Digestive System
15. Describe the composition and function(s) of saliva.
-Cleanses the mouth -Dissolves food chemicals so they can be tasted -Moistens food and helps compact it into a bolus -Contains enzymes that begin the chemical breakdown of starchy food - largely water—97 to 99.5% -slightly acidic (pH 6.75 to 7.00), but its pH may vary -solutes include electrolytes (Na+, K+, Cl-, PO34-, HCO3- -the digestive enzymes salivary amylase and lingual lipase -the proteins mucin, lysozyme, and IgA -metabolic wastes
51. Describe the histological organization of liver lobules.
-Each lobule is a roughly hexagonal (six-sided) structure consisting of plates of liver cells (hepatocytes) organized like bricks in a garden wall -hepatocyte plates radiate outward from a central vein running in the longitudinal axis of the lobule.
19. Describe the structure and function of the esophagus.
-a muscular tube about 25 cm (10 inches) long and is collapsed when not involved in food propulsion - Pierces the diaphragm at the esophageal hiatus to enter the abdomen -four of the basic alimentary canal layers: -The esophageal mucosa contains a nonkeratinized stratified squamous epithelium. At the esophagus-stomach junction simple columnar epithelium of the stomach (specialized for secretion) -The submucosa contains mucus-secreting esophageal glands, which secrete mucus that grease the esophageal walls and aids food passage -The muscularis externa is skeletal muscle in its superior third, a mixture of skeletal and smooth muscle in its middle third, and entirely smooth muscle in its inferior third. -esophagus has a fibrous adventitia composed entirely of connective tissue, which blends with surrounding structures along its route. -function: food propulsion, accomplished by swallowing
16. How is the secretion of saliva controlled?
-controlled primarily by the parasympathetic division of the autonomic nervous system -we ingest food --> chemoreceptors and mechanoreceptors in the mouth send signals to the salivatory nuclei in the brainstem (pons and medulla) --> parasympathetic nervous system activity increases impulses sent via motor fibers in the facial (VII) and glossopharyngeal (IX) nerves --> dramatically increase the output of watery (serous), enzyme-rich saliva.
55. What is the function of bile salts?
-emulsify fats—break them down into smaller pieces and distribute them throughout the watery intestinal contents -physically separate large fat globules entering the small intestine into millions of smaller, more accessible fatty droplets that provide large surface areas for the fat-digesting enzymes to work on -facilitate fat and cholesterol absorption -help solubilize cholesterol, both that contained in bile and that entering the small intestine in food.
41. What effect does the enterogastric reflex have on digestive activity (i.e., secretory activity and gastric motility)?
-gastric secretory activity declines. -these "brakes" on gastric activity protect the small intestine from excessive acidity and match the small intestine's processing abilities to the amount of chyme entering it. - inhibit gastric secretion and prevent further duodenal filling by reducing the force of pyloric contractions
69. Identify the neural and hormonal factors which regulate movement of food residue into from the ileum into the cecum.
-gastroileal reflex, a long reflex triggered by stomach activity, increases the force of segmentation in the ileum and relaxes the sphincter. Hormonal: -gastrin released by the stomach increases the motility of the ileum and relaxes the ileocecal sphincter.
64. Why are the alkaline secretions of the small intestine and pancreas important?
-helps neutralize acidic chyme moving in from the stomach. -prevent the intestinal wall from eroding and resulting in duodenal ulcers
86. What is the function of lipoprotein lipase? Where in the circulatory system is lipoprotein lipase located?
-hydrolyze triglycerides from chylomicrons to fatty acids and glycerol in the bloodstream -these products diffuse into cells - used for E, or stored as fat -chylomicron remnants circulate to liver for further metabolism located in the endothelium of systemic capillaries in adipose tissue, muscle, and heart
49. What are the functions of the liver?
-produce bile for export to the duodenum. -filter and process the nutrient-rich blood delivered to it
26. What are the gastric glands, and where are they located?
-produce the stomach secretion called gastric juice - cardia and pylorus -pyloric antrum
65. Describe the composition of intestinal juice.
-slightly alkaline (7.4-7.8), and isotonic with blood plasma -largely water but also contains some mucus (secreted by the duodenal glands and by goblet cells of the mucosa) -enzyme-poor because intestinal enzymes are limited to the bound enzymes of the brush border.
36. How does gastrin help regulate gastric gland secretion?
-which stimulates secretion of enzymes and HCl, and of hormones produced by the small intestine, which are mostly gastrin antagonists. (look at annie's study guide for more extensive answer)
3. Identify and describe the basic activities performed by the alimentary canal (e.g., ingestion) which aid the digestive process.
1. Ingestion: simply taking food into the digestive tract (usually by mouth) 2. Propulsion: moves food through alimentary canal Swallowing: voluntary Peristalsis: involuntary, major means of propulsion, altering waves of contraction and relaxation, some mixing Squeezes food and mixes 3. Mechanical Digestion/Breakdown: chewing & mixing food with saliva and tongue (mouth), churning food (stomach), segmentation (rhythmic constrictions of the small intestine) Increases surface area of food, mixes food with digestive juices, makes absorption more efficient 4. Chemical Digestion: enzymes secreted in the lumen of alimentary canal breakdown food to chemical building blocks 5. Absorption: passage of digested end products (vitamins, minerals, and water) from the lumen of GI tract by active or passive transport into the blood or lymph 6. Defecation: eliminating of indigestible substances by anus in feces
37. Name the three phases of gastric secretion and describe the characteristics of each.
1. cephalic (reflex phase) -occurs before food enters the -triggered by the aroma, taste, sight, or thought of food, and it gets the stomach ready for its upcoming digestive chore. -Sensory inputs from olfactory receptors and taste buds are relayed to the hypothalamus --> hypothalamus stimulates the vagal nuclei of the medulla oblongata --> transmits motor impulses via the vagus nerves to parasympathetic enteric ganglia --> stimulate the stomach glands 2. gastric phase -initiated by local neural and hormonal mechanisms -important stimuli are distension, peptides, and low acidity -Stomach distension activates stretch receptors and initiates both local (myenteric) reflexes and long (vagovagal) reflexes. -in the long type of reflex, impulses travel to the medulla and then back to the stomach via vagal fibers. -Both types of reflexes lead to acetylcholine (ACh) release --> stimulates the output of more gastric juice. - hormone gastrin probably plays a BIG role in stimulating stomach gland secretion during the gastric phase. ---Chemical stimuli provided by partially digested proteins, caffeine, and rising pH directly activate gastrin-secreting entero-endocrine cells called G cells in the stomach antrum. -Gastrin stimulates the release of enzymes, but its main target is the HCl-secreting parietal cells, which it prods to spew out even more HCl --> rise in pH stimulates gastrin secretion and subsequently HCl release --> provides the acidic conditions needed to digest proteins (more protein, the greater the amount of gastrin and HCl released) -As proteins are digested, the gastric contents gradually become more acidic, which again inhibits the gastrin-secreting cells. This negative feedback mechanism helps maintain optimal pH and working conditions for gastric enzymes. 3. intestinal phase -stage has two components—stimulatory and inhibitory -the excitatory aspect is set into motion as partially digested food fills the initial part (duodenum) of the small intestine --> stimulates intestinal mucosal cells to release intestinal (enteric) gastrin, a hormone that encourages the gastric glands to continue their secretory activity.
21. Describe the swallowing reflex -noting especially the stimuli which trigger swallowing and the motor responses involved.
1. during the buccal phase, the upper esophageal sphincter is contracted. The tongue presses against the hard palate, forcing the food bolus into the oropharynx. 2. the pharyngeal-esophageal phase begins as the uvula and larynx rise to prevent food from entering respiratory passageways. The tongue blocks off the mouth. The upper esophageal sphincter relaxes, allowing food to enter the esophagus. 3. the constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts after food enters 4. peristalsis moves food through the esophagus to the stomach 5. the gastroesophageal sphincter surrounding the cardial oriface opens, and food enters the stomach LOOK AT PHOTO
88. How is water absorbed in the GI tract?
95% absorbed in small intestine by osmosis Rest absorbed in large intestine o Leave 0.1L for feces Water move freely in both directions but net osmosis occurs when there is a concentration gradient due to the active transport of solutes (esp Na+) into the mucosal cells. Water is coupled to solute uptake
47. Describe the pathway pancreatic juice follows as it travels from acinar cells to the duodenum.
Acini (clusters of secretory acinar cells surrounding ducts) are full of rough ER and have zymogen granules containing inactive digestive enzymes the pancreatic juice drains from the pancreas --> through the main pancreatic duct --> pancreatic duct fuses with bile duct as it enters duodenum --> smaller accessory pancreatic duct empties directly into the duodenum just proximal to the main duct
60. How is bile release regulated?
Bile salts secreted by enterohepatic circulation --> enhanced bile secretion Secretin released by intestinal cells exposed to fatty chime --> stimulates liver cells to secrete bile. acidic, fatty chyme enters the duodenum --> releases cholecystokinin (CCK) --> (1) gallbladder contraction (2) stimulates secretion of pancreatic juice and (3) relaxes the hepatopancreatic sphincter so that bile and pancreatic juice can enter the duodenum.
56. From what breakdown product are bile pigments derived?
Bilirubin - waste product of heme during breakdown of hemoglobin
42. Explain the mechanism of vomiting (emesis).
Bloodborne molecules and sensory impulses stream from the irritated sites to the emetic center of the medulla --> initiate a number of motor responses --> diaphragm and abdominal wall muscles contract --> increasing intra-abdominal pressure, the gastroesophageal sphincter relaxes, and the soft palate rises to close off the nasal passages --> the stomach (and perhaps duodenal) contents are forced upward through the esophagus and pharynx and out the mouth
48. How is the secretion of pancreatic juice regulated?
CCK, released in response to proteins and fats in chime --> stimulates the acini to release enzyme-rich pancreatic juice, and potentiates the effect of secretin CCK (1) stimulates secretion of pancreatic juice and (2) relaxes the hepatopancreatic sphincter so that bile and pancreatic juice can enter the duodenum --> both secretin and cholecystokinin prompt the pancreas to secrete its juice --> released in response to the presence of HCl in the intestine --> targets the pancreatic duct cells --> resulting in a watery bicarbonate-rich pancreatic juice. LOOK AT PICTURE
70. Describe the stimulus for secretion and the main action(s) of each of the following hormones: gastrin, secretin, and CCK.
CCK: -secreted in response to proteins and fats in chyme -Action: inhibits stomach's secretory activity, increases pancreatic juice secretion, stimulates gallbladder to contract and release bile, and relaxes hepatopancreatic sphincter Gastrin: -Stimulus: food in stomach and acetycholine released by nerve fibers -Action: increase HCl secretion (by parietal cells), stimulates gastric emptying, stimulates contraction of intestinal muscle, relaxes ileocecal valve, stimulates mass movements Secretin: -Stimulus: acidic chyme (HCl in duodenum) and partially digested fats and proteins -Action: inhibits gastric gland secretion and gastric motility, increases output of pancreatic juice (biocarbonate), potentiates CCK's action, increases bile output
81. What are the digestive end products of each of the dietary macronutrients listed above (#78)?
Carbohydrates o Polysaccharides: glycogen, starch (60%) Cannot digest cellulose (help move food by providing bulk or fiber) o Disaccharides: sucrose (table sugar), lactose (milk sugar), and maltose (grain sugar) o Monosaccharides: glucose (80%), fructose, galactose Proteins o Proteins digested not only include dietary proteins but also enzymes and mucosal cells o Digest to amino acid monomers o Some dipeptides or tripeptides Lipids o Triglycerides are the most abundant fats in the diet o Products are monoglycerides and 2 fatty acids
79. What enzymes are involved in the hydrolysis of each of the above nutrients (#78)? In what regions of the GI tract are each of these enzymes active?
Carbohydrates o Salivary amylase - in the mouth as saliva o Pancreatic amylase - in the small intestine o Dextrinase and glucoamylase - intestinal brush border enzyme o Maltase, sucrose, lactase - intestinal brush border enzyme as well Proteins o Pepsinogen --> Pepsin (10-15% of hydrolysis) - in the stomach by chief cells (Rennin - enzyme that coagulates milk protein but not in adults) o Proteolytic enzymes - in the small intestine 1. Trypsin and chymotrypsin secreted by pancreas 2. Carboxypeptidase - pancreatic and brush border enzyme that splits carboxyl group 3. Aminopeptidase - brush border enzyme that digest protein one at a time starting from amine group Lipids o Linguinal lipase in the mouth o Gastric lipase - stomach o Pancreatic lipase - in the small intestine 1. Not enzyme but bile salts in the duodenum
82. How are each of these digestive end products absorbed?
Carbohydrates: monosaccharides absorbed by facilitated diffusion and Na+- linked cotransport -fructose = facilitated diffusion -glucose and galactose = Na+ linked cotransport monosaccharides move across the basolateral membrane via facilitated diffusion, then diffuse into the capillary blood Protein: 1. primary site of small peptide absorption is duodenum and jejunum a. involves H+ linked secondary active transport b. H+ - Na+ exchanges in the brush border membrane maintain the H+ gradient c. peptidases within the epithelial cells break down most of the peptides --> single amino acids d. absorption across basolateral membrane involves is by either simple or facilitated diffusion 2. ileum is the most active site of amino acid uptake a. amino acids are transported across the brush border via several types of mechanism -- mostly involving Na+ linked secondary active transport b. absorption across basolateral membrane involves is by either simple or facilitated diffusion Lipids: 1. end products of lipid digestion interact with bile salts to form micelles 2. micelles carry lipid digestive products to brush border for absoption 3. inside mucosal ET cells, triglycerides are resynthesized: 2 FAs + MGs --> TGs 4. TGs are combinied with other lipid materials, coated with lipoproteins and packaged by the Golgi apparatus --> chylomicrons 5. chylomicrons are ejected from the epithelial cells by exocytosis - diffuse into the lacteals 6. carried to systemic circulation via lymphatics 7. endothelium of systemic capillaries in adipose tissue, muscle and heart contains lipoprotein lipase a. hydrolyzes TGs b. these products diffuse into cells -- used for E, or stored as fat c. chylomicron remnants circulate to liver for further metabolism
23. Name and locate the main regions of the stomach.
Cardial Part: small ("near the heart"), surrounds the cardial orifice through which food enters the stomach from the esophagus Fundus: dome-shaped part, tucked beneath the diaphragm, that bulges superolaterally to the cardia Body: midportion of the stomach, continuous inferiorly with the superior area of the pyloric part Pyloric Part: wider more superior area, pyloric antrum narrows to form pyloric canal which terminates at the pylorus which is continuous with pyloric sphincter
43. Describe causes and effects of vomiting.
Causes: extreme stretching of the stomach or intestine or irritants such as bacterial toxins, excessive alcohol, spicy foods, and certain drugs. Effects: Excessive vomiting can cause dehydration and severely disrupt the body's electrolyte and acid-base balance. Since large amounts of HCl are lost in vomitus, the blood becomes alkaline as the stomach attempts to replace its lost acid.
72. Name and locate the four main regions of the large intestine.
Cecum: (first part) lies below the ileocecal valve in the right iliac fossa o Appendix: attached to the posteromedial surface of the cecum (blind, wormlike) Contains masses of lymphoid tissue and as part of MALT, helps immunity -Storehouse for bacteria and recolonizes gut when needed -Twisted structure ideal location for enteric bacteria to accumulate and multiply Colon: o Ascending Colon: travels up the right side of the abdominal cavity to the level of the right kidney -Makes right turn (right colic (hepatic) flexure) and travels across abdominal cavity to transverse colon o Transverse Colon: directly anterior to the spleen -Bends at the left colic (splenic) flexure and becomes descending colon -Intraperiotoneal - anchored to the posterior abdominal wall by mesentery sheets (mesocolons) o Descending Colon: descends down the left side of the posterior abdominal wall o Sigmoid colon: it enters pelvis and becomes S-shaped -Intraperiotneal - anchored to posterior abdominal wall by mesentery sheets (mesocolon) Rectum: sigmoid colon joins rectum at level of the third sacral vertebra, runs posteroinferiorly just in front of the sacrum o The position allows rectal exam o Three lateral curves or bends, represented internally as three transverse folds called rectal valves -Rectal valves stop feces from being passed along with gas The anal canal: (last segment) lies in the perineum, entirely external to the abdominopelvic cavity o Beings where rectum penetrates the levator ani muscle of the pelvic floor and opens to the body exterior at the anus o Two sphincters - involuntary internal anal sphincter composed of smooth muscle -Voluntary external anal sphincter composed of skeletal muscle -Act like purse strings to open and close anus, ordinarily closed except during defecation
38. Identify the stimuli which trigger each of the phases of gastric secretion.
Cephalic: triggered by the aroma, taste, sight, or thought of food Gastric: Triggered by distension, peptides, and low acidity Intestinal: partially digested food fills the duodenum of the small intestine
59. Name the ducts which converge to form the hepatopancreatic ampulla, the duct that conducts both bile and pancreatic juice into the duodenum
Common bile duct and main pancreatic duct
58. Name the ducts which converge to form the common bile duct.
Common hepatic duct and cystic duct
77. Describe the defecation reflex.
Defecation reflex: rectum usually empty, but mass movement forces feces into it, stretching the rectal wall o Parasympathetic reflex, mediated by the spinal cord, causes sigmoid colon and rectum to contract, and the internal anal sphincter to relax o Feces forced to anal canal o Messages reach the brain allowing to decide whether the external (voluntary) anal sphincter should open or remain constricted to stop passage of feces temporarily o Defecation delayed: reflex contractions end within seconds and rectal walls relax Next mass movement initiates the defecation reflex again until the person chooses to defecate o During defecation: muscles of the rectum contract to expel feces Closing the glottis and contracting diaphragm and abdominal wall muscles to increase intra-abdominal pressure Contract levator ani muscle - lifts anal canal superiorly Leaves the feces below the anus (PICTURE)
39. How is gastric secretion inhibited?
Depression - loss of appetite Highly acidic content (below pH2) Fight or flight response - sympathetic activation o Stress, fear, anxiety look at picture
11. How are motor impulses of the parasympathetic nervous system conducted to the GI tract? What is the general effect of parasympathetic input on digestive function?
Enhances digestive abilities Afferent visceral fibers -branches (motor fibers) of the in autonomic nervous system enter intestinal wall and synapse with neurons in the intrinsic plexuses.
10. What is the general function of the enteric nervous system?
Enteric nervous system: alimentary canal has own nervous supply - enteric neurons (regulate digestive system) o Semiautonomous o Make intrinsic nerve plexuses (ganglia interconnected by unmyelinated fiber tracts) found in the walls of the alimentary canal Submucosal and myenteric nerve plexuses Provide major nerve supply to GI tract wall and control motility (motion) - peristalsis and segmentation Segmentation and peristalsis involve pacemaker cells and local reflex arc between enteric neurons (automatic)
32. What cells of the gastric gland secrete gastrin? Why are these cells called enteroendocrine cells rather than exocrine cells?
G cells secrete gastrin o Enterodendocrine because they have secretions that act as paracrines (histamine and serotonin) and others that diffuse into the blood capillaries and influence several digestive system target organs
57. What organ stores bile between digestive periods?
Gall bladder
34. What is the function of each of the following components of gastric juice: HCl; pepsin; mucous.
HCl: activate pepsinogen, denature proteins and plant cell wall, kill bacteria Pepsin: digest proteins Infants - renin (enzyme that acts on milk production) Mucous: provide liquid, protect stomach wall against HCl and bacteria
74. Describe the motility patterns of the large intestine. What is the functional significance of each?
Haustral contractions: most movement seen in the colon o Slow segmenting movements (last 1 minute/ 30minute) o Sluggsh, short-lived, mostly inactive except when presented with food o Occur mostly in the ascending and transverse colon o Reflect local controls of smooth muscle within the walls of the individual haustra o Haustrum fills with food residue -->. distension stimulates muscle contraction --> propels luminal contents to next haustrum (movement also mix residue, help water absorption) Mass movements -long, slow-moving, but powerful contractile waves that move over large areas of the colon three or four times daily and force the contents toward the rectum. Segmenting movements; descending and sigmoid colon promote final desiccation (drying out) of feces o Stores feces until mass movements propel the feces into the rectum o Bulk, fiber, in the diet strengths colon contractions and softens feces
62. Identify the sphincter at the juncture of the ileum and the large intestine.
Ileocecal sphincter
12. How are motor impulses of the sympathetic nervous system conducted to the GI tract? What is the general effect of sympathetic input on digestive function?
Inhibits digestive abilities Afferent visceral fibers -branches (motor fibers) of the in autonomic nervous system enter intestinal wall and synapse with neurons in the intrinsic plexuses.
44. Describe the composition of pancreatic juice.
Mainly water, enzymes (proteases, amylase, lipase, nuclease) and electrolytes (bicarbonate ions) Pancreatic proteases (inactive form, activated in duodenum) - chymotrypsinogen and procaroxypeptidase Amylase, lipase, nuclease (active form but require ion or bile in intestinal lumen for optimal activity)
76. What are the functions of the large intestine?
Major digestive functions are to absorb most of the remaining water from indigestible food residues o Store the residues temporarily o Eliminate them from body as semisolid feces o Absorbs metabolites produced by resident bacteria as they avidly ferment carbohydrates not absorbed in the small intestine
75. What is the function of mass movements (mass peristalsis) and the gastrocolic reflex?
Mass movements: long, slow-moving but powerful contractile waves that move over large areas of the colon 3- 4 times daily and force the contents toward rectum o During or just after eating o Gastrocolic reflex: presence of food in the stomach activates it, propulsive
84. What is the difference between a micelle and a chylomicron?
Micelle: monoglyceride and fatty acid with bile salts and lecithin (phospholipid found in bile) o Collections of fatty elements with bile salts that polar (hydrophilic) ends face water and nonpolar (hydrophobic) form the core o There are cholesterol molecules and fat-soluble vitamins in the core o Easily diffuse between microvilli to come into close contact with apical cell surface Chylomicron: when fatty acids and monoglycerides enter the epithelial cell smooth ER converts them to triglycerides o Triglycerides combine with lecithin, other phospholipids, cholesterol, and coat with proteins to form water-soluble lipid droplets called chylomicrons o Dispatched to the golgi apparatus to process for exocytosis o Milk-white, large o Migrate to basolateral membrane and exocytosis o Enter permeable lacteals
1.Name in order the organs of the alimentary canal, beginning at the mouth.
Mouth --> pharynx --> esophagus --> stomach --> small intestine --> large intestine
28. Identify and describe the function of the secretory product(s) of each of the gland cells named above (#27).
Mucous neck cells: scattered in the "neck" and more basal regions of the glands, produce a thin, soluble mucus (function not understood) Parietal cells: simultaneously secrete hydrochloric acid (HCl) and intrinsic factor -structure provides a huge surface area for secreting H+ and Cl- into the stomach lumen -acidity also helps digest food by denaturing proteins and breaking down cell walls of plant foods -kill many of the bacteria ingested with foods -Intrinsic factor is a glycoprotein required for vitamin B12 absorption in the small intestine Chief cells: the cuboidal chief cells produce pepsinogen -when pepsin is present, it also catalyzes the conversion of pepsinogen to pepsin. -Chief cells also secrete lipases which account for about 15% of overall GI lipolysis. Enteroendocrine cells: release a variety of chemical messengers into the interstitial fluid of the lamina propria -ex. Histamine and serotonin: act as paracrines Somatostatin: act both as paracrines locally and as hormones that diffuse into the blood capillaries to influence several digestive system target organs Gastrin: plays essential roles in regulating stomach secretion and motility
83. Describe the mechanism of Na+-linked secondary active transport of nutrients. Is the ATP expenditure involved in this type of nutrient absorption a direct or indirect expenditure? Explain.
Na+/K+ pump stores energy that drives glucose (and galactose) uptake by creating a steep concentration gradient for Na+ entry into intestinal cells- as Na+ moves across the membrane through a membrane cotransporter protein, it drives glucose against its concentration gradient into the cells Indirect because ATP expenditure is to move Na+ from cell into capillary to create concentration gradient that brings nutrients with it
35. What is the most important digestive enzyme in gastric juice?
PEPSIN
45. Name and tell the function of each of the digestive enzymes secreted by the pancreas.
Pancreatic proteases (chymotrypsinogen and procarboxypeptidase)- digest proteins Amylase - digest starch and glycogen/ carbohydrates Lipase - digest lipids/ fats Nuclease - digest nucleic acids
46. Where and how are the protein-digesting enzymes named above (#45) activated?
Pancreatic proteases: produced and released in inactive form from pancreas o Activated in the duodenum by enteropeptidase (intestinal brush border protease) o Enteropeptidase activates trypsinogen into trypsin o Trypsin activates more trypsinogen and two other pancreatic proteases (procarboxypeptidase and chymotrypsinogen) to their active forms (carboxypeptidase and chymotrypsin)
30. Why is it necessary for parietal cells to expend energy (i.e., by H+/K+ proton pumps) in secreting H+?
Parietal cells have to expend energy in secreting H+ because H+ is being pumped against high concentration gradient
80. Pepsin and pancreatic proteases are secreted in an inactive form. How are each of these types of enzymes activate?
Pepsin: HCl exposure in stomach (pepsin also catalyze other pepsin) Pancreatic Proteases: activated by enterokinase (brush border enzyme) activating pepsin which activates chymotrypsin and carboxypeptidase
67. What role does each of the above enzymes (#66) play in nutrient digestion?
Peptidases: breakdown of proteins/ polypeptides --> amino acids Lipases: breakdown triglyceride --> monoglyceride + 2 F.A. Oligosaccharides: digest CHO composed of 3 or more simple sugars o A-dextrinase: breakdown dextrins o Glucoamylase: cleaves off free glucose molecule from complex sugar-based chains that form starch or from maltose Disaccharidases o Maltase: maltose --> glucose + glucose o Sucrase: sucrose --> glucose + fructose o Lactase: lactos --> glucose + galactose
6. In what way do each of the motility patterns (#5) contribute to the digestive process?
Peristalsis: o Alternating waves of contraction and relaxation of muscles in organ walls o Main effect to squeeze food along the tract but mixing occurs as well Segmentation: o Mixes with digestive juices and makes absorption more efficient by repeatedly moving food against intestinal wall
5. Identify and describe the two basic motility patterns of the alimentary canal.
Peristalsis: major means of propulsion that is involuntary (stomach and esophagus) Segmentation: Rhythmic local constrictions of the small intestine
17. Humans have two dentitions. What are they?
Primary and permanent dentitions
18. When do each of the dentitions normally begin to appear? At what age are they typically complete? When complete, how many teeth does each contain?
Primary: appear in 6 months, complete in 24 months, 20 teeth total Permanent: 32 teeth total, all teeth but third molar erupt by end of adolescence, third molar (wisdom teeth) emerge between 17 - 25
71. What effect does CCK have on secretory activity of the pancreas and gallbladder?
Relaxes hepatopancreatic sphincter so juice can enter duodenum Stimulatory and increase secretory activity o Pancreas: increase output of juice o Gallbladder: stimulate organ to contract
68. Describe the motility patterns of the small intestine.
Segmentation: intrinsic pacemaker cells in the circular smooth muscle layer initiate these segmenting movements --> contracting and relaxing rings of smooth muscle simply move the chyme backward and forward a few centimeters at a time -intensity of segmentation is altered by long and short reflexes, which parasympathetic activity enhances and sympathetic activity decreases, and by hormones -more intense the contractions, the greater the mixing, but the basic contractile rhythms of the various intestinal regions remain unchanged. Migrating motor complex: -segmenting movements wane and the duodenal mucosa begins to release the hormone motilin --> motilin blood levels rise --> peristaltic waves are initiated in the proximal duodenum --> each successive wave begins a bit more distally (pattern of peristaltic activity called the migrating motor complex (MMC)) --> process then repeats itself, sweeping the last remnants of the meal plus bacteria, sloughed-off mucosal cells, and other debris into the large intestine. - prevents bacteria in the large intestine from entering the small intestine.
87. How is sodium absorbed in the GI tract? Potassium?
Sodium: coupled with absorption of glucose and amino acids o Anions passively follow the electrical potential by sodium transport o Na+ actively pumped out by Na/K pump after entering those cells Potassium: move passively by facilitated diffusion (leaky tight junctions) in response to changing osmotic gradients o As water is absorbed from lumen and rising potassium levels in chyme create a concentration gradient for absorption. o Anything that interferes with water absorption reduces potassium absorption but also pulls potassium from interstitial space into intestinal lumen
2. Name and describe the general function of the accessory digestive organs.
Teeth (oral cavity): mechanical breakdown (tear and grind food), mastication(chewing) Tongue: grips the food and constantly repositions it between the teeth. -initiates swallowing by pushing the bolus posteriorly into the pharynx -helps us form consonants (k, d, t, and so on) when we speak. -houses taste buds Salivary glands: secretes saliva with salivary amylase which breaks down starches but also compacts food into bolus Pancreas: secretes pancreatic juices, specifically amylase Liver: secretes bile Gall bladder: stores bile which emulsifies fat
22. What are the functions of the stomach?
Temporary "storage tank" where chemical breakdown of proteins begins Food converted to creamy paste (chime)
73. Describe the teniae coli and haustra.
Teniae coli: except for terminal end, the longitudinal muscle layer of muscularis is reduced to three bands of smooth muscle Haustra: their tone puckers the wall of the large intestine into pocketlike sacs
8. Identify the main blood vessels of the splanchnic circulation. What organs are served by each of the blood vessels named?
The arterial supply - the branches of the celiac trunk: serve spleen, liver, and stomach Mesenteric arteries: serve large and small intestine
20. What purpose is served by the lower esophageal sphincter?
The cardial orifice is surrounded by a gastroesophageal/cardiac sphincter o Physiological sphincter (thick circular smooth muscle that acts as a sphincter) o Muscular diaphragm surrounding the sphincter helps keep it closed o Mucous cells on both sides of the sphincter protect it from reflux of stomach acid Prevent backflow and protect from stomach acid
40. What is the enterogastric reflex, and how is it triggered?
a trio of reflexes that (1) inhibit the vagal nuclei in the medulla (2) inhibit local reflexes (3) activate sympathetic fibers that cause the pyloric sphincter to tighten and prevent further food entry into the small intestine. triggered by distension of duodenum, presence of fatty, acidic, or hypertonic chyme; and or irritants in the duodenum
33. Describe the composition of gastric juice.
acidic mucus, HCl and intrinsic factor, pepsinogen
31. How does HCl secretion by parietal cells produce the alkaline tide into the systemic blood?
as H+ is pumped from the cell and HCO3- (bicarbonate ion) accumulates within the cell HCO3- is ejected through the basolateral cell membrane into the capillary blood blood draining from the stomach is more alkaline than the blood serving it. ask evie what this means lul
63. What structural modifications increase the internal surface area, and thus the absorptive ability, of the small intestines?
circular folds, villi, and microvilli
24. What is the function of the pyloric sphincter?
controls stomach emptying
61. Name and locate the three regions of the small intestine.
duodenum: curves around the head of the pancreas, is about 25 cm (10 inches) long jejunum: about 2.5 m (8 ft) long, extends from the duodenum to the ileum ileum: approximately 3.6 m (12 ft) in length, joins the large intestine at the ileocecal valve. -hang in sausagelike coils in the central and lower part of the abdominal cavity, suspended from the posterior abdominal wall by the fan-shaped mesentery -large intestine encircles these more distal parts of the small intestine
53. Name the two sources of blood supply to the liver. Describe the hepatic circulation.
hepatic artery (supplying oxygen-rich arterial blood to the liver) hepatic portal vein (carrying venous blood laden with nutrients from the digestive viscera) -liver --> bile --> small intestine --> enterocyte absorption --> enterocytes to liver
52. What three structures comprise a portal triad?
hepatic artery, hepatic portal vein, bile duct
7. What is the splanchnic circulation?
includes those arteries that branch off the abdominal aorta to serve the digestive organs and the hepatic portal circulation
85. How are chylomicrons carried from the intestines to the systemic circulation?
lacteals
50. What organ produces bile?
liver
14. What is a mesentery? Describe the difference between intraperitoneal and retroperitoneal.
mesentery: a double layer of peritoneum—a sheet of two serous membranes fused back to back—that extends to the digestive organs from the body wall. -provide routes for blood vessels, lymphatics, and nerves to reach the digestive viscera; hold organs in place; and store fat -Intraperitoneal: keep their mesentery and remain in the peritoneal cavity (digestive organs (stomach)) -Retroperitoneal: Organs that lose their mesentery and come to lie posterior to the peritoneum because some regions of the small intestine adhere to the dorsal abdominal wall during development (most of the pancreas, duodenum, parts of the large intestine)
25. Name the simple columnar ET cells which line the stomach and describe their function(s).
mucous cells: produce a cloudy, protective two-layer coat of alkaline mucus in which the surface layer consists of viscous, insoluble mucus that traps a layer of bicarbonate-rich fluid beneath it.
4. Identify and describe the four tissue layers of the alimentary canal wall.
mucous membrane (mucosa): -the innermost layer -a moist epithelial membrane that lines the alimentary canal lumen from mouth to anus -major functions are to: ■Secrete mucus, digestive enzymes, and hormones ■Absorb the end products of digestion into the blood ■Protect against infectious disease -digestive mucosa consists of three sublayers: (1) a lining epithelium, (2) a lamina propria -loose areolar connective tissue -its capillaries nourish the epithelium and absorb digested nutrients -help defend us against bacteria and other pathogens (3) a muscularis mucosae -smooth muscle cells that produces local movements of the mucosa -in the small intestine increases its surface area. -epithelium of the mucosa is a simple columnar epithelium rich in mucus-secreting cells. -produces protects certain digestive organs from being digested by enzymes working within their cavities and eases food passage along the tract. Submucosa: -external to the mucosa -areolar connective tissue -contains a rich supply of blood and lymphatic vessels, lymphoid follicles, and nerve fibers which supply the surrounding tissues of the GI tract wall. -elastic fibers enable the stomach to regain its normal shape after temporarily storing a large meal. Muscularis externa: -responsible for segmentation and peristalsis -has an inner circular layer and an outer longitudinal layer of smooth muscle cells -in places along the tract, the circular layer thickens, forming sphincters that act as valves to control food passage from one organ to the next and prevent backflow. Serosa: -the outermost layer of the intraperitoneal organs, -it is usually formed of areolar connective tissue covered with mesothelium (a single layer of squamous epithelial cells) -In esophagus, called adventitia (ordinary fibrous connective tissue that binds the esophagus to surrounding structures.)
27. Identify the three types of exocrine gland cells located in the gastric glands.
mucous, parietal, chief
66. Name the brush border enzymes and describe their location.
peptidases lipases oligosaccharides: dextrinase and glucoamylase disaccharides location in the apical membrane of the microvilli
89. Where along the GI tract is the greatest amount of water absorbed?
small intestine
9. Name and locate the two nerve plexuses that make up the enteric nervous system.
submucosal nerve plexus: occupies the submucosa myenteric nerve plexus: lies between the circular and longitudinal muscle layers of the muscularis externa
13. Distinguish between the following serous membranes: visceral peritoneum, parietal peritoneum, mesentery, greater omentum, lesser omentum, mesocolon.
visceral peritoneum: covers the external surfaces of most digestive organs and is continuous with the parietal peritoneum that lines the body wall parietal peritoneum: lines the body wall, continuous with visceral peritoneum Mesentery: double layer of peritoneum (sheet of two serous membranes fused) that extends to the digestive organs from the body wall o Provide routes for blood vessels, lymphatics, and nerves to reach the digestive viscera, hold organs in place, and store fat o Most places mesentery is dorsal and attaches to posterior abdominal wall greater omentum: hangs down over small intestine and goes up to join with colon - double layer Lesser omentum: under the liver to the lesser curvature of the stomach then splits Mesocolon: dorsal mesentery that secures the large intestine to the parietal peritoneum of the posterior abdominal wall
29. Describe the mechanism by which parietal cells secrete HCl into the gastric juice.
when parietal cells are stimulated, H+ is actively pumped into the stomach lumen against a tremendous concentration gradient by H+ -K+ -ATPases in exchange for K+ ions that move into the cell then cycles back into the lumen via K+ channels. -Cl- follow H+ into the lumen to maintain an electrical balance in the stomach, completing the process of HCl secretion.
54. Describe the composition of bile.
yellow-green, alkaline solution containing bile salts, bile pigments, cholesterol, triglycerides, phospholipids (lecithin and others), and a variety of electrolytes.
