1. Digestion Summary:
Food digested as passes along ________________________.
-> consists of the mouth, pharynx, esophagus, stomach, small intestine, and large
intestine.
___________________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 the
digestive 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
2. 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 lining
and ________________________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 about
pH 3.0
3. 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
work
Sources of digestive enzymes:
- pepsin & trypsin harmful to exocrine gland cells which secrete them.
-> secreted as ______________________________ (a substance from which another
substance 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 it
into pepsin
Trypsinogen: first secreted by _____________ and enters ________________________.
Then activated by enzyme called __________________ (secreted by lining of small
intestine)
