Download Renal Unit: Overview

MLAB 2401: Clinical Chemistry
Keri Brophy-Martinez
Renal Unit :Overview
Kidney physiology
Renal Physiology
• Three renal processes
– Glomerular filtration
– Tubular reabsorption
– Tubular secretion
Glomerular Filtration
• Glomerulus filters incoming blood
– How?
• High pressure in the glomerular capillaries sets up a
pressure difference
• Semipermeable glomerular basement membrane allows
small dissolved solutes, which have a positive charge to
pass
• Glomerular filtrate, which is cell-free, protein free is made and
can be measured by the GFR( glomerular filtration rate)
Tubular Reabsorption
•
Substance movement from tubular lumen to peritubular capillary
plasma for regulation of concentration
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–
–
•
Assists in conservation of nutrients
Prevents electrolyte loss
Assists in acid-base imbalance
Occurs by Active and Passive transport
– Active Transport
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Tubular epithelial cells use energy to bind and transport substances across plasma membrane
to blood
Transports Glucose, Amino acids, Proteins, Electrolytes
Maintains the sodium pump to prevent the cells from swelling up
– Passive Transport
•
•
No energy requirement
Substances, such as water and urea, move from higher concentrations to lower concentrations
Tubular Reabsorption
•
Occurs in proximal convoluted tubule
– Receives the glomerular filtrate
– Return the bulk of substances back to blood circulation
• Proteins, glucose completely reabsorbed
• Sodium, chloride partially reabsorbed
• Creatinine no reabsorption
– Secretes products of kidney tubular metabolism, such as hydrogen
ions and drug
Tubular Secretion
• Occurs in the proximal convoluted tubule
• How is this used?
– Movement of substances from peritubular capillary
plasma to tubular lumen that were not previously
eliminated
– Secretion of products from tubule cell cellular
metabolism into filtrate, such as hydrogen
Distal Convoluted Tubule
• Most of reabsorption complete
• Function
– Make small adjustments to benefit
electrolyte and acid-base balance
– Adjustments occur under control of ADH
(antidiuretic hormone) and aldosterone
Functions of the Kidney
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Urine formation
Fluid and electrolyte balance
Regulation of acid-base balance
Excretion of waste products of protein
metabolism
• Excretion of drugs and toxins
• Secretion of hormones
Water Balance
• Kidney assists with water balance through water loss or water
conservation
• Water balance regulated by ADH/AVP
– Secretion of ADH
• Increased plasma osmolality or decreased intravascular
volume
– Action of ADH
• ADH increases the permeability of the distal convoluted
tubules and collecting ducts to water
• Results in water reabsorption and concentration of urine
• Activates thirst mechanism
How does it work?
Aldosterone
• Origin
– Adrenal cortex
– Influenced by renin-angiotension system
• Secretion
– Decreased blood flow or blood pressure
– Decreased plasma sodium
• Action
– Stimulates sodium reabsorption in distal tubules and
potassium and hydrogen ion secretion
– Increases water retention
– Raises blood pressure
Acid-Base Balance
• Renal system assists with constant
control of overall pH
– Conserve bicarbonate ions
– Secretes H+ ions attached to phosphate
– Secretes H+ ions attached to ammonia
Elimination of Nonprotein Nitrogen Compounds
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Waste products formed by degradative metabolism of proteins, amino acids and
nucleic acids
Main players are urea, creatinine and uric acid
– Urea
• 75% of the nonprotein nitrogens excreted daily
• By product of ammonia breakdown
• 40-60% reabsorbed
– Creatinine
• Formed from creatine, which is found in muscle
• Not reabsorbed by the tubules
– Uric acid
• Waste product of purine metabolism (nucleic acid)
– Ammonia
• Product of amino acid and protein catabolism
Endocrine Functions
• Produces hormones
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Renin
Erythropoietin
1,25- dihydroxy vitamin D 3
Prostaglandins
• Target for certain hormones produced by
other endocrine glands
Hormones: Renin
• Released by juxtaglomerular cells
• Stimulated by decreases in fluid volume or
blood pressure
• Effect of:
– Promote sodium reabsorption and water
conservation
– Promotes secretion of aldosterone
• Bottom line: Increase blood pressure
Hormones: Erythropoietin
• Made by kidney
• Production regulated by blood oxygen
levels (hypoxia)
• Effect of:
– Stimulate RBC production
Hormones:
1,25-Dihydroxy Vitamin D3
• Made in the kidneys
• Active form of vitamin D
• Determines phosphate and calcium
balance and bone calcification in the
human body
Hormones:
Prostaglandins
• Fatty acids formed from dietary fatty
acids
• Produced in the kidney
• Function
– Increase renal blood flow (vasodilator)
– Sodium and water excretion
– Antagonistic to renin release
References
• Bishop, M., Fody, E., & Schoeff, l. (2010). Clinical Chemistry:
Techniques, principles, Correlations. Baltimore: Wolters Kluwer
Lippincott Williams & Wilkins.
• Sunheimer, R., & Graves, L. (2010). Clinical Laboratory
Chemistry. Upper Saddle River: Pearson .
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