

Renal Failure

• Chronic Kidney Failure (CKF/CKD): Long-term, permanent kidney damage over years.
• Acute Kidney Failure (AKF/AKI): Sudden, short-term loss of kidney function; can lead to CKF if not reversed.
  • Causes (AKI):
    • Prerenal: Decreased blood flow to kidney (e.g., obstruction, low BP/shock, hypovolemia, low cardiac output).
    • Intrarenal: Direct damage inside kidney (e.g., infections like glomerulonephritis, autoimmune diseases, CT contrast dye, nephrotoxic antibiotics like aminoglycosides, NSAIDs). Often Acute Tubular Necrosis (ATN).
    • Postrenal: Blockage after kidneys, obstructing urine outflow (e.g., renal calculi, tumor, Benign Prostatic Hyperplasia (BPH)).
• Waste Products Filtered by Kidneys (HUC):
  • $H^+$ (hydrogen ions)
  • Urea
  • Creatinine