The Urinary System

Introduction to the Urinary System

• Functions:
  • Waste removal:
  • Nitrogenous wastes: urea, uric acid, creatinine
  • Homeostasis:
  • Regulation of fluid, electrolyte, pH, plasma osmolarity, plasma volume, and composition
  • Erythropoietin secretion: hormone produced to stimulate red blood cell production
  • Urine formation: approximately 1.5 L/day of urine produced

Organs of the Urinary System

• Major Organs:
  • 2 kidneys
  • 1 urinary bladder
  • 2 ureters
  • 1 urethra

Structure of the Kidneys

• Kidney Characteristics:
  • Paired retroperitoneal organs
  • Typical dimensions: 10 cm long, 5.5 cm wide, 3 cm thick
  • Weight: approximately 150 g
  • Hilum:
  • Medial indentation; entry/exit points for renal artery, renal nerves, renal vein, and ureter

Kidney Location

• Positioning:
  • Located on either side of the vertebral column
  • Protected by visceral organs anteriorly and body wall musculature and ribs posteriorly
  • The left kidney is slightly superior to the right

Supporting Structures of the Kidneys

• Connective Tissues:
  • Fibrous capsule: collagen layer covering the kidney
  • Perinephric fat: thick layer of adipose tissue providing cushioning
  • Renal fascia: dense connective tissue anchoring kidneys to surrounding structures

Kidney Gross Anatomy

• Outer structures:
  • Renal Cortex: the outer region
  • Renal Medulla: the inner region
  • Renal Pyramids: cone-shaped structures in the medulla
  • Renal Columns: extensions separating the pyramids
  • Minor and Major Calyx: collect urine from lobes of the kidneys
  • Renal Pelvis: funnel-shaped area that collects urine from the major calyces

Nephrons: Functional Units of the Kidney

• Composition of Nephrons:
  • About 1 million nephrons per kidney
  • Cortical Nephrons (85%): primarily in the cortex, performing most regulatory functions
  • Juxtamedullary Nephrons (15%): longer loops extending into the medulla, important for producing concentrated urine

Nephron Structure

• Main Components:
  1. Renal Corpuscle:
  • Glomerulus: capillary network for filtration
  • Glomerular Capsule: surrounds the glomerulus to collect filtrate
  1. Renal Tubule:
  • Proximal Convoluted Tubule (PCT): major site for reabsorption
  • Nephron Loop: responsible for establishing concentration gradients
  • Distal Convoluted Tubule (DCT): adjusts tubular fluid composition
  • Collecting Duct: collects urine from many nephrons and carries it through the renal medulla

Blood Flow in the Kidneys

• Arterial Supply:
  • Blood enters via the renal artery, which branches into segmental, interlobar, and arcuate arteries, culminating in afferent arterioles supplying the glomeruli
• Venous Drainage:
  • Blood is collected from peritubular capillaries into cortical radiate veins, and drains through progressively larger veins to the renal vein and subsequently to the inferior vena cava

Urine Formation Processes

• Three Main Processes:
  1. Filtration:
  • Occurs in the glomerulus; blood pressure forces water and solutes into the glomerular capsule
  1. Reabsorption:
  • Tubular fluid is modified as substances are returned to the blood
  1. Secretion:
  • Additional materials from blood are transferred into the renal tubule

Hormonal Regulation of Kidney Function

• ADH (Antidiuretic Hormone): increases water reabsorption in the collecting duct
• Aldosterone: regulates sodium and potassium levels
• Renin-angiotensin system: responds to low blood pressure by promoting retention of water and sodium to increase volume and pressure

Renal Failure

• Chronic Renal Failure: gradual loss of kidney function; non-reversible and managed by dietary restrictions
• Acute Renal Failure: rapid loss of kidney function; potential for recovery if treated promptly
• Dialysis: artificial process to filter blood, substituting kidney function

Urinary Disorders

• Common signs: changes in urine volume or appearance, increased urgency or frequency, pain during urination, or signs of infection
• Conditions affecting kidney function: e.g., kidney stones, infections (pyelonephritis), and functional disorders leading to incontinence or urinary retention

Urinary Tract Overview

• Comprises ureters, urinary bladder, and urethra, responsible for transporting, storing, and eliminating urine
• Ureters are muscular tubes; the urinary bladder is a distensible organ; the urethra varies in length and function between genders