"a spoof; action of mocking or teasing," by 1958, slang, from the verbal phrase send up "to mock, make fun of" (1931); see send (v.) + up (adv.). This is perhaps a transferred use of the public school colloquial phrase for "to send a boy to the headmaster" (usually for punishment), which is attested from 1821. In U.S. slang, send up could mean "convict of crime and imprison" (1852), and in 19c. nautical language it meant "hoist (a mast or yard) into its place aloft."
To send down (v.) also was a British university punishment: "compel a student to leave the college for a time" (1853), and in U.S. slang this also meant "put in prison" (1840).
As a noun, it is recorded from 1809 in the sense "outburst, quarrel;" 1807 as "an explosion." Meaning "enlargement from a photograph" is attested by 1945 (the verbal phrase in this sense is by 1930). Old English had an adjective upablawan "upblown," used of a volcano, etc.
1660s, "arouse by knocking at the door," from knock (v.) + up (adv.). However it is little used in this sense in American English, where the phrase means "get a woman pregnant" (1813), possibly ultimately from knock in a sense "to copulate with" (1590s; compare slang knocking-shop "brothel," 1860).
Knocked up in the United States, amongst females, the phrase is equivalent to being enciente, so that Englishmen often unconsciously commit themselves when amongst our Yankee cousins. [John Camden Hotten, "The Slang Dictionary," London, 1860]