Chapter 17 The Urinary System Urinary system fnc

• Chapter 17 - The Urinary System • Urinary system - fnc. producing & excreting urine • Essential function in maintaining homeostasis & survival: – body fluid volumes – levels of chemicals (electrolytes) – normal composition of blood (clean waste products - if not > uremia uremic poisoning )

Kidneys - two Location - posterior back, above waist – R little lower than L – Under muscles of back & retroperitoneal – Cushion of fat - place Renal arteries - large – 20% total blood vol/min – High blood flow & normal B/P essential for urine formation

• Internal Structure of the Kidneys – Cortex - Outer layer – Medulla - Inner port. – Pyramids - Triangular divisions of medulla – Papilla - narrow, end of a pyramid – Pelvis - Expansion of upper end of ureter – Calyx - Divisions in renal pelvis where the

Microscopic Structure • Nephron - microscopic unit – Millions in each kidney (2 million) – Shaped like a funnel w/ convoluted stem – Two principle components: – Renal corpuscle (2) – Renal tubule (4)

– Renal corpuscle - 2 parts – Bowman’s capsule - cupshaped top of the nephron (sacklike) – Glomerulus -network of blood capillaries tucked into Bowman’s capsule • Afferent arteriole delivers blood (larger) • Efferent arteriole drains blood (smaller) • Creates hydrostatic pressure > filtration

– Renal Tubule – (4) – Proximal convoluted tubule - 1 st segment, lies nearest to Bowman’s capsule (bends) – Loop of Henle extension of proximal tubule - straight descending limb, hairpin loop, & straight ascending limb

– Distal convoluted tubule - distal to loop of Henle, extension of the ascending limb – Collecting tubule straight part of renal tubule, distal tubules of several nephrons join into these collecting ducts

• Renal corpuscles, proximal & distal convoluted tubules - located in cortex • Loop of Henle & collecting ducts located in medulla • Urine exits from the pyramids thru the papilla & enters calyx & renal pelvis > to ureters

• Functions • Efficient formation of urine is vital • Filtration - 1 st step in urine formationfluid, electrolytes, & waste products from metabolism • Secretion - in tubules, additional waste products • Reabsorption - useful substances the body needs • Protein metabolism > nitrogenous waste • Artificial kidney - may be used if kidneys fail to fnc. appropriately

– Waste Products - toxins, products that contain nitrogen (urea & ammonia) – Regulating chemical levels - chloride, sodium, potassium, & bicarbonate – Water and Salt Balance - retaining or excreting – B/P Regulation - hormone secretion from juxtaglomerular apparatus to make constrict & raise B/P • Normal Characteristics of Urine - pg. 441 – Color – Odor - Components - p. H - Specific Gravity

Filtration - Bowman’s capsules of the renal corpuscles – Blood pressure causes filtration thru membrane – If B/P drops below certain level < filtration & urine formation < – Glomerular filtration rate = 125 ml/min – Glomerular filtrate = 180 liters/day

Reabsorption - mov’t of substances out of renal tubules into blood capillaries (peritubular capillaries) – Occurs in tubule sections – 97% to 99% of water (178 liters) by proximal tubule – Glucose - proximal tubules /glycosuria - DM – Sodium ions - actively transported

Secretion - movement of substances into the urine in the distal & collecting tubules from the blood – Assists in maintaining acid-base balance – Hydrogen & potassium ions, certain drugs are actively transported to urine – Ammonia - diffusion

• Control of Urine Volume • Hormone control of water & substance reabsorption • ADH (antidiuretic hormone) – From posterior pituitary gland – Decreases the amt. of urine by making collecting tubules permeable to water > reabsorption of water – “water-retaining” hormone – “urine-decreasing” hormone

• Aldosterone – Hormone secreted form adrenal cortex – Controls reabsorption of sodium by stimulating the tubules to reabsorb salt at a faster rate – Also increases tubular water reabsorption – “salt- and water-retaining” hormone • ANH (atrial natriuretic hormone) – Form heart’s atrial wall – Opposite effect of aldosterone – Stimulates tubules to secret more Na & therefore water -“salt- and water-losing”

• • Abnormal excretion of urine Anuria - absence of urine Oliguria - scanty amt. of urine Polyuria - an unusually large amt. of urine

• Ureters - Urine begins draining from the renal pelvis – Narrow tubes (1/4 in. wide, 1012 in. long) – Lines w/ mucous membrane – Thick muscular wall - peristaltic mov’t.

• Urinalysis – Physical, chemical, & microscopic examination of urine – Reveals information about the fnc. of the body – Changes in appearance or characteristics of urine may indicate disease process – Characteristics of urine provide general indicators of the composition of urine • Color - Turbidity (cloudiness) • Odor - Specific Gravity (density) – Char. may indicate “something” is wrong, BUT will not provide detailed information

• Chemical Analysis – Information about: • p. H - urea concentration • Presence: glucose, acetone, albumin, bile – Urine specimen - spun in a centrifuge and suspended particles are forced to the bottom of the tube (microscope - look for abnormal cells & other particles (casts)) – Usually ordered in addition to routine urinalysis (microscopic)

• Urinary Bladder • Lies in pelvis behind pubic symphysis • If full - projects upward into the lower abdominal cavity • Renal colic - pain associated w/ urinary tract

– Elastic fibers & involuntary muscle fibers in walls expands - contracts – Lined w/ mucous membrane • Rugae - surface is wrinkled & lays in folds • Trigone - triangular area - posterior surface tightly fixed (for opens)

• Urethra – Lowest part of urinary tract – Exit to the exterior – Covered by the same sheet of mucous membrane (infection can spread up the urinary tract) • F - 1 1/2 inches • M - 8 inches – passageway of

• Micturition • Urination, voiding • Passage of urine from body or emptying bladder • Reflex in infants & small children (trained between 2 to 3 yrs. ) • Two sphincters assist in holding urine in bladder

• Internal urethral sphincter - bladder exit, involuntary • External urethral sphincter - below neck of bladder, striated muscles - voluntary • Accommodates to great varying volumes w/out need to void • 150 ml (need) voiding at 350 ml (adults)

• Emptying reflex occurs when walls stretch & nervous impulses are sent to the 2 nd, 3 rd, & 4 th sacral segments of the spinal cord • Bladder wall contracts Internal sph. relaxes > urine into ureter • If external sph. relaxes - voiding occurs

• Higher centers in the brain also fnc. in voiding - integrate bladder contraction, internal & external sph. relaxation w/ cooperative pelvic & abdominal muscles. • Retention - kidneys work but no urine • Suppression - kidneys don’t work, but bladder will fnc. • Incontinence - pt. voids involuntarily