Physiology (Renal) Flashcards
What is the volume of renal blood flow?
1000 ml/min = 25% of cardiac output
What is the flow equation?
RBF = RPF /1 - Haematocrite
RBF - Renal blood flow
RPF - Renal plasma flow
How to calculate renal plasma flow?
- Same formula as clearance
- Using P-Aminohippuric Acid (Excreted)
Formula for Renal Plasma Flow?
RBF = RPP/RVR
RPP = Renal perfusion pressure
RVR = Renal vascular resistance
What is the tubulo-glomerular feedback?
This is when the renal tubules regulate their own blood flow and therefor the glomerular filtration rate
What is GFR?
This measures the rate at which blood is filtered by the kidney.
GFR = Clearance
What is clearance?
The volume of plasma that is cleared of substance per unit time (ml/min)
Formula for clearance?
Cx = UxV/Px
Cx = Clearance
U = Urinary concentration
V = Urine flow
Px = Plasma concentration
What is the substance used to measure clearance?
- Insulin
- Freely filtered
- Not secreted, reabsorbed, metabolised or stored
- Creatinine is a more practical surrogate
Draw a graph for renal auto-regulation ?
- RBF regulated between MAP of 80-180mmHg
What are the auto-regulatory MAP ranges for different organs?
- Heart - 50-150 mmHg
- Brain - 60-160 mmHg
- Renal - 80-180 mmHg
Glucose handling?
Glucose filtration by the kidney is directly proportional to the plasma glucose concentration
What is T-Max of glucose?
This is the maximal tubular absorption of glucose at 11 mmol/L and 300mg/min
What are the hormones produced by the kidney ?
- Erythropoietin
- 1,25-Di-hydroxycholecalciferol
- Renin
What is Erythropoietin?
- Regulates erythropoiesis
- Secreted from glomerular apparatus in response to - Hypoperfusion & Hypoxia
- Its receptor present on the membrane of RBCs
- Causes increased production of RBC
- Deficiency responsible for anaemia in chronic kidney disease
What is 1,25-dihydroxycholecalciferol?
- It is responsible for calcium balance
- Enhances calcium absorption from proximal bowel
What is Renin?
- Part of the Renin-Angiotensin-Aldosterone system
- Activated by decreased renal perfusion
List the acid-base buffers in the body?
- Bicarbonate
- Haemoglobin
- Plasma protein
- Phosphate
Formula for calculating anion-gap?
AG = (Na+K) - (Cl+HCO)
What is the Davenport diagram?
This shows the relationship between pH, PCO2 and HCO3
- See page 110 of passway for explanation of diagram
- Learn how to draw the diagram
Correction of bicarbonate deficiency ?
NaHCO3 = BD x 30% x Body weight
BD = Base deficit
Base deficit abnormalities?
- Respiratory = HCO normal
- Metabolic = PCO2 normal
Sodium handling ?
- ADH has a significant effect on final conc of urinary Na
- Urine is hypotonic after passing through AL thick - Na 100mmol/L
- With ADH - DCT & CD retain water + Increase urinary Na
How to calculate serum osmolarity?
2Na + Glu/18 + BUN/2.8
Na - mEq/L
Glu & BUN - mg/dL
What are the causes of hypernatraemia ?
- Increased sodium concentration
- ## water depletion
What are the causes of hypernatraemia ?
- Increased sodium concentration
- ## water depletion
What are the causes of hyponatraemia?
- Sodium deficiency
- Hyperaldosteronism
- Hypotonic saline
- TURP syndrome
- Reduced water excretion
- Hyperglycaemia
How is diabetes insipidus treated ?
Desmopressin
Effect of rapid correction of hyponatraemia?
Central demyelinating lesion
Potassium handling in the kidney?
- Usually maintained between 5-10mmol/L - Horizontal
- Potassium secreted in the DCT-Electrochemical gradient
Factors affecting inter-compartmental potassium shift?
- Extracellular pH
- Circulating insulin
- Hypothermia
What are the factors causing extracellular shift of potassium?
- Acidosis
- Decreased insulin
- Beta-blocker
- Increased plasma osmolality
- Hyperthermia
What are the factors causing intracellular shift of potassium?
- Decreased plasma osmolality
- Beta receptor activation
- Hypothermia
- Alkalosis
- Insulin
What are the effects of hyperkalaemia ?
- Muscle weakness
- Nausea & vomiting
- Diarrhoea
- Palpitation
- CVS collapse
What are the characteristic ECG changes in hyperkalaemia?
- Peaked t-waves
- Wide QRS
- Prolonged PR interval
- P-wave loss
- ST depression
- VF / Asystole
What is the treatment of hyperkalaemia?
- Treat the precipitating cause
- Calcium chloride - 10ml / 10% - Potassium antagonist
- Insulin/dextrose over 30 mins
- Salbutamol
- Dialysis
What are the causes of hypokalaemia ?
- Reduced intake
- Increase loss (Renal, burns & GI)
- Inter-compartmental shift
What are the effects of hypokalaemia ?
- Decreased myocardial contractility
- Muscle weakness
- Polyuria
- Ileus
What are the characteristic ECG changes of hypokalaemia ?
- T-wave flattening & inversion
- U-waves and ST depression
- Prolonged QT interval and asystole
Treatment of hypokalaemia ?
- Treat the cause
- Potassium replacement
Properties of calcium ?
- About 98% present in bones
- About 40% bound to albumin
- Range in plasma between 2-2.6mmol/L
What are the hormones regulating calcium levels ?
Read about it **
Hormones enhancing absorption of Calcium?
- Calcitriol
- 1,25-Dihydroxyvitamin D
- PTH - Regulated
Hypercalaemia?
- Present in 98% of cancers
- Hyper-parathyroidism
- Paget’s disease