k2 - physiology of urinary system

8/11/2019 K2 - Physiology of Urinary System

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Physiology of Urinary Sistem


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Main function

Excretion & Elimination Regulating blood volume and blood pressure

Regulating plasma concentrations of ions

Helping to stabilize blood pH

Conserving valuable nutrients

Assisting the liver


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Coordination with Others

digestive respiratory

cardiovascular


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Regulation

Autoregulation Autonomic nervous system

Endocrine


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Nitrogenous Wastes

Ureaproteinsamino acids NH2removed

forms ammonia, liver converts to urea

Uric acidnucleic acid catabolism

Creatinine

creatinine phosphate catabolism Renal failure

azotemia: nitrogenous wastes in blood

uremia: toxic effects as wastes accumulate


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Excretion

Separation of wastes from body fluids andeliminating them

respiratorysystem: CO2

integumentarysystem: water, salts, lactic acid, ureadigestivesystem: water, salts, CO2, lipids, bile

pigments, cholesterol

urinarysystem: many metabolic wastes, toxins, drugs,

hormones, salts, H+and water


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Nephrons

Unit functional of kidney Cortical nephrons (85%)

short nephron loops

efferent arterioles branch offperitubular capillaries

Juxtamedullary nephrons (15%)

very long nephron loops, maintainsalt gradient, helps conserve water

efferent arterioles branch off vasa

recta, blood supply for medulla


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Nephron Diagram

Peritubular

capillaries

shown only onright


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Renal Corpuscle

Glomerular filtrate collects in capsular

space, flows into renal tubule


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Renal (Uriniferous) Tubule Proximal convoluted tubule

(PCT) longest, most coiled, simple

cuboidal with brush border

Nephron 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 permeable

Distal convoluted tubule (DCT)

cuboidal, minimal microvilli


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Renal (Uriniferous) Tubule 2

Juxtaglomerular apparatus:DCT,afferent, efferent arterioles Collecting duct: several DCTs join Flow of glomerular filtrate:

glomerular capsule PCT nephron loop DCT collectingduct papillary duct minor calyxmajor calyx renal pelvis ureter urinary bladder urethra


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Urine Formation

Filtration Reabsorption

Secretion


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Filtration Membrane Diagram


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Filtration Membrane

Fenestrated endothelium70-90nm pores exclude blood cells

Basement membrane

proteoglycan gel, negative chargeexcludes molecules > 8nm

blood plasma 7% protein,

glomerular filtrate 0.03%

Filtration slits

podocyte arms have pedicels with

negatively charged filtration slits,

allow particles < 3nm to pass


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Filtration Pressure


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Glomerular Filtration Rate (GFR)

Filtrate formed per minute Filtration coefficient (Kf) depends on permeability

and surface area of filtration barrier

GFR = NFP x Kf 125 ml/min or 180 L/day 99% of filtrate reabsorbed, 1 to 2 L urine excreted


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Effects of GFR Abnormalities

GFR, urine output rises dehydration,electrolyte depletion

GFR wastes reabsorbed (azotemia possible)

GFR controlled by adjusting glomerular bloodpressure

autoregulation

sympathetic controlhormonal mechanism: renin and angiotensin


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Tubular Reabsorption and Secretion


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Proximal Convoluted Tubules (PCT)

Reabsorbs 65% of GF to peritubular capillaries Great length, prominent microvilli and abundant

mitochondria for active transport

Reabsorbs greater variety of chemicals than otherparts of nephron

transcellular route - through epithelial cells of PCT

paracellular route - between epithelial cells of PCT Transport maximum: when transport proteins of plasma

membrane are saturated; glucose > 180 mg/dL remains in

urine (glycosuria)


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Tubular Secretion of PCT

and Nephron Loop

Waste removal

urea, uric acid, bile salts, ammonia, catecholamines,

many drugs

Acid-base balance

secretion of hydrogen and bicarbonate ions regulates

pH of body fluids

Primary function of nephron loopwater conservation, also involved in electrolyte

reabsorption


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DCT and Collecting Duct

Effect of aldosteroneBP causes angiotensin II formation

angiotensin II stimulates adrenal cortex

adrenal cortex secretes aldosteronealdosterone promotes Na+reabsorption

Na+reabsorption promotes water reabsorption

water reabsorption

urine volumeBP drops less rapidly


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DCT and Collecting Duct 2

Effect of atrial natriuretic factor (ANF)BP stimulates right atrium

atrium secretes ANF

ANF promotes Na+and water excretion

BP drops

Effect of ADH

dehydration stimulates hypothalamus

hypothalamus stimulates posterior pituitary

posterior pituitary releases ADH

ADH water reabsorption

urine volume


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Collecting Duct Concentrates Urine

Osmolarity 4x as highdeep in medulla

Medullary portion of

CD is permeable towater but not to NaCl


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Countercurrent Multiplier

Recaptures NaCl and returns it to renal medulla Descending limb

reabsorbs water but not salt

concentrates tubular fluid Ascending limb

reabsorbs Na+, K+, and Cl-

maintains high osmolarity of renal medulla

impermeable to water

tubular fluid becomes hypotonic

Recycling of urea: collecting duct-medullaurea accounts for 40% of high osmolarity of medulla

C t t M lti li


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Countercurrent Multiplier

of Nephron Loop Diagram


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Countercurrent Exchange System

Formed by vasa rectaprovide blood supply to medulla

Descending capillaries

NaCl diffuses into blood

Ascending capillaries

water diffuses into blood


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Maintenance of Osmolarity in Renal Medulla

S f T b l


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Summary of Tubular

Reabsorption and Secretion


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Composition and Properties of Urine

Appearance

almost colorless to deep amber; yellow color due to

urochrome, from breakdown of hemoglobin (RBCs)

Odor - as it stands bacteria degrade urea to ammonia

Specific gravity

density of urine ranges from 1.000 -1.035

Osmolarity - (blood - 300 mOsm/L) ranges from50 mOsm/L to 1,200 mOsm/L in dehydrated person

pH - range: 4.5 - 8.2, usually 6.0

Chemical composition: 95% water, 5% solutes

urea, NaCl, KCl, creatinine, uric acid


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Urine Volume

Normal volume - 1 to 2 L/day Polyuria > 2L/day

Oliguria < 500 mL/day

Anuria - 0 to 100 mL


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Renal Function Tests

Renal clearance: volume of blood plasma clearedof a waste in 1 minute

Determine renal clearance (C) by assessing blood

and urine samples: C = UV/PU (waste concentration in urine)

V (rate of urine output)

P (waste concentration in plasma) Determine GFR: inulin is neither reabsorbed or

secreted so for this solute GFR = renal clearance

GFR = UV/P


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Renal Function Tests

Creatinine clearance:eliminates 84 mg of creatinine each hour

plasma creatinine concentration of 1.4 mg/dl

100 ml/menit


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Normal parameter

RBF : 1200 ml/min RPF : 625 ml/min

Fraction filtration : 20%

GFR : 125 ml/ min

Urin production : 1-2 ml/ menit


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Aging

A decline in the number of functional nephrons.

The total number of kidney nephrons drops by 3040 %

between ages 25 and 85.

A reduction of the GFR.

decreased numbers of glomeruli, cumulative damage to

the filtration apparatus in the remaining glomeruli, and

reductions in renal blood flow.

A reduced sensitivity to ADH.the distal portions of the nephron and collecting system

become less responsive to ADH. Less reabsorption of

t d di i d di i l t

k2 - physiology of urinary system

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