Physiology Flashcards
What is creatinine?
A product of muscle metabolism.
Will be higher in those with high muscle mass.
How do creatinine levels change in those with a low GFR?
High creatinine
Which eGFR level is described as stage 5 CKD?
<15ml/min
Requires dialysis/renal transplant.
Which eGFR level is described as stage 4 CKD?
15-29ml/min
Requires treatment to preserve function.
Which eGFR level is described as stage 3 CKD?
30-59ml/min
Often seen in elderly patients - normal decline in renal function seen in age.
Which eGFR level is described as stage 2 CKD?
60-90ml/min
Which eGFR level is described as stage 1 CKD?
> 90ml/min
How much protein content is needed to be pathological in urine?
150mg/day
Which group of conditions cause gross oedema and significant proteinuria?
Nephrotic syndrome
How does protein loss lead to oedema?
Proteins should act to drag water out of the tissues and into the blood vessels.
When lost, results in leakage into tissues - producing oedema (nephrotic syndrome).
What may microalbuminuria indicate?
Diabetic neuropathy
What should be given to prevent worsening of diabetic nephropathy?
ACE inhibitor
Does high osmolarity mean high concentration?
Yes, high osmolarity means high ratio of solute compared to water molecules.
Should plasma osmolarity be higher than urine osmolarity?
No, urine osmolarity should be higher.
Which hormones are produced by the kidneys?
Renin (regulates BP)
Erythropoietin (encourages RBC production)
Which hormone controls the reabsorption Na+ in the distal convoluted tubule?
Aldosterone
Results in greater Na+, increasing blood volume (and therefore pressure).
What is the effect of a hypotonic solution?
Increases cell volume
What is the effect of a hypertonic solution?
Decreases cell volume
In which compartment is the majority of water found?
Intracellular - makes up 67%.
What 4 components make up the total extracellular fluid compartment?
Plasma
Interstitial fluid
Lymph
Transcellular fluid
Which ions are most concentrated within the ECF?
Sodium
Chloride
Bicarbonate
Which 2 ions are most concentrated with the ICF?
Potassium
Magnesium
What is responsible for the movement of fluid between the ICF and ECF?
An osmotic gradient
What is the typical kidney output of urine per day?
1.5L/day
How is bilirubin produced?
It is a by-product of haemoglobin metabolism.
How is uric acid produced?
A by-product of purine metabolism.
What is the role of erythropoietin?
To stimulate RBC production.
How does the kidneys process vitamin D?
Converts this to calcitriol (active form).
Can the bladder/ureters alter the composition of urine?
No, last alterations to this are at the kidneys.
Which 3 mechanisms take place at the nephrons to create urine?
Filtration
Reabsorption
Secretion
How does blood pass through the kidneys?
Renal artery > Afferent arteriole > Glomerulus > Efferent arteriole > Peritubular capillaries > Venules > Renal vein > IVC
What is a normal GFR?
120ml/min
What is the first step of urine production?
The passage of some plasma across the Bowman’s capsule, becoming the tubular fluid.
What 3 barriers act to limit the glomerular function?
Glomerular capillary endothelium (blocks passage of RBCs)
Basement membrane (albeit has pores)
Slit processes of podocytes
What is the purpose of podocytes?
To act as a molecular sieve - only small molecules can pass through.
What is GFR?
The rate at which protein-free plasma is filtered from the glomeruli into the Bowman’s capsule, per unit of time.
What is the purpose of the extrinsic regulation of the GFR?
When blood volume drops, afferent arterioles constrict, reducing urine production.
Ensures minimal fluid loss.
Regulated by sympathetic nervous system.
What is meant by the term autoregulation?
The intrinsic regulation of kidney function by the kidney itself.
Which cells produce constriction of the afferent arteriole in order to lower GFR?
Macula densa
Clearance of which molecule is viewed as ‘gold-standard’ in determining GFR?
Inulin
What is creatinine?
An endogenous substance produced during skeletal muscle metabolism.
Released at a constant rate.
Initially, what differs between tubular fluid and plasma?
Not too much, only large plasma proteins are lost.
Exclusion due to the negative charge of the basal lamina.
Which section of the nephron is reached by the interstitial fluid?
Proximal tubule
What is the major site of reabsorption within the nephron?
Proximal tubule
What is the only area of the nephron not involved in sodium reabsorption?
Descending limb of the loop of Henle
Can water be reabsorbed in the ascending limb of the loop of Henle?
Minimally, primarily responsible for the reabsorption of sodium and chlorine ions.
Which form of medication acts on the triple co-transporter of the ascending limb of the loop of Henle?
Loop diuretics
How does the triple co-transporter impact the tubular fluid?
Removes solute from the ascending limb - leaving only water behind.
Results in dilute urine.
Blockage (with loop diuretics) produces concentrated urine.
Which limb of the loop of Henle concentrates urine?
Descending
Which limb of the loop of Henle dilutes urine?
Ascending
What regulates the resorption of water?
ADH
What is the action of aldosterone?
Promotes sodium resorption.
Allows K+ to be secreted.
What is the action of PTH?
Increases calcium resorption
Decreases phosphate resorption
Which part of the nephron is the ONLY area where hormones can influence the resorption of ions?
Collecting duct
What is central diabetes insipidus?
An inability to produce ADH in the posterior pituitary.
What is nephrogenic diabetes insipidus?
An inability of the kidneys to respond to ADH within the circulation.
How is central DI treated?
ADH replacement
How does alcohol impact ADH release?
Reduces it.
Explains why need to pee so much when drinking.
When is aldosterone released?
Released from the adrenal cortex in response to:
High plasma K+
Low plasma Na+
Why does aldosterone cause BP to rise?
As resorption of salt is promoted, which causes a rise in blood volume (as water dragged back in), thus increasing BP.
How does hyponatraemia affect BP?
Lowers it.
Where is renin produced?
Liver
Where is ACE enzyme found?
Lungs
What are the main functions of angiotensin II?
Promotes aldosterone release
Stimulates thirst
Promotes ADH release
Promotes vasoconstriction
What 3 factors can trigger release of renin?
Reduced pressure in the afferent arterioles
Macula densa senses the amount of NaCl in the distal tubule
Increased sympathetic activity due to reduced BP
Which extremes of pH signify a serious risk of death?
<6.8 and >8.0
Which enzyme catalyses the creation of H+ and HCO3- ions from CO2 and H20?
Carbonic anhydrase
Which organ controls HCO3- levels?
Kidneys
Which organ controls PaCO2 levels?
Lungs
Can the kidneys create HCO3 when this is low?
Yes, if low levels detected in the tubular fluid, H+ can be secreted into the nephron, binding with phosphate.
What is respiratory acidosis?
Retention of CO2 within the body.
May be due to lung failure.
What is the primary cause of respiratory alkalosis?
Hyperventilation
Is metabolic acidosis due to CO2 retention?
No, problem not related to CO2.
For respiratory disturbances of acid/base balance, where does compensation occur?
Kidneys
For metabolic disturbances of acid/base balance, where does compensation occur?
Lungs
Which metabolic acid/base disturbance is most commonly seen?
Metabolic acidosis
