chapter 15 - the digestive system

functions of the digestive system

1. ingest food

2. break food down into small molecules that can cross plasma membrane

3. absorb nutrient molecules

4. eliminate nondigestible wastes

mouth (oral cavity)

lips and cheeks

• vestibule = space between teeth, lips, and cheeks

mouth: tongue

papillae, lingual frenulum

taste bud receptors =

sensory

mouth: palate (uvula)

hard = maxilla and palatine bones

soft = muscle and glandular tissue

type of teeth:

• incisors

• canines

• premolars

• molars

incisor teeth =

biting

canine teeth =

tearing

premolar teeth =

grinding

molar teeth =

crushing and grinding

caries =

destruction of tooth enamel by oral bacteria (cavities)

gingivitis =

inflammation of the gums

periodontitis =

inflammation of periodontal membrane

• loss of bone and loosening of teeth

functions of saliva

• moisten food before swallowing

• removed microbes by bathing mouth

• salivary amylase, lysozyme, antibodies

pharynx is the common passageway for _____ and _____

food and air

bolus =

soft mass of chewed food

wall of digestive tract:

1. mucosa

2. submucosa

3. muscularis

4. serosa

mucosa =

lines lumen (central cavity); secrete digestive enzymes and goblet cells that secrete mucus

submucosa =

protects from disease; peyer pacthes

muscularis =

2 layers - circular and longitudinal; smooth muscle

serosa =

secretes serous fluid to keep everything moist

peristalsis =

rhythmic contraction; pushes food along the length of the gut

role of esophageal sphincter:

allows bolus to pass into the stomach

regions of the stomach:

cardiac, fundic, body, and pyloric

digestive functions of the stomach:

acts on food both chemically and physically

gastric juice =

watery digestive fluid secreted by the gastric glands in the stomach

• containing hydrochloric acid and enzymes, such as pepsin

intrinsic factor =

Protein produced by the normal gastrointestinal mucosa that facilitates absorption of vitamin B₁₂

• RBC will fail to develop without vitamin

gastrin =

regulates acid secretion by the stomach and growth of the gastric mucosal layer

• also weakly stimulates muscular contraction of the stomach

• histamine from ECL cells prolong the effect of gastrin

what is absorbed in the stomach?

alcohol and water

chyme =

semifluid food mass leaving the stomach

functions of the small intestine:

all contents of food are digested into molecules that can be absorbed

regions of the small intestine:

• duodenum

• jejunum

• ileum

duodenum =

first portion of the small intestine (25 cm); ducts from the gallbladder and pancreas

jejunum =

middle portion; specifically absorbing sugars, amino acids, and fatty acids into the blood

ileum =

lower portion; peyer patches - absorb b12 and bile salts

what do circular folds, villi, and microvilli do for surface area of absorption?

provide fuzzy boarder (brush boarder)

regions of the large intestine:

• cecum and vermiform appendix

• colon - ascending, transverse, descending, sigmoid

• rectum

• anal canal

function of the large intestine

release hydrogen gas and sulfur-containing compounds (farts/gas)

parietal vs visceral peritoneum

• parietal = lines the wall

• visceral = covers organs

accessory organs of digestion:

• pancreas

• liver

• gallbladder

pancreas =

secretes digestive enzymes into duodenum and produces hormones (insulin)

pancreas: endocrine AND exocrine function

islets secrete insulin, glucagon, and somatostatin

pancreatic juice

• sodium bicarbonate -neutralizes acidic chyme from stomach

• pancreatic amylase - digests starch

• pancreatic lipase - digests fats

• protein digesting enzymes (trypsin, chymotrypsin, carbozypeptidase)

• nucleases

in what genetic disorder does the production of abnormally thick mucus block the pancreatic duct?

cystic fibrosis

liver =

• lobes - structural/functional units

• hepatic cells - separate groups of cells

• kupffer cells - remove pathogens and debris

functions of the liver:

• detoxifies body

• stores iron and fat-soluble vitamins A, D, E, and K

• stores glucose as glycogen after meals

• forms and secretes bile

• helps regulate blood cholesterol level

the gallbladder stores ____ produced by the _____

bile, liver

function of bile salts:

carry out emulsification; break up masses of fat into droplets

carbohydrate digesting enzymes:

• salivary amylase

• pancreatic amylase

• maltase

• sucrase

• lactase

protein digesting enzymes:

• pepsin

• trypsin

• chymotrypsin

• carboxypeptidase

• peptidases

lipid digesting enzymes:

• pancreatic lipase

nucleic acid digesting enzymes:

• nuclease

• phosphatase

• nucleosidase

Effects of aging: digestive system

• structure and function generally decline with age

• various illnesses are associated with the digestive system and are more likely to be seen among the elderly