Physiology Flashcards
Define Osmolarity
Concentration of osmotically active particles present in a solution, units = osmol/l or in body fluids mosmol/l
What 2 things do you need to know to calculate osmolarity?
the number of osmotically active particles and the molar concentration
Explain how a 150mM solution of NaCl has the same osmolarity as 100mM of MgCl2?
A 150mM solution of NaCl will have a osmolarity of 300mosm/l as there are 2 osmotically active particles present (1 sodium and 1 chloride ion) and 150 mols of it. 2x150=300.
100mM of MgCl2 would have a osmolarity of 300mosmol/l as there are 3 osmotically active particles present (1 magnesium and 2 chlorides) 3x100= 300mM.
Describe the difference between osmolarity and osmolality?
Osmolality and Osmolarity when talking about body fluid solutions can be used interchangeably. Osmolality has units of osmol/kg of water whereas osmolarity is osmol/l.
What is the approximate osmolarity of body fluids?
300 mosmol/l
Define tonicity?
The effect a solution has on cell volume. Solutions are hypo, hyper or isotonic.
Explain an isotonic solution?
Observe no change in cell volume if you were to add a cell to this solution
Explain a hypotonic solution
Hypo means less so the solution has less solute and therefore more water than the cell. Solution causes the cell to swell, cell increases in volume. As the solution has a greater concentration of water than the cell water moves into the cell by osmosis and the cell swells and due to lack of cell wall it bursts.
Explain a hypertonic solution?
Hypertonic solution has more solute than the cell but less water. Solution causes a decrease in cell volume, cell shrinks. As there is more water in the cell than outside water moves outside the cell by osmosis hence the cell shrinks.
Tonicity takes into account the permeability of membranes… what does this mean?
If there is a solute that can be actively transported this will change the tonicity of the solution but if it can’t be then you are just considering osmosis (passive diffusion of water from high to low concentration areas).
For example because a cell has transport systems for urea it will actively transport it across the cell and water will follow so solutions you would expect to be isotonic may actually cause lysis and bursting of the cell.
Total body water is about ___1__ in males and __2__ in females. This difference is because ____3____
1) 60%
2) 50%
3) females have a higher percentage of fat and fat cells don’t contain much water
Total body water consists as two major fluid compartments ______ (give percentages)
intracellular (67%) and extracellular (33%)
Describe the divisions of extracellular fluid?
Extracellular fluid can be divided into Plasma (aqueous component of blood) and Interstitial Fluid (immediate aqueous environment around cells). Negligible amounts of lymph and transcellular fluid e.g. CSF and Pleural fluid.
Describe how body fluid compartments can be measured?
Tracers
Useful tracers include tritiated water for total body weight, Inulin for ECF and labelled albumin for plasma
So if you can measure TBW and ECF you can therefore also calculate ICF by subtraction
How do tracers allow measuring of body fluid compartments?
By adding a known amount of tracer to unknown volume and allowing it to equilibrate with the water you can then measure the concentration of the tracer in the solution and use equation volume= dose/ concentration.
Describe the 3 inputs of water into the body?
Food intake
Fluid Intake
Metabolism
Describe 5 outputs of water from the body?
Faeces Urine Sweat Breathing/ Lungs Skin
Describe the insensible losses of water from the body?
Insensible losses are losses of water from body in which there are no physiological control mechanism and include skin (simple diffusion DIFFERENT from sweat) and lungs (lose water on exhalation)
Describe the sensible losses of water from the body?
Sensible losses have physiological mechanisms in place. For example sweat loss is determined by activity and temperature.
Largest loss of water from the body is?
production and excretion of urine (typically produce about 1500ml of urine a day)
Explain how in environmental changes water balance must be maintained?
Water balance in environmental changes is maintained by increased water ingestion, decreased excretion by the kidneys alone is insufficient to maintain water balance. We can never fully turn off urinary output as we need to get rid of some of the waste products by solution.
The ionic composition of plasma and interstitial fluid is different or near identical?
Near identical
Interstitial fluid is separated from intracellular fluid by a _____1______
Plasma fluid is separated from the interstitial fluid by the ___2_____
1) plasma membrane
2) capillary wall
What ions are the main ions of the ECF, what does this mean?
Sodium, chloride and bicarbonate ions
They are the major determinants of plasma osmolarity
Plasma osmolarity can be estimated by?
Doubling the plasma sodium concentration
What are the main ions of the ICF?
K+, Mg2+
Despite changes in composition and cells expressing different transporters the osmolarity of ICF and ECF are ________
near identical.
Define fluid shift?
movement of water between ECF and ICF in response to an osmotic gradient
What are the three challenges to fluid homeostasis?
Gain or loss of water
Gain or loss of salt
Gain or loss of an isotonic solution
Describe the effect of gain and loss of water on the ECF and ICF?
1) LOSS: Osmotic concentration of ECF increases due to dehydration > ECF solution becomes hypertonic so there will be movement of water from ICF so ICF volume decreases and ECF increases to restore osmotic balance
2) GAIN: Osmotic concentration of ECF decreases due to overhydration > ECF becomes hypotonic so water moves from ECF to ICF and as a result cell volume is increased and ECF is decreased
Describe the effect of gain and loss of salt on the ECF and ICF?
Sodium ions are relatively impermeable to cell membrane (so don’t include in gain or losses of salt all to do with ECF).
1) GAIN: If ECF gains salt ECF osmolarity would increase. ECF becomes hypertonic. So water leaves ICF and decreases in ICF and increases ECF.
2) LOSS: If the ECF loses salt osmolarity decreases so the solution becomes hypotonic, so water moves into the ICF and decreases in the ECF.
Describe the effect of gain or loss of isotonic solution on the ECF and ICF?
There is no change in osmolarity so only a change in ECF volume.
Why are kidneys vital for long term control of blood pressure?
Kidneys alter composition and volume of ECF and this includes the plasma.
Define an electrolyte?
any substance that dissociates into free ions when dissolved
2 reasons why electrolyte balance is important?
has knock on effect on water balance and concentrations of different electrolytes can effect cell function
Why is sodium balance important?
Major cation in extracellular fluid, therefore sodium and sodium salts are major determinant of osmolarity and ECF volume (WATER FOLLOWS SODIUM)
Input and output of sodium in the body?
Input: Dietary salts
Output: Urinary excretion
Why is potassium balance important?
Potassium plays an important role in establishing the membrane potential. So if there are changes in membrane potential in excitable cells (muscles, heart and nerves) then serious consequences.
__1__ of the plasma that enters the glomerulus is filtered
__2___ is not filtered and leaves through the efferent arteriole
1) 20%
2) 80%
Define filtration
Transfer of soluble components such as water and waste from the blood into the glomerulus
Define reabsorption
Absorption of molecules ions and water from glomerular filtrate back into the blood
Define secretion
Transfer of substances from the blood into the collecting duct
Define excretion
Removal of waste from the body
Equation for rate of filtration
[X] plasma x GFR (mass of X filtered into Bowmans capsule per unit of time)
Equation for rate of reabsorption
Rate of Filtration X - Rate of Excretion of X (what’s not in urine will have been reabsorbed)
Equation for rate of excretion
[X] urine x Vu (urine production rate)
Equation for rate of secretion
Rate of excretion of X- rate of filtration (- what you filtered into glomerulus so only taking the stuff in urine from secretion)
3 filtration barriers are:
Glomerular Capillary endothelium Basement membrane (Basal lamina) Slit process of podocytes
Define hydrostatic pressure?
Pressure exerted by blood which pushes it out of vessel and into tissue
Define Oncotic/ Osmotic Presure?
Pulling force which keeps blood in the vessel and out of the tissue due to the presence of plasma proteins
What are the four forces involved in glomerular filtration pressure?
Glomerular capillary blood pressure (BPGC)
Capillary oncotic pressure (COPGC)
Bowman’s Capsule hydrostatic pressure (HPBC which drives fluid into the capillary)
Bowmans capsule oncotic pressure (COPBC) which drives fluid into the Bowmans capsule
Net filtration pressure is of _____ favouring _____
10mmHg
movement of fluid into the Bowmans capsule from the capillaries
What pressure is the major determinant of GFR?
Glomerular capillary blood pressure
Describe how control of GFR by alterations in arterial blood pressure would be important in massive blood loss?
- If there was a fall in blood pressure due to massive haemorrhage, there would be hypovolaemia and hypotension.
- This is detected by baroreceptors in the aortic arch and carotid sinus.
- Sympathetic activity is increased.
- There is generalised arteriolar vasoconstriction so constriction of afferent arterioles
- This decreases GFR so decreases urine volume which helps compensate for the blood loss.
Describe how a kidney stone could affect GFR?
would increase the hydrostatic pressure of bowmans capsule therefore decreasing GFR
Describe how diarrhoea could affect GFR?
increase the capillary oncotic pressure (lost fluids so higher concentration of proteins) so decrease GFR
Describe how burns could affect GFR?
decrease capillary oncotic pressure (losing proteins to skin) so increase GFR
Define plasma clearance
• This is a measure of how good the kidneys are at cleaning the blood of a substance
• Defined as the volume of plasma completely cleared of a particular substance per minute
Each substance has different value
Regulation of GFR is by ______ and _______
extrinsic mechanisms and auto regulation
Describe extrinsic mechanisms to regulate GFR?
Regulating the renal blood flow regulates the GFR as if the glomerular capillary blood pressure falls so will the net filtration pressure. Vasoconstriction of the afferent arteriole decreases the GFR (as this decreases blood flow to the glomerulus so BP falls). Vasodilation of the afferent arteriole increases the GFR (as increases blood flow to the glomerulus so BP rises).
Vasoconstriction of the afferent arteriole _1____ the GFR
Vasodilation of the afferent arteriole __2____ the GFR
1) decreases as less blood flow so dropped BP
2) increases as more blood flow so increased BP
Changes in systemic BP don’t necessarily impact GFR as ___________________
auto regulation prevents short term changes in systemic arterial pressure changing GFR
What defines auto regulation?
It is intrinsic to the kidneys so no external input is needed
What are the two mechanisms of auto regulation for GFR in the kidneys?
Myogenic and Tubuloglomerular feedback
How does myogenic autoregulation of GFR work?
If smooth muscle becomes stretched when arterial pressure increases the smooth muscle with contract constricting the arteriole meaning no increase in GFR.
How does tubuloglomerular feedback auto regulation of GFR work?
Mechanism remains unclear but involves the juxtaglomerular apparatus. If GFR rises more NaCl flows through the tubule leading to constriction of the afferent arterioles stopping further increases in GFR
What cells sense the NaCl content of tubular fluid?
Macula densa cells
Define primary active transport
Energy is directly required to operate the carrier and the move the substrate against its concentration gradient
Define secondary active transport
This does not split ATP but instead uses second hand energy stored in the form of an ion gradient (usually Na+). It can occur by:
1) Symport- the sodium and the solute move in the same direction.
2) Antiport- the sodium and the solute move in opposite directions.
Define facilitated diffusion
Passive carrier mediated transport of a substance down its concentration gradient
Described what is reabsorbed in the proximal tubule?
67% of all salt and water are reabsorbed in the proximal tubule
100% of glucose and amino acids are reabsorbed here
Na+ reabsorption in the proximal tubule is driven by the __________ Na+ reabsorption also drives _______
basolateral NaKATPase
Cl- reabsorption through the paracellular pathway
In the proximal tubule water is reabsorbed by ____
osmosis
The tubular fluid is ______ when it leaves the proximal tubule
isosmotic (300mosmol/L)
What is the function of the loop of henle?
Creates a corticomedullary solute concentration gradient which enables the formation of hypertonic urine. Performs countercurrent multiplication.
Describe what countercurrent multiplication is?
Countercurrent multiplication is a mechanism that expends energy to create a concentration gradient. The purpose is to concentrate the medullary interstitial fluid. Refers to the idea that water can be reabsorbed passively in the descending limb as have used energy in the ascending limb to reabsorb ions and make the medulla salty. The amount of water reabsorbed into the interstitial is proportional to the ions.
The descending limb reabsorbs __1___ but is impermeable to ___2____
1) water
2) ions
The ascending limb reabsorbs __1____ but is impermeable to ___2______
1) Na+, Cl- and K+
2) water
Why is countercurrent multiplication important?
It enables the kidneys to produce urine of different volume and concentration according to circulating amounts of ADH
Explain why vasa recta and their structure are important
Essential blood flow through medulla tends to wash away NaCl and urea.
To minimise this problem:
1. Vasa recta capillaries follow hairpin loops
2. Vasa recta capillaries freely permeable to NaCl and water
Blood flow to vasa recta is low (few juxtamedullary nephrons
Passive exchange across the endothelium preserves the medullary gradient
Tubular fluid leaving the loop of henle entering the distal tubule is _________ to plasma
The surrounding interstitial fluid of the renal cortex is ______
hypo-osmotic (100mosmol/L)
300mosmol/L
Have reabsorbed lots of ions and water in the loop so don’t have much solute left hence hypo osmotic
The collecting duct is bathed by progressing ______ concentrations of surrounding interstitial fluid as it descends through the medulla
increasing (300-1200mosmol/L)
All tubules empty into ______
cortical collecting ducts
More than _____ of filtered ion loads are reabsorbed before the filtrate reaches the distal tubule but the residual load of _________
95%
NaCl is very important for salt balance
The late collecting duct has a low ___1___ permeability but permeability to _2_____ and ___3__ which is influenced by ___4__
1) ion
2) water
3) urea
4) ADH
What causes and where is ADH released from?
Low body water in hypovolaemia/ hypotension/ increased serum osmolarity sensed by body and ADH released from posterior pituitary
ADH results in ____ water being reabsorbed in the collecting duct of the kidneys by _______
more
insertion of aquaporin 2 channels into the membrane
Most important stimulus for ADH release? What are others?
Most important= hypothalamic osmoreceptors
Other= stretch receptors in the heart or gut
High ADH =
Low ADH=
High ADH= high water permeability and hypertonic urine
Low ADH= low water permeability and hypotonic urine
Aldosterone is a ____ hormone secreted from the ____
steroid
zona glomerulosa of the adrenal cortex (think glomerulus kidneys have a glomerulus and aldosterone acts directly on the kidneys cortisol and androgens do not!)
Aldosterone is secreted in response to _______
Rising potassium, falling sodium concentration or as part of activation of RAAS (system that increases BP)
What happens when aldosterone is absent?
No potassium is excreted > THIS IS WHY YOU GET HYPERKALAEMIA IN ADDISONS DISEASE
What 3 things can switch on the RAAS system?
Renal artery hypotension (caused by systemic hypotension), stimulation of renal sympathetic nerves and decreased [Na+] in tubular fluid sensed by macula densa cells.
Describe what happens when the RAAS system is activated?
Renin is produced by the kidneys which stimulates formation of angiotensin 1, ACE converts this to angiotensin 2. Angiotensin 2 does 3 things: systemic vasoconstriction, stimulate thirst and ADH release, stimulate aldosterone release. Aldosterone increases Na+ and H2O reabsorption but increases K+ and H+ secretion.
What system counteracts the RAAS system?
Atrial Natriuretic Peptide system
What produces ANP and where is it stored?
The heart- stored in atrial muscle cells
ANP is released when _______
cells are mechanically stretched due to an increase in the circulating plasma volume (ie increased BP)
Action of ANP
Promotes excretion of Na+ and diuresis (increased urination) thus decreasing plasma volume. ANP also exerts effects on the CVS to lower blood pressure.
What is erythropoietin and where is the major site of production?
Hemapoeitic growth factor that stimulates RBC formation
Major site of production is the kidney
Define strong and weak acids
Strong acids fully dissociate in solution, weak acids only partially dissociate into ions
Define strong and weak bases/ alkalis
Strong Alkalis fully dissociate in solution, weak alkalis only partially dissociate into ions
pH of arterial blood = __1___
pH of venous blood = ___2____
Average pH of blood = ___3____
pH of ECF = ___4_____
1) 7.45
2) 7.35
3) 7.40
4) 7.40
Acidosis can lead to __1____ of the CNS
Alkalosis can lead to __2_____ of the PNS and then CNS
1) depression
2) over excitability
H+ is continually being added from 3 sources which are?
1) Carbonic acid formation
2) Inorganic acids produced breakdown of nutrients
3) Organic acids resulting from metabolism
Define a buffer solution?
One that can resist pH change upon the addition of an acidic or basic component.
An acid buffer will consist of __1____
A basic buffer will consist of ___2___
1) a weak acid and one of its salts
2) a weak base and one of its salts
What is the most important physiological buffer system?
CO2 - HCO3 system
Carbon dioxide and water form carbonic acid, this reaction is catalysed by the enzyme?
Carbonic anhydrase
What is Le Chatlier’s principle?
States that if a change is applied to a system in equilibrium it will move to counteract that change
Describe how to the CO2-HCO3 buffer system works?
If extra H+ is added these will react with HCO3 forming H2CO3 as the equilibrium wants to be pushed to the left to counteract the change of increased H+
If OH- is added they will react with H+ to form water. This moves the equilibrium to the right to produce more H+ to counteract there loss as they are removed as water.
Describe the Henderson Hasselbach equation? How is this relevant?
This relates the pH of the solution with the dissociation constant and concentration of these in solution. Hence [HCO3] and [CO2] expressed as PCO2 is very important in maintaining a normal pH
HCO3 concentration is controlled by the ____1____
PCO2 is controlled by the ____2_______
1) kidneys
2) lungs
2 mechanisms by which the kidneys control HCO3 concentration? What are both of these mechanisms dependent on?
1) Variable reabsorption of filtered HCO3-
2) Kidneys can add new HCO3- to the blood
Both dependent on H+ secretion into the tubule
Why is reabsorption of HCO3 important?
A lot is initially filtered out of the blood
Describe what happens to H+ in the tubule?
H+ secretion drives reabsorption of HCO3- which is needed to act as a buffer.
H+ in tubule will form H2PO4 by combining with phosphate or NH4+ by combining with ammonia. The purpose of this is to allow more H+ to be excreted as there is a limit to how much free H+ can be excreted in the urine.
Why does some H+ combine with ammonia or phosphate in the tubule before excretion?
allows more H+ to be excreted as there is a limit to how much free H+ can be excreted in the urine. It also allows you to “make” more bicarbonate.
Describe compensation of acid base balance disruption vs correction
First priority in disruption is to restore pH to 7.4 which involves compensation.
Compensation= restoration of pH irrespective of what happens to [HCO3-] and PCO2
Correction= restoration of pH and [HCO3-] and PCO2 to normal
Cause of respiratory acidosis?
Due to retention of CO2 in the body e.g. COPD, airway restriction or respiratory depression
In respiratory acidosis CO2 retention drives the equilibrium to ________ resulting in ________
right
resulting in an increase in H+
How does the renal system compensate in respiratory acidosis?
H+ secretion is stimulated, all filtered HCO3- is reabsorbed and as H+ is excreted new HCO3- can be added to the blood. In acute there is a slight increase in HCO3- but in chronic respiratory acidosis e.g. in COPD there are actually changes in the tubules with transporters that enhances the bicarbonate reabsorption.
RESPIRATORY ACIDOSIS
Primary changes=
Secondary changes=
Primary changes= Increased PCO2 and decreased pH
Secondary changes= Increased HCO3-
Correction of respiratory acidosis involves _______
Lowering PCO2 by restoration of normal ventilation
Causes of respiratory alkalosis?
Due to excessive removal of CO2 by the body e.g. low inspired PO2 at altitude, hyperventilation in fever or brainstem damage or hysterical over breathing
In respiratory alkalosis excessive CO2 removal drives the eq to the __1___ and both ___2_____ fall which causes a pH __3___
1) left
2) [H+] and [HCO3-]
3) pH rise (as pH is simply a measure of free H+ ions and there are now less)
Describe renal system compensation in respiratory alkalosis?
H+ secretion into the tubule is decreased. H+ secretion now becomes insufficient to reabsorb the filtered HCO3- (this results in alkaline urine). Renal compensation further lowers the [HCO3-].
RESPIRATORY ALKALOSIS
Primary changes=
Secondary changes=
Primary changes= decreased PCO2, increased pH
Secondary changes= decreased HCO3-
Correction of respiratory alkalosis?
Restoration of normal ventilation
Causes of metabolic acidosis?
Due to excess H+ from any source other than CO2 e.g. ingestion of acids or acid producing food stuff, excessive metabolic production of H+ e.g. lactic acid in exercise or ketoacidosis, excessive loss of base from the body in diarrhoea.
What happens to HCO3- in metabolic acidosis and why?
it is depleted as a result of buffering excess H+ or loss of HCO3- from the body
Describe respiratory compensation of metabolic acidosis?
Increase in ventilation to blow off more CO2
Once the underlying cause is sorted how does the body correct metabolic acidosis?
Filtered HCO3- is very low so is readily reabsorbed and H+ secretion continues and more HCO3- is generated. The acid load is excreted in the urine and [HCO3-] is restored.
METABOLIC ACIDOSIS
Primary changes=
Secondary changes=
Primary changes= decreased pH and decreased HCO3-
Secondary changes= Decreased PCO2
Causes of metabolic alkalosis?
Excessive loss of H+ from the body e.g. loss of HCl from the stomach in vomiting, ingestion of alkali or alkali producing foods, aldosterone hyper secretion.
Why does HCO3- rise in metabolic alkalosis?
As a result of loss of H+ or addition of HCO3- that has caused the alkalosis
Describe respiratory compensation of metabolic alkalosis?
Increased pH slows ventilation. As CO2 is retained PCO2 rises so equilibrium is pushed to the right increasing [HCO3-] and importantly [H+]
Describe how the body correct metabolic alkalosis once the underlying cause is corrected?
Filtered HCO3- load is so large compared to normal that not all of the filtered HCO3- is reabsorbed. HCO3- is excreted in the urine and concentration falls back to normal.
METABOLIC ALKALOSIS
Primary changes=
Secondary changes=
Primary changes= increased pH and increased HCO3-
Secondary changes= Increased PCO2
Describe the blood flow through the kidneys in both types of nephrons?
Cortical nephrons (80%) From artery > afferent arteriole > efferent arteriole > Peritubular capillaries (which follow tubules) > venues > vein
Juxtamedullary nephrons (20%) no peri tubular capillaries instead have vasa recta which follow the shape of the loop of henle
What type of cells and where produce renin?
Granular cells in the juxtaglomerular apparatus
What s the juxtaglomerular apparatus?
Portion of distal tubule that passes in-between the fork of the efferent arteriole and afferent arteriole contains specialised cells that sense NaCl and tubule and granular cells that produce renin
What type of nephrons are responsible for concentrating urine? What percentage of nephrons are these in humans? What animals is this higher in?
Juxtamedullarly nephrons takes up 20%
Dessert animals have more than 20% as they need to concentrate urine more to conserve water
What is the GFR in a healthy adult roughly?
125 ml/min
The diameter of the afferent arteriole is ______ than the diameter of the efferent arteriole
greater
Glomerular filtrate is ________ plasma formed as a result of ______ forces acting across the glomerular membrane
protein free
passive
Glomerular capillaries are _______ porous than capillaries elsewhere in the body
100 x more
Glomerular capillary barrier excludes ___1____ and the basement membrane has a net ___2___ which excludes ______3_____
1) RBCs
2) negative charge
3) large plasma proteins
Describe the gold standard way of calculating GFR and the more practical way?
Inulin clearance= GFR= 125ml/min because it’s freely filtered at the glomerulus and is not reabsorbed or secreted however as it is exogenous it needs constant infusion
Creatinine a product of muscle breakdown can give an approximation as similar to inulin (but does undergo small secretion making it less accurate) and is produced at a fairly constant rate
Explain glucose clearance?
Glucose should be fully reabsorbed therefore clearance =0
Describe 2 ways a substance can have a clearance of 0
If it is fully reabsorbed
If it undergoes no filtration or secretion
When will clearance be less than GFR? Give an example?
Urea
When a substance is freely filtered only partly reabsorbed and not secreted.
When will clearance be more than GFR? Give an example?
H+ ions
When a substance is filtered and secreted but not reabsorbed
Net reabsorption has occurred if clearance is __1__ than GFR
No reabsorption or secretion has occurred if ___2____
Net secretion has occurred if clearance is __3____ than GFR
1) less
2) clearance = GFR
3) more
Why is Para-aminohippurate used clinically to measure renal plasma flow?
It is freely filtered at the glomerulus, secreted into the tubule (not reabsorbed) and completely cleared from the plasma.
Renal plasma flow =
650 ml/mim = clearance of PAH
Define filtration fraction? What is it in healthy individual? How is it calculated?
Filtration fraction= fraction of plasma flowing through the glomeruli that is filtered into the tubules
= GFR/ RPF = 125/650 = 20%
Reabsorption is specific or not specific to a substance?
Filtration is specific or not specific to a substance?
Reabsorption is specific
Filtration is relatively non-specific
Glomerular filtrate is almost identical to plasma but _____________
lacking RBCs and large plasma proteins
Sodium ions can be reabsorbed everywhere apart from ________
the descending loop of henle
Apical membrane is touching the ?
Basolateral membrane is touching the?
Apical is facing the tubule, basolateral into space next to capillary
Define renal threshold?
The plasma concentration of a particular substance at which its Tm is reached and the substance first appears in the urine
Define Tm?
Tm represents the maximum rates at which reabsorption or secretion can take place before transport systems become saturated. If transport mechanisms are saturated the substance will start to be excreted e.g. in hyperglycaemia when you get glycosuria.
Fluid leaving the proximal tubule is ____1_____
Fluid leaving the descending limb is ____2______
Fluid leaving the ascending limb is _____3______
1) iso-osmotic
2) hyper-osmotic
3) hypo-osmotic
As well as sodium what else helps set up the gradient in the loop of henle? What is the name given to this mechanism of 2 substances?
Urea
The 2 solute hypothesis
What 2 things make up the countercurrent exchanger?
Loop of Henle + Vasa Recta
Aldosterone is ___1___ hormone and will have a ____2___ effect than ADH which is a ___3___ hormone
1) steroid
2) slower
3) peptide
Describe the difference ways potassium and sodium concentration promote secretion of aldosterone?
An increase in potassium concentration directly stimulates the adrenal cortex to secrete aldosterone
A decrease in plasma sodium promotes indirect secretion of aldosterone by RAAS
ACE is predominantly found in the capillaries of the _____
lungs
Acidosis is pH less than __1____
Alkalosis is pH more than ___2______
1) 7.35
2) 7.45
Explain how HCO3 is “reabsorbed” in the kidney?
HCO3 is freely filtered but cannot cross the apical membrane so reabsorption is indirect, the HCO3 in tubular fluid combines with H+ secreted into the tubule forming H2CO3 which dissociates to CO2 and H2O which enters the cell by diffusion. This then dissociates to HCO3- and H+. The H+ is secreted back into the tubule and HCO3- goes into the interstitial fluid
Describe how the kidneys can make more HCO3?
If HCO3 is depleted H+ combines with phosphate, H+ secretion allows dissociation of carbonic acid formed from CO2 and H2O in the cell allowing formation of bicarbonate ion that can be released.
Why would it be useful to measure the amount of titratable acid in the urine?
The excreted titratable acid = the amount of new HCO3 added to the blood
What is the vast majority of H+ secretion used for?
HCO3 reabsorption to prevent generation of acidosis
In metabolic acid base disturbance:
_____1________ occurs immediately
______2________ occurs within minutes
_______3__________ occurs within hours
_________4_________ occurs within days to weeks
1) extracellular buffering
2) Respiratory compensation
3) intracellular buffering
4) renal excretion of H+
