Urinary System Overview and Kidney Function

Urinary System Overview

• The urinary system comprises organs responsible for filtering waste from the blood and eliminating it as urine.
• Key organs include two kidneys, two ureters, one urinary bladder, and one urethra.

Kidney Structure and Function

• Kidneys are positioned on either side of the vertebral column, extending from the 12th thoracic to 3rd lumbar vertebrae.
• The right kidney is slightly lower than the left.
• Dimensions: 12 cm length, 6 cm width, and 3 cm thickness.
• The hilum is the middle of the medial border, a point of entry/exit for renal vessels and nerves.
• Kidneys have two surfaces, two borders, and two ends, with a convex lateral border and a medial border that's convex at both ends and concave in the middle.
• The kidney tissue differentiates into cortex and medulla.
• Kidneys filter blood, removing waste to form urine.

Kidney Relations

• Anterior Surface (Right Kidney):

  • Right suprarenal gland
  • Duodenum
  • Liver
  • Colon
  • Small intestine

• Anterior Surface (Left Kidney):

  • Left suprarenal gland
  • Spleen
  • Pancreas
  • Stomach
  • Colon
  • Small intestine

• Posterior Surface: 

  • Diaphragm
  • Psoas major muscle
  • Quadratus lumborum muscle
  • Transverse abdominis muscle

Kidney Coverings

• Fibrous capsule
• Perirenal fat
• Renal fascia
• Pararenal fat

Ureters

• Two muscular tubes, one on each side of the body.
• Carry urine from the kidneys to the urinary bladder.
• Approximately 25-30 cm long.
• Part of the ureteral course is within the abdomen, the other in the pelvis.
• Continues from the hilum of the kidney.
• Opens into the postero-superior angle of the urinary bladder.
• Has three constriction sites: pelvi-ureteric junction, crossing the common iliac artery, and uretero-vesical junction.

Urinary Bladder

• A hollow organ that serves as a reservoir for urine.
• Positioned in the pelvic cavity, directly behind the pubic bones.
• Pyramidal shape, with a capacity of 220 cc.
• Can accommodate up to 500 cc without discomfort.
• Parts: Apex, base, and three surfaces (superior and two inferolateral).
• Ureter enters the superolateral angle of the base.
• The inferior angle (neck) leads to the urethra.
  • In males, the neck rests on the prostate and continues as the prostatic urethra.
  • In females, continuous with the urethra.

Male Urethra

• 20 cm long, divided into three parts.
  • Prostatic part: 3 cm long, widest part, starting at the bladder neck, surrounded by the prostate, and where the ejaculatory duct opens.
  • Membranous part: 1 cm long, narrowest and shortest, surrounded by sphincter urethra.
  • Spongy part: 16 cm long, longest part, traversing the penis and ending at the external urethral orifice.

Female Urethra

• Very short (4 cm).
• Begins at the bladder's neck.
• Its upper part is encircled by the sphincter urethra.
• Shorter, wider, and more dilatable compared to the male urethra.