The Urinary System

The Urinary System

• The urinary system has multiple roles, including cleansing the blood, regulating pH, regulating blood pressure, producing erythropoietin (EPO), and synthesizing vitamin D.
• The four major components of the urinary system are the kidneys, ureters, bladder, and urethra.

The Kidney

• The kidneys are located on either side of the spine and are protected by muscle, fat, and ribs.
• They filter approximately 227 liters of fluid every day, equivalent to a large bathtub.
• The kidneys participate in whole-body homeostasis, regulating acid-base balance, electrolyte concentrations, extracellular fluid volume, and blood pressure.
• Each kidney contains over a million filtering units called nephrons, which consist of glomeruli, renal tubules, and nephrons.

Nephron

• Nephrons are the functional units of the kidney, responsible for balancing plasma to homeostatic set points and excreting potential toxins in the urine.
• The nephron consists of the renal corpuscle, proximal convoluted tubule (PCT), loop of Henle, distal convoluted tubule, and collecting duct system.
• The three principal functions of the nephron are filtration, reabsorption, and secretion.

Glomerular Filtration

• Glomerular filtration is the first stage of filtering the blood, where filterable blood components move towards the inside of the glomerulus.
• The glomerular filtration rate (GFR) is the volume of filtration formed by both kidneys per minute.
• The heart pumps about 5 L of blood per minute under resting conditions.

Renal Tubules

• Renal tubules reabsorb and return water, nutrients, and minerals to the body, while removing waste and excess acid and fluids through diffusion.
• The body sends the remaining waste through the collecting chambers, eventually leaving the body as urine.

Urine Formation

• Urine formation occurs during three processes: filtration, reabsorption, and secretion.
• Filtration removes filterable components from the blood, while reabsorption removes molecules and ions into the circulatory system.
• Secretion removes substances such as hydrogen ions, creatinine, and drugs from the blood into the collecting duct.

Ureters

• The ureters are a component of the urinary system, transporting urine from the kidneys to the bladder through regular contractions called peristalsis.

The Bladder

• The bladder is the organ that holds urine until it is ready to be released and then helps to expel it from the body.
• Ureters bring urine to the bladder from the kidneys, passing through the ureterovesical junction.

The Urethra

• The urethra is the tube that lets urine leave the bladder and the body.

Disorders of the Urinary System

• Cystitis: inflammation of the bladder
• Kidney stones
• Nephritis: inflammation of the kidney
• Renal failure
• Uremia: urea in the blood
• Urinary tract infection (UTI)
• Cancer

Lab Tests

• Albumin
• Urea
• Creatinine
• Creatinine Clearance
• Electrolytes
• Osmolality
• Urinalysis
• Urine cultures