CH24 Urinary System
 Most regulatory function
2. Juxtamedullary nephrons
 15%
 Long nephron loop extending deep into
medulla
 Essential to produce concentrated urine
Urinary system organs
Kidneys: rcv 25% of cardiac output, major excretory
organs)
Ureters
Urinary bladder
Urinary tract
Urethra
5 functions of urinary system
1. Adjusting bld volume and bp
2. Regulating bld plasma concentration of sodium,
potassium, chloride, or other ions
3. Stabilize bld pH
4. Conserving valuable nutrients by preventing loss
in urine
5. Removing drugs and toxins from bldstream
2 components of nephron
1. Renal corpuscle: BP forces water and solutes out
of glomerular capillaries (filtration) → produce filtrate
(protein free solution, bld plasma) in surrounding
capsular space
 Glomerular capsule (bowman’s capsule): cup
shaped chamber
 Glomerulus: capillary network
2. Renal tubule: tubular passageway upto 50mm
long, rcv filtrate and modifies it to create urine
 Proximal convoluted tubule (PCT)
i. rcv tubular fluid = filtrate
ii. Lining cells reabsorb nutrients
iii. Reabsorb 60-70% water (108-116L/day), 99100% organic substrates, 60-70% Na+, Cl- in
original filtrate
 Nephron loop (loop of henle)
i. osmotic gradient for water reabsorption.
ii. Each limb has thin segment/thick segment.
iii. 25% of water (45L/day) and 20-25% Na,Cl
reabsorption.
iv. Creates concentration gradient in renal
medulla
 Distal convoluted tubule (DCT)
i. adjust tubular fluid composition by
reabsorption and secretion
ii. 5%, 9L/day water reabsorption under ADH,
variable amount of Na reabsorption under
aldosterone
Kidney structure: paired retroperitoneal organs
Reddish brown, 4” L x 2.2” w x 1.2” thick / ~150g (5.25oz)
Hilum: medial indentation, point of exit/entry for renal
artery, nerves, vein and ureter
Location: btwn muscle wall and parietal peritoneum,
protected by organs & body musculature & 11,12th ribs, L
is superior than R
Positioned by
1. overlying peritoneum
2. adjacent visceral organs
3. supporting connective tissues
Connective tissues:
 Fibrous capsule (collagen fiber layer): outer surface,
project fibers into perinephric fat to renal fascia
 Perinephric fat (perinephric fat capsule): thick fat tissue
 Renal fascia (dense, fibrous outer layer): anchors to
surrounding structure
Major structure of kidney
Fibrous capsule: lines renal sinus
Renal cortex: superficial region, outer most
Renal medulla: inner region, includes belos;
1. Renal pyramid: conical structure
2. Renal papilla: tip of pyramid
3. Renal column: separates adjacent pyramids
Kidney lobe: pyramid, cortex and columns. 6-18 lobes each
Hilum
Minor calyx: collect urine from single kidney lobe
Major calyx: form from fusion of 4-5 minor calyces
Renal pelvis: funnel shaped collects urine from major
calyces, continuous with ureter
Collecting system: tubes carrying tubular fluid away from
nephrons
1. Collecting duct: fluid from many nephrons, carry
fluids through renal medulla. Reabsorption variable
amount of water (9%, 16.8L/day) under ADH and Na
reabsorption under aldosterone.
2 lining cells:
 intercalated cells (secrete, reabsorb hydrogen
and bicarbonate ions)
 Principal cells (reabsorb water and secrete
potassium)
2. Papillary duct: fluid from collecting ducts, deliver
to ureter
2 types of nephrons (microscopic functional units)
1. Cortical nephrons
 85% of all nephrons
 Primarily in cortex
Arterial system
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CH24 Urinary System
Renal artery → segmental arteries → interlobar arteries →
arcuate arteries → cortical radiate arteries (=interlobular
arteries) → afferent arterioles → glomerulus
(pedicels) that wrap around glomerular
capillaries, gap between pedicels are
filtration slits
 Filtration membrane: fenestrated glomerular
capillaries → dense layer basement
membrane → filtration slits
 Efferent arteriole < Afferent arteriole
(increase BP in glomerular capillaries)
 Juxtaglomerular complex: secretes renin
when glomerular bp decreases
 Intraglomerular mesangial cells: supporting
cells, btwn adjacent glomerular capillaries,
control capillary diameter and bld flow rate
 Glomerular filtration rate: amount of filtrate
produced each minute. Net filtration pressure
(NFP) being positive and filtrate move into
capsular space
2. Reabsorption
 Transport water and solutes from tubular fluid
across tubular epithelium into peritubular
fluid and the peritubular capillaries
 Predominates in proximal convoluted tubule
(PCT)
i. >99% of glucose, amino acids, organic
nutrients
ii. Sodium, potassium, bicarbonate,
magnesium, phosphate, sulfate ions
iii. Water (108L /day); solute concentration of
tubular fluid↓, water moves into
peritubular fluid
3. Secretion
 Transport of solutes from peritubular fluid
across tubular epithelium into tubular fluid
 Mvmt of water and solutes (peritubular fluid
→ tubular fluid)
 15-20% of initial filtrate volume reaches DCT
Venous system
Cortical radiate veins → arcuate veins → interlobar veins
→ segmental vein → renal vein
Bld flow in cortical nephron
Afferent arteriole → glomerulus → efferent arteriole →
peritubular capillaries (surround entire renal tubule,
surrounded by peritubular fluid, reabsorb water and
solutes drain into cortical radiate veins)
Bld flow in juxtamedullary nephron
Same until after peritubular capillaries
Vasa recta: connected to distal end of peritubular
capillaries. Long, straight capillaries parallel to nephron
loop. Transport & redistribute water and solutes within
medulla; stabilize concentration gradient of medulla.
Drain into cortical radiate veins
Nephron innervation
 1.25 M nephrons each kidney
 Cortical and juxtamedullary nephrons innervated by
renal nerves (enter at hilum, follow renal artery)
 Mostly sympathetic postganglionic fibers from celiac
plexus and inferior splanchnic nerves that provides…
o Sympathetic stimuli adjusting bld flow and bp at
glomeruli
o Stimulate release of renin
Renal physiology and homeostasis
 By regulating volume and composition of bld
 Concentrates urine to 855-1355mOsm/L
 Excretes solutes and metabolic wastes
Metabolic wastes (much higher in Urine than Bld plasma)
Urea: abundant organic waste, by product of amino acid
breakdown
Creatinine: byproduct of creatine phosphate breakdown in
muscles
Uric acid: recycling of nitrogenous bases of RNA
Functions of nephron segment
 Filtration only in renal corpuscle (180L/day)
 Balance btwn reabsorption and secretion varies in
remaining nephron segments
 Final volume and concentration regulation is btwn
collecting system and nephron loops
3 processes in urine formation
1. Filtration
 BP forces water and solutes across the
membrane of glomerular capillaries into
capsular space (btwn layers of glomerular
capsule)
 Glomerular capsule: receiving container
i. parietal layer (outer capsule)
ii. Visceral layer: cover capillary, composed of
podocytes, large cells with food processes
Normal urine
 1200mL/day with osmotic concentration of 1000
mOsm/L
 Differ from person and day; kidney alter function for
homeostasis
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CH24 Urinary System
 Shunts (silicone rubber tubes) connect bld vessels with
machine
Renal failure treatment
Dialysis relieves symptoms but not a cure; kidney
transplant is only real cure for severe renal failure
 >90% survival at 2yrs after transplant
 Close relative donor increases success rate
 Immunosuppressive drugs are necessary to reduce
rejection
Urinary tract: transports, stores, eliminates urine
 Visualized by pyelogram; x-ray image taken after an
intravenous radiopaque dye administration
 Ureters: muscular tube about 30cm
o retroperitoneal and attached to posterior
abdominal wall
o penetrate posterior bladder wall at oblique angle
 Bladder: hollow, muscular organ, ~1L, outside of
peritoneal cavity
o Supporting ligaments (lateral umbilical ligaments,
middle umbilical ligaments)
o Rugae: folds in lining for expansion
o Ureteric orifices: slit-like shape prevent backflow
of urine into ureters with bladder contraction
o Trigone: triangular area bounded by ureteral
opening and entrance to urethra
o Neck of urinary bladder: surrounds urethral
opening, internal urethral sphincter (involuntary
smth muscle)
o External urethral sphincter: located where urethra
passes through urogenital diaphragm, voluntary
control (must relax to urinate)
 Urethra: neck of bladder to exterior of the body
Renal failure: kidney cannot remove wastes. Results in
 Decrease in urine production
 BP ↑
 Anemia from decline erythropoietin production
 Central nerve system problems (sleeplessness, seizures,
delirium, coma)
Chronic renal failure: function deteriorate gradually over
time. slow progression, irreversible condition
 Manage by restricting water, salt, protein intake →
reduce strain by minimizing V of urine produced and
amount of nitrogenous waste generated
 Acidosis: common problem with renal failure. Countered
by ingesting bicarbonate ions
Lining of ureters
1. Inner mucosa: transitional epithelium and
surrounding lamina propria
2. Middle muscular layer: bands of smth muscle
creating peristaltic waves to move urine
3. Outer connective tissue layer: continuous with
fibrous capsule and peritoneum
Acute renal failure: rapid deteriorates of kidney function
in few days; may be impaired for wks
 Sudden slowing or sopping of filtration caused by toxic
drugs, renal ischemia, urinary obstruction, trauma, allergic
response to antibiotics or anesthetics in sensitized
individuals
 Partial or complete recovery is possible; ~50% survival
rate with supportive treatment
Wall of bladder
1. Mucosa
2. Submucosa
3. Muscularis layer: form detrusor muscle, 3 layers
 Inner longitudinal
 Circular
 Outer longitudinal
Dialysis: process of passive diffusion across selectively
permeable membrane
Hemodialysis: Regulates composition of bld using dialysis
machine with artificial membrane
 Dialysis fluid containing specific concentrations of
solutes in the other side of membrane
Wall of urethra
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CH24 Urinary System
 Thick & elastic lamina propria, longitudinal folds in
mucous membrane (mucin secreting cells in epithelial
pocket)
 Stratified epithelium that varies by location
1. Transitional at neck
2. Stratified columnar at mid
3. Stratified squamous near external urethral orifice
Dysuria: painful or difficult urination. Ex. Cystitis,
urethritis, urinary obstructions (enlarged prostate in male)
<clinical signs of urinary system disorders>
Edema(swelling): renal disorders lead to proteinuria
(protein in urine). Facial swelling especially around eyes
Fever: when urinary system is infected with pathogens
 Cystitis: bladder infection; low-grade fever
 Pyelonephritis: kidney infection; very high fever
Micturition reflex (urinary reflex)
Coordinates process of urination by both
1. Local reflex pathway
2. Central pathway through cerebral cortex
Urine storage reflex: stretch receptors of bladder wall →
a. In vertebrae, sympathetic stimulation to detrusor and
contraction of internal urethral sphincter
b. Pontine storage center: parasympathetic activity↓,
somatic motor nerve activity of external urethral
sphincter↑
Urine voiding reflex: by pontine micturition center→
 Interneuron relays sensation of bladder fullness to
thalamus
 Projection fibers relay info to cerebral cortex
 Voluntary relaxation of external urethral sphincter
(causes relaxation of internal urethral sphincter) leads
urination due to increased pressure
Urinary disorders
<volume and appearance change>
Polyuria: excessive urine production from H or metabolic
problems, possibly diabetes or glomerulonephritis
Oliguria: reduced urine production (50-500mL/day)
Anuria: severely reduced urine production (0-50mL/day)
 Oliguria and anuria indicate serious kidney
problems and potential renal failure
<frequency change>
Increased urgency or frequency can be caused by irritation
of the lining of ureter or bladder
Incontinence: inability to control urination voluntarily
 Periodic involuntary leakage = stress incontinence
 Inability to delay = urge incontinence
 Continual trickle of urine from full bladder =
overflow incontinence
Urinary retention: initially normal renal function, urination
does not occur (commonly by enlarged prostate gland,
compression of prostatic urethra)
<pain>
Superior pubic region: urinary bladder disorders
Superior lumbar or flank region radiating to right or left
upper quadrants: kidney infection (pyelonephritis) or
kidney stones (renal calculi)
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