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Flashcards in Urinary System Deck (118):


Organs of the urinary system




Main Waste Products excreted in urine

  1. urea-comes from the breakdown of amino acids during recylcling of body's proteins
  2. uric acid- results from the body's turnover over of nucleic acids
  3. creatine- formed by the breakdown of creatine phosphate:
    • a molecule in muscle that stores energy for the manufacture of ATP


Functions of the kidney

  • dispose of wastes and excess ions
  • regulate the volume and chemical makeup of the blood
  • maintain the proper balance of water and salts and of acids and bases



  • bean shaped
  • lie retroperitoneal in lumbar region of the posterior abdominal wall
  • from 3rd lumbar vertebrae to to 11th or 12th thoracic vertebrae
  • avg=12cm high, 6cm wide and 3 cm thick


differences between left and right kidney

  • right kidney is crowded by the liver
  • right kidney lies slightly inferior to left kidney


hilum of kidney

  • a vertical cleft on the medial (concave) surface
  • site where vessels, ureters, and nerves enter and exit kidney


Fibrous capsule of kidney

  • a thin, tough layer of dense connective tissue
  • adheres directly to surface of kidney
  • inhibits spread of infection from surrounding regions


perirenal fat capsule of kidney

  • external to the fibrous capsule
  • supportive tissue
  • cushion the kidney against blows and holds it in place


renal fascia

  • envelope between perirenal capsule and pararenal fat


pararenal fat

  • external to and posterior to renal fascia
  • cushions kidney against blows and helps keep kidneys in place


surgical approach to kidney


  • Through posterolateral abdominal wall
  • very few muscles, vessels or nerves need to be cut
  • need to avoid t12 area to avoid puncturing pleural cavity and causing pneumothorax


two distinct regions of kidney tissue

  1. renal cortex:
    • most superficial region
    • light in color
    • more granular appearance
  2. renal medulla:
    • darker in color
    • consists of cone-shaped masses called renal pyramids


renal lobes

  • a single renal pyramid plus the cortical tissue that surrounds that pyramid
  • each kidney has 5-11 lobes and pyramids


renal pyramids

  • apex (papilla) points interiorly
  • exhibit striations:
    • roughly parallel bundles of tiny urine collecting tubules


renal sinus

  • a large space within the medial part of the kidney opening to the exterior through the renal hilium
  • a "filled space" full of:
    • renal vessels and nerves
    • some fat
    • renal pelvis and calices


renal pelvis

  • pelvis=basin
  • a flat, funnel-shaped tube
  • the expanded superior part of the ureter
  • branches with major calices
  • urine from calices flows into the pelvis and on to the ureter


major calices 

  • calyx singular
  • 2-3 branching extensions of renal pelvis
  • urine filled tubes
  • divide further to form several minor calices


minor calices

  • extensions from the major calices
  • cup-shaped tubes that enclose the papillae of the pyramids
  • collect urine during draining from papillae and empty it into the renal pelvis



  • infection/inflammation of the renal pelvis and calices



  • when pyelitis spreads to involve the rest of the kidney
  • nephros=kidney
  • results from
    • spread of fecal bacterium (escherichia coli) from the anal region superiorly through the urinary tract
    • bloodborne bacteria lodge in the kidneys and proliferate there
  • kidney scars, abcesses form, and the renal pelvis fills with pus
  • left untreated, the infected kidneys may be severely damaged
  • antibiotics usually totally cures it


renal arteries

  • offers rich blood supply to kidneys
  • about 1/4 of heart's systemic output reaches kidneys through here
  • branch at right angles from the abdominal aorta
  • right renal artery is longer than left (due aorta slightly off midline)


segmental arteries of kidney

  • the five divisions of the renal artery
  • enter the hilium


interlobar arteries of kidneys

  • division of segmental arteries
  • division occurs in renal sinus
  • lie in the renal columns between renal pyramids


arcuate arteries

  • the division of interlobar arteries at the medulla cortex
  • "shaped like a bow"
  • arch over the bases of the renal pyramids


cortical radiate arteries of kidneys

  • division of arcuate arteries
  • radiate outward
  • supply the cortical tissue with blood
  • more than 90% of the blood entering the kidneys comes through the cortex


glomerular arterioles of kidneys

  • stem from cortical radiate arteries
  • feed into peritubular capillaries


Peritubular Capillaries of kidneys

  • surround the tubules in the kidney
  • come from glomerular arterioles


Veins of kidney

  • trace the pathway of arteries in reverse
  • blood leaving the renal cortex drains sequentially:
    • cortical radiate
    • arcuate
    • interlobar
    • renal veins (no segmental veins)
  • renal vein exits at hilium and empties into inferior vena cava
  • left renal vein is longer (about twice as long) because inferior vena cava lies on the right side of the vertebral column 


renal plexus

  • the nerve supply of the kidney
  • a network of autonomic ganglia on the renal arteries
  • offshoot of the celiac plexus


uriniferous tubule

(microscopic anatomy of kidneys)

  • The main structural and functional unit of the kidney
  • lined by simple epithelium adapted for production of urine
  • more than a million in each kidney
  • uriniferous=urine carrying
  • two parts:
    1. urine-forming nephron
    2. collecting duct


Mechanisms of urine production

  • filtration
  • resorption
  • secretion



mechanism of urine production

  • filtered blood leaves kidney capillaries and enters uriniferous tubule
  • filtrate resembles tissue fluid 
  • as it proceeds through the uriniferous tube the filtrate is processed into urine through resorption and secretion



mechanism of urine production

  • most nutrients (water/essential ions) are recovered from filtrate and returned to blood of capillaries
  • 99% of the volume of renal filtrate is resorbed
  • remaining wastes and unneeded substances contribute to urine that eventually leaves body



mechanism of urine production

  • moves additional undesirable molecules into the tubule from blood of surrounding capillaries
  • active process



(microscopic anatomy of kidneys)

  • where filtration, resorption, and secretion occur
  • Composed of:
    • renal corpsucle
    • tubular section


renal corpsucle

of the nephron

of uriniferous tubule

  • the first part of the nephron
  • where filtration occurs
  • occur strictly in the cortex
  • consist of:
    • glomerulus
    • glomerular capsule



of the renal corpsucle

of the nephron

of the uriniferous tubules

of the kidney

  • a tuft of capillaries
  • "ball of yarn"
  • surrounded by glomerular capsule like a fist in an underinflated balloon


glomerular capsule

of the renal corpsucle

of the nephron

of the uriniferous tubules

of the kidney

  • aka Bowman's capsule
  • cup-shaped 
  • hollow


capsular space 

of the renal corpsucle

of the nephron

of the uriniferous tubules

of the kidney

  • the hollow interior of the glomerular capsule
  • large quantities of fluid passes from capillary blood into here


fluid of the capsular space

of the renal corpsucle

of the nephron

of the uriniferous tubules

of the kidney

  • the filtrate that is ultimately processed into urine
  • only about 20% of fluid leaves the glomerulus and enters the capsular space
  • the remaining 80% remains in the blood


parietal layer

of glomerular capsule

of the renal corpsucle

of the nephron

of the uriniferous tubules

of the kidney

  • Simple squamous epithelium
  • plays no part in formation of filtrate


visceral layer

of glomerular capsule

of the renal corpsucle

of the nephron

of the uriniferous tubules

of the kidney

  • clings to the glomerulus
  • consists of branching epithelial cells called podocytes



of the visceral layer

of glomerular capsule

of the renal corpsucle

of the nephron

of the uriniferous tubules

of the kidney

  • unusual branching octopus-like epithelial cells
  • end in foot processes, or pedicles, that surround the glomerular capillaries
  • filtrate passes into capsular space through filtration slits or slit pores
    • thin clefts between the foot processes


Filtration membrane

of the renal corpsucle

of the nephron

of the uriniferous tubules

of the kidney

  • filter that lies between the blood in the glomerulus and the capsular space
  • 3 layers:
    1. fenestrated endothelium (pores) of the capillary
      • restrict the passage of largest elements like blood cells
    2. the filtration slits between the foot processes of the podocyte
    3. an intervening basement membrane composed of the fused basal laminae of the endothelium and the podocyte epithelium
      • filtration slits and basement membrane hold back all but the smallest proteins. Allow passage of ions, water, glucose, amino acids, urea and small proteins


tubular section 

of the nephron

of the uriniferous tubules

of the kidney

  • filtrate comes here from renal corpsucle 
  • contains:
    • proximal convoluted tubule
    • the loop of henle
    • the distal convoluted tubule
  • ends by joining a collecting duct
  • meandering nature of the nephron:
    • increases length
    • enhances its capabilities in processing the filtrate


proximal convoluted tubule

of the tubular section

of the nephron

of the uriniferous tubules

of the kidney

  • confined entirely to renal cortex
  • most active in resorption and secretion
  • cuboidal epithelia with fuzzy microvilli to increase surface area for resorption
  • contain many mitochondria which provide energy for resorption


Loop of Henle

of the tubular section

of the nephron

of the uriniferous tubules

of the kidney

  • aka Loop of Nephron
  • consists of a ascending and descending limb
  • U-Shaped


Descending limb

of the 

Loop of Henle

of the tubular section

of the nephron

of the uriniferous tubules

of the kidney

  • continuous with the proximal tubule 
  • has a singular structure
  • the rest of the descending limb is the thin segment
    • the narrowest part of the nephron
    • permeable simple squamous epithelium
    • continues into the ascending limb


Thick ascending limb

of the Loop of Henle

of the tubular section

of the nephron

of the uriniferous tubules

of the kidney

  • cell structure resembles that of the distal convoluted tube
  • continuation of the thin segment


Distal Convoluted Tubule

of the tubular section

of the nephron

of the uriniferous tubules

of the kidney

  • confined to the renal cortex
  • simple cuboidal epithelial walls
  • specialized for selective secretion and absorption of ions
  • less active in absorption than proximal tube
  • no abundance of microvilli
  • many mitochondria and infoldings of the basolateral membrane


Classes of Nephrons

  • Two categories:
    • cortical nephrons
    • juxtamedullary nephrons


Cortical Nephrons

  • 85% of nephrons
  • located entirely within the cortex
  • loops of henle dips only a short distance into the medulla


Juxtamedullary Nephrons

  • remaining 15% of Nephrons
  • "near the medulla"
  • renal corpuscles lie near the cortex-medulla junction
  • loops of henle deeply invade medulla
  • thin segments are much longer than those of cortical nephrons
  • loop of henle contribute to kidney's ability to produce concentrated urine


Collecting ducts

of Uniferous Tubules 

of Kidneys

  • consist of simple cuboidal epithelium
  • Urine passes here from distal tubules of nephrons
  • each receives urine from several nephrons
  • runs straight through the cortex into the deep medulla
  • at the papilla of the pyramid, adjacent collecting ducts join together to form larger papillary ducts


Role of Collecting Ducts

  • a few are rich in mitochondria and participate in resorption and secretion of ions
  • most important role:
    • conserve body fluids (along with the distal tubules of nephrons)
      1. Body needs to conserve water
      2.  ADH hormone is secreted by posterior part of pituitary gland
      3. permeability of collecting ducts and distal tubues to water increases
      4. water is resorbed from filtrate
      5. total volume of urine produced is decreased


Alcohol and Antidiuretic Hormone (ADH)

  • inhibits the release of ADH
  • water resorption from renal tubules is reduced
  • copious amounts of dilute urine is produced
  • potential dehyrdration can occur


papillary ducts 

  • adjacent collecting ducts joined together
  • empties into the minor calices
  • simple cuboidal epithelium of collecting ducts thickens to become simple columnar epithelium


Microscopic Blood Vessels associated with Uriniferous Tubules

  1. Glomeruli
  2. Peritubular Capillaries
  3. Vasa Recta



(Microscopic Blood Vessels Associated with Uniferous Tubules)

of the Kidney

  • Capillary bed
  • both fed and drained by arterioles
    • afferent and efferent arterioles


Filtrate generation of Kidneys

  • Kidneys generate 1 liter (about 1 quart) of filtrate every 8 minutes
  • only 1% ends up as urine
  • 99% is resorbed by uniferous tubule and returned to the blood in peritubular capillary beds


afferent/efferent arterioles 

of Glomeruli

(Microscopic Blood Vessels Associated with Uriniferous Tubules)

  • afferent feed glomeruli
  • efferent drain glomeruli
  • Afferent arise from the cortical radiate arteries that run through the renal cortex
  • high-resistance vessels
  • efferent are narrower than afferent
    • blood pressure in glomerulus is extra high for cappilary bed and easily forces the filtrate out of the blood and into the glomerular capsule


peritubular capillaries

(microscopic blood vessels associated with uriniferous tubules)

  • intertubular capillaries
  • arise from the efferent arterioles draining in the cortical glomeruli
  • lie in the interstitial loose connective tissue that surrounds the uriniferous tubules
  • empty into nearby venules of the renal venous system
  • adapted for absorption
    • low pressure
    • porous
  • all molecules secreted bt nephrons into the urine are from the blood of nearby peritubular capillaries


vasa recta

(microscopic blood vessels associated with uriniferous tubules)

  • "straight vessels"
  • part of the kidney's urine-concentrating mechanism
  • in the deepest part of the renal cortex
  • thin-walled looping vessels
  • efferent arterioles from the juxtamedullary glomeruli
  • hairpin loops descend into the medulla
  • run alongside the loops of henle


Juxtaglomerular Apparatus

of the uriniferous tubulules 

of the kidneys

  • "near the glomerulus"
  • functions in the regulation of blood pressure
  • an area of specialized contact between the terminal end of the ascending limb of the loop of Henle and the afferent arteriole


granular cells 

of the Juxtaglomerular Apparatus

of the uriniferous tubulules 

of the kidneys

  • aka juxtaglomerular cells
  • modified smooth muscle cells
  • have secretory granules containing the hormone RENIN (Kidney Hormone)
  • mechanoreceptors that secrete renin in response to falling blood pressure in the afferent arteriole


Macula Densa

of the Juxtaglomerular Apparatus

of the uriniferous tubulules 

of the kidneys

  • "dense spot"
  • terminal portion of the loop of Henle adjacent to the granular cells
  • consists of tall, closely packed epithelial cells that act as chemoreceptors for monitoring solute concentrations in the filtrate


Action of the Juxtaglomerular Apparatus

of the uriniferous tubules

  1. solute concentration falls below certain level
  2. macula densa cells signal granular cells
  3. granular cells secrete renin
  4. renin initiates a sequence of chemical reactions in the blood (renin-angiotensin mechanism)
  5. results in secretion of aldosterone to increase sodium resorption from distal convoluted tubules
  6. blood-solute concentration increases


extraglomerular mesangial cells

of the Juxtaglomerular Apparatus

of the uriniferous tubulules 

of the kidneys

  • interact with cells of the macula densa and granular cells to regulate blood pressure



  • slender tubes (25 cm/10 inches)
  • carry urine from kidneys to bladder
  • begins superiorly at L2 as continuation of the renal pelvis
  • descends retroperitoneal through the abdomen
  • enters the true pelvis by crossing the pelvic brim at the sacroiliac joint
  • enters the posterolateral corner of the bladder
  • then runs medially within the posterior bladder wall before opening into the bladder's interior
  • this oblique entry prevents backflow of urine into the ureters
    • any increase of pressure within bladder compresses the bladder wall, closing the distal ends of the ureters



  • radiograhic procedure for examining the ureters and renal calices
  • image=pyelogram


Histology of the Ureters

(Microscopic Anatomy)

  • same as renal calices and renal pelvis
    1. mucosa
    2. muscularis
    3. adentitia



of the ureters

(Microscopic Anatomy)

  • transitional epithelium that stretches when ureters fill with urine
  • lamina propria composed of stretchy fibroelastic connective tissue with rare patches of lymphoid tissue



of the ureters

(Microscopic Anatomy)

  • middle layer of wall
  • consists of two layers of smooth muscle:
    1. inner longitudinal layer
    2. outer circular layer 
  • A third layer of muscularis, an external longitudinal layer, appears in the inferior third of the ureter



of the ureters

(Microscopic Anatomy)

  • exernal layer of wall
  • typical connective tissue


Function or Ureters

  • active role in transporting urine
  • contraction of muscularis sets up peristalstic waves that propel urine to the bladder
  • urine does not reach bladder by gravity alone


Urinary Bladder

  • a collapsible muscular sac that stores and expels urine
  • lies inferior to the peritoneal cavity on the pelvic floor posterior to the pubic symphysis
  • In males it lies anterior to rectum
  • In females it lies anterior to vagina and uterus



of urinary bladder

  • "urinary canal of the fetus"
  • at the apex or anterior angle of bladder
  • a fibrous band
  • closed remnant of an embryonic tube called allantois


Orientation of Urinary bladder

  • two posterolateral angles receive ureters
  • anterior angle has urachus
  • inferior angle drains into urethra
  • in maes, the prostate lies directly inferior to the bladder, surrounding the urethra


Histology of Urinary Bladder

  1. mucosa with a distensible transitional epithelium and lamina propria
  2. thick muscular layer
  3. fibrous adventitia (except on the superior surface which is covered by parietal peritoneum


Detrusor muscle

of the urinary bladder

  • the middle, muscular layer 
  • highly intermingled smooth muscle fibers
    • inner and outer longitudinal layers
    • middle circular layer
  • contraction squeezes urine from bladder during urination


Adult Bladder

  • full can hold up to about 500 ml (1 pint) of urine
    • 15 times its empty volume



of the urinary bladder


  • triangular region on posterior wall
  • infections tend to persist in this region



  • a thin-walled tube that drains urine from the bladder out of the body
  • consists of smooth muscle and inner mucosa
  • in males the muscle layer becomes very thin toward the distal end


Histology of Urethra

  • towards bladder it is transitional epithelium
  • in the midurethra it is stratified and pseudostratified columnar epithelium
  • near the end of the urethra it turns stratified squamous


internal urethra sphincter

  • a thickening of the detrusor muscle ath the bladder-urethra junction
  • involuntary sphincter
  • smooth muscle
  • keeps urethra closed when urine is not being passed and prevents dribbling of urine between voidings


external urethral sphincter

  • surrounds the urethra within the sheet of muscle called urogenital diaphragm
  • a skeletal muscle used to inhibit urination voluntarily until proper time


Urethra in females

  • 3-4 cm (1.5 inches)
  • bound to the anterior wall of vagina by connective tissue
  • opens to the outside at the external urethral orifice


external urethral orifice

  • in females only
  • the outside opening of urethra
  • a small opening
  • lies anterior to the vaginal opening 
  • lies posterior to the clitoris
  • often difficult to locate


Urethra in males

  • about 20 cm long (8 inches)
  • 3 named regions:
    1. prostatic urethra
    2. membranous urethra
    3. spongy urethra
  • Carries ejaculating semen as well as urine (not simultaneously)


Prostatic Urethra

  • in males only
  • 2.5 cm long 
  • runs in prostate


membranous urethra

  • In males only
  • 2.5 cm long 
  • runs through the membranelike urogenital diaphragm


spongy urethra

  • 15 cm long
  • passes through entire penis
  • opens at tip of penis via the external urethral orifice



  • aka voiding
  • aka urination
  • Detrusor muscle contracts, assisted by muscles in abdominal wall
  • controlled by the brain


Neuronal pathways involved in Micturition

  • urine accumulates in the bladder, distension activates stretch receptors
  • They send sensory impulses through visceral sensory neurons to sacral region of spinal cord
  • from spinal cord up to a micurition center in dorsal part of pons
  • neurons in micturition center in lower pons signal parasympathetic neurons
  • which stimulate detrusor muscle
  • emptying bladder 


urinary tract infections

  • most occur in sexually active young women
  • occur in 40% of women
  • intercourse drives bacteria from vagina/external genital region/anus through the opening of the urethra and toward the bladder
  • STD's can also inflame urinary tract, clogging some ducts


Escherichia coli

  • a normal bacterium of the lower digestive tract
  • produces 80% of all urinary tract infections



  • infection of the bladder
  • can spread superiorly to infect ureters and kidneys
  • can cause pyelitis and pyelonephritis


Symptoms/treatment of Urinary tract infections

  • burning sensation during micturition
  • increased urgency and frequency of micturition
  • fever
  • cloudy or blood-tinged urine
  • when kidneys are involved: 
    • back pain
    • severe headaches

Easily cured by antibiotics


Urinary Tract Infections in Men

  • usually result from long term catheterization of the penile urethra
    • it is difficult to keep indwelling catheters sterile


Renal Calculi

  • kidney stones
  • 12% of men and 5% of women in North America
  • calcium, magnesium, or uric acid salts in the urin crystallize and precipitate in the calices or renal pelvis
  • most calculi are smaller than 5mm in diameter and can pass through without causing serious problems


Pain from Renal Calculi

  • Calculi cause pain when they obstruct a ureter, blocking the drainage of urine and increasing intrarenal pressure
  • the most severe pain results when the contracting walls of the ureter contact the sharp calculi during peristaltic contractions
  • pain radiates from the lateral abdominal region to the anterior abdominal wall then perhaps to the groin


Predisposing factors for Renal Calculi

  1. oversaturation of calcium ions, uric acid, or oxalate
  2. abnormal acidity of urine
  3. dehydration
  4. blockage of urine flow in urinary tract
  5. bacterial infection


Treatment for Renal Calculi

  • surgical removal
  • extracoporeal shock wave therapy
    • ultrasonic shock waves from outside body break up calculi


Childhood Polycystic Kidney Disease

  • a rare, inherited condition in infants
  • kidneys contain many urine-filled sacs (cysts)
  • Cysts impede the drainage of urine and crush renal tissue
  • most children die of kidney failure early in life


Autosomal dominant polycystic kidney disease


(embryological development of urinary system)


  • inherited disorder 
  • predominantly affects the kidneys
  • may affect liver, pancreas, brain, and arterial blood vessels
  • 50% of people with this disease will develop end stage kidney disease and require dialysis or kidney transplantation


Bladder Cancer

  • accounts for 3% of cancer deaths
  • 5 times more common in men than women
  • typically involves neoplasms of the bladder's lining epithelium
  • blood in urine is a common warning sign
  • Substances linked to this cancer:
    • tars from tobacco smoke
    • industrial chemicals
    • artificial sweeteners
  • lethal if it metastasizes
  • surgical removal of bladder and chemotherapy increase survival time significantly


Kidney Cancer

  • 2% of cancer deaths in USA and rising
  • arises from epithelial cells of uriniferous tubules or renal pelvis and calices
  • Risk Factors:
    • twice as common in men
    • obesity
    • high blood pressure
    • high protein diet
  • most tumors are over 3cm in diameter and have metastasized when detected
  • prognosis is poor, survival time is 12-18 months
  • surgical removal is standard procedure



(embryological development of urinary system)

  • week for
  • the first kidney forms as set of nephrons
  • degenerates by week 6
  • leaves pronephric duct


pronephric duct


(embryological development of urinary system)

  • forms from pronephros
  • primary excretory duct
  •  sent to cloaca
  • used by the kidneys that develop later



(embryological development of urinary system)

  • second nephron system formed
  • "middle kidney"
  • claims the pronephric duct
  • forms mesonephric duct
  • degenerates after third kidney (metanephros) develops



(embryological development of urinary system)

  • third kidney
  • the definitive kidney


horseshoe kidney

  • 1 of 600 people
  • kidneys fuse into U shape during development
  • usually harmless
  • can be associated with obstructed drainage and hydronephrosis 


ectopic kidney

  • a kidney that fails to ascend to its normal position
  • difficulties draining can arise
    • kidney stones
    • urinary tract infection


Pelvic Kidney

  • one of the two kidneys stays in bony pelvis throughout life
  • often blocks birth canal
  • women may have difficulty giving birth


Ureteric Bud

(embryological development of urinary system)

  • week 5
  • hollow
  • grows from mesonephric duct into the urogenital ridge
  • induces the mesoderm to form nephrons
  • develops into:
    • renal pelvis
    • calices
    • collecting ducts
    • ureter


renal agenesis

(embryological development of urinary system)

  • failure of metanephros to develop
  • the absence of kidneys
  • unilateral=just one kidney and child can survive
  • bilateral=not compatible with life


urogenital sinus

(embryological development of urinary system)

  • Cloaca divides into two parts:
    1. future rectum and anal canal
    2. urogenital sinus
      • urinary and genital ducts empy into here
      • become urinary bladder and urethra
      • allantois (extension into umbilical cord) becomes urachus of bladder