| The American Heritage® Book of English Usage. |
A Practical and Authoritative Guide to Contemporary English. 1996.
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4. Science Terms: Distinctions, Restrictions, and Confusions
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| § 39. renin / rennet / rennin |
| It was probably just another recipe swapped among Renaissance homemakers. To make cheese, first slaughter a calf, then remove the inner lining of the fourth stomach, pour in milk, allow it to curdle, remove the curds, squeeze them together to remove all the liquid, and set the unripened cheese aside to age. The initial component for this concoction—the bag made of a calf’s stomach lining—was called rennet, a word linked to an Old English and Old German verb meaning “to flow” or “to run.” Exactly why the rennet caused milk to curdle remained unanswered for a couple of centuries. Investigations in the late 1800s revealed the curdling was produced by a compound known as an enzyme present in the juices of the stomach. This compound, it was shown, helped break apart a protein called casein in the milk and, in the process, triggered the formation of another compound that then bonded to the calcium in the milk, forming curds. The enzyme was dubbed rennin, a combination of rennet and the suffix -in, “neutral chemical compound.” This suffix appears in the names of other enzymes such as trypsin, the compound produced in the pancreas that breaks proteins into smaller bits for use by the body. | 1 |
| While the stomach is the site of rennin production, the kidneys are the source for renin. Renin, in fact, comes from Latin renes, “kidneys,” combined with -in. When a major upset such as dehydration or hemorrhage causes the body’s blood pressure to become dangerously low, specialized cells in the kidneys begin to produce renin. The renin circulates in the bloodstream ready to perform its very specialized task: it clips two component parts, called amino acids, from another blood-borne protein known as angiotensin. This newly abbreviated protein, now called angiotensin I, is clipped further by another blood-carried compound to form angiotensin II. This substance causes blood vessels to constrict, thus raising blood pressure back to normal levels and ensuring the continued proper functioning of the body. | 2 |
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| The American Heritage® Book of English Usage. Copyright © 1996 by Houghton Mifflin Company. All rights reserved. |
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