Anp2001 Week 4 Urinary Syst

The Urinary SystemFunctions of the urinary systemAnatomy of the kidneyUrine formationglomerular filtrationtubular reabsorptionwater conservationUrine and renal function testsUrine storage and elimination

Urinary SystemTwo kidneysTwo uretersUrethra

Kidney FunctionsFilters blood plasma, eliminates waste, returns useful chemicals to bloodRegulates blood volume and pressureRegulates osmolarity of body fluidsSecretes renin, activates angiotensin, aldosterone controls BP, electrolyte balanceSecretes erythropoietin, controls RBC countRegulates PCO2 and acid base balanceDetoxifies free radicals and drugsGluconeogenesis

Nitrogenous WastesUreaproteinsamino acids NH2 removed forms ammonia, liver converts to urea Uric acidnucleic acid catabolismCreatininecreatinine phosphate catabolismRenal failureazotemia: nitrogenous wastes in blooduremia: toxic effects as wastes accumulate

ExcretionSeparation of wastes from body fluids and eliminating themrespiratory system: CO2integumentary system: water, salts, lactic acid, ureadigestive system: water, salts, CO2, lipids, bile pigments, cholesterolurinary system: many metabolic wastes, toxins, drugs, hormones, salts, H+ and water

Anatomy of KidneyPosition, weight and sizeretroperitoneal, level of T12 to L3about 160 g eachabout size of a bar of soap (12x6x3 cm)Shapelateral surface - convex; medial - concaveCT coveringsrenal fascia: binds to abdominal wall adipose capsule: cushions kidneyrenal capsule: encloses kidney like cellophane wrap

Anatomy of KidneyRenal cortex: outer 1 cm Renal medulla: renal columns, pyramids - papillaLobe of kidney: pyramid and its overlying cortex

Lobe of Kidney

Kidney: Frontal SectionMinor calyx: cup over papilla collects urine

Path of Blood Through KidneyRenal artery interlobar arteries (up renal columns, between lobes) arcuate arteries (over pyramids) interlobular arteries (up into cortex) afferent arterioles glomerulus (cluster of capillaries) efferent arterioles (near medulla vasa recta) peritubular capillaries interlobular veins arcuate veins interlobar veinsRenal vein

Blood Supply Diagram

Renal CorpuscleGlomerular filtrate collects in capsular space, flows into renal tubule

Renal (Uriniferous) TubuleProximal convoluted tubule (PCT) longest, most coiled, simple cuboidal with brush borderNephron loop - U shaped; descending + ascending limbsthick segment (simple cuboidal) initial part of descending limb and part or all of ascending limb, active transport of saltsthin segment (simple squamous) very water permeableDistal convoluted tubule (DCT)cuboidal, minimal microvilli

Renal (Uriniferous) Tubule 2Juxtaglomerular apparatus: DCT, afferent, efferent arteriolesCollecting duct: several DCTs joinFlow of glomerular filtrate:glomerular capsule PCT nephron loop DCT collecting duct papillary duct minor calyx major calyx renal pelvis ureter urinary bladder urethra

Nephron DiagramPeritubular capillaries shown only on right

The Nephron

BOWMANS CAPSULE:

A spherical capsule around glomerulus (blood vessels).

PROXIMAL CONVOLUTED TUBULE:

About 75% of sodium is removed from fluid here (by active transport, chlorine follows passively.)

LOOP OF HENLE:

The counter current exchanger:

DESCENDING LOOP OF HENLE:

Permeable to water and other solutes.

LOOP OF HENLE:

The counter current exchanger:

ASCENDING LOOP OF HENLE:

Chlorine ions--active transport out. Sodium follows. Water does NOT.

LOOP OF HENLE:

The counter current exchanger sets up a gradient of more salt toward turn in loop, less near convoluted tubules.

DISTAL CONVOLUTED TUBULE:

NaCl, Potassium, ammonia, carbonate removed here.

COLLECTING TUBULE:

Passes parallel to Loop of Henle, THROUGH PROGRESSIVELY MORE CONCENTRATED INTERSTITIAL SPACE.

In Collecting Tubule, water wants to move from region of higher to lower water concentration (OSMOSIS). The tendency to do this increases as it passes through more distal regions of collecting tubule.

NephronsTrue proportions of nephron loops to convoluted tubules shownCortical nephrons (85%)short nephron loopsefferent arterioles branch off peritubular capillariesJuxtamedullary nephrons (15%)very long nephron loops, maintain salt gradient, helps conserve waterefferent arterioles branch off vasa recta, blood supply for medulla

Urine Formation Preview

Filtration Membrane Diagram

Filtration MembraneFenestrated endothelium70-90nm pores exclude blood cellsBasement membraneproteoglycan gel, negative charge excludes molecules > 8nm blood plasma 7% protein, glomerular filtrate 0.03%Filtration slitspodocyte arms have pedicels with negatively charged filtration slits, allow particles < 3nm to pass

Filtration Pressure

Glomerular Filtration Rate (GFR)Filtrate formed per minuteFiltration coefficient (Kf) depends on permeability and surface area of filtration barrierGFR = NFP x Kf 125 ml/min or 180 L/day99% of filtrate reabsorbed, 1 to 2 L urine excreted

Effects of GFR AbnormalitiesGFR, urine output rises dehydration, electrolyte depletionGFR wastes reabsorbed (azotemia possible)GFR controlled by adjusting glomerular blood pressure autoregulationsympathetic controlhormonal mechanism: renin and angiotensin

Juxtaglomerular Apparatus

Renal Autoregulation of GFR BP constrict afferent arteriole, dilate efferent BP dilate afferent arteriole, constrict efferentStable for BP range of 80 to 170 mmHg (systolic)Cannot compensate for extreme BP

Negative Feedback Control of GFR

Sympathetic Control of GFRStrenuous exercise or acute conditions (circulatory shock) stimulate afferent arterioles to constrict GFR and urine production, redirecting blood flow to heart, brain and skeletal muscles

Hormonal Control of GFR

Effects of Angiotensin II

Tubular Reabsorption and Secretion

Peritubular CapillariesBlood has unusually high COP here, and BHP is only 8 mm Hg (or lower when constricted by angiotensin II); this favors reabsorptionWater absorbed by osmosis and carries other solutes with it (solvent drag)

Proximal Convoluted Tubules (PCT)Reabsorbs 65% of GF to peritubular capillaries Great length, prominent microvilli and abundant mitochondria for active transportReabsorbs greater variety of chemicals than other parts of nephrontranscellular route - through epithelial cells of PCTparacellular route - between epithelial cells of PCTTransport maximum: when transport proteins of plasma membrane are saturated; glucose > 220 mg/dL remains in urine (glycosuria)

Tubular Secretion of PCT and Nephron LoopWaste removalurea, uric acid, bile salts, ammonia, catecholamines, many drugsAcid-base balancesecretion of hydrogen and bicarbonate ions regulates pH of body fluidsPrimary function of nephron loop water conservation, also involved in electrolyte reabsorption

DCT and Collecting DuctEffect of aldosterone BP causes angiotensin II formation angiotensin II stimulates adrenal cortexadrenal cortex secretes aldosterone aldosterone promotes Na+ reabsorptionNa+ reabsorption promotes water reabsorptionwater reabsorption urine volumeBP drops less rapidly

DCT and Collecting Duct 2Effect of atrial natriuretic factor (ANF) BP stimulates right atriumatrium secretes ANFANF promotes Na+ and water excretionBP dropsEffect of ADHdehydration stimulates hypothalamus hypothalamus stimulates posterior pituitary posterior pituitary releases ADHADH water reabsorptionurine volume

Collecting Duct Concentrates UrineOsmolarity 4x as high deep in medulla Medullary portion of CD is permeable to water but not to NaCl

Control of Water LossProducing hypotonic urineNaCl reabsorbed by cortical CDwater remains in urineProducing hypertonic urineGFR dropstubular reabsorption less NaCl remains in CDADH CDs water permeabilitymore water is reabsorbedurine is more concentrated

Countercurrent MultiplierRecaptures NaCl and returns it to renal medullaDescending limbreabsorbs water but not saltconcentrates tubular fluidAscending limb reabsorbs Na+, K+, and Cl-maintains high osmolarity of renal medullaimpermeable to watertubular fluid becomes hypotonicRecycling of urea: collecting duct-medulla urea accounts for 40% of high osmolarity of medulla

Countercurrent Multiplier of Nephron Loop Diagram

Countercurrent Exchange SystemFormed by vasa rectaprovide blood supply to medulla do not remove NaCl from medullaDescending capillarieswater diffuses out of bloodNaCl diffuses into bloodAscending capillarieswater diffuses into bloodNaCl diffuses out of blood

Maintenance of Osmolarity in Renal Medulla

Summary of Tubular Reabsorption and Secretion

Composition and Properties of UrineAppearancealmost colorless to deep amber; yellow color due to urochrome, from breakdown of hemoglobin (RBCs)Odor - as it stands bacteria degrade urea to ammoniaSpecific gravity density of urine ranges from 1.000 -1.035Osmolarity - (blood - 300 mOsm/L) ranges from 50 mOsm/L to 1,200 mOsm/L in dehydrated personpH - range: 4.5 - 8.2, usually 6.0Chemical composition: 95% water, 5% solutesurea, NaCl, KCl, creatinine, uric acid

Urine VolumeNormal volume - 1 to 2 L/dayPolyuria > 2L/dayOliguria < 500 mL/dayAnuria - 0 to 100 mL

DiabetesChronic polyuria of metabolic originWith hyperglycemia and glycosuriadiabetes mellitus I and II, insulin hyposecretion/insensitivitygestational diabetes, 1 to 3% of pregnanciespituitary diabetes, hypersecretion of GHadrenal diabetes, hypersecretion of cortisolWith glycosuria but no hyperglycemiarenal diabetes, hereditary deficiency of glucose transportersWith no hyperglycemia or glycosuriadiabetes insipidus, ADH hyposecretion

DiureticsEffects urine output blood volumeUseshypertension and congestive heart failureMechanisms of action GFR tubular reabsorption

Urine Storage and EliminationUretersfrom renal pelvis passes dorsal to bladder and enters it from below, about 25 cm long3 layersadventitia - CTmuscularis - 2 layers of smooth muscleurine enters, it stretches and contracts in peristaltic wavemucosa - transitional epitheliumlumen very narrow, easily obstructed

Urinary Bladder and Urethra - Female

Urinary BladderLocated in pelvic cavity, posterior to pubic symphysis3 layersparietal peritoneum, superiorly; fibrous adventitia restmuscularis: detrusor muscle, 3 layers of smooth musclemucosa: transitional epitheliumtrigone: openings of ureters and urethra, triangular rugae: relaxed bladder wrinkled, highly distensiblecapacity: moderately full - 500 ml, max. - 800 ml

Female Urethra3 to 4 cm longExternal urethral orifice between vaginal orifice and clitorisInternal urethral sphincterdetrusor muscle thickened, smooth muscle, involuntary controlExternal urethral sphincterskeletal muscle, voluntary control

Male Bladder and Urethra18 cm longInternal urethral sphincterExternal urethral sphincter3 regionsprostatic urethraduring orgasm receives semenmembranous urethrapasses through pelvic cavitypenile urethra

KIDNEYS AND BLOOD PRESSURE RUGULATIONTHE RENIN-ANGIOTENSIN SYSTEM

1. Decrease in blood pressure causes decrease in amount of extracellular fluid.


2. Decrease in extracellular pressure near distal convoluted tubule causes juxtaglomerular cells to release the hormone RENIN.


3. RENIN in blood stream converts the liver enzyme ANGIOTENSINOGEN into ANGIOTENSIN I.


4. ANGIOTENSIN CONVERTING ENZYME (in the lung) converts Angiotensin I into ANGIOTENSIN II.


5. Angiotensin II causes ADRENAL GLAND to secrete/release ALDOSTERONE.


6. Aldosterone is a vasoconstrictor (increasing blood pressure) and INCREASES COLLECTING DUCT PERMIABILITY.


7:Urine volume decreasedFluid retainedBlood volume increasesBlood pressure up.

Voiding Urine - MicturitionMicturition reflex1) 200 ml urine in bladder, stretch receptors send signal to spinal cord (S2, S3)2) parasympathetic reflex arc from spinal cord, stimulates contraction of detrusor muscle 3) relaxation of internal urethral sphincter4) this reflex predominates in infants

Voluntary Control of Micturition5) micturition center in pons receives stretch signals and integrates cortical input (voluntary control)6) sends signal for stimulation of detrussor and relaxes internal urethral sphincter7) to delay urination impulses sent through pudendal nerve to external urethral sphincter keep it contracted until you wish to urinate8) valsalva maneuver aids in expulsion of urine by pressure on bladdercan also activate micturition reflex voluntarily

Adult Micturition Reflex Diagram

Hemodialysis

Anp2001 Week 4 Urinary Syst

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