Kidney and Liver Function Tests
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Functions of the urinary system
• excretion and elimination (removal of organic waste products from body fluids such as urea, creatinine and uric acid: terminal prods of metabolism) • homeostatic regulation (water, electrolyte, acid-base balance) • endocrine function (kidney hormone production)
What are some hormones produced by kidneys
• renin • erythropoietin • 1,25-dihydroxy vitamin D3 • Prostaglandins
Main function of kidney (multifunctional)
storage of liquids by concentration of urine
Urine excreted daily in adults is
about 1.5 L (kidney is only 1% of total body weight)
Renal blood flow accounts for what % of cardiac output
20% plasma renal flow: 600 ml/min/1.73 meter squared
Two processes involved in renal blood flow
ultrafiltration (GFR): 180 L/day Reabsorption (>99% of amount filtered gets reabsorbed)
functional units of kidney
nephrons (600,000-1.5 million) *decrease in functioning nephrons =impaired kidney function
number of nephrons an individual is born with which may determine that individual’s susceptibility to renal injury
nephron dose
Parts of the nephron
• Glomerulus • Distal tubule • Proximal tubule • Collecting duct • Loop of Henle
What is formed when collecting ducts ultimately combine? This is where urine collects before passing along the ureter and into the bladder
renal calyces
Where does transport of solutes and water occur?
across and between the epithelial cells that line the renal tubules
Kinds of transport observed in nephrons
active and passive *many passive transport are dependent upon active ie sodium transport
mediator of filtration which is formed from a specialized capillary network (capillary endothelial cells are ~40 nm thick)
glomerulus
Purpose of circular fenestrations/pores with diameters of ~60 nmn in glomerulus endothelium
Permits virtually free access of plasma solutes to the basement membrane
What is the renal threshold for glucose?
180 mg/dL
What is renal threshold?
Blood concentration of a substance that when surpassed, is excreted in urine
[Renal threshold] What is tubular maximum?
maximum capacity of the kidneys to absorb a particular substance *Tm for Glucose = 350 mg/min
What is the pre-renal cause of kidney functional disorder?
pre-renal: decreased intravascular volume
What is the renal cause of kidney functional disorder?
acute tubular necrosis
What is the post-renal cause of kidney functional disorder?
ureteral obstruction
What are the terminal products of hemoglobin catabolism?
bilirubin urobilin
Hormone metabolites excreted from bloodstream
cortisol testosterone *other substances: organic acid, drugs, food additives
Other mechanisms of excretory function of kidneys
• Regulation of blood pressure, circulating volume, and water balance by urine concentration • Regulation of electrolytes by excretion and resorption • Maintenance of blood pH in a physiological range by eliminating radical acids, reabsorbing and forming bases
[Homeostatic regulation] What hormone regulates maintenance of water balance
antidiuretic hormone