The urinary system plays a crucial role in maintaining homeostasis and overall health through the following functions:
It disposes of various waste products via urine, including:
Nitrogenous wastes: Such as urea, uric acid, and creatinine, which are byproducts of protein metabolism and cellular processes.
Toxins: Harmful substances that need to be eliminated to maintain body health.
Drugs: Pharmaceuticals and their metabolites that the body must expel after their functions are completed.
Excess ions: Includes ions such as sodium, potassium, and calcium that must be balanced to ensure proper cellular function.
The urinary system also performs key regulatory functions, including:
Production of renin: An enzyme important in regulating blood pressure by influencing vasoconstriction and sodium balance.
Production of erythropoietin: A hormone that stimulates the production of red blood cells in response to low oxygen levels, impacting oxygen transport throughout the body.
Conversion of vitamin D to its active form: Crucial for calcium absorption and bone health, thereby playing a key role in maintaining skeletal integrity.
The major organs involved in the urinary system include:
Kidneys
Ureters
Urinary Bladder
Urethra
Positioned retroperitoneally, which means they are located behind the parietal peritoneum in the abdominal cavity.
Extends from the level of the T12 to L3 vertebrae in adults.
The right kidney is typically positioned slightly lower than the left kidney due to the placement of the liver.
Size: Approximately 12 cm long and 6 cm wide, with a bean-like shape.
Renal hilum: This is the entry and exit point for the ureters, blood vessels, and nerves.
Adrenal glands: Located atop each kidney, these glands produce hormones that regulate metabolism, immune response, and blood pressure.
Fibrous Capsule: A dense connective tissue that encloses and protects the kidneys from physical damage.
Perirenal Fat Capsule: Layers of fat that cushion the kidneys and help maintain their position.
Renal Fascia: A connective tissue layer that anchors the kidneys and adrenal glands to surrounding structures.
Renal Cortex: The outer region of the kidney that contains the renal corpuscles and parts of the nephrons.
Renal Medulla: The inner region that contains renal pyramids, which are structures involved in urine formation.
Renal Pelvis: A funnel-shaped tube that collects urine from the calyces before it moves into the ureters.
The renal artery branches into segmental, interlobar, arcuate, and cortical radiate arteries to supply blood to the kidneys.
Blood is returned through cortical radiate veins, arcuate veins, interlobar veins, and finally to the renal vein, which carries deoxygenated blood back to the heart.
Each kidney contains approximately 1 million nephrons, the basic functioning units of the kidney engaged in urine production.
Composed of:
Renal Corpuscle: Contains the glomerulus and Bowman’s capsule where filtration occurs.
Renal Tubule: Comprises the proximal convoluted tubule (PCT), nephron loop, and distal convoluted tubule (DCT) where reabsorption and secretion processes take place.
Glomerulus: High pressure within this capillary tuft facilitates the initial filtration of blood to form urine.
Peritubular capillaries: Surround the nephron tubule and are specialized for reabsorption of filtered substances back into the bloodstream.
Glomerular filtration: Water and solutes move from blood into the renal tubule through the glomerular capillaries.
Tubular reabsorption: Essential substances such as glucose, ions, and water are reabsorbed back into the bloodstream from the tubular fluid.
Tubular secretion: Additional wastes and excess ions are secreted into the tubular fluid to be excreted.
Normal urine output ranges between 1.0 to 1.8 liters per day.
Urine composition includes nitrogenous wastes (urea, uric acid, creatinine), and its characteristics such as color, odor, and pH can vary depending on diet, hydration status, and metabolic health.
Slender tubes (approximately 25-30 cm in length) that transport urine from the kidneys to the urinary bladder.
Continuous with the renal pelvis, aided by peristaltic contractions to propel urine downward.
Serves as a reservoir to store urine temporarily until it is expelled from the body. The trigone region indicates the openings for the ureters and urethra.
Composed of smooth muscle walls, which allow for significant expansion as the bladder fills.
A moderately full bladder typically holds about 500 ml of urine.
Conducts urine from the bladder to the outside of the body.
In females, the urethra is typically 3-4 cm long and solely carries urine.
In males, it is approximately 20 cm long and serves a dual purpose of carrying both urine and sperm.
Two sphincters regulate urine release:
Internal sphincter: Involuntary control, relaxing as the bladder fills.
External sphincter: Voluntary control, allowing for conscious decision to urinate.
The process of voiding urine, which is controlled by the urethral sphincters and pelvic floor muscles.
Stretch receptors in the bladder wall trigger impulses that stimulate bladder contractions, leading to the expulsion of urine.
Managed by factors such as dietary intake, metabolic processes, and urine output. Proper balance is crucial for normal cellular function and homeostasis.
The kidneys help regulate acid-base balance through the reabsorption and secretion of bicarbonate ions and hydrogen ions, aiding in the maintenance of a stable pH in the blood.
The development of kidneys begins early in fetal life, around the 5th week of gestation, demonstrating the importance of renal function from early stages of life.
Urinary issues may arise due to complications such as infections, congenital defects, or abnormalities in the structure and function of the urinary tract.
Aging can impact the urinary system by altering the concentration of urine, affecting bladder control, and