Chapter 17 - Urinary System

17.1 Introduction

-Cells produce waste that can become toxic if they accumulate

Functions

-the urinary system removes salts and nitrogenous wastes
-maintains normal concentration of water and electrolytes
-maintains pH, controls red blood cell production and blood pressure

Composition

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

-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

Nephrons

-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 --> bladder

17.3 Urine Formation (section is abbreviated)

glomerular filtration - urine formation begins, plasma is filtered
tubular reabsorption - returns most of the fluid to the body
tubular secretion - removes what is not needed; produces urine

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

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. Pulses of sonic waves pulverize the stones, which are then more easily passed through the ureter and out of the body in the urine.

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

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