Kidney Function and Non-Protein Nitrogen Compounds

Study Notes

Kidneys are bean-shaped organs found in vertebrates, located in the retroperitoneal space.
In adults, they are about 11 cm long.
Kidneys receive blood from renal arteries and send blood out through renal veins.
The ureter carries urine from the kidneys to the bladder.
The nephron is the functional unit of the kidney, responsible for urine formation (filtration, secretion, and reabsorption).
Each kidney contains roughly 1.25 million nephrons.
Kidneys are responsible for eliminating waste products and regulating plasma and water volume, maintaining ionic balance, and regulating acid-base balance.

Elimination of metabolic waste products: Kidneys are the major excretory organs of the body, responsible for removing waste and toxic metabolites. This is carried out through urine formation.
Regulation of plasma and water volume: Kidneys play a crucial role in maintaining the appropriate volume and composition of the blood and interstitial fluids, by adjusting the water and solute content of the blood.
Regulation of ionic equilibrium: Kidneys regulate the concentration of various electrolytes.
Maintenance of acid-base balance: Kidneys, along with the lungs, work together to maintain optimal pH levels.

Inulin clearance test: Considered the most accurate measure of glomerular filtration rate (GFR). Involves IV transfusion and multiple urine samples.
Creatinine clearance test: Often used to estimate GFR, particularly for patient muscle mass assessment. It's sensitive to kidney function, but not perfectly reliable.
Urea clearance test: Measures the clearance of urea from the blood. Less reliable than creatinine, given variable urea reabsorption in the nephron.

Cystatin C: Produced by all nucleated cells, not secreted, but completely reabsorbed. Used as an indicator of GFR. Levels increase more rapidly than creatinine in early stages of GFR problems.
Beta-trace proteins: Function as prostaglandin synthase, easily filtered and reabsorbed. Elevated levels can indicate myeloproliferative and lymphoproliferative disorders, inflammation and renal failure.
Myoglobin: Associated with acute skeletal muscle injury. Used as a potential marker of myocardial infarction and rhabdomyolysis.
Microalbuminuria: Small amount of albumin in the urine, which typically isn't present. An indicator of kidney problems.
Phenolsulfonphthalein (PSP) test: Measure renal tubular mass based on dye excretion.
Specific Gravity: Measures concentration of solutes in the urine. High values indicate more concentrated urine.
Osmolality: Reflects the total number of solutes in a solution. Useful for assessing water balance.

Urea, uric acid, creatinine, and others are NPN compounds that are waste products from protein metabolism.
Elevated NPN levels suggest impaired kidney function. Tests (such as BUN and others) aid in kidney disease diagnosis and assessment of treatment efficacy.

A screening test for kidney disease. Elevated BUN generally indicates kidney problems.
Used in evaluating renal function and hydration status, and to assess responses to dialysis therapy.

A waste product produced by muscle metabolism.
Its levels in the blood are a good indicator of glomerular filtration rate (GFR).

Elevated levels of nitrogenous waste products in the blood, often due to impaired kidney function.
Azotemia can be classified as pre-renal, renal, and post-renal.