Kidney Anatomy and Function Quiz

Kidney Anatomy

• The nephron is the functional unit of the kidney, with approximately 1.2 million in each kidney
• The nephron consists of:
  • Glomerulus within Bowman's capsule
  • Afferent arteriole that carries blood to the glomerulus
  • Efferent arteriole that carries blood from the glomerulus

Nephron Functions

• Maintains extracellular environment for cell function
• Excretes waste products of metabolism
• Maintains fluid, electrolyte, and acid-base balance
• Secretes hormones that modulate hemodynamics (e.g., erythropoietin and vitamin D)

Diagnostic Procedures

• Measure glomerular filtration rate (GFR)
• Clearance calculations
• Tubular function tests
• Microscopic evaluation of the urine
• Radiologic evaluation (IVP, MRI, ultrasound)
• Biopsy

Nephrotic Syndrome

• Deficiency of albumin in blood and excretion in urine due to altered glomerular function
• Characterized by:
  • Proteinuria (>3.5 g/day)
  • Hyperlipidemia
  • Hypoalbuminemia
• More prevalent in children
• Clinical manifestations:
  • Frothy urine
  • Anorexia, malaise, puffy eyelids, abdominal pain, muscle wasting
  • Ascites and plural effusion
  • Altered blood pressure
  • Oliguria due to hypovolemia
  • Edema
  • Loss of zinc, copper, vitamin D, and iron bound to proteins

Treatment of Nephrotic Syndrome

• Treat underlying cause
• Reduce cholesterol
• Control blood pressure
• Reduce protein in urine
• ACE inhibitors
• Check potassium levels
• Nutrition therapy: control protein intake (0.8-1.0 g/kg/day), soy- or flaxseed-based proteins, and protein supplementation with no benefit

Chronic Kidney Disease (CKD)

• Syndrome characterized by progressive loss of kidney function
• Not reversible
• Progression to end-stage renal disease (ESRD or CKD stage 5)
• Requires medication and specialized diet
• Risk factors:
  • Proteinuria
  • Ethnicity (African Americans with diabetes are at highest risk)
  • Gender (males)
  • Smoking
  • Heavy non-narcotic analgesic use
  • Obesity
• Most frequent causes:
  • Diabetes
  • Hypertension
  • Glomerulonephritis
  • Hereditary and cystic congenital renal disease
  • Interstitial nephritis
  • Neoplasm/tumor
• Common complications:
  • Malnutrition
  • Cardiovascular disease (aggressive management recommended)
  • Bone and mineral disorders
  • Anemia
• Stages:
  • Stage 1 & 2: kidney damage with normal or increased GFR
  • Stage 3: moderate decrease in GFR (30-59 mL/min)
  • Stage 4: severe decrease in GFR (15-29 mL/min)
  • Stage 5: inadequate to sustain life (ESRD)

Renal Replacement Therapy

• Dialysis: removal of excessive and toxic by-products of metabolism from the blood
• Types:
  • Hemodialysis (HD)
  • Peritoneal dialysis (PD)
• Indications:
  • Serum creatinine ≥ 6 mg/dL for non-diabetics
  • Creatine clearance < 15 mL/min for diabetics
• Nutrition therapy:
  • Focus on co-morbid conditions (diabetes, hypertension, hyperlipidemia, progression of CVD)
  • K/DOQI guidelines for GFR ≤ 20
  • Dietary interviews and food intake or nPNA every 3-4 months

Stages 1 & 2 Nutrition Therapy

• Focus on co-morbid conditions
• K/DOQI guidelines for GFR ≤ 20
• Dietary protein: 0.6-0.75 g/kg
• Energy: 30-35 kcal/kg

Stages 3 & 4 Nutrition Therapy

• See ADA guidelines
• Nutrition assessment recommendations
• Nutrient recommendations (protein, energy, sodium, potassium, phosphorus, calcium, vitamins, minerals, fluid)
• Emphasize usual foods

Stage 5 Nutrition Therapy

• On dialysis:
  • Hemodialysis (HD): high protein, control intake of potassium, phosphorus, fluids, and sodium
  • Peritoneal dialysis (PD): more liberalized; higher in protein, sodium, potassium, and fluids, and limit phosphorus
• Goals:
  • Meet nutritional requirements
  • Prevent malnutrition
  • Minimize uremia
  • Minimize complications
• Maintain blood pressure, fluid status
• Adjusted edema-free body weight should be used to calculate body weight for calculating protein and kcal needs

Post-Transplant Nutrition Therapy

• Protein and energy: increased for up to 6-8 weeks, then RDA for protein and low in saturated fat
• Carbohydrate: glucose intolerance common; insulin or OHA may be warranted, emphasize dietary fiber
• Fat: low-fat diet
• Sodium: hypertensions common; restrict sodium
• Potassium: restrict potassium in acute period
• Immunosuppressants: avoid grapefruit and grapefruit juice
• Cardiovascular disease: TLC, lipid-lowering agents
• Hypomagnesemia: supplementation to lower LDL and apolipoprotein B
• Obesity: diet, behavior modification, exercise
• Calcium, phosphorus, and altered bone metabolism: osteoporosis and altered vitamin D, hypercalcuria from corticosteroids

CKD - Stage 5

• Obtained post-dialysis for HD patients, and after drainage for PD patients
• Nutrition Intervention:
  • Fat: increased risk for CAD and stroke
  • HD: typically have normal LDL, HDL, TG
  • PD: higher TC, LDL, TG
  • Recommend TLC diet guidelines for both
• Fluid and Sodium:
  • Highly individualized based on residual urine output and dialysis modality
  • Interdialytic weight gain (HD) should not exceed 5% of body weight
  • 2-gram sodium diet
  • Not more than 1 L fluid daily
  • If urine output > 1 L/day, sodium and fluid can be liberalized to 2-4 g and 2 L
• Phosphorus:
  • Hyperphosphatemia: GFR 20-30 mL/min
  • Dietary phosphorus restriction: 800-1000 mg/day, < 17 mg/kg body weight
  • Phosphate binders; calcium salts
  • Limit calcium intake
• Calcium requirements:
  • Higher in CKD
  • Restrict foods high in calcium
  • Take supplements on empty stomach
  • Limit to 2000 mg/day from all sources
• Vitamin Supplementation:
  • Water-soluble vitamins
  • Daily requirements - Table 20.14
  • "Renal" vitamins include B12, folic acid, vitamin C
  • Avoid high doses of vitamins A & C
  • May need vitamin K if on antibiotics
• Mineral supplementation:
  • Avoid Mg-containing phosphate binders, antacids, and supplements
  • Iron
  • Zinc

Post Transplant

• Protein and Energy:
  • Increased for up to 6-8 weeks
  • After 8 weeks: RDA for protein and low in saturated fat
• Carbohydrate:
  • Glucose intolerance common; insulin or OHA may be warranted
  • Emphasize dietary fiber
• Fat:
  • Low-fat diet
• Sodium:
  • Hypertension common; restrict sodium
• Potassium:
  • Potassium restriction in acute period
• Immunosuppressants:
  • Used to prevent acute rejection
  • Avoid grapefruit and grapefruit juice
• Cardiovascular Disease:
  • TLC
  • Lipid-lowering agents
• Hypomagnesemia:
  • Supplementation of Mg to lower LDL and apolipoprotein B
• Obesity:
  • Weight gain common; may complicate hyperlipidemia and glucose intolerance
  • Emphasize diet, behavior modification, exercise
• Calcium, Phosphorus, Altered Bone Metabolism:
  • Osteoporosis and altered vitamin D
  • Hypercalcuria from corticosteroids
  • Supplement with calcium, vitamin D, anti-resorptive agents
  • Increase phosphorus
  • Monitor serum potassium

Kidneys - Anatomy

• Regulatory and metabolic functions
• Nephron: functional unit; approximately 1.2 million in each kidney
• Glomerulus within Bowman's capsule:
  • Afferent arteriole - carries blood to glomerulus
  • Efferent arteriole - carries blood from glomerulus
• Nephron:
  • Ultrafiltrate formed by glomerulus
  • Similar to composition of blood
  • Filters large proteins and blood cells
  • Modified by tubules
    • Reabsorption of amino acids, glucose, select minerals, water
    • Secretion of solutes, water
  • 65% of filtered sodium and water reabsorbed (active transport in proximal tubule)
• Nephron functions:
  • Maintain extracellular environment for cell function
  • Excretion of waste products of metabolism
  • Maintain fluid, electrolyte, and acid-base balance
  • Vasopressin - in response to blood volume, maintains fluid balance
  • Secretion of hormones that modulate hemodynamics
  • Erythropoietin - red blood cell production
  • Vitamin D - bone metabolism

Diagnostic Procedures

• GFR: glomerular filtration rate; rate at which substances are cleared from plasma
• Clearance calculations - see p. 613
• Tubular function tests
• Microscopic evaluation of the urine
• Radiologic evaluation (IVP, MRI, ultrasound)
• Biopsy

Nephrotic Syndrome

• Deficiency of albumin in blood and its excretion in the urine due to altered glomerular function
• Proteinuria > 3.5
• Hyperlipidemia
• Hypoalbuminemia
• Result of underlying disease
• More prevalent in children
• Clinical manifestations:
  • Frothy urine
  • Anorexia, malaise, puffy eyelids, abdominal pain, muscle wasting
  • Anasarca with ascites, plural effusion
  • Altered blood pressure
  • Oliguria due to hypovolemia
  • Edema
  • Loss of zinc, copper, vitamin D; iron bound to proteins lost
• Treatment:
  • Treat underlying cause
  • Reduce cholesterol
  • Control blood pressure
  • Reduce protein in urine
  • ACE inhibitors
  • Check potassium levels
• Nutrition therapy:
  • Control intake of protein
  • 0.8-1.0 g/kg/day
  • Soy- or flaxseed-based proteins
  • Protein supplementation no benefit

Chronic Kidney Disease (CKD)

• Syndrome in which progressive loss of kidney function occurs
• Not reversible
• Progression to end-stage renal disease (ESRD or CKD stage 5)
• Requires medication and specialized diet
• Risk factors:
  • Proteinuria
  • Ethnicity - African American with diabetes highest
  • Gender - males
  • Smoking
  • Heavy consumption of non-narcotic analgesics
  • Obesity
• Most frequent causes:
  • Diabetes
  • Hypertension
  • Glomerulonephritis
  • Hereditary and cystic congenital renal disease
  • Interstitial nephritis
  • Neoplasm/tumor
• Common complications:
  • Malnutrition
  • CVD - aggressive management recommended
  • Bone and mineral disorders
  • Anemia
• Stages:
  • Stages 1 & 2 - kidney damage with:
    • Normal or increased GFR, mild decrease in GFR
  • Stage 3 - moderate decrease: GFR 30-59 mL/min
  • Stage 4 - severe decrease: GFR 15-29 mL/min
  • Stage 5 - inadequate to sustain life
• Pathophysiology:
  • Microcytic anemia and iron deficiency
    • Inadequate erythropoietin
  • Renal osteodystrophy
    • d/t impaired intestinal calcium absorption and secondary hyperparathyroidism
• Treatment:
  • Treat underlying disease, delay progression
  • Stages 1 & 2 - EPO replacement, vitamin D supplementation
  • Stage 5 - renal replacement therapy, nutrition therapy crucial, transplant
  • Post-transplant - immunosuppresants
• Renal Replacement Therapy:
  • Dialysis - removal of excessive and toxic by-products of metabolism from the blood, replacing the filtering function of the kidney
  • Fluid and electrolyte balance must be maintained
  • Passing blood across selective membrane exposed to rinsing fluid (dialysate)
  • Serum creatinine 6 mg/dL for non-diabetics or
  • Creatine clearance < 15 mL per minute for diabetics
• Hemodialysis (HD) or Peritoneal Dialysis (PD):
  • Type based on underlying kidney disease and co-morbid factors
  • Both require selective, permeable membrane
  • Allows passage of water and small molecules
  • Excludes larger molecules such as protein
• Hemodialysis (HD):
  • Membrane is man-made dialyzer - "artificial kidney"
  • Preferred access site - AVF, AVG
  • Typical regimen - 3 days/week for 4 hrs/treatment
• Peritoneal Dialysis (PD):
  • Lining of patient's peritoneal wall is the selective membrane
  • Types - CAPD, CCPD
  • Access via catheter into peritoneal cavity
  • Range of dextrose concentrations
  • Dwell time and number of exchanges