absorption of digested products

Definition

The transport of enzymatically broken-down nutrients—simple sugars, amino acids, fatty acids, and ions—across the epithelium of the midgut (or equivalent digestive region) into the hemolymph or circulatory system of an arthropod. In insects, this process occurs primarily through the columnar cells of the midgut epithelium, often involving active transport, facilitated diffusion, and pinocytosis; in arachnids, analogous absorption takes place in the midgut diverticula or ceca. The efficiency and mechanisms vary with diet type (fluid-feeding versus solid-feeding), developmental stage, and physiological state such as diapause or starvation.

Etymology

From Latin 'absorbere' (to swallow up) and 'digestus' (distributed, dissolved); the phrase denotes the uptake phase following chemical digestion.

Example

In the tobacco hornworm (Manduca sexta), absorption of digested products peaks during the final larval instar, when midgut columnar cells dramatically increase their microvillar surface area and upregulate amino acid transporters to support the rapid protein synthesis required for metamorphosis.

Synonyms

• nutrient absorption
• intestinal uptake
• enteric absorption

Related Terms

• Midgut
• peritrophic matrix
• digestive enzymes
• Hemolymph
• Malpighian tubules
• metabolic assimilation
• gut epithelium
• nutrient transport

Usage Notes

Distinguished from 'digestion' (the chemical breakdown of food) and 'assimilation' (the broader incorporation of absorbed nutrients into tissues and metabolic pools). Specialists reserve 'absorption' for the membrane-crossing step at the gut level, whereas 'assimilation' encompasses subsequent metabolic fates. In fluid-feeding insects such as aphids or mosquitoes, absorption occurs rapidly across the midgut because the incoming meal is already largely liquid and pre-digested by salivary enzymes or plant sap chemistry.