Elements and physiology Of Renal Function Flashcards
What are the major anions and cations in both extracellular and intracellular fluids?
Intracellular fluid (ICF) 66% of TBW
1) cations
- potassium
- magnesium
2) anions
- phosphate ions
- proteins
Extracellular fluid (ECF) 33% of TBW
1) cations
- sodium
2) anions
- chloride
- bicarbonate
How are body fluid volumes measured in the body
1) can use the 60-40-20 rule to estimate
- 60% of total body weight (kg) is equal to total fluid in body (L)
- 40% is the total water in the intracellular fluid
- 20% is the total water in the extracellular fluid
2) mass = (volume * concentration)
Indicators to measure certain body fluid volumes
Total body water = heavy water (D20) and antipyrine
ECF = mannitol, sodium, thiosulfate, inulin
ICF = (total body water - ECF volume)
Plasma volume = I-albumin (radioactive albumin), Evans blue dye
Blood volume = radioactively labeled RBCs or (plasma volume/(1-hematocrit))
Interstital fluid = (ECF volume - plasma volume)
Where is the most resistance found in the renal blood supply?
Between the arterioles
- this is the location for where renal blood flow resistance is controlled
How are filterability of blood substances organized?
The more cationic (positively charged) a substance is, the better the filtration through the glomerulus is
- examples, water, sodium, glucose, inulin
Myoglobin is in between so filterable in high amounts, but in low amounts relatively impermeable
albumin is super impermeable since it is highly anionic (negatively charged). If it is found in the urine almost always means pathology
What is the net filtration pressure of the glomerulus?
Determines how water and solutes are moving across capillaries and bowman’s capsule
equation
(Net filtration pressure) = (glomerular hydrostatic pressure) - (bowmans capsule pressure) - (glomerular oncotic pressure)
under normal condtions
10 = 60 - 18 - 32
(Having a positive pressure means that solutes and fluid are being moved into the bowmans capsule)
What is the purpose of the filtration coeffiecnt in the GFR equation?
GFR equation = Kf x (glomerular pressure) - (bowmans pressure) - (globular colloid osmotic pressure)
Kf under normal condtions is negative and represents the GBM charge barrier. This negatively charged barrier repels proteins from being filtered
- * in pathology (such as nephrotic syndrome) this negative charge goes away, so proteins leak into urine)
Effects of hormones and antacids on GFR
NE/epinephrine = decreases GFR
- increases vasoconstriction in the afferent arterioles
endothelin = decreases GFR
- increases vasoconstriction in the afferent arterioles
Angiotensin 2 = usually balanced
- increases vasoconstriction in both efferent and afferent articles
Nitric oxide and prostaglandins = increases GFR
- NO = vasodilator across the board and PGE constricts efferent arterioles
What are the mechanisms that control auto regulation of blood flow into the kidneys?
Myogenic control (stretch within vessels) - as smooth muscles within renal vasculature stretch due to increased transmural pressure, calcium channels are activated in kidney vessel cells ONLY which causes vasoconstriction and prevents overstretch
Tubuloglomerular feedback
- as GFR drops due to arterial pressure decreasing, the macula dense cells sense the decrease sodium chloride concentration. This causes the Macula dense cells to send a signal (increases NO/PGE release) to the JG cells in the renal vasculature to vasodilate the afferent arterioles ultimately decrease afferent arteriolar resistance. This decrease in afferent resistance causes a feedback-increase in glomerulus hydrostatic pressure and GFR
- in addition, the macula densa also releases renin in response to low sodium chloride concentration which activates RAAS. Angiotensin-2 has a side effect to constrict efferent arterioles and increases resistance which increases GFR and hydrostatic pressure
- if the GFR is too high, the same process occurs except now the manual dense cells release ATP to the JG cells and tell them to decrease afferent arteriolar resistance and decrease glomeruluar hydrostatic pressure
What does the fractional excretion mean?
(Amount excreted/filtered load)
Determines if a solution is more likely to be excreted or reabsorbed
How is the glomerular filtration barrier organized?
3 layers
- 1) fenestrated capillary endothelium
- 2) basement membrane with type 4 collagen chains and heparan sulfate
- 3) visceral epithelial layer with podocyte foot processes
all 3 layers contain (-) charged glycoproteins that prevent entry (-) charged molecules to pass through
Size barrier
- fenestrated capillaries prevent > 100nm molecules. Glomerular basement membrane prevents > 50-60nm molecules
What is normal GFR on average?
100 mL/min
What is the acid used to measure effective renal plasma flow (eRPF)?
Para-AminoHippuric acid (PAH)
What is the #1 trigger for ADH in the body?
Plasma osmolarity
- low osmolarity = NO ADH
- high osmolarity = ADH release
Differential between central and nephrogenic DI
Causes of Central:
- idiopathic, trauma/surgery, tumors, sarcoidosis
Causes of Nephrogenic:
- hypercalcemia, hypokalemia
- lithium and demedocycline use can also cause this
- pylonephritis and aquaporin/vasopressin mutations
Urine changes in central:
- the osmolarity doesnt change with water deprivation since the pituitary gland doesnt respond
- DOES respond to ADH injections
Urine changes in nephrogenic:
- the osmolarity doesnt change with water deprivation since the V2 receptors dont respond to ADH
- DOESNT respond to ADH injections
