Chapter 23 Digestive System Flashcards
digestion
- to obtain energy for ATP production through food sources
- raw material needed for building and repair
- needs to be converted to cellular level
- mechanical and chemical digestion
two groups of organs
- alimentary canal
- accessory digestive organs
alimentary canal (gastrointestinal or GI tract)
- digests and absorbs food
- mouth, pharynx, esophagus, stomach, small intestine, and large intestine
accessory digestive organs
- teeth, tongue, gallbladder
- digestive glands:
- salivary glands
- liver
- pancreas
digestive processes
- ingestion- eating
- propulsion- swallowing, peristalsis
- peristalsis- mechanical digestion
- chemical digestion- enzymes
- absorption
- defecation
teeth: accessory digestive organs
- teeth do much of mechanical work of digestion
- human teeth include sharp incisors and cuspids which tear and grasp food
- molar crush and grind
tongue: accessory digestive organs
- -positioning and mixing of food
- formation of the bolus
- initiation of swallowing, speech, and taste
- surface bears papillae for friction, licking, taste buds, secretes lingual lipase
salivary glands
- intrinsic glands- are scattered in the oral mucosa -> keeps mouth moist
- extrinsic- produce majority of saliva
- functions:
- cleanses the mouth
- moistens and dissolves food chemicals
- contains enzymes (salivary amylase) that begin the chemical breakdown of starch
- contains chemicals (IgA antibodies and defenses) that protects against microorganisms
- the brain stem sends impulses along parasympathetic fibers to activation secretions
- sympathetic NS inhibits saliva production
- ex. sublingual, submaxillary, parotid glands
digestive processes: mouth
- ingestion
- mechanical digestion- mastication is partly voluntary, partly reflexive
- chemical digestion- salivary amylase and lingual lipase
- absorption- only certain medications (blood vessels under the tongue) -> no nutrients
- propulsion- deglutition (swallowing)
pharynx
- oropharynx and laryngopharynx (nasopharynx no digestive role)
- allow passage of food, fluids, and air
- skeletal muscle layers: inner longitudinal, outer pharyngeal constrictors
histology of the alimentary canal
- four basic layers (tunics) - from esophagus to anal canal
- from inner to outer
- mucosa- secretes mucous, enzymes and hormones, absorption and protection
- submucosa- houses vessels, nerves and lymph vessels, made up of CT
- muscularis externa- 2 layers of smooth MM (circular/longitudinal), responsible for segmentation and peristalsis
- serosa- outermost layer, made up of CT
- exception: in esophagus the adventia replaces the serosa layer
mucosa lauer
- epithelium
- lamina propria
- muscularis mucosae
muscularis externa
- longitudinal muscle
- circular muscle
serosa
- epithelium
- connective tissue
esophagus
- flat muscular tube from laryngopharynx to stomach
- bolus of food (aided by mucous) travels through esophagus by smooth MM contractions- perstalsis
- joins stomach at the cardiac orifice
deglutition (swallowing): buccal and pharyngeal-esophagus phase
- involves the tongue, soft palate, pharynx, esophagus, and 22 muscles groups
- buccal phase- voluntary contraction of the tongue, forces bolus into oropharynx
- pharyngeal-esophageal phase:
- involuntary
- control center in the medulla and lower pons
- all routes are blocked, soft palate blocks nasopharynx, epiglottis covers trachea
two enzymes in the mouth
- lingual lipase
- amylase
peristalsis
- peristalsis- adjacent segments of alimentary
- tract organs alternately contract and relax
- which moves food along the tract distally
- video-fluoroscopy- examines how well a person carries out peristalsis
stomach: gross anatomy
- cardial region (cardia)- surrounds the cardiac orifice
- fundus- dome-shaped region beneath the diaphragm
- body- midportion
- pyloric region- pylorus is continuous with the duodenum through the pyloric valve (sphincter)
- greater curvature- convex lateral surface
- lesser curvature- concave medial surface
muscularis externa: stomach layer
-longitudinal layer
-circular layer
-oblique layer**
3!!!
pyloric sphincter
- between duodenum and stomach
- bottom of stomach
stomach: microscopic anatomy
- mucosa (lining of the stomach)
- produces mucus which traps bicarbonate-rich fluid beneath it
- gastric pits lead into gastric glands (produce stomach secretions)
- enzymes in the pits to aid in digestion
gastric glands: cell types
- cell types:
- mucous neck cells- secrete thin acidic mucus
- parietal cells- secrete HCl and intrinsic factor
- chief cells- pepsinogen
- enteroendocrine cells (g cells)- gastrin
- 3 liters of gastric juice daily
gastric gland secretions
- glands in the fundus and body produce most of the gastric juice
- parietal cell secretions
- HCl- pH 1.5-3.5- denatures protein in food, activates pepsin, and kills many bacteria
- intrinsic factor- protein required for absorption of vitamin B12 in small intestine
chief cell secretions: gastric gland secretion
- produce pepsinogen
- activated to pepsin by HCl and by pepsin itself (positive feedback mechanism)
- secrete lipases (fat digestion
enteroendocrine cells: gastric gland secretions
- lower portion of gastric pit
- paracrine (act locally)- serotonin and histamine
- hormones- somatostatin and gastrin (g cells) (regulates secretions and mobility)
- gastric secretion is controlled by both neural and normal mechanisms*
mucosal barrier
- layer of bicarbonate rich mucus
- tight junctions between epithelial cells
- damaged epithelial cells are quickly replaced by division of stem cells
- peptic or gastric ulcers: erosion of the stomach wall- most are caused by H pylori bacteria (imbalance)
- stomach enzymes are strong enough to digest the stomach -> ulcers
why does your mouth suddenly go dry when you are about to deliver a presentation to a large crowd
- parasympathetic activity stimulates salivation
- parasympathetic activity inhibits salivation
- sympathetic activity stimulates salivation
- sympathetic activity inhibits salivation**
all of the following are part of the alimentary canal EXCEPT
- pharynx
- esophagus
- small intestine
- liver **
- mouth
___ involves over 22 muscles groups and includes the buccal phase and the pharyngeal esophageal phase
- mastication
- bolus formation
- deglutition**
- peristalsis
digestive processes in the stomach
- physical digestion (3 layers of muscle)
- denaturation of proteins (HCl)
- enzymatic digestion of proteins by pepsin
- secretes intrinsic factor required for absorption of vitamin B12
- lack of intrinsic factor -> pernicious anemia
- delivers chyme (product of its activity) to the small intestine
- bolus -> chyme
neural reflex pathways
- control of digestive activity are both intrinsic and extrinsic
- cephalic phase- initiated by stimuli arising inside or outside the GI tract and involved CNS centers
- gastric phase- mediated inside GI tract by local stimuli (local distention, pH, presence of substrates)
- 3-4 hours after food enters stomach
- intestinal phase- controls rate of emptying into intestines
nerve response
- cephalic phase
- external stimuli
- CNS and extrinsic autonomic nerves activate
- local (intrinsic) nerve plexus
- effectors- smooth muscle or glands
- response- change in contractile or secretory activity
- vagus nerve stimulation
- gastric phase- stomach distension -> stretch receptors, g-cells -> gastrin
- intestinal phase- negative feedback with too much coming in from the stomach
response of the stomach filling
- stretches to accommodate incoming food
- reflex-mediated receptive relaxation- coordinated by the swallowing center of the brain stem
- gastric accommodation- plasticity (stress-relaxation response) of smooth muscle, can stretch without contracting
intestinal phase- stimulatory and inhibitory
- stimulatory- brief filling of initial part of small intestine of partially digested food
- inhibitory- enterogastric reflex- a trio of reflexes that puts brakes on gastric activity to protect small intestine from excessive acidity
- dumping syndrome- seen in stomach volume reduction surgeries (nausea/vomiting)
gastric contractile acitivty
- -peristaltic waves move towards the pylorus
- basic electrical rhythm (BER) initiated by pacemaker cells (cells of cajal)
- distension (stretch receptors) and gastrin increase force of contraction (peristalsis)
- most vigorous near the pylorus
- chyme is either:
- delivered in about 3 ml spurts to the duodenum (small amount but continuous)
- forced backward into the stomach