Functions of the Kidney
- Excretory.
2. Endocrine.
3. Fluid and electrolyte balance.
4. Acid-base balance.
1.Excretory Functions
¨Removal of excess fluid and waste products
¨180 L of filtrate pass through the kidneys each day ® producing 1-2 L of urine
”Wastes excreted from the body in urine include urea (byproduct of protein metabolism); excess vitamins and minerals; metabolites of some drugs and poisons.
2.Acid-Base Functions
¨Acid-base balance is maintained through a buffer system, which maintains blood at pH of 7.4
¨Bicarbonate carries hydrogen ions to the kidneys where they are removed from extracellular fluid in the tubules, returned to the bloodstream as needed.
¨Phosphate buffers intracellular fluid.
3.Acid-Base Balance Functions
¨When fluid volume is low, anti-diuretic hormone (ADH) or vasopressin is released from the anterior pituitary; increases absorption of water in the collecting duct
¨When extracellular volume (ECV) decreases, the renin-angiotensin-aldosterone system is activated ® excretes less sodium chloride
4.Endocrine Functions
¨1,25-dihydroxy-vitamin D3 or calcitriol is produced in the kidney; enhances calcium absorption
¨Activation of Vitamin D and excretion of excess phosphate maintain healthy bones
¨Erythropoietin: acts on the bone marrow to increase production of red blood cells
The Nephron
The Most Common Kidney Diseases
¨Diabetic Nephropathy damage to the nephrons in the kidneys from unused sugar in the blood, usually due to Diabetes.
¨High Blood Pressure can damage the small blood vessels in the kidneys. The damaged vessels cannot filter poison from the blood as they are supposed to.
¨Polycystic Kidney Disease (PKD) is a hereditary kidney disease in which many cysts grow in the kidneys. These cysts may lead to kidney failure.
The Most Common Kidney Diseases
¨Acute Renal Failure – Sudden kidney failure caused by blood loss, drugs or poisons. If the kidneys are not seriously damaged, acute renal failure may be reversed.
¨Chronic Renal Failure – Gradual loss of kidney function is called Chronic Renal Failure or Chronic Renal Disease.
¨End-Stage Renal Disease – The condition of total or nearly total and permanent kidney failure.
¨
Kidney Diseases
Glomerular diseases
a. Nephrotic syndrome
b. Nephritic syndrome—tubular or interstitial
Tubular defects
a. Acute renal failure (ARF)
Other
a. End-stage renal disease (ESRD)
b. Kidney stones
Nephrotic Syndrome
¨Alterations of the glomerular basement membrane allows persistent loss of large amounts of protein in the urine
¨Associated with diabetes, glomerulonephritis, amyloidosis, lupus
¨High risk for cardiovascular disease
¨Hypercoagulability
¨Abnormal bone metabolism
Nephrotic Syndrome
¨Albuminuria: more than 3 g/day urinary albumin losses, with proportionally lesser amounts for children
¨Hypoalbuminemia
¨Hypertension
¨Hyperlipidemia
¨Edema
Medical Management of Nephrotic Syndrome
¨Corticosteroids
¨Immunosuppressants
¨ACE inhibitors/angiotensin receptor blockers to reduce protein losses, control blood pressure and fluid balance
¨Coenzyme A reductase inhibitors to control hyperlipidemia
MNT in Nephrotic Syndrome
¨Protein 0.8 to 1 g/kg IBW 80% HBV
¨ Sodium based on fluid status
¨ Potassium and other minerals (calcium, phosphorus) monitored and individualized
¨ Fluid unrestricted
¨ Diet therapy probably not effective for hyperlipidemia; may require medication
Nephritic syndrome
¨Acute glomerulonephritis (inflammation of the glomerulus
¨Sudden onset, often after streptococcus infections
¨Symptoms include hematuria, hypertension
¨Usually resolve on their own or advance to nephrotic syndrome or ESRD
Nephritic syndrome: Nutritional Management
¨Diet to treat underlying disease
¨Restrict diet if necessary to control symptoms
¨Protein restricted in uremia
¨Sodium restriction in hypertension
¨Potassium restriction in hyperkalemia
Acute Renal Failure
¨Rapid, often reversible deterioration of renal function
¨GFR declines over hours to days
¨Most commonly occurs during hospitalization (5% of hospitalized pts; 30% of ICU pts)
¨Associated with major in-hospital morbidity and mortality (7 to 80%)
Causes of Acute Renal Failure.
¨Pre-renal: caused by intravascular volume depletion, decreased cardiac output
¨Post-renal: benign prostatic hypertrophy, prostate cancer, cervical cancer, colorectal cancer, neurogenic bladder, urethral strictures
¨Intrinsic or parenchymal ARF: vascular disease, interstitial nephritis, glomerular disease, acute tubular necrosis.
Causes of Acute Renal Failure
¨Ischemic Injury (50% of all incidence) d/t loss of blood supply to the kidneys secondary to surgical complications, thrombosis, hypotension, hypovolemia
¨Nephrotoxic injury: medications, contrast medium, chemotherapy, poisons (35%)
¨Multiorgan system failure, particularly liver failure
¨Sepsis, especially bacterial
¨Obstructive uropathy (trauma during surgery, urolithiasis, enlarged prostate)
¨Acute glomerular nephritis.
