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
What are the three actions of calcitrol in the body?
Reabsorption of calcium in the kidney collecting ductAbsorption of calcium In the GI tractActivation of osteoclasts - calcium release
Which hormone is responsible for the secretion of potassium from the kidney?
Aldosterone
What is the effect of hyperkalaemia in the body?
Hyperpolarisation of cells preventing repolarisation
Potassium is excreted in exchange for which other ions reabsorption in the distal convoluted tubule?
Na+
What is meant by respiratory acidosis?
An acidosis caused by the build up of respiratory products, ie CO2 leading to the build up of H+
What is meant by a metabolic acidosis?
Acidosis in response to a build up of metabolic products, for example lactic acid
Name the three mechanisms which decrease glomerular filtration rate by affecting the arterioles entering and leaving the glomerulus.
RAAS causes vasoconstriction of the afferent arterioleSympathetic nervous system restricts blood flow to the kidneyMyogenic response to an increase in pressure in the afferent vessel
What effect does ADH have on the collecting duct?
Increases its permeability to water by causing exocytosis of aquaporin 2 channels to the duct cells membrane therefore causing reabsorption of water.
Vasopressin (ie ADH) is released from which endocrine organ of the brain?
Posterior pituitary
What effects does Aldosterone have on the body?
Increases thirstIncreased Na+ retentionIncreased BPIncreased K+ excretion
Which part of the adrenal gland is aldosterone released from?
Zona glomerulosa
Aldosterone is considered what type of steroid hormone?
What effect does it have on the nephron?
Mineralocorticoid (Zglomer)
Aldosterone increases K+ secretion by increasing Na+/K+ pump activity in the DCT
Which part of the hypothalamus monitors plasma osmolarity?
Osmoreceptors
What effect does ANP have on renal water excretion?
Increases it
Which aspect of the ANS causes bladder emptying? Which muscles does it cause to contract and relax?
ParasympatheticContraction of the detrusor muscle and relaxation of the internal sphincter muscle
The detrusor muscle is found where?
Bladder wall
True or false”The internal sphincter muscle is a voluntarily controlled muscle”
False
Does urine composition change between the collecting ducts and the bladder?
No, unless you are a horse. Ureter and renal pelvis glands release mucus into the urine in the horse.
Is the external sphincter an example of a voluntary or involuntary muscle?
Voluntary muscle in the mature animal
Name a chemical buffer of the blood which reduces acidosis.
Bicarbonate ions
What is the cardinal rule of a buffering system?
“A system cannot buffer itself”
Which adrenoceptors are found in the detrusor muscle?
Beta 2
Which adrenoceptors are found in the internal sphincter muscle?
Alpha 1
Which neurotransmitters are involved in bladder filling?
Noradrenaline and acetylcholine
Parasympathetic innervation of the bladder arises from which spinal segments?
L1 and L2
Which part of the brain controls urination?
The pons
What is the trigone?
The area of the bladder where the ureters enter the bladder and the urethra leaves.
Outline the myogenic reflex of the bladder.
Bladder wall stretches as urine fills the bladder, increasing pressure, stretch of the muscular wall activates the PSNS. This leads to detrusor contraction, ISM relaxation and ESM inhibition leading to urination.
Which ACh receptors are found in the detrusor and ISM muscle?
Muscarinic
What is the difference between colloids and Crystalloids?
Colloid solutions have high molecular weight and therefore are unable to freely pass through capillary membranes. Crystalloids have small molecular weights and are therefore freely able to pass through capillary membranes.
Name two types of colloids fluids and give examples for each.
Natural - whole blood, albumen, plasma Synthetic - gelatin, dextrans, starches
How can isotonic, hypotonic and hypertonic Crystalloids actions be classified?
Isotonic Crystalloids - act as ECF volume replacers Hypotonic Crystalloids - maintenance/ water replacers, they cause fluid to be redistributed to the intracellular space Hypertonic Crystalloids - plasma expanders
Name two types of plasma expander fluids.
Colloids - create a colloid osmotic gradient Hypertonic saline - alters the osmotic gradient of blood Both types draw blood into the vascular space
Name three types of synthetic colloid and briefly describe them.
Gelatins - can be urea-linked or succinated. Their action is transient (2-3hrs)Dextrans - synthetic glucose polymers, rapid and transient action (2-3hr)Starches - generations 1-3, expensive but minimal side effects
What side effects can be caused by colloids?
Anaphylaxis, coagulopathies, renal impairment
What is a buffered Crystalloid?
A Crystalloid which contains bicarbonate or precursors (glutamate)
What is a balanced crystalloid? Give an example of one.
One which contains electrolytes similar to plasma. Lactated Ringers
Outline the changes implemented in oral fluid therapy across the generations.
1 - corrects dehydration 1+ - the addition of bicarbonate addressed acidosis 2 - glucose is used to address nutritional demand 3 - glutamine promotes villus repair and regeneration
Discuss the advantages and disadvantages of feeding milk during oral rehydration therapy.
Adv - feeds the calf, assists in repair of the gut mucosa, ensures proper electrolyte balance Dis - worsen diarrhoea or acidosis which will discourage farmers compliance
Where is the juxtaglomerular apparatus situated in the nephron?
They are a specialised cell group consisting of the macula dense (DCT) and the granular cells which are a group of juxtaglomerular cells.
How would you calculate renal clearance of a substance?
Urine [X] x Urine flow (mg/min) / Plasma [X] mg/ml (C=UV/P)
Explain why creatinine is used as a guide for measuring GFR rather than glucose or penicillin.
Creatinine is used since it is fully filtered in the glomerulus and is not reabsorbed in the later nephron. Glucose is fully filtered but also pretty much fully reabsorbed in the PCT, penicillin is not fully filtered in the glomerulus and is also secreted into the tubular fluid later in the nephron, ie these two are useless.
What is the normal SG of a healthy dog/cat?
D - 1.030, C - 1.035
Name and describe the characteristic features of the GOLD STANDARD for measuring GFR.
Inulin. Plant polysaccaride, 100% filtered, Not reabsorbed or secreted, Need continuous IV infusion, Not very practical
Changes in blood levels of urea can indicate what pathologies?
Low - Severe liver disease / PSS, Low protein diet, Aggressive fluid therapy High - Decreased GFR, Blocked or ruptured lower urinary tract,High protein diet, Recent meal, Catabolism (fever), GI haemorrhage, Dehydration
Changes in blood levels of creatinine can indicate what pathologies?
High - Azotaemia Low - Loss of muscle mass Since creatinine is pretty black and white it is a more reliable measure of kidney function
Is azotaemia always an indicator of kidney disease? Explain.
No, azotaemia can have pre-renal, renal and post-renal aetiology. Pre - cardiac disease acute/ severe hypovolaemia, renal - ethyl glycol poisoning, post - urolithiasis
What is the normal urine output of a healthy animal?
1ml/kg/hr
Explain how and where potassium excretion and reabsorption occurs in the kidney
Excretion - K+ secretion occurs in exchange for Na+ in the principle cells of the late DCT. This process is mediated by aldosterone in an attempt to increase water reabsorption in this area. Na+/K+ ATPase is located on the basolateral surface. Reabsorption - K+ reabsorption occurs in the intercalated cells of the DCT. K+ is exchanged for H+ in these cells.
What is the normal water intake of a healthy animal?
2ml/kg/hr
How is phosphate reabsorbed in the nephron?
80%+ reabsorbed in the PCT whilst further % is cotransported into the cells of the DCT with Na+.
Outline the mode of action of osmotic diuretics.
Freely filtered in the glomerulus and alter the osmotic pressure of the tubular fluid therefore reducing water reabsorption. These are the only types of diuretics which DON’T cause diuresis through manipulation of Na+/Cl- reabsorption. Mannitol
Outline the mode of action of carbonic anhydrase inhibitors.
H+ secretion and HCO3- reabsorption occurs in the PCT.
H+ secreted for Na+
CA inhibited = reduced H2CO3 production and dissociation = reduced Na+/H+ exchange > less water reabsorbed.
These are weak diuretics-Dichlofenamine, Acetazolamide
How does the use of certain diuretics lead to hypokalaemia?
Since Na+ reabsorption is inhibited upstream of the DCT greater Na+ reaches the DCT. The body attempts to combat this by activating RAAS leading to reabsorption of Na+ and excretion of K+.
Outline the mode of action of loop diuretics.
They inhibit the Na+/K+/Cl- ATPase of the ascending loop of henle. This therefore decreases the hyperosmolarity of the renal medulla and leads to decrease water reabsorption from the descending limb. Furosemide
Outline the mode of action of thiazines.
Inhibit Na+/Cl- cotransport in the DCT (before aldosterone action occurs. Chlorothiazine
Outline the mode of action of potassium-sparing diuretics.
1) Inhibit the active reabsorption of Na+ thereby reducing Na+/K+ coexchanger activity.
2) Steroids competitively inhibit the action of aldosterone on the principle cells of the DCT.
Amiloride and Triamterine - active Na+ reabsorption Spironolactone - steroid
State the equation for calculating volume of fluid required for an animal in practice.
Volume required (L) = Volume deficit (mLx1000) + Abnormal ongoing losses + Maintenance Volume deficit = BW x %dehydrated = mL Abnormal ongoing losses = mL for mL for vomiting, diarrhoea, polyuria Maintenance = 50mL/kg/day or 2mL/kg/hour
How can acidosis be corrected in the distal convoluted tubule?
In A cells.
H+ ions are exchanged for K+ ions which are then lost to the interstitial space coupled with bicarbonate.
Once in the tubular space H+ ions combine with phosphate ions to form phospheric acid which is excreted.
How can alkalosis be corrected in the distal convoluted tubule?
In B cells.
Bicarbonate ions are secreted with K+ ions into the tubular lumen. K+ ions move into the tubular cells via H+/K+ ATPase exchanger
