Urinary System Notes

Urinary System Overview (CSEP421 - 11.2)

Objectives

• Briefly describe the functions of the urinary system.
• Name selected components of the urinary system and briefly describe the functions of each.
• Briefly describe bacterial infection of the urinary system.

Functions of the Urinary System

• Regulates the composition and volume of the blood by:
  • Filtering the blood.
  • Returning more or less water to the blood.
  • Removing wastes and H^+ out of the body.
• Produces hormones:
  • Calcitriol.
  • Erythropoietin.
• Regulates blood pressure.

Components of the Urinary System

• Right Kidney
• Left Kidney
• Left Renal Vein
• Left Ureter
• Urinary Bladder
• Urethra
• Right Ureter
• Inferior Vena Cava
• Descending Aorta
• Adrenal Gland

Detailed Component Functions

Kidneys

• Located in the abdominal cavity.
• Surrounded by:
  • Transparent sheath (renal capsule).
  • Adipose (fatty) tissue.
• Contain microscopic nephrons (filtering units).

Ureters

• Transport urine away from the kidneys.

Urinary Bladder

• Located in the pelvic cavity.
• Hollow, distensible, muscular organ.
• Capacity averages 700-800mL.

Urethra

• Transports urine away from the bladder.

Functions of Components

Kidneys

• Produce urine as a by-product of filtering blood.
  • Excretion of wastes and foreign substances (drugs and environmental toxins) from the blood.
  • Regulation of the ionic composition of the blood.
  • Regulation of blood pH.
  • Regulation of blood volume.
  • Regulation of blood pressure.
  • Production of hormones (e.g., erythropoietin).
  • Regulation of blood glucose level (by synthesis of new glucose molecules).

Ureters

• Each ureter transports urine from the kidneys to the urinary bladder.

Urinary Bladder

• Stores urine prior to urination / micturition (discharge of urine from bladder).

Urethra

• Small tube leading from the bladder to exterior of the body which passes urine out of the body.
• In males, the urethra is longer and discharges semen as well as urine.

Blood Supply of the Kidneys

• Descending Aorta
• Renal Artery (posterior to the renal vein)
• Kidneys
• Renal Vein
• Inferior Vena Cava

Normal Microbiota of the Urinary System

• Apart from the urethra, most of the urinary system and urine is usually free from microbes.
• The urethra normally supports growth of some commensal flora, including Lactobacillus, Streptococcus, and Staphylococcus.
• Urinary tract infections caused by bacterial infection are common causes of pain and inflammation in the urethra, urinary bladder, and kidneys.
• In both males and females, microorganisms infecting the urethra rarely move up to infect the bladder, or up the ureters to infect the kidneys.

Urinary Tract Infection (UTI)

• In a typical UTI, E. coli bacteria is introduced to the urethra via faecal contamination.
• The bacteria adhere to urethral epithelial cells via fimbriae and begin to multiply, causing painful urination.
• Bacterial cells swim up the urethra to invade epithelial cells lining the urinary bladder.
• As the E. coli multiply in the bladder, they can ascend up the ureters to the kidneys.