Excretion and osmoregulation

1. EXCRETION
&
OSMOREGULATIO
N
dr.aari
f

2. Excreti
on
The process of separation, collection and elimination
of toxic waste products (especially nitrogenous wastes)
from the body
Waste products are formed due to catabolism of
amino acids, glucose, glycerol and fatty acids.
Unwanted substances like
Drugs, pigments, excessive vitamins, CO
2, H
2O
Excess of inorganic salts, hormones
Bilirubinand biliverdin.
Kidneysplay a major role as an excretory organ in all
vertebrates.
Skinhelps in elimination of urea; inorganic salts and
water through sweat glands.
Lungshelp in the elimination of CO
2and H
2O

3. Osmoregulatio
n
The process by which the
relative proportion of water and solutes
(salts, glucose, etc) in the body-fluids
and cells are kept constant.
Osmoregulation controls the
osmotic pressure of body fluidsand
maintains the volume of blood constant
Osmoregulation maintains the
necessary required concentration of
electrolytes in the body fluids

4. AMMONOTELISM UREOTELISM URICOTELISM
Nitrogenous waste in the
form ofammonia
Nitrogenous waste in the
form ofurea
Nitrogenous waste in
the form of uric-acid
formed in the liver by
deaminationof amino-acids
formed in liver by ornithine
cycle. (NH
2-CO-NH
2)
formed in the liver by the
ionosinicpathway.
least expenditure of energy.relatively more expenditure
of energy.
high expenditure of energy.
highly toxic comparatively less-toxic Uric-acid is non-toxic.
highly soluble in water.a good solubility in water.is insoluble water.
excreted rapidly in urineexcreted at a (comparatively)
slower rate.
excreted very slowly
Dilute urine
500 ml of water is
Required for elimination
Of 1 gm of ammonia
concentrated urine
50 ml of water for
elimination of 1 gm ofurea.
ofthick paste or semi-solid
pellets
10 ml ofwater for
elimination of one gm
uric acid.

5. AMMONOTELISM UREOTELISM URICOTELISM
Aquatic invertebrates
sponges ,bonyfish, jelly-fish
aquatic amphibians,
aquatic insects etc
mammals like man,whale,
amphibianslikefrog,aquatic
reptiles like turtles and
tortoise and
cartilagenous fish.
land-animals like birds,
reptiles (lizard, snakes), land
snailsand insects

7. Inmanandothermammals,smallquantityofuricacidisformedinthebodyby
breakdownofpurineandpyrimidinenitrogenbasesofnucleicacid.
Insomepersons,duetodefectivemetabolism,excessuricacidisproducedwhich
getsdepositedinjointsofbonescausingpainfularthritiscalledgout.
GUANOTELISM–Arachnids(spiders,scorpions)andpenguinsexcretemostlyguanine
(nitrogenbase)andhencearecalledguanotelic.
Protonephridiaor flame cells--Platyhelminthes(Flatworms, e.g., Planaria),
rotifers, some annelids and the cephalochordate –Amphioxus
Nephridia--Earthworms and other annelids..
Malpighiantubules--most of the insects including cockroaches..
Antennal glands orgreen glands--crustaceans like prawns

10. Kidneys
Pair of bean shaped, chocolate brown
structures situated in the dorsal side of the
abdominal cavity
-behind the peritoneum (retroperitoneal)
-one on either sideof the vertebral-column
between the 12
th
thoracic and 3
rd
lumbar
vertebrae.
The right kidney is slightly lower than the left
kidney
-11 cmslong, 6 cmsbroad and 3 cmsthick
-150 grams in males and 135 grams in females

11. Each kidney is covered by a fibrous
capsule,over which lies a layer of adipose
tissue (peri-renal fat) and the outermost
fibrous sheath (renal-fascia)
.
The outer margin of both kidneys is
convex. The inner margin is concave and
shows a notch, called hilum.
The renal-artery, renal-vein, lymphatic-
vessels, nerves, renal-pelvis(upper
expanded end of the ureter) enter the
kidney through the hilum.
The upper pole of each kidney is broad
and has an adrenal(suprarenal) gland
attached to it
Kidneys

12. Eachureterarisesfromthehilumof
thekidneybyformingafunnelshaped
expanded renal-pelvis, runs
downwards,entersthebladderwall
obliquely(onthedorsalside)and
opensintoit.
Structure:Theyareapairof
narrow,thin-walledmusculartubes
measuringabout25cmsinlengthand
3-6mmindiameter.
Function:Theycarryurinefromthe
kidneystotheurinarybladderby
rhythmiccontractionofitsmuscle-
walls(peristalticmovements).
Ureters

13. •Position:Itissituatedinthepelvic-cavityin
frontoftherectuminthemaleandinfrontof
theuterusinthefemale.(i.e.thewomb,which
liesbetweenthebladder&therectum).
Structure:
•Itisamedian(central),single,hollow,ovoidor
pearshaped,distensiblemuscularsac.Italso
showsathicklayerofsmoothmusclescalled
detrusormuscleslinedbytransitional
epitheliumthatallowsexpansion.
•Inthelowerpartoftheposteriorwallliesan
invertedtriangularareacalledthetrigone.The
uretersopenintotheupperlateralanglesof
thisareawhiletheopeningoftheurethra
(internalurethralorifice)islocatedatthe
lowerend(apexofthetriangle).
Function:
•Itactsasatemporaryreservoirforthestorage
ofurine.
•Ithelpsinmicturition(urination).(The
processofvoidingofurinebycontractionof
thebladderwallandrelaxationoftheurethral
sphincters).
Bladder

14. Males:Urethrais20cmslongextendsfrom
thelowerend(neck)ofthebladder(internal
urethralorifice)tothetipofthepenis
(externalurethralorifice).
Infemalesitis4cmslongitopens
separatelyjustinfrontofvagina.
Theflowofurineisguardedbysphincters.
Theinternalurethralsphincterattheneck
ofthebladder(i.e.internalurethralorifice)
isinvoluntary,whiletheexternalurethral
sphincter,situatedatalowerlevel(i.e.
belowprostategland)isundervoluntary
control(after2yearsofage).
Females:itcarriesurineonly.
Inmalestheurethrajoinswiththe
ejaculatoryduct(toformtheurinogenital
duct)andcarriesbothurine&semen.
Urethra

15. Urine formed by the nephronsis
ultimately carried to the urinary
bladder where it is stored till a
voluntary signal is given by the central
nervous system (CNS).
This signal is initiated by the
stretching of the urinary bladder as it
gets filled with urine. In response, the
stretch receptorson the walls of the
bladder send signals to the CNS
The CNS passes on motor messages
to initiate the contraction of smooth
muscles of the bladder and
simultaneous relaxation of the urethral
sphincter causing the release of urine.
The process of release of urine is
called micturitionand the neural
mechanisms causing it is called the
micturitionreflex

17. A longitudinal section through the kidney
shows the following parts from outside in :
1) The outer reddish brown cortex,
2) The innerpale medullaand
3) Therenal-sinus
A)MEDULLA:
•Itistheinner,pale,striatedpart.
Itismadeupofabout4-14,striatedconical
massescalledtherenalpyramids.
Eachpyramidhasitsbasedirectedoutwards
(towardsthecortex)anditsapexinwards
(calledrenal-papillae).
B)CORTEX:
Itformstheouter(peripheral),reddish-
brown,granularpart.
•Partsofthecorticaltissueinvadethe
medullaandliebetweenadjacentpyramids
andarecalledrenal-columns(Bertini’s
columns).

18. C)RENAL-SINUS:
Internally,thehilumleadstoa
spacecalledtherenal-sinus,whichisoccupied
bytheupper,expandedpartoftheureter
calledtherenal-pelvis.
Therenal-pelvisdividesintotwoor
threepartscalledmajor-calices(singlecalyx→
cupofaflower).
Eachmajorcalyxdividesinto6-
20minor-calices.Eachminor-calyxisshaped
likeacup.
•Thepapillaofamedullarypyramidfitsinto
theminorcalyx.
Eachkidneyconsistsofclosely
packedmicroscopiccoiledtubularstructures
callednephrons.Thenephronsarethe
structuralandfunctionalunitsofthekidney.
Thereareabout1.2millionnephronsineach
kidney.

20. NEPHRON : 1. Malphigianbody
2. Renal Tubule
Malphigianbody : 1. Bowman’s capsule
2. Glomerulus
Renal Tubule : 1. Proximal convoluted tubule (PCT)
2. Loop of Henle
3. Distal convoluted tubule (DCT)

21. It is double-walled, cup shapedblind-opening in
the cortex. It is about 1.2 mm in width
Outer wall : PARIETAL LAYER : squampousepithelium
Inner wall : VISCERAL LAYER : special squamouscells
called PODOCYTES
The body of the podocytesrest on feet like
processes called ‘pedicels’.
The individual legs, have foot processes.
The gaps (slits) between the foot processes are in
intimate contact with poresinthe endothelium of
blood capillaries, through a permeable basement
membrane

24. GLOMERULUS (BLOOD-SUPPLY):
Itisaroundedtuftofblood
capillariesfoundinthecupofthe
Bowman’scapsule.
Therenalartery(abranchofthe
abdominalaorta)entersthroughthe
hilus,dividesandre-dividestoform
manybranches.Onebranchcalledthe
afferentrenalarterioleentersthecup
anddividestoformtheGlomerulus
.
•Thecapillariesreunitetoformthe
efferentrenalarteriole.Itleavesthe
glomerulus.
•Thediameteroftheefferentarterioleis
lesserthanthatoftheafferentone.

25. THEPROXIMAL CONVOLUTED
TUBULE(P.C.T)
Itisahighlycoiledstructure,
connectedtotheneckandliesinthe
cortex.
Itislinedbycuboidalcells,richin
mitochondria,andhavingmicrovilli
(brushbordertoincreasesurface
area)andthushelpinactive
reabsorption.

26. B) THE MIDDLE LOOP OF HENLE:
The renal tubule now descends
into the medulla (thin walled descending
limb),takes a hair pin turn (the U-shaped
loop) and ascends back towards the
cortex (thick walled ascending-limb).
The ascending limb is not permeable to
water.
The Henle’sloop is mainly meant for
concentration of urine.

27. THE DISTAL CONVOLUTED
TUBULE(P.C.T)
The D.C.T leads to a straight, large
collecting-tubule. Many nephronsopen
into the same collecting tubule. Many
collecting tubules join to form a collecting
ductwhich descends into the medullary
pyramids.
The medullarypyramidsare
basically a bunch of these collecting
ducts. About 7-8 collecting ducts draining
different nephronsjoin to form ducts of
Bellini, each of which opens into a minor
calyx at the apex (papilla) of a medullary
pyramid.

28. BLOODSUPPLY:
Theefferentrenalarteriolewhichleaves
theBowman’scapsulebreakstoform
peritubular-capillariesaroundthewhole
renaltubule.
ThecapillariesaroundtheloopofHenle
arecalledasvasarectae.
Thecapillariesreunitetoformarenal
venuleandcarrythebloodawayfromthe
nephrons.Therenalvenulesjointoform
therenal-vein,whichpassesoutofthe
kidneytojointheinferiorvenacava.
Functionsoftherenal-tubule:
•Helpsintheselectivereabsorptionof
essentialsubstanceslikeH
2
O,glucose,
saltsetc.
•Helpsinthetubular-secretionof
unwantedsubstances.

32. Site:In the malpighianbody
Principle:Itisaphysicalprocess.Thediameterof
theafferentarterioleisbiggerthantheefferent
arteriolethuscreatingpressureintheglomerulus.
The glomerularhydrostaticpressureis the blood
pressure in the glomerular capillaries which is
about 55mm of Hg.
The colloidal osmotic pressureof blood which is
30 mm of Hgdue to the presence of plasma
proteins. It opposes the glomerular (capillary)
hydrostatic pressure.
The capsular (filtrate) hydrostatic pressureof
glomerular capsule is caused by filtrate
thatreachesinto the Bowman's capsule. It is about
15 mm of Hg.Italso opposes the
glomerularhydrostaticpressure
Thenet(effective)filtrationpressure
EFP=GHP-(BCOP+CHP)
=55-(30+15)
=10mmofHg

33. Theafferentarteriolebringsinbloodat625ml/min.
1/5
th
ofitgetsfiltered.
i.e.theultrafiltrationrateis125ml/minorabout180litres/day
Thisrateofformationoffiltrateiscalledglomerularfiltraterate(GFR)
Process:TheepithelialcellsoftheviscerallayeroftheBowman’scuparecalledpodocytes.The
bodyofthepodocytesrestonfeetlikeprocessescalled‘pedicels’.Theindividuallegs,havefoot
processes.Thegaps(slits)betweenthefootprocessesareinintimatecontactwithporesinthe
endotheliumofbloodcapillaries,throughthepermeablebasementmembrane.Thisarrangement
facilitatesthetransferoffluids.
Becauseofthehighbloodpressure,about1/5
th
oftheblood(plasma)getsfilteredviathesefiltration
pathsintotheurinaryspaceoftheBowman’scapsule.
Finalproduct:Theglomerularfiltrate,whichcontainsalltheconstituentsofblood(i.e.glucose,
amino-acid,salts,water,ureaetc.)exceptblood-cells,plasma-proteinsandfats(toobigforthepore-
size),hencecalledasdeproteinizedplasma.

35. P.C.T
Activereabsorption
Passive reabsorption
Glucose, Amino acids,
Vitamins, Na
+
,K
+
,Ca
+
,PO
4
-
Water (75%), Urea and Cl
-
(ISOTONIC)
Desc.Limb
H2O : Permeable
Solutes : Impermeable
Passive reabsorption
(Due to Increased medullary
tissue osmotic pressure)
Water (5%)
(HYPERTONIC)
At the bend
Asc.Limb
H2O : Impermeable
Solutes : Permeable
Passivereabsorption
Active reabsorption
First Na
+
followed byboth
Na
+
and Cl
-
Cl
-
, K
+
(HYPOTONIC)
D.C.T
C.T
Passivereabsorption
(under the influence of ADH)
Water(15%)
Water(4%)
(HYPERTONIC)

36. Site: Proximal and Distal convoluted tubule and partially in
the collecting tubule.
Principle: Some substances that escape ultra filtration are
taken to the peritubular capillaries and excreted in the filtrate.
Process: Ammonia, Creatinine, K
+
, H
+
, drugs (e.gpenicillin)
are excreted in this process.
For every K
+
or H
+
ion excreted a Na
+
ion is reabsorbed.
The H
+
ion concentration (& thus acid-base balance) can be
maintained.
Final product: Concentrated Urine, containing 50% of urea
found in glomerular filtrate.

40. FLUID BALANCE ELECTROLYTE BALANCE
Controlled by ADHfrom the post pituitaryControlled byAldosteronefrom the adrenal cortex
i) When the amount of water in the
body is less,ADH secretion isincreased,
which increases the reabsorptionof
water (facultative reabsorption) from
the distal convoluted tubule and
collecting tubule thereby secreting a
small amount of concentrated
(hypertonic) urine.
ii) When the water intake ismore, ADH
secretion is decreased, which makes
the DCT and collecting tubuleless
permeable to waterand a large
amount ofdilute urineis excreted
•The concentration of Na
+
, K
+
, Cl
-
, Ca
+
Mg
+
,
HCO
3
-
etc. is regulated by their increased or
decreased reabsorptionin the P.C.T.
•Calcium ion concentration is maintained by
CALCITONIN(thyroid gland) and
PARATHORMONE(parathyroid gland).
ALDOSTERONE, a hormone secreted by the
adrenal-gland helps in reabsorptionof Na
+
by
excreting K
+
in exchange, in the DCT &
collecting tubule

41. COMPOSITION OF URINE :
a)Volume : Average 1,200-1,500 ml/day.
b) Colour :Pale yellow, due to mainly urochromea bile derivative urobilin&
urethrincontribute to it.
c)Specific gravity :1.01 to 1.03.
d)Reaction :Slightly acidic (pH 5-7)
e)Odour :Ammoniac.
f)Constituents
Organic :Urea mainly, Uric acid, Ammonia and Creatinine.
Inorganic :95% Water and chlorides, sulphates & phosphates of sodium,
potassium, calcium and magnesium. (sodium-chloride is the most abundant of all
these salts).

42. •CarbohydratesProteinsketone bodiesBloodBile saltsBile pigmentsFats
CARBOHYDRATES
Carbohydrates present in it such as lactose and fructose.
Physiologicallyin pregnanyand lactation, lactose is excreted in pregnant women.
Pathologically: if lactose is excreted in the urine, then this is due to lactose intolerance.
Glucose could be excreted in the urine in Diabetes mellitus, glucosuria, renal glycosuriaetc
Fructose in essential fructosuria
Galactosein galactosemia
PROTEINS:
Secretion of proteins in urine is due to:
1-Increase in the permeability of the glomerularcapillaries as in nephroticsyndrome etc
2-Damage to the capillaries membranes as in glomerulonephritis
Following proteins can be excreted in abnormal urine:
•Albumin
•Globulin
•Hemoglobin (protein of RBC)
•Myoglobin

43. Albumin and globulin are found in the urine in the condition called proteinuria, also in
nephroticsyndrome and glomerularnephritis.
Hemoglobin is excreted in urinaytract infections.
Myoglobinis excreted due to muscular atrophyetc.
KETONE BODIES
they are basically three chemicals viz.
•acetone
•acetoaceticacid
•beta hydroxybutaricacid
All the three are the intermediates in the fats metabolism.
Increased catabolism of fats is due to
•starvation
•increased fat intake in diet
•decreased carbohydrates in the diet
•diabetes ketoacidosis

44. FUNCTIONS OF KIDNEY:
1.By excretion, they eliminate poisonous nitrogenous wasteproducts (like urea,
uric-acid, ammonia) in the urine.
2. During excretion, they remove unwanted substances like drugs, pigments
excessive vitamins etc. from the body.
3. By Osmoregulation, they regulate the amount of water and salts i.e. the
osmotic pressure of body fluids and maintain the volume of blood constant.
4. By Osmoregulation, they maintain a necessary required concentration of
electrolytes(Na
+
, K
+
, Cl
-
, Ca
+
) in the blood.
5. They regulate the pH and acid basebalance of the body by removing excessive
acidic or basic substances (H
+
ions concentration) from it.
6. During hypotension (low B.P.), they maintain the pressure of the blood
constantby secreting enzyme reninfrom it which increases the B.P.
7. They help in production of R.B.C.s (erythropoiesisby secreting ‘ renal-
erythropoieticfactor (REF) i.e. erythropoietinintothe blood.
8. They help in formation of active form of Vit-D(1,25 dihydroxycholecalciferol

45. SKINASANEXCRETORYORGAN:
Theskinisdouble-layeredi.e.outerepidermisandinnerdermis.
Withinthedermisarepresenthair-follicles,sweatglandsandsebaceousglands.
SWEAT-GLANDS:
Theyarehighlycoiledglandsfoundmoreinforehead,armpits,palmsandsolesoffeet.
Thesecretorypart(coiled)liesdeepbelowinthedermisandisconnectedtotheskinsurfaceas
perspirationporeviaalong,narrowduct.Theyaresimple,unbranched,tubularglands.
Functions:
•Theysecreteacolourlesssalty-fluidcalledsweatcarryingexcessivewater,sodium-chloride,urea,uric-
acid,lacticacid,glucoseandamino-acids.
•Thusitregulatesthewater-balance,salt-balance,excretion(littleurea)andcoolsdownthebody
(thermoregulation)i.e.waterconvertedintovapourbyexcessiveheat.
SEBACEOUS GLANDS :
They are alveolar glands present in connection with the hair follicles.
Functions :
They secrete ‘sebum’,which is rich in waxes, sterols, hydro-carbons and fatty acids.
Sebum makes the skin water-proof (due to wax) and has an antiviral & antibacterial activity.

47. LUNGSASEXCRETORY-ORGANS:
Thebyproductsofcellularrespirationarewater&CO
2.
ThepartialpressureofCO
2
ishigherinthedeoxygenatedbloodofalveolarcapillariesof
lungs,broughtfromallthepartsofthebody,thaninthealveolarair.Henceitdiffuses
intothealveoliandisexhaledout.OurlungsremovelargeamountsofCO
2
(18litres/day).
Waterisalsolostfromthelungsurfacebyevaporation(Vapour).Thishasacooling
effect(thermoregulation)inmanyanimals.
LIVER :
The largest gland in our body, secretes bile-containing substances like
bilirubin, biliverdin, cholesterol, degraded steroid hormones, vitamins and drugs.
Most of these substances ultimately pass out alongwithdigestive wastes and some in
urine

49. The Henle’sloop and vasarecta play a significant role in this.
The flow of filtrate in the two limbs of Henle’sloop is in opposite directions and thus
forms a counter current.
The flow of blood through the two limbs of vasarecta is also in a counter current pattern.
The proximity between the Henle’sloop and vasarecta, as well as the counter current in
them help in maintaining an increasing osmolaritytowards the inner medullaryinterstitium,
i.e., from 300 mOsmolL
–1
in the cortex to about 1200 mOsmolL
–1
in the inner medulla. This
gradient is mainly caused by NaCland urea.
NaClis transported by the ascending limb of Henle’sloop which is exchanged with the
descending limb of vasarecta. NaClis returned to the medullaryinterstitiumby the
ascending portion of vasarecta. Similarly, small amounts of urea enter the thin segment of
the ascending limb of Henle’sloop which is transported back to the medullaryinterstitium
by the collecting tubule. The above described transport of substances facilitated by the
special arrangement of Henle’sloop and vasarecta is called the counter current
mechanism.
This mechanism helps to maintain a concentration gradient in the medullaryinterstitium.
Presence of such interstitial gradient helps in an easy passage of water from the collecting
tubule thereby concentrating the filtrate (urine). Human kidneys can produce urine nearly
four times concentrated than the initial filtrate formed.

50. Failure of kidneys to adequately filter toxins and waste products from the blood
1.Decreaseintheglomerularfiltrationrate.
2.Elevatedserumcreatininelevel.
3.Abnormalfluidlevelsinthebody,
4.Derangedacidlevels,abnormallevelsofelectrolytespotassium,calcium,
phosphate,and(inthelongerterm)anaemia.
5.Dependingonthecause,hematuria(bloodlossintheurine)andproteinuria
(protein
-
lossintheurine)mayoccur.
6.Long-termkidneyproblemshavesignificantrepercussionsonotherdiseases,
suchascardiovasculardisease.

51. Acute Kidney Injury Chronic Renal Failure
-Rapidly progressive loss of renal function
-Oliguria
-Pre renal, intrinsic or post renal causes
-body water and body fluids disturbances
and electrolyte derangement
-AKI may result from a variety of causes,
generally classified as prerenal, intrinsic
and postrenal.
-Chronic kidney disease (CKD) may develop
slowly and initially, show few symptoms.
-CKD can be the long term consequence of
irreversible acute disease or part of a disease
progression

53. Blood drained from a convenient artery is pumped into a dialysing unit after adding an
anticoagulant like heparin.
The unit contains a coiled cellophane tube surrounded by a fluid (dialysing fluid) having
the same composition as that of plasma except the nitrogenous wastes.
The porous cellophane membrane of the tube allows the passage of molecules based on
concentration gradient.
As nitrogenous wastes are absent in the dialysing fluid, these substances freely move
out, thereby clearing the blood.
The cleared blood is pumped back to the body through a vein after adding anti-heparin
to it.

54. Thestonesaresolidconcretionsorcalculi(crystalaggregations)formedinthekidneys
fromdissolvedurinaryminerals.
Nephrolithiasisreferstotheconditionofhavingkidneystones.
Urolithiasisreferstotheconditionofhavingcalculiintheurinarytract(whichalso
includesthekidneys),whichmayformorpassintotheurinarybladder.
Ureterolithiasisistheconditionofhavingacalculusintheureter,thetubeconnecting
thekidneysandthebladder.
Thereareseveraltypesofkidneystonesbasedonthetypeofcrystalsofwhichthey
consist.
Themajorityarecalciumoxalatestones,followedbycalciumphosphatestones.
Morerarely,struvitestones(magnesiumamminiumphosphate)areproducedbyurea-
splittingbacteriainpeoplewithurinarytractinfections,
Peoplewithcertainmetabolicabnormalitiesmayproduceuricacidstonesorcystine
stones.

56. URAEMIA:
Normalvalueofureainbloodis0.01to0.03%,butwhenthelevelrisestoabove
0.05%thenitiscalleduraemia.Itishighlyharmfulanditmayleadtokidney
failure.
NEPHRITIS:
ItisreferredtoasGlomerulonephritisorBright’sdiseaseisthetermusedfor
diseasesthatprimarilyinvolverenalglomerulilikehaematuria,proteinuria,
hypertenstion,oedemaandoligouria.
Streptococcalglomerulornephritisiscommonformseenmostlyinchildren
childrenof6to16years.Itisduetoinfectionofthroatcalledstreptococcal
pharyngitis.

57. dr.aari
f