extracellular digestion

(noun)

Extracellular digestion is a process in which animals feed by secreting enzymes through the cell membrane onto the food. The enzymes break the food into molecules small enough to be taken pass through the cell membrane into the cell. These nutrients are transferred into the blood or other body fluids and distributed to the rest of the body.

Related Terms

Examples of extracellular digestion in the following topics:

  • Invertebrate Digestive Systems

    • Invertebrates can be classified as those that use intracellular digestion and those with extracellular digestion.
    • The alimentary canal is a more advanced digestive system than a gastrovascular cavity and carries out extracellular digestion.
    • Because the food has been broken down exterior to the cells, this type of digestion is called extracellular digestion.
    • Most invertebrates use some form of extracellular digestion to break down their food.
    • Their food is broken down in their digestive tract (extracellular digestion), rather than inside their individual cells (intracellular digestion).

  • Phylum Cnidaria

    • Cnidarians are diploblastic, have organized tissue, undergo extracellular digestion, and use cnidocytes for protection and to capture prey.
    • Polyp forms are sessile as adults, with a single opening to the digestive system (the mouth) facing up with tentacles surrounding it.
    • Despite the simplicity of the nervous system, it coordinates the movement of tentacles, the drawing of captured prey to the mouth, the digestion of food, and the expulsion of waste.
    • The cnidarians perform extracellular digestion in which the food is taken into the gastrovascular cavity, enzymes are secreted into the cavity, and the cells lining the cavity absorb nutrients.
    • The gastrovascular cavity has only one opening that serves as both a mouth and an anus; this is termed an incomplete digestive system.

  • Starvation-Induced Fruiting Bodies

    • Individuals benefit from aggregation as it allows accumulation of extracellular enzymes which are used to digest food that increases feeding efficiency.
    • This behavior facilitates predatory feeding, as the concentration of extracellular digestive enzymes secreted by the bacteria increases.

  • Phylum Platyhelminthes

    • The flatworms are acoelomates: their bodies are solid between the outer surface and the cavity of the digestive system.
    • Most flatworms have a gastrovascular cavity rather than a complete digestive system; in such animals, the "mouth" is also used to expel waste materials from the digestive system.
    • Digestion is extracellular, with digested materials taken in to the cells of the gut lining by phagocytosis.
    • One group, the cestodes, lacks a digestive system.
    • The worms may produce enzymes that digest the host tissues or simply graze on surface mucus and skin particles.

  • The Deltaproteobacteria

    • Individuals benefit from aggregation as it allows accumulation of extracellular enzymes which are used to digest food.

  • Extracellular Immune Avoidance

    • These adherent cells are frequently embedded within a self-produced matrix of extracellular polymeric substance (EPS).
    • Biofilm EPS, which is also referred to as slime, is a polymeric conglomeration generally composed of extracellular DNA, proteins, and polysaccharides.
    • Bacteria usually overcome physical barriers by secreting enzymes that digest the barrier in the manner of a type II secretion system.

  • Complex Tissue Structure

    • As multicellular organisms, animals differ from plants and fungi because their cells don't have cell walls; their cells may be embedded in an extracellular matrix (such as bone, skin, or connective tissue); and their cells have unique structures for intercellular communication (such as gap junctions).
    • This connective tissue constitutes the extracellular surroundings of cells and is made up of organic and inorganic materials.
    • Epithelial tissues cover, line, protect, and secrete; these tissues include the epidermis of the integument: the lining of the digestive tract and trachea.

  • Types of Catabolism

    • Several common classes of enzymes digest these polymers.
    • These digestive enzymes include proteases that digest proteins into amino acids, as well as glycoside hydrolases that digest polysaccharides into monosaccharides.
    • Microbes secrete digestive enzymes into their surroundings, while animals only secrete these enzymes from specialized cells in their guts.
    • The amino acids or sugars released by these extracellular enzymes are then pumped into cells by specific active transport proteins.
    • Carbohydrates are usually taken into cells once they have been digested into monosaccharides.

  • Extracellular Matrix of Animal Cells

    • Most animal cells release materials into the extracellular space.
    • Collectively, these materials are called the extracellular matrix .
    • Cells have protein receptors on the extracellular surfaces of their plasma membranes.
    • An example of the role of the extracellular matrix in cell communication can be seen in blood clotting.
    • The extracellular matrix consists of a network of proteins and carbohydrates.

  • Selective Permeability

    • There are peripheral proteins on the exterior of the membrane that bind elements of the extracellular matrix.
    • These carbohydrate complexes help the cell bind substances that the cell needs in the extracellular fluid.
    • Substances such as the fat-soluble vitamins A, D, E, and K readily pass through the plasma membranes in the digestive tract and other tissues.