Download The Urinary System

The Urinary
System
Chapter 15
Organs of the Urinary
System
• Kidneys are the major
organs
– Other organs store &
pass urine
• Two kidneys, two
ureters, one bladder,
one urethra
Kidney Functions
• Regulate blood ionic composition
– Na+, K+, Ca2+, Cl-, HPO4-2
• Aldosterone: reabsorption of sodium
(water follows)
– Alters blood volume and pressure
• Regulate blood pH (7.35-7.45)
– Excreting H+ and HCO3– Conserving/reabsorbing or
generating new bicarbonate ions
Kidney Functions
• Regulate blood volume
– Conserve or eliminate water (ADH)
• Regulation of blood pressure
– Secrete renin (enzyme)
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Converts angiotensinogen (released by liver) to angtiotensin I, which is
then converted to angiotensin II.
Causes vasoconstriction, raises blood pressure, and stimulates release
of aldosterone
Aldosterone causes reabsorption of sodium and water into blood, so
blood volume & pressure increases
Some blood pressure medications interfere with this process to lower
blood pressure
– JG cells of kidney stimulated by solute concentrations of
filtrate
Regulating Blood
Volume
Regulating Blood
Pressure
Kidney Functions
• Maintenance of blood osmolarity
– Regulate dissolved substances in blood
• Production of hormones
– Calcitriol (active form of vitamin D)
– Erythropoietin (stimulates red blood cell
production)
• Regulate blood glucose level
– Can form glucose from amino acid glutamine
• Excretion of wastes & foreign substances
– Urine production (good indicator of kidney health)
Hormone Production
Kidney Exterior
Anatomy
• Location: retroperitoneal (behind peritoneal
membrane)
– Peritoneum: serous membrane in abdomen
• Three layers of tissue surround kidney:
– Renal capsule (deep layer) – connective tissue
– Adipose capsule – protects, cushions, keeps in place
– Renal fascia – anchors to surroundings (connective
tissue)
• Protected by floating ribs
• Renal hilum – deep fissure where ureter &
vessels emerge (blood vessels, nerves, lymphatic
vessels)
Kidney Exterior
Anatomy
Kidney Interior
Anatomy
• Two distinct regions:
– Renal cortex (outer)
– Renal medulla (inner) – made up of 8-18
cone-shaped pyramids
• Nephron: functional unit of kidney
(mostly in cortex)
– About 1,000,000 of them
• Abundant blood supply (blood filtration)
– ¼ of blood supply goes through kidneys each
minute; supplied by renal arteries
Kidney Interior
Anatomy
• Nephrons product
urine
•
Urine drained into ducts
in pyramids to minor
calyces
– Calyces enclose tips of
pyramids (“cup-shaped”)
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Then drains to major
calyces, then to renal
pelvis
Renal pelvis  ureter 
bladder
Nephron Anatomy
• Page 516 (Figure 15.3)
• Two parts:
– Renal corpuscle – blood plasma filtered
• Glomerulus: capillary network (knot of capillaries)
• Glomerular (Bowman’s) capsule: surrounds glomerulus;
contains filtrate from capillaries
– Renal tubule – passes filtered fluid
• Three sections; convoluted (tightly coiled); substances
are added or removed from filtrate
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Proximal convoluted tubule (PCT): renal cortex
Loop of Henle (nephron loop): renal medulla
Distal convoluted tubule (DCT): renal cortex
» DCT empties into collecting duct that goes down through the
pyramid to the calyces
– 80-85% of nephrons are cortical nephrons
Nephron Anatomy
Renal Physiology
• Page 518 (Figure 15.4)
• Urine formation has three processes
– Glomerular filtration
• Blood  tubule
– Tubular reabsorption
• Tubule  blood
– Tubular secretion
• Blood & tubule cells  urine
Glomerular Filtration
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Filtration: the use of pressure to force fluids and solutes
through a membrane
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Water and solutes move across capillary wall
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Nonselective, passive process
Produces “filtrate”
Membrane permits filtration of water and small solutes, but not
large solutes
»
i.e. blood cells, proteins, etc. (presence indicates a problem)
Afferent artery of glomerulus has higher pressure than efferent
artery
Blood pressure very important for process
More than 99% of what is filtered out of the capillaries returns to
the blood stream
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
Regulated by adjusting blood flow and altering surface area of
glomerular capillary with contractile cells
Glomerular Filtration
Chronic Kidney Disease
Tubular Reabsorption
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Tubule  blood
99% of water filtered from glomerulus is returned to
the blood
Mostly occurs in the PCT, but DCT & collecting duct
also active
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)
Regulated by hormones
–
Renin & aldosterone
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Both increase reabsorption (increase blood volume)
ADH (pituitary)
Tubular Reabsorption
Tubular Secretion
• Tubular reabsorption in reverse!
– Blood & tubule cells  urine
• Get rid of substances not already in
filtrate
– drugs, creatinine, ions, additional means for
regulating pH
Tubular Secretion
Hormone Regulation
• Tubular reabsorption and secretion are
regulated by four hormones
– Angiotensin II – lowers GFR
• Vasoconstriction of afferent arterioles
• Increases reabsorption of Na+, Cl-, water
aldosterone
– ADH – regulates water loss
• Stimulates release of
(Na+ reabsorption)
• Released from pituitary gland, increases water
permeability of cells by inserting aquaporins
• Inhibited by alcohol
– ANP – atrial natriuretic peptide
• Causes increased urine output
Hormone Regulation
Urinalysis
• Check for normal and abnormal excretions
in urine
• Reveals kidney health
link
Dialysis
• Used to clean blood if kidneys not functioning
• Dialysate: formulated to maintain diffusion
gradients to filter out wastes (urea, creatine,
uric acid, some ions) & adds needed
substances (glucose, bicarbonate)
• Blood also passes through air embolis detector
– removes air
• Heparain given to prevent clotting
• Approximately 6-12 hours per week (3
sessions)
Dialysis
link
Urine Transportation,
Storage, & Elimination
• Ureters (pair) – transport urine from
kidney to bladder
– No valves at opening; pressure in bladder
compresses opening and prevents backflow
• Bladder – stores urine (approximately 700800 ml)
• Urethra (one) – transports urine from
bladder to outside of body
– Separate urethra for women; common with
reproductive tract for men
Kidneys’ Role in
Homeostasis
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Excretion of nitrogen-containing wastes
Maintaining water balance of blood
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ICF is 2/3 of body fluid, ECF is 1/3 of body fluid
Water gained & lost by ingestion and metabolic synthesis
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Maintaining electrolyte balance of blood
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Hypothalamus: thirst mechanism (most water intake from fluids & foods)
Regulated by hormones (ADH & aldosterone)
Aldosterone regulates sodium ion content of ECF (and Cl-, K+, and
Mg2+)
80% of sodium reabsorbed from filtrate in PCT
Water follows salt!
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)
Mechanisms include buffer systems, exhalation of CO2, and kidney
excretion of H+
Renin-Angiotensin
Mechanism
Polycystic Kidney
Disease
• Degenerative hereditary disease
• Kidneys enlarge and have cysts (contain
urine)
• Eventual outcome: end stage renal failure
(transplant needed)
link
Renal Calculi
• Solutes form crystals that precipitate in
the renal pelvis (kidney stones)
link
link
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