Transcript kidney 6
بسم هللا الرحمن الرحيم
﴿و ما أوتيتم من العلم إال قليال﴾
صدق هللا العظيم
االسراء اية 58
By
Dr. Abdel Aziz M. Hussein
Lecturer of Medical Physiology
Measurement of :
1. Reabsorption rate = filtered load – excretion rate
2. Secretion rate = excretion rate – filtered load
3. Excretion fraction (fraction excretion) (Fex):
•
It is the fraction of the filtered load of substance that's
excreted
Measurement of :
4. Clearance ratio;
• It is the ratio between clearance of a substance x and
clearance of inulin
1. If Clearance ratio = 1 substance is not reabsorbed
nor secreted i.e. substance reacts as inulin).
2. If the ratio is < 1 substance is partially reabsorbed
as urea.
3. If ratio equals zero substance is filtered but
completely reabsorbed e.g. glucose when Pglucose <
renal threshold.
4. If ratio is > 1 substance is secreted e.g. PAH.
125 ml/min
124 ml/min
1 ml/min
Clearance ratio is = 1
125 ml/min
124 ml/min
1 ml/min
Clearance ratio less than 1
125 ml/min
124 ml/min
1 ml/min
Clearance more than 1
125 ml/min
124 ml/min
1 ml/min
Clearance = zero
Transport Maximum (Tm
Def.,
• It is the maximal amount of substance transported by
renal tubules per min
Types:
• 2 types;
1. Reabsorptive Tm e.g. Tm for glucose (TmG)
2. Secretory Tm e.g. Tm for PAH (TmPAH)
Filtered load = 3
Normal Plasma Concentration
Reabsorption rate = 3
Filtered load = 3
Normal Plasma Concentration
↑ Filtered load = 6
High Plasma Concentration
Reabsorption rate = 4
(Tm)
Filtered load = 6
Excretion rate = 2
Transport Maximum (TmG)
Def.,
• It is the maximum amount of glucose reabsorbed by
the renal tubules/min
Types:
• It is 375 mg/min in male and 300 mg/min in female
• It occurs when plasma glucose concentration [PG] 300
mg/dl.
Def.,
• It is the plasma concentration of substance above it;
the filtered substance begins to appear in urine.
Value:
• It is 180 mg/dl for glucose
Cause:
• When PG is below 180 mg/dl, any filtered load of
glucose is completely reabsorbed
• If PG increase above 180 mg/dl filtered load
exceeds reabsorptive capacity of renal tubules
glucose starts to appear in urine.
Secretion rate = 4
Filtered load = 3
Excretion Rate = 7
Normal Plasma Concentration
Secretion rate = 7
Filtered load = 4
Excretion Rate = 11
High Plasma Concentration
Transport Maximum (TmPAH)
Def.,
• It is the maximum amount of PAH secreted by the
renal tubules/min.
Types:
• It is 80 mg/min corresponding to [PPAH] of 20 mg/dl
• Below [PG] 180 mg/dl: all filtered glucose will be
reabsorbed and so, no glucose will appear in urine and
hence the clearance of glucose = zero
• Increase PG above 180 mg/dl, glucose starts to appear in
urine, and so its clearance starts.
• Further increase of PG above 180 mg/dl will be
accompanied by increase in glucose clearance
Excreted glucose = filtered glucose – reabsorbed glucose
UG . Vo = GFR.PG – TG
• By dividing the equation by [PG] the result will be:
Gradually decrease as long as [PG] is increasing till
theoretically reach very low value and so can be
neglected and CG will equal Cin.
Excreted PAH = filtered PAH + secreted PAH
UPAH. Vo = GFR. PPAH + TPAH
By dividing the equation by [PPAH] the result will be
gradually decrease with any increase in PPAH till by time
it will be much decreased to the degree that can be
neglected and CPAH will equal Cin.
Clearance (ml/min)
CPAH
CG
Plasma concentration
26
• Glomerular filtration rate would be increased by
:
a) constriction of the afferent arteriole
b) a decrease in afferent arteriolar pressure
c) compression of the renal capsule
d) a decrease in the concentration of plasma
protein
e) a decrease in renal blood flow
• The volume of plasma needed each minute to
supply a substance at the rate at which it is
excreted in the urine is known as the :
a) diffusion constant of the substance
b) clearance of the substance
c) extraction ratio of the substance
d) tubular mass of the substance
e) filtration rate of the substance .
• The glomerular filtration barrier is composed
of all the following except :
•
a) fenestrated capillary endothelium .
•
b) macula densa .
•
c) basement membrane .
•
d) podocytes .
•
e) mesangial cells .
•
موقف على الدهر
• سالما ً شباب النيل في كل
ٍ
يجلب الفخرا
المجدَ أو
يجني
ُ
ٌ
بكور
عيون فإننا بكرنا
شباب اذا نامت
•
ٌ
َ
الطير نستقبل الفجرا
ِ
مصنع يدر
• تعالوا نشيّ ْد مصنعا ً رب
ٍ
صناعنا المغن َم الوفرا
على ُ
شباب نزلنا حومةَ المج ِد كلنا َ ومن
•
ٌ
ع النصرا
يغتدي للنصر ينتز ُ
1. Reabsorption:
•
Transport of materials from tubular lumen (filtrate) to
peritubular space or interstitial fluid to peritubular
capillaries (PTC).
2. Secretion:
•
Transport of materials from blood in PTC to interstitial
fluid to tubular lumen.
1) Surface area
Is very large since
every tubule
receives only 60
nl/min (SNGFR).
2) Flux
is the rate of
transport/unit
time/unit
surface area
1) Properties of the
membrane of epithelial
cells
•
The difference between the
apical and basolateral
membranes properties
account for the transepithelial
transport of all solutes
Apical
membrane
Basolateral membrane
2) Tight junctions
•
Attach cells at their apical
borders
• The tight junction may be;
a. Loose tight junction (allows
passage of solutes and
water) or
b. Tight junction (doesn't'
allow transport or difficult
transport).
Tight junction
Paracellular space
3) Establishment of transport maximum (Tm) & development
of concentration gradient between the lumen and peritubular
space
• This allow back diffusion of substance across the leaky tight
junction. Both characters limit the transport process.
4) Metabolic state and vitality of the epithelium:
• Any transport whether active or passive needs energy.
• O2 is needed for reabsorption of Na+ which is
responsible for reabsorption of other. So, O2 lack
affects tubular transport.
5) Hormonal & chemical substance as epinephrine,
aldosterone, parathormone calcitonin, AII, ADH, ANP,
PG and diuretics.
6) Removal of reabsorbed materials by PTC:
• The dynamics of reabsorption in PTC is determined by Starling
forces:
• a) Capillary hydrostatic pressure (13 mmHg).
• b) Capillary oncotic pressure of plasma proteins (32 mmHg)
• c) Peritubular interstitial pressure (6 mmHg)
• d) Interstitial oncotic pressure (15 mmHg)
• If the algebraic sum of forces favoring reabsorption it
will be faster.
• If not, back diffusion to tubular lumen will occur and
reabsorption will be decreased.
• Net reabsorbing force: = (32+ 6 ) – (13+ 15) = 10 mmHg
1. Cuboidal in shape.
2. Have two surfaces: luminal and basolateral surfaces:
a. Luminal surface:
• has microvilli (making the brush border) that increases
its surface area.
• Held together by leaky tight Junction
b. Basolateral surface:
• Has many process that interdigitate each other
• Are separated by paracellular spaces
3.The cells have abundant mitochondria especially
near basolateral border supplying energy for Na+K+ pump.
4. The cells are rich in intracellular and brush border
carbonic anhydrous enzyme.
5. The proximal tubule is divided into two segments,
convoluted and straighted segments;
Convoluted segment
Straighted segment
(pars convolute)
Represents segments 1 & 2.
Early 2/3 which lies in the
cortex.
Convoluted.
Have greater surface area due
to numerous microvilli.
Preferential reabsorption of
essential nutrients as
glucose, amino acids &
HCO3-.
Transepithelial potential
difference (TEPD) is -4 m.v.
(pars recta)
Segment 3.
Late 1/3 which lies in cortex
and outer medulla.
Straighted.
Smaller surface area.
Preferential Cl- reabsorption
TEPD is +4 m.v.
THANKS