Urinary Flashcards
Name the three layers of between blood and tubular fluid in the glomerulus.
Fenstrated capillary epithelium
Basal lamina
Podocyte slit membrane
What does the Fenstrated epithelium filter from the blood?
Plasma - small proteinsCells and large protein remain in the capillaries
Describe the mechanism of decreasing glomerular filtration rate instigated by the macula densa.
The macula densa releases renin which causes activation of the RAAS system therefore causing vasoconstriction of the afferent arterioles, reducing GFR
What does a refractometer measure?
Specific gravityAbility of the kidney to concentrate urine
Where are the macula densa cells situated?
They are specialized cells of the distal convoluted tubule.
Where is glucose reabsorbed in the nephron? What mechanism is it absorbed by?
Proximal convoluted tubuleGlucose is reabsorbed by secondary active transport
What is specific gravity?
The density of a substance relative to a reference - water
What parameter value is used for hypostheuria?
What could this finding suggest?
SG < 1.007
Unable to concentrate, i.e. unresponsive to ADH,
Primary ADH deficiency (central diabetes insipidus)
Lack of responsiveness of renal tubules to ADH due to renal tubular disease or inhibitors of ADH (nephrogenic diabetes insipidus)
A specific gravity of 1.008 to 1.012 is also describe as what?
Isostheuria
A dog with hypovolaemia would be expected to have a _____ value for their urine SG that a normal dog.
HigherMore concentrated since they are trying to conserve fluid
What would a SG finding of 1.008 - 1.012 suggest?
Since it is similar to a protein free plasma value it suggests inadequate medullary function or renal tubular damage.
What is Azotaemia?
High levels of urea, creatinine or other nitrogenous compounds within the blood.
How would you distinguish between prerenal and renal Azotaemia?
With prerenal Azotaemia the kidney would still be able to concentrate urine and so SG would still be high.
Excessive protein content of urine could suggest what?
InflammationInfectionIncorrect filtration of proteins in the glomerulusGenital tract contamination
Glucose should never be present in the urine. True or false
True
What could the presence of glucose in the urine suggest about kidney function?
Proximal convoluted tubule reabsorption failure
Renal threshold exceeded
When might you see ketones within the urine?
Starvation
Ketosis in ruminants
Diabetes mellitus (poorly controlled)
The pH of carnivores is more _____ than herbivores.
Acidic
Stimulation of the sympathetic nervous system affects GFR how?
Decreases it due to vasoconstriction of the afferent arteriole
State the equation used to calculate clearance of a substance from the body.
Clearance (X) = urine (X) * urine flow (mg/min) / plasma (X)
Why is urine penicillin not a good measure of GFR?
Because it is partially filtered into the tubule at the glomerulus and also secreted into the tubule at the DCT, therefore it’s excretion is greater than that filtered at the glomerulus.
Where is the site of reabsorption of urea in the nephron?
Decending limb of the LOH only.Therefore recirculation in the medulla is necessary
How would blood urea nitrogen change if the GFR was decreased?
It would increase rapidly
Which membrane surface of the proximal convoluted tubule is impermeable to bicarbonate?
How does the body work around this?
Apical
Combines H+ with HCO3- using CA - H2O and CO2 are able to move across membrane.
Which transporter is responsible for secretion of H+ in the PCT?
Na+ H+ exchanger
Reabsorption of bicarbonate in the PCT is coupled with cell absorption of which anion? On which membrane surface of the tubular cell is the x+/HCO3- transporter found?
Na+Basolateral
Outline the transport of glucose back into the blood in the proximal convoluted tubule.
Glucose is transported by secondary active transport.Passes through apical membrane by contransport with Na+ (active Na+) Passes across basal membrane via facilitated diffusion
Which parts of the nephron are permeable to urea?
Decending limb of the loop of Henle and collecting duct
State the equation for net pressure in the glomerulus.
Net GFR pressure = Glomerular blood hydrostatic pressure - capsule hydrostatic pressure - blood colloid osmotic pressure
What aspect of the afferent and efferent vessels of the glomerulus causes glomerular filtration?
Difference in radius of the vessels
Anions in the proximal convoluted tubule are reabsorbed by which process?
Down their electrochemical gradient due to reabsorption of sodium
What is the significance of the direction of flow of the vasa recta compared with the loop of Henle?
Since the descending limb of the LOH is the only part of the LOH which is permeable to water vasa recta flow needs to be in the opposite direction to allow the build up of Na+ in the medulla before H2O reaches the ascending limb, allowing it to be reabsorbed.
How does the kidney prevent excessive reabsorption of urea in the proximal convoluted tubule?
Maintaining a high filtration rate in the glomerulus
How does the glomerulus prevent protein filtration into the tubule?
Size of fenestration holesNegative charge of glycoproteins repels negatively charged proteins
Which cells of the body release ANP? What is the stimulus for its release? What is the outcome of its action?
Atrial cardiac myocytes
Stretch of the atria (volume overload)
Reduce blood pressure by causing excretion of Na+ and H2O
Which substances create a hyper osmotic medulla environment causing the movement of water into the vasa recta?
Urea and Na+ (mainly sodium)
Calcitrol, which causes the reabsorption of calcium in the collecting duct is also known as what?
How is this hormone activated and what effects does it have on nephron cells?
Activated vitamin D3
AVD3 is activated by parathyroid hormone.
Its increases the activity of binding proteins which increase calcium reabsorption efficiency.
A pathological decrease in blood volume would have what effects?
- Arteriole constriction
- Hypothalamus - ADH secretion, increased thirst
- Cardiac compensations (via baroreceptors) increased force of contraction
- Activation of the RAAS - increased Na+ absorption (+H2O) and vasoconstriction
- Aldosterone release (via RAAS)
What is the action of calcitonin in the kidney?
Inhibits the reabsorption of calcium therefore causing calcium excretion