Urinary System Overview

Overview of the Urinary System

• Comprises 2 kidneys, 2 ureters, bladder, and urethra.
• Key functions include blood property regulation, water and electrolyte balance, acid-base balance, and excretion of metabolic wastes.

Functions of the Urinary System

• Regulates fluid balance by adjusting water secretion.
• Maintains proper cell function by controlling inorganic ion levels (e.g., sodium).
• Supports pH balance by excreting hydrogen ions and reabsorbing bicarbonate.
• Filters metabolic wastes and excess electrolytes into urine via the ureters.
• Secretes renin (involved in blood pressure regulation) and erythropoietin (stimulates red blood cell production).
• Converts vitamin D to its active form, calcitriol, essential for calcium absorption.
• Engages in gluconeogenesis during starvation, aiding blood sugar maintenance.

Anatomy of the Kidneys

• Each kidney contains a hilum for entry of nerves and exit of ureters.
• Surrounded by a fibrous layer; outer layer consists of fibroblasts, inner layer consists of myofibroblasts.
• Renal pelvis branches into major calyces, which further divide into minor calyces.

Kidney Structure

• Parenchyma (functional tissue) divided into renal cortex (outer, darker) and renal medulla (inner region with tubules).
• Renal cortex contains renal corpuscles and tubules along with intestinal cells.
• Renal medulla consists of renal pyramids (8-15) and renal columns between them.

Nephrons: The Functional Units

• Each nephron consists of a renal corpuscle and a long renal tubule.

• Renal Corpuscle:

  • Glomerulus: Capillary tuft for initial blood filtration.
  • Bowman's Capsule: Collects filtrate; contains visceral and parietal layers.

• Renal Tubule:

  • Proximal Convoluted Tubule: Major site for reabsorption of water, ions, glucose, and amino acids.
  • Loop of Henle: Involved in the reabsorption of water (descending limb) and salts (ascending limb).
  • Distal Convoluted Tubule: Regulates further reabsorption influenced by hormones like aldosterone.
  • Collecting Duct: Concentrates urine, regulated by antidiuretic hormone (ADH).

Blood Flow in Kidneys

• Renal arteries supply oxygenated blood; renal veins return deoxygenated blood to the heart.
• Blood flow follows the pathway: renal artery → segmental arteries → interlobar arteries → arcuate arteries → interlobular arteries → afferent arterioles → glomerulus → efferent arterioles → peritubular capillaries → renal vein.

Renal Corpuscle Structure

• Contains glomerulus surrounded by glomerular capsule (visceral and parietal layers).
• Mesangial cells provide structural support, contract in response to blood pressure, and contribute to immune defense.

Proximal Convoluted Tubule Characteristics

• Specialized cells for reabsorption with a dense brush border, abundant mitochondria, and extensive membrane invaginations.
• Critical for maintaining body homeostasis.

Loop of Henle Morphology

• Thin descending and ascending limbs: simple squamous epithelium.
• Thick ascending limb: simple cuboidal epithelium with many mitochondria.

Distal Convoluted Tubule Role

• Lined by simple cuboidal cells; not as tall as proximal cells.
• Responsible for regulated reabsorption under hormonal control (aldosterone).

Ureters Structure and Function

• Muscular tubes transporting urine from kidneys to bladder.
• Composed of three layers: mucosa (transitional epithelium), muscularis (smooth muscle for peristalsis), and adventitia (connective tissue).

Urinary Bladder Composition

• Hollow organ with expandable walls: mucosa (transitional epithelium), muscularis (detrusor muscle), and adventitia/serosa.
• Stores 400-600 mL of urine; expels it during micturition.

Urethra Structure

• Male Urethra: 3-4 cm long through the prostate.
• Female Urethra: 3-5 cm, lined with transitional epithelium and then stratified squamous epithelium.
• Conducts urine from bladder; allows semen passage in males.

Urine Transport and Storage

• Ureters move urine via peristaltic contractions; bladder stores urine until fullness triggers urination.
• Detrusor muscle contracts to expel urine.

Cellular and Structural Adaptations

• Transitional epithelium: umbrella cells adapt surface area during bladder filling.
• Smooth muscle contractions facilitate urine movement; detrusor muscle essential for urination.
• Highly vascularized lamina propria and submucosa ensure organ function and health.

This quiz covers the components and functions of the urinary system, including the kidneys, ureters, bladder, and urethra. It explores the system's role in regulating blood properties, water-electrolyte balance, and metabolic waste excretion.