Food Pathway Throughout the Gastrointestinal Tract (GIT)

Flashcards covering the mechanical and chemical processes, structures, enzymes, and transit times associated with the human gastrointestinal tract.

Gastrointestinal system

A series of organs that functions to prepare ingested nutrients for digestion and absorption.

Ingestion

The process of taking food into the mouth through the digestive tract.

Digestion

The process whereby food is broken down into smaller parts, chemically changed, and moved through the GI system from a complex to a simpler form and from an insoluble to a soluble state.

Mechanical Digestion

The part of digestion requiring physical movements such as chewing, swallowing, and peristalsis that divide food into smaller pieces.

Peristalsis

The rhythmic contractions of the muscular walls of the tract causing wavelike motions that move food down the GIT.

Bolus

A masticated food mass or lump of food ready to be swallowed.

Chemical Digestion

The chemical altering effects of digestive secretions, gastric juices, and enzymes on food substance composition caused by hydrolysis.

Absorption

The process by which substances pass through the intestinal mucosa into the blood or lymph.

Metabolism

A set of processes through which absorbed nutrients are used by the body for energy and to form and maintain body structures and functions.

Defecation

Excretion of the residues of the digestive process (feces) from the rectum through the anus.

Mastication

The act of chewing whereby the teeth grind and crush food into smaller particles mixed with salivary secretions.

Ptyalin

Also known as salivary amylase, an enzyme that begins the chemical digestion of starch (complex CHO) in the mouth.

Salivary glands

Three pairs of glands (parotid, submaxillary, and sublingual) that produce about $1.5\,L$ of saliva daily.

Cardiac sphincter

The opening that allows the passage of the bolus into the stomach, located above the entrance of the stomach (also related to the lower esophageal sphincter).

Fundus

The upper portion of the stomach that acts as a temporary storage place for food.

Chyme

A semi-liquid mass of food that contains approximately $50\%$ water, formed in the stomach.

Gastrin

A hormone secreted by the stomach that increases the release of gastric juices.

Gastric juices

Digestive secretions of the stomach containing hydrochloric acid, pepsin, and mucin, with an average daily secretion of $2000-2500\,mL$.

HCl (Hydrochloric acid)

Secreted by parietal cells in the stomach walls to provide acidity and activate the enzyme pepsin.

Pepsin

An enzyme in the stomach that aids in the digestion of protein into polypeptides.

Rennin

An additional gastric enzyme in children that acts on milk protein and casein.

Intrinsic factor

A glycoprotein secreted by the stomach essential for Vit. $B12$ absorption.

Bile

A substance produced by the liver and stored in the gall bladder that facilitates the digestion and emulsification of fats.

Cholecystokinin (CCK)

Also called pancreozymin, a hormone secreted by the small intestine that activates the gall bladder to release bile.

Pancreatic proteases

Protein-splitting enzymes including trypsin, chymotrypsin, and carboxypeptidases that break down proteins into amino acids.

Secretin

A hormone that causes the pancreas to release sodium bicarbonate to neutralize the acidity of chyme in the small intestine.

Small intestine

The primary site for digestion of foods and nutrients, specifically the duodenum and upper jejunum.

Large intestine (colon)

Consisting of the cecum, colon, and rectum, it is the site of absorption for remaining water and salts and the collection of food residue.

Stomach transit time

The duration food remains in the stomach, typically between $2-6$ hours.

Total GI transit time

The total time from ingestion to elimination, which ranges from $16-27$ hours.