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Lecture 2 the urinary system
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Copyright 2010, John Wiley & Sons, Inc.
Chapter 21
The Urinary System
Copyright 2010, John Wiley & Sons, Inc.
End of Chapter 21
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Urinary System Two kidneys and two ureters Urinary bladder & urethra Effector organ for
1. Regulation of Plasma ion composition2. Regulation of Body water Volume (BP)3. Regulation of blood pH (with lung)4. Production of Hormones5. Excretion of waste
Copyright 2010, John Wiley & Sons, Inc.
Urinary System
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Kidney Divided into cortex –outer portion Medulla- inner portion
Contain renal pyramids & renal columns Urine goes into renal pelvis
Edges are made of major & minor calyces Then out ureter
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Kidney
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Renal Blood Supply 20-25% resting CO goes through kidneys L. & R. renal arteries then
Segmental interlobar arcuate interlobular afferent arterioles glomerulus (capillary network) efferent arterioles peritubular capillaries veins renal vein Capillaris Units –nephrons grouped at pyramids
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Renal Blood Supply
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Renal Blood Supply
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Nephron Unit of renal function: corpuscle & tubule Corpuscle: forms filtrate Glomerulus & Glomerular capsule (cortex) Proximal convoluted tubule (cortex) Descending Loop of Henle (into medulla) ascending Loop of Henle (into medulla) Distal convoluted tubule (cortex) Collecting duct minor calyx
Copyright 2010, John Wiley & Sons, Inc.
Nephron
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Basic Operation Glomerular filtration-filter plasma Tubular reabsorption
Reabsorb needed compounds & water from filtrate
Tubular Secretion Secrete some materials into filtrate
Let rest go out as a solution called urine–see Table 21.1
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Basic Operation
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Glomerular Filtration Two layers of capsule surround glomerulus Between is capsular space Podocytes support capillary epithelium Form filtration membrane Permeable to water & solute but not most proteins & blood cells
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Filtration Pressure Blood pressure for filtration Opposed by colloid osmotic pressure and
capsular pressure Efferent and afferent arteriole diameters
adjust to maintain a net filtration pressure Even with small changes in blood pressure
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Glomerular Filtration Rate = GFR 105-125 ml/min Determines net reabsorption because it
determines filtrate flow ANP increases GFR
Responds to increased blood volume Sympathetic stimulation vasoconstriction
decreased GFR Urine production
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Glomerular Filtration
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Tubular Reabsorption Proximal tubule
~65% Na+ & H2O Normally 100% nutrients ~100% HCO3
- (depends on blood pH) Active transport of solutes Osmosis moves water Cells distal to proximal tubule fine tune
reabsorption under control
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Tubular Secretion Takes place all along tubule Major substances : H+, K+, ammonia, urea,
creatine, drugs like penicillin Helps regulate plasma pH 7.35-7.45 Diet is acid urine is typically acidic
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Urine Route Collecting ducts to calyces Calyces to ureter Ureter to bladder Bladder to urethra
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Filtration, Reabsorption,Secretion
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Hormonal Regulation Angiotensin II & aldosterone
Angiotensin II- stimulates NaCl in proximal tube Aldosterone- increases Na+ reabsorption & K+
secretion in DCT & CD More ions reabsorbed more water
ANP-increases GFR & inhibits aldosterone action less Na+ reabsorbed
ADH- responds to increased concentration of solute in blood + fall in BP
Copyright 2010, John Wiley & Sons, Inc.
Hormonal Regulation ADH: important to body water balance Increased concentration of solute in blood +
fall in BP ADH With no ADH: DCT & CD walls are
impermeable to water dilute urine With ADH: water reabsorption occurs
concentrated urine
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Components of Urine Urine = 1-2 l /day 95% water + urea, creatine, K+, ammonia, uric acid, Na+,
Cl-, Mg2+, sulfate, phosphate & Ca2+
Depends on diet and state of health See table 21.3
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Regulation of Water Reabsorption
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Urine Route Collecting ducts calyces Ureter
Lined with mucus & transitional epithelium Pass under bladder Full bladder prevents backflow
Bladder- directly in front of rectum Can stretch (700-800 ml) Smaller in females because of uterus Three layers of detrussor muscle
Urethra- internal urethral sphincter External urethral sphincter (voluntary)
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Urine Route
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Micturition = Urination Autonomic reflex- internal sphincter
Responds to stretch like rectum Parasympathetic detrusor muscle
contraction Conscious control-external sphincter
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Aging Kidneys shrink- decrease in capacity Thirst decreases dehydration urinary tract infections Males: prostate enlargement frequent
urination & slow flow Females: more prone to leakage of external
sphincter (incontinence) Both: nocturia
