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Digestion Summary:Food digested as passes along ________________________.-> consists of the mouth, pharynx, esophagus, stomach, small intestine, and largeintestine.___________________and _____________ muscle fibers in its wall contract and relax,squeezing food and breaking up large solid lumps. Digestive juices (secreted by________________________, _______________________________and ____________=_______________________) with enzymes mix with food to break down the molecules(proteins, nucleic acids, starch etc.) into smaller soluble forms.Indigestible macromolecules: e.g. _____________(part of dietary fiber). Humans lack________________(enzyme which digests cellulose). Cellulose moves food through thedigestive tract quickly and efficiently, though.Exocrine glands- secrete their products into ducts which lead directly to external environment- digestive juice released from cells by exocytosis => discharged from gland by traveling along ducts
Exocrine glands and their cells:Digestive juice secretion:- controlled by ___________ and _______________- before food reaches stomach, sight or smell of food stimulate brain to send nerve impulses to _____________________in stomach wall to produce _________________.- More gastric juice secreted when food enters stomach and comes into contact with__________________________ and ______________________ in the stomach liningand ________________________in the stomach wall. - Receptors send nerve impulses to brain -> sends impulses to ____________ gland cells - Receptors send nerve impulses to ___________ gland cells in stomach lining -> secrete hormone: ___________ -> carried to exocrine gland cells to stimulate_______________________________ => causes ph of food in stomach to fall to aboutpH 3.0
Membrane-bound digestive enzymes:- some enzymes, produced by the wall of the small intestine, don’t mix with the food but remain in the ________________________ of cells on the surface of the villi (epithelium cells)- the ___________________ of the enzymes are exposed to the food in the small intestine-> digest substrates and the products of digestion can be immediately absorbed.- After abrasion of tips of villi, the enzymes mix with food in small intestine and continue workSources of digestive enzymes:- pepsin & trypsin harmful to exocrine gland cells which secrete them.-> secreted as ______________________________ (a substance from which anothersubstance is formed) called pepsinogen and trypsinogen.Pepsinogen: first secreted by cells in ____________________ and then activated by_______________________(also secreted by cells in stomach wall), which converts itinto pepsinTrypsinogen: first secreted by _____________ and enters ________________________.Then activated by enzyme called __________________ (secreted by lining of smallintestine)