The urinary system is a complex network of organs and structures that work together to filter blood, remove waste products, and regulate water and electrolyte balance within the body. The system is responsible for producing urine, which is a waste product of metabolism, and eliminating it from the body. The urinary system is made up of four main components: the kidneys, ureters, bladder, and urethra.
肾脏 (Kidneys)
The kidneys are the primary organs of the urinary system and are located in the retroperitoneal space near the spine. They have abean-shaped appearance and are about 12 cm in length and 6 cm wide. The kidneys are highly血管ized, receiving approximately 25 percent of the cardiac output at rest.
Each kidney is composed of two regions: the cortex and the medulla. The cortex is the outer layer, which contains the renal corpuscles, glomeruli, and Bowman's capsule. The medulla is the inner core, which contains the loops of Henle, the collecting ducts, and the Reni-Neural-Juxtaglomerular Apparatus (JGA). The main function of the kidneys is to filter blood and form urine, which is then excreted from the body through the urethra.
肾小球 (Glomeruli)
Glomeruli are the main filtering units of the kidney. They consist of a ball-shaped structure called the glomerulus, which is encircled by a double-layered epithelial capsule known as the bowman's capsule. In healthy individuals, the glomerular filtration rate (GFR) is approximately 125 mL/min per 1.73 m², allowing for the consistent excretion of about 200 liters of urine daily.
肾小管 (Tubules)
The remainder of the nephron, including the distal convoluted tubule (DCT), the connecting tubule (CNT), and the collecting tubule (CT), plays a crucial role in urine formation. The DCT begins at the cortex, dives into the medulla, and then extends into the cortico-medullary junction. In the DCT, water and solutes are actively reabsorbed, while electrolytes and toxins remain in the filtrate. Sodium离子, potassium离子,氯离子,碳酸氢根离子和氢离子等是在肾小管的分泌部位主动分泌到滤过液中。碳酸氢根离子和氢离子由皮质集合管细胞分泌到滤过液中，以维持酸碱平衡。
膀胱 (Bladder)
The bladder is a highly distensible muscular sac located in the pelvic cavity behind the pubic symphysis. It serves as a temporary storage vessel for尿液, holding up to two cups of liquid. When the bladder is filled, it sends signals to the nervous system to initiate the process of voiding or micturition. In males, theneck of the bladder is surrounded by the prostate gland.
尿道 (Urethra)
The urethra serves as the channel that allows the urine to exit the body. It is surrounded by two urethral sphincters— an internal smooth muscle sphincter (involuntary) and an external skeletal muscle sphincter (voluntary). The male urethra is longer, traveling the entire length of the penis, while the female urethra is shorter and opens anteriorly to the vestibule. The urethra may carry both urine and semen in males.
Urinary System Function
The primary function of the urinary system is to remove waste products from the body and maintain water, electrolyte, and pH balance in the blood. Urine is formed when blood filters through the glomeruli and is then excreted from the body through the urethra. The system works in harmony with other body systems, such as the endocrine system, cardiovascular system, and nervous system, to regulate various bodily functions.
泌尿系统的神经和血管供应
The kidneys are supply by the renal artery and drained by the renal vein. Neural supply is provided by therenal plexus, which lies outside the gerota's fascia. The ureters receive blood supply from multiple sources, including the major and minor ureteric branches of the abdominal aorta, the common iliac arteries, the internal iliac arteries, and the inferior vesical, uterine, and superior rectal arteries.
The urethra is supplied by the internal pudendal artery, the vaginal artery, the vaginal plexus, the inferior hypogastric plexus, and the pudendal nerve in women. In males, the pudendal nerve provides both motor and sensory innervation.
尿液的形成过程
As the blood flows through the kidney, materials such as glucose, amino acids, and urea are filtered out during glomerular filtration. The filtered substance passes through the tubules and is reabsorbed and secreted by the walls of the convoluted tubules. Reabsorption returns water and solutes to the blood, while secretion releases materials that may be harmful.
The final product of urine formation is excreted outside the body through the urethra when the Detrusor muscle contracts and the internal urethral sphincter relaxes, initiating the micturition process.
