Exam 4: Tubular Processing of Glomerular Filtrate Flashcards
What is the filtration of glucose like?
Freely
100% is reabsorbed
What is the filtration of amino acids like?
Freely
100% is reabsorbed
What is the filtration of protein like?
Limited
100% is reabsorbed
What is the filtration of bicarb like?
Freely
More than 99.9% reabsorbed, but variable in the small intestine
What is the filtration of sodium like?
Freely
99.4% is reabsorbed, moderately variable
What is the filtration of chloride like?
Freely
99.1% is reabsorbed, moderately variable
What is the filtration of potassium like?
Freely
87.8% is reabsorbed, highly variable
What is the filtration of urea like?
Freely
50% is reabsorbed, highly variable
What is the filtration of creatinine like?
Freely
0%
Why is the Na-K ATPase particularly important?
It provides a chemical gradient for the absorption of many solutes
What has a transport maximum in the tubules?
Glucose
Amino acids
Protein
What can glucosuria (increased glucose in the urine) be caused by?
Hyperglycemia
Normoglycemic glucosuria
What is hyperglycemia?
Increased glucose in the blood, as seen in diabetes mellitus or pituitary adenoma (Cushings disease), to a point that more glucose is filtered and presented to the tubular epithelium than there are transport molecules for reabsorption
What does normoglycemic glucosuria indicate?
Sick and injured tubular epithelium where there are a diminished number of transport molecules that can’t handle a normal glucose load
Describe the proximal tubule
High cell surface area High metabolic rate 65% of reabsorption of Na and H2O Reabsorbs essentially all glucose and AA Secrete organic acids and other waste products
What gives the proximal tubule a high metabolic rate?
Many mitochondria
High O2 consumption
What happens to Na as the total amount decreases throughout the proximal tubule?
The concentration does not decrease as water moves with Na, but the total volume decreases significantly
Describe the thin loop of henle
No brush border
Few mitochondria
Minimal metabolic activity
Describe the thin descending loop of henle
Very permeable to H2O with 20% being absorbed here
Renal medullary interstitial fluid hypertonicity is essential
Describe the thin ascending loop of henle
Not permeable to H2O
Moderately permeable to urea, facilitated passive, moving into tubule
Slightly to moderately permeable to Na, but mostly passive
Describe the thick ascending loop of henle
Increased surface area Increased mitochondria High metabolic activity Impermeable to H2O Impermeable to urea 25% of Na, K, Cl absorbed, but H2O does not follow
What happens to the filtrate in the thick ascending loop of henle?
It is becoming more dilute
What decreases sodium reabsorption at the thick ascending limb of the loop of henle during dehydration?
Prostaglandin E2
What increases sodium reabsorption? How?
Administration of NSAIDs
By decreasing PGE2
What does the early distal tubule contain?
Macula densa
Describe the early distal tubule
Impermeable to water
Impermeable to urea
Active reabsorption of Na, Cl, and other electrolytes
What does the permeability to H2O in the late distal tubule and collecting duct depend on?
ADH
What is the late distal tubule and collecting duct impermeable to?
Urea
What is the permeability and absorption of Na partially dependent on in the late distal tubule and collecting duct?
Aldosterone and angiotensin
What do principle cells secrete?
Potassium
What do intercalated A cells secrete?
H+
What begins at the late distal tubule and collecting duct?
Regulated reabsorption and/or secretion
What are intercalated cells important for?
pH control
What are intercalated cells able to utilize?
The Na concentration gradient created by the Na-K ATPase pump to move H+ out
K secreted by principle cells to enable an energy dependent K/H+ counter transport to pump H+ out against a larger concentration gradient
How is hydrogen generated?
Within the cell via the action of carbonic anhydrase on water and CO2
What is H2O permeability controlled by in the medullary collecting duct?
ADH
What is the medullary collecting duct permeable to?
Urea
What does the medullary collecting duct being permeable to urea help with?
Helping keep medullary tonicity high- both passive and facilitated
What is the permeability to Na and K in the medullary collecting duct controlled by in the medullary collecting duct?
Aldosterone
What hormones are involved in the tubular resorption regulation?
Angiotensin II
Aldosterone
ADH
Atrial natriuretic factor
What does angiotensin II do?
Increase efferent arteriole constriction
Increases tubular Na resorption directly
Increase tubular Na resorption via increased aldosterone secretion
What would proteinuria and glucosuria with a normal blood glucose indicate?
Tubulonephritis resulting in diminished total transport capacity of the tubular epithelial cells so even normal altered amounts of exceeded tubular transport threshold
What would proteinuria without glucosuria most likely indicate?
Glomerulonephritis resulting in increased albumin presentation to the tubules exceeding transport threshold
Why doesn’t glomerulonephritis result in increased glucose presentation to the tubules as it does protein?
Because the glomerulus does not present a barrier to the filtration of glucose to begin with
What would increase peritubular capillary reabsorption?
Increased efferent arteriolar resistance
Increased peritubular capillary albumin concentration
