Urinary System 16-22

Formation of dilute or concentrated urine (16) Filtrate is diluted in the loop of Henle as long as ADH (antidiuretic hormone) is not being secreted Collecting ducts remain impermeable to water; no further water reabsorption occurs Sodium and selected ions can be removed by active and passive transport Urine osmolality can be as low as one-sixth that of plasma

Formation of dilute or concentrated urine (16) Antidiuretic hormone (ADH) inhibits diuresis as it equalizes the osmolality of the filtrate and the interstitial fluid In the presence of ADH, 99% of the water in filtrate is reabsorbed ADH is the signal to produce concentrated urine The kidneys’ ability to respond depends upon the high medullary osmotic gradient

The role of osmotic diuretics like glucose, alcohol & caffeine (17) Chemicals that enhance the urinary output are called diuretics: Any substance not reabsorbed: substances that exceed the ability of the renal tubules to reabsorb it Substances that inhibit Na+ reabsorption

Osmotic diuretics include High glucose levels – carries water out with the glucose (sugary drinks) Alcohol – inhibits the release of ADH Caffeine and most diuretic drugs – inhibit sodium ion reabsorption (losing your salt)

The color of urine (18) Clear, pale to deep yellow (due to urochrome a pigment that is a breakdown product of the blood's hemoglobin and is removed by the kidneys) Concentrated urine has a deeper yellow color Drugs, vitamin supplements, and diet can change the color of urine Cloudy urine may indicate infection of the urinary tract (or not)

Odor of urine (19) standing urine, effects of asparagus! Fresh urine is slightly aromatic Standing urine develops an ammonia odor Some drugs and vegetables (asparagus) alter the usual odor

pH of urine & what affects pH (20) Slightly acidic (pH 6) with a range of 4.5 to 8.0 Diet can alter pH – vegans tend to have more alkaline urine A diet rich in citrus fruits, most vegetables, and legumes will keep the urine alkaline. A diet high in meat and cranberry juice will keep the urine acidic.

Sphincters & muscles that control urine flow (21) 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

Levitator ani muscle

Micturation reflex (22) 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

Detrusor muscle? The detrusor urinae muscle, also detrusor muscle, muscularis propria of the urinary bladder, contracts when urinating to squeeze out urine. Otherwise, it remains relaxed to allow the bladder to fill.