The Urinary System

The Urinary System

The urinary system is a vital part of the body responsible for filtering blood, eliminating waste products, and maintaining water and electrolyte balance. This system consists of two kidneys, two ureters, the bladder, and the urethra.

Kidneys:

• The kidneys are the primary organs of the urinary system, bean-shaped and enclosed in a fibrous capsule called the renal capsule.

• Each kidney is divided into multiple lobes, with an average size of 12x6x3 cm and weighing approximately 150g.

• The kidneys are located behind the peritoneum, surrounded by a layer of fat called the perirenal fat pad.

• The right kidney is about 2cm lower than the left kidney.

• The upper pole of the kidney aligns with the 11th rib, while the lower pole is 3-5cm away from the highest point of the iliac crest.

• The kidneys are usually not palpable during examination unless they are enlarged.

Internal Structure of the Kidney:

• The kidney has a hollow cavity, about 3cm deep, called the renal sinus.

• Inside the renal sinus lies the renal pelvis, containing the major and minor calyces.

• The renal parenchyma comprises the renal medulla and renal cortex.

• The renal cortex is divided into two smaller parts: the radiate and the convoluted parts.

• The renal parenchyma is composed of approximately 500,000 functional units called nephrons.

• Each nephron includes the renal corpuscle, proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct.

• The renal corpuscle consists of the glomerular capsule and the glomerulus.

Vascular System of the Kidney:

• The renal artery is the primary artery supplying blood to the kidneys, originating from the abdominal aorta at the level of the first lumbar vertebra.

• The renal artery branches into numerous interlobar arteries, arcuate arteries, and interlobular arteries.

• The kidney has a portal venous system, and the renal vein originates from the stellate venules.

Ureters:

• The ureters are tubes that carry urine from the renal pelvis to the bladder, approximately 25cm long.

• The ureters have three constrictions: the ureteropelvic junction, the point where they cross the iliac vessels, and within the bladder wall.

• The ureter is divided into two segments: the abdominal segment and the pelvic segment.

• The abdominal segment of the ureter starts from the ureteropelvic junction to the iliac crest, running anterior to the psoas muscle.

• The pelvic segment of the ureter runs from the iliac crest to the bladder, relating posteriorly to the sacroiliac joint and the internal obturator muscle, internally to the rectum, and anteriorly to the reproductive organs.

• In females, the ureters run at the base of the broad ligament, crossing the uterine artery.

• In males, the ureters cross the vas deferens and lie between the seminal vesicle and the base of the bladder.

• The two ureters enter the bladder 4-5cm apart.

Bladder:

• The bladder is the organ that stores urine, with an average capacity of 250-300ml, which can increase to 2-3 liters when withholding urination.

• The bladder is a subperitoneal organ, located behind the pubic bone when empty and becoming spherical and protruding into the abdominal cavity when full of urine.

• The apex of the bladder has the median umbilical ligament.

• The superior surface of the bladder relates to the jejunum and sigmoid colon.

• The posterior surface of the bladder relates in males to the rectum, seminal vesicles, vas deferens, and base of the prostate, and in females to the rectum, uterus, and vagina.

• Inside the bladder are three openings: two ureteral orifices and the internal urethral orifice.

• The two ureteral orifices are located on the posterior wall, and the internal urethral orifice lies at the neck of the bladder.

• The three openings inside the bladder form the trigone of the bladder.

Urethra:

• The urethra is the tube that carries urine from the bladder to the outside.

• The male urethra is about 16cm long and serves as both a urinary and ejaculatory pathway, divided into the prostatic, membranous, and spongy urethra.

• The female urethra is only about 3cm long.

Note: This is general information about the urinary system. For a deeper understanding of each part and its specific function, consult reliable sources such as medical textbooks, websites of health organizations, or speak directly with a doctor.