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2. KIDNEYS Functions Excretes toxins and nitrogenous wastes
Regulates levels of many chemicals in blood
Maintains water balance
Helps regulate blood pressure via secretion of renin
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3. FORMATION OF URINE (FIGURE 17-5)
Occurs by a series of three processes that take place in successive parts of nephron
Filtration—goes on continually in renal corpuscles; glomerular blood pressure causes water and dissolved substances to filter out of glomeruli into Bowman’s capsule; normal glomerular filtration rate 125 mL per minute
Reabsorption—movement of substances out of renal tubules into blood in peritubular capillaries; water, nutrients, and ions are reabsorbed; water is reabsorbed by osmosis from proximal tubules
Secretion—movement of substances into urine in the distal and collecting tubules from blood in peritubular capillaries; hydrogen ions, potassium ions, and certain drugs are secreted by active transport; ammonia is secreted by diffusion
Control of urine volume—mainly by posterior pituitary hormone’s ADH, which decreases it
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5. URETERS
Structure (Figure 17-6)—narrow, long tubes with expanded upper end (renal pelvis) located inside kidney and lined with mucous membrane
Function—drain urine from renal pelvis to urinary bladder
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7. URINARY BLADDER Structure (Figure 17-7) Functions
Elastic muscular organ, capable of great expansion
Lined with mucous membrane arranged in rugae, as is stomach mucosa
Functions
Storage of urine before voiding
Voiding
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10. URETHRA Structure Narrow tube from urinary bladder to exterior
Lined with mucous membrane
Opening of urethra to the exterior called urinary meatus
Functions
Passage of urine from bladder to exterior of the body
Passage of male reproductive fluid (semen) from the body
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11. MICTURITION
Passage of urine from body (also called urination or voiding)
Regulatory sphincters
Internal urethral sphincter (involuntary)
External urethral sphincter (voluntary)
Bladder wall permits storage of urine with little increase in pressure
Emptying reflex
Initiated by stretch reflex in bladder wall
Bladder wall contracts
Internal sphincter relaxes
External sphincter relaxes, and urination occurs
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12. MICTURITION Urinary retention—urine produced but not voided
Urinary suppression—no urine produced but bladder is normal
Incontinence—urine is voided involuntarily
May be caused by spinal injury or stroke
Retention of urine may cause cystitis
Cystitis—bladder infection
Overactive bladder—need for frequent urination
Called interstitial cystitis
Amounts voided are small
Extreme urgency and pain are common
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