The lamina propria is a thin vascular layer of connective tissue beneath the epithelium of an organ. It contains capillaries and a central lacteal (lymph vessel) in the small intestine. Vascular is an adjective for the word vessel and refers to tube-like structures. ... Biological tissue is a substance made up of cells that perform a similar function. ... In zootomy, epithelium is a tissue composed of a layer of cells. ... In biology, an organ (Latin: organum, instrument, tool) is a group of tissues, which perform a specific function or group of functions. ...