Urinary

Kidneys: The primary organs responsible for filtering blood and forming urine, maintaining homeostasis.
Ureters: Muscular tubes that transport urine from the kidneys to the urinary bladder, utilizing peristaltic movements.
Urinary Bladder: A hollow organ that collects and stores urine until it is excreted.
Urethra: The duct through which urine is conveyed from the bladder to the outside of the body.

The kidneys play a crucial role in homeostasis by regulating the composition, pH, and volume of body fluids.
They remove metabolic wastes and excess substances, including drugs and their metabolites, from the bloodstream.
The kidneys secrete hormones such as erythropoietin, which stimulates red blood cell production, and renin, which regulates blood pressure.
They also produce calcitriol, the active form of Vitamin D, which enhances calcium absorption in the intestines.

Kidney Structure and Function

Location: The kidneys are located on either side of the vertebral column in the posterior abdominal wall, with the left kidney positioned higher than the right due to the liver's location.
Structure: The kidney has a convex lateral surface and a concave medial surface, with a renal sinus that houses the renal pelvis and blood vessels.
Renal Cortex: The outer region containing renal corpuscles, where filtration begins.
Renal Medulla: The inner region composed of renal pyramids, which contain the nephron loops.

Structure of Nephrons: Each nephron consists of a renal corpuscle (glomerulus and Bowman’s capsule) and a renal tubule (proximal tubule, nephron loop, distal tubule, and collecting duct).
Types of Nephrons: Cortical nephrons (85%) have short loops, while juxtamedullary nephrons (15%) have long loops that help concentrate urine.

The first step in urine formation, where blood is filtered in the glomerulus, allowing water and small molecules to pass into the Bowman’s capsule.
Large molecules, such as proteins and blood cells, remain in the bloodstream due to their size.
The resulting glomerular filtrate resembles plasma but lacks large proteins.

Tubular Reabsorption: Primarily occurs in the proximal tubule, where about 70% of filtered substances, including glucose and sodium, are reabsorbed back into the bloodstream.
Active Transport: Mechanism that requires energy to move substances against their concentration gradient, crucial for reabsorbing glucose and amino acids.
Tubular Secretion: The process of transferring substances from the peritubular capillaries into the renal tubules, adding waste products to the urine.

Aldosterone: A hormone that conserves sodium and promotes potassium excretion, influencing blood pressure and fluid balance.
Antidiuretic Hormone (ADH): Increases water reabsorption in the collecting ducts, concentrating urine and reducing its volume.

Urine typically consists of about 95% water, with metabolic waste products such as urea, uric acid, and creatinine.
The composition can vary based on dietary intake and physical activity, with no blood cells or large proteins present in normal urine.

Kidney Stones: Formed from calcium oxalate or uric acid, can cause severe pain and may require treatment such as lithotripsy.
Gout: A condition caused by excess uric acid, leading to painful joint inflammation.

Micturition Reflex: The process of urination, which involves the contraction of the bladder and relaxation of the external urethral sphincter, allowing urine to exit the body.