The Urinary System

17.1 Introduction

-Cells produce waste that can become toxic if they accumulate


the urinary system removes salts and nitrogenous wastes

maintains normal concentration of water and electrolytes

maintains pH, controls blood cell production and blood pressure


consists of a pair of kidneys which remove substances from the blood

ureters which transport urine from the kidneys to the bladder

urinary bladder stores urine

urethra conveys urine to the outside of the body

17.2 Kidneys

lie on either side of the verebral column deep in the abdominal cavity

positioned behind the parietal peritoneum (retroperitoneally)

lateral side is convex, medial is concave, kidneys sit in a depression called the renal sinus

Entrance is called the HILUM

-superior end of the kidney forms a funnel shaped sac - renal pelvis
-renal medulla = center of the kidney
-renal cortex = outer shell around the medulla; the cortex appears granulated due to the presence of nephrons
-renal arteries and veins supply blood to the kidneys

Renal Arteries & Veins

Arteries attach to the abdominal aorta

Veins attach to the inferior vena cava

Interlobar arteries pass between the renal pyramids

Afferent arterioles lead to the nephrons

NEPHRONS -  functional unit of the urinary system

Quick Analogy:  A nephron is to the urinary system as the ______________________ is to the nervous system

-each kidney contains about 1 million nephrons
-renal corpuscle: composed of a tangled cluster called a glomerulus which filters fluid

Pathway = glomerulus » proximal tubulue » nephron loop (also called loop of henle) » distal tubule » collecting duct » ureter » bladder


Also see Kidney and Nephron Coloring

17.3 Urine Formation

glomerular filtration - urine formation begins, plasma is filtered

tubular reabsorption - returns most of the fluid to the body - PROXIMAL TUBULE

tubular secretion - removes what is not needed; produces urine - DISTAL TUBULE

Urine Composition

95 % Water
Contains urea and uric acid (characteristic smell)
Can contain trace amino acids
Urine may also contain other chemicals that can be detected.

Hormones present in a pregnant woman are detectable in urine

*Diuretic – any substance that increases urine production

17.4 Urine Elimination

After urine forms in the nephrons, the ureters (starting with the renal pelvis) carry the urine away to the bladder

Bladder is an expandable structure that stores urine before it is eliminated from the body.

Transitional epithelial cells change shape to allow for expansion and contraction.

Micturation = urination; as the bladder fills this reflex occurs though it is also under voluntary control

Detruser Muscles – muscles that attach to bladder and sphincter that control urination

Urethra = tube carries urine to the outside of the body

Disorders Related to the Urinary System

Kidney Stones

Extracorporeal shock wave lithotripsy (ESWL) is a procedure used to shatter simple stones in the kidney or upper urinary tract. Ultrasonic waves are passed through the body until they strike the dense stones.

Kidney Failure – kidneys no longer filter substances from the blood. This can result in death if not treated with dialysis. Eventually a person will need a new kidney. Causes of kidney failure vary.

Cystitis = bacteria enters the bladder or kidneys (kidney infection); more common in women because the urethra is shorter
Commonly known as a "bladder infection"

Overactive Bladder = sudden contractions of the bladder produce sensation of urgency, also more common in women

Incontinence - inability to control urination (or defecation)