Kidney 1 Flashcards
What is the functional unit of the kidney?
Nephron
What are the X2 main parts of the nephron?
1) renal corpuscle
2) tubule
What are the main components of the renal corpuscle?
1) glomerulus = tangle of capillaries
2) Bowmans capsule = supporting structure of epithelia
Which type of arteriolar enters the glomerulus and which exits?
Afferent = arrives
Efferent = exits
What is the process by which plasma entering the glomerulus via the afferent arteriole enters the bowmans space?
What percentage of plasma undergoes this process?
Filtration
20%
What are the X3 layers of the filtration interface?
1) fenestrated capillary endothelium
2) basement membrane with fixed polyanions
3) podocytes with filtration slits
What is the structure of podocytes?
A central body with long extending foot processes
What are some examples of filtration slit proteins?
Nephrin
Podocin
What are the parts of the nephron?
Go through them step by step.
1) glomerulus
2) bowmans capsule
3) proximal convoluted tubule
4) proximal straight tubule
5) descending thin limb of loop of Henle
6) ascending thin limb of loop of Henle
7) ascending thick limb of loop of Henle
8) distal convoluted tubule (to include macula densa cells)
9) collecting ducts
What are the X2 types of nephron?
What are the distinguishing features of each?
What percentage of each type are there?
1) cortical nephrons
= 85% of nephrons
= renal corpuscle is in outer 2/3 of the cortex
= have a short loop of Henle which may not even reach the medulla
2) juxtamedullary nephrons
= 15% of nephrons
= renal corpuscle is in inner 1/3 of the cortex
= have a long loop of Henle
What is the significance of having the X2 types of nephrons?
They are important in the production of concentrated urine
What is the name of the group of cells found in the distal convoluted tubule and the afferent arteriole which help regulate filtration rate and blood pressure?
Juxtaglomerular apparatus
Which X2 specialised cells make up the juxtaglomerular apparatus?
Where are each of these located?
1) macula densa cells = on the distal convoluted tubule
2) juxtaglomerular cells = on the afferent arteriole
What do the juxtaglomerular cells do?
Secrete renin, which hydrolyses angiotensinogen to angiotensin 1
What do the macula densa cells do?
Monitor sodium levels
What does the juxtaglomerular apparatus imply about the arrangement of certain structure in the nephron?
That the distal convoluted tubule passes between the afferent and efferent arteriole
Which smooth muscle cells (not part of the juxtaglomerular apparatus) aid with the surface area available for filtration?
Where are these cells found?
The mesangial cells located around the glomerular capillaries
What is unusual about the blood supply to the nephron?
It has X2 arteriole a (afferent and efferent) with the efferent continuing to form a capillary bed around the renal tubules.
What is the name of the capillary bed formed by the efferent arteriole around the renal tubules?
What are these capillaries called when in the region around the loop of Henle
The peritubular capillary bed
The VASA RECTA
What are the main X3 renal processes?
1) glomerular filtration
2) tubule re-absorption
3) tubular secretion
What is the name of the filtered fluid found in the bowmans space?
Ultrafiltrate
What is the difference between glomerular filtration and tubular reabsorption and secretion?
Glomerular filtration is non-selective process, whereas the other two are selective.
What is tubular secretion?
The secretion of solutes from the peritubular capillaries or the renal tubule walls itself into its lumen.
What is tubular re-absorption?
The movement of solutes from the filtrate in the lumen into the peritubular capillaries.
Name a substance that is filtered and secreted but not reabsorbed?
Will this substance be found in the urine?
Para-aminohippuric acid (PAH)
Yes it will all be in the urine
Name a substance that is filtered and reabsorbed at varying quantities but not secreted?
Will this substance be found in the urine?
H2O and most electrolytes!
In urine in varying amounts
Name a substance that is filtered and 100% reabsorbed but not secreted?
Will this substance be found in the urine?
Glucose and bicarbonate
No it will not be in the urine at all
What is the peptide size that is the cut off for the filtration interface?
7KD
Molecules with what type of charge have a larger filtrate/plasma ratio than others?
Why is this?
Which type of charge will have the lowest?
Cations, due to the fixed polyanions in the basement membrane of the filtration interface
Anions will therefore have the lowest for the same reason
What is the composition of ultrafiltrate?
Similar to that of plasma except:
- proteins
- molecules bound to proteins (e.g. calcium)
What percentage of calcium is free in the plasma?
60%
What is GFR?
Glomerular filtration rate = the volume of fluid filtered by the glomeruli per minute
What are starlings forces?
1) hydrostatic pressure
2) colloid/oncotic pressure
What factors affect GFR?
1) starlings forces
2) surface area for filtration
3) permeability of the capillaries
What is the hydrostatic pressure in the:
1) capillaries
2) bowmans space
1) 8kPa
2) 2kPa
What is the oncotic/colloid pressure in the:
1) capillaries
2) bowmans space
1) 4kPa
2) 0kPa
What is the net glomerular filtration pressure?
In which direction is this pressure?
2kPa into the bowmans capsule
What can be done to increase or decrease the hydrostatic pressure in the glomerulus?
Constrict or dilate the afferent or efferent arteriole
Which cells regulate the surface area over which glomerular filtration May occur?
Meaengial cells
What is a normal GFR in a day?
What is a normal daily urine output?
Why are these values different?
125ml/min = 180L/day
1.5L/day
Because of reabsorption
What is renal clearance?
The volume of plasma that is cleared of a specific substance in a given amount of time
What is the formula for renal clearance?
Renal clearance = (U x V) / P
U = concentration of substance in urine V = volume of urine per minute P = concentration of substance in plasma
What property would a substance have to have in order to act as a method of GFR calculation using the renal clearance formula?
Name an appropriate substance.
Something that is fully filtered but not reabsorbed or secreted.
E.g. inulin but in practice creatinine
What is the excretion rate of a substance?
What is its formula?
The rate at which a substance is excreted.
= U x V (the top half of the renal clearance formula)
What is the issue with using creatinine?
It is slightly secreted therefore GFR estimation will be slightly high (as the amount will include some extra creatinine that has not been filtered, therefore not a correct estimate for GFR)
What can the renal clearance of PAH be used to work out?
What is a normal value for this?
The renal plasma flow = the amount of plasma delivered to the kidneys per unit time
Normal = 600ml/min
What can be calculated from renal plasma flow?
How is the worked out and what is a normal value?
Renal blood flow
Plasma is 55% of blood, therefore if we know renal plasma flow we can scale this up to calculate a normal renal blood flow = 1100ml/min
Where does the most amount of reabsorption occur?
In the proximal tubules
Which organic nutrients are absorbed in the proximal tubule?
- glucose
- amino acids
How are glucose and amino acids absorbed into the proximal tubules both:
1) luminally
2) basolaterally
1) Na co-transport (same as glucose absorption in the GI tract) but via SLG2 transporters!
2) GLUT2 facilitates transport (as with GI tract glucose absorption) based on its concentration gradient
Above what concentration of of glucose in the plasma does it begin to appear in the urine?
What is a normal blood glucose concentration?
> 200mg/dL = 11mmol/L
Normal = 150mg/dL = 3.9-5.5mmol/L
In terms of secretion of organic cations, what is the process by which they enter the tubule lumen?
What transporters are involved?
1) basolaterally located organic cation transporters (OCT2) aids their facilitated diffusion
2) luminally located multidrug and toxin extrusion protein exchangers (MATE1 and MATE2K) allow organic cations to enter the lumen via exchanging them for H ions.
In terms of secretion of organic anions, what is the process by which they enter the tubule lumen?
What transporters are involved?
1) basolaterally located organic anion transporters (OAT1 and OAT3) aid their facilitated diffusion
2) luminally located ATP-dependant transporters allow organic cations to enter the lumen.
