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hapter 23: The Urinary System

1. Introduction:a. Urinary system: principal means of waste excretionb. idneys: !lands that separate metabolic waste from blood

2. "unctions of the Urinary Systema. Urinary System: !roup of or!ans in the body concerned w# filterin! out excess fluid $ other substances from bloodstream

i. The substances are filtered out from the body in the form of urineii. Consists of % principal or!ans:

1. 2 kidneys& 2 ureters& urinary bladder& $ urethrab. Functions of Kidney:

i. 'xcretion (primary function)ii. "ilter blood plasma $ excrete toxic metabolic wastesiii. *e!ulate blood +olume $ pressure $ osmolarity by re!ulatin! water outputi+. *e!ulate the electrolyte $ acid,balance of the body fluids+. Secrete en-yme *enin

+i. ormone secretion1. 'rythropoietin: stimulate production of */C2. Calcitriol: re!ulate calcium homeostasis $ bone metabolism

+ii. Clear hormones $ dru!s from blood+iii. 0etoxify free radicalsix. luconeo!enesis (mae new !lucose from amino acids) in conditions of extreme star+ation

c. itro!enous 4astesi. 4aste: any substance that is useless to the body or present in excess of the body5s needsii. 6etabolic waste: waste substance produced by the body

1. Nitrogenous waste: small nitro!en,containin! compounds that are the most toxic metabolic wastei. Ammonia ii. Urea: mae up 789& by,product of protein catabolismiii. Uric Acid: produced by catabolism of nucleic acidsi+. Creatinine: produced by catabolism of creatine phosphate

b. Blood Urea Nitrogen (BUN!le+el of nitro!enous waste in the bloodi. A"otemia: ele+ated /U may indicate renal insufficiency $ can pro!ress to uremia

d. #$cretion: process of separatin! wastes from the body fluids $ eliminatin! themi. Carried out by ; systems:

1. *espiratory Systema. 'xcretes Cnatomy of idneya. ?osition $ >ssociation Structures

i. idney lies a!ainst posterior abdominal wallii. *i!ht idney is sli!htly lower than left because of the lar!e ri!ht lobe of the li+er

iii. *etroperitoneal: idney& ureters& urinary bladder& renal artery $ +eins1. ?eritoneal: serous membrane that forms the linin! of abdominal ca+ity

b. ross >natomyi. &ilum: a slit on the medial surface that admits the renal ner+es& blood +essels& lympathics& $ ureterii. ?rotected by 3 layers of connecti+e tissue:

1. 'enal fascia: binds idney $ associated to abdominal wall2. erirenal fat ca)sule: cushions idney $ holds it in place3. Fibrous ca)sule: encloses the idney anchorin! at the hilum& $ protects it from trauma $ infection

iii. *enal parenchyma (functional part of or!an): the !landular tissue that forms the urine1. 'enal sinus: the medial ca+ity (encircle by the renal parenchyma) occupied blood $ lymphatic +essels&

ner+es& $ urine,collectin! structures2. 2 -ones

a. 'enal Corte$(outer layer)

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b. 'enal *edulla(inner layer facin! the sinus)3. 'enal columns: extensions of the cortex that pro@ects toward the sinus $ di+ide the medulla into %,18 re

)yramidsa. 'ach renal pyramid is conical w# broad base facin! the cortex $ a renal )a)illa (a blunt point) f

the sinusi+. *inor caly$: a cup where the renal papilla nestles in which collects its urine+. *a+or caly$: formed by the con+ersion of 2,3 minor calyces

+i. 'enal )el,is: a funnel in the sinus formed by 2,3 ma@or calyces con+er!in!+ii. Ureter: tubular continuation of renal pel+is that drains the urine down to the urinary bladder

+iii.c. *enal Circulation

i. idneys recei+e 219 of the cardiac output for the purpose of waste remo+alii. 'ach idney is supplied by a renal arteryarisin! from aorta.iii. In the hilum& renal artery di+ides into a few segmental arteriesi+. Se!mental arteries di+ides into interlobar arteries

1. Interlobar artery enter each renal column $ tra+els between pyramids toward corticomedullary @unction

(boundary between cortex $ medulla)+. Interlobar arteries branch into arcuate arteries(tra+el alon! base of pyramids)+i. 'ach arcuate artery !i+es rise to se+eral cortical radiate(interlobar) arteriesthat pass upward into cortex+ii. >s interlobar artery ascends to cortex& afferent arteriolesarise from it at nearly ri!ht trian!les

1. >fferent arterioles supplies a functional unit of idney (ne)hron)+iii. >fferent arteriole lead to a ball of capillaries (glomerulus)

1. lomerulus is enclosed in a sphere (!lomerulus capsule)ix. /lood lea+es the !lomerus by way of an efferent arteriolex. 'fferent arteriole usually leads to a plexus of )eritubular ca)illaries(form a networ around the renal tubule of th

cortical nephron, renal cortex)1. *enal tubule reabsorbs most of the 2< $ solutes that filtered out of the blood at the !lomerulus $ return

bloodstream by way of peritubular capillaries

xi. ?eritubular capillaries carries it away to cortical radiate(interlobar) ,einsA arcuate ,einsA interlobar,einsArenal ,eins

1. *enal +ein lea+es the hilum $ drains into inferior +ena ca+axii. *enal medulla recei+es only 1,29 of total renal blood flow& supplied by ,asa recta(a networ of +essels)

1. In the medulla& efferent capillary !i+e rise to +asa recta instead of peritubular capillaries2. Basa recta capillares empties into arcuate $ cortical radiate +eins

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xiii.d. Ne)hron: functional unit of idney

i. 2 principal parts:-. 'enal Cor)uscle

a. Consists of:i. lomerulusii. 2 layered lomerular (Bowman Ca)sule

1. arietal (outer layer:a. Simple suamous epithelium

2. /isceral (inner layer:a. ?odocytes: cells that wrap around !lomerus5s capillaries

3. Capsular space: filtrate collector that separate the 2 layers;. Bascular pole:

a. >fferent arteriole enters capsule to brin! blood to !lomerulusb. 'fferent arteriole lea+es capsule $ carries blood awayc. >fferent is lar!er than efferent

7. Urinary pole: opposite end that !i+es rise to renal tube

iii.0. 'enal 1ubule: duct that leads away from the !lomerular capsule $ ends at tip of a medullary pyramid

a. ; *e!ionsi. ?roximal Con+oluted Tubule (?CT)

-. >rises from !lomerular capsule0. Don!est $ most coiled re!ion2. ?rominent micro+illi for ma@ority of absorption

ii. ephron Doop (Doop of enle)

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-. Don! U,shaped portion of renal tubule found mostly in medulla0. 0escendin! $ >scendin! limb2. Thic (transports salts) $ Thin (permeable to 2

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iii. Urine: fluid in collectin! duct4. Urine "ormation -! lomerular Filtration

i. ?rocess where 2< $ small dissol+ed solute molecules are forced throu!h fenestrations of capillary tuft w#in the r

corpuscle& $ throu!h endothelial capsular membrane $ filtration slits formed by the pedicels of the podocytes (the

+isceral layer of the renal corpuscle)& $ into the capsular space the main dri,ing force is the glomerular blood

hydrostatic )ressureb. lomerular filtration! process in which 2< $ some solutes in blood plasma pass from capillaries of the !lomerulus into t

capsular space of the nephroni. "luid passes throu!h 3 barriers that consists ofFiltration *embrane

1. "enestrated endothelium of the capillary

2. /asement membrane (/etween capillary $ !lomerular capsule)3. "iltration slits (between each podocyte)

ii. 6olecules that can pass freely throu!h the filtration membrane1. 28& electrolytes& !lucose& fatty acids& amino acids& nitro!enous wastes (urea& uric acid& creatinine)& $ +ita

iii. Thin!s that cannot pass throu!h1. /lood cells& plasma proteins& lar!e anions& protein,bound minerals $ hormones& most molecules A E nm

diameter

2.

i+. idney infections $ trauma can dama!e the filtration membrane $ allow albumin or blood cells to filter throu!h1. ?roteinuria (albuminuria) $ hematuria

c. "iltration ?ressurei. ?ressure that fa+ors filtration (outward from !lomerulus to /owman5s capsule)

1. Blood &ydrostatic ressure (B&is much hi!her in the !lomerulus than blood capillaries

a. *esults because the afferent arteriole is lar!er than efferent arterioles& !i+in! the !lomerulus a inlet $ small outletii. ?ressure that oppose filtration (Inward from /owman5s capsule to !lomerulus)

1. Colloid

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2. "iltration coefficient (f) depends on permeability $ surface area of filtration barriera. 6easured by the surface area of !lomerular capillary a+ailable for filtration $ permeability

iii. Total amount of filtrate produced euals 78 to %8 times the amount of blood in the body1. HH9 of filtrate is reabsorbed since only to 2 D of urine excreted# day

e. *e!ulation of lomerular "iltration ("*F indicator of idney function)i. F' too high

1. "luid flows throu!h the renal tubules too rapidly for them to reabsorb the usual amount of the water $ so2. Increased urine output3. 0ehyration $ electrolyte depletion

ii. F' too low

-. "luid flows slu!!ishly throu!h the tubules $ reabsorb wastes that should be eliminated in the urine2. 4astes reabsorbed3. >-otemia may occur

iii. "* controlled by ad@ustin! glomerular blood )ressure (B&i+. "* control is achie+ed by 3 homestatic mechanisms:

-. 'enal Autoregulationa. ephrons to ad@ust their own blood flow $ "* w#out external (ner+ous or hormonal) controlb. "* fluctuates sli!htlyc. elps to ensure stable fluid $ electrolyte balance in spite of many circumstances that substantia

alter one5s blood pressured. 2 methods of autore!ulation:

i. *yogenic mechanism: smooth muscle contracts when stretched myoF muscleJ

1. Increased blood pressure stretches the afferent arteriolea. >rteriole constricts $ pre+ents chan!e in blood flow to the !lomerulu2. 4hen blood pressure falls

a. >fferent arteriole relaxes $ allows blood flow more easily into !lomeii. 1ubuloglomerular feedback (!lomerulus recei+es feedbac on the status of tubular fl

1. >d@ust filtration to re!ulate the composition of the fluid& stabili-e its own nephr

performance& $ compensate for fluctuation in systemic blood pressure0. 3u$taglomerular a))aratus! at the end of nephron loop reenterin! renal cor

loop comes in contact w# afferent $ efferent arterioles. 3 special cell types:a. *acula densa: senses +ariations in flow or fluid composition

i. Stimulate K cellsb. 3u$taglomerular (3 cells: enlar!ed smooth muscle cells in the af

arteriole when stimulated by macula:i. 0ilate or constrict the arteriolesii. Secrete renin (in response to drop in blood pressure $ initia

the renin,a!iotensin,aldosterone mechanism to raise /?)c. *esangial cells: between arterioles $ amon! capillaries of !lomeru

i. Constrict or relax capillaries to re!ulate blood flow $ "*e. e!ati+e "eedbac Control of "*

i. 5f F' rises...1. *acula densestimulate 3 cells& which constrict afferent arteriole& reducin!2. *esangial cellsmay contract& which constricts capillaries& reducin! filtration

ii. 5f F' falls...-. *acula densarelaxes afferent arterioles $ mesangial cells

2. /lood flow increases $ "* rises0. Sym)athetic Control

a. Sympathetic ner+ous system $ adrenal epinephrine constrict the afferent arterioles in strenuous

exercise or acute conditions lie circulatory shoci. *educes "* $ urine outputii. /lood redirected to heart& brain& $ seletal muscleiii. "* may be low as a few mD#min

2. &ormonal Controla. 4hen /? drops& sympathetic fibers stimulate the @uxta!lomerular cells to secrete the en-yme re

*enin acts on an!iotensino!en (a protein) to split into an!iotensin I. >n!iotensin, con+ertin! en-

(>C') from lun!s con+erts it to an!iotensin IIb. *enin,>n!iotensin,>ldosterone System

i. 'eninsecreted by K cells in response to low /?

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ii. Angiotensinogencon+erted to angiotensin 5iii. AC#con+erts angiotensin 5to angiotensin 55& the acti+e hormone

1. >n!iotensin II is a hormone that wors in se+eral ways to restore fluid +olume

/?a. Cardio+ascular system: +asocontriction to ele+ate /?b. Stimulate adrenal cortex to secrete aldosterone (promotes 2ater Conser,ationa. idney eliminates metabolic wastes from the body& but also pre+ents excessi+e water loss as wellb. >s the idney returns water to the tissue fluid $ bloodstream& the fluid remainin! in the renal tubules passes as urine& $

becomes more concentratedc. Collecting @uct Concentrates Urine

i. Collecting duct (C@: be!ins in the cortex where it recei+es tubular fluid from se+eral nephrons

ii. >s C0 passes throu!h the medulla& it reabsorbs water& concentratin! urine up to ;x (C0 become hypertonic)

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iii. 2 facts that enable C0 to produce a hypertonic urine:1.

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1. Chronic polyuria can lead to diseases (diabetes)iii. liguria: output of less than 788mD#dayi+. Anuria: 8 to 188 mD#day

1. Dow output from idney disease& dehydration& circulatory shoc& prostate enlar!ement2. Dow urine output of less than ;88 mD# day& the body cannot maintain a safe& low concentration of wastes

the plasma+. @iabetes: any metabolic disorder resultin! in chronic polyuria

1. >t least ; forms of diabetesa. @iabetes mellitus(1y)e -$ 0) $ estational diabetes(durin! pre!nancy)

i. i!h concentration of !lucose in renal tubule

ii. lucose opposes the osmotic reabsorption of wateriii. lycosuria: !lucose in the urineb. @iabetes insi)idus

i. >0 hyposecretion (low amountF less water retentionF more water in urine)ii. ot enou!h water to be reabsorbed in the collectin! ductiii. 6ore water passes in urine

,i. @iuretics1. >ny chemical that increases urine +olume

a. Some increase "*i. Caffeine dilates the afferent arteriole

b. *educe tubular reabsorption of wateri. >lcohol inhibits >0 secretion (reduce reabsorption in collectin! duct)

c. >cts on nephron loop (loop diuretic): inhibits a=& =& Cl, symporti. Impaires countercurrent multiplier reducin! the osmotic !radient in medulla2. Treat hypertension (hi!h /?) $ Con!esti+e eart "ailure (by reducin! body5s fluid +olume $ /?)

H. Urine Stora!e $ 'liminationa. 1he Ureters

i. 6uscular tube from the idney that extends to the urinary bladder1. *etroperitonealL about 27cm lon!2. ?asses posterior to the bladder $ enters it from below3. "lap of mucosa acts as a +al+e into the bladder

ii. 3 layers of ureter1. Ad,entitia: CT layer that connects ureters to surroundin! structures2. *uscularis: 2 layers of smooth muscle

a. Stretches $ contracts in peristaltic wa+e (mils urine down to bladder)3. *ucosa: transitional epitheliuma. /e!ins at minor calyces $ extends throu!h the bladder

;. Dumen +ery narrow& easily obstructed (idney stones)4. Kidney Stone

a. 'enal calculus: hard !ranule of calcium phosphate& calcium oxalate& uric acid& or ma!nesium s

(stru+ite)b. Usually small enou!h to pass unnoticedc. Dar!e stones mi!ht bloc renal pel+is or ureter $ can cause pressure build up in idney which

destroys nephronsi. ?ainful ematuria

d. Causes include hypercalcemia& dehydration& p imbalances& freuent UTIs& or enlar!ed prostat

!land (urine retention)e. Treatments

i. 0issol+in! dru!sii. Sur!eryiii. Dithotripsy

b. Urinary Bladderi. 6uscular sac on floor of pel+ic ca+ityii. @etursor muscle: muscularis consistin! of 3 layers of smooth muscle

1. Contracts when you want to urinatec. Uretha: con+eys urine out of body

i. 5nternal urethral s)hincter1. 0etrusor muscle thicenin!

2. 5n,oluntarycontrol

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ii. #$ternal urethral s)hincter:1. Urethra passes throu!h pel+ic floor2. /oluntarycontrol3. ?art of seletal muscle of pel+ic floor

iii. FemaleUrethra1. 3 to ; cm lon!0. #$ternal urethral orifice

a. /etween +a!inal orifice $ clitorisi+. *aleUrethra

1. 1E cm lon!

2. 3 re!ions of male urethraa. rostatic urethra(2.7 cm)i. ?asses throu!h prostate !land

b. *embranous urethra(8.7 cm)i. ?asses throu!h muscular floor of pel+ic ca+ity

c. S)ongy ()enile urethra(17cm)i. ?asses throu!h penis in corpus spon!iosum

d. Urinary 1ract 5nfection (U15i. Cystitis: infection of the urinary bladder

1. Common in females. 4hyR Smaller urethra& easier for bacteria to pass throu!h2. "reuently tri!!ered by sexual intercourse3. Can spread up the ureter causin! pyelitis& infection of renal pel+is

ii. yelone)hritis: infection that reaches the cortex $ the nephrons1. Can result from blood,borne bacteria

e. /oiding Urinei. 4hen bladder is fillin!

1. 0etrusor muscle relaxes2. Urethral spincters are ti!htly closed

a. Sympathetic pathwayi. ?ost!an!lionic fibers tra+el to the detrusor muscle (relax) $ internal urethral sphincter

(excite)3. Somatic motor fibers (pudendal ner+e) supply the external sphincter with +oluntary control

ii. *icturition: the act of urinatin!iii. *icturition refle$: spinal reflex that partly controls urination

i+. eural Control of micturition-. 5n,oluntary *icturition 'efle$a. Stretch rece)torsdetect fillin! of bladder& transmit afferent si!nals to spinal cordb. Si!nals return to bladder from spinal cord +ia parasympatic fibers in pel+ic ner+ec. 'fferent si!nals excite detrusor musclesd. 'fferent si!nals relax internal urethral sphincter. Urine is in+oluntarily +oided if not inhibited by b

0. /oluntary Controla. 6icturition center in pons recei+es si!nals from stretch receptorsb. If it is timely to urinate& pons returns si!nals to excite detursor $ relax internal urethral sphincter

Urine is +oidedc. If it5s untimelyto urinate& si!nals from pons excite spinal interneurons that eeps external ureth

sphincter contracted. Urine is retained

d. If it5s timelyto urinate& si!nals from pons cease $ external urethral sphincter relaxes. Urine is +18. &emodialysis: a procedure for artifically clearin! wastes from the blood when the idneys are not adeuately doin! so (renal

insufficiency)

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