1 Urinary System Objectives 1. Identify organs belonging to the urinary system 2. Describe the gross and microscopic structures of the kidney 3. Describe.

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Urinary System ObjectivesUrinary System Objectives

• 1. Identify organs belonging to the urinary system

• 2. Describe the gross and microscopic structures of the kidney

• 3. Describe the structure and function of the nephron in urine formation

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Urinary System ObjectivesUrinary System Objectives

• 4. Identify the pattern of blood supply and urine output from the kidneys

• 5. Describe the function, histology, location and structure of the ureters, urinary bladder and urethra

• 5. Define and use the correct terminology associated with the urinary system

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Urinary SystemUrinary System

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Urinary SystemUrinary System

• Kidneys

• Ureters

• Urinary Bladder

• Urethra

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KidneysKidneys

• Paired

• 11 cm x 6 cm x 2.5 cm

• Retroperitoneal

• Between T12 and L3, left kidney higher than the right

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KidneysKidneys

• Held in place by two layers of fascia– Perirenal fat– Renal capsule - fibrous CT

• Indented region = hilus where vessels enter and exit medially

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Kidney RegionsKidney Regions

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Kidney RegionsKidney Regions

• Cortex - outer, reddish

–Two layers

• cortical layer

• Juxtamedullary

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Kidney RegionsKidney Regions

• Medulla – inner

–Contains renal pyramids• Apex of renal pyramid = renal papillae• Pyramids separated by renal columns

– interlobar vessels within the columns

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Renal PyramidsRenal Pyramids

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Kidney RegionsKidney Regions

• Minor and major calyces = funnel shaped spaces for urine collection– Drain via renal pelvis into ureters

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Blood SupplyBlood Supply

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Kidney Blood SupplyKidney Blood Supply

• Arterial - nutrient, O2 and waste product rich– Aorta– Renal artery– Interlobar artery– Arcuate artery– Interlobular artery

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Kidney Blood SupplyKidney Blood Supply

• Venous - O2, nutrient poor, nitrogenous waste eliminated

• Interlobular veins• Arcuate veins• Interlobar veins• Renal veins• Vena cava

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Kidney Blood SupplyKidney Blood Supply

• Microscopic blood supply– Afferent arteriole

– Glomerulus

– Efferent arteriole– Capillary

– Peritubular capillaries

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MicrocirculationMicrocirculation

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MicrocirculationMicrocirculation

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NephronNephron

• Nephrons - microscopic units responsible for urine formation

• 1-3 million per kidney

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NephronNephron

• Two kinds of nephrons (location)

– Cortical (80%)- renal corpuscle and majority of loop of Henle in cortex

– Juxtamedullary (20%) - renal corpuscle near junction of cortex - medulla, long loop of Henle penetrates well into medulla

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NephronNephron

• Consist of two kinds of tubular components– Vascular– Tubular

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Vascular NephronVascular Nephron

• Containing blood

• Afferent arteriole

• Glomerulus

• Efferent arteriole( )

• .

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Tubular NephronTubular Nephron

• Containing urine components

• Bowman’s capsule– double layered epithelium, visceral &

parietal

– visceral layer formed by podocytes, perforated to allow filtration of plasma

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Tubular NephronTubular Nephron

• Proximal convoluted tubule – PCT

• Loop of Henle– descending limb - Thin loop

– ascending limb - Thick loop

– distal convoluted tubule – DCT

• Collecting tubule

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Renal CorpuscleRenal Corpuscle

• Together glomerulus + Bowman’s capsule = renal corpuscle

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GlomerulusGlomerulus

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PodocytePodocyte

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Filtration MechanismFiltration Mechanism

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FiltrationFiltration

• Movement of “plasma” from glomerulus into Bowman’s capsule, primarily a function of hydrostatic pressure on blood within glomerulus and “leaky” condition of visceral Bowman’s capsule.

• Product of this process is a dilute glomerular filtrate, similar to plasma without proteins or formed elements.

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SecretionSecretion

• Movement from capillaries into tubule via active transport of materials not filtered or added to filtrate.

• Secreted products include H+, nitrogenous waste, some drugs, etc.

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ReabsorptionReabsorption

• Movement from tubules into capillaries or vasa recta.

• 99% of H2O filtered is reabsorbed.

• Other products reabsorbed include amino acids, glucose, ions, water soluble vitamins.

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ReabsorptionReabsorption

• ~180 liters glomerular filtrate produces per day, 1-2 liters actually becomes urine.

• ADH stimulates H20 reabsorption, primarily at DCT.

• Aldosterone stimulates reabsorption of Na+ and indirectly, H20 at the DCT.

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Counter-current ExchangeCounter-current Exchange

• Method by which ions are secreted and reabsorbed to allow for concentration of glomerular filtrate

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Counter-current ExchangeCounter-current Exchange

• Tubes are “leaky”

• Tubes pass close together

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Counter-current ExchangeCounter-current Exchange

• Flow in opposite directions

• Ions secreted on one side are reabsorbed on the other

• Provides surface area, time for H20 reabsorption without loss of essential ions (Na+)

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UretersUreters

• Exit kidney at renal hilus

• Retroperitoneal

• 25-30 cm

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UretersUreters

• Transport urine from kidney to bladder via peristalsis, gravity, hydrostatic pressure

• 3 layers (deep to superficial)– Tunica mucosa

• Transitional epithelium• Lamina propria

– Tunica muscularis• Longitudinal and circular smooth muscle

– Tunica adventitia• Fibrous CT, continuous with renal capsule

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Kidney StonesKidney Stones

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Urinary BladderUrinary Bladder

• Functions as urine storage site

• Variable size and shape dependent on condition

• Posterior to symphysis pubis, anterior to rectum

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Urinary BladderUrinary Bladder

• Held in place by ligaments and peritoneum– Lateral umbilical ligaments (remnants of

hypogastric arteries of fetus)– Middle umbilical ligament

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Urinary BladderUrinary Bladder

• Three openings for inferior triangular region = trigone– 2 ureters– 1 urethra

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Urinary BladderUrinary Bladder

• Three layers (deep to superficial)– Tunica mucosa

• Transitional epithelium• Submucosa

– Tunica muscularis• Smooth muscle

– Tunica Adventitia/serosa• Peritoneum only on superior aspect• Lower 2/3 CT only, attaching bladder to surrounding

structures

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MicturitionMicturition

• Reflex mechanism to allow elimination of urine involves:

• Internal sphincter - smooth muscle, involuntary

• External sphincter - skeletal muscle, voluntary

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UrethraUrethra• Male and female differ in structure and

function

• Female

• For elimination of urine only

• 4-5 cm

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Female UrethraFemale Urethra

• Anterior to vagina

• Lined with transitional epithelium proximally, becoming squamous distally

• Smooth muscle

• Opens at external urethral meatus

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Female UrethraFemale Urethra

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Male UrethraMale Urethra

• Carries urine and semen (not simultaneously)• ~20 cm• Three portions (proximal to distal)

– Prostatic ~3 cm, surrounded by prostate– Membranous ~2cm, receives bulbourethral gland

secretions– Cavernous/penile ~15 cm, surrounded by corpus

spongiosum

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Male Male UrethraUrethra