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The Excretory System. By Duncan, Liana, Katie, Lauren. The Function of the Urinary System. Kidneys filter the blood! In general, the process excretes urine, eliminating excess water and solutes.

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The excretory system

The Excretory System

By Duncan, Liana, Katie, Lauren

The function of the urinary system
The Function of the Urinary System

  • Kidneys filter the blood!

  • In general, the process excretes urine, eliminating excess water and solutes.

    • This is the main way water and solutes are eliminated (also sweat, respiration, eliminations in feces etc.)


  • A pair of organs, as large as a fist and bean shaped

    •  remove excess liquid and waste in the form of urine1

    • keep a stable balance of salts in the blood by filtering mineral ions, organic waste, and other substances5

    •  Adjust the filtrate's composition and return 99% of water and solutes back into the blood because cells need these to survive! 

    • The kidneys keep the blood relatively isotonic when compared to cells.

  • Because of its need to absorb polar molecules, the kidney's tubules contain special channel proteins to absorb these molecules2.

  • Receives roughly 20% of cardiac output

Path to pee

nephron: kidney's functional unit, millions in kidney4

Bowman's capsule

next, renal tubule which has three sections:

filtrate enters proximal tubule where reabsorption of ions and molecules into blood (peritubular capillaries) occurs

continues to loop of Henle where water and salt leave

in distal tubule, water and other solutes are reabsorbed by blood and other solutes secreted into tubule (it's trying to regulate blood's pH, water, sodium, and other solutes levels)4

What remains in the tubule=urine

Path to Pee!


Urine made in nephrons by:

1)Filtration: pressure of the blood forces water and small solutes, not proteins, red blood cells or other large molecules, out of glomerular capillaries (in Bowman's Capsule)4

  • works quickly because these capillary walls are extremely permeable to water and small solutes (in comparison to other capillary walls)4

  • also, capillaries are narrow here to increase blood pressure

Tubular reabsorption

2)Tubular Reabsorption: in the nephron's tubular regions4

Process where solutes and water are removed from the tubular fluid and transported back into the blood

How it crosses the tubule's walls: 

Water moves by osmosis. 

Channel proteins move solutes across the wall. 

Protein pumps actively transport things like glucose and amino acids back into the blood.

Solutes also move because with water gone--> higher concentration of solutes--> they diffuse out.

Tubular Reabsorption!


3)Tubular secretion:excess solutes from unfiltered blood are secreted into tubule including ions, mainly H+ and K+ 

substances produced from metabolism and drugs are also secreted2


Summarize that
Summarize that!

  • in Proximal Tubule sugar and amino acids and water reabsorbed back into blood

  • in loop of Henle

    • descending: osmosis occurs

    • ascending: impermeable to water and Na+ and Cl- active pumped out to concentrate waste

    • now solution in tubule hypertonic to nephron

  • in distal tubule permeable to water therefore concentrated pee

After the kidney
After the Kidney...

  • Once through the Kidneys, urine goes through one of the ureters, which is a long thin tube leading into the bladder4.

  • The bladder is a stretchable container for temporarily holding urine

  • From the bladder, the urine goes to the urethra, which is the channel between the bladder and the body surface4.

Diabetes and the excretory system
Diabetes and the Excretory System

  • Glucose = sugar found in blood 

  • Normally there is very little or no glucose in urine

  • When someone has diabetes and is not taking care of it, or does not know, they have very high blood sugar levels

    • --> The sugar then spills over into the urine. 

  • Side note: Glucose can also be found in urine when the kidneys are damaged or diseased3.

    • (not always a sign of diabetes)


  • "Anatomy and Function of the Urinary System." Packard Children's Hospital at Stanford LPCH: Northern California Children's Hospital . Lucile Packard Foundation for Children's health, n.d. Web. 4 Nov. 2010. <>. 

  • Casiday, Rachel, and Regina Frey. "Kidney Dialysis." Department of Chemistry. Washington University, n.d. Web. 4 Nov. 2010. <>.

  • Colds, e Bye. "Urine Test: Color, pH, Nitrates, and Protein in Urine."WebMD - Better information. Better health.. Healthwise, n.d. Web. 4 Nov. 2010. <>.

  • Starr, Cecie, and Ralph Taggart.  Biology: The Unity and Diversity of Life. 11 Har/Cdr ed. New York: Brooks/Cole Pub Co, 2006. Print.

  • "excretory system | science4all." science4all. N.p., n.d. Web. 4 Nov. 2010. <>.