Renal Physiology Flashcards
What are the 3 basic renal processes?
Filtration
Reabsorption
Secretion
What is the GFR?
Glomerular filtration rate
180l/day
What % of fluid is reabsorped back into the body?
99%
Where are alot of drugs metabolised?
Liver
How long does it take for a volume equal to BV to pass through the kidneys?
5 minutes
Are red BC filtered in the kidney?
No
What factors determine the filterability of solutes across the glomerular filtration barrier?
Molecular size
Electrical charge
Molecular shape
What does the first layer of membrane in the glomerulus filter out?
Everything except blood cells
What does the second layer in glomerulus prevent the filtration of?
Larger proteins
What does third layer in the glomerulus
prevent the filtration of?
prevent filtration of medium sized proteins
Which membrane layer of the glomerulus prevents the filtration of larger proteins?
Basal lamina
Which membrane of the glomerulus prevents the filtration of medium sized proteins?
Silt membrane
Which membrane in the glomerulus prevents the filtration of blood cells but allows components of plasma to get through?
Fenestration (pore) of glomerular endothelial cell
Which is glomerular pressure higher than most capillaries in the body?
Because afferent arterioles are short and wide offering little resistance to flow
Describe the unique arrangement of efferent arterioles
Long and narrow
What is the overall effect of having little resistance in the afferent arteriole and high resistance in the efferent arteriole?
High hydrostatic pressure
How does hydrostatic pressure at the glomerular capillaries compare to oncotic pressure?
Exceeds oncotic pressure
Which process occurs at the glomerular capillaries?
Only filtration
Which is the major factor in determining GFR?
Afferent and efferent arteriolar diameter
Which extrinsic factors control afferent and efferent arteriolar diameter?
Sympathetic VC nerves
Circulating catecholamines
Angiotensin II
How do sympathetic nerves affect afferent and efferent diameters?
Give afferent and efferent constriction
If you have high resistance how does this affect hydrostatic pressure upstream?
Increases it
If you have high resistance how does this affect hydrostatic pressure downstream?
Decreases it
How do circulating catecholamines affect afferent and efferent arterioles?
Constriction of only afferent
How does angiotensin II affect afferent and efferent arteriole?
Constriction of efferent at low
Both afferent and efferent at high
Which major factor is crucial in determining GFR?
Diameter of afferent and efferent arterioles
What is the minimum pressure needed to drive filtration?
50 mmHg
If mean arterial pressure what is the effect on afferent arteriolar constriction?
There is an increase in constriction to slow down GFR
What is meant by autoregulation of GFR?
There is a zone of atuoregulation where GFR will alter and autoregulate over a range of BP
What happens to kidney blood flow during haemorrhage?
It reduces to flow to immediately important organs
What happens in prolonged reduction in renal BF?
Can lead to irreparable damage and can lead to death due to disruption of the kidney’s role in homeostasis
What % of plasma is filtered though the glomerulus?
20%
What % of filtered fluid is reabsorbed along the remaining nephron?
19%
What % of plasma entering the kidneys return back to the systemic circulation?
> 99%
What is the volume excreted to the external environment known as?
Urine
Where does filtration only occur?
At the glomerular capillaries
Describe the concentration of plasma proteins in the blood remaining in the efferent arteriole compared to the proximal tube
Higher concentration of plasma proteins in efferent
Due to only 20% being filtered into Bowman’s capsule
What is the consequence of the low Ppc and high oncotic pressure in the peritubular capillaries?
Balance of Starling’s forces in the peritubular capillaries is entirely in favour of reabsorption
Where are molecules mainly reabsorbed in the nephron?
Proximal convoluted tubule
Why is hydrostatic pressure in the peritubular capillaries very low?
Because of hydrostatic pressure having to overcome the frictional resistance in the efferent arterioles
Why is the plasma protein concentration higher in the efferent capillary than it was in the afferent?
Due to the loss of 20% of proteins in the glomerular concentrating that in in remaining plasma
What is the function of Bowman’s Capsule?
To collect the filtrate that is filtered out at the glomerulus
What is the effect of increased afferent diameter on GFR?
it increases
What is the effect of increased efferent diameter on GFR?
It decreases
What is the effect of decreased afferent diameter on GFR?
It decreases
What is the effect of decreased efferent diameter on GFR?
It increases
What is meant by Tm?
Maximum transport capacit
What happens to a substrate when Tm is exceeded?
It is passed out int he urine
Why does Tm exist?
Because there are only so many transporters to reabsorb substances
What is the effect of transport molecules bonding to their carrier?
A conformational change
What is capacity of transportation limited by?
The number of carriers
What is the effect on transportation once maximum saturation has been reached?
Transportation levels out
What is renal threshold?
Plasma threshold at which saturation occurs
What is the renal threshold for glucose?
10mmol/l
What happens to glucose beyond 10mmol/l?
Excess is excreted in the urine
If 5 mmol/l of glucose is present how much do we reabsorb?
5mmol/l
If 10mmol/l of glucose is present how much do we reabsorb?
10mmol/l
If 15mmol/l of glucose is present how much do we reabsorb?
10mmol/l other 5mmol/l is excreted in the urine
Do the kidneys regulate glucose?
No
What is responsible for regulating glucose in the body?
Insulin and other counter regulatory hormones
What is glycosuria due to the failure of?
Insulin NOT the kidney
Why is Tm for glucose set way above any possible level of diabetes?
To ensure all variants of glucose are normally reabsorbed
How does Tm mechanism achieve plasma regulation for substrates such as sulphate and phosphate?
Tm is set at a level whereby the normal plasma conc. causes saturation
So any level above normal will be excreted
Therefore achieving its plasma regulation
Where are sodium ions most abundant?
In the ECF
What % of sodium is reabsorbed by the kidneys?
99.5%
Where does most Na reabsorption occur?
In the proximal tubule
How is sodium reabsorbed?
By active transport
Explain the active transport of sodium?
Active Na+ pumps are located on the basolateral membrane pumping sodium into the ISF and K+ into the proximal tubule cell
This passively drives Na+ from the tubule lumen into the proximal tubule cell
To then be actively pumped out by the pump
Describe the permeability of the proximal tubule cells to Na+ ions?
Higher permeability than most other membranes of the body
What does sodium also drive the transport of?
Glucose
How is Cl- reabsorbed?
Passively crosses across the proximal tubular membrane down the electrical gradient established and maintained by the active transport of Na+
What is the effect of the active transport of Na+ out of the tubule followed by Cl- on water?
Creates an osmotic force drawing H2O out of the tubules
What is the effect of H2O removed by osmosis from the proximal tubule?
Concentrates all the substances left in the tubule creating outgoing concentration gradients
What does the rate of reabsorption of non-actively reabsorbed solutes depend on?
Amount of H2O removed - determining concentration gradient
Permeability of the membrane to any particular solute
Describe the tubules membrane permeability to urea?
Moderately permeable to that 50% is reabsorbed and 50% remains in the tubule
Describe the permeability of the tubular membrane to insulin and mannitol?
The membrane is impermeable
What happens to mannitol with a concentration gradient favouring reabsorption?
Despite a concentration gradient favouring reabsorption they cannot gain access through the tubular membrane so that ALL is filtered and stays in the tubule to be passed out in the urine
Give examples of substances which share the same carrier molecule as sodium?
Glucose
Amino acids
What is the effect of high sodium conc. on the tubule on glucose transport?
It facilitates it
What is the effect os low sodium conc. on the tubule transport of glucose?
It inhibits it
Can sodium pump transport glucose across its concentration gradient
Yes
Indirectly it can
Where does the energy to drive glucose against its concentration gradient come from?
The energy used in the ATP pump to transport sodium
Na/ATP ase
What is the secondary route from the peritubular capillaries into the tubule lumen?
Secretory mechanisms
How are protein bound substances usually excreted?
Their filtration at the glomerulus is restricted
So they can be secreted form the peritubular capillaries into the tubule lumen
Where are substances secreted?
At the proximal tube
Why are secretory mechanisms not very specific?
So that they can be used for a wide range of endogenous or exogenous substances
What do organic acid secretory mechanisms secrete?
Lactic acid and uric acid
But can also be used for things like penicillin, aspirin
What are organic base secretory mechanisms used to secrete?
Choline and creatine ect
But can be used for morphine and atrophine
What is normal ECF potassium conc.?
4mmoles/l
What mmol/l is classed as hyperkalaemia?
> 5.5 mmoles/l
What mmol/l is classed as hypokalaemia?
<3.5 mmol/l
What can be the result of hyperkalaemia?
Decrease in resting membrane potential
Eventually VF and death
What can be the result of hypokalaemia?
Increase in resting potential
Can cause cardiac arrhythmias and eventually death
What is the effect of increased renal tubule cell potassium concentration?
Increase in K+ secretion
What is the effect of decreased renal tubule cell potassium concentration?
Decrease in K+ secretion
What are changes in K+ excretion due to?
Changes in its secretion in the distal parts of the tubule
Which adrenal cortical hormone regulates potassium?
Aldosterone
What is the role of aldosterone in increased K+ conc. in ECF?
Increase in K+ in ECF
Stimulates aldosterone release
Stimulates increase in renal tubule K+ secretion
What is the effect of increased aldosterone on potassium?
Increases renal tubule cell K+ secretion
How are proteins reabsorbed in the proximal tubule?
Tm carrier mechanism
What does the liver do to drugs and pollutants?
Metabolises it to polar compounds
That can not be reabsorbed
Facilitating their excretion
What is the loop of henle important for?
Reabsorbing only
Why is all fluid leaving the proximal tubule isosmotic?
Because all the solute movements are accompanied by osmosis so that osmotic equilibrium is maintained
Where do all nephrons have their proximal and distal tubes located?
In the cortex
Where is the location of the loop of henle in the kidney?
Medulla of the kidney
What is the minimum obligatory loss of H2O?
500mls
What is the effect of no H2O intake on urintation?
Still excrete 500ml a day
Can urinate to death
Why are the kidneys able to produce urine of varying concentration?
Because the loops of henle of juxtamedullary nephrons act as counter-current multipliers
What is the main function of the loop of henle?
To create a concentration gradient in the medulla
What is meant by isosmotic?
That the concentration on one side is the same as on the other side
Why does the medulla interstitial space need to become more concentrated with ions?
To allow water to move out at the collecting ducts oft he nephron
What are the 2 critical characteristics of the loop of henle that make then counter-current multipliers?
The ascending limb transports Na+ and Cl- out of the tubule into the lumen being impermeable to water
The descending limb is freely permeably to H2O but relatively impermeable to NaCl
What is the osmolarity of fluid as it enters the loop of henle?
300 mOsm/l
What happens in the ascending limb as the NaCl is pumped out?
Concentration in the tubule decreases
As the concentration in the interstitium increases
What is the limiting gradient different between the ascending limb and the interstitium?
200mOsm
Due to NaCl being removed in the ascending limb what is the effect in the descending limb?
Water is permeable
Will diffuse out to equate osmolarity between the descending limb and the interstitium
Does the H2O stay in the interstitium once pulled out of the descending limb?
No it is reabsorbed by the high oncotic pressure into the vasa recta
What happens to fluid as it moves down the descending limb?
It becomes more and more concentrated due to the loss of water
What happens to the fluid as it moves back up the ascending limb>
There is active NaCl removal
Further concentrating the interstitium
Describe the fluid as it moves down the descending limb and back up the ascending limb?
The fluid in the tubule is progressively concentrated as it moves down the descending limb and progressively diluted as it moves up the ascending limb
Why is the fluid between the descending loop tubule fluid and interstitial fluid equal?
Because water moves freely to create isosmotic fluid
Why is the fluid between the descending limb and interstitial fluid a difference of 200mOsmole?
Due to the pumping of active pumps in the ascending limb
What is the key key step in the loop of henle?
The active transport of NaCl out of the ascending limb
What mOsm does the fluid leave the loop of henle at?
100
Why do we want to deliver hypotonic fluid to the distal tubule?
So we can regulate the osmolarity of the urine based on the needs of the body at the time
What are the functions of the vasa recta?
To provide O2 for the medulla
Removed volume from the interstitium
Why is the flow rate through the vasa recta very low?
So that there is plenty of time for equilibrium to occur with the interstitium
Why is it important that the medullary capillaries follow the loop of Henle and don’t drain straight through?
If they were straight would carry away the NaCl removed from the loop of henle and disrupt the interestital gradient
What is water regulation controlled by?
ADH
What type of hormone is ADH?
Polypeptide
Where is ADH synthesised?
In the supraoptic and paraventricular nuclei in the hypothalamus in the brain
Where is ADH stored?
Posterior pituitary gland
What is the half life of ADH?
10 minutes
Where is the effect of increased cell osmolarity on ADH?
Increased osmolarity Drags water out of the cell
Cell shrinkage
So increase in neural discharge
And increase in ADH secretion
What is the effect of decreased cell osmolarity on ADH?
Decreased osmolarity
Drags water into the cell
Decrease in neural discharge
Decrease in ADH secretion
What is the effect of changes of volume of the osmoreceptors?
Changes in osmoreceptor discharge
What is normal plasma osmolarity?
280-290mOsm/kg H20
What is the effect of an increase in osmolarity that does not cause an increase in tonicity on ADH?
Ineffective at causing an increase in ADH
What is tonicity?
A term that takes into account the total concentration of non-penetrating solutes only
What is the maximum concentration of urine we can secrete?
1200-1400mOsm/l
Why does ingestion of hypertonic solutions such as seawater cause more dehydration?
Because there is increase in solute to be excreted
Increase in urine flow
Leads to dehydration
Because more H20 is require to secrete the solute than was ingested with it
What does urine osmolarity depend on?
Reabsorption in the collecting duct
Where is the site of water regulation?
Collecting duct
What is the permeability of the collecting duct under the control of?
ADH/Vasopressin
What happens generally if there is more ADH?
More concentrated urine is secreted
As more water is reabsorbed in the body
What does ADH mediate the change in permeability of?
The collecting duct
Where is ADH produced?
In the posterior PG
How does ADH increase water reabsorption?
By the recruitment of aquaporin 2 to the cell membrane of the collecting ducts
What happens when more aquaporin 2 is recruited to the cell under the control of ADH?
The cortical collecting duct becomes equilibrated with that of the cortical interstitium
What drives the movement of water in the collecting duct?
The hypertonic medullary intersitital gradient created by the countercurrent multiplier of the loop of henle
When is maximum ADH present in terms of the medullary interstitium?
When the contents of the collecting duct equilibriate with that of the medullary interstitium via osmotic efflux of H2O
Describe urine concentration when ADH is maximum?
Small volume of concentrated urine
When is maximum ADH released?
When there is maximum water deficit
Which forces drive the reabsorption of H2O from the medullary interstitium once moved out of the collecting duct?
H2O reabsorbed by oncotic pressure in vasa recta which will be even greater that usual due to H2O deficit
What is the result of absent ADH?
Collecting duct impermeable to water
So the medullary interstitium gradient is ineffective in inducing H2O movements out of the CD
Compensating for H2O excess
What is the consequence of H2O excess on ADH and the CD?
No ADH
CD impermeable to water
Medullary interstitial gradient is inneffective
so a large volume of dilute urine is excreted
Compensating for H2O excess
Describe the permeability of CD membranes to urea
Relatively permeable particularly towards medullary tips
What happens as urea approaches the medullary tipes?
there is an increasing tendency for it to move out down its concentration gradient.
What is the permeability of the late medullary CD to urea enhanced by?
ADH
Why is it important that urea is reabsorbed in the CD?
So that it can reinforce the intersitial gradient in the ascending loop of henle
and prevent water retention in the CD
What would urea do if it all remained in the CD?
Would hold onto the water and reduce the potential for rehydration
What is more important the conservation of H2O or urea?
H2O
How does an increase in ECF volume affect ADH secretion?
Decreases it
How does a decrease in ECF volume affect ADH secretion?
Increases it
Where are low pressure receptors located?
In the L and R atria and great veins
Where are high pressure receptors located?
At the carotid and aortic arch baroreceptors
Which receptors does a moderate decrease in ECF volume affect?
Atrial receptors
What is the effect when atrial receptors detect a moderate decrease in ECF vol.?
Decrease in ECF vol.
Decrease Atrial receptor discharge
Increase in ADH release
Which receptors will also contribute to ADH change in secretion when volume changes enough to affect MPB?
Carotid and aortic baroreceptors
What type of cells are ADH secreting cells?
Neurones
Which OTHER stimuli increase ADH release?
Pain, emotion, stress, exercise, nicotine, morphine. Following traumatic surgery,
Which OTHER stimuli decrease ADH release?
Alcohol
Suppresses ADH release
Which receptors detect a decrease in atrial stretch due to low blood volume?
Atrial stretch receptors
Which receptors detect a decrease in BP?
Carotid and aortic baroreceptors
What is there a lack of in diabetes insipidus?
ADH deficiency
What are the potential causes for central diabetes insipidus?
Hypothalamic area may become diseased due to tumours or meningitis
May be damaged during surgery
What are the potential causes for peripheral diabetes insipidus?
The collecting duct may be insensitive to ADH
What are the characteristic symptoms of diabetes insipidus?
Passage of very large volumes of very dilute urine - polyuria
How can central diabetes insipidus be treated?
By giving ADH
What determines how much fluid we have in out compartments?
Osmotically active particles in each compound
What are the major ECF osmoles?
Na+ and Cl-
What are the major ICF osmoles?
K+ salts
What is the distribution of body water?
1/3 ECF
2/3 ICF
How many L of water do we have in our bodies?
42l
What is the main determinant in determining ECF volume?
Na+
What are the cardiovascular effects of increased salt and water loss?
decrease in venous pressure, decrease in venous return, decrease in atrial pressure, decrease in EDV, decrease in SV, decrease in CO , decrease in BP
What is the effect of increased sympathetic discharge on vessels?
Potent vasoconstriction
Increasing TPH
Increasing BP towards normal
What may the release of only ADH to bring back up ECF volume cause?
Hypoosmolarity as no ions or substrates have been absorbed too
What does renin allow the release of?
Angiotensin II
What does angiotensin II do (generally)?
Increases sodium chloride and water absorption
What is the effect of increased sympathetic discharge on the renal nerve activity?
Increases renal VC nerve activity
Increases renal arteriolar constriction and increases renin production
What does renin allow the release of?
Angiotensin II
Where is angiotensin II a strong vasoconstrictor in the kidney?
Afferent tubule
What is the effect of angiotensin II being a strong vascoonstrictor of the afferent tubule on both the forces and sodium absorption?
Decreases peritubular capillary hydrostatic pressure and increased oncotic pressure in the peritutublar capillaries in the proximal tubule
Meaning more reabsorption of Na+
What is the effect of renin and angiotensin on the distal tubule?
increase in renin increase in angiotensin II
increase in aldosterone increase in distal tubule Na+ reabsorption and less Na+ excreted.
What pressure determines the uptake of sodium in the proximal tubules as determined by angiotensin II?
oncotic pressure
What is the reabsorptive range for the proximal tubule under normal circumstances and when in volume deficit?
65% - normally
75% - vol. deficit
When does GFR begin to be affected?
When BP drops below 60mmHg
How is GFR maintained at different pressures?
Due to autoregulation
By means of vasconstriction of afferent and efferent arterioles
Does angiotensin II work largely on the afferent or efferent tubule?
Efferent
What is the regulation of distal tubule Na+ reabsorption under the control of?
hormone aldosterone
What type of hormone is aldosterone?
Steroid
Where is aldosterone released from?
Adrenal cortex
What are the 2 components of the juxtaglomerular apparatus?
Macular densa
Juxtaglomerular cells
Where are juxtaglomerular cells located?
Smooth muscle of the media of the afferent arteriole just before it enters the glomerulus
What do JG cells produce?
Renin
How does renin convert angiotensin to angiotensin II?
Renin splits off the decapeptide angiotensin I which is then converted by enzymes in the endothelium to the active octapeptide = angiotensin II
Where is angiotensin produced?
In the liver
Is angiotensin constantly produced?
Yes
Which enzyme converts angiotensin I to II?
ACE enzyme
What is the effect of ANG II on arteriole?
Vascoconstriction
Increasing BP
What is the effect of angiotensin II on cardiovascular control centres in the medulla?
Increases cardiac response
Increasing BP
What is the effect of angiotensin II on the hypothalamus?
Increase in ADH
and thirst
Increasing volume and maintaining osmolarity
What is the effect of ANG II on the adrenal cortex?
Increases aldosterone
Increasing Na+ reabsorption
Increasing vol. and maintaining osmolarity
What is the rate limiting step in the renin-angiotensin-aldosterone system?
Presence of renin
What controls renin release?
Decrease in pressure in the afferent arterioles
Increase in sympathetic nerve activity
What do JC cells act as?
Renal baroreceptors
What is the rate of renin secretion inversely proportional to?
The rate of delivery of NaCL at the macula densa
Decrease in NaCl delivery increases renin
What are the feedback controls of renin?
- Angiotensin II feeds back to inhibit renin.
2. ADH inhibits renin release (osmolarity control).
How much more potent is angiotensin II than NE as a vasoconstrictor?
4-8 x
What is the effect of angiotensin II on the hypothalamus?
Stimulated ADH secretion
Increasing water reabsorption from the CD
Also stimulates the thirst mechanism and salt apetite
How is GFR regulated in the tubules when GFR increases?
GFR increases
Flow through tubule increases
Flow past macular densa increases
Paracrine from macula densa to afferent arteriole
Resistance in afferent arteriole increases
Hydrostatic pressure in glomerulus decreases
GFR decreases
What 2 systems will oppose each other in a situation where a person has lost 3L of salt and water… then drinks 2 litres of pure water?
decrease in ECF osmolarity causes inhibition of ADH via osmoreceptors
decrease in ECF volume ADH via baroreceptors
Which system would take over in a situation where there was low ECF volume yet hypoosmolarity in the system?
Volume considerations have primacy if ECV is compromised
Why does low ECV take priority over hyposmolarity?
To save perfusion to the brain
What should be the replacement if there are large losses of salt and water?
Infuse or drink saline
Replace water and salt
What ion is the main determinant in maintaining ECF volume?
Na+
How does aldosterone affect Na+?
Promotes its reabsorption
What is the effect of ANP on Na+
Promotes Na+ excretion
What is the effect of aldosterone on potassium?
Increases K+ secretion
Why does aldosterone given to normal subject on an adequate Na+ diet cause weight gain?
Increase in weight
Due to increase retention of water with the sodium
When does ANP override the effect of aldosterone?
AN overrides effects of Na+ eabsorption because of volume expansion
Which system does ANP counteract?
Renin-angiotensin system
What system will kick in if there is increased weight gain due to increased aldosterone?
ANP will be secreted in response to expansion of ECF volume and cause natriuresis
What is natriuresis?
Loss of Na+ and H2O in the urine
Does ANP affect K+?
No
What is the effect ofK+ when the ANP system has kicked in to override the aldosterone system?
Na+ and H2O are excreted
However still K_ loss because still increase in K+ secretion
Which cells secrete ANP?
Atrial cells
What is the effect of ANP on the hypothalamus?
Less ADH secretion
What is the effect of ANP on the kidneys?
Increased GFR
Decreased renin
What is the effect of ANP on the adrenal cortex?
Less aldosterone
In uncontrolled DM what is the effect of excess glucose remaining in the tubule on water?
Exerts an osmotic effect to retain H2O in the tubule
What is the effect of increased glucose and water in the tubule on sodium?
Na+ concentration in the lumen is decreased because the Na+ is present in a larger volume of water
What is the effect of decreased Na+ conc. in the proximal tubule on the reabsorption of Na+?
Since Na+ gains access to the proximal tubule cells by passive diffusion down a concentration gradient created by active transport
Na+ reabsorption will be decreased as the concentration gradient difference will no longer be as high
Why does decreased Na+ reabsorption cause decrease glucose reabsorption?
Because they share a symport
What is the effect of decreased Na+, chloride and glucose reabsorption on the descending loop of henle?
Movement of H2O out the tubule is reduced because the glucose and excess Na+ exert an osmotic effect to retain H2O.
Increased H2O retention
Fluid in the descending limb is not so concentrated
What is the knock on effect of increased water retention in the descending loop on the ascending loop?
Fluid delivered to the ascending limb is less concentrated
NaCl pumps are gradient limited but the gradient is now much less
Considerable reduction in the NaCl reabsorbed from the ascending limb
What is the effect of a considerable reduction in the volume of NaCl and H2O reabsorbed from the loops of Henle on the distal tubule and interstitial gradient?
Large volume of NaCl and H2O is delivered to the distal tubule
Interstitial gradient is gradually abolished
What is the effect of increased NaCl delivery at the macula densa?
Rein secreton will be suppressed (will think the whole body has too much sodium)
Therefore Na+ reabsorption at the distal tubule will be decreased
What is the effect of a large volume of nearly isotonic urine being excreted on PV?
Decrease in PV
What will the decrease in PV stimulate the release of?
ADH
Why can ADH not be effective when a large volume of nearly isotonic urine is delivered to the distal tubule?
Because the interstitial gradient driving the water reabsorption has run down
What are 2 main signs of diabetes?
Increase urination
Increased thirst
How can DM cause a hyperglycaemic coma?
If ingestion of water is not adequate then hypotension may be so severe that there is lack of perfusion/BF to the brain
How can DM cause a hypoglycaemic coma?
Inadequate glucose for the brain due to low glucose levels
Why can we survive with one kidney?
Because one kidney has more nephrons than we need
When is measuring GFR particularly useful in clinical situations?
In patients with renal disease
When prescribing drugs will have to take into consideration their renal function
What tests are used to measure renal function?
Plasma clearance tests
How is plasma clearance of X measured?
Cx = (Ux) V/(Px)
Wha is Ux?
Urine concentration of X
What is V?
Urine flow rate
What is Px?
plasma concentration of X
What is inulin clearance a measure of?
GFR
Describe inulin at the nephron?
Inulin is freely filtered at the glomerulus and neither reabsorbed nor secreted
It is not metabolised by the kidney nor does it interfere with normal renal function
What clearance is routinely used to estimate GFR?
Creatinine clearance
Why will substances that are filtered and reabsorbed have a lower clearance than inulin?
Because (Ux) will be less than if only filtered
And (Px) will be higher
Why will substances that are filtered and secreted have a higher clearance than inulin?
Because (Ux) will be higher and (Px) will be lower
Why is inulin no longer used in clinical practice?
Because it is too cumbersome
What is creatinine the breakdown product of?
Muscle creatine
What is eGFR?
Estimated glomerular filtration rate
What factors affect serum creatinine?
Muscle mass
Dietary intake
Drugs
What is normal GFR approx?
100mls/min/1.73m squared
Why does glucose have a clearance of 0?
Because all is normally rebsorbed
Describe glucose clearance?
Glucose that is filtered is reabsorbed
Therefore clearance is 0
Why is urea clearance less than that of inulin?
Because some urea is reabsorbed
What is the clearance of urea?
50%
What is PAH used to measure?
Renal plasma flow
Describe PAH at the nephron?
Freely filtered at the glomerulus and then remaining PAH in plasma is actively secreted into tubule >90% of plasma is cleared of its PAH content in one transit of the kidney
Why does penicillin have a greater clearance than inulin?
Because it is filtered then secreted
How does urine flow from the kidneys to the ureters?
Via peristaltic contraction of the smooth muscle of the ureters
How do the ureters enter the bladder?
At an oblique angle
Why do the ureters enter the bladder at an oblique angle?
To prevent reflux
Does the composition of urine change once left the kidneys?
No
What is the external urethral sphincter made up of?
Skeleteal muscle
Under what control is the external urethral sphincter?
Under voluntary somatic control
Where does the bladder lie anatomically?
Midline posterior to pubic bones
Lies anterior to repro system and rectum
What muscle is the bladder made up of?
Smooth muscle
Detrusor muscle
What type of epithelium is found in the bladder?
Transitional epithelium
What is the trigon of the bladder?
Smooth triangular region of the internal urinary bladder formed by the two ureteric orifices and the internal urethral orifice.
What is the bladder overlain with?
Peritoneum
What do urethral obstructions cause?
Bilateral renal problems
What does a ureter obstruction cause?
Unilateral renal problems
Hoe does urethral obstruction cause renal problems?
Increased renal pressure
Back flow will eventually cause acute renal failure
Will oppose filtration
What is the normal daily variation of urine production?
750ml-2500ml
What is the normal clearance of glucose?
0
Normal pH
7.4 (7.37-7.43)
Normal pCO2
40mmHg (36-44)
5.3kPa
Normal HCO3-
24mmoles/L
(22-26)§
