Digestion
Vocabulary:
Malnourished: to be missing one or more essential nutrients
Undernourishment: caloric deficiency
Vitamins: organic molecules required in the diet
Minerals: simple inorganic molecules
Substrate-feeders: live on or in their food source, eating their way through the
food
Deposit-feeder: eat their way through dirt or partially decayed organic material
Fluid-feeders: suck nutrient-rich fluids from a living host
Bulk-feeders: eat relatively large pieces of food
Ingestion: the act of eating, first stage of food processing
Digestion: the process of breaking food down into molecules small enough for the
body to absorb, second stage of food processing
Enzymatic hydrolysis: the splitting process by adding a molecule of water and
breaking covalent bonds
Absorption: the animal’s cells take up (absorb) small molecules such as amino acids
and simple sugars from the digestive compartment, third stage
Elimination: the passing of undigested material out of the digestive compartment
Intracellular digestion: the joining of food vacuoles and lysosomes to allow chemical
digestion to occur within the cytoplasm of a cell
Extracellular digestion: the breakdown of food outside cells
Gastrovascular cavities: digestive sacs with single openings that function in both
digestion and distribution of nutrients throughout the body (simple body)
Complete digestive tracts/Alimentary canals: digestive tube extending between
two openings, a mouth and an anus (most body types)
Gastric juice: digestive fluid
Pepsin: an enzyme in gastric juice the begins hydrolysis of proteins
Acid chyme: nutrient-rich broth in the stomach
Pyloric sphincter: helps regulate the passage of chyme into the intestine
Bile: produced by the liver, stored in the gallbladder, contain bile salts that act as
Detergents that aid in digestion/absorption of fats
Emulsification: a process that keeps tiny fat droplets from coalescing
Peristalsis: rhythmic waves of contraction by smooth muscles in the wall of the
canals, pushes food along the tract
Sphincters: ring like valves that close off the tube like draw strings, regulating
the passage of material between chambers of the canal
Salivary glands: exocrine glands that lubricate food, adhere together chewed
Pieces, and begin process of chemical digestion
Salivary amylase: an enzyme in saliva that hydrolyzes starch and glycogen
Pharynx: a junction that opens to both the esophagus and the wind pipe (trachea)
Epiglottis: a cartilage flap at the top of the trachea blocking the glottis
Esophagus: conducts food from the pharynx to the stomach
Stomach: secretes gastric juice and mixes this secretion with the food by the
churning action of smooth muscles
Small intestine: enzymatic hydrolysis and nutrient absorption
Large intestine/colon: between the small intestine and the anus, water absorption
and formation of poop
Cecum: a blind outpocket of a hollow organ such as an intestine
Appendix: small, finger-like extension of the cecum, contains a mass of white
blood cells that contribute to immunity
Rectum: where poop is stored until it can be eliminated
Nutritional Requirements:
Satisfy 3 needs:
 Fuel(Chemical energy)
 Organic raw materials used in biosynthesis(carbon skeletons make many of
their own molecules)
 Nutrients that the animal cannot make for itself
Glucose Regulation/ Example of Homeostasis:
1. The level of glucose rises above a set point
2. The pancreas secretes insulin
3. Insulin enhances the transport of glucose into body cells and stimulates the
liver and muscle cells to store glycogen. Blood glucose levels drop
4. Sometimes it falls below the set point
5. In this situation the pancreas secretes the hormone glucagon(opposes the
effect of insulin)
6. Glucagon promotes the breakdown of glycogen and the release of glucose
into the blood, increasing blood glucose level
 Excess calories used for biosynthesis
 Liver and muscle cells store energy in the form of glycogen
 If caloric intake exceeds caloric expenditure, excess is stored as fat
Essential Amino Acids
 Animals require 20 amino acids to make proteins

8 amino acids are not produced by oneself
Overview of Food Processing:

Chewing breaks apart the food while the enzyme amylase, in saliva, breaks it
apart further
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In the throat/pharynx, the swallowed food goes through the esophagus
because the epiglottis is blocking off the trachea

The esophagus sends the food to the stomach
Stomach

the stomach makes gastric juice secreted by the epithelium lining, and
makes pepsin the enzyme that begins the hydrolysis of proteins

pepsin is first secreted in its inactive form pepsinogen and parietal cells
secrete hydrochloric acid that converts it into its active from pepsin

epithelial cells secrete mucus to prevent the stomach from digesting itself

acid chyme is slowly released from the stomach, through the pyloric
sphincter to the small intestine
Small Intestine:
 Where most of the absorption of nutrients into the blood and enymatic
hydrolysis occurs
 In the first 25cm of the small intestine, the duodenum, the chyme from the
stomach mixes with digestive juices from the pancreas, liver, gallbladder,
and gland cells
 The jejunum and ileum function mainly in the absorption of nutrients and
water
Pancreas:
 Produces several hydrolytic enzymes and an alkaline solution rich in
bicarbonate
 The bicarbonate acts as an buffer that offsets the acidity of the chyme
Liver:
 Produces bile that contains no digestive enzymes, but contains bile salts,
that aid in the digestion and absorption of fats
Gallbladder:
 stores bile until needed
Absorption of Nutrients
 Large circular folds in the lining of the small intestine have finger like
projections called villi, and each epithelial cell of a villus as microvilli that
are exposed to the intestinal lumen
 Nutrients are pumped against the concentration gradient by epithelial
membranes. This active transport allows the intestine to absorb a lot of
nutrients
Large Intestine/Colon:
 Connected to the small intestine at a T shape junction with the cecum
 Recovers water that has entered the alimentary canal
 Helps in vitamin synthesis
 Wastes of the digestive tract (feces) becomes more solid as it passes
through the colon by peristalsis
 Living in the colon is a rich flora of mostly harmless bacteria (E. Coli)
 At the end of the colon is the rectum where poop is stored until it can be
eliminated
Hormones Help Regulate Digestion:

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When we see, smell, or taste food, impulses from the brain to the stomach
initiates the secretion of gastric juice
Certain substances in the food stimulate the stomach wall to release the
hormone gastrin into the circulatory system
Other hormones, collectively called enterogastrones, are secreted by the
wall of the duodenum
The acidic pH of the chyme that eneters the duodenum stimulates the cells
in the wall to release the hormone secretin
Cholecystokinin is secreted in response to the presence of amino or fatty
acids