Chapter 15: The Urinary System
Organs of the Urinary System
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Kidneys are the major organs
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Other organs store & pass urine
Two kidneys, two ureters, one bladder, one urethra
Kidney Functions
1.
Regulate blood ionic composition
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2+
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Na , K , Ca , Cl , HPO
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Aldosterone: reabsorption of sodium (water follows)
Alters blood volume and pressure
2. Regulate blood pH (7.35-7.45)
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Excreting H and HCO
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Conserving/reabsorbing or generating new bicarbonate ions
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3. Regulate blood volume - Conserve or eliminate water (ADH)
4. Regulation of blood pressure
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Secrete renin (enzyme)
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Converts angiotensinogen (released by liver) to angtiotensin I, which is then converted to
angiotensin II.
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Causes vasoconstriction, raises blood pressure, and stimulates release of aldosterone
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Aldosterone causes reabsorption of sodium and water into blood, so blood volume &
pressure increases
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Some blood pressure medications interfere with this process to lower blood pressure
JG cells of kidney stimulated by solute concentrations of filtrate
5. Maintenance of blood osmolarity
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Regulate dissolved substances in blood
6. Production of hormones
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Calcitriol (active form of vitamin D)
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Erythropoietin (stimulates red blood cell production)
7. Regulate blood glucose level - Can form glucose from amino acid glutamine
8. Excretion of wastes & foreign substances - Urine production (good indicator of kidney health)
Kidney Exterior Anatomy
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Location: retroperitoneal (behind peritoneal membrane)
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Peritoneium: serous membrane in abdomen
Three layers of tissue surround kidney:
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Renal capsule (deep layer) – connective tissue
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Adipose capsule – protects, cushions, keeps in place
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Renal fascia – anchors to surroundings (connective tissue)
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Protected by floating ribs
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Renal hilum – deep fissure where ureter & vessels emerge (blood vessels, nerves, lymphatic vessels)
Kidney Interior Anatomy
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Two distinct regions:
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Renal cortex (outer)
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Renal medulla (inner) – made up of 8-18 cone-shaped pyramids
Nephron: functional unit of kidney (mostly in cortex)
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Abundant blood supply (blood filtration)
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About 1,000,000 of them
¼ of blood supply goes through kidneys each minute; supplied by renal arteries
Nephrons produce urine
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Urine drained into ducts in pyramids to minor calyces
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Calyces enclose tips of pyramids (“cup-shaped”)
Then drains to major calyces, then to renal pelvis
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Renal pelvis  ureter  bladder
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Nerve supply from renal plexus
Nephron Anatomy Page 516 (Figure 15.3)
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Two parts:
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Renal corpuscle – blood plasma filtered
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Glomerulus: capillary network (knot of capillaries)
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Glomerular (Bowman’s) capsule: surrounds glomerulus; contains filtrate from capillaries
Renal tubule – passes filtered fluid
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Three sections; convoluted (tightly coiled); substances are added or removed from filtrate
1.
Proximal convoluted tubule (PCT): renal cortex
2.
Loop of Henle (nephron loop): renal medulla
3.
Distal convoluted tubule (DCT): renal cortex
a.
DCT empties into collecting duct that goes down through the pyramid
to the calyces
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Lined with epithelial tissue of varying types
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80-85% of nephrons are cortical nephrons
Renal Physiology Page 518 (Figure 15.4)
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Urine formation has three processes
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Glomerular filtration (blood to tubule)
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Filtration: the use of pressure to force fluids and solutes through a membrane
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Nonselective, passive process, Produces “filtrate”
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Membrane permits filtration of water and small solutes, but not large solutes
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i.e. blood cells, proteins, etc. (presence indicates a problem)
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Afferent artery of glomerulus has higher pressure than efferent artery
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Blood pressure very important for process
Water and solutes move across capillary wall
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More than 99% of what is filtered out of the capillaries returns to the blood
stream
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GFR: glomerular filtration rate: maintained by kidneys
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If too fast, some substances not reabsorbed. If too slow, too much reabsorbed
including waste
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Regulated by adjusting blood flow and altering surface area of glomerular capillary
with contractile cells
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Constant GFR promotes health – maintained by kidneys (autoregulation) through
feedback loops, nervous system (ANS produces norepinephrine), and endocrine
system
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Tubular reabsorption (tubule to blood)
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99% of water filtered from glomerulus is returned to the blood
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Mostly occurs in the PCT, but DCT & collecting duct also active
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Water and solutes (useful substances) reabsorbed by passive and active transport
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Reabsorb amino acids, glucose, urea, ions, small proteins, and peptides
Nitrogenous waste is poorly reabsorbed: urea, uric acid, and creatinine (found in high
concentrations in urine)
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Regulated by hormones
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Renin & aldosterone
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Both increase reabsorption (increase blood volume) – reinin secreted by
glomerular cells which stimulates aldosterone secretion by adrenal cortex
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ADH (pituitary)
Tubular secretion (blood & tubule to urine)
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Tubular reabsorption in reverse! Blood & tubule cells
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Get rid of substances not already in filtrate
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 urine
drugs, creatinine, ions, additional means for regulating pH
Hormone Regulation
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Tubular reabsorption and secretion are regulated by four hormones
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Angiotensin II – lowers GFR
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Vasoconstriction of afferent arterioles
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Increases reabsorption of Na+, Cl-, water
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Stimulates release of aldosterone (Na+ reabsorption)
ADH – regulates water loss
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Released from pituitary gland, increases water permeability of cells by inserting aquaporins
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Inhibited by alcohol
ANP – atrial natriuretic peptide
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Causes increased urine output
Urinalysis
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Check for normal and abnormal excretions in urine
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Reveals kidney health
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Normal kidneys produce large volume of dilute urine when fluid intake high and small amount of dilute
urine when water intake low
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Controlled by ADH
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Urinalysis can reveal health of kidneys
Dialysis
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Used to clean blood if kidneys not functioning
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Dialysate: formulated to maintain diffusion gradients to filter out wastes (urea, creatine, uric acid,
some ions) & adds needed substances (glucose, bicarbonate)
Urine Transportation, Storage, & Elimination
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Ureters (pair) – transport urine from kidney to bladder
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No valves at opening; pressure in bladder compresses opening and prevents backflow
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Bladder – stores urine (approximately 700-800 ml)
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Urethra (one) – transports urine from bladder to outside of body
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Separate for women; common with reproductive tract for men
Kidneys’ Role in Homeostasis
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Excretion of nitrogen-containing wastes
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Maintaining water balance of blood
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ICF is 2/3 of body fluid, ECF is 1/3 of body fluid
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Water gained & lost by ingestion and metabolic synthesis
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Hypothalamus: thirst mechanism (most water intake from fluids & foods)
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Regulated by hormones (ADH & aldosterone)
Maintaining electrolyte balance of blood
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Ion concentrations control osmosis, help m aintain pH, carry electrical current, serve as cofactors
for enzymes
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Aldosterone regulates sodium ion content of ECF (and Cl , K , and Mg )
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80% of sodium reabsorbed from filtrate in PCT
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Water follows salt!
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Renin-angiotensin mechanism (diagram on next slide)
Ensuring proper blood pH
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Maintain 7.35-7.45 pH (acidosis or alkalosis if out of balance)
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Mechanisms include buffer systems, exhalation of CO , and kidney excretion of H
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Polycystic Kidney Disease
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Degenerative hereditary disease
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Kidneys enlarge and have cysts (contain urine)
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Eventual outcome: end stage renal failure (transplant needed)
Renal Calculi
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2+
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Solutes form crystals that precipitate in the renal pelvis (kidney stones)
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