Urinary System
Chapter 17
Functions
• Filtration of blood
• Body fluid regulation
– Water/salt balance
– pH balance
• Waste removal
Key Structures
•
•
•
•
•
•
Kidneys
Renal Veins
Renal Arteries
Ureters
Urinary Bladder
Urethra
Path of Urine
• Blood to kidney
• Urine Out
– Ureter
– Bladder
– Urethra
– Out
Kidneys
• Red/Brown color, bean shaped
• 12 cm long
• Enclosed by a capsule
Functions of Kidneys
• Filter blood
– Keep what is needed; excrete what is not
• Maintain content, volume, pH of body fluid
• Other functions
– Maintain RBC production
– Regulate blood volume and pressure
Kidney Structures
• Renal Medulla
• Renal Cortex
– Nephrons
• Major Calyx
• Minor Calyx
Blood Flow to Kidneys
• Blood from abdominal aorta to renal arteries
– Blood filtered 1st
– Gas exchange 2nd
• Renal veins take deoxygenated blood from
kidneys
• Veins lead to inferior vena cava
Nephrons
• A kidney has 1 million of these
• Smallest unit of filtration
• Blood supply to nephron
– Blood taken to nephron by afferent arteriole
– Efferent arteriole takes filtered (but not
deoxygenated blood) to peritubular capillaries
(surround tubes of nephron)
Fig17.02
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Renal capsule
Renal cortex
Renal medulla
Renal corpuscle
Nephrons
Renal
cortex
Minor calyx
Major calyx
Renal
medulla
Renal sinus
Renal column
Fat
in renal sinus
Renal pelvis
Collecting
duct
Renal
tubule
Papilla
Minor calyx
Renal papilla
(b)
Renal pyramid
Ureter
(a)
(c)
Fig17.03
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cortical radiate
artery and vein
Cortex
Proximal
convoluted
tubule
Cortical radiate
artery and vein
Afferent arteriole
Arcuate vein
and artery
Interlobar
vein and artery
Renal
artery
Renal
vein
Renal pelvis
Ureter
Medulla
Efferent
arteriole
Peritubular
capillary
Distal convoluted
tubule
Blood Supply cont.
• Glomerulus: cluster of blood capillaries
• Bowman’s capsule: cup like structure that
surrounds blood capillaries
Parts of Nephron
•
•
•
•
•
Bowman’s Capsule
Proximal (Convoluted) Tubule
Loop of Henle (Desecending/Ascending)
Distal (Convoluted) Tubule
Collecting Duct
Fig17.03
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cortical radiate
artery and vein
Cortex
Proximal
convoluted
tubule
Cortical radiate
artery and vein
Afferent arteriole
Arcuate vein
and artery
Interlobar
vein and artery
Renal
artery
Renal
vein
Renal pelvis
Ureter
Medulla
Efferent
arteriole
Peritubular
capillary
Distal convoluted
tubule
Fig17.06
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Glomerular
capsule
Proximal
convoluted
tubule
Cortical radiate
artery
Cortical radiate
vein
Glomerulus
Afferent
arteriole
Efferent
arteriole
Distal
convoluted
tubule
Renal
cortex
From renal
artery
Peritubular
capillary
To renal
vein
Renal
medulla
Nephron
loop
Descending
limb
Ascending
limb
Collecting duct
21
Fig17.07
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Glomerular
capsule
Afferent
arteriole
Glomerulus
Juxtaglomerular
apparatus
Distal
convoluted
tubule
Efferent
arteriole
Proximal
convoluted
tubule
Glomerulus
Podocyte
Afferent arteriole
Nephron loop
(a)
Juxtaglomerular
cells
Macula densa
Juxtaglomerular
apparatus
Ascending limb
of nephron loop
Glomerular capsule
Efferent arteriole
(b)
22
Urine Formation
• Three Stages
1. Filtration
• Glomerulus/Bowman’s Capsule
2. Secretion
3. Reabsorption
• 2 & 3 happen in rest of the nephron
Filtration
• Glomerulus is leaky; so portion of the blood
is filtered out of it and into the Bowman’s
capsule
• Filtration depends on pressure
Pressure
• High Pressure
– Forces small things from glomerulus to
Bowman’s capsule
– Anything that leaves blood and enters capsule is
called filtrate
Pressures to Know
• Hydrostatic pressure: pressure due to
presence of water
• Osmotic pressure: pressure due to high
concentration of dissolved solutes
– “Pulling pressure”
– Water is pulled toward solutes
Fig17.10
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Blood
flow
Blood
flow
Plasma colloid
osmotic pressure
Glomerular
hydrostatic
pressure
Net filtration
pressure
Capsular
hydrostatic pressure
Net Outward Pressure
Outward force, glomerular hydrostatic pressure
Inward force of plasma colloid osmotic pressure
Inward force of capsular hydrostatic pressure
Net filtration pressure
= +60 mm
= –32 mm
= –18 mm
= +10 mm
27
Overall
• Net filtration pressure forces substances out
of glomerulus and into capsule
Factors Affecting Filtration
• Change in diameter of arterioles
– Smaller afferent arteriole = less filtration
– Smaller efferent arteriole = more filtration
• Less proteins in blood = less glomerular
osmotic pressure = more filtration
• More pressure in capsule = less filtration
Reabsorption
• Mostly in proximal tubule
– Microvilli
• Glucose, amino acids, water, protein
• There is a limit to reabsorption, so these are
still excreted in urine as well
Fig17.06
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Glomerular
capsule
Proximal
convoluted
tubule
Cortical radiate
artery
Cortical radiate
vein
Glomerulus
Afferent
arteriole
Efferent
arteriole
Distal
convoluted
tubule
Renal
cortex
From renal
artery
Peritubular
capillary
To renal
vein
Renal
medulla
Nephron
loop
Descending
limb
Ascending
limb
Collecting duct
31
Secretion
• Opposite of reabsorption
• Excess H ions and organic compounds
Urine Composition
• Varies from time to time; reflects the
amounts of water/solutes that the kidneys
eliminate to maintain homeostasis
• 95% water, and also contains urea, uric acid,
a trace of amino acids, and electrolytes
Urine Elimination
• Pathway of urine after forming in nephron:
– Collecting Duct
– Minor calyces
– Major calyces
– Renal Pelvis
– Ureter
– Bladder
– Urethra
– OUT!
Fig17.03
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cortical radiate
artery and vein
Cortex
Proximal
convoluted
tubule
Cortical radiate
artery and vein
Afferent arteriole
Arcuate vein
and artery
Interlobar
vein and artery
Renal
artery
Renal
vein
Renal pelvis
Ureter
Medulla
Efferent
arteriole
Peritubular
capillary
Distal convoluted
tubule
Ureters
• 1 per kidney
• Peristalsis forces urine down
• Valve at end allows urine into bladder
Bladder
• Muscular, hollow, sphere, highly folded
• Stores urine, forces it into urethra
Micturition Reflex
• Process by which urine leaves bladder
• Stretching of bladder detected by micturition
reflex center of spinal cord
• Causes:
– Bladder muscle contraction
– Urge to urinate
– Internal urethral sphincter relaxes
– External urethral sphincter relaxes (voluntary
control)
Urethra
• Opening from bladder to external
environment
Diuretics
Kidney Stones