Urinary System Overview

Urinary System Function

• The urinary system excretes waste and maintains homeostasis of bodily fluids
• It regulates blood volume and pressure
• It controls electrolyte and metabolite levels
• It regulates blood pH by removing toxins, excess water, salts, and minerals from the body

Urinary System Components

• Kidneys: Two reddish bean-shaped organs located above the waist, behind the stomach
• Ureters: Connect the kidneys to the urinary bladder
• Urinary Bladder: A smooth muscle sac that stores urine
• Urethra: Connects the bladder to the outside of the body, allowing urine to exit

Nephron Structure and Function

• The nephron is the functional unit of the kidney
• It is responsible for filtering blood, reabsorbing essential substances, and excreting waste as urine
• Each kidney contains about 1 million nephrons
• Bowman's capsule, Proximal Convoluted Tubule (PCT), Loop of Henle, Distal Convoluted Tubule (DCT), and Collecting Duct are the key components of a nephron

Materials Not Reabsorbed

• Some substances, like urea, creatinine, and toxins, are not reabsorbed to be excreted in urine
• Size and charge of molecules affect their ability to be reabsorbed
• pH regulation prevents the reabsorption of some ions, like H+

Urine Formation Process

• Filtration: Blood is filtered, allowing water and small molecules into the nephron
• Reabsorption: Essential substances like water, glucose, and ions are reabsorbed into the bloodstream
• Secretion: Additional drugs and waste products are secreted into the urine
• Excretion: Final urine contains filtered and secreted substances, ready for elimination

Urinary System Diseases

• Kidney Stones: Minerals and salts form crystals in the kidney if urine is overly concentrated
• Urinary Tract Infections (UTIs): Infections in any part of the urinary system, including the kidneys, ureters, bladder, and urethra, can cause symptoms such as pain, frequent urination, and cloudy urine.

Clinical Implications for Pharmacists

• Monitoring renal function includes serum creatinine, creatinine clearance, and GFR estimation
• Elderly patients, those with kidney disease, and patients on nephrotoxic drugs require careful drug dosage adjustments.
• Therapeutic drug monitoring ensures drug levels remain within the therapeutic range.