Urinary System Overview

Urinary System Functions

• Regulates ion concentrations in plasma
• Regulates blood volume and pressure
• Helps stabilize blood pH
• Conserves nutrients
• Eliminates organic wastes
• Synthesizes calcitriol

Urinary System Structures

• Kidneys
• Ureters
• Urinary bladder
• Urethra

Kidneys

• Located on either side of the vertebral column, between the last thoracic and third lumbar vertebrae
• Position maintained by the overlying peritoneum, contact with adjacent visceral organs, and supporting connective tissues
• Three concentric layers of connective tissue: fibrous capsule, perinephric fat, and renal fascia
• Ureter and renal blood vessels attach to the hilum
• Inner layer of the fibrous capsule lines the renal sinus

Kidney Anatomy

• Divided into outer renal cortex, central renal medulla, and inner renal sinus
• Medulla contains renal pyramids, with tips (renal papillae) projecting into the renal sinus
• Renal columns composed of cortex separate adjacent pyramids
• Renal lobe contains a renal pyramid, overlying renal cortex, and adjacent tissues of the renal columns
• Minor calyces lead to major calyces, which lead to the renal pelvis and then the ureter

Blood Supply to the Kidneys

• Includes renal, segmental, interlobar, arcuate, and cortical radiate arteries, which supply the nephrons
• Blood flows through arcuate, interlobar, and renal veins

Kidney Innervation

• Innervated by renal nerves
• Sympathetic activation regulates glomerular blood flow and pressure, stimulates renin release, accelerates sodium ion and water reabsorption

Kidney Histology - Nephron

• Basic functional unit of the kidney
• Consists of a renal tubule
• Tubular fluid travels through proximal convoluted tubule (PCT), nephron loop (Loop of Henle), and distal convoluted tubule (DCT); then into the collecting tubule, collecting duct, and papillary duct to the renal minor calyx.
• Roughly 85% of nephrons are cortical nephrons, with short loops
• Juxtamedullary nephrons are closer to the medulla with longer loops extending into the renal pyramids

Nephron Function

• Responsible for filtrate production, reabsorption of organic nutrients, reabsorption of water and ions
• Parietal epithelium lines the outer wall of the renal corpuscle
• Glomerulus is a capillary knot within the glomerular capsule, with podocytes wrapping around capillaries and filtration slits.

Micturition Reflex and Urination

• Process coordinated by the micturition reflex
• Stretch receptors in bladder wall initiate the reflex
• Voluntary urination involves relaxation of the external urethral sphincter

Aging and the Urinary System

• Associated with increased kidney problems
• Declining number of functional nephrons, reduced glomerular filtration, reduced sensitivity to ADH, and problems with the micturition reflex (potential urinary retention)

Ureters

• Transport urine from the renal pelvis to the urinary bladder
• Wall consists of inner mucosal layer, middle muscular layer, and outer connective tissue layer (adventitia)

Urinary Bladder

• Hollow muscular organ that serves as a storage reservoir for urine
• Stabilized by median umbilical ligament and lateral umbilical ligaments
• Internal features include trigone, neck, and internal urethral sphincter. Mucosal lining contains prominent rugae

Urethra

• Extends from neck of urinary bladder to the exterior
• Different structures in males and females
• In males: prostatic, membranous, and penile sections
• In females: short, ending at the external urethral orifice

Clinical Terms (from pages 15-16)

• Calculi
• Cystitis
• Dysuria
• Hemodialysis
• Incontinence
• Nephrolithiasis
• Pyelogram
• Urethritis
• urinary obstruction
• Urinary tract infection
• Endometriosis
• Orchiectomy