• 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 papilla open into

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 - cup-shaped 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 - 1st 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 - 1st step in urine formation-

fluid, 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 - Components

– Odor - pH - 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 = 125ml/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, 10-12 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:

• pH - 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 reproductive fluid

• 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 2nd, 3rd, & 4th 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