Urine formation and excretion Urine Formation3 steps What

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, acid amino acids, water, urea (about 50% of it), and uric � 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