Elements and physiology Of Renal Function Flashcards Preview

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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

(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


Hyperaldosteronism “conn syndrome” vs secondary hyperaldosteronism

Primary = usually due to a tumor or lesion that causes excess release of aldosterone

Secondary = some sort of pathology that causes excessive activation of the RAAS pathway


What is pressure natriuresis and pressure diuresis?

A phenomenon that occurs when arterial pressure rises
- causes kidney to increase excretion of sodium and water

Usually requires at least 15-25 mmHg increase
- seen after 5-15 percent increase of ECF

*the return to normal sodium and water levels via pressure-esis is known as aldosterone escape


What does filtration fraction mean? (FF)

It is the fraction of total renal plasma flow that’s is filtered across the glomerular capillaries
- the rest of the plasma that is not filtered leaves through the efferent arterioles and becomes the peritubular capillary blood flow


20% is the normal FF


What does the term filtered load mean?

The amount of interstital fluid that is filtered from the capillary blood per unit of time


How does mean arterial pressure affect renal blood flow and GFR

As mean arterial pressure goes up, renal blood flow and GFR tends to remain constant
- exception is if arterial pressure drops below 70mmHg
- this is due to myogenic stretch and tubuloglomerular feedback

Urine output is direct proportional to mean arterial pressure as well


How do you know if a substance is being secreted?

If the excretion of a substance > the filtration of a substance

Reabsorbed = filtered load - excretion

**if excretion of a substance is < filtration of a substance = reabsorbed


What three concentrations with clearance rates can be used to estimate GFR?

Inulin and creatinine and BUN


What is the relationship between GFR and plasma creatinine?

Inversely proportional


How to tell prerenal azotemia (hypoperfusion to kidneys) from Chronic renal disease/failure only using BUN/Creatinine levels and ratio?

Prerenal azotemia
- both BUN and creatinine increase
- the ratio increases since BUN increases faster

Chronic renal disease
- both BUN and creatinine increase
- the ratio however STAYS the SAME


What is the cut off for acute vs chronic kidney diseases?

less than 3 months = acute
- usually has GFR less than 60 or increases in creatinine by 50% from baseline

Greater than 3 months = chronic
- always GFR less than 60

**both require markers of kidney damage with proteinuria, albuminuria, pyuria being the most common**