L17 Flashcards
what does Asparagus contain that makes you pee smell bad
Asparagus contains sulfur compounds called mercaptan.
you need to have a gene to produce an enzyme to brake down mercaptan into its sulfur bioproducts to get the unpleasant smell
what are the 3 basic processes of the nephron
- glomerular filtration
- tubular secretion
- tubular reabsorption
Glomerular filtration, tubular secretion and reabsorption
are energy intensive processes, so why do we do this?
although it seems wasteful to filter large amounts of substances from the plasma only to reabsorb most back
again, this allows the body to quickly rid
the body of toxic or harmful substances from the blood
therefore it has to do with renal clearance
what is Tubular Reabsorption
As the filtrate passes down the tubule, most is reabsorbed back into the blood (plasma) (filtrate to blood)
how is Tubular Reabsorption achieved
• This is achieved through action of specific channels and
transporters in the membranes of the epithelial cells of the
tubule, and through the tight junctions of some of the segments of the nephron.
what kind of epithelium does the Proximal tubule contain
Leaky absorptive epithelium
what kind of solution is the Proximal tubule responsible for producing
• Isosmotic solution
what kind of epithelium do the Late Distal tubule and Collecting duct contain
• Tight absorptive epithelia
what kind of solution do the Late Distal tubule and Collecting duct produce
• Hyperosmotic solution
what part of the nephron is under hormonal control
Late Distal tubule and Collecting duct
different parts of the nephron have different roles. what is this dependent on
What the different parts of the nephrons are doing is dependent on the polarity of the cells and what transport proteins are on the apical and basolateral membranes
where is SGLT1 and SGLT2 located in the nephron
SGLT1 in the straight tubules and SGLT2 in the proximal tubule
what amount of water is filtered per day
180L
what amount of water is excreted per day
1.8L
what % of water is reabsorbed per day
99%
what causes Diabetes mellitus
- too much glucose
where are substances secreted from in the nephron
Substances can be secreted from the peritubular capillaries (peritubular blood to the filtrate)
note peritubular capillaries = first part of the nephron (before the loop of henle) - secretion
vasa recta = loop of henle - absorption
what is the difference between glomerular filtration, tubular secretion
Like glomerular filtration, tubular secretion constitutes a
pathway of moving substances from the blood to the
tubule lumen
Secretion at peritubular capillaries enables disposal of substances at a higher rate than depending on filtration
alone
what things would be secreted from the body
• H+, K+, penicillin, metabolites from pesticides and many
substances
what is metabolic acidosis
is when the body has too much H+
why do we secrete K+
because we have a lot of it in our diet
Which of the following statements is TRUE?
A. 100% of the filtered urea is reabsorbed by the nephron.
B. Reabsorption is the only renal process that ‘recovers’ filtered substances and water.
C. Secretion is not an energy intensive process.
D. Normally, 95% of the filtered glucose is reabsorbed by your kidneys, unless you are a diabetic.
B
what is Glomerular Filtration Rate (GFR)
• Amount of filtrate produced per unit of time
what is the normal value for Glomerular Filtration Rate (GFR)
Normal value = 125 ml / min (180 L / day)
Equal to sum of filtration rate of all functioning nephrons in the two kidneys
what is Glomerular Filtration Rate (GFR) = to
Equal to sum of filtration rate of all functioning nephrons in the two kidneys
what is GFR a indicator for
• GFR is a useful indicator of renal functioning
what is Renal Clearance (RC)
• RC = the volume of plasma from which a substance is completely cleared by the kidneys per unit time
what do you need to calculate Renal Clearance (RC)
• One must know the concentration of the substance in the urine and plasma and rate of urine produced
As we get older we tend to lose nephrons but we maintain the same GFR. how is this?
The remaining nephrons will increase their rate so that it stays constant
what is the equation for RC
Clearance (Cs) = (Us x V)/Ps
Us = concentration of S in urine (mg/L or mmol/L)
V = volume of urine per unit time (ml/min or L/hour)
Ps = concentration of S in plasma (mg/L or mmol/L)
what does the equation for RC describe
• The equation describes the rate at which substance S is cleared by the kidneys (unit per time)
the equation describes the clearance via the kidneys for all substances that can be detected in plasma and urine!
• Can the equation for RC be used to estimate GFR?
yes
To be used as a measure of GFR a substance must……
- Not be reabsorbed from the tubule
- Not be secreted into the tubule
- Not be metabolised
what are two main substances that are often used to estimate GFR
- Inulin (not to be confused with insulin!!)
* Creatinine
what is Inulin
• Polysaccharide not metabolised by body
how is Inulin used to calc GFR
because it is not metabolised and is not found in body and must be constantly infused
You would be in the hospital and you would be pufused with inulin and then they would see how long it takes your body to filter it out. (How long till it is not longer present in the urine)
what is Creatinine
• Waste product produced by muscles
why is Creatinine used to mesure GFR
- Filtered but not reabsorbed
- Small amount of secretion (~10% secreted)
- Already in body so most commonly used clinically
Measuring the renal clearance of creatinine is therefore ideal for clinically estimating GFR
what is the most common why to measure GFR
Creatinine
125mL/min = what in L per day
180
what can GFR be described as
A measure of the function of the kidney
what does a low GFR mean
kidney failure
Which of the following statements is FALSE?
A. The typical GFR for a healthy person is 125 ml/min.
B. Renal clearance is the volume of plasma from which a
substance is cleared by the kidneys per unit time.
C. GFR is not a useful indicator of renal function.
D. Creatinine is a substance that can be used to determine
GFR
C
what do you need to know in order to be able to calc daily filtered load
• Provided we know the GFR and the plasma concentration of a substance we can calculate the daily filtered load of that substance
what is the equation for daily filtered load
Daily filtered load = GFR x [substance]plasma
what is the normal daily filtered load for glucose and how would that change for a diabetic
all of the glucose in a normal person is reabsorbed therefore it would be 180g/day
in a diabetic there glucose conc in the blood would be higher therefore DFL would be higher
How does the kidney handle this filtered load of ions and
glucose?
Ion channels and transporter proteins
can Mediated reabsorptive transport proteins saturate
yes
what would Mediated reabsorptive transport proteins need to be able to saturate
to limit to amount of a substance transported per unit of time
what is it called when mediated reabsorptive transport proteins saturate
This is the transport maximum (TM)
• Binding sites on transport proteins become saturated
when the concentration of the transported substance
increases beyond a certain limit (TM)
what is the transport maximum
• Binding sites on transport proteins become saturated
when the concentration of the transported substance
increases beyond a certain limit (TM)
where is Glucose is reabsorbed
in proximal tubule
how is glucose reabsorbed
across leaky
absorptive epithelia using Na+-glucose cotransporters
the concentration of glucose in the plasma does not usually exceed what concentration in a healthy person
150 mg / 100 ml as it is under strict control by hormone insulin
In diabetes mellitus there is a lack of control by insulin leading to hyperglycaemia (too much glucose in the blood)
this causes the plasma conc of glucose to increase to what
• [glucose]plasma can exceed 200 mg / 100 ml
Therefore, a large increase in the filtered load of glucose
At 200 mg / 100 ml, tubular Na+-glucose co-transporters become saturated and can not reabsorb all of the filtered glucose
what does this cause
Glucose appears in urine = Glucosuria
