Renal Flashcards
What percentage of the bodies blood supply does the kidney receive?
20-25%
What two factors affect the permeability of a molecule in the kidneys?
Size and charge
What is average (textbook) GFR?
125ml/min
How does each nephron regulate it’s own GFR?
Constricting/dilating afferent and efferent capillaries
How would a nephron reduce it’s own GFR?
Constricting afferent and dilating efferent
Where does reabsorption mostly occur in the nephron?
The PCT (proximal convoluted tubule)
In the PCT what two ways are substances reabsorbed across cells?
Paracellular - in-between cells
Transcellular - Through cells
What substances are reabsorbed in the PCT? (4)
Electrolytes such as Na+, Cl- and K+
Glucose, amino acids
Proteins, urea
Some water
What are the two types of nephron, their differences?
Which is more common?
Cortical - Glomeruli in outer cortex of kidney, and loop of henle descends into outer medulla (most common)
Juxtamedullary Nephrons have their glomeruli near the cortex-medulla boundary and their loops of henle descend into the deep medulla.
Why is the reabsorption of water in the loop of henle not coupled the the reabsorption of solutes?
The descending limb is only permeable to water (due to presence of aquaporins)
Briefly, in steps, how does the loop of henle function?
- Na+ and Cl- efflux from the thick ascending limb (pumped out) makes the interstitium hyperosmolar
- Because the descending limb is permeable to water, it is drawn out of the loop into the interstitium.
- As the fluid in the loop reaches the thin ascending limb Na+ and Cl- diffuse out (as the interstitium is less concentrated)
- In the thick ascending limb Na+ and Cl- are actively pumped out.
Where does aldosterone act and what does it do?
In the DCT, it regulates Na+ and K+ balance and the acid/base balance.
How does ADH regulate water balance in the DCT?
Increased amounts of ADH inserts aquaporins in the DCT meaning water diffuses out of the lumen.
Why are Creatinine and Urea used as markers for kidney clearance?
Constantly produced and filtered at constant rates so the only reason for their clearance to change would be due to a change in the kidney.
Why is there a 10% discrepancy in the textbook GFR and actual GFR of creatinine?
The excretion exceeds the filtration due to a small amount of secretion in the proximal tubule.
What three things does the Creatinine formation in the body depend on?
Muscle mass, Age and Gender
What two factors affect the plasma urea levels?
Protein turnover (more protein intake = more urea)
Hydration status
Why is the Urea:creatinine ratio useful?
As both are constantly produced and filtered if the GFR naturally falls then both would be expected to fall in parallel.
Is urine output more likely to be reduced in chronic or acute kidney Injury?
In acute, in chronic there may be compensation.
What can changes in urinary pH indicate?
High pH may indicate certain urinary tract infections
Low pH may indicate metabolic acidosis
What might increased Na+ in the urine indicate?
Tubular kidney problems, due to an inability to reabsorb Na+ (as it is freely filtered)
What is specific gravity?
The weight of a solution compared to pure water (similar to osmolality but not as accurate)
What does a high specific gravity and normal osmolality indicate?
The presence of large molecules, e.g. protein and glucose
If glucose appears in the urine what does that indicate? Why does glucose appear in the urine?
Indicative of uncontrolled diabetes
Blood glucose levels are high and the glucose transporters in the PCT are saturated.
Apart from glucosuria what else in a dipstick test can be indicative of diabetes?
Ketoacidosis
Three types of proteinuria?
Glomerular proteinuria (Increased glomerular permeability)
Tubular proteinuria (Impaired reabsorption)
Overflow proteinuria (Overproduction of small proteins)
What can you use the albumin/creatinine ratio for?
To test the concentration of the urine (both will be reduced in dilute urine)
How do you define AKI?
A significant drop in GFR, 50% or more
two types of hypovolaemia?
Relative - The plasma is still in the body but not in circulation
Absolute - The plasma is not in the body
How can NSAIDS be nephrotoxic?
Prostaglandins maintain dilation of afferent arterioles in the kidney, NSAIDS can reduce them.
The 4 stages of acute tubular necrosis?
Initiation
Maintenance (Oliguric)
Diuretic (Polyuric)
recovery
Pre-existing risk factors for AKI?
eGFR below 60ml/min
> 65 yrs
Diffuse Vascular disease
Liver disease/cardiac disease/diabetes
Previous AKI
Polypharmacy (lots of medications)
Three types of AKI?
Pre-renal
Renal
Post-renal
What is pre-renal AKI?
Common causes?
Decreased renal perfusion resulting in a reduced GFR,
Hypovolaemia
Pump failure
interfering factors e.g. NSAIDS
What is the mnemonic to do with the causes of AKI?
STOP
Sepsis
Toxins
Obstruction
Parenchymal
The three step process of forming urine?
Filtration
Tubular reabsorption
Tubular secretion
What are the three mechanisms for changing filtration?
Myogenic regulation (dilating or constricting afferent and efferent arterioles)
Tubuloglomerular feedback - changes in response to sodium concentration in the DCT (juxtaglomerlar apparatus)
RAAS pathway
What hormones regulate reabsorption, what do they regulate?
Aldosterone - active Na+ reabsorption
ADH - water reabsorption
What is renal AKI?
Common causes?
Intrinsic damage to the kidney parenchyma e.g. tubule, glomerulus, vessels and interstitium
Tubular disease most common cause either ischaemic or toxin related
Glomerular, vascular and interstitial also are causes
What is acute tubular necrosis?
Symptom of acute usually oliguric potentially reversible AKI, a medical emergency§
What is post-renal AKI?
Obstruction to the urinary outflow tract anywhere from kidney to urethra
Categories of post-renal AKI?
External obstruction
Internal obstruction
What type of acid/base disturbance is seen in CKD?
Metabolic acidosis
What is erythropoietin (EPO)?
How is it involved in anaemia in CKD?
Glycoprotein produced mainly in the kidneys, that increases red cell production and maturation in the bone marrow.
Anaemia in CKD can be due to a lack of EPO
Why are results of calcium measurement returned as corrected ca2+?
Need to measure the ionised Ca2+ in the body, so the equipment assumes plasma albumin is normal and takes away any calcium that is bound to plasma proteins.
Main hormonal control of Ca2+?
Parathyroid hormone
Vit D3
What is the effect of increased PTH on plasma Calcium levels?
How is this achieved?
Increased plasma calcium
PTH on the kidney:
- Reabsorption of Ca2+
- stimulates Vit D3 production
Effects of Vitamin D and it’s active form calcitriol (D3)?
Promotes Ca2+ absorption from the gut
Promotes Ca2+ absorption in the kidney
Vitamin D promotes the absorption of Ca2+ into bone
Quick overview of the RAAS pathway?
Angiotensin converted to angiotensin I
by Renin
Ang I converted to Ang II
by ACE
Ang II, will produce vasoconstriction and aldosterone production increasing BP
What is chronic kidney disease characterised by?
Nephron loss, glomerular hyperfiltration
Mesangial cell proliferation
glomerolosclerosis
What is glomerulosclerosis?
Thickening of blood vessel intima
Media hypertrophy and replacement of smoot muscle with fibrous material
nephron loss
What is the positive feedback loop associated with nephron loss?
Nephron loss = more nephron loss
Nephron loss = Increased glomerular pressure + hyperfiltration = Glomerulosclerosis
Glomerulosclerosis = nephron loss
Complications associated with CKD?
Acid/base inbalance
Potassium inbalance
Water regulation issues
Urea excretion
Anaemia
Calcium metabolism
What is the kidneys role in regulating pH?
What enzyme is involved in this?
Retain filtered bicarbonate
Generate new bicarbonate
Excrete H+
Excrete acid anion
Carbonic anhydrase
In CKD is water balance maintained well or not?
Why?
Well maintained
Due to the action of ANP
What is the action of ANP?
Increases GFR (by dilating afferent and constricting efferent.
Counteracts aldosterone and inhibits NA/K ATPase
Common causes of CKD?
Hypertension
Diabetes
Two types of dialysis?
Haemodialysis
Peritoneal dialysis
How does haemodialysis and peritoneal dialysis work?
Haemodialysis - uses blood from an artery puts it through a pump and filter then puts the filtrate back into the venous circulation
Peritoneal - Pump dialysate into the space between the peritoneum (highly vascular) this causes filtration
What is wilms tumour?
Childhood nephroblastoma
What is the main metabolic vasodilator?
Adenosine
What factors determine the work load of the heart?
Heart rate
Preload
Contractility
Afterload
Two types of congenital heart disease?
An example of each?
Acyanotic - ventricular septal defect
Cyanotic (blue/hypoxic at birth) - transposition of the great vessels
What is the involution of the pulmonary vascular bed?
The fact that pulmonary arterioles begin to vasodilate before birth and up to 6 weeks
This means that as a foetus the pulmonary and systemic circulation are at the same pressure, but the pressure begins to fall as the baby grows
What is a congenital ventricular septal defect? How does it present?
When there is a hole in the septum between the left and right ventricles
Baby is fine at birth as the systemic and pulmonary pressures are the same, as the pulmonary arterioles begin to involute (vasodilate) the pulmonary pressure falls and blood from the left side moves to the right and preload increases.
Symptoms:
- Breathlessness
- Poor feeding
- Poor weight gain
Signs:
- murmur
- tachyponea
- Chest recession
- Hepatomegaly
What would happen to the single (undamaged) nephron GFR rate in CKD?
It will increase
Type of innervation to the kidneys?
Sympathetic
