urinary system

The Columbia Encyclopedia, 6th ed.

urinary system

urinary system, group of organs of the body concerned with excretion of urine, that is, water and the waste products of metabolism. In humans, the kidneys are two small organs situated near the vertebral column at the small of the back, the left lying somewhat higher than the right. They are bean-shaped, about 4 in. (10 cm) long and about 21/2 in. (6.4 cm) wide. Their purpose is to separate urea, mineral salts, toxins, and other waste products from the blood, and to conserve water, salts, and electrolytes. At least one kidney must function properly for life to be maintained. Each kidney contains 1.2 million filtering units called nephrons. One end of the nephron is expanded into a structure called the renal corpuscle, or glomerulus, which surrounds a cluster of blood capillaries. The remainder of the nephron consists of a very long narrow tubule, in alternately convoluted and looping sections. Blood containing waste products enters the glomerulus through an afferent arteriole from the renal artery. The cells of the glomerulus extract the water and waste products as the blood leaves through the outgoing blood vessel (the efferent arteriole) of the glomerulus, in a process called filtration. Blood leaving the glomerulus flows through the network of capillaries that surrounds each tubule; there the substances that the body still needs, such as water and certain salts, are restored to the blood. The purified blood returns to the general circulation through blood vessels leading to the renal vein. The ends of the tubules unite to form collecting tubules, which empty the urine into the kidney pelvis, a collecting chamber in the middle of the kidney. Urine from the kidney pelvis then passes into the ureters, a pair of tubes 16 to 18 in. (40–45 cm) long. Muscles in the walls of the ureters send the urine in small spurts into the bladder, a collapsible sac found on the forward part of the cavity of the bony pelvis that allows temporary storage of urine. The outlet of the bladder is controlled by a sphincter muscle. A full bladder stimulates sensory nerves in the bladder wall that relax the sphincter and allow release of the urine. However, relaxation of the sphincter is also in part a learned response under voluntary control. The released urine enters the urethra, a tube lined with mucus membrane that conveys the urine to the outside. The male urethra, about 8 in. (20 cm) long, terminates at the tip of the penis, and serves as the passage through which semen is released (see reproductive system). The female urethra is less than 2 in. (5 cm) long and opens just in front of the entrance to the vagina; it has no function other than excretion of urine. There are many types of urinary system disorders, including congenital malformation, injury, infection, presence of kidney stones, or calculi, other types of obstruction, and tumors. See cystitis; nephritis; nephrosis. Abnormal urine output may indicate other diseases, such as diabetes.

Notes for this article

Add a new note
If you are trying to select text to create highlights or citations, remember that you must now click or tap on the first word, and then click or tap on the last word.
One moment ...
Default project is now your active project.
Project items

Items saved from this article

This article has been saved
Highlights (0)
Some of your highlights are legacy items.

Highlights saved before July 30, 2012 will not be displayed on their respective source pages.

You can easily re-create the highlights by opening the book page or article, selecting the text, and clicking “Highlight.”

Citations (0)
Some of your citations are legacy items.

Any citation created before July 30, 2012 will labeled as a “Cited page.” New citations will be saved as cited passages, pages or articles.

We also added the ability to view new citations from your projects or the book or article where you created them.

Notes (0)
Bookmarks (0)

You have no saved items from this article

Project items include:
  • Saved book/article
  • Highlights
  • Quotes/citations
  • Notes
  • Bookmarks
Notes
Cite this article

Cited article

Style
Citations are available only to our active members.
Sign up now to cite pages or passages in MLA, APA and Chicago citation styles.

(Einhorn, 1992, p. 25)

(Einhorn 25)

1

1. Lois J. Einhorn, Abraham Lincoln, the Orator: Penetrating the Lincoln Legend (Westport, CT: Greenwood Press, 1992), 25, http://www.questia.com/read/27419298.

Cited article

urinary system
Settings

Settings

Typeface
Text size Smaller Larger Reset View mode
Search within

Search within this article

Look up

Look up a word

  • Dictionary
  • Thesaurus
Please submit a word or phrase above.
Print this page

Print this page

Why can't I print more than one page at a time?

Full screen

matching results for page

Cited passage

Style
Citations are available only to our active members.
Sign up now to cite pages or passages in MLA, APA and Chicago citation styles.

"Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences." (Einhorn, 1992, p. 25).

"Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences." (Einhorn 25)

"Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences."1

1. Lois J. Einhorn, Abraham Lincoln, the Orator: Penetrating the Lincoln Legend (Westport, CT: Greenwood Press, 1992), 25, http://www.questia.com/read/27419298.

Cited passage

Thanks for trying Questia!

Please continue trying out our research tools, but please note, full functionality is available only to our active members.

Your work will be lost once you leave this Web page.

For full access in an ad-free environment, sign up now for a FREE, 1-day trial.

Already a member? Log in now.