Structure And Function Of The Renal Tubule Flashcards
How does the glomerular filtrate composition compare to the plasma?
Almost the same, but no cells and only a small amount of protein in the glomerular filtrate
What happens when you remove one component of the glomerular filtrate?
Concentrates the other components
What are people with familial renal glycosuria missing?
SGLUT2 symporter
What type of inhibitors are used for diabetes treatment?
SGLT2
What are the three techniques to investigate tubular function?
Clearance studies, micropuncture and isolated perfused tubule and electrophysiological analysis
What types of organisms are clearance studies done on?
Humans
What types of organisms are micropuncture and isolated perfused tubule and electrophysiological analysis done on?
Lab animals
What are the two types of electrophysiological analysis?
Potential measurement and patch clamping
What are the four steps in the micropuncture technique?
Puncture, inject vicious oil, inject fluid for study and leave to infuse, sample and analyse
Why do you inject a viscous oil in the micropuncture technique?
Stops any mixing of fluid between the stuff we want to study and any other fluid in the glomerulus already
How do you carry out an electrical potential measurement?
Use a micro electrode to measure the potential across a membrane (measure whether an ion is moving with or against the electrochemical gradient)
What are you measuring when taking a potential measurement?
measure whether an ion is moving with or against the electrochemical gradient
How do you do patch clamping?
Dock the pipette to the membrane (Doesn’t puncture the membrane)
What are you measuring with a patch clamp?
Current flow through individual ion channels and electrical resistance
What are the two types of nephron and their prevalence?
Juxta-medullary nephron- 15%
Cortical nephron - 85%
What is special about the juxta-medullary nephrons?
Long loop of Henle
Peritubular capillaries run around the loop of henle
What is a vasa recta?
Peritubular capillaries running around the loop of henle
What is the function of juxta-medullary nephrons?
Facilitate the uptake of water
What are the features of a cortical nephron?
Short loop of henle
Peritubular capillaries run around the proximal and distal convoluted tubules
What is the function of the cortical nephron?
Where most of the reabsorption and secretion takes place
What are special about kangaroo rats?
Super long loops of henle
- barely drinks
- most concentrated urine of any mammal
What is the function of the proximal convoluted tubule?
Reabsorption of sodium, chloride, bicarbonate, potassium, water, glucose and amino acids
And secretion of organic acids and bases
What are the epithelial cell characteristics in the proximal convoluted tubule?
- highly metabolic (lots of mitochondria)
- brush border on luminal side
What is reabsorption in the proximal convoluted tubule driven by?
ATP controlled sodium efflux into the blood stream - allows sodium from the lumen into epithelial cell
What % of glucose and amino acids are reabsorbed in the proximal convoluted tubule?
100
How is water reabsorbed in the proximal convoluted tubule?
Osmosis
How is chloride taken up in the proximal convoluted tubule?
Symporters
How are proteins taken up in the proximal convoluted tubule?
Pinocytosis
What happens in Fanconi’s syndrome?
All the proximal convoluted tubules reabsorption mechanisms are defective
What are the three segments of the loop of henle?
thin descending, thin ascending and thick ascending
What are the structural features of the thin descending and ascending segments of the loop of henle?
Both have thin epithelial cells, no brush border, few mitochondria and low metabolic acitivity
What are the thin descending and ascending segments of the loops of henle used for?
Reabsorption of water
What are the structural features of the thick ascending segment of the loop of henle?
Thick epithelial cells, lots of intracellular folding, few microvilli, many mitochondria and a high metabolic activity
What is the thick ascending limb of the loop of henle used for?
Reabsorption of ions and hydrogen ion secretion
What are the functions of the loop of henle?
Concentrating/ diluting urine and adjusting rate of water secretion/ absorption
How permeable is the thin descending limb of the loop of henle to water?
Very
How permeable are the thin ascending and the thick ascending limbs of the loop of henle to water?
Virtually impermeable
How is sodium moved from the thick ascending loop of henle into the peritubular capillary?
Sodium chloride potassium symporter from tubular lumen into the epithelial cell
Sodium potassium ATPase from epithelial cell into peritubular capillary
What can the sodium chloride potassium symporter be inhibited by?
Loop diuretics
What type of exchange system does the vasa recta act as?
Counter current
What happens as the blood in the vasa recta descends into the medulla?
Water diffuses out of the blood and the salts diffuse in
What happens as the blood in the vasa recta ascends from the medulla?
Water diffuses into the blood and salts diffuse out
What % of blood flow is in the vasa recta?
5
Why is the blood flow in the vasa recta so slow?
Minimises solute loss from interstitium and maintains medullary interstitial gradient
What are the two parts of the distal convoluted tubule?
Early and late
Where is the macula densa found?
Early distal convoluted tubule- juxtaglomerular apparatus
What is the function of the early distal convoluted tubule?
Provide feedback control of the glomerular filtration rate and tubular fluid flow in the same nephron
What happens in the late distal convoluted tubule?
Solute reabsorption, high Na/K ATPase activity, acid base balance
Which is the more convoluted part of the distal convoluted tubule?
Late
What does the collecting tubule do?
Connects end of distal convoluted tubule to the collecting duct- mainly in the outer cortex
What is the collecting duct made up of?
Cuboidal to columnar epithelia and very few mitochondria
What are the two types of cells in the collecting duct?
Intercalated and principle cells
What are the intercalated cells involved in?
Acidification of urine and acid base balance
What are the principal cells involved in?
Sodium balance and ECF volume regulation
What are the functions of the collecting duct?
Final site for processing urine
What makes the collecting duct very permeable to water?
ADH
What is ADH secretion triggered by?
Changes in the plasma osmolality
How does ADH make collecting duct more permeable?
Binds to ADH receptor 2 which stimulates a signalling cascade involving inc cAMP and pKa which triggers the synthesis of aquaporin 2 and causing it to be transported to the plasma membrane
How are urea levels monitored?
BUN test (blood, urea, nitrogen)
What are the major factors contributing to a build up of solute concentration in renal medulla?
- active transport of Na+ and cotransport of K+ and Cl- out of thick ascending limb
- facilitated diffusion of large amounts of urea from collecting ducts
- little diffusion of water
How is hypertension related to kidney disease?
Kidneys regulate ECF volume and therefore influence blood pressure
How is congestive heart failure related to kidney disease?
Fall in cardiac output -> renal hypoperfusion-> hypovolaemia resulting in pulmonary oedema
How does diabetic nephropathy occur?
As a consequence of diabetes, filtering system of kidneys get destroyed over time
How does lithium treatment result in acquired nephrogenic diabetes insipidus?
Reduction of AQP2 expression
