Human Anatomy & Physiology FIFTH EDITION Elaine N. Marieb PowerPoint ® Lecture Slide Presentation by Vince Austin Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Chapter 26 The Urinary System Part D
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Urethra Muscular tube that: Drains urine from the bladder Conveys it out of the body Sphincters keep the urethra closed when urine is not being passed Internal urethral sphincter – involuntary sphincter at the bladder-urethra junction External urethral sphincter – voluntary sphincter surrounding the urethra as it passes through the urogenital diaphragm Levator ani muscle – voluntary urethral sphincter
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Urethra The female urethra is tightly bound to the anterior vaginal wall Its external opening lies anterior to the vaginal opening and posterior to the clitoris The male urethra has three named regions Prostatic urethra – runs within the prostate gland Membranous urethra – runs through the urogenital diaphragm Spongy (penile) urethra – passes through the penis and opens via the external urethral orifice
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Urethra Figure 26.18a, b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Micturition (Voiding or Urination) The act of emptying the bladder Distension of bladder walls initiates spinal reflexes that: Stimulate contraction of the external urethral sphincter Inhibit the detrusor muscle and internal sphincter (temporarily) Voiding reflexes: Stimulate the detrusor muscle to contract Inhibit the internal and external sphincters
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Micturition (Voiding or Urination) Figure 26.20
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Developmental Aspects Three sets of embryonic kidneys develop, with only the last set persisting The pronephros never functions but its pronephric duct persists and connects to the cloaca The mesonephros claims this duct and it becomes the mesonephric duct The final metanephros develop by the fifth week and develop into adult kidneys
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Developmental Aspects Figure 26.21a, b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Developmental Aspects Figure 26.21c, d
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Developmental Aspects Metanephros develop as ureteric buds that incline mesoderm to form nephrons Distal ends of ureteric tubes form the renal pelves, calyces, and collecting ducts Proximal ends called ureteric ducts become the ureters Metanephric kidneys are excreting urine by the third month The cloaca eventually develops into the rectum and anal canal
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Developmental Aspects Infants have small bladders and the kidneys cannot concentrate urine, resulting in frequent micturition Control of the voluntary urethral sphincter develops with the nervous system E. coli bacteria account for 80% of all urinary tract infections Sexually transmitted diseases can also inflame the urinary tract Kidney function declines with age, with many elderly becoming incontinent