Renal Physiology Flashcards
How is micturition controlled
cortical centre causes bladder sensation and conscious inhibition of micturition
Where is the micturition centre
pons
where is the micturition reflex
s2-s4
Relaxation of internal urethral sphincter is said to be
autonomic - sympathetic
relaxation of external urethral sphincter is said to be
somatic
contraction of detrusor muscle is said to be
autonomic parasympathetic
How much protein free filtrate of plasma is there in renal physiology
20%
What is the glomerular filtration rate
180/l a day
what does the glomerular filtration rate do
regulates ecf volume and composition
Where do the substances that the body doesn’t want go in renal physiology
tubule then excreted
substances the body wants in renal physiology are
reabsorbed
which substances are reabsorbed in proximal tubule
NACI
Water
Amino Acid
sugar
which substances are reabsorbed in distal tubule
NaCI
Water
which substances are secreted in proximal tubule
Organic Ions
Drugs
which substances are secreted in distal tubule
K and H
Kidneys blood flow is
1200mls
How much of cardiac output does kidneys receive
20-25%
Kidneys weight what of Body Weight
<1%
What is filtered through into Bowmen Capsule
Fraction of plasma no red cells
Remainder of Plasma that doesn’t go through Bowman capsule goes via
efferent arterioles into peritubular capillaries and then to renal vein
Plasma constitutes how much of total body volume
55%
what is renal plasma flow total
660mls
GFR is normally
125mls
how much of renal plasma becomes glomerular filtrate
19%
Glomerular filtration is dependent on balance between
hydrostatic forces favouring filtration and oncotic pressures forces favouring reabsorption (starling forces)
what prevents filtration of larger proteins
basal lamina of glomerulus
Why is glomerular capillary pressure higher than in most of capillaries in body
afferent arteriole short/wide/little resistance to flow
blood arriving at glomerulus has what hydrostatic pressure
high
The efferent arteriole in glomerulus is
Long/Narrow/High Resistance
If you have a high resistance hydrostatic pressure upstream is
increased and pressure downstream decreased
what contributes to very high glomerular capillaries pressure
afferent and efferent arterioles
at glomerular capillaries what exceeds oncotic pressure
hydrostatic pressure favouring filtration
What occurs at glomerular capillaries
only filtration
What is net filtration pressure at glomerulus
10mmHg
What factors affect GFR
Afferent and Efferent Arteriolar Diameter/Resistance.
Subject to Extrinsic Control
a) Sympathetic VC nerves - afferent and efferent constriction, greater sensitivity of afferent arteriole.
b) Circulating catecholamines - constriction 1 degree afferent
c) Angiotensin II to constriction, of efferent at [low], both afferent and efferent at [high].
Afferent and Efferent Arteriolar Diameter/Resistance is subject to what control
extrinsic control
There is greater sensitivity of what arteriole afferent or efferent
afferent
circulating catecholamines cause what to happen to afferent arteriole
constriction by 1 degrees
angiotensin ii causes constriction of efferent at what pressure
low
angiotensin ii causes constriction of afferent and efferent at what pressure
high
GFR does what as glomerular capillary pressure increases
It increases
decreased capillary blood pressure causes
decreased GFR and RBF through increased resistance in afferent arteriole
when resistance increases in afferent arteriole what happens to gfr and capillary blood pressure
decrease
in increased resistance to efferent arteriole what happens to ph and gfr
increased but rbf decreases
Renal vasculature has a intrinsic or extrinsic ability
intrinsic which allows for auto regulation
When MBP is below 50
Filtration ceases
If mean arterial pressure increases what happens to afferent arteriolar constriction
increases preventing rise in glomerular pic
dilation occurs if what happens
pressure falls
auto regulation is independent of
everything
how much plasma volume enters afferent arteriole
100%
how much fluid is reabsorbed from afferent arteriole plasma volume
19%
what is responsible for reabsorption
peritubular capillaries
how much is filtered through glomerulus into renal tubule
180 l/day
what is hydrostatic pressure figure
15mmhg
what only occurs at glomerular capillaries
filtration
how much plasma filters into bowmen capsule and is known as filtration fracture
20%
which substances are reabsorbed by carrier mediated transport system
glucose amino acids organic adis sulphate phosphate ions
If Maximum Transport Capacity is exceeded then what happens to excess substrate
it enters urine
what is renal threshold
plasma threshold at which saturation occurs
How much glucose can be reabsorbed
up to 10mmols
what is the renal plasma threshold for glucose
10mmls the rest will be excreted in urine
does kidney regulate glucose or insulin
no
the appearance of glucose in urine in diabetic patients is called
glycosuria
glycosuria is due to failure of
insulin not the kidney
Which substances does the kidney regulate by Tm mechanism
Sulphate and Phosphate
which substances does the kidney not regulate
Glucose
Insulin
Amino Acids
which ions are the most abundant in ECF
Na+
how much Na+ is reabsorbed
99.5%
65-75% of ion reabsorption occurs in
prox tubule by active transport which establishes gradient
ion reabsorption does not occur by
Tm mechanism
where are active Na+ pumps found
basolateral surfaces where high density of mitochondria
basolateral surfaces having na+ pumps what does this do to epithelial cells
decreased na+ in epithelial cells
increasing gradient for na ions to move into cells passively across luminal membrane
na+ is pumped out basolateral side of cell by what
Na+/K+ ATPase
Where has higher permeability to Na+ ions than most other membranes in body
Brush border of prox tubule
Negative Ions such as CI diffuse how across prox tubular membrane
Passively by Electrical Gradient Na+ made by it’s active transport
The active transport of Na+ out of the tubule followed by Cl- creates an
osmotic force drawing water out into tubules
H2O removed by osmosis from the tubule fluid does what
concentrates all substances left in tubule creating outgoing concentration gradients
How is na+ reabsorbed
active transport
what will determine extent of concentration gradient
amount of water removed
tubule membrane is what to urea
moderately permeable
how much urea is reabsorbed in tubule
50%
For insulin and mannitol what is the tubular membrane to them
impermeable so it passes out into urine
What establishes the gradients down with ions, water and solutes pass passively
active transport of Na+
Low Na+ inhibits what
glucose transport
To transport glucose what does Na+ need
SGLT
Where are substances secreted from
Peritbular capillaries into tubule lumen.
Where is Penicllin, Asprin, PAH, Choline, creatinine secreted
Prox Tubule
How to calculate amount of solute excreted
Amount Filtered - Amount Reabsorbed + Amount Secreted = Amount of Solute Excreted
What is the major cation in cells of body and essential for life
K+
Normal ECF K+
4%
If K is up to to 5.5mmols =
Hyperkalaemia
Hyperkalaemia leads to
Decreased RM potential of excitable cells = Vent Fib = Death
If K is <3.5 =
Hypokalaemia
Hypokalaemia =
Increased RM Potential = Hyperpolarise = Arrythmias = Death
what happens to K Filtered at Glomerulus i
reabsorbed with some at prox tubule
Changes in K excretion are due to changes in
secretion in distal tubule
Any increase in renal tubule cell K+ due to increased ingestion will do what to K+
increase secretion
Any decrease in renal tubule cell K+ will
reduce secretion
what is k secretion regulated by
adrenal cortical hormone aldosterone
Aldosterone stimulates kidneys to stimulate
increase in renal tubule cell k secretion
H+ ions are actively secreted from
tubule cells into lumen
K+ is regulated by
aldosterone
Where is a major site of reabsorption in kidney
proximal tubule in particular 65-75% of all NaCI and H20
How much albumin gets through Proximal Tubule
30g per day which 0.5 of total amount presented at glomerulus
The rest of Albumin is reabsorbed where
By Tm carrier mechanism in Prox Tubule
Where is a major site of tubular secretion in kidney
proximal tubule
collecting duct of medulla is site of
water regulation under control of ADH
The fluid that leaves the proximal tubule is
isomotic with plasma
All solute movements from proximal tubule is accompanied by
equivalent water movements so maintain osmotic equilibrium
Nephrons have all of their proximal and distal tubules in
Cortex
Maximum concentration of urine that can be produced by the human kidney
1200-1400mOsmoles
The urea, sulphate, phosphate, other waste products and non-waste ions (Na+ and K+ ) which must be excreted each day amount to
600 mOsmoles requires minimum water loss of 500mls
even if no water and kidneys functioning what volume will be excreted every day
600mOsmoles
In conditions of excess H20 intake, H20 is excreted in excess of
solute
What acts as counter current multiples in renal physiology
loops of hence of juxtamedullary nephrons
Loops of hence and juxtamedullary nephrons allows fluid to do what
flow down descending limb and up ascending limb
Ascending limb of loop of hence actively co-transports what?
Na+ and CI+ ions out of tubule lumen into interstitum
The ascending limb is impermeable to
water
descending limb is freely permeable to
water
what is a key step in loop of hence counter current multiple
active removal of NaCi from ascending limb. Decreasing osmolarity in tubule and increase in interstitum.
H20 does not stay in interstitum it is reabsorbed by
High osmotic pressure
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.
As more and more concentrated fluid is delivered to the ascending limb, what happens to interstitial
becomes more and more concentrated.
Vertical gradient in interstitium goes from
300 to 1200
Active transport of NaCi is out of
ascending limb
what can abolish active transport of NaCi out of ascending limb
frusemide therefore kidney would only produce isotonic urine
How does countercurrent multiple work
Concentrates fluid on the way down and promptly re-dilutes it on the way back up, NOT by adding H2O, but by removing NaCl.
how much of initial filtrate is removed from loop of hence
15-20%
fluid which enters distal tubule is what than plasma
more dilute
what is the overwhelming significance of countercurrent multiple
creates increasingly concentrated gradient in interstitial
Countercurrent Multiple also delivers what to distal tubule
Hypotonic Fluid
Fluid enters distal tubule at
300
fluid leaves distal tubule at
100
Hypotonic fluid needs to be delivered to
distal tubule
What acts as countercurrent exchangers
Peritubular Capillaries
Vasa recta are freely permeable to what
Water and Solutes and equilibrate with medullary interstitial gradient
Vasa Recta does not disturb
Interstitial Gradient
Vasa Recta delivers what and removes what
delivers 02
removes volume
functions of vasa recta
provide 02 for medulla
does not disturb gradient
removes volume from interstitial up to 36l/day
flow rate through vasa recta
is very low
site of water regulation is
collecting duct whose permeability is under control of ADH
what is ADH also called
vasopressin
collecting duct is under control of
ADH/Vasopressin
Isomotic fluid leaving prox tubule becomes progressively more what in descending limb
concentrated
what creates hyposomotic fluid
removal of solute in thick ascending limb
what controls distal nephron permeability to water and solutes
hormones
urine osmolarity depends on
reabsorption in collecting duct
water regulation is controlled by
ADH/Vasopressin
polypeptide (9aas) is synthesised in
synthesized in the supraoptic (SO) and paraventricular (PVN) nuclei of the hypothalamus in the brain.
vasopressin/adh half life
10 mins
What happens when the effective osmotic pressure of plasma increases
Rate of discharge of ADH secreting hormones in SO and PVN Increases = more release of adh from posterior pituitary
where is adh released from
posterior pituitary
changes in neuronal discharge are mediated by
osmoreceptors in ant hypothalamus
lateral hypothalamus mediates
thirst
what happens when osmolarity increases
h20 increased out of cell
cell shrinks
increased neural discharge and adh secretion
what happens when osmolarity decreases
h20 enters cell
cell swells
decreased neural discharge and adh secretion
normal plasma osmolarity is
289-290
what happens with increase in osmolarity that does not cause increase in tonicity
no adh increase
the amount of urine produced depends on
adh and amount of solute to be excreted
urine osmolarity depends on
reabsorption in collecting duct
If ADH is present then water is
able to leave collecting duct
what creates hypertonic medullary interstitial gradient
countercurrent multiple of loop of henle
If maximum ADH then contents become highly concentrated where
Tip of Medulla and small volume of highly concentrated urine produced
When there is no adh what happens to collecting ducts in terms of water
Collecting ducts impermeable to water
Large volume dilute urine excreted
In water deficit
we keep water
what influences concentration of urea in duct in presence of adh
movement of water out of collecting ducts
permeability of medullary collecting duct enhanced by
adh
Urea needs to be reabsorbed why
If held in tubule it would hold water in tubule and reduce potential for rehydration
When ECF volume increases what does ADH do
Decrease
when ecf volume decreases what does adh do
Increase
where are low p receptors found
L+R Atria and Great veins
Where are high p receptors found
carotid and aortic arch baroreceptors
adh secreting cells are
neurons
what else can stimulate increase adh
pain emotion stress exercise nicotine morphine trauma surgery
what can stimulate decrease adh
alcohol
where is adh/vasopressin released from
posterior pituitary
when osmolarity is greater than 280mmo what receptors set of f
Hypothalamic Osmoreceptors to Interneurons to Hypothalamus overall water reabsorption
when decreased blood pressure what do you want to happen to water reabsorption
increased
What happens when collecting duct insensitive to adh
peripheral diabetes insipidus
cranial diabetes insipidius can be treated with
adh
what is adh receptor called
v2
what are the major ECF osmoses
Na+ and CI+
what are major ICF osmoles
K+
what happens when decreased ECF volume
hypovolaemia
Increased salt and water loss in diarrhoea, vomit or excess sweat causes everything to
decrease due to
- increased renal arterial constriction
- increased renin
- increased angiotensin II
- Increased Symptoms VC and TPR and BP
- Increased adh
- Increased prox tubule NaCi and H20 reabsorb
- Increased aldosterone and distal tubule reabsorption
Changes in proximal tubule Na+ reabsorption are due to
changes in the rate of uptake by the peritubular capillaries.
changes in the rate of uptake by the peritubular capillaries determined by
osmotic pressure
↑in Na+ reabsorption is because of
greater reabsorptive forces in the peritubular capillaries.
The active transport mechanism that operates on the luminal surface of the thick ascending loop of Henle, actually involves
K+ ions as well as NaCI
Passive Process
Energy by Active Transport
Loop Diuresis can cause
K+ ion wasting
Any solute which remains in the tubule can cause an
osmotic diuresis to eliminate excess
How to restore Alkalosis
NaCi
Liquiorice can cause
Metabolic Alkalosis as it is similar to aldosterone
Only what ion contribute to Ph
Free H+ Ions
What represents respiratory acid
CO2 + H2O H2CO3 H+ + HCO3-
Carbonic acid can cause
Increase in Ventilation
H2s04 is produced from
Phospholipids
normal diet net gain to body of 50-100 mols of what a day
organic acids
Major source of alkali is
oxidation of organic anions such as citrate
what are buffers
Minimize changes in pH when H+ ions are added or removed
what does Henderson hasselbalch equation define
pH in terms of the ratio of [A-]/[HA] NOT the absolute amounts
Most important extracellular buffer
Bicarbonate
Normal ph
7.4
Range of ph compatible with life
7-7.6
normal pco2 compatible with life
5.3
elimination of h from body is by
kidneys coupled to regulation of plasma Hco3
Intracellular buffer in erythrocytes
haemoglobin
primary intracellular buffers
proteins
phosphates
In acidosis the movement of K+ OUT OF CELLS INTO PLASMA CAN CAUSE
HYPERKALAEMIA = VENT FIB = DEATH = DEPOLARISE
Increases in H+ in acidosis leads to
HYPERKALAEMIA
How do the kidneys regulate Hco3
Reabsorb filtered HCo3
Generate new Hco3
Where is H+ ion secretion taking place
tubule cells into lumen
Mechanism of Reabsorption of HCo3
Active H+secretion from the tubule cells
coupled to passive Na+ reabsorption
filtered HCO3- reacts with the secreted H+ to form H2CO3. In the presence of carbonic anhydrase on the luminal membrane leads to CO2 and H2O
CO2 is freely permeable and enters the cell
Within the cell, CO2 H2CO3 in the presence of carbonic anhydrase (present in all tubule cells) which then dissociates to form H+ and HCO3-
Carbonic Ahydrase is present
In all tubule cells
HCO3 ions pass into
peritubular capillaries with Na+
Bulk (90%) of HCo3 reabsorption occurs in
Prox Tubule
There is no excretion of H+ ions during
HCo3 reabsorption
Minimum Urine PH
4.5-5
