"Stomach" - what is it, definition of the term
The gastric organ is a muscular, J‑shaped pouch situated in the upper abdomen, functioning as the principal site for mechanical disruption and chemical digestion of ingested material; its inner lining houses gastric glands that release hydrochloric acid and pepsinogen to create an acidic environment for protein denaturation and proteolysis, while coordinated peristaltic contractions mix contents with secretions and propel chyme toward the small intestine, and the organ also participates in nutrient‑absorption signaling and immune defense via its mucosal barrier.
Detailed information
The gastric compartment of arachnids and insects varies according to feeding habits and phylogeny. In all groups, the foregut transports ingested material to a muscular midsection where enzymatic breakdown occurs, followed by absorption in the hindgut. The organ is lined with cuticular epithelium and contains glands that secrete digestive enzymes.
Ticks possess a dilated midsection that expands during blood meals. The organ stores large volumes of host plasma and concentrates nutrients. Key features include:
- Muscular wall enabling peristaltic movement
- Salivary glands that inject anticoagulants before ingestion
- Intracellular digestion of hemoglobin
True bugs (Hemiptera) have a piercing‑sucking mouthpart linked to a narrow foregut. Their digestive sac contains:
- Catalytic enzymes for plant sap breakdown
- Symbiotic bacteria in the posterior midgut aiding amino‑acid synthesis
- Specialized filtering structures to remove excess water
Lice, as obligate ectoparasites of mammals and birds, exhibit a reduced digestive system. Their gastric organ is streamlined for continuous consumption of blood or keratin. Notable aspects:
- Thin muscular layer for rapid processing
- High surface‑area epithelium for nutrient absorption
- Absence of extensive storage capacity, reflecting constant feeding
Fleas ingest blood in frequent, small meals. Their midsection is adapted for rapid digestion and waste elimination. Characteristics include:
- Strong peristaltic contractions to move blood through the gut
- Production of proteolytic enzymes that degrade host proteins
- Efficient excretion of excess water via Malpighian tubules
Across these arthropods, the gastric organ demonstrates convergence toward efficient processing of liquid or semi‑liquid meals, while structural modifications reflect each group’s ecological niche.