BIOL 102 The Urinary System Notes

Chapter 15: The Urinary System

Urinary System Regulates Body Fluids
 Excretion: processes that remove waste and excess materials from
the body
 Digestive System: excretes food residues and waste produced by
the liver
 Respiratory System (lungs): excretes carbon dioxide
 Integumentary System (skin): excretes water and salt
 Urinary System (kidneys): excretes nitrogenous wastes, excess
solutes and water

The Kidneys Regulate Water Levels:
 To maintain homeostasis,
Water input = water output
 Kidneys adjust water output as necessary
-water input: food, drink, metabolism
-water output: lungs, skin, feces, kidneys
-kidneys modify output based on intake and loss
-output varies from ½ liter/day to 1 liter/hour

The Kidneys Regulate Nitrogenous Wastes and Other Solutes:
 Protein metabolism produces nitrogenous wastes
 Initially, NH3 (ammonia) is produced during breakdown of amino
acids
 Liver detoxifies NH3, producing urea
 Urea is transported from liver to kidneys for disposal
 Other solutes regulated by kidneys
-Sodium, chloride, potassium, calcium, hydrogen ions, creatinine

Organs and Urinary System:

,  Kidneys
– Principal organ of urinary system
– Cortex: outer portion of the kidney
– Medulla: inner region of the kidney
– Renal pelvis: hollow space in center of kidney where urine
collects
 Ureters
– Muscular tubes that transport urine from kidneys to bladder
 Urinary bladder
– Three layers of smooth muscle, lined with epithelial cells
– Stores urine (600–1,000 ml)
 Urethra
– Carries urine from bladder to outside of body
– Two sphincters control urination

The Internal Structure of the Kidney:
 Nephron: functional unit of the kidney
– Two functional parts:
– Tubule
– Associated blood supply
 1 million nephrons per kidney
 Each nephron consists of a long thin hollow tube (tubule) plus
associated blood supply
 Role of nephrons: remove approximately 180 liters of fluid from the
blood daily, and return most of it, minus the wastes that are excreted
 Nephron structure
– Glomerular capsule: cuplike end of nephron tubule surrounding
glomerulus (network of capillaries)—this is where filtration
occurs
– Four distinct regions of tubule
– Proximal tubule: extends from glomerular capsule to
renal medulla




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