The Excretory System
By: Madeline Frazer, Mark Sibold,
Catherine Peta, Catie Ward and
Delaney Secrest
Function of the Urinary System
To rid the body of water and solutes that are in excess of the amounts required to
maintain extracellular fluid, reclaim certain solutes (potassium, sodium) and water
that the body needs. (1, pg 751) Also, the urinary system works with the digestive
system to maintain the balance of chemicals and water in the body. (2)
https://www.youtube.com/watch?v=OkyFPMXa28c
Urine under a microscope
Filtration
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In the Urinary System, blood is filtered through kidneys so that big molecules such as cells and proteins,
which are important to the body, can be retained and used by the body, yet unneeded waste can be
exported from the body.
Structure: the filtrate, which is in the nephron, is composed of water, ions (sodium, potassium, chloride),
glucose and small proteins.
The filtrate (known as glomerular capillaries) are 10 to 100 times more permeable to water and small
solutes than other capillaries are. Therefore there is a high filtration rate.
Rate: Filtration rates depend on flow volume to the kidneys. For example, when you run a race the
nervous system diverts an above normal volume of blood away from kidneys, towards the heart and
skeletal muscles.
Fun Fact: The rate of filtration is approximately 125 ml/min or 45 gallons (180 liters) each day. Humans
have about 7 to 8 liters of blood in their bodies, meaning that your entire blood volume gets filtered
approximately 20 to 25 times each day. (3)
Filtration of blood in the Urinary
System
Kidneys
● pair of bean shaped organs
● kidneys filter water and other substances from blood
● after filtration- return to blood
● anything unclaimed becomes urine
(1)
Nephrons
● (1) millions throughout kidney
● where filtration takes place
● blood enters glomerulus and
moves through proximal tube
● loop of henle where water and
solute’s volume are reduced to
create a hypertonic medulla
● loop of henle dilutes the filtrate by
drawing out water and sodium chloride
● collection tube draws out water. Anything left over flows through kidney
and into urinary tract
Tubular Reabsorption
-Nutrients are absorbed in 6 different places throughout the Nephron
-Luminal Membrane
-active and passive transport of filtrate from tubule lumen-->peritubular capillary
-concentration gradient created by Na+
-channel proteins move Glucose+Amino Acids
-water-->osmosis
-Proximal Convoluted Tubule
-65% of reabsorption occurs here
-Loop of Henle
-Descending
Ascending
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-becomes increasingly concentrated as H20 leaves
reabsorbed
-filtrate becomes increas. dilute as Na+ is
-Renal Tubules and Collecting Duct
-reabsorption is regulated by hormones (PTH, ADH, aldosterone, and ANP)
-Distal Convoluted Tubule
-Collecting Duct
Tubular Reabsorption
Active+Passive Transport through the
Luminal Membrane-->peritubular capillary
Overview of tubular
reabsorption/where it takes place
in nephron
Tubular Secretion
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Tubular secretion is the opposite of tubular
reabsorption. Cells along the walls of the nephron
secrete solutes, mostly H+ and K+, after absorbing
water and solutes from the fluid. (1)
After the hairpin turn, sodium and chloride ions are
pumped in, making the fluid saltier, while water is
absorbed from the fluid. (1)
● Secretion prevents certain metabolites (like uric acid)
and foreign substances (like any drugs) from collecting
in the bloodstream. (1)
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Homeostasis
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urine formation is a fluid that rids the body of excess
and waste products
o
we can lose water through urine, evaporation
(sweat), elimination in feces
o
we gain solutes from absorption (eating),
secretion from cells, respiration and metabolism
the kidney is responsible for filtering out as much or as
little solute as necessary to maintain a balance in the
body
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the bloods system’s preferred pH is 7.4
Before the “hairpin” turn, water moves out of filtrate
by osmosis. After the turn, only salt is able to
permeate the walls of the nephron
ADH is the hormone responsible for monitoring the
levels of water in the body
References:
❏ (1) Starr, Cecie, Ralph Taggart, and Lisa Starr. Biology: The Unity and Diversity of Life. 9th ed.
Australia: Brooks/Cole, 2001. Print.
❏ (2) Zimmermann, Kim Ann. "Urinary System: Facts, functions and diseases." Livescience.com .
Tech Media Network , 11 Feb 2013. Web. 31 Oct 2013. <http://www.livescience.com/27012urinary-system.html>.
❏ (3) Freudenrich, Craig. "How Your Kidneys Work ."howstuffworks.com . HowStuffWorks.inc, n.d.
Web. 31 Oct 2013. <http://science.howstuffworks.com/life/human-biology/kidney2.htm>.)
❏ (4) U of New Mexico. "Homeostasis." UNM Biology Undergraduate Labs. U of New Mexico, n.d.
Web. 3 Nov. 2013. <http://biology.unm.edu/ccouncil/Biology_124/
Summaries/Homeostasis.html>.
❏ (5) McGraw-Hill College Division. "Body Systems and Homeostasis." Body Systems and
Homeostasis. N.p., n.d. Web. 3 Nov. 2013.
<http://www.mhhe.com/biosci/genbio/maderbiology/supp/homeo.html>.