Physiology Lecture 15: Renal System (Part One)

Structure of Renal System

• The renal system consists of kidneys, ureters, bladder, and urethra, involved in forming and releasing urine.
• The kidneys are bean-shaped organs that produce urine to eliminate waste substances.
• Tubes called ureters transport urine from the kidneys to the urinary bladder.

Kidneys

• The kidney has a pale outer region called the cortex and a darker inner region called the medulla.
• The medulla is divided into 8-18 conical regions called renal pyramids, which merge to form the renal pelvis and then the ureter.
• Each kidney contains about 1.3 million nephrons, the functional units of the kidney.
• The cortex and medulla are made up of nephrons.

Bladder

• The bladder is a pyramid-shaped organ that sits in the pelvis and stores urine.
• The bladder can hold up to 500 mL of urine.
• The bladder has three openings: two for the ureters and one for the urethra.
• The bladder consists of smooth muscles, with the main muscle being the detrusor muscle.
• Muscle fibers around the opening of the urethra form a ring-like muscle that controls the passage of urine.
• The blood supply of the bladder is from multiple blood vessels, including the vesical arteries, obturator, uterine, gluteal, and vaginal arteries.
• In females, a venous network drains blood from the bladder arteries into the internal iliac vein.

Urethra

• The male urethra is 18-20 cm long, running from the bladder to the tip of the penis.
• The male urethra is supplied by the inferior vesical and middle rectal arteries.
• The nerve supply of the male urethra is via the pudendal nerve.
• The female urethra is 4-6 cm long and 6 mm wide, running from the bladder neck to the top of the vaginal opening.
• The female urethra is supplied by the internal pudendal and vaginal arteries.
• The female urethra is shorter than the male urethra, making it more prone to infections from bacteria in the vagina.