Lecture 8: The Digestive System Flashcards
what does the digestive system do
-acquires nutrients from the environment
-anabolism: essential compounds
-catabolism: yield energy for cells
what is anabolism
a biochemical process in metabolism where the simple molecules combine to generate complex molecules
what is catabolism
breaking down body tissues and energy stores to get more fuel for body functions
what are the categories of components of the digestive system (DS)
- Gastrointestinal (GI) tract: alimentary canal (AC)
-continuous muscular tube that runs from the mouth to anus
-digests food: breaks down into smaller fragments
-absorbs fragments through lining into blood - Accessory Organs: teeth, tongue, gall bladder and various glandular organs (salivary glands, liver, pancreas)
what are the 6 primary functions of the digestive system
- ingestion
- secretion
- motility
- digestion
- absorption
- defecation
what is ingestion
eating: occurs when food enters oral canal
what is secretion
-release of water, acids, enzymes, buffers, and salts
-by epithelium of GI tract, glandular organs, and gallbladder
what is motility
-food mixed; peristaltic movement of food along the GI tract
-food is propelled to the anus
what is digestion and the two types of breakdown mechanisms
-digestion: breakdown of ingested food into smaller pieces that are useable by body tissue
-mechanical breakdown: mastication (chewing) and shearing of food, churning food, bolus formation
-chemical breakdown: catabolic processes mediated by digestive enzymes, macromolecules are hydrolyzed into small fragments for absorption by digestive epithelium
what is absorption
-movement of digested products across digestive epithelium into interstitial fluid and lymph
-some absorbed with digestions- organic molecules, electrolytes, vitamins, minerals, and water
what is defecation
elimination of wastes (indigestible substances), microbes, cells sloughed from GIT wall, from body
how many layers are there in the GI tract
-four layers from inside-out: mucosa, submucosa, muscular layer (muscularis externa), and serosa/adventitia
-lining of AC varies by region: empty stomach= longitudinal folds, small intestine= permanent transverse fold (circular folds)
what are the different parts (3 sublayers) of the mucosa layer
inner lining of DT, made up of three sub layers:
1. digestive epithelium (moistened by glandular secretions)
2. lamina propria of alveolar tissue
3. muscularis mucosae
describe the digestive epithelium (in mucosa layer)
-epithelium is simple or stratified: depends on location, function, and stresses
a) oral cavity, pharynx, esophagus, anal canal: stratified squamous epithelium
b)stomach, small intestine, most of large intestine: simple columnar epithelium
-enteroendocrine cells which are disperesed among the columnar cells: secrete hormones that coordinate activities of GIT
describe the lamina propria (in the mucosa layer)
a layer of areolar tissue containing:
-blood vessels, lymphatic vessels, sensory nerve endings
-binds epithelium to overlying muscularis mucosae
-has mucosa-associated lymphatic tissues (MALT) for protection
describe the muscularis mucosae (in the mucosa layer)
-deep to lamin propria
-a narrow sheet of smooth muscle and elastic fibers
-give rise to folds-increase surface area for digestion and absorption
what is the submucosa layer of the GIT
-connects mucosa to muscular layer
-numerous blood and lymphatic vessels
-contain exocrine glands which secrete enzymes
-contains the submucosal neural plexus which innervates mucosa and submucosa
what is the muscular layer (muscularis) of the GIT
-mainly smooth, and some skeletal muscle cells: inner circular and outer longitudinal layers
-involved in mechanical disgestion and peristalsis
-between two muscle layers is myentric plexus
-movements coordinated by enteric nervous system (ENS)
what is the serosa- visceral peritoneum layer of the GIT
serous membrane of areolar CT covering the muscular layer
what does the enteric nervous system (ENS) do in the digestive system
enteric neurons make up bulk of the two interconnecting intrinsic nerve plexuses
-submucosal plexus: glands and smooth muscle in mucosa
-myenteric plexus: between circular and longitudinal smooth muscle layers of the muscularis- GI tract motility
what does the autonomic nervous system (ANS) do in the digestive system
-parasympathetic: vagus and sacral nerves
-sympathetic: thoracic and upper lumber segments
what is the protective function of the lining of the GI tract
-safeguards surrounding tissues against: corrosive effects of digestive acids and enzymes, mechanical stress such as abrasion, and bacteria either ingested with food or that reside in the tract
what is the peritoneum
-largest serous membrane in the body
-parietal and visceral peritoneum form the peritoneal cavity
-ascites: acculumation of fluid in the peritoneal cavity
-retroperitoneal organs: kidneys, pancreas, duodenum, ascending and descending colon
-peritonitis:
what are the 5 peritoneal folds
greater omentum, falciform ligament, lesser omentum, mesentery, and mesocolon
what is the greater omentum (peritoneal fold)
-enlargement of dorsal mesectery
-double-layered membrane (folds back on itself)
-site of adipose tissues-> beer belly
what is the falciform ligament (peritoneal fold)
stabilizes position of liver relative to diaphragm and anterior abdominal wall
what is the lesser omentum (peritoneal fold)
-conntects stomach and duodenum to the liver, stabilizing them in position
-route for blood vessels and other structures entering or leaving the liver
what is the mesentery (peritoneal fold)
-double layers of peritoneal membrane, laden with fat
-hold jejunum and ilium to posterior abdominal wall
-between the layers are blood and lymphatic vessels
what is the mesocolon (peritoneal fold)
-holds transverse and sigmoid colon to posterior abdominal wall
-route for blood and lymphatic vessels
what are the functins of the oral cavity
-sensory analysis: before swallowing
-mechanical digestion: teeth, tongue, and palatal surfaces
-lubrication: mucus and saliva
-limited chemical digestion: carbohydrates and lipids
what is the oral mucosa
-lining of oral cavity: stratified squamous epithelium
-cheeks, lips, and inferior surface of tongue: relatively thin and non-keratinized
content of the oral cavity
superior lip, superior labial frenulum, gingivae, fauces, palatoglossal arch, palatopharyngeal arch, palatine tonsil, tongue, lingual frenulu, inferior labial frenulum, oral vestibule, incisors, canines, premolars, molars, cheek, uvula, soft palate, hard palate
what is the superior labial freulum
attaches superior lip to gum (the little flap of skin at front of mouth)
what are gingivae
gums which cover tooth sockets and help to anchor teeth
what is the fauces
the opening between the oral cavity and the oropharynx
where is the palatoglossal arch
between the soft palate and base of the tongue
where is the palatopharyngeal arch
from soft palate to pharyngeal wall
what is the tongue
forms the flood of the mought, manipulates food for chewing and swallowing, shapes food, and senses taste
what is the lingual frenulum
limits the movment of the tongue posteriorly (the line of skin under your tongue (where babies can be “tongue tied”)
what is the inferior labial frenulum
attaches inferior lip to gum
what is the oral vestibule
is the space between the cheeks, lips, gums, and teeth
what do the incisors do (teeth)
cut food
what do the canines do (teeth)
tear food
what do the premolars do (teeth)
crush and grind food
what do the molars do (teeth)
grind food
what is the cheek
forms lateral wall of oral cavity
what is the uvula
prevents swallowed food from entering the nasal cavity
what is the soft palate
(muscular) forms the rest of the mouths roof
what is the hard palate
(bony) forms most of the roof of the mouth
what are the functions and contents of the tongue
forms floor of oral cavity
~Functions: chewing,secretion of lingual lipase, analysis by touch/ temerature/ and taste receptors
~content
-anterior body
-posterior root
-frenulum of tongue (along inferior midline)
-extrinsic tongue muscles (perform all gross movements)
-intrinsic tongue muscles (smaller; perform precise movements speech, swallowing)
what are the three sections of a tooth
crown, neck, and body
what are the components of teeth
enamel, dentin, pulp cavity, cemetum, root canal, periodontal ligament, apical foramen, nerves, and blood supply
what is enamel (forms occusal/biting surface?????)
made of calcium salts, protects the tooth from wear and tear
what is dentin
calcified connective tissue
makes up the majority of the tooth
what is the pulp cavity
contains pulp (connective tissue containing nerve and blood vessels)
what is cementum
a bone-like sibstance that attaches the root to the periodontal ligament
what is a root canal
is an extension of the pulp cavity that contains nerves and blood vessels
what is the periodontal ligament
helps anchor the tooth to the underlying bone
what is the apical foramen
is an opening at the base of a root canal through which blood vessels, lymphatic vessels, and nerves enter a tooth
what are the 4 types of teeth
incisor, canine, premolar, and molar
what are the incisor teeth
-middlemost, blade or chisel-shaped; single-roots
-clipping or cutting
what are the canine teeth (cuspids)
-conical with single pointed cusp; single rooted
-tearing or slashing
what are the premolar teeth (bicuspids)
-two prominent rounded cusps
-crushing, mashing, and grinding
-one or two roots
what are the molar teeth
-very large, flattened crowns
-4-5 prominent, rounded cusps
-crushing and grinding
-2-3 roots
slide 21
what is the composition of saliva
three pairs that secrete saliva
-mostly water (97-99.5%) so hypo-osmotic
-slightly acidic (pH 6.75 to 7.00)
-electrolytes: Na+, K+, Cl-, PO4-2, HCO3-
-salivary amylase and lingual lipase
-proteins: mucin, lysozyme, and IgA
-metabolic wastes: urea and uric acid
-lysozyme, IgA, defensins, and nitric oxide from nitrates in food protect against microorganisms
how many primary teeth are there (deciduous, milk or baby teeth)
20
(2I, 1C, 2M) x2 (this is upper jaw)
(2I, 1C, 2M) x2 (this is lower jaw)
how many permanent teeth are there
32 teeth
(2I, 1C, 2M, 3M) x2
(2I, 1C, 2M, 3M) x2
what are the cells of the salivary glands
slaivary glands are composed of two types of secretory cells
-serous cells: produce watery secretion, enzymes, ions, but of mucin
-mucous cells: produce mucus
-parotid and aubmandibular glands contain mostly serous cells, but sublingual gland consists mostly of mucous cells
what is the pharynx
throat
-passageway for food
-skeletal muscles
-food moves from mouth to oropharynx
what are the regions of the pharynx
pasopharynx, oropharynx, and laryngopharynx
what is the esophpagus
-a flot hollow muscular tube
-from laryngopharynx to stomach
-posterior to cricoid cartilage, trachea, and heart
-collapsed when not involved in food propulsion
what is deglutition
swallowing
how many muscles work in deglutition
it involves coordination of 22 muscle groups
what are the two phases of deglutition
-buccal phase: viluntary contraction of tongue
-pharyngeal-esophageal phase: involuntary phase that primarily involves vagus nerve, controlled by swallowing center in medulla and lower pons
what are the 5 steps in deglutition
- buccal phase: the upper esophageal sphincter is contracted (closed), the tongue presses against the hard palate forcing the food bolus into the oropharynx
2.pharyngeal-esophageal phase begins: the tongue blocks the mouth, the soft palate and its uvula rise clsoing off the nasopharynx, larynx rises so that the epiglottis blocks the trachea, upper esophageal sphincter relaxes; food enters the esophagus - pharyngeal-esophageal phase continues: the constrictor muscles of the pharynx contract forcing food into the esophagus inferiorly, upper esophageal sphincter contracts after food enters
- peristalsis moves food thorugh the esophagus to the stomach
- the gastroesophageal sphincter surrounding the cardial orfice opens, after food enters the stomach the sphincter closes preventing regurgitation
what is the stomach
-extnads between T7 and L3
-mechanical digestion: muscular contractions (breakdown bolus)
-chemical digestion: acids and enzymes (breakdown bolus)
what is chyme
bolus mixed with acidic secretions of the stomach
anatomically the stomach…
-short lesser curvature: medial surface
-long greater curvature: lateral surface
rounded anterior and posterior surfaces
what are the regions of the stomach
-cardia: superomedial part; mucous glands
-fundus: contacts with diaphragm
-body: largest region; food mixes with secretions
-pyloric part: between body and duodenum
what is rugae (stomach)
-folds in mucosa of empty stomach
-flatten out as stomach fills
-allow for expansion of gastric lumen; up to 50x its empty size
histology of the stomach
-simple columnar epithelium
-epithelium: secretory sheet
-gastric pits: depressions opening into gastric surface
-mucous cells: meck (base) of each gastric pit; actively divide replacing superficial cells
what are gastric pits
-gastric pits: depressions opening into gastric surface
-mucous cells: meck (base) of each gastric pit; actively divide replacing superficial cells
what are gastric glands
fundus and body of stomach
-extend deep into underlying lamina propria
-gastric pits communicate with numerous gastric glands
-parietal cells nad cheif cells
what are parietal cells (histology of stomach)
proximal portions of gastric glands
-secrete intrinsic factor: glycoprotein that absorbs vitamin B12
-secrete HCl (hP 1.3-3.5)
which activate pepsinogen, denatures proteins, destroys bacteria
what are chief cells (histology of stomach)
they are at the base of gastric glands
-secrete pepsinogen: converted to pepsin by HCl in gastric lumen and by pepsin itself
-secrete gastric lipase
what do chief cells in infants secrete
-rennin (chymosin): moagulates milk proteins (casein)
-gastric lipase: digest milk fats
where are pyloric glands
pyloric part of stomach
what are enteroendocrine cells (stomach)
produce several hormones
what are G cells (stomach)
produce gastrin
-stimulates secretion by parietal and chief cells
-stimulates contractions of gastric wall
what are D cells (stomach)
release somatostatin
-inhibits release of gastrin
describe chemical digestion in the stomach
-salivar amylase: carbohydrates
-lingual lipase: lipids
-as stomach contents become more fluid: pH approaches 2.0, digestive activities of pepsin increases
what are the main functions of the stomach
- mixez saliva, food, and gastric juice to form chyme
- serves as a resevoir for food before release into the small intestine
- secretes gastric juice, which contains HCl, pepsin, intrsinsic factor, and gastric lipase
- secretes gastrin into the blood
what is the digestive activity of the muscularis
mixing waves (gentle peristaltic movements)
-churns and physically breaks down food nad mixes it with gastric juice, forming chyme, forces chyme through pyloric sphincter
what is the digestive activity of the pyloric sphincter
opens to permit passage of chyme into duodenum
result: regulates passage of chyme from stomach to duodenum; prevents backflow of chyme from duodenum to stomach
check slide 32 from lecture
what is the site of production, stimulus for production, target organ, and activity of cholecystokinin (CCK)
-site of production: duodenal mucosa
-stimulus for production: fatty chyme (also partially digested proteins)
-target organ: stomach, liver, pancreas, gallbladder, hepatopancreatic sphincter
-activity: inhibits stomach’s secretory activity, potentiates secretin’s actions on the organs, increases output to enzyme-rich pancreatic juice, stimulates organ to contract and expel stored bile, relaxes sphincter to allow entry of bile and pancratic juice into the duodenum
what is the site of production, stimulus for production, target organ, and activity of glucose-dependent insulinotropic peptide (GIP) (or gastric inhibitory peptide)
-site of production: duodenal mucosa
-stimulus for production: fatty chyme
-target organ: stomach & pancreas (beta cells)
-activity: inhibits HCl production (minor effect), stimulates insulin release
what is the site of production, stimulus for production, target organ, and activity of gastrin
-site of production: stomach mucosa (G cells)
-stimulus for production: food (particularly partially digested proteins) in stomach (chemical stimulation); acytylcholine ACh released by nerve fibers
-target organ: stomach (parietal cells), small intestine, ileocecal valve, large intestine
-activity: increases HCl secretion, stimulates gastric emptying (minor effect), stimulates contraction of intestinal muscle, relaxes ileocecal valve, stimulates mass movements
what is the site of production, stimulus for production, target organ, and activity of histamine
-site of production: stomach mucosa
-stimulus for production: food in stomach
-target organ: stomach
-activity: activates parietal cells to release HCl
what is the site of production, stimulus for production, target organ, and activity of intestinal gastrin
-site of production: duodenal mucosa
-stimulus for production: acidic and partially digested foods in duodenum
-target organ: stomach
-activity: stimulates gastric glands and motility
what is the site of production, stimulus for production, target organ, and activity of motilin
-site of production: duodenal mucosa
-stimulus for production: fasting: periodic release ever 1.5-2 hours by neural stimule
-target organ: proximal duodenum
-activity: stimulates migrating motor complex
what is the site of production, stimulus for production, target organ, and activity of secretin
-site of production: duodenal mucosa
-stimulus for production: acidic chyme (also partially digested proteins and fats)
-target organ: stomach, pancreas, & liver
-activity: inhibits gastric gland secretion and gastric motility, increases output of pancreatic juice rich in bicarbonate ions; potentiaties CCK’s action, increases bile output
what is the site of production, stimulus for production, target organ, and activity of serotonin
-site of production: stomach mucosa
-stimulus for production: food in stomach
-target organ: stomach
-activity: causes contraction of stomach muscle
what is the site of production, stimulus for production, target organ, and activity of somatostatin
-site of production: stomach mucosa; duodenal mucosa
-stimulus for production: food in stomach; stimulation by sympathetic nerve fibers
-target organ: stomach, pncreas, small intestine, gallbladder & liver
-activity: inhibits gastric secretion of all products, inhibits secretion, inhibits GI blood flow; thus inhibits intestinal absorption, inhibits contraction and bile release
what is the site of production, stimulus for production, target organ, and activity of vasoactive intestinal peptide (VIP)
-site of production: enteric neurons
-stimulus for production: chyme containing partially digested foods
-target organ: small intestine, pancreas, stomach
-activity: stimulates budffer secretion, increases blood flow through intestinal capillaries, relaxes intestinal smooth muscle, increases secretion, inhibits acid secretion
