case 7 - introduction to the kidney Flashcards
what is the function of the kidney via the maintenance of the extracellular fluid volume
via sodium and water
what is the endocrine secretion function of the kidney
renin-angiotensin system
erythropoeitin
vitamin D - calcium regulation
what are the different parts of the nephron
renal corpuscle
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
what does the renal corpuscle do
produces filtrate
what does the loop of henle do
further reabsorption of water (descending limb)
And both sodium and chloride ions (ascending limb)
what does the distant convoluted tubule do
secretion of ions, acids, drugs and toxins
variable reabsorption of water, sodium ions and calcium
what does the collecting duct do
variable reabsorption of water and reabsorption or secretion of hydrogen and bicarbonate ions
what does the papillary duct do
delivery of urine to minor calyx
what are the different parts of the collecting system
collecting duct
papillary duct
where does filtration happen
in the nephron
where does selective reabsorption happen
in the proximal convoluted tubule
where does secretion happen
in the collecting duct
what surrounds the nephron
the vasa recta
what happens in the vasa recta
this is where the substances that are reabsorbed from the tubular fluid and that we need to retain, re-enter the blood supply and then drain into the vein to eventually come back and leave via the hillum into the renal vein to then be returned to the general circulation
what is normal cardiac output
5 litres per minute
how much of the cardiac output do the kidneys recieve
20% - 1L per minute
what is the equation for glomerular filtration rate
GFR = Kf × [PGC - (PBC + p(pie)GC)]
what is Kf
filtration coefficient
what is PGC
glomerular capillary hydrostatic pressure
- favours filtration
what is pie(GC)
glomerular capillary oncotic pressure
- opposed filtration
what is PBC
Bowman’s capsule hydrostatic pressure
- opposes filtration
what should oncotic pressure be
0
where does blood enter the glomerulus through
the afferent arteriole and then enters the glomerular capillary network
where does filtration occur
in the ball of capillary
what is part of the filtration barrier
podocytes are part of the filtration barrier - stops larger molecules from leaving the blood and entering the tubular fluid
what is the cut off point at which the physical barrier prevents filtration
approximately the size of albumin
what is the charge in the membrane
it has negative charge - there is also a charge barrier
do the GFR in notes in the introduction to kidney example!!!
the next few flashcards are explaining the mechanism of autoregulation
what happens as blood pressure in the renal artery increases
there is a corresponding increase in the resistance to flow of the afferent arteriole.
what happens to the afferent arteriole when this happens
it begins to constrict as renal artery pressure goes up
what happens to the efferent arteriole leading out of the glomerulus
it does not change
what does this mean and what is the result
therefore, the resistance to the outflow stays constant as renal arterial pressure increases as afferent pressure goes up.
the result of this is in response to the increase in resistance as the pressure goes up, the glomerular capillary pressure within the glomerular capillaries remains constant and as a result, over the normal pressure range, renal blood flow remains constant and glomerular filtration rate remains constant
therefore, what is it that helps maintain a constant blood flow and a constant GFR
the afferent arteriole contracting and relaxing
what is the myogenic tone autoregulation mechanism
vascular smooth muscle responds by vasoconstricting
what is the tubuloglomerular feedback autoregulation mechanism
distal tubular flow regulates vasocontriction by monitoring what goes through it
what lecture for explanation of diagram in notes
GO TO NOTES THIS IS IMPORTANT
what is the concept of renal clearance measurement of GFR equation
Ux V
(over)
Px
what is Ux
urinary concentration of x
what is V
urine volume per unit of time
what is Px
plasma concentration of x
what is the equation for renal clearance
‘Volume of plasma which is cleared of substance x per unit time’
what is the gold standard ideal marker of GFR
insulin
what is also used clinically as a marker for GFR
creatinine; used clinically but affected by diet, gender, age, ethnicity
what is the filtered load of salt in the nephron
around 1.5 kg per day although we only use 9g of salt per day
what does plasma Na+ determine
extracellular fluid volumes
arterial blood pressure
what is the transporter responsible for the majority of sodium reabsorption
NHE-3
where does the bulk of reabsorption occur
proximal tubule
67% Na+ reabsorbed
where does fine tuning reabsorption occur
distal and collecting duct
8% Na+ reabsorbed
where does the rest of Na+ get reabsorbed
Loop of Henle
through what does the reabsorption of sodium in the proximal tubule occur
through the exchange of the sodium hydrogen exchanger and it is NHE-3.
what is the official name of NHE-3
SLC9A3
what does this exchanger do
it takes up a sodium ions and moves it down its concentration gradient into the cell and exchanges it for a hydrogen ion, taking it out of the cell into the tubular fluid.
what is this then linked to
the movement of chloride coming into the cell through a chloride anion exchanger
what happens to the sodium that has been reabsorbed
it has been pumped out by the NaK ATPase
what is the other transporter on the basolateral side of the membrane
the sodium hydrogen exchanger; NHE-1 (SCL9A1)
what is this exchanger involved in
the regulation of cell volume, not in the regulation of sodium
what happens in the late distal/collecting duct
fine turning
under what control does this happen
under hormonal control
how and where is aldosterone released from
aldosterone from the adrenal cortex is released as a result of the stimulation by angiotensin II
what does this aldosterone do
makes ENaC channels be produced and inserted into the membrane and stimulates these channels to open
what happens at the same time
aldosterone allows K+ channels to be open and allows this K+ to be lost and added to the filtrate
what is the glucose transport solute carrier family
SLC5
what are the two transporters in this category and what do they do
SGLT1 - transports 1 glucose: 2 Na
SGLT2 - transports 1 glucose: 1 Na
what does the GLUT family transporters do
facilitated diffusion
what are the two GLUT family exchangers that we are concerned with
GLUT 1 and GLUT 2
what are low-affinity, high-capacity (early proximal) transporters
SGLT2 and GLUT2
what are high-affinity, low-capacity (late proximal) transporters
SGLT1 and GLUT1
what is the fasting glucose excretion rate and the GFR
Fasting glucose ~ 5 mmol/L and GFR = 125 mL/min
therefore what is the filtered glucose
Filtered glucose = 5 x 0.125 = 0.63 mmol/min
what is the transport maximum
Transport maximum (Tm) ~ 1.25 mmol/min
what is the plasma glucose and what does this value mean
Plasma glucose ~ 10 mmol/L - this is the value when Tm is exceeded and cannot reabsorb all the glucose
what happens if Tm is exceeded
you see glucose in the urine
what is splay
splay reflects the fact that the transport properties of each individual nephron are slightly different. so the maximum that each individual nephron can reabsorb is not exactly the same
splay is uraemic toxins and therefore means loss of glucose in the urine
what happens in the cortex
there is gluconeogenesis - 20% of glucose production
what happens in the medulla
there is glycolysis
glucose is broken down into pyruvate
