Robyn renal Flashcards
1
Q
What’s the total body water?
A
Varies between: 50-70% of body weight (60%).
In an average person (70Kg): this is: 0.6 X 70Kg
= 42Kg or 42L- water found inside and outside the cell
2
Q
What does transcellular fluid consist of?
A
- Specialist fluids like urine, stomach fluid, cerebrospinal fluid
- 3% of extracellular fluid which makes up 1.5-2 litres
3
Q
What does the plasma consist of?
A
- 7% of extracellular fluid
- makes up 3-4 litres
4
Q
What does the interstitial fluid consist of?
A
- 28% of extracellular fluid
- 11-12 litres
5
Q
what does the Intracellular fluid consist of?
A
- fluid inside cells
- 62%
- 20-30 litres
6
Q
What are the intracellular ion concentrations?
A
- high sodium concentration outside cell compared to inside
- membrane potential inside is negative, positive sodium ions move inside cell through a transport protein due to a driving force
- at rest potassium ion channels open, influx of K+ ions setting negative membrane potential.
- K+ important to set a driving force for sodium
- high chloride concentration outside, low inside
- lots of protein inside cell, less in ICF, more in plasma
7
Q
What determines blood pressure
A
volume of plasma
8
Q
State the daily balances of water and sodium
A
Input: 150 mmoles sodium, 2.6l/day water
Output: Sodium- 10 mmoles (stool + sweat) and 140 mmoles (urine) = 150 mmoles/day . Water- 1.5 l/day (urine) and 1.1 l/day (respiration, stool, sweat) = 2.6 l/day
9
Q
Describe the general renal morphology
A
- weighs 150g
- 12th thoracic to 3rd lumbar - 10cm tall, 5.5cm across
- abdominal aorta, celiac trunk, left suprarenal artery, left suprarenal vein, adrenal gland, left renal vein overlying renal artery, ureter, renal pelvis
- pale outer layer: cortex, outer most
- dark inner layer: medulla, inner most, rich blood supply
- Hilus: where ureter comes out
- Calyx: fibrous layer, holds all components of kidney renal chambers together, protection
- Papilla: where renal pyramids in medulla empty urine into calyx
- Medulla ray: middle part of cortical lobule, group of straight tubes connected to collecting duct
10
Q
List the congenital renal abnormalities
A
Renal agenesis: 1 in 2500 foetuses, incompatible life
Ectopic kidney: 1 in 800, leads to damage and stones. kidney develops in pelvis causing damage to it
Horseshoe kidney: 1 in 1000, kidney fused across midline, causes renal stones. As fused don’t have separate kidneys
11
Q
Describe the morphology of the nephron
A
- A functional unit- 1-1.5 million per kidney
- consists of plasma fluid, Bowman’s capsule, proximal tubule, loop of Henle, distal tubule, collecting duct (drains 6 nephrons), ureter
12
Q
How does filtration occur at the glomerulus
A
A ball of capillaries which come from renal arteries from the renal artery and leave through efferent arterioles. Fluid is forced out by force in glomerular capillary bed into the Bowman’s capsule. The drains to proximal tubule.
20% of plasma is filtered. 80% continues through efferent
13
Q
Describe the two types of nephron
A
Superficial: glomerular sits towards outer cortex - 85%
Juxtamedullary: glomerulus sits close to outer medulla - 15%. loop of Henle goes into inner medulla
14
Q
What is renal failure and what are the two types?
A
Renal failure is defined as a fall in glomerular filtration rate, which leads to a increase in serum urea and creatinine
Chronic: irreversible - dialysis or transplant needed
Acute: reversible - sudden onset
15
Q
What happens in chronic renal failure?
A
- less urine produced leading to accumulation of toxins
- size of kidney decreases
- haemoglobin levels decrease
- peripheral neuropathy- damage to PNS which causes problems with sensation and movement
16
Q
Describe the progression of renal failure
A
- thickening of glomerular membrane - reduced function, damaged glomeruli due to pressure
- fibrous tissue deposited
- tubular atrophy
- interstitial inflammation and fibrosis: pressure and scarring
- reduction in renal size
- once nephron and tubules are damaged cannot be regenerated
- leads to uraemia (a group of symptoms)
17
Q
What does failure to excrete salt and water lead to?
A
- hypertension
- hyperkalaemia
- mild acidosis
18
Q
what does poor excretion of urea/creatinine lead to?
A
- anorexia, nausea, vomiting
- neuropathy
- pericarditis
- inflammation pericardium
19
Q
What does failure in production of erythrocytes lead to?
A
- anaemia
- lethargy
20
Q
What does failure to excrete PO2- lead to?
A
- it lowers serum Ca2+
- metastatic calcification - pruritus (itch)
- bone disease - osteomalacia, osteoporosis
21
Q
What are the causes of chronic renal failure?
A
- glomerulonephritis: 30%
- hypertension: 10%
- diabetes mellitus: 25%
- polycystic kidney disease: 5%
- unknown: 10%
- other: 20%
22
Q
What are the steps of treatments for chronic renal disease?
A
- Aetiology and severity- treat the cause
- treat reversible factors and complications to reduce symptoms and slow progression
- diet: restrict protein, salt, water
- phosphate binder: hyper phosphate
- Na bicarbonate: acidosis
- Diuretics: Sodium retention - Plan dialysis and transplantation
23
Q
What is ultrafiltration?
A
Ultrafiltration is a variety of membrane filtration in which forces like pressure or concentration gradients lead to a separation through a semipermeable membrane.
24
Q
What is transcellular transport?
A
substances travel through the cell, passing through both apical membrane and basolateral membrane
25
What is paracellular transport?
transfer of substances across an epithelium by passing through the intercellular space between the cells
26
What does and doesn't get reabsorbed in filtration?
* Permits: H2O & small molecules
| * Restricts: Blood cells & proteins
27
What does ultrafiltration consist of?
* Consists of protein free plasma
| * 1% protein filtered (albumin)
28
Overview of proximal tubule function
```
Bulk reabsorption 70% filtrate
70% H2O & Na+
~100% glucose & amino acids
90% HCO3-
High surface of apical membrane to maximise transport
Reabsorption of phosphate
```
29
What property do epithelial cells have and what does this mean?
Epithelial cells are polarised so they have different transport proteins on the apical and basolateral membrane - so we can have net transport/reabsorption/secretion
30
What channels are critical for normal function?
Sodium potassium ATPase
31
What do potassium channels and sodium-potassium ATPase do and what does this lead to?
work together to set a negative membrane potential and a low intracellular sodium concentration- this sets up a driving force for sodium influx across apical membrane
32
Name two sodium-glucose transport proteins in the proximal tubule and their function
SGLT1 and SGLT2
| both reabsorb sodium and glucose.
33
What's the mechanism of sodium and glucose transport across the membrane?
when both are bound, the protein (SGLT1, SGLT2) undergoes a conformational change, moves sodium and glucose into the cell, sodium is then lost across basolateral membrane via sodium-potassium ATPase and glucose is lost from basolateral membrane via a facilitated transport protein
34
Name a Sodium-phosphate co transport protein in the proximal tubule and its function
NaPiII
| bind sodium ion and phosphate
35
What's the mechanism of sodium and phosphate transport across the proximal tubule apical and basolateral membrane?
Sodium-phosphate co transport protein NaPiII binds sodium ion and phosphate, moves them into the cell, sodium is reabsorbed via sodium potassium ATPase, and the phosphate leaves by facilitated transport proteins of basolateral membrane, so diffuses down its concentration gradient
36
How many kinds of sodium and amino acid co transport proteins do we have in the proximal tubule and what do they rely on?
Four different kinds of sodium and amino acids co transport proteins as we have different kinds of amino acids, all work in same way, relies of sodium gradient.
37
how do Amino acids move across basolateral membrane?
by facilitated transport protein
38
In the proximal tubule what does water follow and what does this mean? How does the movement of water across the membrane occur?
- water always follows ion and solutes, so the reabsorption of ions and solutes in the proximal tubule is important
- moves across the cell transcellularly through aquaporins
- move paracellularly between the cells
39
What can be seen in NaPiII knockout mouse phenotype?
- knockout cannot produce NaPiII
- phosphate is not reabsorbed and lost in urine
- issues with mineralisation (also seen in patients) as not enough phosphate in bone and too much deposited in kidney
- deposits of phosphate in interstitial fluid also seen in human patients
40
What does the lack of production of NaPiII in knockout mice lead to?
- more Pi in tubular fluid
- increased calcification (calcium phosphate)
- intraluminal stones- nephrolithiasis
- deposits renal parenchyma - nephrocalcinosis
- all lead to damage in kidney
41
Describe Familial Renal Glycosuria
- increase in urinary glucose
- few gms to > 100g/day
- normal plasma glucose
- no general tubule damage
- inherited condition- autosomal recessive
- carriers: mild
- both genes: severe
42
What causes Familial Renal Glycosuria?
- 21 mutations in SGLT2 identified
- deletion mutation inP324 ……347X
- part of protein missing
43
Name a sodium-hydrogen exchange protein in the proximal tubule and how does it work?
NHE3
sodium coming in via the protein on apical membrane of proximal tubule drives loss of hydrogen through same protein out the cell
44
What's the mechanism of sodium and hydrogen transport across the membrane?
- Hydrogen ions excreted into tubular fluid combine with bicarbonate that have been filtered to from carbonic acid – H2CO3 – in tubular fluid carbonic acid dissociates into CO2 and H2O under influence of carbonic anhydrase on the extracellular surface.
- Carbon dioxide freely diffuses down its concentration gradient across apical membrane.
- Water follows the sodium via aquaporin.
- Once inside cell, the carbon dioxide and water forms carbonic acid again by carbonic anhydrase inside the cell.
- Carbonic acid then dissociates back into the hydrogen ion and bicarbonate.
- The hydrogen ion recycles across apical membrane to allow more sodium to be reabsorbed.
- Bicarbonate that's generated moves across basolateral membrane via a sodium-bicarbonate co transport protein (bicarbonate is the driving force)
45
what does bicarbonate play a critical role in?
maintain and regulating body fluid pH
46
What does Renal NHE3 knockout mice show and how are they effected?
- Shows importance of apical sodium-hydrogen exchange protein
- Both genes have been deleted so protein cannot be made
- The plasma bicarbonate is lower than wildtype - Struggling to maintain normal bicarbonate level as excreted in urine which would have retained
- Not enough H+ ions being secreted via NHE3 therefore cannot reabsorb bicarbonate
- pH in knockout has dropped
- slightly lower systolic pressure
47
What happens if no hydrogen is being secreted?
Sodium cannot be reabsorbed so water will not follow. leading to increased urine flow rate
48
Why is there a fall in pH in NHE3 knockout mice?
1. Inhibition H+ secretion
2. Inhibition Na+ & HCO-3 transport - reabsorption
3. Fall fluid reabsorption
4. Drop plasma HCO-3
5. This leads to pH fall due to HCO-3 compensation -acidosis
Some studies show BP fall, due to ECFV decrease
49
What is the Transport maximum?
Substances reabsorbed via membrane carriers
e.g. glucose, amino acids via Na+ cotransport
Consequence of limited no. of carriers in the cell membrane
when you have a transport protein, you have a max rate it can transport- cannot go any higher
50
What is the Renal threshold? (use glucose as example)
plasma concentration of glucose where can be seen in urine
In physiology, the renal threshold is the concentration of a substance dissolved in the blood above which the kidneys begin to remove it into the urine
51
Why extrapolate renal threshold?
The range in mg/min of glucose, detection of this is quite hard in the clinical situation, detection mechanisms aren’t accurate enough to be able to detect that level of glucose. So, they would up the plasma glucose, do measurement and extrapolate back to the X-axis and this would be classed as the renal threshold.
52
What are the two secretion systems in proximal tubule?
organic cations, organic anions
53
How do the two secretion systems work in proximal tubule?
- Rapid removal
- Removal plasma protein bound substances
- Foreign compounds
e. g. penicillin dose given is higher than needed as kidneys will removed some of the penicillin
- substances which are hard to get rid of are removed by help of anions/cations
organic cations and organic anions are transport proteins that remove the substances from the plasma, go across the basal lateral membrane across the cell and out the apical membrane into the tubular fluid.
54
Summary of what happens in the Loop of Henle
* Concentration of the urine
* Reabsorption of Na+, Cl- & H20
* Reabsorption Ca2+ & Mg2+
* Site of action of loop diuretics
55
What does the reabsorption of sodium and chloride drive?
the reabsorption of calcium and magnesium
This is another example of paracellular transport. Calcium and magnesium going between cells driven by uptake of sodium and chloride.
56
What do diuretics do?
increase urine flow rate
57
What do loop diuretics target?
target specific proteins in the membrane of cells in loop on Henle
58
Brief description of structure of loop of Henle
Subdivided into three structural and functional compartments
59
What are the functions and properties of the Thin descending limb?
- water permeable
- impermeable to sodium and chloride, driving forces which produce an osmotic gradient for water to leave the tubular fluid and go out into the interstitial fluid.
- Longer than thin ascending limb so able to dissect more easily and therefore know a lot more about the mechanism
60
What are the function and properties of the Thin ascending limb?
- permeable to sodium and chloride
- impermeable to water.
- Unsure on transport mechanisms on how sodium and chloride are reabsorbed – due to it being hard to study in research as it had a small diameter and its quite short, also very hard to dissect
61
What are the functions are properties of the Thick ascending limb?
- reabsorbs sodium and chloride
- impermeable to water
- know a lot on the mechanisms on how sodium and chloride are reabsorbed.
- We know more about thick ascending limb due to the structure due to its large diameter
62
What is the sodium transport protein specific to thick ascending limb?
NKCC2 -sodium/potassium/2 chloride transport protein
| On apical membrane
63
How does NKCC2 work to transfer sodium, potassium and chloride across the apical membrane?
Low intracellular sodium concentration and negative membrane potential provides the driving fore of the influx of sodium and with NKCC2, the influx of sodium is coupled to 2 chloride ions binding to the protein and one potassium ion. All four ions have to bind for the protein to undergo a conformational protein change and release these four ions, into the intracellular fluid compartment.
64
How is sodium excreted across the basolateral membrane
Via the sodium potassium ATPase
65
What membrane transport proteins does chloride use to move across the cell in the thick ascending limb?
NKCC2 (sodium/potassium/2 chloride) on apical membrane to move into cell
CLCK (chloride channel) on basolateral membrane to move out of cell
66
What is Barttin?
Barttin is a small molecular weight protein, a beta subunit/ accessory subunit, it’s a protein that regulates another protein. Barttin allows CLCK to function normally
67
What happens if there's a problem with Barttin?
chloride channel CLCK wont function normally
68
What membrane transport proteins does potassium use to move across the cell in the thick ascending limb?
NKCC2 (sodium/potassium/2 chloride) on apical membrane to move into cell
ROMK/Kir1.1 (potassium channel) on apical membrane to recycle out of cell
69
Why is the recycling process of potassium critical?
potassium that comes in through NKCC2 recycles across the apical membrane via ROMK. The recycling of potassium is critical because in the tubular fluid of the thick ascending there is insufficient potassium to maintain the function of NKCC2. If not enough potassium, NKCC2 will stop functioning.
70
What is salt wasting and polyuria?
loss of sodium and chloride in urine. water does not follow- leads to loss of water
71
What is hypertension/hypotension?
high/low blood pressure
72
what is hyperkalaemia/hypokalaemia?
high/low plasma potassium, due to not secreting enough sodium and chloride
73
What is metabolic alkalosis
High body pH, due to less hydrogen ions
74
What is metabolic acidosis?
Low body pH
75
What is hypercalciuria/hypocalciuria?
High/low concentration of calcium in fluid/urine as not being reabsorbed
76
What is Nephrocalcinosis?
Stone formation in renal parenchyma due to hypercalciuria
77
What type of inheritance is Bartters syndrome?
Recessive genetic inheritance
78
Name the symptoms of Bartters syndrome
```
Salt wasting & polyuria
Hypotension
Hypokalaemia
Metabolic alkalosis
Hypercalciuria
Nephrocalcinosis
```
79
Where can the mutations occur in Bartters syndrome and what to they all lead to?
Mutation in NKCC2, CLCK, Barttin, ROMK
All mutations lead to inhibition of sodium and chloride reabsorption at thick ascending limb
80
What happens if there's a mutation in NKCC2?
loss of function mutation lead to a decrease in sodium, chloride and water reabsorption.
impacting on blood pressure hydrogen ions and calcium
81
What happens if there's a mutation in CLCK?
loss of function mutation could lead to calcium efflux being blocked. concentration of calcium inside cell will build up so will inhibit NKCC2 therefore stop sodium chloride reabsorption
82
What happens if there's a mutation in ROMK?
don't get a potassium efflux across apical membrane, NKCC2 wont work
83
What is Fractional excretion (FE)? give examples
Fractional excretion (FE) = Amount in urine / amount filtered
100% = all filtered excreted
<100% some reabsorbed - only some of whats been filtered reabsorbed
>100% some secreted - more urine
if there's differences in FE = tubule defect
84
What can a difference in fractional excretion tell us?
A difference in fractional excretion in sodium (for example) in wildtype and knockout mouse, this gives us information about whether kidney function has been altered in that knockout
Different in fractional excretion in wildtype and knockout mouse tell us that in the knockout there is a change in how the tubule is working- could be a loss of function or function enhancement in the tubule.
85
What is shown in ROMK knockout mice and how can we compare to humnas?
Salt wasting: losing salt in urine. FE higher in knockout compared to wildtype
Polyuria: more urine flow. No reabsorption of water in thick ascending limb
Plasma potassium: in humans it goes down. however in mice it doesn't. A limitation to the model
Plasma pH: in humans it goes up. However, goes down in knockout mice. A limitation in model
86
Why are ROMK knockout mice useful?
a useful model for understanding thick ascending limb in barters syndrome
87
Name two loop diuretics and what do they do
Furosemide and Bumetanide
| Block NKCC2
88
What patients do loop diuretic treat and how do they work?
patient who need to lose excess fluids (have hypertension), put them of a loop diuretic, one of these diuretics comes along, gets to kidney, in tubular fluid, blocks NKCC2. So it inhibits sodium and chloride reabsorption by thick ascending limb (therefore no reabsorption of water). Causes salt loss in the urine of patients on the drug, they will loss the excess fluid.
89
What are the side effects to loop diuretics? (like barters)
impacts on plasma potassium
on pH of body fluids
calcium handling
so need to be careful when treating and keep monitored
90
Summary of Early Distal tubule
Reabsorption Na+ & Cl-
Reabsorption Mg2+
Sensitive to thiazide diuretics
91
Give basic model of early distal tubule
NCC and magnesium selective channel on apical membrane
| Sodium potassium ATPase, potassium transport channel, CLCK (splice variant) and barttin on basolateral membrane
92
What membrane transport proteins does Sodium use to move across the cell in the Early distal tubule?
NCC (sodium chloride co transport protein) on apical membrane to move into cell
Sodium lost through basolateral membrane
93
What membrane transport proteins does Chloride use to move across the cell in the Early distal tubule?
NCC (sodium chloride co transport protein) on apical membrane to move into cell
CLCK chloride channel on basolateral membrane out of cell which is regulated by barttin found on basolateral membrane.
94
Name a sodium chloride co transport protein on the early distal tubule? how does it work?
NCC on apical membrane
only needs to bind one sodium and one chloride ion, for protein to undergo conformational change and release them into the intracellular fluid.
95
Describe splice variant of CLCK
Splice-variant- proteins with slightly different amino acid sequences
The CLCK family has splice-variants (slightly different versions) in early distal tubule to the thick ascending limb
96
What type of inheritance is Gitelmans syndrome
Genetic inheritance - recessive
97
What are the symptoms of Gitelmans syndrome
```
Salt wasting & polyuria
Hypotension
Hypokalaemia
Metabolic alkalosis
Hypocalciuria
```
98
What causes Gitelmans syndrome
Mutations in NCC - sodium and chloride cannot be reabsorbed
99
Xenopus oocyte studies summary
- Inject RNA
- Protein of interest made
- Functional analysis
100
What is the mechanism of Xenopus Oocyte experiment studies
- Stick electrode in and inject into the interior of the Oocyte, the RNA of the protein of interest (in this case NCC)
- Inject wildtype RNA and in different Oocyte inject mutant RNA
- This RNA taken by the cell and processed and makes the protein of interest- functional analysis then takes place – for sodium chloride co transport protein we would look at the uptake of sodium 22 into the Oocyte.
- Because if we’ve got lots of functioning sodium chloride co transport protein there then we will see lots of sodium being taken up and then we can look at the mutant and see how much sodium is taken up in the mutant
- To do this we would inject everything except its RNA (control- wildtype), inject RNA for wildtype for NCC or we would inject for the mutant NCC and do a functional analysis
101
If you get a reduction in transport of the protein, there’s two main reasons:
Protein itself isn’t able to transport as many ions (sodium, chloride) as normal
Or
The number of proteins that you have in cell membrane are less than normal
102
What do Thiazide diuretics treat, target and name one
Treat high blood pressure
Target is sodium chloride co transport protein
Chlorothiazide
103
How does Chlorothiazide work?
Chlorothiazide gets into the fluid, early distal tubule, it blocks sodium chloride co transport protein, it blocks sodium and chloride reabsorption, so it reduced water reabsorption, they lose salt and water and their blood pressure comes back down
104
What do you get if there's too much Chlorothiazide
Too much you get side effects of Gitelmans syndrome
105
Nature Genetics 2008: Carrying one mutation for ROMK, NCC, or NKCC2 protects against hypertension! - Explain this paper
Paper shows individuals who are carriers for Bartters or Gitelmans syndrome were less likely to have hypertension
If you had a mutation in one of the alleles of ROMK, NCC or NKCC2 then blood pressure was lower than normal
Carriers have no symptoms but show to have a lower blood pressure than normal patients – they are less likely to have high blood pressure problems later in life as their normal BP is lower than normal
106
Give a summary of Late distal, connecting tubules & cortical collecting duct
* Concentration of the urine
* Reabsorption of Na+ & H20
* Secretion K+ & H+
107
What two cell types of the Late Distal and Cortical collecting duct composed of?
Principle and intercalated cells
108
What's the role of principle cells?
- Na+ & H2O reabsorption
| - K+ and H+ secretion
109
What's the role of intercalated cells?
- Alpha IC & beta IC
- H+ secretion & reabsorption
- HCO3- reabsorption & secretion
- Help regulate pH of body fluids
110
What's the general structure of a principle cell
On apical side: ENaC, ROMK, Aquaporin 2
| On basolateral side: sodium potassium ATPase, Kir2.3. Aquaporin 3 and Aquaporin 4
111
What are the Sodium-potassium ATPase and basolateral potassium channel (Kir2.3) of the principle cell working together to maintain?
they are maintaining a negative membrane potential and low intracellular sodium concentration which provides a electrochemical driving force for the uptake of sodium across the apical membrane.
112
What is ENaC and what is it regulated by?
ENaC is a sodium selective ion channel on the apical membrane, it constituently open and regulated by signalling pathways such as phosphorylation, ATP, G-proteins.
113
What membrane transport proteins does Sodium use to move across the cell in the Principle cell?
ENaC on the apical membrane to move into the cell
| Sodium-potassium ATPase on the basolateral membrane to move into the cell
114
What does the Reabsorption of sodium in the principle cell drive? why is this important?
drives the secretion of potassium, this become important because if you have too much sodium reabsorption through ENaC across the principle cells you will have too much potassium secretion. - this is the mechanism in Bartters syndrome (increased loss of potassium)
115
What's the role of Aquaporin 3 and 4 on basolateral membrane?
there are lots of these channels, they are not regulated, can reabsorb water if there is an osmotic driving force across basolateral membrane.
116
What does the number of Aquaporin 2 depend on?
number of these vary depending on fluid status in body
117
What's the importance of Aquaporin 2 in the principle cell's of the collecting duct?
it's the rate limiting step for water reabsorption across the principle cells and therefore across the collecting duct, the aquaporin 2 water channels will shuttle in and out of the membrane depending on whether you need them.
118
Why is the osmotic driving force for water reabsorption for when aquaporin 2 is present 2-fold?
1- when you’ve got sodium reabsorption, water follows
2- all of that sodium and chloride that you’ve reabsorbed from the thick ascending limb in the loop of Henle is in the interstitial fluid of the kidney all around near the basolateral membrane. So, you have a very high concentration of sodium and chloride in the interstitial fluid and that sets up a driving force for water reabsorption as well.
119
State some diseases of the principle cell of the collecting duct and give brief description
Diabetes insipidus – AQP2 problem concentrating urine, problem is aquaporin 2
Liddle’s syndrome – ENaC too much sodium and water reabsorbed, hypertension, mutation on ENaC
Pseudohypoaldosteronism- symptoms mimic low levels of aldosterone
120
Name a diuretic used in the collecting duct and principle cells and what is it used to treat?
Amiloride (potassium sparing diuretic)
| used to treat high blood pressure
121
How does Amiloride work?
Amiloride blocks ENaC
If you block ENaC you block sodium reabsorption by the principle cells and block water reabsorption- so patients excrete a high urine volume per unit time, and if they’ve got oedema- this will be reversed, they are going to lose the excess fluid that they’ve got
122
Describe the general structure of Alpha intercalated cells
Proton pump on apical membrane
| On basolateral membrane we have a chloride channel and a anion exchange protein, AE1
123
What is the role of AE1 of the Alpha intercalated cell?
AE1 which brings chloride ions into the cell in exchange for bicarbonate ions moving out of cell,
124
What's the role of the proton pump of the Apical membrane of the Alpha intercalated cell?
its directly utilising ATP, it hydrolysis ATP to allow it to pump hydrogen ions out of the cell against the electrochemical driving force, it needs ATP to do this
125
What's the role of the Chloride channel on the basolateral membrane of Alpha intercalated cells?
Chloride channel on basolateral membrane is important as it allows the chloride ions to recycle across the basolateral membrane. Allows the transport protein to work.
126
Where do the bicarbonate cells used by AE1 come from?
these bicarbonate ions come from inside the cell from the consequence of metabolism (being generated in the cell).
127
What's the overall role of Alpha intercalated cells?
hydrogen ion secretion and reabsorption of the bicarbonate generated within the cells.
128
What's type of inheritance of Distal renal tubular acidosis
Genetic inheritance
129
What are the symptoms of Distal renal tubular acidosis?
Nephrocalcinosis (stones kidney parenchyma)
Metabolic acidosis
Nephrolithiasis (stones tubules / urinary tract)
130
Where are the mutations found for Distal renal tubular acidosis?
The mutations of this disease are in the Anion Exchange 1 (AE1) protein, which is normally found in the basolateral membrane of the alpha intercalated cells.
131
What happens if there is too much acid (high hydrogen conc)?
Secrete hydrogen ions across the apical membrane through ATPase of Alpha intercalated cells
If we need to secrete lots of hydrogen ions, we are going to have lots of Alpha intercalated cells in the collecting duct. But if we want to retain hydrogen ions then the cells will turn themselves into beta intercalated cells.
132
What happens when AE1 protein is mutated?
starts to appear on the apical membrane. It is miss targeted- a targeting mutation.
133
What are the consequences of AE1 being mutated in Distal renal tubular acidosis
Affects AE1 of alpha intercalated cells
All the bicarbonate in the cell that’s been generated that would normally have been absorbed across the basolateral membrane, some of it is now leaking across the apical membrane.
If it’s leaking out across the apical membrane into the tubular fluid, then we are going to lose it in our urine. We normally reabsorb lots of new bicarbonate from the renal epithelial cells to help us maintain our body fluid pH.
So, if we are losing bicarbonate that we should have retained this means that we are now going to struggle to regulate the pH of our body fluids. If we a losing bicarbonate, we are at risk of acidosis.
134
What is the general structure of Beta intercalated cells?
Proton pump on basolateral membrane
| On apical membrane we have a chloride channel and a anion exchange protein, AE1
135
What's the mechanism of Beta intercalated cells?
So the proton ATPase is now trafficked to the basolateral membrane so it can lead to the absorption of hydrogen ions and the chloride bicarbonate exchanger is now trafficked to the apical membrane. And now we have chloride coming in which was in the tubular fluid, bicarbonate going out and we can lose that bicarbonate in the urine.
136
Medullary Collecting duct summary
•Low Na+ permeability
•High H2O & urea permeability in the presence of vasopressin
part sits in the medulla
137
Where are hydrogen ions secreted and reabsorbed?
Secretion: PT, principal & alpha IC cell
Reabsorption: Beta IC cell
138
Where is bicarbonate secreted and reabsorbed?
Secretion: Beta IC cell
Reabsorption: PT, principal & Alpha IC cell
139
What is Acute renal failure? what are the causes? how long does it last? what are the treatments?
Fall in glomerular filtration rate over hrs / days
Causes: pre-renal / renal / post renal
Impaired fluid and electrolyte homeostasis
Accumulation nitrogenous waste
Lasts ~ 1 week (different chronic)
Treatment: dialysis for period of failure, when recovered wont need dialysis to continue
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What are the general Symptoms of acute renal failure?
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Hypervolaemia – oliguria (a fall in GFR)
Urine flow rate is low
Hyperkalaemia – lack of K+ secretion
Cardiac excitability
Impacts of electrical activity in the cells
Risk of heart suddenly stopping
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Acidosis – depression central nervous system reduces activity in nervous system
High urea / creatinine – impaired mental function, nausea, vomiting impaired mental function
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What are the Treatments for acute renal failure?
IV saline – treat hyperkalaemia
HCO3- - to bring level to normal
Rehydrate in this case
Dialysis if oliguria persists
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Name 3 hormones used for body fluid composition
Vasopressin - (Anti-diuretic hormone ADH)
Aldosterone
Renin angiotensin
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Vasopressin
Works in a non-genomic way – hence why so quick
Released from posterior pituitary gland
When excited they release the hormone which moves into capillaries and around the body
Stimulated when needed
Action potential fired through pituitary stalk
Vesicles containing hormones fuse with membrane of cell and vasopressin is released into circulatory system and can exert its function on the body
Regulates body fluid osmolality
Conserves H2O
Body fluid osmolality increases (dehydrated)- vasopressin increases
Body fluid osmolality decreases (hydrated)- vasopressin decreases
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Hypothalamic osmoreceptors
Detect delta of ± 3 mosmol/kg H2O
Supra-optic & paraventricular nuclei
Stimulation (increase osmolality)
i) Release vasopressin from posterior pituitary
ii) Feeling of thirst
respond to changes up or down
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Regulation of release of vasopressin- increase and decrease
Increase: increase osmolality plasma
Solute ingestion or H2O deficiency lots of salt, increased osmolality
Stress & Drugs - nicotine,
3,4-Methylenedioxymethamphetamine (ecstasy)
Decrease: decrease osmolality plasma
Excessive fluid ingestion
Drugs - alcohol decreased amounts of vasopressin
More frequent urination- inhibited vasopressin, losing water should have retained, now dehydrated
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Relationship between Vasopressin and plasma osmolarity
as plasma osmolarity increases (dehydration), vasopressin increases
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Relationship between Vasopressin and urine osmolality
as urine osmolality increases the plasma vasopressin increases
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Principle cell H2O model
Vasopressin regulates aquaporin 2 channels.
Does this by binding to a vasopressin receptor, V2, found on the basolateral membrane of the principle cells.
diffuses into the interstitial fluid from the blood and binds to the vasopressin2 receptor, activates it which then activates enzyme called protein kinase A (PKA), which phosphorylates other proteins and it phosphorylates proteins found on the vesicles in the membrane of these vesicles are the Aquaporin 2 water channels. So, when phosphorylation occurs, these vesicles move to the plasma membrane, fuse with the plasma membrane and therefore inserts into the apical membrane Aquaporin 2 water channels. The more water channels you have the more reabsorption across collecting duct cell layer.
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Net effect of vasopressin
Increased reabsorption of water into the plasma
Fall in body fluid osmolality
When mechanism fails, can excrete up to 23l of water a day
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Diabetes Insipidus
Copious quantities dilute urine ~ 23 l/day
Central DI –
• No release vasopressin
• Nasal spray DDAVP - treatment
Nephrogenic DI – can’t respond to vasopressin- still has it
• No response to VP
• Defect V2 receptor
• H2O channel defect mutations in genes that code for aquaporin 2
• Other treatments (L2)
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Aldosterone, where is it released from? What are the 3 subdivisions? which one releases aldosterone?
Released from adrenal cortex
Adrenal gland is subdivided into outer part: cortex and inner part: medulla.
3 subdivisions: zona glomerulosa, zona fasciculata, zona reticularis. – play different roles in the release of different hormones.
Zona glomerulosa releases aldosterone.
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What does aldosterone regulate and why is it released?
Mineralocorticoid,
Regulates plasma Na+, K+ & body fluid volume
Released in response to:
increased plasma K+ - 0.1 mM
Decreased plasma Na+ - minor, concentration maintained by osmoregulation
Decreased ECF volume - via renin-angiotensin
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What does aldosterone act on?
- Distal tubule
| - Collecting duct
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What does the release of aldosterone cause?
- Increase in reabsorption of sodium
- Increase reabsorption in H2O
- Increase in potassium and hydrogen
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How does aldosterone affect the principle cell?
| What is aldosterone classified as?
So the aldosterone diffuses across the membrane of the cell into the cytoplasm and binds to mineral corticoid receptor, that receptor aldosterone complex moves to the nucleus of the cell and stimulates RNA transcription of more sodium-potassium ATPases, ENaC, potassium channels and more sodium-hydrogen exchangers, they go into the membrane and we now have an increased capacity for transport via the cells.
This is classed as a genomic action of aldosterone, as it works at the level of the gene to stimulate the production of new and additional protein.
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How does aldosterone affect Alpha IC cell?
Aldosterone bind to cytosolic receptor stimulates RNA transcription of proton ATPase, and if you’ve got more of this in apical membrane, you will secrete more hydrogen ions.
So, it’s by upregulating protein production that aldosterone actually stimulates sodium reabsorption, water follows the sodium, potassium secretion and hydrogen ion secretion.
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Net effect of aldosterone
Increase plasma Na+ Decrease plasma K+
Decrease plasma H+ Increase ECF volume
Co-ordinate regulation with renin-angiotensin system
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Liddle's syndrome
Liddle’s syndrome: hypertension
High Na+ reabs Low aldosterone
Increased no. Na+ channels principal cell
What goes wrong in Liddle syndrome is that the mutation means the channels get to the membrane and that’s where they stay for a long time and don’t come out when they should.
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Pseudo hypoaldosteronism in Liddle syndrome
• Salt loss but high aldosterone- lost ability to respond to high aldosterone levels
• Loss response to aldosterone
• Mineralocorticoid receptor problem mutations in this receptor
Problem with receptor means downstream signalling never happens, so don’t have the ability to upregulate protein production and so cannot upregulate sodium reabsorption.
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What does Renin-angiotensin regulate?
Body fluid volume, plasma Na+ & K+
| Renin - released from juxtaglomerular apparatus (JGA)
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JGA- juxtaglomerular apparatus- what does it consist of? what are the functions of its components?
In early distal tubule are macula densa cells, these cells can monitor and detect changes in the tubular flow rate.
When there’s a change in extracellular fluid volume, this means that there is a change in glomerular filtration rate. Which means a change in tubular flow rate which is picked up by the macula densa cells who have an ability to signalling molecules to the afferent arteriole. In the afferent arteriole we have got cells that have an ability to release renin.
In addition, these granular cells, in afferent arteriole have input from sympathetic nervous system as well and stimulation of sympathetic nervous system can stimulate the release of renin. The renin can go into the plasma.
So, the afferent arteriole in the kidney is the source of renin.
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Renin-angiotensin cascade- what causes the relsease of renin? what does renin catalyse? How do we get angiotensin II?
Fall in extracellular fluid volume, which is detected at the juxtaglomerular apparatus by the macula densa cell, stimulation of sympathetic nervous system.
This leads to the release of renin by the granular cells in to the general circulation.
Renin catalyses the conversion of angiotensinogen to angiotensin I.
Angiotensin I is then converted into angiotensin II which is the active component of the renin-angiotensin cascade.
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Net effect of Angiotensin II,
Increased plasma Na+ + ECFV
Increased blood pressure
ACE inhibitors
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Integration – volume vs osmolality
How are they both regulated?
How are they working against/with each other
which is the most important to regulate?
Ingesting salt increases the concentration of sodium in the plasma.
This increase in sodium increases the osmolality of the plasma. This increase in osmolality stimulates the osmoreceptors leading to increase in vasopressin, stimulating water reabsorption (to bring osmolality back down) but this leads to a increase in extracellular fluid volume.
At the same time, the increase of sodium plasma concentration is a driving force for water to move out of the intracellular fluid of the cells. This increases extracellular fluid volume, which means levels of aldosterone will decrease. Leading to increase loss of sodium, therefore loss of water as it follows. Then there will be a decrease in extracellular fluid volume.
Trying to do this to try and get blood pressure under control again at the same time as the vasopressin system trying to retain more water – so there’s a conflict as two opposite things going on
Blood volume is more important than osmolality as blood volume impacts on blood pressure.
Vasopressin system can be reset depending on sensitivity
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What is most important to be regulated and what does it effect?
Change in volume will be protected at all costs, as that effects your blood pressure.
