acid base balance and renal failure Flashcards
pH of plasma
cells like us to have that pH around 7.4
what happens we have changes in pH in plasma
- when we have extremes of acidity or alkalinity then the body is always trying to bring it back through using the renal system or the respiratory system
acidosis/ acidemia
- If our pH of the plasma or interstitial fluid surrounding the cell’s goes below 7.35 then we call it acidosis or if talking about the plasma is acidemia
alkalosis or Alkaliemia
if it goes above 7.45 we would suggest it was alkalosis or Alkaliemia
how do we regulate H+ - respiration
we are producing protons all the time in the body.
- One of the ways we’re producing them is through cellular respiration.
- when we have cell metabolism, we metabolize within the cell during cellular respiration and we produce carbon dioxide
- carbon dioxide combines with water to produce carbonic acid, which is an unstable volatile acid.
- This can dissociate to protons and bicarbonate ions.
- if we gain more CO2, plasma more acidic
- if we lose more CO2, plasma more alkaline
chemical buffering to maintain equilibrium of pH
2 substances which as part of a reversible reaction can either liberate or bind free H+ depending on the [H+]
- lungs eliminate carbon dioxide
- kidneys excrete H+ and conserve HCO3
Carbonic acid and bicarbonate buffer
major buffer in ECF
- CO2 and H20 diffuse into the cytoplasm
- carbonic anhydrase and the combination of water and co2 leads to carbonic acid, which is unstable and dissociates into bicarbonate and protons
- excess H+ drives this reaction to the left, so more carbon dioxide and water produced
the henderson - Hasselbalch equation
describes the relationship between pH carbon dioxide and bicarbonate
when can metabolic acidosis occur
metabolic acidosis can occur when the concentration of bicarbonate ions Falls or when the concentration of protons increases
- so we can have metabolic acidosis if we’ve got somebody who has got undiagnosed diabetes mellitus.
- Or if you’ve got somebody who’s got renal failure and they can’t excrete the protons So the proton levels also increase and they can’t reabsorb bicarbonate.
respiratory acidosis
we can get respiratory acidosis when you can’t get rid of the carbon dioxide. So if you’ve got a respiratory issue, so for example, you’ve got COPD or chronic bronchial asthma you can’t get rid of that excess carbon dioxide. So it starts to build up in the plasma and therefore the
individual have respiratory acidosis.
metabolic alkalosis
Metabolic alkalosis occurs when we have an increase in the amount of bicarbonate. (So if you ingest large amounts of bicarbonate) or if you’re losing a lot of acid because you vomiting and losing a lot of hydrochloric acid that way that can also cause problems with metabolic alkalosis.
respiratory alkalosis
respiratory alkalosis can occur if you’re getting rid of too much carbon dioxide. So if you’re hyperventilating your breathing off too much carbon dioxide, then the pH of your plasma will increase and you’ll have alkalosis
PCT cells
- secrete H+ ions
- reabsorb HCO3-
- excrete ammonium ions (helps generate bicarbonate ions)
type 4 intercalated cells in the collecting duct
- secrete H+ ions
- reabsorb bicarbonate ions
- excrete dihydrogen phosphate ions (helps generate bicarbonate
during alkalosis what do type B intercalated cells secrete
bicarbonate
what are the 3 ways kidneys excrete H+
- carbonic anhydrase (bicarbonate reabsorption)
- phosphate buffering
- ammonia/ammonium buffering. proteins acid (COO-)/base (NH4+) accept/donate H+
what is going on all the time to provide a source of bicarbonate or protons if required
the Carbonic anhydrase equation is happening inside the cells all the time and because of that we can either produce water and carbon dioxide or we can produce bicarbonate and protons - reversible reaction.
- The bicarbonate ions can be reabsorbed along with sodium and the protons can be then secreted back out into the Lumen where they can either be excreted or they can combine with bicarbonate ions that are already in the filtrate to form carbonic acid to then form water and carbon dioxide
- water can then be excreted in the urine
- carbon Dioxide can actually be reabsorbed through some of the aquaporins.
phosphate buffering
this occurs in many of the cells in the nephron
- occurs in PCT/DCT/CD
because we’ve got this going on in all the cells we can always combine
and form protons and bicarbonate ions.
The only difference here using the phosphate buffering system is in the filtrate We can get disodium hydrogen phosphate which can dissociate quite easily to free up protons.
- protons are readily available because this has been activated they can recombine to produce sodium dihydrogen phosphate and that’s quite stable.
excretion via the ammonium ion
we’ve got metabolism of some of the amino acids
when they metabolize they can produce bicarbonate ions as a by-product which can then be reabsorbed or they can produce ammonia
-Ammonia can cross the membrane again utilizing some of the pores
- We can get movement of your ammonia into the filtrate.
- Once it’s in the filtrate. It can mop up some of those free protons to produce the ammonium ion the nh4 plus
- the ammonium ion is impermeable to the apical membrane. So once the ammonium ions been produced it won’t dissociate and it’s another way That protons can be excreted in the urine.
kidney disease UK - the facts
- 1 in 10 will suffer chronic kidney disease, affecting all ages including children
- over 3 million people in the UK are being treated ofr kidney disease
- 1 in 5 people admitted to A&E have acute kidney injury
- 40-45000 die from chronic kidney disease each year
kidney disease - diabetes
- single largest cause of renal failure
- 2.6 million diabetics and climbing
- damage to large and small renal blood vessels due to hyperglycaemia
- results in lack of blood supply and sebsequent cell death
kidney disease causes - hypertension
high blood pressure can cause chronic kidney failure
- nephron glomeruli damaged and lose ability to filter blood
kidney cancer
over 8000 new cases of kidney cancer diagnosed each year and rising
- causes around 3,800 deaths each year
risk factors for renal failure - race
black, asian people and minority ethnic communities are 5 x more likely to develop CKD than other groups
- researchers ascribe this to the prevalence of type 2 diabetes mellitus in these populations
risk factors for renal failure - weight
obesity important risk factor for diabetes and hypertension, the 2 most common causes of kidney failure
- but obesity itself may increase CKD
- weight loss has indeed been shown to improve glomerular function and reduce urine albumin excretion
genetic factors for kidney disease
- poorly understood
- family history of chronic kidney disease, diabetes or hypertension increases risk
Acute kidney failure
- sudden loss of renal function, most common among hospitalised patients
- variety of causes including:
- extremely low blood pressure
- blockage of renal blood supply
- toxic injury
- ureter or bladder obstruction
chronic kidney failure
- hereditary disease (autosomal PCK
- glomerular disease
urinalysis
- can detect proteinuria (sensitive early marker of kidney damage)
- most abundant protein in urine is albumin
- normally 30mg = day
- clinical proteinuria >300 mg/day
chronic kidney disease GFR
<60 ml/min for more than 3 months
normal GFR = 90-140 ml/min
stages of chronic kidney disease
stage 1 - GFR >90
Stage 2 - GFR 60-89
Stage 3 - GFR 30-59
stage 4 - GFR 15-29
stage 5 - GFR < 15 renal failure
functions of the kidney
-regulation of osmolality/ volume of body fluids
- electrolyte balance
- acid-base balance
- formation of urine/ excretion of toxins
- production of hormones - eryhtropoietin
- vitamin D metabolism
cardiovascular effects of renal failure
- the inability to control fluid levels
- lead to an increase in ECV, increasing BP - hypertension
- water and sodium retention
- due to disruption of concentrating ability and sodium balance
- oedema in peripheral tissues and the lungs - breathing difficulties
more cardiovascular effects
- potassium imbalance - hyperkalaemia
- leads to cardiac arrhythmias leading to cardiac arrest
- inability to produce eryhtropoeitin so lower number of red blood cells
respiratory effects of kidney failure
metabolic acidosis
- kidneys fail to excrete H+ so deeper breathing to try to get rid of carbon dioxide
laboured breathing
- as increase risk of pulmonary oedema
kidney failure effects on the nervous system
elevated plasma potassium concentrations and an increase in toxic metabolic waste products
- depolarisation of neurones, action potential conduction along nerves decreases, peripheral neuropathy
- lethargy and confusion
ionic imbalance (Na+ Ca2+)
- termor herring/ twitching
effects on muscular/ skeletal system
vitamin D deficienct
- disrupiton of vit D metabolism
- reduced PTH induced reabsorption of calcium
- bone reabsopriotn due to and loss of calcium in the urine
- bone pain and weakness
hypocalcaemia hyperphosphatemia
- tetany and cramps
effects on the digestive system
build-up of toxic waste products/ ionic imbalance
- anorexia, vomiting, nausea
effects on endocrine system
insufficient erythropoietin secretion
- anaemia
vitamin D deficiency
- bone disease/ pain
renin angiotensin aldosterone disruption
- high BP// hyponatraemia
disrupted regulation of sex hormones impaired fertility
effects on the skin
build-up of ureamic toxins
- pallor/ yellow tinge
- pruritus ( itching)
clotting mechanisms impaired and impaired iron transport
- bruising
anemia
- paleness
controlling blood pressure for people with kidney disease
tight control of blood pressure slows progress of kidney disease
- early stage CKD patients, aim to keep their blood pressure below 130/85 mmHg
- late stage CDK patients, aim to keep their blood pressure blow 125/75 mmHg
what drug is effective at lowering blood pressure while protecting kidneys
angiotensin-converting enzyme inhibitor drugs
what diet can help relieve kidney workload
limit the following:
- protein = urea build up
- phosphorous = removes calcium from skeleton and weakens bones
- sodium = high intake tends to raise blood pressure
types of dialysis
haemodialysis
peritoneal dialysis
haemodialysis
- blood from arm vein pumped to dialysis machine
- passes over selectively permeable membrane (dialysate fluid)
- balanced electrolyte solution withdraws water from blood (osmosis)
- no mixing - solute and water exchange by diffusion
haemodialysis negatives
- time consuming (3-5 hours)
- regularly at appropriate clinic = lot of travelling
- not perfect kidney replacement - does not replace blood cells, poor calcium control, uraemia; not remove completely
peritoneal dialysis
- peritoneum acts as selectively permeable dialysis membrane
- dialysate fluid put into peritoneal cavity
- exchange with blood occurs
- peritoneal fluid drained away
peritoneal dialysis positive
- changes blood composition slowly
- continuous ambulatory peritoneal dialysis can be performed at home throughout day
- dwell time 4-8 hours
- automated - can be done during the night
negatives of peritoneal dialysis
risk of infection
kidney transplantation history
1954 - first successful kidney transplant
1962 - tissue typing and immune suppression with drugs was used for the first time in a human kidney transplant
1980s - more powerful immunosuppressant medicines used
kidney transplantation
- 2-3 hour operation
- kidney is placed in the lower abdomen
- renal vein joined to iliac vein in the leg
- renal artery joined onto iliac artery
- once blood vessels connected, the circulation to kidney is released; kidney becomes pink
- urine passes out of the ureter
- ureter joined to the bladder to complete the operation
considerations of transplant
requires donors
risk of rejection
immunosuppressive drugs
- increased cancer risk
- increased infection risk
effect of aging on kidney function
- gradual decrease in size of kidney
- due to changes in blood supply BF decrease - 10% decrease every 10 years
- functioning glomeruli lost - obstruction/ thickening
- nephrons shorten/ thicken
- ability to concentrate urine declines
- ability to eliminate waste products declines
- decreased repsonsiveness to ADH/aldosterone
