Urinary System

Function and Overview■ Major organs: kidneys, ureters,urinary bladder, urethra■ Function: waste removal and fluid-balance

  1. What are the major organs of the urinary system?: kidneys, ureters, urinary bladder, urethra

  2. What is the function of the urinary system?: waste removal and fluid balance


Kidney: ExternalFeatures■ Medial surface is concavewith vertical cleft called therenal hilum■ Fibrous capsule surroundseach kidney and preventsinfections in surroundingregions from spreading to thekidney■ Atop each kidney is anadrenal (suprarenal) gland,an endocrine glands that isfunctionally unrelated to thekidney

  1. What is the medial surface of the kidney characterized by?: A concave with a vertical cleft called the renal hilum.

  2. What surrounds each kidney to prevent infections from spreading to the kidney?: A fibrous capsule surrounds each kidney.

  3. What is located atop each kidney?: An adrenal (suprarenal) gland, which is an endocrine gland functionally unrelated to the kidney.

Kidney: InternalFeatures■ Renal cortex: most superficial region■ Deep to the cortex is the darker, reddish-brown renal medulla■ Cone-shaped tissue masses called medullary, or renal, pyramids■ Broad base of each pyramid faces toward the cortex. Apex or papilla points internally.■ Renal columns separate the pyramids■ Renal pelvis: tube continuous with theureter leaving the hilum■ Major calyces: branching extensions of the pelvis■ Minor calyces: cup-shaped areas that enclose the papillae

InternalBloodVessels■ As each renal artery approaches a kidney,it divides into five segmental arteries■ Within the renal sinus, each segmentalartery branches further to form severalinterlobar arteries■ Interlobar arteries branch into the arcuatearteries■ Small cortical radiate arteries radiateoutward from the arcuate arteries to supplycortical tissue■ Afferent arterioles begin a complexarrangement of microscopic blood vessels■ Veins mostly trace the pathway of thearterial supply in reverse (no segmentalveins

Nephron■ Nephrons are the structural and functional units of the kidneys■ Each nephron consists of a renal corpuscle and a renal tubule■ Each renal corpuscle consists of a tuft of capillaries called the glomerulus anda glomerular capsule (or Bowman’s capsule)■ The endothelium of the glomerular capillaries is fenestrated (penetrated bymany pores)■ Glomerular capsule has a parietal layer and visceral layer■ Visceral layer has epithelial cells called podocytes

  1. What are nephrons?: The structural and functional units of the kidneys.

  2. What are the components of a nephron?: Each nephron consists of a renal corpuscle and a renal tubule.

  3. What does a renal corpuscle consist of?: Consists of a tuft of capillaries called the glomerulus and a glomerular capsule (or Bowman’s capsule).

  4. What is the endothelium of the glomerular capillaries like?: Is fenestrated (penetrated by many pores).

  5. How is the glomerular capsule structured?: Has a parietal layer and a visceral layer.

  6. What are the epithelial cells in the visceral layer of the glomerular capsule called: Has epithelial cells called podocytes.

Renal Tubule and Collecting Duct■ Renal tubule has 3 parts■ Proximal convoluted tubule (PCT): filtrate passes through here first, cuboidalepithelial cells with large mitochondria, apical surfaces bear dense microvilli■ Nephron loop (formerly called loop of Henle): has descending and ascendinglimbs■ Distal convoluted tubule (DCT): cuboidal cells confined to the cortex, thinnerand almost entirely lack microvilli■ Collecting duct receives filtrate from the many nephrons

  1. What are the three parts of the renal tubule?: Proximal convoluted tubule (PCT), Nephron loop, Distal convoluted tubule (DCT)

  2. What is the function of the proximal convoluted tubule (PCT)?: Filtrate passes through here first, cuboidal epithelial cells with large mitochondria, apical surfaces bear dense microvilli

  3. What is the structure of the distal convoluted tubule (DCT)?: Cuboidal cells confined to the cortex, thinner and almost entirely lack microvilli

  4. What receives filtrate from many nephrons?: Collecting duct

JuxtaglomerularComplex (JGC)■ Region in each nephron where themost distal portion of the ascendinglimb of the nephron loop lies againstthe afferent arteriole feeding theglomerulus (and sometimes theefferent arteriole).■ Macula densa cells monitor the NaClcontent of the filtrate entering theDCT■ Granular cells sense blood pressurein the afferent arteriole

  1. What is the Juxtaglomerular Complex (JGC)?: Region in each nephron where the distal portion of the ascending limb of the nephron loop lies against the afferent arteriole feeding the glomerulus.

  2. What is the role of Macula densa cells in the Juxtaglomerular Complex (JGC)?: Monitor the NaCl content of the filtrate entering the DCT.

  3. What do Granular cells in the Juxtaglomerular Complex (JGC) sense?: Blood pressure in the afferent arteriole.

Classes ofNephrons■ Cortical nephrons:account for 85% of thenephrons in the kidneys.Short nephron loops,glomerulus further from thecortex-medulla junction.■ Juxtamedullarynephrons: long nephronloops that deeply invade themedulla, glomerulus closerto the cortex-medullajunction

  1. What is the percentage of cortical nephrons in the kidneys?: 85%

  2. How do cortical nephrons differ from juxtamedullary nephrons in terms of nephron loop length?: Cortical nephrons have short nephron loops, while juxtamedullary nephrons have long nephron loops.

  3. Where is the glomerulus located in relation to the cortex-medulla junction in juxtamedullary nephrons?: The glomerulus is closer to the cortex-medulla junction in juxtamedullary nephrons.

Ureter■ Slender tubes that convey urinefrom the kidneys to the bladder■ 3 layers: mucosa, muscularis,adventitia

  1. What is the function of the ureter?: Convey urine from the kidneys to the bladder.

  2. How many layers make up the structure of the ureter?: Three layers - mucosa, muscularis, adventitia.

Bladder■ Smooth, collapsible, muscular sac thatstores urine temporarily■ Receives urine via the ureters anddischarges it via the urethra■ 3 layers: mucosa, middle layer(detrusor), fibrous adventitia■ Inner layer has openings for both uretersand the urethra■ Smooth, triangular region of the bladderbase outlined by three openings for uretersand the urethra is called the trigone

  1. What is the function of the bladder?: The bladder is a smooth, collapsible, muscular sac that stores urine temporarily.

  2. What are the three layers of the bladder?: Mucosa, middle layer (detrusor), and fibrous adventitia.

  3. What is the triangular region of the bladder base outlined by three openings for ureters and the urethra called?: The smooth, triangular region of the bladder base is called the trigone.

Urethra■ Thin-walled muscular tube that drains urine from the bladder and out of the body■ Internal urethral sphincter is involuntary and controlled by the autonomicnervous system■ External urethral sphincter is under voluntary control■ length and functions differ between male and females■ Females: 3-4 cm, external urethral orifice lies anterior to the vaginal openingand posterior to the clitoris■ Males: aprox. 20 cm, 3 regions, functions to carry semen as well as urine

  1. What is the urethra?: A thin-walled muscular tube that drains urine from the bladder and out of the body.

  2. How is the internal urethral sphincter controlled?: Ivoluntary and controlled by the autonomic nervous system.

  3. What controls the external urethral sphincter?: The external urethral sphincter is under voluntary control.

  4. How do the length and functions of the urethra differ between males and females?: In females, the urethra is 3-4 cm long, with the external urethral orifice lying anterior to the vaginal opening and posterior to the clitoris. In males, the urethra is approximately 20 cm long, divided into 3 regions, and functions to carry semen as well as urine.

Histology■ Top image: detailedstructure of the nephron■ Lower image: low-power view of the renalcortex

  1. What is histology?: Histology is the study of the microscopic structure of tissues.

  2. What does the top image in histology show?: The top image in histology shows the detailed structure of the nephron.

  3. What does the lower image in histology show?: The lower image in histology shows a low-power view of the renal cortex.