Download Urine formation and excretion

Urine Formation-3 steps
What controls the urinary system?
-It is mostly constant but may need to
increase or decrease
 Renin-angiotensin system (controls ADH and aldosterone)
 Regulates filtration
 Renin is released from juxtaglomerular cells of the kidney
 3 different circumstances:
 Drop in blood pressure
 Sympathetic stimuli
Macula densa sense decrease in chloride, potassium, and sodium
 ADH-antidiuretic hormone (you will need to rewrite this on your guide)
 Regulate water reabsorption
 When there is low water levels in the blood, ADH is released by the
pituitary gland.
 Causes tubules to reabsorb more water
 Effect-urine volume down and very concentrated
 Aldosterone-causes kidney to conserve sodium and excrete potassium
 Released from adrenal glands
 Due to low blood volume
 Causes water conservation of the body

Renin-angiotensin system
 Renin is released
 It reacts with angiotensinogen
 Renin will form angiotensin I
 Angiotensin I combines with an enzyme (released by
lungs and in plasma) to form angiotensin II.
 Angiotensin II
 Maintains water, sodium, and blood pressure


Causes vasoconstriction (less filtering)
Causes vasodialation (more filtering)
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Glomerulus Filtration
 Capillaries drop off particles in the blood the body
needs to get rid of
 Driven by blood pressure (filtration pressure)
 Produces 180 L of fluid every 24 hours
 Particles filter into the glomerulus capsule (mostly
water)
 Composition is very close to tissue fluid
Tubular Reabsorption
 Occurs mostly in the proximal tubule
 Transports items out of the tubular fluid (urine) back
into the blood (peritubular capillary)
 What the body still needs (what is reabsorbed)

Glucose, amino acids, water, urea (about 50% of it), and uric
acid
 65% of filtrate is reabsorbed here
 Reabsorption of sodium and potassium
Tubular secretion
 Late filtering process
 Transports items out of the blood (peritubular
capillaries) into the renal tubules
 Processing of potassium, water, and some uric acid and
urea
Elimination of Urine
 Urine passes through the collecting ducts to the renal
papillae
 Then to the minor and major calyces
 Out the renal pelvis to the ureters
 To the bladder
 To the urethra and out of the body
Urine Summary
 Urine composition
 Reflects the quantities of water and solutes that the
kidney must eliminate for the body to maintain
homeostasis
 Diet
 Activity levels
 Urine
 95% water
 Also has urea, uric acid, trace amounts of amino acids,
and electrolytes
Micturition (not on noteguide)
 Urinating (write this one)
 Contracts detrusor muscle and relaxes the external
urethral sphincter
 Distension stimulates stretch receptors in the bladder
 Impulses are sent to the detrusor muscle from the CNS
 As bladder fills, internal pressure increases, and forces
sphincter to open
 A second reflex relaxes the sphincter unless voluntary
control maintains its contraction