nèi​pí

endothelium

内皮 (內皮) nèi​pí
endothelium noun
the layer of cells lining the blood vessels and other closed cavities of the body

Vascular endothelial cells play a key role in regulating blood flow.

inner skin noun
the thin, often white membrane or skin found on the inside of fruits like oranges or pomelos

The white pith of an orange is slightly bitter but good for the body.

Frequency

Written text
8.38 per million

Sources

Definitions
CC-CEDICT
Frequency data
BCC Corpus (BLCU)