renal processing of glomerular filtrate
TRANSCRIPT
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Tubular Processing of Glomerular Filtrate
By Dr. Karishma R. Pandey
Assistant Professor
BPKIHS, Nepal
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Overview
Steps in urine formation
Processing of glomerular filtrate by Reabsorption and secretion
Substances reabsorbed in different parts of renal tubule and its mechanism
Substances secreted in different parts of renal tubule and its mechanism
Regulation of renal processing
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Steps in Urine Formation
Cortical
radiate
artery
Afferent arteriole
Glomerular capillaries
Efferent arteriole
Glomerular capsule
Rest of renal tubule
containing filtrate
Peritubular
capillary
To cortical radiate vein
Urine
Glomerular filtration
Tubular reabsorption
Tubular secretion
Three major
renal processes:
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Processing of glomerular filtrate by Reabsorption and secretion
• Reabsorption is defined as movement of a substance from the tubular fluid to the blood, and this process occurs either via the tubular cells ”the transcellular route” or between the cells” the paracellular route .
• Tubular secretion is defined as movement of a substance from the blood into the tubular fluid.
• The reabsorption and secretion that occur via the transcellular route are largely the result of secondary active transport of solutes by the tubular cells.
• Paracellular reabsorption occurs as a result of concentration or electrical gradients that favor movement of solutes out of the tubular fluid.
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Routes of Water and Solute Reabsorption
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Cells at renal tubules and collecting duct
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Proximal Convoluted Tubule (PCT); Reabsorption
Figure 25.4b
• PCT is the most active in reabsorption
• All glucose, lactate, & amino acids
• Most Na+, H2O, HCO3- , CL-
• and K+
– 65% Na+ and H2O– 90% HCO3
-
– 50% CL-
– 55% K+
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Protein absorption
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Reabsorption of water / ions / nutrients
• Passive tubular reabsorption:
– Na+ ions establish an electro-chemical gradient favoring anions (Cl-
& HCO3-)
– Na+ establishes an osmotic gradient allowing water (via aquaporins) to leave water permeable region (PCT & Loop)
As water leaves the tubules the remaining solutes become more concentrated & follow their diffusion gradient out of the filtrate (cations, fatty acids, urea)
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Transport maximum for substances that are actively reabsorbed
For most substances that are actively reabsorbed or secreted, there is a limit to the rate at which the solute can be transported, often referred to as the transport maximum.
This limit is due to saturation of the specific transport systems involved when the amount of solute delivered to the tubule exceeds the capacity of the carrier proteins and specific enzymes involved in the transport process.
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Non-Reabsorbed Substances
• Non-reabsorption due to:
– Lack of carriers
– Lipid insolubility
– Molecules too large to pass through membrane pores
• Non-reabsorbed substances are usually nitrogenous wastes
– Urea (50-60% reclaimed)
– Creatinine: not reabsorbed
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Loop of Henle: Reabsorption
• Descending limb:
– H2O reabsorbed by osmosis
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Loop of Henle: ReabsorptionAscending limb:
Na+, Cl-, K+ active transport
Ca2+, Mg2+ passive transport
H2O : impermeable
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Distal Convoluted Tubule: Reabsorption
Early tubule:
• Na+ : symporter mediated
• Ca2+ : PTH mediated
• Cl- : diffusion
• H2O : impermeable
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Distal Convoluted Tubule & Collecting Tubule: Reabsorption
Principal cells:
• Na+ : Aldosterone mediated
• Ca2+ : PTH mediated
• H2O : ADH mediated
Intercalated cells
• H2CO3
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Mechanism of Action of Aldosterone
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Mechanism of Action of Antidiuretic Hormone
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Mechanism of Action of Parathyroid Hormone
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Medullary Collecting Duct: Reabsorption
HCO3-
H2O : ADH dependent
Urea: facilitated diffusion
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Tubular Secretion
• Tubules also secrete substances into the filtrate.
• H+, K+, NH4+, creatinine
• Important functions:– Disposes of substances not in original filtrate (certain drugs
and toxins)
– Bile salts, oxalate, urate and catecholamines
– Disposes of excess K+
• Urine consists of filtered & secreted substances
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Regulation of renal processing
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Regulation of renal processing
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Regulation of renal processing
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Mechanism of Action of Angiotensin II
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Mechanism of Action of Atrial Natriuretic Peptide
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References
1. Textbook of Medical Physiology-12th
edition(Guyton and Hall)
2. Ganong’s Review of Medical Physiology-23rd
edition
3. Textbook of Physiology-6th edition(Berne and Levy)
4. Textbook of Medical Physiology-2nd
edition(Walter F. Boron, Emile L. Boulpaep)
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Thank you!!!