Tubular Function Flashcards
What is osmolarity?
A measure of the solute concentration in a solution that depends on the number of dissolved solutes present
What is osmolarity dependent on?
Number of particles in a solution, not the nature of the particles.
How is osmolarity calculated?
Calculated by all the concentrations of different solutes added together measured in mmol/l and each ion counted separately
What is the normal plasma osmolarity?
285-295 mosmol/l
What is the normal urine osmolarity?
50-1200mosmol/l
How can molecules be passively transported through the kidneys? What is the rate and solute concentration relationship using these forms of transport?
Protein independent transport - lipophilic molecules have a linear rate to solute conc relationship
Protein dependent transport - hydrophilic molecules has a curved rate to solute conc
What does secretion do in tubular functions?
Moves substances from peritubular capillaries to tubular lumen, constituting a pathway into the tubule.
How can secretion occur in the tubules
Diffusion
Transcellular mediated transport
What are the most important substances secreted in the tubules?
H+ and K+
What drugs are secreted in the tubules?
Choline
Creatine
Penicillin + others
Where are most solutes reabsorbed in the kidney nephron thingys, what percentage is that?
Proximal convoluted tubule - 60-70%
100% glucose
65% Na
90% bicarb
What drugs regulate collecting duct absorption?
Aldosterone and vasopressin
What is found in the inner medulla of the kidney?
Loop of henle thin descending limb
What is found in the outer medulla of the kidney?
Loop of Henle thick ascending limb
What is found in the cortex of the kidney?
Proximal and distal convoluted tubules
Glomerulus
Collecting duct
What happens in the basolateral membrane?
Na/K pump keeps intracellular Na low and K high
Large conc and electrical gradients favour Na movements into the cell - occurs in most nephron segments
What happens in the early PCT?
Na+ entry down a large electrochemical gradient can bring about the uphill entry of glucose and aas and exit of H+
Carbonic anhydrase activity leads to Na+ reabsorption and increased urinary activity
What is passively reabsorbed in the PCT?
Urea
Water
What is actively reabsorbed in the PCT?
Glucose Amino acids Sodium Potassium Calcium Vit C Uric acid
Why is a net secretion by the PCT important?
It is a route of excretion for some substances
Some drugs enter the tubular fluid here and act further down the nephron
What kind of epithelium does the descending loop of henle have? What happens here?
Squamous epithelia with few mitochondria
Water passively reabsorbed, draws in Na and K
THIN limb
What kind of epithelium does the ascending limb of loop of henle have?
Cuboidal epithelium with few microvilli but many mitochondria
THICK limb
What happens in the ascending limb of the loop of henle?
Chloride actively reabsorbed
Sodium passively reabsorbed with it
Bicarbonate reabsorbed
Impermable to water
How much water and sodium is reabsorbed by the point of reaching the end of the loop of Henle?
85% of water
90% of sodium
What is the tubular fluid that leaves the loop of Henle like?
Hypo-osmolar with respect to plasma
Because more salt than water has been reabsorbed so the loop is hypo-osmolar with repect to plasma
What is the distal convoluted tubule epithelium like? (structure)
Cuboidal with few microvilli.
Complex lateral membrane interdigitations with Na+ pumps
Numerous large mitochondria
What happens in the distal convoluted tubule?
Na+ and Cl- co transporter linked to Ca2+ reabsorption
How are Na+ and Cl- reabsorbed in the distal convoluted tubules?
By a channel sensitive to thiazides. Thiazides cause a rise in plasma Ca2+
What happens at the macula densa of the distal convoluted tubule, what is the macula densa?
Part of juxtaglomerular apparatus, detects changes of Na+ conc of filtrate
What happens in the distal part of distal covoluted tubule and cortical collecting duct?
Fine tuning of the filtrate to maintain homeostasis
DCT - sodium reabsorbed (dependent on aldosterone)
CT - sodium reabsorbed (dependent on aldosterone)
Adjustment of Na/K/H/NH4
Water reabsorbed under control of ADH
What is special about distal part of nephron and water?
Distal part of nephron impermable to water without ADH
What does the principal cell do in the collecting duct and distal part of distal tubule?
Important in Na/K/water balance mediated with Na/K ATP pump
What does the intercalated cell do in the collecting duct and distal part of distal tubule?
Important in acid base balance mediated by H+/ATP pump
What is special abou the cortical collecting duct principle cell epithelium
Very tight epithelium, very little paracellular transport
What are single gene defect conditions that affect tubular function?
Renal tubule acidosis Bartter syndrome Fanconi syndrome (dent's disease)
What happens in renal tubular acidosis?
Hypercholermic metabolic acidosis
Impaired growth
Hypokalemia
What happens in Bartter syndrome?
Excessive electrolyte secretion
Antenatal Barterr sydrome:
premature birth, polyhydroamnios, severe salt loss, moderate metabolic alkalosis, hypokalemia, renin and aldosterone hypersecretion
What happens in Fanconi syndrome?
Increased excretion of uric acid, glucose, phosphate and bicarbonate
Increased excretion of low MW proteins
Disease of proximal tubules associated with renal tubular acidosis
