The Digestive SystemThe Digestive SystemLabLab

Organs of the Digestive System Gastrointestinal tract (GIT) – continuous passageway which contains the food from the time it enters the body until it leaves; organs include:

mouth (oral cavity), pharynx (oropharynx & laryngopharynx), esophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine (cecum, colon, rectum), anal canal, anus

Accessory organs - participate in digestive processes; organs include:

teeth, tongue, salivary glands, liver, gall bladder, pancreas

Function of the Digestive System

To break down food into a “usable” (absorbable) form – occurs through mechanical processing & chemical digestion

To supply our cells with the nutrients they need for energy, growth & repair

carbohydrates – including

polysaccharides (“complex” carbohydrates )

starch

disaccharides (“simple” sugars)

maltose, sucrose, lactose

proteins

fats (lipids/triglycerides)

vitamins

minerals

water

Classes of Nutrients:

No digestive processes necessary, just absorption

Digestive processes

Mechanical processing – physical breakdown of food; e.g. mastication, emulsification, mixing waves, segmentation

Chemical digestion – chemical breakdown of food; disassembling of organic molecules into their component parts; requires enzymes

carbohydrates (polysaccharides) disaccharides monosaccharides

proteins amino acids lipids (triglycerides) fatty acids & glycerol (monoglycerides)

Mouth (oral cavity)

Parotid gland

Submandibular gland

Sublingual gland

saliva – made of H2O, salts & salivary amylase; moistens foods to create “bolus” to help with deglutition, & begins chemical digestion of starch

Digestion (mechanical & chemical) begins within the oral cavity –

mastication

production of saliva by salivary glands

Starch (polysaccharide) Maltose (disaccharide)amylase

StomachMechanical digestion – mixing waves to change bolus of food to “chyme”

Chemical digestion - secretions from cells of stomach to begin protein digestion: Peptic (chief) cells – pepsinogen

Parietal cells – hydrochloric acid (HCL)

Pepsinogen + HCL Pepsin

Proteins Pepsin

HCL

polypeptides

Small intestineChyme from stomach (with partially digested starch & proteins) + Bile from liver & gall bladder + Pancreatic juice from pancreas – released into duodenum of small intestine

Segmentation mixes chyme with other secretions

Fats + bile emulsified fats

bile

Stomach

HeadBody

Tail

PancreasPancreatic juice – mixture of enzymes & buffers (sodium bicarbonate) secreted by acinar cells into pancreatic duct & released into duodenum

lipase

Lipids (triglycerides) fatty acids + monoglycerol proteases (trypsin, chymotrypsin, carboxypeptidase)

Proteins & polypeptides small peptides (tripeptides & dipeptides)

nucleases – digest RNA & DNA

sodium bicarbonate – neutralizes acidic chyme because enzymes in small intestine need an alkaline pH

pancreatic amylaseStarch maltose

Small intestineCells in jejunum and ileum produce peptidases and disaccharidases for final digestion of proteins and sugars

small polypeptides, tripeptides, dipeptides

peptidases amino acids

maltosemaltase

glucose + glucose

sucrosesucrase

glucose + fructose

lactoselactase

glucose + galactose

Absorption

Absorption of monosaccharides (glucose, fructose, galactose), amino acids and fatty acids (as well as vitamins/minerals) occurs in small intestine (into blood or lymph (fatty acids)Absorption of water (and some vitamins) occurs in large intestine