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(pĭ-răm′ĭ-dăl) [L. pyramidalis] In the shape of a pyramid.


(pĭ-ram″ĭ-dā′lis) The muscle that arises from the crest of the pubis and is inserted into the linea alba upward about halfway to the navel. Its contraction tenses the linea alba.

pyramidal system

The direct output from the motor cortices of the cerebral hemispheres to the brainstem and spinal cord. It deals with the regulation of fine muscle movements.


(pī′răn) The compound C5H6O, the ring structure that consists of five carbon atoms and one oxygen atom.


(pī′ră-nōs) A cyclic sugar or glycoside with a structure similar to a pyran.


(pī-rē′thrĭnz) The general name given to substances derived from pyrethrum flowers (chrysanthemums); used as insecticides.


(pī-rĕt′ĭk) [Gr. pyretos, fever] Pert. to fever.

pyreto-, pyret-

[Gr. pyretos, burning heat, fever] Prefixes meaning fever.


(pī-rĕk′sē-ă) [Gr. pyressein, to be feverish] Fever.


(pēr′ĭ-dēn) A colorless, volatile liquid with a charred odor. It is obtained by dry distillation of nitrogen-containing organic matter. It is used as an industrial solvent.

pyridoxal 5-phosphate, pyridoxal phosphate

(pir-ĭ-dok′sal″) A derivative of pyridoxine and the biologically active form of vitamin B6. It serves as a coenzyme/catalyst of certain amino-acid decarboxylases in bacteria, and in animal tissues of 3,4-dihydroxyphenylalanine (dopa) decarboxylase.


(pĭr″ĭ-dŏks′ă-mēn″) One of the vitamin B6 group; a 4-aminoethyl analog of pyridoxine.

pyridoxine dependency

(pir″ĭ-dok′sēn″, sĕn) [pyrid(ine) + ox(ygen) + -ine] A rare autosomal recessive cause of neonatal seizures. The disorder requires lifelong supplementation of pyridoxine (vitamin B6).

pyridoxine hydrochloride

(pĭ-rĭ-dŏks′ēn) One of a group of substances, including pyridoxal and pyridoxamine, that make up vitamin B6. SEE: Vitamins Appendix.

pyriform, piriform

(pĭr′ĭ-fŏrm″) [L. pi-rum, pear, + forma, shape] Shaped like a pear. Also spelled piriform.


(pĭ-rĭm′ĭd-ĭn) The parent of a group of heterocyclic nitrogen compounds, C4H4N2. Cytosine and thymine are found in DNA; cytosine and uracil, in RNA.


(pĭr″ĭ-thī′ă-mēn″) A synthetic analog of thiamine that blocks thiamine transport. It was used experimentally in studies of human lymphoblasts to mimic nutritional diseases such as beriberi and Wernicke-Korsakoff syndrome, two forms of thiamine deficiency.

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