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Human Anatomy, First Edition McKinley & O\'Loughlin. Chapter 27 : Urinary System. General Structure and Functions of the Urinary System. General Concept: Waste products accumulate in blood Are toxic Must be removed to maintain homeostasis Urinary System organs

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general structure and functions of the urinary system
General Structure and Functions of the Urinary System
  • General Concept:
    • Waste products accumulate in blood
    • Are toxic
    • Must be removed to maintain homeostasis
    • Urinary System organs
      • remove waste products from the blood
      • then from the body
    • Major homeostatic system
general structure and functions of the urinary system3
General Structure and Functions of the Urinary System
  • Organs of the Urinary System:
    • Kidneys
    • Ureters
    • Urinary Bladder
    • Urethra
  • Primary organs: kidneys
    • filter waste products from the bloodstream
    • convert the filtrate into urine.
  • The Urinary Tract:
    • Includes:
      • ureters
      • urinary bladder
      • urethra
    • Because they transport the urine out of the body.
functions of the urinary system
Functions of the Urinary System
  • Removing waste products from the bloodstream.
  • Storage of urine.
    • the urinary bladder is an expandable, muscular sac that can store as much as 1 liter of urine
  • Excretion of urine.
  • Blood volume regulation.
    • the kidneys control the volume of interstitial fluid and blood under the direction of certain hormones
  • Regulation of erythrocyte production.
    • as the kidneys filter the blood, they are also indirectly measuring the oxygen level in the blood
    • Erythropoietin (EPO): hormone produced by kidney
      • Released if blood oxygen levels fall
      • Stimulates RBC production in red bone marrow
kidneys gross and sectional anatomy
Kidneys: Gross and Sectional Anatomy
  • Retroperitoneal
    • Anterior surface covered with peritoneum
    • Posterior surface against posterior abdominal wall
  • Superior pole: T-12
  • Inferior pole: L-3
  • Right kidney ~ 2cm lower than left
  • Adrenal gland on superior pole
kidneys gross and sectional anatomy10
Kidneys: Gross and Sectional Anatomy
  • Hilum: concave medial border
  • Renal sinus: internal space
    • Houses blood vessels, lymphatic vessels, nerves
    • Houses renal pelvis, renal calyces
    • Also fat
kidneys gross and sectional anatomy11
Kidneys: Gross and Sectional Anatomy
  • Surrounding tissues, from deep to superficial:
    • Fibrous capsule (renal capsule)
      • Dense irregular CT
      • Covers outer surface
    • Perinephric fat (adipose capsule)
      • Also called perirenal fat
      • Completely surrounds kidney
      • Cushioning and insulation
    • Renal fascia
      • Dense irregular CT
      • Anchors kidney to posterior wall and peritoneum
    • Paranephric fat
      • Between renal fascia and peritoneum
kidneys gross and sectional anatomy13
Kidneys: Gross and Sectional Anatomy
  • Sectioned on a coronal plane:
    • Renal Cortex
      • Renal arches
      • Renal columns
    • Renal Medulla
      • Divided into renal pyramids
      • 8 to 15 per kidney
      • Base against cortex
      • Apex called renal papilla
kidneys gross and sectional anatomy14
Kidneys: Gross and Sectional Anatomy
  • Minor calyx:
    • Funnel shaped
    • Receives renal papilla
    • 8 to 15 per kidney, one per pyramid
  • Major calyx
    • Fusion of minor calyces
    • 2 to 3 per kidney
  • Major calyces merge to form renal pelvis
  • Renal Lobe
    • Pyramid plus some cortical tissue
    • 8 to 15 per kidney
blood supply to the kidney
Blood Supply to the Kidney
  • About 20 to 25% of cardiac output to kidneys
  • Path:
    • Renal artery to segmental arteries to interlobar arteries to arcuate arteries to interlobular arteries to:
    • Afferent arteriole to glomerulus to efferent arteriole to peritubular capilaries and vasa recta
blood supply to the kidney19
Blood Supply to the Kidney
  • Blood plasma is filtered across the glomerulus into the glomerular space.
  • Once the blood plasma is filtered
    • blood leaves the glomerulus
    • enters an efferent arteriole.
  • efferent arteriole is still carrying oxygenated blood
    • a gas and nutrient exchange with the kidney tissues has not yet occurred.
blood supply to the kidney20
Blood Supply to the Kidney
  • The efferent arterioles branch into one of two types of capillary networks:
    • peritubular capillaries
    • vasa recta
    • these capillary networks are responsible for the actual exchange of gases and nutrients
  • Peritubular capillaries: primarily in cortex
  • Vasa recta: surround the thin tubes that project into the medulla.
blood supply to the kidney21
Blood Supply to the Kidney
  • Path for veins:
    • Interlobar veins to arcuate veins to interlobar veins to the renal vein
  • The functional filtration unit in the kidney.
  • Consists of the following:
    • Renal corpuscle
      • Glomerulus
      • Glomerular capsule (Bowman’s capsule)
    • Proximal convoluted tubule (PCT)
    • Nephron loop (loop of Henle)
      • Ascending loop of Henle
      • Descending loop of Henle
    • Distal convoluted tubule (DCT)
    • collectively called the renal tubule
  • In both kidneys: approximately 2.5 million nephrons.
  • Are microscopic: measure about 5 centimeters in length.
  • Cortical Nephrons
    • Near peripheral edge of cortex
    • Short nephron loops
    • Have peritubular capillaries
  • Juxtamedullary nephrons
    • Near corticomedullary border
    • Long nephron loops
    • Have vasa recta
urine formation
Urine Formation
  • Three processes
  • Filtration
    • Renal corpuscle: forms filtrate
    • From blood to tubule
  • Reabsorption
    • Mostly PCT
    • Water and salt: rest of nephron
    • From tubule to blood
  • Secretion
    • From blood to tubule
renal corpuscle
Renal Corpuscle
  • Vascular pole
    • Afferent and efferent arterioles
  • Tubular pole
    • Connects to PCT
  • Two structures:
    • Glomerulus and glomerular capsule
  • Glomerulus
    • Capillary bed
    • High pressure
    • fenestrations
renal corpuscle28
Renal Corpuscle
  • Glomerular Capsule
    • Parietal layer
      • Simple squamous epithelium
    • Visceral layer
      • Podocytes
        • Pedicels
        • Filtration slits
    • Capsular space (Bowman’s capsule): location of filtrate
    • Filtration membrane
      • Fenestrations
      • Filtration slits
proximal convoluted tubule
Proximal Convoluted Tubule
  • Begins at tubular pole of the renal corpuscle.
  • Cells: simple cuboidal epithelium
    • actively reabsorb from the filtrate:
      • almost all nutrients (glucose and amino acids)
      • electrolytes
      • plasma proteins
    • Osmosis: reabsorption of 60% to 65% of the water in filtrate.
    • Have microvilli
  • Solutes and water:
    • moved into blood plasma
    • via the peritubular capillaries.
nephron loop loop of henle
Nephron Loop (loop of Henle)
  • originates at end of proximal convoluted tubule
  • projects toward and/or into the medulla.
  • Each loop has two limbs.
    • descending limb:
      • from cortex toward and/or into the medulla
    • ascending limb:
      • returns back to the renal cortex
distal convoluted tubule
Distal Convoluted Tubule
  • begins at the end of the thick ascending limb of the nephron loop
    • adjacent to the afferent arteriole (important physiologically)
      • Juxtaglomerular apparatus.
  • primary function:
    • Secretion
    • From blood plasma to filtrate.
    • secretes ions
      • potassium (K+)
      • acid (H+)
  • Reabsorption of water also occurs:
    • influenced by two hormones
      • Aldosterone
      • antidiuretic hormone (ADH).
collecting collecting ducts
Collecting Collecting Ducts
  • Function in a well hydrated person:
    • transport the tubular fluid into the papillary duct and then into the minor calyx.
  • Function in a dehydrated person:
    • water conservation
    • more-concentrated urine is produced.
  • ADH can act on the collecting duct epithelium
    • Cells become permeable to water
    • Water moves from filtrate into blood plasma
    • Involves vasa recta.
innervation of the kidney
Innervation of the Kidney
  • innervated by a mass of autonomic nervous system fibers
    • called the renal plexus.
  • The renal plexus
    • accompanies each renal artery
    • enters the kidney through the hilum.
urinary tract ureters
Urinary Tract : Ureters
  • long, fibromuscular tubes
  • conduct urine from the kidneys to the urinary bladder.
  • average 25 centimeters in length
  • retroperitoneal.
  • ureters originate at the renal pelvis
  • extend inferiorly to enter the posterolateral wall of the base of the urinary bladder.
  • wall is composed of three concentric tunics.
    • mucosa
    • muscularis
    • adventitia.
urinary tract urinary bladder
Urinary Tract – Urinary Bladder
  • The urinary bladder:
    • expandable, muscular container
    • serves as a reservoir for urine
  • positioned immediately superior and posterior to the pubic symphysis.
  • in females
    • the urinary bladder is in contact with the uterus posterosuperiorly and with the vagina posteroinferiorly.
  • in males
    • it is in contact with the rectum posterosuperiorly and is immediately superior to the prostate gland.
  • is a retroperitoneal organ.
  • when empty exhibits an upside-down pyramidal shape.
  • Filling with urine distends it superiorly until it assumes an oval shape.
urinary tract urinary bladder40
Urinary Tract – Urinary Bladder
  • Trigone
    • posteroinferior triangular area of the urinary bladder wall
    • formed by imaginary lines
      • connect the two posterior ureteral openings
      • and the anterior urethral opening.
  • The trigone remains immovable as the urinary bladder fills and evacuates.
  • It functions as a funnel
    • directs urine into the urethra as the bladder wall contracts
  • four tunics
    • mucosa
    • submucosa
    • Muscularis: called the detrusor muscle
    • adventitia.
  • Internal urethral sphincter (smooth muscle)
micturition urination
Micturition (Urination)
  • The expulsion of urine from the bladder.
  • Initiated by a complex sequence of events called the micturition reflex.
  • The bladder is supplied by both parasympathetic and sympathetic nerve fibers of the autonomic nervous system.
  • Fibromuscular tube
    • exits the urinary bladder through the urethral opening
    • at anteroinferior surface
  • conducts urine to the exterior of the body.
  • Tunica mucosa: is a protective mucous membrane
    • houses clusters of mucin-producing cells called urethral glands.
  • Tunica muscularis: primarily smooth muscle fibers
    • help propel urine to the outside of the body.
  • Two urethral sphincters:
    • Internal urethral sphincter
      • restrict the release of urine until the pressure within the urinary bladder is high enough
    • External urethral sphincter
      • and voluntary activities needed to release the urine are activated.
  • The internal urethral sphincter
    • involuntary (smooth muscle)
    • superior sphincter surrounding the neck of the bladder, where the urethra originates.
    • a circular thickening of the detrusor muscle
    • controlled by the autonomic nervous system
  • The external urethral sphincter
    • inferior to the internal urethral sphincter
    • formed by skeletal muscle fibers of the urogenital diaphragm.
    • a voluntary sphincter
    • controlled by the somatic nervous system
    • this is the muscle children learn to control when they become “toilet-trained”
female urethra
Female Urethra
  • Has a single function:
    • to transport urine from the urinary bladder to the vestibule, an external space immediately internal to the labia minora
  • 3 to 5 centimeters long, and opens to the outside of the body at the external urethral orifice located in the female perineum.
male urethra
Male Urethra
  • Urinary and reproductive functions:
    • passageway for both urine and semen
  • Approximately 18 to 20 centimeters long.
  • Partitioned into three segments:
    • prostatic urethra is approximately 3 to 4 centimeters long and is the most dilatable portion of the urethra
      • extends through the prostate gland, immediately inferior to the male bladder, where multiple small prostatic ducts enter it
    • membranous urethra is the shortest and least dilatable portion
      • extends from the inferior surface of the prostate gland through the urogenital diaphragm
    • spongy urethra is the longest part (15 centimeters)
      • encased within a cylinder of erectile tissue in the penis called the corpus spongiosum
      • extends to the external urethral orifice
aging and the urinary system
Aging and the Urinary System
  • Changes in the size and functioning of the kidneys begin at 30.
  • Gradual reduction in kidney size.
  • Reduced blood flow to the kidneys.
  • Decrease in the number of functional nephrons.
  • Reabsorption and secretion are reduced.
  • Diminished ability to filter and cleanse the blood.
  • Less aldosterone or antidiuretic hormone.
  • Ability to control blood volume and blood pressure is reduced.
  • Bladder decreases in size.
  • More frequent urination.
  • Control of the urethral sphincters—and micturition—may be lost.