Urine formation and excretion
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Transcript 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