Lect 18 The Urinary System

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Lect 18 The Urinary System

• Kidneys
• Ureters
• Urinary bladder
• Urethra
• Hypertonic
• Hypotonic

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• Functions of Urinary System
• Regulation of blood
• Volume
• Pressure
• pH
• Endocrine hormone release
• Calcitriol absorption of Ca
• Renin
• Erythropoietin
• Conservation of nutrients
• Role in toxin degradation
• Production and elimination of wastes in
  hypertonic urine

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• Location of Kidneys
• 4-5 in long, 2-3 in wide,1 in thick
• 4-5 in long, 2-3 in wide,1 in thick
• Retroperitoneal
• Protected by
• 11 12 ribs
• Perinephric and pararenal fat
• Anchored by
• Collagen fibers to fascia (renal fascia)
• Fascia continuous with deep fascia of muscles

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• Fibrous capsule
• Renal fasacia
• Deep fascia
• Pararenal fat
• Perinephric fat

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• Pelvis
• Hilum
• Renal sinus
• ureter

• Capsule
• Cortex
• Renal medulla
• Minor calyx
• Major calyx
• Renal pyramid
• Renal papilla
• Renal column

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• Blood Vessel and Nerves Supply
• Abundantly supplied with blood vessels
• receive 25 of resting cardiac output via renal
  arteries
• Enter/leave at hilus
• Blood vessels divide giving rise to afferent
  arterioles
• Filtration and reabsorption of materials from
  blood occurs at nephron
• Nerve supply
• Sympathetic nerve supply regulation of
• Regul of blood flow/pressure
• Renin (endocrine hormone) release
• Stimul of Na/water reabsorption

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• Renal artery
• Segmental artery
• Interlobar artery
• Arcuate artery
• Afferent arteriole
• Veins carry same names

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The Nephron

• Kidney has over 1 million nephrons composed of a
  corpuscle and tubule site of filtration/reabsorp
  tion in kindey
• Renal corpuscle site of plasma filtration
• glomerulus is capillaries where filtration occurs
• glomerular (Bowmans) capsule is double-walled
  epithelial cup that collects filtrate
• Renal tubule
• proximal convoluted tubule
• loop of Henle dips down into medulla
• distal convoluted tubule
• Collecting ducts and papillary ducts drain urine
  to the renal pelvis and ureter

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1 - renal corpuscle 2 - proximal convoluted
tubules 3 - distal convoluted tubules 4 -
Bowman's capsulae space
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• Two types of nephrons
• Cortical nephron
• 80-85 of nephrons are cortical nephrons
• Renal corpuscles are in outer cortex and loops of
  Henle lie mainly in cortex
• Juxtamedullary nephrons
• 15-20 of nephrons are juxtamedullary nephrons
• Renal corpuscles close to medulla and long loops
  of Henle extend into deepest medulla enabling
  excretion of dilute or concentrated urine

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Structure of Renal Corpuscle

• Bowmans capsule surrounds capsular space
• podocytes cover capillaries to form visceral
  layer
• simple squamous cells form parietal layer of
  capsule
• Glomerular capillaries arise from afferent
  arteriole form a ball before emptying into
  efferent arteriole

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Cortical Nephron
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Juxtamedullary Nephronhttp//www.lakemichigancoll
ege.edu/liberal/bio/anat/urin.html
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Histology of the Nephron Collecting Duct

• Single layer of epithelial cells forms walls of
  entire tube
• Distinctive features due to function of each
  region
• microvilli
• cuboidal versus simple
• hormone receptors

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• Juxtaglomerular Apparatus
• Involved in release of renin
• Endocrine release of renin and erythropoietin
• Renin increases blood pressure
• Erythropoietin stimulation of hemopoiesis
• Components
• macula densa ( dense spot) - specialized DCT
  epithelial cells monitor electrolyte conc. -
  chemoreceptors
• juxtaglomerular cells modified smooth muscle
  cells in wall of afferent arteriole respond to
  changes in bp
• granular cells contain and release renin
• Extraglomerular mesangial cells function?

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Overview of Renal Physiology

• Nephrons and collecting ducts perform 3 basic
  processes
• glomerular filtration
• a portion of the blood plasma is filtered into
  the kidney
• tubular reabsorption
• water useful substances are reabsorbed into the
  blood
• tubular secretion
• wastes are removed from the blood secreted into
  urine
• Rate of excretion of any substance is its rate of
  filtration, plus its rate of secretion, minus its
  rate of reabsorption

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Number of Nephrons

• Remains constant from birth
• any increase in size of kidney is size increase
  of individual nephrons
• If injured, no replacement occurs
• Dysfunction is not evident until function
  declines by 25 of normal (other nephrons handle
  the extra work)
• Removal of one kidney causes enlargement of the
  remaining until it can filter at 80 of normal
  rate of 2 kidneys

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Anatomy of Ureters

• 10 to 12 in long
• Varies in diameter from 1-10 mm
• Extends from renal pelvis to bladder
• Retroperitoneal
• Enters posterior wall of bladder
• Physiological valve only
• bladder wall compresses arterial opening as it
  expands during filling
• flow results from peristalsis, gravity
  hydrostatic pressure

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Location of Urinary Bladder

• Posterior to pubic symphysis
• In females is anterior to vagina inferior to
  uterus
• In males lies anterior to rectum

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Anatomy of Urinary Bladder

• Hollow, distensible muscular organ with capacity
  of 700 - 800 mL
• Trigone is smooth flat area bordered by 2
  ureteral openings and one urethral opening

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Histology of Urinary Bladder

• 3 layers in wall
• mucosa is transitional epithelium lamina
  propria
• since organ must inflate deflate
• mucus prevents the cells from being contacted by
  urine
• muscularis (known as detrusor muscle)
• 3 layers of smooth muscle
• inner longitudinal, middle circular outer
  longitudinal
• circular smooth muscle fibers form internal
  urethral sphincter
• circular skeletal muscle forms external urethral
  sphincter
• adventitia layer of loose connective tissue
  anchors in place
• superior surface has serosal layer (visceral
  peritoneum)

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Anatomy of the Urethra

• Females
• length of 1.5 in., orifice between clitoris
  vagina
• histology
• transitional changing to nonkeratinized
  stratified squamous epithelium, lamina propria
  with elastic fibers circular smooth muscle
• Males
• tube passes through prostate, UG diaphragm
  penis
• 3 regions of urethra
• prostatic urethra, membranous urethra spongy
  urethra
• circular smooth muscle forms internal urethral
  sphincter UG diaphragm forms external urethral
  sphincter

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