The Urinary System

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The Urinary System
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System Overview

• Consists of
• Kidneys
• Ureters
• Urinary bladder
• Urethra

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System Functions

• Removes certain salts and nitrogenous wastes from
  blood
• Helps maintain normal concentrations of water and
  electrolytes within body fluids
• Regulates the pH and volume of body fluids
• Helps control red blood cell (RBC) production and
  blood pressure

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Kidneys - Function

• Remove substances from the blood
• Form urine
• Help regulate some metabolic processes by
  secreting hormones
• Erythropoietin
• Renin

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Kidneys - Location

• Either side of the vertebral column
• In a depression on the posterior wall of the
  abdominal cavity
• Between 12th thoracic and 3rd lumbar vertebrae
• Left kidney is usually higher
• Behind the parietal peritoneum
• Held in place by CT and adipose

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Kidney Structure

• Hilium
• Renal pelvis
• Calyces
• Renal papillae
• Renal medulla
• Renal cortex
• Nephrons

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Kidney Blood Supply

• Renal arteries
• From abdominal aorta
• Branches in kidney to form afferent arterioles
• Renal veins
• Join the inferior vena cava

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Nephron Structure

• Renal corpuscle
• Glomerulus
• Glomerular (Bowmans) capsule
• Renal tubules
• Nephron loops (loop of Henle)
• Dump filtrate into collecting ducts ? calyces
• Efferent arteriole
• Peritubular capillaries

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Urine Formation

• Urine is a product of nephron activity.
• It is formed by 3 processes
• Glomerular filtration
• Tubular reabsorption
• Tubular secretion

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Glomerular Filtration

• Produces filtrate (mostly water)
• Pressure for filtration comes from blood pressure
• Filtrate is similar to blood plasma

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Tubular Reabsorption

• Substances are transported out of the tubular
  fluid and into the peritubular capillaries
• Allows reabsorption of glucose, amino acids,
  creatine, lactic, citric, uric, and ascorbic
  acids, phosphates, sulfates, Ca, K, Na, and
  water
• Urea
• Uric acid
• Gout

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Tubular Secretion

• Substances move from the plasma in the
  peritubular capillary into the fluid of the renal
  tubule
• Mostly hydrogen and potassium ions

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Urine Composition

• Reflects the amounts of water and solutes that
  the kidneys must eliminate or retain to maintain
  homeostasis
• Contains urea, uric acid, electrolytes, traces of
  amino acids

• Average urine volume 0.6-2.5 L/day
• Volume depends on fluid intake, temperature,
  relative humidity, emotional state, respiratory
  rate, body temperature
• Abnormal components
• Glucose, proteins, hemoglobin, ketones, and blood
  cells

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Urine Elimination

• Nephron ? collecting ducts ? calyces ? renal
  pelvis ? ureter ? urinary bladder ? urethra ?
  outside of the body

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Ureters

• About 25 cm long
• Extend from renal pelvis to the underside of the
  urinary bladder
• Muscular walls propel urine by peristalsis
• Flaplike fold acts as valve into the bladder

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Urinary Bladder

• Hollow, distensible, muscular organ
• Stores urine
• Forces urine into the urethra
• Behind the symphysis pubis
• Trigone
• Detrusor muscle
• Internal urethral sphincter

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Micturition

• Aka urination
• Reflex triggered by stretching of the bladder
• Detrusor muscle contracts.
• Abdominal wall and pelvic floor muscles contract.
• Voluntary relaxation of external urethral
  sphincter
• Reflex center located in the spinal cord.
• Reflex accompanied by sense of urgency.
• Bladder holds 600 ml,but urge begins at 150-300
  ml.

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Urethra

• Tube that conveys urine from the bladder to the
  outside of the body
• Contains urethral glands that secrete mucus into
  the urethral canal
• Incontinence

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