Anatomy and Physiology Marieb’s Human Anatomy and Physiology Ninth Edition Marieb w Hoehn Chapter 25 Urinary system Lecture 16 Part 3: Urine Formation and the Micturition Reflex Slides 1-15; 80 min (with review of syllabus and Web sites) [Lecture 1] Slides 16 – 38; 50 min [Lecture 2] 118 min (38 slides plus review of course Web sites and syllabus)

Urine Urine composition varies depending upon Diet Level of activity Major constituents of urine H2O (95%) Creatinine (remember, NONE of this is reabsorbed) Urea (most abundant solute), uric acid Trace amounts of amino acids Electrolytes Urochrome (yellow color), urobilin, trace of bilirubin Normal urine output is 0.6-2.5 L/day (25-100 ml/hr) Output below about 25 ml/hour = kidney failure (oliguria - anuria)

Terms to know… Anuria – absence of urine Diuresis – increased production of urine Dysuria – difficult or painful urination Enuresis – uncontrolled (involuntary) urination Glycosuria (glucosuria) – glucose in the urine Hematuria – blood in the urine Oliguria – scanty output of urine Polyuria – excessive urine output

Elimination of Urine Flow of Urine Know this… nephrons collecting ducts renal papillae minor and major calyces renal pelvis ureters urinary bladder urethra outside world Know this…

Ureters 25 cm long extend downward posterior to the parietal peritoneum parallel to vertebral column in pelvic cavity, joins urinary bladder peristaltic contractions Figure from: Hole’s Human A&P, 12th edition, 2010 Walls of the ureters: Mucous coat – transitional epithelium continuous with linings of the renal tubules and urinary bladder Muscular coat – smooth muscle in longitudinal and circular bundles; carries out peristalsis to move urine toward bladder Fibrous coat (adventitia)– CT layer continuous with the renal capsule and peritoneum

Urinary Bladder [Cyst(o)] Temporary reservoir for storage of urine Four layers: Mucous layer (transitional epi.) Submucous coat Muscular coat Serous layer Figure from: Hole’s Human A&P, 12th edition, 2010 Muscular layer runs in all directions (detrusor muscle) under parasympathetic control. Contraction compresses the bladder and causes urine to flow into urethra Internal urethral sphincter (IUS) is a thickening of the detrusor muscle at the neck of the bladder. When the detrusor muscle is relaxed, the IUS is CLOSED. When the detrusor muscle contracts during the micturition reflex, the IUS OPENS. Frontal section, anterior posterior Note the internal sphincter at neck of bladder

Urinary Bladder and Urethra - Female Urinary bladder is inferior to the uterus and is separated from the rectum by the vagina. Note the short urethra (about 4 cm) Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001 Pelvic region, midsagittal section Note the passage of the urethra through the urogenital diaphragm that forms the external urethral sphincter

Urinary Bladder and Urethra - Male Base of the urinary bladder lies between the rectum and pubis symphysis. Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001 Pelvic region, midsagittal section

Urinary Bladder and Urethra - Male Note the long urethra (about 18-20 cm). There are three sections to the male urethra: - Prostatic urethra - Membranous urethra - Penile urethra Note the passage of the urethra through the urogenital diaphagm that forms the external urethral sphincter Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

The Pelvic Diaphragm (Female) Figure from: Hole’s Human A&P, 12th edition, 2010 These are DEEP muscles that form the pelvic floor and extend between the pubic bones

Cross Section of Urethra Extends from neck of bladder to exterior Epithelium varies from - Transitional at neck of bladder - Stratified columnar at midpoint - Stratified squamous near external urethral meatus Figure from: Hole’s Human A&P, 12th edition, 2010

Micturition (Urination) Reflex trigger = bladder distention & stimulation of stretch receptors micturition center activated in sacral portion of spinal cord parasympathetic nerve impulses cause detrusor muscle to contract (short reflex) and internal urethral sphincter to open need to urinate is sensed (spinal cord -> thalamus - > cortex) - urge to urinate at about 150-200 ml of urine - discomfort at about 300 ml of urine - maximum capacity of bladder is about 600-1000 ml voluntary (tonal) contraction of external urethral sphincter prevents urination and also closes the internal sphincter when decision is made to urinate, external and internal urethral sphincters relax, detrusor muscle contracts, and urine is expelled

Micturition Reflex Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

Review Elimination of Urine Know pathway of urine flow Ureters transport urine from kidney to urinary bladder Urinary bladder is a temporary storage site for urine has muscular coat (detrusor) under parasympathetic control Urethra is the conduit for urine from the bladder to the exterior Varies in length between males (18-20 cm) and females (4 cm) Has different types of epithelium along its length

Review Micturition (urination) reflex Begins with distension of urinary bladder Activates mild contraction of the detrusor muscle Sends impulses to higher brain centers Requires voluntary relaxation of the external urethral sphincter in order for urination to occur