Urinary System Overview

Urinary System Functions

• Removes metabolic waste
• Regulates blood volume and blood pressure
• Regulates plasma concentrations of sodium, potassium, chloride, etc.
• Helps stabilize blood pH (H+)
• Conserves valuable nutrients

Urinary System Organs/Tissues

• Kidneys
• Ureters
• Urinary Bladder
• Urethra

Kidney Anatomy

• Two kidneys, located on either side of the spine between T12 and L3; the left kidney is slightly superior to the right.
• Stabilized by surrounding connective tissue.
• Reddish-brown, approximately 10 cm long, 5.5 cm wide, and 3 cm thick, with a mass of 150 g.
• Renal cortex
• Renal medulla
• Renal pyramids
• Renal column
• Renal vein
• Renal artery
• Renal pelvis
• Major/minor calyx
• Hilum
• Ureter
• Capsule
• Papillae

Urine Formation Summary

• Three processes occur in the nephron:
  • Filtration: Blood pressure forces water into Bowman's capsule.
  • Reabsorption: Water and solutes are removed from the tubule and enter the peritubular fluid; important fluids and nutrients are reabsorbed into the blood.
  • Secretion: Solutes are transported from the peritubular fluid back into the tubule; this is necessary because filtration alone is not enough to remove unwanted wastes from the plasma.

Ureters

• Pair of muscular tubes connecting kidneys to the urinary bladder.
• Firmly attached to the posterior abdominal wall.
• Three tissue layers: mucosa, muscular layer, and outer connective tissue.
• Peristalsis moves urine through the ureters to the bladder.

Loop of Henle

• Located in the medulla of the kidneys.
• Has a descending and ascending limb.
• Pumps sodium and chloride ions, which move water out of the tubule.
• Water movement out of the loop concentrates tubular fluid.

Urethra

• Extends from the neck of the urinary bladder and transports urine out of the body.
• Longer in males than females.
• External urethral sphincter (voluntary control).
• Micturition

Collecting System

• Final filtration, secretion, and reabsorption occur here.
• Concentrated urine passes through collecting ducts, which merge into papillary ducts.
• Fluid empties into minor calyx, then to major calyx, and to renal pelvis, and then to ureters.

Proximal Convoluted Tubule (PCT)

• First segment of the renal tubule.
• Lined with simple cuboidal epithelium with microvilli.
• Reabsorption of nutrients, ions, water, and plasma proteins occurs here.
• Released into the peritubular fluid.

Urinary Bladder

• Hollow, muscular organ that temporarily stores urine.
• Can hold up to 1 liter.
• Rugae (folds in the bladder wall)
• Trigone (triangular area at the base of the bladder).
• Internal urethral sphincter.

Urinary Conditions/Disorders

• Urinary tract infection (UTI)
• Kidney stones (renal calculi)
• Kidney dialysis
• Glomerulonephritis
• Incontinence

Nephrons

• Microscopic, tubular structures in the kidney cortex.
• Filter blood and produce urine.
• 1.25 million nephrons per kidney.
• Glomerulus
• Bowman's capsule
• Proximal convoluted tubule (PCT)
• Loop of Henle
• Distal convoluted tubule (DCT)