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, 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