Urinary System Review

Overview of the Urinary System

• Key Functions:

  • Elimination of waste products and biologically active molecules.

  • Regulation of blood pressure, ion levels, and acid-base balance.

  • Production and secretion of hormones such as erythropoietin (EPO) and calcitriol.

  • Gluconeogenesis (only during prolonged fasting or starvation).

Structures of the Urinary System

• **Main Organs: **

  • Kidneys: Filter blood to produce urine, regulate blood pressure, and secrete hormones.

  • Ureters: Muscular tubes that transport urine from kidneys to bladder.

  • Urinary bladder: Stores urine.

  • Urethra: Excretes urine from body.

• Kidney Anatomy:

  • Location: Left kidney between T12 and L3 vertebrae; right kidney approximately 2 cm lower due to liver.

  • Protecting structures: Ribcage, adrenal glands sit atop kidneys.

• Gross Anatomy of Kidneys:

  • Bean-shaped with a medial indentation known as the hilum.

  • Each kidney has connective tissue layers: paranephric fat, renal fascia, perinephric fat, and fibrous capsule.

• Regions of Kidney:

  • Renal Cortex: Outermost layer, extensions into medulla known as renal columns.

  • Renal Medulla: Contains renal pyramids and renal sinus (drains urine).

Blood Flow through the Kidneys

• Renal artery branches from the descending abdominal aorta.

• Smaller arteries reach the nephrons:

  • Afferent arterioles lead to the glomerulus (site of filtration).

  • Efferent arterioles lead to peritubular capillaries and vasa recta.

• Blood exits the kidney via the renal vein and ultimately to the inferior vena cava.

Nephron Structure

• Basic Unit of the Kidney:

  • Renal corpuscle and renal tubule.

  • Renal corpuscle: Includes the glomerulus (capillaries for filtration) and glomerular capsule.

  • Renal tubule: Composed of proximal convoluted tubule (PCT), nephron loop, and distal convoluted tubule (DCT).

• Types of Nephrons:

  • Cortical Nephrons: Mainly in the renal cortex, shorter loops.

  • Juxtamedullary Nephrons: Near the cortex-medulla junction, with longer loops extending into the medulla.

Urine Formation Processes

1. **Glomerular Filtration: **

   • Movement of substances from blood in glomerulus to the capsular space.

   • Influenced by pressure differences (e.g., glomerular hydrostatic pressure).

   • Net filtration pressure (NFP) = HPg - (OPg + HPc).

2. **Tubular Reabsorption: **

   • Movement of substances from tubular fluid back into the blood.

   • Occurs in various regions of nephron, particularly in the PCT.

   • Uses transport processes like diffusion, osmosis, and active transport.

3. **Tubular Secretion: **

   • Substances secreted from blood into tubular fluid.

   • Plays a role in disposing of substances, and regulating pH and potassium levels.

Evaluation of Kidney Function

• Glomerular Filtration Rate (GFR):

  • Average GFR is about 105-125 ml/min; equivalent to 150-180 L/day.

  • Influenced by pressure, kidney health, and blood volume.

Urinary Tract Infections (UTIs)

• Common Symptoms: Painful urination, increased frequency, urgency.

• Gender Differences: Women more likely due to shorter urethra.

• Prevention: Hydration, urination after intercourse, proper hygiene practices.

Urine Characteristics

• Normal Composition:

  • Water, urea, uric acid, creatinine (nitrogenous wastes).

  • Electrolytes like sodium, potassium, and calcium.

• Volume: Normally ranges from 1 to 2 L per day.

  • Influenced by factors such as fluid intake, hormonal balance (e.g., ADH, aldosterone).

Clinical Views

• Clinical View 24.8: UTIs, treatments with antibiotics.

• Clinical View 24.4 and 24.5: Focuses on glomerular filtration rate, renal plasma clearance, diuretics, renal failure, dialysis, and kidney transplants.

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