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APHY 102 Exam 4a
The Digestive System
| Question | Answer |
|---|---|
| the alimentary canal or GI tract is known as a disassembly line that digests and absorbs food. what structures make up the canal? | mouth, pharynx (back of throat), esphagus, stomach, small intestine, large intestine |
| what are the accessory digestive organs? | teeth, tongue, gallbladder, salivary glands, liver, and pancreas |
| what are the 3 salivary glands? | parotid in the cheek near the ear, sublingual gland under the tongue, and submandibular gland under the mandible |
| true or false, nutrients become less available to the body in each step of digestion | false, they become more available |
| what are the 6 essential activities of digestion? (know for multiple choice) | ingestion, propulsion, mechanical digestion, chemical digestion, absorption, defecation |
| for mechanical digestion, where does churning happen and where does segmentation happen? | stomach and small intestine respectively |
| what is the difference between peristalsis vs segmentation (Fig. 22.3)? | peristalsis is one-way moving food along quickly and mechanically, segmentation is a two-way muscle process in the small intestine that divides and mixes the chyme by alternating backwards and forward movement of the GI tract contents |
| how are lymph vessels involved in absorption? | essential for absorbing fats and fat-soluble vitamins (A, D, E, K) as these molecules are too large to enter capillaries. specialized lymph capillaries called lacteals within the villi absorb these fat-rich products, transporting them as chyle |
| what is the process of taking food into the digestive tract? | ingestion |
| what is the process of swallowing (deglutition) and peristalsis? | propulsion |
| what are the waves of contraction and relaxation of mucsles in the organ walls? | peristalsis |
| what is process called of chewing, mixing (segmentation), and churning food? | mechanical digestion |
| what is the catabolic breakdown of food? | chemical digestion |
| what is the movement of nutrients from the GI tract to the blood or lymph? | absorption |
| true or false, hormones are involved in touching the food | false, they never touch the food |
| what is the elimination of indigestible solid wastes? | defecation |
| which are enzymes and which are hormones? | lipase (enzyme) vs. leptin (hormone); pepsin (enzyme) vs. gastrin/secretin (hormones) |
| true or false, the GI tract is technically an external environment | true (donut) |
| how does osmolarity play a role in digestion? | digestion increases osmolarity in the intestine, drawing water into the intestinal lumen to dilute the chyme |
| which stimuli are involved in mechnical and chemical regulation of digestion? | stretch receptors, osmolarity, and presence of substrate in the lumen |
| besides mechanical and chemical stimuli, what sort of control is exerted by the body onto digestion? | extrinsic control by CNS centers and intrinsic control by local centers (mainly) |
| what is fermentation? note it is not one of the 6 functions of digestion. | making energy without oxygen, allowing cells to generate a small amount of ATP (energy) when oxygen is not available |
| there are receptors of the GI tract responding to stretch; osmolarity, pH, presence of substract and end products of digestion. which types are these? | mechanoreceptors respond to stretch and chemoreceptors respond to the rest |
| the receptors of the GI tract initiate reflexes that do what 2 things? | 1. activite/inhibit digestive glands 2. mix lumen contnts and move them along |
| what are the 3 fundamental, interconnected processes that drive the digestion system? | glandular secretion (chemical tools), communication (timing and coordination), and motility (mechanical force) |
| there are 2 important enteric plexuses (gut brains) that initiate short reflexes intrinsically. what are they and what are their differences? | in the viscera wall, part of the PSNS (CN X), the 2 plexuses are the myenteric plexus (Aurebach's), and submucosal plexus (Meissner's). Auerbach’s controls GI tract motility, while Meissner’s controls gland secretion, blood flow & smooth muscle in mucosa |
| what is the position of the submucosal nerve plexus? | (Meissner's)--between the submucosa and muscularis externa |
| what is the position of the myenteric nerve plexus? | (Auerbach's)--btween the two layers of the muscularis externa |
| the intrinsic controls of the GI tract are regulated by local enteric plexuses. what are the extrinsic controls of the GI tract (Fig. 22.4)? | CNS centers and extrinsic autonomic nerves are LONG reflexes arising within or outside the GI tract (versus nerve plexuses being near the GI tract and initiating short reflexes) |
| in digestion, what is the region referred to where the food is? | lumen |
| what is the role of the peritoneum and peritoneal cavity? | the peritoneum (serous membrane) lines the cavity and covers organs, while the cavity contains lubricating fluid. reduces friction during organ movement, supports organs via ligaments, provides immune defense, and aids in exchange of fluids/substances |
| what are the 2 parts of the peritoneum? | visceral & parietal; visceral covers external surface of most digestive organs while parietal lines the body walls |
| true or false, there's fluid in the peritoneal cavity, which is the tiny space between visceral and parietal peritonea | true, it lubricates digestive organs and allows them to slide across one another |
| what does the mesentery look like? | a continuous, 2-layer, fan-shaped fold of tissue, often appearing as a yellowish, thin membrane in the abdominal cavity. it is made of two layers of peritoneum that suspends intestines from the posterior abdominal wall |
| what is the double layer of peritoneum that provides vascular and nerve supplies to the viscrea, as well as holds digestive organs in place and stores fat? | mesentery |
| what are the famous retroperitoneal organs/outside the peritoneum? | kidneys, though pancrease and parts of the intestine are also retroperitoneal |
| what are the peritoneal/intraperitoneal organs? /surrounded by peritoneum | liver, gallbladder, stomach, etc. |
| what is the term for blood vessels supplying the abdominal viscera—including the liver, spleen, pancreas, and intestines—receiving 20-25% of cardiac output? | splanchnic circulation |
| true or false, there are 3 main arteries of the splanchnic circulation and they are direct branches of the abdominal aorta | true |
| what are the 3 main arteries of the splanchnic circulation? | celiac trunk, superior mesenteric artery, inferior mesenteric artery |
| what ar the divisions of the celiac trunk and which organs does it supply? | celiac trunk divids into hepatic, splenic, and left gastric arteries that supply the liver, spleen, stomach respectively |
| what does the superior mesenteric artery supply? | the small intestine and proximal large intestine |
| what does the inferior mesenteric artery supply? | the distal large intestine |
| what is the difference between the hepatic portal vein vs. the hepatic vein? | the hepatic portal vein carries nutrient-rich, deoxy blood into the liver from the digestive system, while the hepatic vein carries processed, deoxy blood out of the liver to the heart |
| histology: from esophagus to anal canal the walls of the GI tract have the same what 4 tunics? | from lumen outward: mucosa, submucosa, muscularis externa, and serosa |
| true or false, each tunic shares tissue types with other tunics | false, each tunic has predominant tissue type and a specific digestive function |
| the mucosa is the innermost tunic of the alimentary canal. what is the mucosa layer made of? | it's a moist epithelial layer with itself having 3 layers: lining epithelium (simple columnar epithelium & goblet cells), lamina propria, and muscularis mucosae |
| what are the 3 functions of the mucosa tunic layer? | secretion of mucus, absorption of end products of digestion, protection against infectious disease |
| true or false, stomach and small intestine mucosa contain only enzyme-secreting cells that do chemical digestion | false, they also contain hormone-secreting cells to add endocrine functions to their digestive functions |
| what are the anatomical features of the lamina propria of the mucosa? | loose areolar and connective tissue that nourishes the epithelium and absorbs nutrients, thus BLOOD VESSELS must be present. lamina propria contains lymph nodes (MALT = mucosa-associated lymphatic tissue) important in defense against bacteria |
| what are the features of the muscularis mucosae of the mucosa? | these are smooth muscle cells that produce local movements of mucosa (twitching to loosen stuck particles), but their main claim to fame is to draw the mucosa of the sm. intestine into folds that greatly increase the surface area for absorption |
| what are the other tunics of the alimentary canal besides the mucosa? | |
| what is the tunic containing areolar and dense connective tissue, containing elastic fibers, blood and lymphatic vessels, lymph nodes, and nerves? | submucosa |
| what is the tunic responsible for segmentation (kneading in place) and peristalsis (moving the food down and along)? | muscularis externa |
| what is the tunic also known as the protective visceral peritoneum? it is replaced by the fibrous adventitia in the esophagus. | serosa |
| true or false, retroperitoneal organs have a serosa only | false, they have both an adventitia and a serosa |
| true or false, retroperitoneal organs have both an adventitia and serosa | true, one on one side and one on the other side |
| segmentation and peristalsis are largely automatic involving which type of reflex arc? | local (short) reflex arcs--control is in the wall of the viscus (piece of alimentary canal) |
| how is the enteric nervous system linked to the CNS | via long autonomic reflex arc |
| what is the structure known as the oral or buccal cavity? | mouth |
| what are the anotomical features of the mouth? | bounded by lips, cheeks, palate, tongue; has oral orifice as its anterior opening; is continuous with the oropharynx posteriorly |
| to withstand abrasions, the mouth is lined with what tissue type? | stratified squamous epithelium. also, the gums, hard palate, and dosum of the tongue are slightly keratinized |
| true or false: the buccinators of the cheeks are muscles of mastication | false |
| what is the muscle of the lips? | orbicularis oris |
| what is the vestibule and oral cavity proper, relative to the lips and cheeks? | the oral vestibule is the area between the lips and teeth especially visible when grimacing, and the oral cavity proper is on the inside of the teeth and gums |
| what is the median fold called that joins the internal aspect of each lip to the gum? | labial frenulum |
| are the palatine tonsils inside or outside the fauces? | inside the fauces (fauces are the space on either side of the uvula) |
| which is deeper, the palatoglossal arch or palatopharyngeal arch? | palatopharyngeal arch |
| what is the structure underlain by palatine bones and palatine processes of the maxillae? it is slightly corrugated on either side of the raphe (midline ridge), and has palatal rugae | hard palate |
| what does the hard palate do? | assists the tongue in chewing |
| what is the mobile fold in the mouth formed mostly of skeletal muscle? | soft palate--closes off the nasopharynx during swallowing; uvula projects downward from the free edge of the soft palate |
| palatoglossal and palatopharyngeal arches form the borders of the what? | fauces, where palatine tonsils reside |
| what structure occupies the floor of the mouth and fills the oral cavity when the mouth is closed? | tongue |
| what are some functions of the tongue? | grip and reposition food during chewing, mix food with saliva and form the bolus, initiate swallowing, speech |
| what is the difference in function between the intrinsic muscles (inside tongue) and extrinsic muscles (outside tongue)? | intrinsic muscles change the shape while extrinsic muscles change alter the position |
| which cranial nerve is tested by asking someone to stick out their tongue? | CN 12 |
| what is the structure that secures the tongue to the floor of the mouth? | lingual frenulum |
| what are the 4 types of papillae on the tongue? | foliate, filiform, fungiform, circumvallate |
| which of the 4 papillae types on the tongue have no taste buds in adulthood? | foliate |
| which of the 4 papillae types on the tongue give the tongue roughness and provide friction and a sense of texture (also no taste buds are here)? | filiform |
| which of the 4 papillae types on the tongue are scattered widely of the tongue and give it a reddish hue? these have taste buds. | fungiform |
| which of the 4 papillae types on the tongue form a V-shaped row in back of tongue (about 10-12 papillae of these), and have taste buds? | circumvallate |
| what is the name of the groove that separates the tongue into the anterior 2/3 and posterior third? | sulcus terminalis |
| true or false, the posterior third of the tongue resides in the oral cavity | false, it resides in the oropharynx |
| which cranial nerve innervates the anterior 2/3 of the tongue? | facial nerve--CN VII |
| which cranial nerve innervates the posterior 1/3 of the tongue? | glossopharyngeal nerve--CN IX |
| what is the enzyme that breaks down starch? | (salivary) amylase |
| salivary glands produce and secrete saliva that does what 4 things? (recognize multiple choice) | cleanses the mouth, moistens and dissolves food chemicals, aids in bolus formation, contains enzymes that break down starch |
| which salivary gland did we "milk" during the salivary amylase lab? | parotid |
| besides the 3 pairs of extrinsic salivary glands (parotid, submandibular, sublingual), there are what kind of salivary glands scattered throughout the oral mucosa? | intrinsic or bucal glands / lingual if on tongue |
| where does the parotid duct open in the vestibule? | next to the second upper molar |
| where do the submandibular ducts open? | at the base of the lingual frenulum |
| where do the 10-12 ducts of the sublingual gland open | into the floor of the mouth |
| what type of cells are saliva secreted from? | serous and mucous cells of salivary glands |
| true or false, saliva is a fairly neutral yet slightly acidic solution? contains electrolytes, digestive enzyme, proteins including mucin, lysozyme, defensins, IgA (antibody), and metabolic wastes--urea and uric acid | true |
| which glands partake in control of salivation by keeping the mouth moist? | intrinsic glands |
| intrinsic glands keep the mouth moist. what do extrinsic salivary glands do in contrast? | secrete serous, enzyme-rich saliva in response to the thought of food, as well as ingested food which stimulates chemoreceptors and ressoreceptors |
| strong sympathetic stimulation would affect salivation in what way? | inhibits salivation and results in dry mouth (xerostomia) |
| what is the name for the 20 deciduous teeth tha terupt at intervals between 6 and 24 months? starts with P. | primary teeth (also as baby teeth or milk teeth) |
| how many permanent teeth do adults usually have? | 32 permanent teeth |
| from front to back, what is the dental formula of deciduous (primary) teeth? | 2I: central incisors, lateral incisors, 1C: canines, 2M, first molars, second molars |
| from front to back, what is the dental formula of permanent teeth? | 2I: central incisors, lateral incisors, 1C: canines, 2PM, premolars I and II (bicuspids), 3M: first, second and third molars |
| teeth are classified by shape and function. which are chisel-shaped for cutting or nipping? | incisors |
| teeth are classified by shape and function. which are fanglike teeth that tear or pierce? | canines |
| teeth are classified by shape and function. which have broad crowns with rounded tips best suited for grinding or crushing? | premolars (bicuspids) and molars |
| what is the term for poor meeting of the teeth? | malocclusion |
| what are the terms for the 2 main regions of a tooth? | crown and root |
| what is the crown of the tooth? | part you can see: the exposed part of the tooth above the gingiva |
| what is the root of the tooth? | portion of the tooth embedded in the jawbone |
| what are the 3 bones of the skull a tooth could reside in? | mandible, right maxilla, left maxilla |
| what is the acelluar, brittle material composed of calcium salts and hydroxyapatite crystals--the hardest substance in the body? | enamel, which encapsulates the crown of the tooth |
| what is the part of the tooth, aka constriction, where the crown and root come together? | neck |
| what are the names of the calcified connective tissue that covers the root and attaches it to the periodontal ligament? | cementum, or cement |
| "periodontal" means around the tooth. which ligament anchors teeth in the alveoli of the jaw and forms fibrous joints called gomphoses? | periodontal ligament |
| what is the depression where the gingiva borders the tooth? | gingival sulcus |
| what is the bonelike material deep the the enamel cap that forms the bulk of the tooth? | dentin |
| what is the cavity surrounded by dentin that contains pulp? | pulp cavity |
| what is pulp of a tooth? | connective tissue, blood vessels, and nerves (hole for nerves is called apical foramen) |
| tooth structure: what is the portion of the pulp cavity that extends into the root? | root canal |
| what is the proximal opening to the root canal? | apical foramen |
| what are the cells that secrete and maintain dentin throughout life? | odontoblasts |
| what is the technical term for a tooth cavity? | dental caries (singular and plural) |
| what is the gradual demineralization of enamel and dentin by bacterial action? | dental caries |
| what is the (yucky) term for a film of sugar, bacteria, and mouth debris that adheres to teeth? | dental plaque |
| why is plaque bad? i.e., what dissolves the calcium salts? | the plaque has bacteria that produces acid that dissolves the calcium salts. when calcium is absent, proteolytic enzymes—which break down proteins—are free to digest the organic material |
| what is the difference between gingivitis and periodontitis? | gingivitis is early-stage and forms calculus or tartar as plaque accumulates, while periodontitis is advanced, long-term inflammation that results from an immune response, carving pockets around the teeth and dissolving bone |
| what structures allow passage of food and fluids to the esophagus, and passage of air to the trachea? | oropharynx and laryngopharynx |
| the pharynx is lined with what type of epithelium? | stratified squamous to resist abrasion |
| the pharynx has what 2 skeletal muscle layers? | inner longitudinal and outer pharyngeal constrictors (circular muscles) --- this order is reversed at esophagus |
| what is the muscular tube going from the laryngopharynx to the stomach? it travels through the mediastinum and pierces the diaphragm; joins the stomach at the cardiac orifice | esophagus |
| true or false, the esophagus has serosa and adventitia | false, doesn't have serosa but does have adventitia |
| what epithelium characterizes the esophageal mucosa? | nonkeratinized stratified squamous epithelium |
| does the esophagus' muscularis change from skeletal superiorly to smooth inferiorly or vice versa, smooth superiorly to skeletal inferiorly? | skeletal superiorly to smooth inferiorly |
| how is propulsion initiated/ what is it initiated by? | swallowing (deglutition). then, the pharynx and esophagus serve as conduits to pass food from the mouth to the stomach |
| what begins mechanical digestion? | chewing |
| where does chemical breakdown of starch begin? | the mouth via salivary amylase |
| what act involves the coordinated activity of the tongue, soft palate, pharynx, esophagus, and 22 separate muscle groups? | deglutition (swallowing) |
| what are the phases of deglutition? | buccal and pharyngeal-esophageal |
| what is the buccal phase of swallowing? | when bolus is forced into the oropharynx? |
| what is the pharyngeal-esophageal phase? | controlled by the medulla and lower pons; all routes except into the digestive tract are sealed off and peristalsis moves food through the pharynx to the esophagus |
| true or false, the upper esophageal sphincter is always closed/contracted except when food is moving through it | true, and same for the gastroesophageal sphincter too |
| what is chyme? | a thick, acidic, semifluid mass of partially digested food and digestive secretions (gastric juices, enzymes, acid) created in the stomach |
| what is the cardiac orifice? | the superior opening of the stomach, located at the junction with the esophagus, where food enters the stomach. Surrounded by the lower esophageal sphincter, it helps control food passage and prevents acid reflux |
| what are the different regions of the stomach? | cardiac region, fundus, body, pyloric region |
| the pylorus of the stomach is continuous with the duodenum of the small intestine through what structure? | the pyloric sphincter |
| which stomach strucure contains the gastric air bubble? | the fundus, which is the dome-shaped region beneath the diaphragm |
| what constitutes the pyloric region of the stomach? | made of of the antrum and pyloric canal which terminates at the pylorus |
| what are the greater curvature and the lesser curvature? | the greater curvature is the entire extent of the convex lateral surface and the lesser curvature is the concave medial surface |
| what are the greater and lesser omenta? | the greater and lesser omenta are specialized, fatty folds of peritoneum that suspend abdominal organs, primarily the stomach, and provide immune and vascular support |
| what is the anatomy of the omenta of the stomach? | the lesser omentum of the stomach runs from the liver to the lesser curvature, aka gastrohepatic ligament(!), and the greater omentum drapes inferiorly from the greater curvature to the small intestine like an apron over the small intestine |
| what are the 3 layers of the muscularis externa of the stomach? | longitudinal layer, circular layer, oblique layer (from superficial to deep)--the oblique later is an additional layer that allows the stomach to churn, mix, and pummel food physically into smaller fragments |
| true or false, parts of the GI tract usually have 2 layers of the muscularis externa... (what is the exception?) | true, except the stomach which has 3 |
| what supplies the stomach's nerves? | sympathetic and parasympathetic fibers of the autonomic nervous system |
| what supplies the stomach's blood? | celiac trunk, and corresponding veins leading to the hepatic portal system |
| why is it important for the stomach's epithelial lining to have goblet cells that produce a coat of alkaline mucus, which also traps a bicarbonate-rich fluid beneath it? | to protect the underlying tissue from the stomach's acid |
| what are the structures that contain gastric glands that secrete gastric juice, mucus, and gastrin | |
| what are some key hormones of the GI tract? | gastrin, cholecystokinin (CCK), secretin, ghrelin, and GIP |
| what is the added layer of the stomach's muscularis externa? | the oblique layer |
| which tunic layer of the stomach contains the Meissner's plexus? | the submucosa |
| which tunic layer of the stomach contains the myenteric plexus (Auerbach's)? | muscularis externa, specifically between the inner circular and outer longitudinal smooth muscle layers |
| there are several kinds of cells in the gastric pits of the stomach: enteroendocrine, chief, parietal cells, mucous neck cells, and surface epithelia. what does each do? | epithelia=mucus, neck=protective mucus, parietal=HCl, intrinsic factor, chief=pepsinogen, lipase; enteroendocrine=hormones such as gastrin, histamine, endorphins, serotonin, CCK, and somatostatin into the lamina propria (a layer of the mucosa) |
| what do parietal cells produce? | HCl and intrinsic factor |
| what is intrinsic factor required for? | the absorption of vitamin B12 |
| what do chief cells produce? | pepsinogen and lipase |
| what is the positive feedback loop related to pepsin? | pepsinogen is activated to pepsin by HCl and by pepsin itself so pepsin can make more of itself (called an autocatalytic effect) |
| what does autocatalytic literally mean? | self-making |
| is gastrin a hormone? | yes, it's a polypeptide hormone that regulates digestion by stimulating the stomach to produce hydrochloric acid |
| thus gastrin would stimulate what cells? | parietal cells |
| what 3 things does the stomach's mucosal barrier have to keep from digesting itself? | thick coat of bicarb-rich mucus, epithelial cells joined by TIGHT JUNCTIONS, gastric glands impermeable to HCl |
| what 3 muscular layers from superficial to deep degrade the stomach's ingested food physically? | longitudinal, circular in the middle, oblique deepest |
| what types of mechanisms regulate the release of gastric juice? | neural and hormonal (surprising... I thought it would be chemical and neural) |
| regulation of gastric secretion: stimulatory and inhibitory events occur in what 3 phases (Fig. 22.16.1)? | cephalic (reflex) phase=head control prior to food entry; gastric phase=stomach controls itself once food enters the stomach; intestinal phase=intestine controls what stomach does as partially digested food enters the duodenum |
| for the cephalic phase, excitatory events include what possibilities? | sight/thought of food, stimulation of taste or smell receptors |
| for the cephalic phase, inhibitory events include what possibilities? | loss of appetite or depression, decrease in stimulation of the parasympathetic division |
| for the gastric phase, excitatory events include what? | stomach distension, activation of stretch receptors (neural activation), activation of chemoreceptors by peptides, caffeine, rising pH, release of gastrin to the blood |
| for the gastric phase, inhibitory events include what? | pH lower than 2; pH will fall when the stomach has emptied (HCl secreted); emotional upset that trips the SNS and overrides the parasympathetic division |
| for the intestinal phase, excitatory events include what? | low pH |
| for which phase does low pH inhibit activity and for which phase does low pH stimulate activity? | intestinal phase of gastric secretion is stimulated by low pH whereas gastric phase is excited by rising pH and inhibited by pH lower than 2 |
| what would stimulate and encourage gastric gland activity in the stomach? | as partially digested food enters the duodenum, stomach activity is encouraged |
| for the intestinal phase, it has an inhibitory phase caused by what possibilities? | distension of duodenum, presence of fatty/acidic/hypertonic chyme, and/or irritants in the duodenum |
| what three steps occur in the inhibitory phase of the intestinal phase of gastric secretion? | local reflexes and vagal nuclei are inhibited, pyloric sphincter is closed, and secretion-inhibiting enterogastrones are released |
| what phase initiates inhibition of local reflexes and vagal nuclei? | inhibitory phase of intestinal phase of gastric secretion |
| what happens in the intestinal inhibitory phase if the chyme is fatty? | add bile from liver for emulsification |
| what happens in the intestinal inhibitory phase if the chyme is acidic? | add bicarbonate ion from pancreas & other ducts to neutralize, hence secretion is important |
| what is the enterogastric reflex? | is a nervous system mechanism that inhibits gastric motility and secretion when the duodenum is stretched or irritated by acidic chyme; acts as a "brake" on gastric emptying |
| why is the regulation and mechanism of HCl (hydrochloric acid) important? | crucial for enabling protein digestion, activating digestive enzymes (pepsin), aiding mineral absorption, and acting as an antiseptic to destroy pathogens |
| what stimulates HCl secretion from parietal cells? | the 3 ligands, ACh, histamine, and gastrin, through 2nd-messenger systems |
| when is release of HCl low? high? | low if only one ligand binds to parietal cells; high if all 3 bind to parietal cells (ACh, histamine, gastrin) |
| if histamines stimulate HCl secretion from parietal cells, how do antihistamines decrease HCl release? | block H2 receptors |
| what does a portal vein do? | connect 2 capillary systems whereas most veins drain into the venae cavae |
| what drains into the hepatic portal vein? | the superior mesenteric and and splenic veins both drain into the hepatic portal vein, through the liver, into the regular hepatic veins, and into the IVC. the inferior mesenteric drains into the splenic vein. |
| the pressure in the stomach remains constant until about 1L of food is digested. what does the relative unchanging pressure result from? | reflex-mediated relaxation and plasticity |
| reflex-mediated events include what 2 relaxations? | 1. receptive relaxation and 2. adaptive relaxation |
| what is receptive relaxation? | as food travels in the esophagus, stomach muscles relax |
| what is adaptive relaxation? | the stomach dilates in response to gastric filling |
| what is the difference between receptive relaxation and adaptive relaxation? | receptive relaxation is a fast, vagally-mediated reflex occurring when food passes through the pharynx/esophagus, whereas adaptive relaxation is a slower, sustained relaxation triggered by direct stretch (distension) of the gastric fundus by food |
| what is the term for the intrinsic ability of smooth muscle to exhibit the stress-relaxation response, meaning that when smooth muscle is stretched it will first contract slightly then relax to allow filling of a hollow organ | plasticity |
| gastric contractile activity: peristaltic waves move toward the pylorus at what 3 waves a minute. this BER (basic electrical rhythm) is initiated by what from where? | pacemaker cells/cells of Cajal, specialized pacemaker cells located within the muscularis propria of the gastrointestinal (GI) tract, specifically around the myenteric plexus, intramuscular layers, and submucosal borders |
| where does the most vigorous peristalsis and mixing occur? | near the pylorus |
| is it normal for chyme to be forced backward into the stomach for further mixing? | yes, it is entirely normal and essential for chyme to be forced backward into the stomach for further mixing |
| what two directions does chyme go? how does this happen? | chyme is either delivered in small amounts to the duodenum or forced backward into the stomach for further mixing |
| what 2 things is gastric emptying regulated by? | (1) the neural enterogastric reflex and (2) hormonal (enterogastrone) mechanisms, both of which inhibit gastric secretion and duodenal filling |
| which sphincter causes heartburn? | the primary sphincter that causes acid reflux when it becomes weak or relaxes inappropriately is the lower esophageal sphincter (LES) |
| what is the difference between carbohydrate-rich chyme and fat-laden chyme? | fat-laden chyme is digested more slowly causing food to remain in the stomach longer; carb-rich chyme moves quickly through |
| what organ runs from the pyloric sphincter to the ileocecal valve? | the small intestine |
| what are the 3 subdivisions of the small intestine? | duodenum, jejunum, and ileum (not ilium, that is the hip bone) |
| which 2 ducts join the duodenum at the hepatopancreatic ampulla and are controlled by the sphincter of Oddi? | the bile duct and main pancreatic duct |
| where does the ileum join the large intestine? | at the ileocecal valve |
| true or false, the stomach has villi and microvilli. | false, these are found in the small intestine |
| what 3 structural modifications of the small intestine wall increase surface area? | plicae circulares, villi, and microvilli |
| what are plicae circulares? | deep circular folds of the mucosa and submucosa which histologically speaking are created by muscularis mucosae |
| gallbladder and associated ducts: know this tree | at sm intestine is sphincter of Oddi: goes & forks at bile sphincter, main pancreatic duct & sphincter; then the bile duct: forks into cystic duct & common hepatic duct. cystic duct goes up into gallblader; common hepatic duct goes into R/L hepatic ducts |
| what is a lacteal? | a lacteal is a specialized lymphatic capillary in the center of each villus in the small intestine that absorbs dietary fats and fat-soluble vitamins (A, D, E, K). |
| what do lacteals do? | these vessels transport chylomicrons (emulsified fats) to the lymphatic system, appearing milky-white after meals, and are crucial for nutrient transport and immune response |
| small intestine histology: epithelium of small intestine mucosa is made of what? | absorptive cells and goblet cells, enteroendocrine cells, interspersed T cells (IELS--these are immune cells, which release cytokines upon encountering antigens) |
| true or false, the small intestine plays a role in the immune system | true, crucially harbors a massive network of immune cells (gut-associated lymphoid tissue/GALT) that distinguish between beneficial nutrients and harmful pathogens |
| histology of the small intestine wall: what cells here secrete intestinal juice? | cells of intestinal crypts, called crypts of Lieberkuhn) |
| what important aggregations of cells are found in the submucosa of the small intestine? | Peyer's patches, which are collections of lymphoid cells to mount immune response against invaders |
| between gastric juice and instestinal juice, which one is rich in enzymes and which is poor in enzymes? | gastric juice is rich, intestinal juirce is poor although it does have enzymes; pancreas importantly dumps enzymes in duodenum not from intestine |
| what structures in the duodenum secrete alkaline mucus (8 or 9 / with bicarb ion) to neutralize the incoming acidic chyme? Brunner's glands | |
| what is secreted by intestinal glands in response to distension or irritation of the mucosa? | intestinal juice |
| chemically speaking, what are the features of intestinal juice? | slightly alkaline, isotonic with blood plasma, largely water, enzyme-poor, but contains mucus |
| what is the purpose of intestinal juice functionally? | serves as a carrier fluid for absorbing nutrients from chyme |
| what is the largest gland in the body? largest internal organ? | the liver |
| where are each of the four lobes and what are their names? | right and left anteriorly; caudate and quadrate posteriorly |
| what is the falciform ligament of the liver (look up visual as needed)? | separates the right and left lobes anteriorly, suspends the liver from the diaphragm and anterior abdominal wall |
| which ligament runs along the free edge of the falciform ligament? | ligamentum teres (aka round ligament), and it is a remnant of the fetal umbilical vein |
| what structure anchors the liver to the stomach? | lesser omentum (gastrohepatic ligament) |
| what is the structure where the hepatic blood vessels enter the liver? | porta hepatis |
| what important structure rests in a recess of the liver on the inferior surface of the right lobe? | the gallbladder |
| what two ducts form the bile duct? bile leaves the liver via these. | the bile duct (formed of the common hepatic duct which fuses too with the cystic duct), and bile ductules |
| what to note about the biliary and pancreatic duct systems? | they are connected at the hepatopancreatic ampulla and sphincter |
| microscopic anatomy of liver: what are the structural and functional units of the liver? | hexagonal liver lobules composed of hepatocyte plates radiating outward from a central vein; portal triads are found at each of the six corners of each liver lobule |
| what do liver lobules' portal triads consist of? | a bile duct(ule) and both the hepatic artery and hepatic portal vein |
| what capillaries are located between hepatic plates? | sinusoids of the liver, which contain hepatic macrophages (Kupffer cells) |
| what are 4 functions of hepatocytes? | bile production, processing bloodborne nutrients, storage of fat-soluble vitamins, detoxification |
| how does bile get from hepatocytes, out? /pathway | secreted bile flows between hepatocytes toward the bile ductules in the portal triads |
| how does oxygenated blood arrive at the liver's lobules? | via the hepatic arteries. it trickles through to the sinusoids where it drops off O2 and picks up CO2 |
| what is the significance of Kupffer cells? | Kupffer cells eat physical debris, hepatocytes perform chemical cleansing |
| how does all blood that entered the liver leave the liver? | through the central vein, which is like a drain in the middle of the sink. the central vein forms the interlobular veins and eventually one hepatic vein |
| bile is a yellow-green, alkaline solution containing what? | bile salts, bile pigments, cholesterol, neutral fats, phospholipids, and electrolytes |
| bile salts are cholesterol derivatives that do what 3 things? | emulsify fat (obviously), facilitate fat and cholesterol absorption (less obviously), and help solubilize cholesterol (least obviously) |
| what process recyles bile salts to send them back to the liver? | enterohepatic circulation |
| why does poop look brown? | the chief bile pigment is bilirubin, a waste product of heme, which is part of hemoglobin |
| what happens if you don't have bile? | large fat globules don't get broken down by lipase |
| what is the thin-walled, green muscular sac on the ventral surface of the liver? | gallbladder |
| what does the gallbladder do? | stores and concentrates bile by absorbing its water and ions; if it absorbs too much water you get gallstones |
| through what structure does the gallbladder release bile? | cystic duct, which flows into the bile duct |
| regulation of bile release: why does acidic, fatty chyme cause the duodenum to release CCK (for fat and protein) and secretin (for acidic chyme) into the bloodstream? | duodenum releases these hormones because it acts as the "control center" for digestion |
| why do bile salts and secretin transported in blood stimulate the liver to produce bile? | bile salts stimulate bile production thru recycling called enterohepatic circulation- 95% of bile salts released to intestine are reabsorbed in ileum & sent back to liver via portal vein. "returning" bile salts arrive at liver=strongest stimulant for more |
| what is an important point about synthesis vs secretion about bile? | while returning bile salts increase the flow of bile, they actually inhibit the synthesis of new bile acids from cholesterol to prevent an oversupply |
| does the vagus nerve also regulate bile release? | yes, vagal stimulation causes weak contractions of the gallbladder |
| what is cholecystokinin? | a peptide hormone that plays a central role in your digestive system and brain function. lit. "to move the gallbladder" (chole = bile, cysto = sac, kinin = move) |
| is CCK a hormone or an enzyme? | hormone, secreted by specialized "I-cells" in the duodenum and jejunum |
| what does CCK do? | causes the gallbladder to contract, and the hepatopancreatic sphincter to relax; as a result, bile enters the duodenum |
| what are the steps of bile release regulation? (1) | acidic, fatty chyme enters duodenum and CCK/secretin is released |
| what are the steps of bile release regulation? (2) | CCK and secretin enter the blood stream |
| what are the steps of bile release regulation? (3) | bile salts and secretin via bloodstream stimulate liver to produce bile |
| what are the steps of bile release regulation? (4) | vagal stimulation causes weak contractions of bladder |
| what are the steps of bile release regulation? (5) | CCK via bloodstream causes gallbladder to contract and hepatopancreatic sphincter ro relax; bile enters duodenum |
| what are the steps of bile release regulation? (6) | bile salts reabsorbed into blood |
| what organ lies deep to the greater curvature of the stomach? its head is encircled by the duodenum and the tail abuts the spleen. | pancreas |
| what are the functional secretory units of the exocrine pancreas? | acini, which contain zymogen granules with digestive enzymes |
| what are the 2 cell types that have an exocrine function in the pancreas? | acinar cells (arranged in clusters called acini) produce and secrete digestive enzymes (amylase, lipase, proteases), while ductal cells produce a bicarbonate-rich, alkaline fluid that neutralizes stomach acid and transports the enzymes to small intestine |
| where does bicarbonate come from? | kidneys and pancreas. bicarb acts as a crucial buffer to maintain pH balance. the kidneys create new bicarbonate while reabsorbing it to regulate blood acidity, while the pancreas secretes it into the digestive tract to neutralize stomach acid |
| what is H2CO3? | carbonic acid |
| what is HCO3-? | bicarbonate ion |
| what is the composition of pancreatic juice? | it's a water solution of enzymes and electrolytes (primarily HCO3-) |
| what does pancreatic juice do? | neutralizes acid chyme and provides optimal environment for pancreatic enzymes |
| note that zymogen granules protectively package inactive catabolic enzymes (zymogens). so enzymes are released in inactive form and activated where? | the duodenum |
| there are active and inactive enzymes released by the pancreas in the pancreatic juice. what are examples of each? | trypsinogen-->trypsin, procarboxypeptidase-->carbodypeptidase; active enzymes include amylase at pH 8 or 9, lipases, and nucleases, all of which require ions or bile for optimal activity |
| true or false, the vagus nerve stimulates anything that enhances digestion | true |
| what hormones play a role in pancreatic secretion? | secretin and CCK, released from the enteroendocrine cells of the duodenal epithelium when fatty or acidic chyme enters the duodenum |
| what does CCK induce upon reaching the pancreas? | the secretion of enzyme-rich pancreatic juice |
| what does secretin cause upon reaching the pancreas? | secretin causes the secretion of bicarbonate-rich pancreatic juice to neutralize acidic chyme from stomach |
| digestion in the small intestine: as chyme leaves the stomach and enters the duodenum, carbs and proteins have been only partially digested by what? | CHOs by salivary amylase and proteins by pepsin |
| has fat digestion taken place by the time it gets to the stomach? | lingual lipase was secreted in the mouth and activated in the stomach by the low pH there, so a small amount has occurred |
| why does hyptertonic and low pH chyme require mixing for proper digestion? | without this mixing, the acidic, concentrated chyme would damage the intestinal lining and inhibit the digestive enzymes required to break down nutrients |
| for digestion in the small intestine, required substances are supplied by the what and the what? | liver and pancreas |
| what is the difference between digestion and absorption? | digestion prepares nutrients; absorption transports them |
| where does virtually all nutrient absorption take place? | in the small intestine |
| the most common motion of the small intestine is what? | segmentation, accomplished by the circular muscle layer of the muscularis externa, which contracts to mix chyme with digestive juices and move it back and forth |
| segmentation is initiated by what type of cells? | Cajal cells, aka intrinsic pacemaker cells |
| what is the difference between segmentation and peristalsis? | segmentation mixes food in place, peristalsis moves it along |
| the chyme must make physical contact with enzymes embedded in the epithelial cell membranes. what are these enzymes and this process called? | brush-border enzymes in a process called contact digestion |
| when does peristalsis begin in the small intestine? | after nutrients have been absorbed |
| in peristalsis, how would you describe the pattern of the waves moving the food along? | each wave starts distal to the previous, in what's called a migrating motility complex (MMC) |
| what does peristalsis accomplish in the small intestine? | meal remnants, bacteria, mucosal cells, and debris are all moved into the large intestine |
| what coordinates intestinal motility? | local enteric neurons of the GI tract coordinate intestinal motility |
| what 3 things do cholinergic neurons cause (controlled by parasympathetic vs. adrenergic or dopaminergic being controlled by postganglionic sympathetic)? | contraction and shortening of the circular muscle layer, shortening of longitudinal muscle, distension of the intestine |
| what allows chyme to pass into the large intestine? | the gastroileal reflex and gastrin relax the ileocecal sphincter, allowing chyme to pass into the large intestine |
| what are the 3 unique features of the large intestine, or colon? | teniae coli, haustra, and epiploic appendages |
| what are teniae coli? | three bands of longitudinal smooth muscle in the muscularis of the large intestine |
| what are haustra? | pocketlike sacs/pouches of the large intestine causes by the tone of the teniae coli. (a bad, additional pouch on haustrum would be diverticulum/itis) |
| what are epiploic appendages? | fat-filled pouches of visceral peritoneum; found only on the intraperitoneal sections of the large intestine (transverse and sigmoid colon) |
| what are the divisions of the large intestine? | cecum, appendix, colon, rectum, and anal canal |
| what is the first part of the large intestine? it lies below the ileocecal valve in the right iliac fossa, and contains a wormlike veriform appendix | the saclike cecum |
| what is another name for the right colic flexure of the large intestine? | hepatic flexure |
| what is another name for the left colic flexure of the large intestine? | splenic flexure |
| what are the distinct regions of the colon? | ascending, hepatic flexure, transverse colon, splenic flexure, descending colon, and sigmoid colon |
| what are the names for the mesenteries anchoring the transverse and sigmoid portions of the colon? | mesocolons, usually associated with the small intestine |
| which region of the colon joins the rectum? | sigmoid colon |
| what structure opens to the exterior at the anus? it's the last segment of the large intestine. | anal canal |
| the rectum has how many valves? | 3 |
| average person produces how much flatus per day? | 500 mL |
| what causes the odor of feces and flatus? | hydrogen sulfide, indole, and skatole |
| what gases are in flatus? | hydrogen, nitrogen, carbon dioxide, methane, hydrogen sulfide, indole, skatole |
| the anus has how many sphincters? composed of what? | 2. internal anal sphincter is of smooth muscle; external anal sphincter is of skeletal muscle. these are closed except during defecation |
| which mesentery is "under" the liver when the liver is lifted during a dissection, and adjoining the stomach? | lesser omentum aka gastrohepatic ligament |
| which mesentery is over the transverse colon like an apron? | greater omentum. it's the reason guts can't just fall out like in a horror movie |
| the colon's mucosa is what type of tissue? | simple columnar epithelium except in anal canal |
| the small intestine wall secretes intestinal juice via intestinal crypts, called crypts of Lieberkuhn. in the large intestine, these crypts are deeper and are lined with what? | goblet cells |
| the anal canal mucosa needs to withstand abrasion. thus what type of tissue is there? | stratified squamous epithelium |
| what structures exude mucus and compress feces at the large intestine? | anal sinuses |
| what capillary beds are associated with the anal canal? their inflammation results in itchy varicosities called hemorrhoids. | superficial venous plexuses |
| where did bacterial flora of the large intestine come from? | that which survived the small intestine and entered the cecum, and, those entering via the anus |
| what do the bacterial flora of the large intestine do? | colonize colon, ferment indigestible carbohydrates, release irritating acids and gases (flatus), synthesize B complex vitamins and vitamin K(!) |
| other than digestion of enteric bacteria, no further digestion takes place in the colon | true |
| vitamins, water, and electrolytes are reclaimed in which portion of the alimentary canal? | large intestine |
| what is the major function of the large intestine? | propulsion of fecal material toward the anus |
| is the colon essential for life? | no--hence colostomy bag |
| how does the large intestine demonstrate motility? | haustral contractions: slow segmenting movements that move the contents of the colon. |
| haustra sequentially contract as they are stimulated by what? | distension |
| think of how a dog has to go potty right after they eat. the presence of food in the stomach activates which reflex? | gastrocolic reflex, which initiates the peristaltic mass movements that force contents toward the rectum |
| the distension of rectal walls caused by feces results in what reflex? | the defecation reflex |
| when feces are passing through, they distend the rectal walls. what 2 things happen as a result? | stimulates contraction of the rectal walls and relaxes the internal anal sphincter involuntarily (PSNS control) |
| is the external anal sphincter controlled by voluntary signals to allow defecation to occur? | yes |
| polar carbohydrates are absorbed at the small intestine via cotransport with what molecule as well as what process? | Na+, and facilitated diffusion |
| where do carbohydrates go when being absorbed at the small intestine? | they enter the capillary bed in the villi and are transported to the liver via the hepatic portal vein |
| which enzymes are used to chemically digest carbohydrates? | salivary amylase, pancreatic amylase, and brush-border enzymes including dextrinase, glucoamylase, maltase, sucrase, lactase |
| which sugar is indigestible after age 4 in most people (lack of lactase)? | lactose |
| maltase would break down a molecule into which monosaccharides? | glucose and glucose in the form of maltose |
| sucrase would break down a molecule into which monosaccharides? | glucose and sucrose in the form of sucrose |
| lactase would break down a molecule into which monosaccharides? | galactose and glucose in the form of lactose |
| what are zymogens? | aka proenzymes, they are inactive precursors of an enzyme that requires a biochemical change—typically the cleavage of a peptide bond—to become active. ex) pepsinogen (activated to pepsin) and trypsinogen |
| are proteins and carbohydrates' absorption similar? | yes |
| which enzymes are used to chemically digest proteins? | pepsin in the stomach; trypsin, chymotrypsin, and carboxypeptidase in the pancreas; brush border enzymes in the small intestine such as aminopeptidases, carboxypeptidases, and dipeptidases |
| which enzymes from the pancreas act on proteins? | trypsin, chymotrypsin, carboxypeptidase |
| which enzymes from the small intestine act on proteins? these are brush border enzymes. | aminopeptidases, carboxypeptidases, and dipeptidases |
| how and where are fats absorbed? | diffuse into intestinal cells |
| what happens to fats after they diffuse into intestinal cells? | combine with proteins and extrude chylomicrons |
| what are the lipoproteins that package reassembled triglycerides within enterocytes for transport via the lymph and blood to body tissues? | chylomicrons |
| what are the small, bile-salt aggregates that shuttle fatty acids and monoglycerides from the lumen to the intestinal wall for absorption? | micelles |
| into what structure do fats enter/where, and how are they transported to systemic circulation? | chylomicrons enter specialized lymphatic vessels called lacteals in the villi, travel through the lymphatic system, and enter the bloodstream |
| why would the absorption process be different for chylomicrons versus glycerol and short chain fatty acids? | chylomicrons are processing long chain fatty acids; short chain fatty acids are water-soluble and tiny enough to diffuse right into the bloodstream |
| what is the pathway for glycerol and short chain fatty acids at the small intestine? | they are absorbed into the capillary blood in villi and transported via the hepatic portal vein |
| what enzymes/chemicals are used for glycerol and short chain fatty acids? | bile salts and pancreatic lipase |
| bile salts chop the fat globules into smaller pieces called what? | emulsification droplets |
| pancreatic lipase cleaves the 1st and 3rd fatty acids from triglycerides to form what? | monoglycerides and free fatty acids (FFA) |
| what is the difference between emulsification droplets and micelles? | emulsification droplets increase surface area for enzymes to work while micelles transport digested fat through water to reach cells |
| what about the number of emulsification droplets and micells as lipase works? | the emulsification droplets shrink and eventually disappear, while the number of micelles increases as they ferry the broken-down fat to intestinal epithelial cells, where they diffuse |
| how do fatty acids and monoglycerides enter intestinal cells? | via diffusion from micelles (the shuttles) |
| after chylomicrons are extruded, they enter where? and how are they transported to the circulation? | they enter lacteals and are transported to the circulation via lymph |
| true or false, as a general rule, fat is absorbed into the blood. | false, fat is absorbed into the lymphatic system NOT the blood |
| what are the steps of fatty acid absorption? (1) | fatty acids and monoglycerides resulting from fat digestion leave micells and enter epithelial cells by diffusion |
| what are the steps of fatty acid absorption? (2) | fatty acids are used to synthesize triglycerides in the smooth endoplasmic reticulum |
| what are the steps of fatty acid absorption? (3) | fatty globules are combined with proteins to form chylomicrons within Golgi apparatus |
| what are the steps of fatty acid absorption? (4) | vesicles containing chylomicrons migrate to the basal membrane, are extruded from the epithelial cell, and enter a lacteal (lymphatic capillary) |
| what are the steps of fatty acid absorption? (5) | lymph in the lacteal transports chylomicrons away from intestine |
| are nucleic acids absorbed via active or passive transport? | active transports via membrane carriers. nucleic acids are highly polar |
| where are nucleic acids absorbed and transported to? | nucleic acids are absorbed in villi at the small intestine and are transported to the liver via the hepatic portal vein |
| which enzymes are used in the small intestines to digest nucleic acids? | pancreatic ribonucleases and deoxyribonuclease in the small intestines--these split them up into phosphate ions, ribose or deoxyribose sugar, and nitrogenous bases |
| how/where are electrolytes absorbed? | most ions are actively absorbed along the length of the small intestine. |
| most ions are actively absorbed along the length of the small intestine. Na+ is coupled with absorption of what two substsances? | glucose and amino acids |
| how is ionic ion absorbed? | transported into mucosal cells where it binds to ferritin |
| anions passively follow the electrial potential established by which molecule? | Na+ |
| true or false, K+ diffuses across the intestinal mucosa in response to osmotic gradients | true |
| unlike most electrolytes, calcium absorption is inefficient, selective, and hormonal. what regulates it? | vitamin D and parathyroid hormone |
| what percentage of water is absorbed in the small intestines by osmosis? | 95% |
| true or false, the intestinal mucosa do not secrete any enzymes | true; brush border enzymes are there, but it secretes only alkaline mucus and water |
| true or false, as water is taken up by the small intestine, the remaining chyme is concentrated and the chyme particles move into the cells as well | true |
| malabsorption of nutrients results in anything that interferes with delivery of what 2 things? | bile or pancreatic juice |
| what else could damage the intestinal mucosa or intestinal villi? | bacterial infection could damage the intestinal mucosa and gluten enteropathy (adult celiac disease) could damage the intestinal villi |
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