AP2 Ch24 Digestive System

ingestion

occurs when materials enter the digestive tract by the mouth

mechanical processing

breakdown of food by chemicals into small fragments suitable for absorption

• glucose can be absorbed intact

• proteins polysaccharides and triglycerides must be broken down prior to absorption

secretion

release of water, acids, enzymes, buffers and salts by digestive tract and by glandular organs

absorption

movement of substrates, electrolytes, vitamins and water across digestive epithelium and into digestive tract

excretion

removal of waste products from body

• types: defecation, protection

defecation

the ejection of materials from digestive tract

protection

the lining of digestive system protects body from corrosive acids, abrasion and bacteria

oral cavity

organ: mouth (teeth, tongue, etc.); mechanical processing, moistening, mixing with salivary secretions

salivary glands

organs: secrete fluid which contains enzymes which help to break down foods; located at back of throat and in mouth

pharynx

organ: its muscles propel materials down esophagus

esophagus

organ: tube that leads from throat to stomach; this transports nutrients/food to stomach

stomach

organ: chemical breakdown of food by acids and enzymes; mechanical processing occurs through muscle contractions

liver

organ: secretes bile which is used to breakdown lipids; stores nutrients and inactivates drugs

• vitamins stored: A, D, E, K, B12

• stores iron as ferritin

gall bladder

organ: storage and concentration of bile; cystic duct leads from this to unite with common hepatic duct to make common bile duct

pancreas

organ: exocrine cells secrete buffers and digestive enzymes; endocrine cells secrete hormones

small intestine

organ: enzymatic digestion and absorption of water, organic substrates, vitamins and ions

large intestine

organ: dehydration and compaction of indigestible materials in preparation for elimination

• includes cecum, colon, rectum

gut layers

mucosa, submucous, muscularis externa, serosa

peritoneal cavity

consists of parietal peritoneum (mesenteries), visceral peritoneum

peristalsis

contractions of the muscles (muscularis externa) of digestive tract behind material to be digested pushing material downward through the digestive system

bolus

small mass of digestive contents

segmentation

churning or mixing of food; these movements churn and fragment the bolus, mixing the contents with intestinal secretions

oral (buccal) cavity

the mouth opens to lead into this cavity; ingestion and food entry occurs at this location

• made up primarily of stratified squamous epithelia tissue

• formed by: lips, cheeks, palate, tongue

• functions: ingestion, mechanical digestion, chemical digestion

tongue

manipulates food mechanically (compression, abrasion, distortion) to prepare for swallowing; sensory analysis by touch, temp, taste

• secretes mucins and lingual lipase

• divided into anterior body and posterior root

• 2 groups of skeletal muscle both controlled by hypoglossal nerve (XII)

lingual frenulum

membrane on inferior side of tongue which connects tongue to floor of oral cavity

• 2 pairs of salivary glands on each side that are linked to oral cavity by submandibular and sublingual ducts

• glands secrete lingual lipase

intrinsic tongue muscles

smaller tongue muscles; used in speech

extrinsic tongue muscles

larger tongue muscles; used in gross movement of tongue

salivary glands

3 pairs of glands that secrete into oral cavity; includes parotid, sublingual, submandibular

parotid salivary glands

salivary glands: located in back of throat inferior to zygomatic arch; produces saliva with salivary amylase, which is drained into the oral cavity by parotid (Stenson’s) duct

sublingual salivary glands

salivary glands: covered by mucous membrane on floor of mouth; produces a watery secretion that acts as buffer and lubricant, which is drained into the oral cavity by the sublingual (Rivinus) duct

submandibular salivary glands

salivary glands: found in floor of mouth; produces glycoproteins and salivary amylase, which are drained into oral cavity by submandibular (Wharton’s) duct

salivary amylase

proteins that break down complex carbohydrates; secreted by parotid and submandibular salivary glands

V; VII; IX; X

Any object in the mouth can trigger the salivary reflex by stimulating one of which 4 cranial nerves?

• answer format: []; []; []; []

teeth

breaks down connective tissue in meats through chewing; bacteria sticks to surface and consumes tartar (food particles)

• types: incisors, cuspids, bicuspids, molars

incisors

teeth: blade shaped teeth in front of oral cavity used for cutting or clipping; has a single root

cuspids

teeth: have a pointed tip; used for tearing or slashing; have a single root; aka canines

bicuspids

teeth: have flat crowns; they mash, crush, and grind; have one or two roots; aka premolars

molars

teeth: large flattened crowns; good at crushing and grinding; have 2 or 3 roots

deciduous dentition

first of 2 sets of teeth formed in embryo; most kids have 20; aka primary/milk/baby dentition/teeth

permanent dentition

second of 2 sets of teeth; most adults have 32; push out deciduous dentition (eruption/emergence); aka secondary dentition/teeth

crown

tooth location: visible top portion of tooth

neck

tooth location: area between crown and root

root

tooth location: inferior invisible portion of tooth

enamel

tooth location: outer protective covering

cementum

tooth location: protective covering along side of tooth

root canal

tooth location: where nerves and blood vessels pass through to dentin

dentin

tooth location: mineral component; soft section of tooth

apical foramen

tooth location: hole where vessels and nerves first enter tooth

gingiva

tooth location: skin between teeth

pharynx

common passageway for solid, liquids, air; includes:

• includes pharyngeal constrictor muscle, palatopharyngeus and stylopharyngeus muscle, palatal muscle, nasopharynx, oropharynx, laryngopharynx

pharyngeal constrictor muscle

pharynx part: pushes bolus towards esophagus

palatopharyngeus and stylopharyngeus

pharynx part: 2 muscles that elevate the larynx

• answer format: [] and []

palatal muscle

pharynx part: elevates the soft palate

nasopharynx

pharynx part: superior portion posterior to nasal cavity; air passageway only; epithelium produces mucus; houses pharyngeal tonsils; extends from internal nares to soft palate

oropharynx

pharynx part: posterior to and continuous with oral cavity; air and food passageway; epithelium changes to deal with abrasive food; houses palatine and lingual tonsils; extends from soft palate to base of tongue

laryngopharynx

pharynx part: posterior to epiglottis and continuous with oral cavity; increases mucosal surface area exposed to air and enhances turbulence in nasal cavity; extends from base of tongue/hyoid bone to larynx/esophagus

esophagus

organ whose primary function is to carry food from mouth to stomach; ~1 foot long and ~0.75 inch in diameter; begins ~C6; innervated by both parasympathetic and sympathetic NS

• enters into abdominopelvic cavity through esophageal hiatus

• muscular wall layers: mucosa, submucosa, muscularis externa

mucosa

esophagus muscular wall layer: internal section of the wall which comes into contact with food

submucosa

esophagus muscular wall layer: connective tissue

muscularis externa

esophagus muscular wall layer: contains both skeletal (superior portion) and smooth (inferior portion) muscle

deglutition

swallowing; starts off as voluntary action but becomes involuntary; 3 phases: buccal, pharyngeal, esophageal

buccal phase

deglutition phase: begins with compression of bolus against hard palate, then tongue forces bolus towards pharynx; voluntary

pharyngeal phase

deglutition phase: starts when bolus contacts palatoglossal and palatopharyngeal arches which have “tactile receptors” that are activated by bolus; brain sends a command to swallow; peristalsis begins in this phase

esophageal phase

deglutition phase: begins as bolus enters esophagus; peristalsis takes place during this phase; as bolus gets close to stomach it triggers the opening of esophageal sphincter to allow entrance into stomach

greater curvature

lateral surface of stomach

lesser curvature

medial surface of stomach

stomach

bulk stores and mechanically breaks down ingested food; disrupts chemical bonds in food by acid and enzymes; produces intrinsic factor for B12 absorption

• 4 regions: cardia, fundus, body, pylorus

• gastric glands consist of parietal and chief cells

chyme

mixture ingested food, enzymes, acid in stomach

rugae

folds in the stomach that allow it to expand; stomach volume increases as you eat, decreases as chyme enters small intestine

cardia

stomach region: smallest part of stomach, most superior; contains many mucous glands that coat and protect esophagus from acid and enzymes in stomach; only has mucus cells

fundus

stomach region: portion of stomach that is superior to the stomach/esophagus connection

body

stomach region: area between fundus and curve of the J (pylorus); largest part of stomach; mixes food and secretions produced in stomach; gastric glands in body secrete most of the acids in stomach

pylorus

stomach region: the curve of the J; has 2 sections; has both gastrin and mucus cells; consists of pyloric antrum and pyloric canal

pyloric antrum

pylorus part: connects to body of stomach

pyloric canal

pylorus part: empties into duodenum; a sphincter (pyloric sphincter) regulates the release of chyme into duodenum; gastrin, a hormone which stimulates gastric glands is produced here

parietal cells

gastric gland cell: produce intrinsic factors and HCl (keeps stomach pH 1.5-2.0)

intrinsic factor

glycoproteins produced by parietal cells that cause B12 absorption across small intestine membrane

chief cells

gastric gland cell: produce pepsinogen, which is converted to pepsin by stomach acid

pepsin

breaks down proteins by cleaving amino acid bonds (dipeptide bonds); made from pepsinogen; requires low pH to be active

G cells

cells that produce gastrin, which causes secretions of both parietal and chief cells

mucous cells

cells that produce mucus to keep acid from destroying stomach lining

D cells

cells that produce somatostatin (GH-IH), which inhibits gastrin release; found in stomach, small intestine, pancreas

gastritis

inflammation of gastric mucosa due to excessive alcohol, drug, or aspirin use

peptic ulcer

occurs when acid erodes stomach lining in stomach (gastric ulcer) or intestine (duodenal ulcer)

CNS; enteric nervous system; hormones

The production of acid and enzymes can be controlled by _____ (NS, abbrev.), _____ _____ _____ (NS) in stomach, and _____ in digestive tract.

• answer format: []; []; []

cephalic phase

digestion stage: begins when you see, smell, taste, or think of food; CNS (by way of parasympathetic) directs this stage, causing activation of stomach’s mucous, chief, parietal, G cells

gastric phase

digestion stage: begins when food arrives in stomach due to distention of stomach, ↑ pH of gastric contents, presence of proteins and peptides

• continues for 3-4 hours while stomach contents are processed by acid and enzymes

intestinal phase

digestion stage: begins when chyme enters the small intestine

• each time the pylorus contracts, a small amount of chyme squirts through pyloric sphincter into intestine

• the arrival of chyme in intestine also triggers other neural and hormonal activities

neural responses

responses: involves stretch receptors and chemoreceptors in stomach and SI

• stomach: contractions occur, causing mixing of contents

• SI: send neural stimuli back to stomach to temporarily decrease gastric production and gastric contractions to give SI time to deal with chyme

stretch receptors

neural response receptor:

• stomach: stimulated in stomach wall as food enters stomach

• SI: in walls of duodenum; detect distention due to chyme arrival

chemoreceptors

neural response receptor:

• stomach: in mucosa; stimulated as pH of stomach is raised by food

• SI: detect a decrease in pH (due to acid in stomach getting into SI)

hormonal responses

responses: involves enzymes in stomach and SI

• stomach: pepsin (protease) digests proteins, salivary amylase digests carbs, lingual lipase digests lipids

• SI: monitors peptide/protein + lipid/carb presence and pH in chyme in duodenum

  • if peptides/proteins are detected: G cells produce gastrin to travel back to the stomach, causing parietal and chief cells to increase secretions to stimulate gastric motility and increase dipeptide bond destruction

  • if lipids/carbs are detected: secrete cholecystokinin (CCK) and gastric inhibitory peptide (GIP), which inhibit gastric acid secretion and reduce force of gastric contractions

    • CCK also causes pancreas enzyme release to degrade lipids, proteins, carbs

    • GIP also causes pancreas’ insulin production

  • pH < 4.5: secrete secretin to inhibit parietal and chief cells to stimulate buffers that protect duodenum from acid

local responses

responses: distortion (stretching) of stomach wall causes the local release of histamine by mast cells, which causes parietal cells to also secrete acid

small intestine

organ where 90% of nutrient absorption takes place; 3 subdivisions: duodenum, jejunum, ileum

duodenum

SI subdivision: closest to stomach; considered the “mixing bowl”; smallest of 3 sections

jejunum

SI subdivision: where bulk of chemical digestion and nutrient secretion occurs

ileum

SI subdivision: largest of the three sections and ends in ileocecal valve, which is a sphincter that controls flow of materials to large intestine

intestinal villi

finger-like extensions in SI on simple columnar cells; allows increased surface area for nutrient absorption from chyme to capillaries to liver, which then adjusts nutrient concentration in blood

lacteal

lymphatic capillary that transports fatty acids/lipids in packages called chylomicrons from intestinal villi to venous return

Peyer’s patches

lymphoid tissue at end of ileum that prevent LI bacteria from entering SI