complete us-neha
TRANSCRIPT
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e r nary
System
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Introduction� The urinary system consists of
± Two kidneys
± Two ureters± One urinary bladder
± One urethra
� Kidneys filter blood plasma and returnmost of the water and solutes to the
bloodstream
� The urine passes through the ureters�
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Organs of the urinary
system
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Transverse sections show retroperitoneal position of kidneys
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Kidney Functions
1. Regulation and Maintenance
2. Production
3. Excretion
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egu a on an
maintenance� Regulation of blood ionic composition: Na+, K+,
Ca2+, Cl- and HPO42-
� Regulation of blood pH: excrete H+ and conserve
HCO3-
� Regulation of blood volume: conserving or
eliminating water
� Regulation of blood pressure: secreting renin� Regulation of blood glucose levels: use amino
acid glutamine in synthesis of new glucose
molecules (gluconeogenesis)
� Maintenance of blood osmolarity: regulating loss
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Production of hormones
� Two hormones:
±Calcitriol ± active form of vitamin D ±
regulates calcium homeostasis±Erythropoietin ± stimulates production of
RBCs
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foreign substrates
� By forming urine, kidney excretes waste.
� Waste maybe from 2 sources:
± Metabolic reactions in body ± examples
� Ammonia and urea ± deamination of amino acids
� Bilirubin ± catabolism of hemoglobin
� Creatinine ± breakdown of creatinphosphate in muscle fibres
� Uric acid ± catabolism of nucleic acids
± Foreign substances from diet ± drugs and
environmental toxins
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Anatomy of kidneys� Reddish kidney bean-shaped organs
� Located above the waist betweenperitoneum and posterior wall of theabdomen
� Retorperitoneal ± posterior toperitoneum
� Located between the levels of the lastthoracic and third lumbar vertebrae
� Partially protected by eleventh and twelfth
pair of ribs�
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x erna ana omy o
kidneys
� Typical adult kidney:
± Length ± 10-12 cm
± Width ± 5-7 cm
± Thickness ± 3 cm
± Mass ± 135-150 g
� Concave medial border ± faces vertebral
column
� Near the center of concave border ± renal
hilum ± through which ureter emerges from
kidney along with blood vessels, lymph
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Sr.
no.
Locatio
n
Name Description Function
1 Deeplayer
RenalCapsul
e
Smoothtransparent sheet
of dense irregular
connective tissue.
It is continuouswith the outer coat
of ureter
1. barrier againsttrauma
2. maintain the
shape of the
kidney.
2 Middle
layer
Adipos
e
Capsul
e
Mass of fatty
tissue surrounding
the renal capsule
1. Protects
kidney from
trauma
2. Holds it firmly
in place
3 Superfi
cial
Renal
fascia
Thin layer of
dense irregular
1. Anchors the
kidney to the
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Internal anatomy of
kidneys� Frontal section reveals two distinct
regions:
±Renal cortex ± superficiallight red area
±Renal medulla ± deep,darker reddish brown inner
region
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Renal cortex
� Smooth textured area
� Extends from renal capsule to the bases of renal pyramids and into the spaces between
them� Divided into two zones:
± Cortical zone ± outer
± Juxtamedullary zone ± inner � Renal columns ± renal cortex extending
between the renal pyramids
� Renal lobe ± renal pyramids, its overlying
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Renal medulla
� Renal pyramids ± cone shaped structure
� Base of each pyramid faces the renal
cortex� Apex (renal papilla) points towards renal
hilum
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� Parenchyma ± renal cortex and renal
pyramids constitute the parenchyma. It is
the functional part of the kidney.
� Nephrons ± functional units of kidney.
Present in the parenchyma. About one
million in number.
� Papillary ducts ± extends through renalpapillae of pyramids. Urine formed by the
nephrons is drained into them.
� Calyces ± two types ± major (2-3) and
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� Renal pelvis ± single large cavity into which
urine from major calyces in drained.
� The urine is then drained out through the
ureter to the urinary bladder.
� Renal sinus ± cavity into which the hilum
expands. It contains part of renal pelvis, the
calyces, and the branches of renal bloodvessels and nerves. These structures are
stabilised by adipose tissue in the renal
sinus.
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Blood supply to the kidneys
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� Abundantly supplied with blood
vessels
� They constitute less than 0.5% of total body mass but 20-25%
resting cardiac output.
� In adults, renal blood flow ± 1200
mL/min
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Arteries
� S egmentals branch into
lobar arteries
� Lobars (enters
parenchyma) divides
into interlobars
� Interlobars into arcuate
in junction of medulla
and cortex
� Arcuates send
interlobular arteries into
Aorta gives off right and left renal arteriesRenal arteries divides into 5 segmental arteries as enters hilus
of kidney
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� Interlobular arteries in the cortex branches
off as afferent arterioles.
� Each nephron receives one afferentarteriole
� It divides into a tangled, ball-shaped
network of capillary ± glomerulus
� Glomerular capillaries then reunite to form
the efferent arteriole
� Glomerular capillaries ± unique as they
are ositioned between two arterioles
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� Efferent arterioles divide to form peritubular
capillaries which surround the tubular part of
nephron in the renal cortex� Vasa recta ± long loop-shaped capillaries
extending from some efferent arteries. They
supply to tubular portions of nephron in therenal medulla
� Peritubular capillaries reunite to form
peritubular venules
� They form interlobular veins ± receive blood
from vasa recta
� The blood drains through arcuate veins to
interlobar veins.
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Vasculature of kidneys
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Nerve supply to the
kidneys� Renal nerves originate in renal ganglion
� Pass through renal plexus into the kidneys
along with renal artery� They are a part of sympathetic division of
ANS
� They are mostly vasomotor nerves ±regulate the flow of blood through the
kidneys by causing vasodilation or
vasoconstriction of renal arterioles.
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Uretersy
Slender tubes about 25-30 cm (10-12 ) longleaving each renal pelvis
y Diameter 1-10 mm
y One for each kidneycarrying urine from renalpelvis to the bladder
y Descend retroperitonealyand cross pelvic brim
y Enter posterolateralcorners of bladder
y Run medially withinposterior bladder wallbefore opening intointerior
y This oblique entry helps
prevent backflow of urine
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� Peristaltic contractions ± push urine ± 1-5
contractions/min
� Hydrostatic pressure and gravity also aid
� As bladder if filled with urine, pressure
within it compresses the oblique openings
and prevents backflow of urine� If this physiological valve doesn¶t function
properly chances of kidney infection
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Three basic layers
y Mucosa made up of transitionalepithelium stretches withunderlying lamina propria made upof areolar connective tissue withcollagen, elastic fibers andlymphatic tissue
y Mucus secreted protects cell fromurine (pH and solute conc)
y Muscularis Inner longitudinal, outer circular
layers ofsmooth muscles
Stimulated to contract whenurine in ureter: peristaltic wavesto propel urine to bladder
y Adventitia (external) areolar connective tissuecontaining blood vessels,lymphatic vessels and nerves
y Anchors the ureters in place
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Urinary Bladder
y Hollow distensiblemuscular organ situatedin the pelvic cavity
y Held in place by folds of peritoneum
y Stores and expels urine
y Bladder capacity 700-800 ml
Males: anterior to rectum
Females: just anterior tothe vagina and uterus.Smaller due to uterus
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The Urethra
� Male: about 20 cm (8´) long
� Female: 3-4 cm (1.5´) long± Short length is why females have more urinary tract
infections than males - ascending bacteria from stool
contamination
Urethra____
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� Urethral sphincters± Internal: involuntary sphincter of smooth muscle
± External: skeletal muscle inhibits urination voluntarily
until proper time (levator anni muscle also helpsvoluntary constriction)
Males: urethra has three
regions (see right)
1. Prostatic urethra__________
2. Membranous urethra____
3. Spongy or penile urethra_____
_________trigone
female
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Wi th all the labels
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�M icturitionAKA:± Voiding
± Urinating
± Emptying the bladder
KNOW:Mictur ition center of
brain: pons
(but heavily inf luenced byhigher centers)
Parasympathetic: to voidSympathetic: inhibits
mictur ition
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Micturition
� Act of emptying the bladder
� Exceeding 200 ml of urine, the bladder isstretched and stretch receptors are
activated� Impulses are transmitted via the pelvic
splanchnic nerves to the sacral region
� Bladder go into contractions and forceurine pass the IUS (feeling of urge to void )
� After a certain volume limit, micturition will occur whether one wills it or not
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Anatomy of uriniferous tubule
± Nephron
� Renal corpuscle (in cortex)
± Glomerulus (tuft of capillaries)
± Glomerular (Bowman¶s) capsule� Tubular section
± Proximal convoluted tubule
± Loop of Henle
± Distal convoluted tubule
± Collecting duct
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Nephron
Renal corpuscleTubular section
Renal corpuscle: only in
cortex
Tuft of capillaries calledglomerulus
Surrounded by cup-
shaped, hollow glomerular
(Bowman¶s) capsule
Tubular sectionProximal
convoluted tubule
Loop of Henle
Distal
convoluted tubule
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Renal Corpuscle
� Blood plasma is filtered
� Lies entirely in cortex
� Two components:
± Glomerulus ± capillary network± Glomerular capsule (Bowman¶s capsule) ±
surrounds capillaries
� Visceral layer of capsule has pod ocytes
± Unusual branching epithelial cells
± Foot processes with slit processes betweenthem
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Scanning EM of podocytes clinging
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Scanning EM of podocytes clinging
to capillaries (left) and filtration
membrane diagram (right)
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Loop of Henle
� Descending limb ± dips into medulla
� Thin segment ± hairpin turn
� Thick ascending limb ± returns to cortex
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Distal Convoluted Tubule
� Confined to the renal cortex
� Simple cuboidal epithelium
� Selective secretion and resorption of ions
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� Cortical nephrons± 85% of all nephrons
± Almost entirely within cortex± Corpuscle lie in outer portion of cortex
± Have short loop of Henle which penetrate onlythe outer region of medulla
± Blood supply from peritubular capillaries only
� Juxtamedullary nephrons± Renal corpuscles near cortex-medulla junction
± Loon loop of Henle extending into deepestregions of medulla
± Blood supply ± peritubular capillaries and vasarecta
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Collecting Ducts
� Each receives urine from several
nephrons
� Run straight through cortex into the deep
medulla
� At papilla of pyramid, ducts join to form
larger papillary ducts
� Empty into minor calices
� Role: conserve body fluids
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Blood Vessels�Afferent and efferent arterioles
associated with glomerular
capillaries
�Allows high pressure for
forcing filtrate out of blood
�About 20% of renal plasma
flow is filtered each minute
(125 ml/min): this is the
glomerular filtration rate
(GFR), an important
clinical measure of renal
f unction
�This is about one liter
every 8 minutes (only1% ends up as urine)
�Peritubular capillaries arise from
efferent arterioles
�Absorb solutes and water
from tubule cells
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Vasa RectaThe Vasa recta is a
portion of the peritubular capillary system whichenters the medulla wherethe solute concentrationin the interstitium is high.
It acts with the loop of Henle to concentrate the
urine by a complexmechanism of counter current exchange usingurea.
If the vasa recta did notexist, the highconcentration of solutesin the medullaryinterstitium would be
washed out.
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Histology
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Juxtaglomerular apparatus� Regulation of blood pressure
� Macula densa ± crowded columnar cells - chemoreceptors whichsecrete renin if solute concentration falls
� Granule (JG cells) ± alongside macula densa - modified muscle cellssecreting renin in response to falling blood pressure in afferent arteriole
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Production of urineProduction of urine
Three
processes1. Filtration
2. Reabsorptio
n3. Secretion
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Filtration
� Filtrate formed (ultrafiltrate): blood plasma
without blood proteins
� Proteins and blood cells to large to pass
through the filtration membrane
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Reabsorption
� Reclamation of useful substances from the
filtrate and returned to the blood
± Water, glucose, amino acids, ions, etc
� Begins at the PCT
� Depends mostly on active transport
� Nitrogenous waste products are poorly
reabsorbed (eg, urea, uric acid, creatinine)
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Secretion
� Movement of substances from the blood or
tubule cells to be eliminated in urine
± Hydrogen ions, potassium ions, creatinine,
certain drugs
Rate of urine formation = glomerular filtration
rate + rate of secretion rate of reabsorption
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Glomerular filtration
� Glomerular filtrate (GF) ± fluid entering thecapsular space
� Filtration fraction ± the fraction of blood plasma
in the afferent arterioles that becomes GF. 16-20%
� Daily volume of GF in adults:± Males ± 180 L
± Females ± 150 L
� > 99% GF returns to bloodstream via tubular reabsorption.
� Only 1-2 L excreted as urine
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Filtration membrane
� Filtration membrane = endothelial cells of capillaries + podocytes encircling capillaries
� It is a sandwich like assembly ± leaky barrier
� Permits filtration of water and small solutes� Prevents filtration of most plasma proteins,
blood cells and platelets.
� 3 layers
± Glomerular endothelium
± Basal lamina
± Podocytes
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Gl l d th li
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Glomerular endothelium
� Large fenestrations ± 0.07-0.1 µm. Thus
leaky.� Filters all solute in blood plasma except
blood cells and platelets.
Basal lamina
� Layer of acellular material containing
collagen fibers and proteoglycans inglycoprotein matrix.
� Prevents filtration of larger plasma
proteins.
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Podocytes
� Thousands of foot-like processes ±
pedicelthat wrap around capillaries.
� Spaces between pedicels ± filtration slits
� A thin slit membrane extends across each
slit.
� Permits passage of molecules having
diameter < 0.006-0.007 µm.
� Includes water, glucose, vitamins, aminoacids, very small plasma proteins,
ammonia, urea and ions
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� Large volume of fluid can be filtered by
glomerular capillaries because:
1.They are long and extensive ± large surface
area for filtration.
2.Filtration membrane is thin (0.1 µm) and
porous (50 times leakier).
3.Efferent arteriole smaller than afferent
arteriole ± high resistance to outflow of blood ± Glomerular capillary blood pressure
is high
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Net filtration pressure (NFP)
� 3 main pressures
1.Glomerular blood hydrostatic pressure(GBHP) ± blood pressure in capillaries (55
mmHg). Forces water and solutes inplasma through filtration membrane.
2.Capsular hydrostatic pressure (CHP) ±pressure exerted by fluid present incapillaries and tubule (15 mmHg). ³BackPressure´ opposes filtration.
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3. Blood colloid osmotic pressure (BCOP) ±
pressure due to plasma proteins such as
albumin, globulins and fibrinogen (30
mmHg). Opposes filtration.
� NFP = GBHP ± CHP ± BCOP
= 55 ± 15 ± 30
= 10 mmHg
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Glomerular filtration rate
� GFR ± the amount of filtrate formed in all
renal corpuscles of both kidneys each
minute.
� Adult GFR
± Males: 125 ml/min
± Females: 120 ml/min
� If GFR too high ± needed substance maynot be reabsorbed and maybe excreted.
� If GFR too low ± waste substances maybe
reabsorbed.
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� GFR ± directly related to pressure
� Severe blood loss ± reduces mean arterialblood pressure ± reduces GBHP.
� Min GBHP ± 45 mmHg. After this filtrationstops.
� When systemic blood pressure rises ±
GFR increases.� GFR constants between 80-180 mmHG
mean arterial pressure
� Mechanisms regulating GFR
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� Mechanisms regulating GFR
� Adjusting blood flow into and out of the
glomerulus� Altering the glomerular capillary surface
area available for filtration
� Mechanisms controlling GFR:
1.Renal autoregulation
2.Neural regulation3.Hormonal regulation
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Renal autoregulation of GFR
� Two mechanisms:
1.Myogenic mechanism
2.Tubuloglomerular mechanism
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Myogenic mechanism
Tubuloglomerular feedback
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Tubuloglomerular feedback
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Hormonal regulation of GFR
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Hormonal regulation of GFR
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Hormonal regulation (contd)
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Tubular Reabsorption and
Tubular Secretion
Composition of Glomerular
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Composition of Glomerular
Filtrate�� Water Water
�� Small Soluble Organic MoleculesSmall Soluble Organic Molecules
�� MineralI
onsMineralI
ons
P i l C l t d
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Proximal Convoluted
TubuleReabsorbs: water, glucose,Reabsorbs: water, glucose,
amino acids, and sodium.amino acids, and sodium.
65% of Na+
65% of H2O
90% of filtered bicarbonate (HCO3-)
50% of Cl- and K+
100% of glucose and amino acids
50% of urea
Variable amounts of H+, NH4+ and urea
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Tubular Secretion
� H+
� NH4+
� Creatinine� Some drugs
� Imp ± to test athletes for performance
enhancing substances like anabolic
steroids, amphetamine etc.
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Routes of reabsorption
� Substance to be reabsorbed can take
TWO routes before entering a
paratubular capillary:
1. Move between adjacent tubule cells
2. Move through a single tubule cell
� Along renal tubule there are tight
junctions joining neighboring cells.
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Luminal sur f aceLuminal sur f ace
Basolateral sur f aceBasolateral sur f ace
EpithelialEpithelialtighttight
junctionsjunctions
Just thinkof it as aSix soda pack
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�� The luminal cell membranes (apicalThe luminal cell membranes (apical
membrane) are those that face themembrane) are those that face the
tubular lumen (³urine´ side)tubular lumen (³urine´ side)
�� The basolateral cell membranes areThe basolateral cell membranes are
those are in contact with the lateralthose are in contact with the lateral
intercellular spaces and peritubular intercellular spaces and peritubular interstitium (³blood´ side)interstitium (³blood´ side)
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�� The termThe term transcellular transcellular refers torefers to
movement of solutes and water throughmovement of solutes and water through
cellscells
�� The termThe term paracellular paracellular refers to movementrefers to movement
of solutes and water between cellsof solutes and water between cells
�� Epithelial cell junctions can be ³leaky´Epithelial cell junctions can be ³leaky´
(proximal tubule) or ³tight´ (distal(proximal tubule) or ³tight´ (distal
convoluted tubule, collecting duct)convoluted tubule, collecting duct)
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Transport mechanisms
�� Passive transport (simple diffusion)Passive transport (simple diffusion)
�� Facilitated diffusionFacilitated diffusion
�� Primary active transportPrimary active transport
�� Secondary active transportSecondary active transport
�� PinocytosisPinocytosis
�� Solvent dragSolvent drag
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� Reabsorption of sodium is very important
� Cells of renal tubule have very low conc of
Na+ in their cytosol due to the activity of
Na+/K+ ATPase pump ± located in
basolateral membrane
� Absence of this pump in apical membrane
ensures one way movement of Na+
� Energy obtained from hydrolysis of ATP.
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� Solute reabsorption drives water
reabsorption ± due to osmosis.
� Water reabsorbed with solutes in tubular
fluid ± obligatory water reabsorption.
Occurs in PCT and descending loop of
Henle
� Reabsorption of final 10% of water ±facultative water reabsorption. Regulated
by ADH and occurs in collecting ducts
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R b ti i l f H l
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Reabsorption in loop of Henle
� Fluid enters the loop at the rate of 40-45
mL/min.
� 15% water
� 20-30% Na+ and K+
� 35% Cl-
� 10-20% HCO3
-
� Variable amounts of Ca2+ and Mg2+
� Apical cell membrane has Na+/ K+/ 2Cl-
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p
symporter ± reclaims one Na+, one K+ and
two Cl-
from the fluid in tubular lumen� Many K+ leakage channels are there in the
apical membrane ± K+ moves back into the
tubular fluid. Thus there is reabsorption of
mainly sodium and chloride ions
� Movement of K+ into the tubular fluid leaves
the interstitial fluid and blood negatively
charged as compared to tubular fluid. Thispromotes reabsorption of Na+, K+. Mg2+ and
Ca2+ by paracellular routes
R b ti i l DCT
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Reabsorption in early DCT
� Rate of fluid entry ± 25 mL/min
� 10-15% water
� 5% of Na+
� 5% of Cl-
� Variable amount of Ca2+ - due to
stimulation of parathyroid hormone
Reabsorption and secretion in late
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Reabsorption and secretion in late
DCT and collecting ducts
� Two types of cells ± principal cells and
intercalated cells
� Principal cells ± reabsorbs Na+ and
secretes K+
� Intercalated cells reabsorb K+ and HCO3-
and secrete H+
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secretion and tubular
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secretion and tubular
reabsorption� ADH
± Secreted by posterior
pituitary
± Increases water
permeability in distal
tubules and collecting
ducts
� Aldosterone
± Produced in adrenal
cortex
± Affects Na+ and Cl-
transport in nephron and
� Renin± Produced by kidneys,
causes production of angiotensin II ±enhances reabsorption
of Na+ and Cl-
� Atrial natriuretichormone± Produced by heart
when blood pressureincreases� Inhibits ADH production
� Reduces ability of kidneyt t t i