The Digestive System

6. In what way do each of the motility patterns (#5) contribute to the digestive process?

- Peristalsis - propels food along the tract with some mixing - Segmentation - churns and mechanically digests food; Segmentation mixes food with digestive juices and makes absorption more efficient by repeatedly moving different parts of the food mass over the intestinal wall.

20. What purpose is served by the lower esophageal sphincter?

- also called cardiac sphincter and gastroesophageal sphincter -it is a physiologic sphincter in that it acts as a sphincter but the only structural evidence of this sphincter is a slight thickening of the circular smooth muscle at that point. the muscular diaphragm, which surrounds this sphincter, helps keep it closed when food is not being swallowed. - relaxes to allow bolus to be propelled into stomach - usu. tonically constricted to prevent gastric juice reflux ***Mucous cells on both sides of the sphincter help protect the esophagus from reflux of stomach acid

70. Describe the stimulus for secretion and the main action(s) of each of the following hormones: gastrin, secretin, and CCK

*CCK: stimulus: fatty chyme and partially digested proteins action: inhibits stomach secretion SO I GUESS IT IS ALSO INHIBITORY LIKE SECRITIN?, Potinates secretins actions on organs (liver), increases output of enzyme ricH pancreatic juice (pancreas), stimulates explosion of bile (gallbladder) , relaxes sphincter (bile- duodenum), stimulates insulin release *Gastrin: stimulus: food in stomach, ACh released by nerves action: increases in HCl production (stomach), contraction of intestinal muscle (small intestine), relaxes ileocecal valve, stimulates mass movements (large intestine) *Secretin: WHILE CCK IS INHIBITORY THIS IS THE ONLY ONE THAT LIKE STOPS THINGS - CCK INHIBITS GASTRIC EMPTYING AND INCREASES BILE SECRETION AND PANCREATIC DIGESTIVE ENZYMES - SO PROMOTES DIGESTION - KINDA SAME WITH GASTRIN - STARTS THE MASS MOVEMENTS BUT ISN'T TRYNA ACTUALLY REVERSE THINGS LIKE SECRETIN IS THE GIVING MORE BICARBONATE TO RAISE PH stimulus: food in stomach action: inhibits gastric gland (stomach) , activity and gastric motility, increases bile output (liver), increases output of bicarb rich pancreatic juice (pancreas) BOTH SECRETIN AND CCK INCREASE BILE THOUGH

72. Name and locate the four main regions of the large intestine.

*cecum- lies below ileocecal valve in the right iliac fossa *appendix- attached to the posteriomedial surface of cecum *colon- throughout abdominal cavity *rectum- in pelvis, runs posteriorinferiorly just in front of the sacrum *anal canal- lies in the perineum, external to the abdominopelvic cavity

33. Describe the composition of gastric juice.

*it is corrosively acidic - the secretions of the mucous neck, parietal, and chief cells - mucous neck - acidic mucous - parietal - HCL and intrinsic factor for vit B12 digestion - chief cells - pepsinogen; activated by HCl, then self activates (positive feedback cycle) so, basically: secretion of the exocrine cells: acidic mucus, HCl & intrinsic factor, and pepsinogen

15. Describe the composition and function(s) of saliva.

- Composition - mosly H2O, dissolved solutes (electrolytes, digestive enzymes of salivary amylase, and lingual lipase, proteins of mucins, lysozyme, and IgA, defensins, and metabolic wastes of urea and uric acid); slightly acidic -functions: cleanses the mouth, dissolves food chemicals so they can be tasted, moistens food and helps compact it into a bolus, contains the enzyme amylase that begins the digestion of starchy foods

5. Identify and describe the two basic motility patterns of the alimentary canal.

- peristalsis - propelling motion produced by alternate waves of contraction and relaxation of muscles in tract wall (major means of propulsion) - Segmentation - (rhythmic local constrictions of the small intestine).

8. Identify the main blood vessels of the splanchnic circulation. What organs are served by each of the blood vessels named?

- arterial supply: branches of the celiac trunk that serve the spleen/liver/stomach, mesenteric arteries that serve the small/large intestine - hepatic portal circulation: collects nutrient-rich venous blood draining from the digestive viscera and delivers it to the liver

29. Describe the mechanism by which parietal cells secrete HCl into the gastric juice.

- b/c it's a strong acid, the H and the Cl- need to be secreted separatly into the stomach lumen - how this happens: CO2 + H2O =H2CO3 which breaks down into HCO3- + H+ - the H+ is pumped into the stomach lumen by a H+/K+ ATPase pump; the K just leaks back out of cell - the HCO3- is transported into the blood by a HCO3-/Cl- pump and that is what pumps the Cl into the stomach from the blood (replaces the bicarb)

82. How are each of these digestive end products absorbed? CAPS ARE THE IMPORTANT STUFF IMO

- carbs: glucose and galactose are absorbed via cotransport with Na ions (Na-linked transport-secondary transport) - out of epithelia via facilitated transport, fructose passes via facilitated diffusion (gets transported along basolateral membrane into blood also moves into cell via facilitated diffusion); all monosaccharides leave the epithelial cells via facilitated diffusion, ENTER CAPILLARY BLOOD IN VILLI, and are transported to liver via hepatic portal vein - proteins: most active site for AA uptake is the ileum. the aa's are usually transported across brush border via Na linked active transport; other small peptides, primary sites for absorption are the duodenum and jejunum. This H+ -linked secondary active transport, as opposed to Na-linked active transport in ileum. In duodenum and jejunum, the H-Na exchanges maintain the H concentration in brush border; absorption across basolateral membrane usually simple or facilitated diffusion ABSORBED BY CAPILLARY BLOOD IN VILLI TOO - I THINK MORE THAN SUGARS ARE - THE FAT HEADS TO LYMPHATIC SYSTEM - lipids: fatty acids and monogycerides enter intestinal cells via diffusion; fatty acids and monoglycerides are recombines to form triglycerides and then combined with other lipids and proteins within cells. The resulting chylomicrons are extracted by exocytosis. The chylomicrons enter the lacteals of the villi and are transported to the systemic circulation via the lymph in the thoracic duct; some short chain fatty acids are absorbed - CHILOMICRONS FROM FAT DIGESTION ENTER LACTEALS OF VILLI AND ARE CARRIED BY LIPOPROTEIN SO CARRIERS ARE NA TWICE THEN LIPOPROTEINS

23. Name and locate the main regions of the stomach.

- cardial part of cardia ("near the heart") - surrounds the cardial orifice through which food enters the stomach from the esophagus - fundus - dome-shaped and beneath the diaphragm; bulges superolaterally to the cardia - body - mid portion of the stomach; main part; continuous inferiorly with the funnel-shaped pyloric part -the wider and more superior area of the pyloric part, the pyloric antrum, narrows to form the pyloric canal, which terminates at the pylorus. The pylorus is continuous with the duodenum through the pyloric sphincter or valve.

77. Describe the defecation reflex

- eliminates feces from the body - parasympathetic reflex, mediated by the spinal cord, causes the sigmoid colon and the rectum to contract and the internal anal sphincter relaxes; as feces are forced into the anal canal, messages reach the brain allowing us to decide whether the external (voluntary) anal sphincter should open or remain constricted to stop passage of feces temporarily. - if delayed, reflex contractions end w/in a few seconds, rectal walls relax - mass movement can initiate it until the person chooses to defecate or is unable to resist the urge

69. Identify the neural and hormonal factors which regulate movement of food residue into from the ileum into the cecum.

- gastroileal reflex (n): a long reflex triggered by stomach activity, increases the force of segmentation in the ileum and relaxes the sphincter - (h) gastrin released by the stomach increases the motility of the ileum and relaxes the ileocecal sphincter

14. What is a mesentery? Describe the difference between intraperitoneal and retroperitoneal.

- mesentery = a fused double layer of parietal peritoneum; functions to connect visceral and parietal peritoneun, anchor organs, encase lymphatics, blood vessels and nerves - intraperitoneal - digestive organs (like the stomach) that keep their mesentery and remain in the peritoneal cavity - retroperitoneal organs - adhere to dorsal abdominal wall: in doing so, the lose their mesentery and come to lie posterior to the peritoneum.; have no surrounding mesentery (some parts of small intestine and large intestine, most of pancreas and duodenum)

71. What effect does CCK have on secretory activity of the pancreas and gallbladder?

- pancreas: increases output of enzyme-rich pancreatic juice - gallbladder: stimulates organ to contract and expel stored bile

80. Pepsin and pancreatic proteases are secreted in an inactive form. How are each of these types of enzymes activated?

- pepsin: chief cells produce pepsinogen (inactive form of pepsin); pepsinogen comes together with HCL to produce the pepsin and HCL is secreted by parietal cells making the stomach extremely acidic; HCL and pepsinogen meet in apical region of the gland; once pepsin is activated also helps to activate more of pepsinogen; activation involves removing a single peptide from the pepsinogen, causes it to change shape and exposes its active site (it is positive feedback) - only limited by amount of pepsinogen available - pancreatic proteases: enteropeptidase activates trypsinogen into trypsin and trypsin activates more trypsinogen and other proteases of the pancreas to activate chymotrypsin and carboxypeptidase.

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: around 6 months, additional pairs erupt 1 to 2 month intervals until 24 months, 20 milk teeth - permanent: loosen and fall between 6 to 12 years, third molars (wisdom teeth) emerge around 17-25, usually 32 permanent teeth but wisdom teeth can sometimes not erupt or are absent

30. Why is it necessary for parietal cells to expend energy (i.e., by H+/K+ proton pumps) in secreting H+?

- they have to secrete HCl separatly (as H and Cl) into the stomach lumen - they are pumping H+ against its concentration gradient (has to be actively pumped), to create a strong acid in the stomach

84. What is the difference between a micelle and a chylomicron?

-As the water-insoluble products of fat digestion---the monoglycerides and free fatty acids---are liberated by lipase activity, they quickly become associated with bile salts and lecithin (a phospholipid found in bile) to form micelles. Micelles are collections of fatty elements clustered together with bile salts in such a way that the polar (hydrophilic) ends of the molecules face the water and the non polar portions form the core. Also nestled in the hydrophobic core are cholesterol molecules and fat-soluble vitamins. Without micelles, the lipids would simply float on the surface of the chyme (like oil on water), inaccessible to the absorptive surfaces of the epithelial cells. -Once the free fatty acids and monoglycerides enter the epithelial cells, the smooth ER converts them back into triglycerides. The triglycerides are then combined with lecithin and other phospholipids and cholesterol, and coated with a "skin" of proteins to form water-soluble lipoprotein droplets called chylomicrons. (milky-white and very large)

34. What is the function of each of the following components of gastric juice: HCl; pepsin; mucous.

-HCl : makes stomach remain at low pH to kill ingested microorganisms, denature ingested proteins in food (HCL + pepsinogen = pepsin) -pepsin: protein digestive enzyme, only active at a low pH; begins protein digestion by cleaving off single AAs @ end of polypeptide strands -mucous: protects the lining of the stomach from acidity

87. How is sodium absorbed in the GI tract? potassium?

-Na is absorbed along the entire length of the intestine. Absorption of Na ions in the small intestine is coupled to active absorption of glucose and amino acids. For the most part, anions passively follow the electrical potential established by Na transport. In other words, Na is actively pumped out of the epithelial cells by a Na-K pump after entering those cells. Usually, chloride ions passively follow Na. In the terminus of the small intestine, HCO3- is actively secreted into the lumen in exchange for Cl-. -K ions move across the intestinal mucosa passively by facilitated diffusion (or leaky tight junctions). As water is absorbed from the lumen, rising K levels in chyme create a concentration gradient for its absorption (it becomes more concentrated)...it can then be easily absorbed by simple diffusion. Anything that interferes with water absorption (resulting in diarrhea) not only reduces K absorption but also "pulls" K from the interstitial space into the intestinal lumen. ; K may be other secreted or absorbed in the colon.

66. Name the brush border enzymes and describe their location.

-Peptidases (carboxy, amino, di) -Lipases Oligosaccharidases -digest CHO composed of 3 or more simple sugars -α-dextrinase -glucoamylase *Disaccharidases: 1. Maltase: Maltose → 2 Glucose 2. Sucrase: Sucrose → Glucose + Fructose 3. Lactase: Lactose → Glucose + Galactose -FOUND IN THE APICAL SURFACE OF THE MICROVILLI

45. Name and tell the function of each of the digestive enzymes secreted by the pancreas

-Proteases - break down proteins; activated in the duodenum where they do their work (protects the pancreas from digesting itself); enteropeptidase that activates the trypsinogen to trypsin and trypsin activates secondary enzymes -Amylase - digest CHO -Lipases - digest fats -Nucleases - digest nucleic acids

74. Describe the motility patterns of the large intestine. What is the functional significance of each?

-When food residue enters the colon through the ileocecal valve, the colon becomes motile, but its contractions are sluggish or short-lived compared to those of the small intestine. -The movements most seen in the small intestine are haustral contractions- slow, segmenting movements lasting one minute occurring every 30 minutes (occur mainly in the ascending and transverse colon); as a haustrum fills with food residue, the distention stimulates its muscle to contract. These movements mix the residue, which aids in water absorption. -mass movements (mass peristalsis)- slow moving, long but powerful contractile waves that move over large areas of the colon 3-4 times a day and force the contents toward the rectum stimulated by the gastrocolic reflex (occur during or just after eating)

19. Describe the structure and function of the esophagus.

-a muscular tube about 25 cm (10 in) long and is collapsed when not involved in food propulsion - cardiac/gastroesophaeal sphincter usually tonically constricted; only relaxes to swallow - only a passageway; no digestion occurs - courses through the mediastinum of the thorax and pierces the diaphragm at the esophageal hiatus to enter the abdomen, joins the stomach - has all 4 alimentary canal layers - mucosa contains a nonkeratinized stratified squamous epithelium - submucosa has esophageal glands - muscularis has skeletal, smooth, & a mix - has fibrous adventitia instead of serosa

1. Name in order the organs of the alimentary canal, beginning at the mouth.

-also called the gastrointestinal (GI) tract or gut, is the continuous muscular tube that winds through the body from the mouth to the anus. -include the mouth, pharynx, esophagus, stomach, small intestine, and large intestine -> leads to the terminal opening, or anus.

88. How is water absorbed in the GI tract?

-approximately 9L/day of water enters the GI tract-only about 100 mL/day is lost in the feces -water moves (in both directions) freely across the interstitial mucosa via osmosis...but net osmosis occurs whenever a concentration gradient is established by the active transport of solutes (particularly Na) into the mucosal cells. In this way, water uptake is effectively coupled to solute uptake, and, in turn, affects the absorption of substances that normally pass by diffusion. As water moves into mucosal cells, these substances follow along their concentration gradients. -water reabsorption is coupled to solute uptake

46. Where and how are the protein-digesting enzymes named above (#45) activated?

-enteropeptidase and trypsin are activated in the duodenum; Like pepsin of the stomach, pancreatic proteases are produced and released in inactive forms that are activated in the duodenum, where they do their work -amylase, lipase, nucleases - secreted in active form but require ions in bile in intestinal lumen in order to work optimally

31. How does HCl secretion by parietal cells produce the alkaline tide into the systemic blood?

-in the formation of HCL you have a build up of biccarbonate within the cell, the blood draining from the stomach is more alkaline (basic) than the blood serving it -as acid is pumped into the stomach, base (HCO3-) is exported into the blood (and CO3 goes into the stomach) -results in increased pH in the blood (basic/alkaline) and decreased pH in the stomach. This flow of base is called the alkaline tide.

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.

-indirect because ATP is needed to pull out the Na and glucose then moves along the concentration gradient into the cell -you are using the ATP to pull the Na out and then glucose nicely strolls along its gradient into (the glucose is a secondary effect)

3. Identify and describe the basic activities performed by the alimentary canal (e.g., ingestion) which aid the digestive process.

-ingestion: taking food into the digestive tract (eating) -propulsion: moves food through the alimentary canal, includes swallowing, which is initiated voluntarily, and peristalsis (alternating waves of contraction and relaxation of muscles in the organ walls - squeeze food along the tract), an involuntary process -mechanical breakdown: increases the surface area of digested food, physically preparing it for digestion by enzymes. Mechanical processes include chewing, mixing food with saliva by the tongue, churning food in the stomach, and segmentation (rhythmic local constrictions of the small intestine). Segmentation mixes food with digestive juices and makes absorption more efficient by repeatedly moving different parts of the food mass over the intestinal wall. -digestion: involves a series of catabolic steps in which enzymes secreted into the lumen (cavity) of the alimentary canal break down complex food molecules to their chemical building blocks -absorption: passage of digested end products (plus vitamins, minerals, and water) from the lumen of the GI tract through the mucosal cells by active or passive transport into the blood or lymph -defecation: eliminates indigestible substances from the body via the anus in the form of feces

10. What is the general function of the enteric nervous system?

-is the in-house nerve supply of the alimentary canal; it is staffed by enteric neurons that communicate widely with one another to regulate digestive system activity -the enteric nervous system participates in both short and long reflex arcs that help provide optimal digestive conditions (via osmo, chemo and mechano receptors)

51. Describe the histological organization of liver lobules.

-liver is composed of sesame seed sized structure called lobules. each lobule is roughly hexagonal (6-sided) consisting of plates of liver cells (hepatocytes), organized like bricks in a garden wall. The hepatocyte plates radiate outward from a central vein running in the longitudinal axis of the lobule. at each of the six corners of a lobule there is a portal triad

49. What are the functions of the liver?

-produce bile for export to the duodenum (digestive role) -(bile-> fat emulsifier that breaks down fat into tiny particles to make them more readily digestible) -the liver also processes nutrient-laden venous blood delivered to it from the digestive organs (metabolic role)

9. Name and locate the two nerve plexuses that make up the enteric nervous system.

-submucosal nerve plexus (in the submucosa) -myenteric nerve plexus (lies between circular and longitudinal muscle layers of the muscularis externa) - Submucosal - coordinate/regulate movements of mucosa, vasoconstriction/dilation of local blood vessels; secretory function of glands - myenteric - regulating motility of tract walls; helps regulate glandular secretions in lumen

22. What are the functions of the stomach?

-temporary storage tank where chemical breakdown of proteins begins and food is converted to a paste called "chyme" - store food for gradual delivery to small intestine - mix food material with gastic juice (convert it to chyme)

40. What is the enterogastric reflex, and how is it triggered?

-the duodenum inhibits acid secretion in the stomach by short reflexes through the enteric nervous system and by long reflexes involving sympathetic and vagus nerves -consists of three reflexes coming together that 1) inhibit the vagal nuclei in the medulla 2) inhibit local reflexes 3) activate symp. fibers that cause the pyloric sphincter to tighten and prevent further food entry into the small intestine *acts as the brakes on gastric activity in order to protect the small intestines from excessive excessive acidity and helps match their ability to process with how much chyme is going inside, this happens when the intestine distends with H+, fats, partially digested proteins, and irritating substances.

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. -A mesentery is 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. (convex lateral surface of the stomach is its greater curvature and the concave medial surface of the stomach is its lesser curvature); extending from these two curvatures are the mesenteries/omentum (help tether the stomach to the other digestive organs against the body wall) -lesser omentum: a mesentary: runs from liver to the lesser curvature of the stomach it then meets the visceral peritoneum that covers the stomach -greater omentum: a mesentary: drapes inferiorly from the greater curvature of the stomach to cover the coils of the small intestine. wraps the spleen and the transverse portion of the large intestine. -mesocolon: dorsal mesentary: secures the large intestine to the parietal peritoneum of the posterior abdominal wall

37. Name the three phases of gastric secretion and describe the characteristics of each

1. (only a few minutes long) cephalic phase (reflex) occurs before food enters the stomach, the stomach begins to get ready after it gets triggered by aroma/taste/sight/thought of food. sensory input from olfactory and taste buds is taken to the hypothalamus, this stimulates the medulla oblongata which transmits motor impulses via the vagus nerves to parasympathetic, these neurons stimulate gastric glands, getting the stomach ready for its digestive chore. 2. gastric phase (3-4 hours and provides 2/3 of gastric juice released) food in the stomach: local neural and hormonal mechanisms initiate this phase. stimulation: stomach distention activates stretch receptors and initiates both short and long reflexes. in long reflexes, impulses travel to the medulla and then back to the stomach via vagal fibers. in both there is a release of ACh (acetylcholine), this stimualtes the release of more gastric juice. chemical stimuli provided by caffeine, partially digested proteins, and rising pH stimulate G cells which secrete gastrin. gastrin plays the largest role in the secretion of gastric juices. *the more protein, the more gastrin, the more hcl released* HCL needs all three messengers histamine, ACh, and gastrin *highly acidic gastric contents inhibit gastrin secretion (occurs between meals) 3. intestinal phase begins with a brief stimulatory component followed by inhibition stimulation: partially digested food fills the duodenum of the small intestine, stimulates intestinal mucous cells to release intestinal (enteric) gastrin, this hormone encourages the gastric glands to continue secretory activity. stimulatory effect is brief because it is overridden by inhibitory stimuli as the intestine fills (enterogastric reflex?). -release of entergogastrones (secretin, CCK, and VIP), →these also inhibit gastric secretions

28. Identify and describe the function of the secretory product(s) of each of the gland cells named above (#27).

1. Mucous neck cells: produce a thin, soluble and acidic mucus quite different from that secreted by the mucous cells of the surface epithelium; not understood what function the mucous performs 2. Parietal Cells: secrete HCl and intrinsic factor; HCl makes the stomach contents extremely acidic (1.5-3.5), a condition necessary for activation and optimal activity of the protein-digesting enzyme pepsin. The acidity also helps digest food by denaturing proteins and breaking down cell walls of plant foods, and is harsh enough to kill many of the bacteria ingested with foods. Intrinsic factor is a glycoprotein required for vitamin B12 absorption in the small intestine 3. Chief cells: the cuboidal chief cells produce pepsinogen, the inactive form of pepsin. when these cells are stimulated, the first pepsinogen molecules they release are activated by HCl encountered in the apical region of the gland. But once pepsin is present, it also catalyzed the conversion of pepsinogen to pepsin. Chief cells also secrete lipases (fat-digesting enzymes) that account for about 15% of all GI lipolysis

67. What role does each of the above enzymes (#66) play in nutrient digestion?

1. Peptidases—hydrolyze proteins from polypeptides to single AA 2. Lipase—hydrolyze fat to a triglyceride and 2 FA chains 3. Oligosaccharidase (a-dextrinase and glucoamylase): act on carbohydrates with three or more simple sugars 4. Disaccharides: - Maltase—breaks maltose into 2 glucose - Sucrase—breaks sucrose into glucose and fructose - Lactase—breaks lactose into glucose and galactose

52. What three structures comprise a portal triad?

1. branch of the hepatic artery proper (supplying oxygen rich blood to the liver) 2. branch of the hepatic portal vein (carrying venous blood laden with nutrients from the digestive viscera) 3. a bile duct

38. Identify the stimuli which trigger each of the phases of gastric secretion.

1. cephalic phase aroma, taste, sight, or toughts of food 2. gastric phase distension (activate stretch receptors), peptides, low acidity 3. intestinal phase distention in the duodenum of small intestine by partially digested food activates intestinal mucosal cells to secrete intestinal (enteric) gastrin STRETCH RECEPTORS IN SMALL INTESTINE INHIBIT STOMACH MUSCLES FROM SENDING MORE FOOD DOWN SI AS WELL

63. What structural modifications increase the internal surface area, and thus the absorptive ability, of the small intestines?

1. circular folds (plicae circularis) of the mucosa and submucosa- are deep, permanent folds. These folds force chyme to spiral through the lumen, slowing its movement and allowing time for full nutrient absorption 2. villi i.e. finger-like folds of intestinal mucosa; lamina propria of the villi contains extensive capillary network; in the core of each villus is a dense capillary bed and a wide lymphatic capillary called a lacteal. digested foodstuffs are absorbed through the epithelial cells into both the capillary blood and the lacteal. 3. microvilli cover lumenal surfaces of mucosa - create the brush border; long, densely packed cytoplasmic extensions of the absorptive cells of the mucosa that give the mucosal surface a fuzzy appearance called the brush border

4. Identify and describe the four tissue layers of the alimentary canal wall.

1. mucosa/mucous membrane - innermost layer, simple columnar ET EXCEPT FOR STRATIFIED SQUAMOUS AT MOUTH, ESOPHAGUS AND ANUS, it secretes mucus/digestive enzymes/hormones, absorbs the end products of digestion in the blood, protects against infectious disease; has 3 sublayers: lining epithelium, lamina propria, and a muscularis mucosae 2. submucosa: just external to the mucosa, areolar CT containing a rich supply of blood and lymphatic vessels, lymphoid follicles, and nerve fibers which supply the surrounding tissues of the GI tract wall; its abundant elastic fibers enable the stomach, for example, to regain its normal shape after temporarily storing a large meal 3. muscularis externa: surrounding the submucosa; responsible for segmentation and peristalsis; Has three layers of muscle - an innner oblique layer , a middle circular and an external longitudinal layer; In several layers along the tract, the circular layer thickens, forming spinchters that act as valves to control food passage from one organ to the next and prevent back flow. 4. serosa: outermost layer of the intraperitoneal organs, is the visceral peritoneum. Formed of areolar CT covered with mesothelium, a single layer of squamous epithelial cells. in the esophagus, the series is replaced by adventitia (ordinary dense CT that binds the esophagus to surrounding structures).

17. Humans have two dentitions. What are they?

1. primary dentition: consists of the deciduous teeth also called milk or baby teeth; the first teeth to appear, at about age 6 months, are the lower central incisors. Additional pairs of teeth erupt at one to two month intervals until about 24 months, when all 20 milk teeth have emerged 2. permanent dentition: they enlarge and develop and the roots of the milk teeth are resorbed from below

89. Where along the GI tract is the greatest amount of water absorbed?

95% in small intestine. nutrients too

81. What are the digestive end products of each of the dietary macronutrients listed above (#78)?

CHO-> monosaccharides with glucose as major one protein-> AA, dipeptides, tripeptides fats -> free fatty acids, monoglycerides, one fatty acid chain

85. How are chylomicrons carried from the intestines to the systemic circulation?

Chylomicrons are ejected from the epithelial cells by exocytosis because they are so big, and they diffuse into the lacteals. IVE FOUND THIS AND LIPOPROTEINS

41. What effect does the enterogastric reflex have on digestive activity (i.e., secretory activity and gastric motility)?

Decreases the secretion of the stomach and inhibits things from moving into the duodenum.

75. What is the function of mass movements (mass peristalsis) and the gastrocolic reflex?

During or right after eating, the presence of food in stomach activates the gastroileal reflex in small intestine and the propulsive gastrocolic reflex in colon. This initiates the mass movements (powerful contractile waves that move over large areas of colon 3 to 4 times a day that force contents toward rectum.

50. What organ produces bile?

LIVER

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?

Motor impulses of the PS nervous system are conducted to the GI tract via the vagus tract (vagus nerve). - "rest and digest"; increases motility and secretory activity of digestive system (aka enhances digestive activity)

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?

Motor impulses of the S nervous system are conducted to the GI tract via the greater and lesser splanchnic nerves (T1-T5 roots); inhibits digestive activity

78. Describe the chemical digestion of carbohydrates, proteins and lipids.

PICTURE -carbohydrates: 1. amylases (salivary start in the mouth and pancreatic in the duodenum) convert oligosaccharides to di or trisaccharides; 2. brush border enzymes in small intestine: the oligosaccharidases (dextrinase and glucoamylase) in the duodenum break down trisaccharides; and disaccharidases (maltase; sucrase; lactase) break down disaccharides; both end products are monosaccharides -proteins: begins in the stomach, hydrolysis: pepsin causes protein to break down into polypeptides (all in stomach); move into SI and pancreatic enzymes (enterokinase and trypsin): they break down polypeptides into small polypeptide chains; brush border enzymes (chymotrypsin and carboxypeptidase and the dipeptidase); they break down polypeptide chains into amino acids or di and tripeptides -lipids: lingual lipase (mouth) and gastric juice (stomach) limited digestion occurring with these two; there but have limited effect bc fat globules are too large at this point; most digestion in duodenum and jejunum (SI); bile salts break down fat globules from chyme; pancreatic lipases cleave/break down the fat globules even more; left with monoglycerides (glycerol) and free fatty acids

35. What is the most important digestive enzyme in gastric juice?

Pepsin

16. How is the secretion of saliva controlled?

Salivation is controlled primarily by the PNS of the ANS. When we ingest food, chemoreceptors and mechanoreceptors in the mouth send signals to the salivary nuclei in the brain stem (pons and medulla). As a result, PNS activity increases. Impulses sent via motor fivers in the facial (VII) and glossopharyngeal (IX) nerves dramatically increase the output of watery (serous), enzyme-rich saliva -the chemoreceptors are activated most strongly by acidic substances. The mechanoreceptors are activated by virtually any mechanical stimulus in the mouth--even chewing rubber bands. -The sympathetic division, (specifically in fibers T1-T3) causes release of a thick, mucin-rich saliva. Strong activation of the SNS constricts blood vessels serving the salivary glands and almost completely inhibits saliva release, causing a dry mouth (xerostomia); dehydration also inhibits salivation because low blood volume reduces filtration pressure at capillary beds

53. Name the two sources of blood supply to the liver. Describe the hepatic circulation.

The first is the hepatic artery which delivers oxygenated blood from the general circulation. The second is the hepatic portal vein delivering deoxygenated blood from the small intestine containing nutrients. -blood from both the hepatic portal vein and the hepatic artery goes from the triad region, to the liver sinusoids and empties into the central vein. from the central vein the blood enters the hepatic veins, which drain into the liver, and then the inferior vena cava. stellate/hepatic macrophages remove debris or worn our RBCs from the blood as it flows past -Venous blood from the GI tract drains into the superior and inferior mesenteric veins; these two vessels are then joined by the splenic vein just to form the portal vein splits to form the right and left branches, each supplying about half of the liver. the blood drains into the hepatic sinusoids screened by specialised macrophages (Kupffer cells) to remove any pathogens that manage to get past the GI defences. plasma is filtered through the endothelial lining of the sinusoids and bathes the hepatocytes

86. What is the function of lipoprotein lipase? Where in the circulatory system is lipoprotein lipase located?

While in the bloodstream, the triglycerides of the chylomicrons are hydrolyzed to free fatty acids and glycerol by lipoprotein lipase, an enzyme associated with capillary endothelium. The fatty acids and glycerol can then pass through the capillary walls to be used by tissue cells for energy or stored as fats in adipose tissue. Liver cells then endocytose and process the residual chylomicron material.

26. What are the gastric glands, and where are they located?

a tubular gland that produces gastric juice - found in lamina propria (loose CT layer) of mucosa of stomach - deep gastric pits in stomach mucosa leads to the glands

27. Identify the three types of exocrine gland cells located in the gastric glands.

a. Mucous neck cells b. Parietal cells -(PITCH FORK PARIETAL) c. Chief cells - mucous neck cells - (scattered in the neck and more basal regions of the glands) - parietal cells - found mainly in the more apical region of the glands scattered among the chief cells; have three prongs that bear dense microvilli to provide a huge surface area for secreting H+ and Cl- into the stomach lumen - chief cells - occur mainly in the basal regions of the gastric glands.

76. What are the functions of the large intestine?

absorb remaining water from indigestible food residues, store them and eliminate then as feces

68. Describe the motility patterns of the small intestine.

alternately contracting and relaxing rings of smooth muscle simply move the chyme backward and forward a few centimeters at a time. movement initiated because of pacemaker cells, stimulated by parasym, decreased by sym. the more intense the contractions the more mixing that happens, but rhythm stays the same. AFTER NUTRIENTS HAVE BEEN ABSORBED→duodenal mucosa releases motilin hormone. this hormone begins the process of peristalsis, called migrating motor complex MMC, each wave begins slightly more distally than the last. this sweeps the remnants of the meal and bacteria into the large intestine. THERE WAS ALSO THE THING ABOUT MECHANORECEPTORS IN SI WHEN STRETCHED STOP THE PRODUCTION OF ENZYMES ETC SO SI HAS TIME TO ABSORB NUTRIENTS - OPPOSITE IN STOMACH - STRETCH= MORE RELEASE OF STUFF

64. Why are the alkaline secretions of the small intestine and pancreas important?

because they neutralize the highly acidic chyme entering from the stomach into the small intestine so the acidity does not damage the wall 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.

bile duct and main pancreatic duct

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- salivary amylase (mouth), pancreatic amylase (SI), brush border enzymes (SI), sugar ases protein- pepsin (w/ HCl present, stomach), pancreatic enzymes- trypsin, chymotrpsin, elastase, craboxypeptidase (SI), brush border enzymes (SI), peptidases fats- lingual lipase (mouth), gastric lipase (stomach), bile salt emulsification (SI), pancreatic lipases (SI)

43. Describe causes and effects of vomiting.

caused by extreme stomach or intestinal stretching, or other irritants like bacteria, excessive alcohol, spicy foods, and some drugs. person feels nauseated, is pale, and salivates excessively. excessive vomiting can cause dehydration, and body electrolyte imbalance, acid-base imbalance *lots of HCL get lost, so the blood becomes alkaline and the body tries to replace its lost acid

58. Name the ducts which converge to form the common bile duct.

common hepatic duct and cystic duct

24. What is the function of the pyloric sphincter?

controls stomach emptying (gatekeeper); controls rate

61. Name and locate the three regions of the small intestine.

duodenum- curves around the head of the pancreas, 25 cm long jejunum- 2.5 m long, extends from the duodenum to ileum ileum- 3.6 m long, from jejunum to large intestine; joins large intestine at ileocecal valve

42. Explain the mechanism of vomiting (emesis).

empties the stomach through a different route, Bloodborne molecules and sensory impulses stream from the irritated sites to the emetic center of the medulla where they initiate a number of various motor responses. Before vomiting, an individual typically feels nauseated, is pale, and salivates excessively. A deep inspiration directly precedes vomiting, diaphragm and abdominal wall muscles contract, increasing in intra-abdominal pressure., the gastroesophageal sphincter relaxes, softpalate rises to close of the nasal passages. As a result, the stomach (and perhaps duodenal) contents are forced upwards through the esophagus and pharynx and out the mouth.

32. What cells of the gastric gland secrete gastrin? Why are these cells called enteroendocrine cells rather than exocrine cells?

g cells: enteroendocrine cells, typically located deep in the gastric glands, release a variety of chemical messengers directly into the interstitial fluid of the lamina propria. Some of these, for example histamine and serotonin, act locally as paracrine. Others, such as somatostatin, act both as paracrines locally and as hormones that diffuse into the blood capillaries to influence several digestive system target organs. Gastrin, a hormone, plays essential roles in regulating stomach secretion and motility - secretion functions as paracrines; to help regulate the digestive activities (releases paracrines which are local, and hormones which are systemic); Endocrine glands release chemical substances directly into the bloodstream or tissues of the body.

57. What organ stores bile between digestive periods?

gallbladder

56. From what breakdown product are bile pigments derived?

heme in hemoglobin, get it from the breaking down worn out RBCs, main pigment is bilirubin.

39. How is gastric secretion inhibited?

high acidic (below two) gastric contents: happens between meals → negative feedback. stress, fear, anxiety, anything that triggers fight or flight bc the SNS overrides PNS controls of the digestive system -distension of the duodenum or the presence of acidic, fatty, or hypertonic chyme ENTERGASTRONES ARE THE INHIBITORS - secretins and CCK

48. How is the secretion of pancreatic juice regulated?

hormones and neural ((para sym vagal) stimuli regulate. hormones like choleccystokinin, and secretin (which are enterogastrones). stimulants: bile salts, fatty meals, major stimulus that causes the pancreas to contract is CCK, this is released into the blood when acidic fatty chyme enters the duodenum. CCK causes contraction of pancreas, stimulate the secretion of pancreatic juice, and relaxes the hepatopancreatic sphicter so that bile and pancreatic juice can enter the duodenum. secretin is released in response to the presence of HCl in the intestine PICTURE P 889 1. chyme entering the duodenum causes duodenal enteroendocrine cells to release cholecystokinin (CCK) and secretin 2. CCK and secretin enter the blood stream 3. CCK -> secretion of enzyme rich pancreatic juice secretin -> release of HCO3- rich juice

62. Identify the sphincter at the juncture of the ileum and the large intestine.

ileocecal valve

7. What is the splanchnic circulation?

includes arteries that branch off the abdominal aorta to serve the digestive organs and the hepatic portal circulation.

25. Name the simple columnar ET cells which line the stomach and describe their function(s).

mucous cells; produce a cloudy, protective two layer of alkaline mucus in which the surface layer consists of viscous, insoluble mucus that traps a layer of bicarbonate-rich fluid beneath it

21. Describe the swallowing reflex -noting especially the stimuli which trigger swallowing and the motor responses involved.

p. 872 deglutition(swallowing) w/ 2 major phases: - the buccal: occurs in the mouth and is voluntary; (ends when a food bolus or a "bit of saliva" leaves the mouth and stimulates tactile receptors in the posterior pharynx, initiating the next phase) 1. Upper esophageal sphincter is contracted (closed), 2. tongue presses against the hard palate, forcing the food bolus into the oropharynx, food enters pharynx and stimulate tactile receptors - the pharyngeal-esophageal: (is involuntary and is controlled by swallowing center in the brain stem) 1. the tongue blocks the mouth, 2. the soft palate and its uvula rise, closing off the nasopharynx 3. the larynx rises so that the epiglottis blocks the trachea 4. the upper esophageal sphincter relaxes; food enters the esophagus -4. constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly; the upper esophageal sphincter contracts after food enters 5. peristalsis moves food through the esophagus to the stomach; gastroesophageal sphincter opens and food enters the stomach UES contracts after food enters to avoid regurgitation *vagus nerves transmit impulses from the swallowing centers to the muscles of the pharynx and esophagus *once food enters the pharynx, respiration is momentarily inhibited and all routes except the desired one in the digestive tract are blocked off.

60. How is bile release regulated?

p.888-889 Hormones and neural stimuli regulate both the secretion of bile and pancreatic juice and their release into the small intestine. The hormones include two ENTEROGASTRONES - SECRETIN AND CHOLECYSTOKININ. Bile salts themselves are the major stimulus for enhanced bile secretion. After a fatty meal, when the enterohepatic circulation is returning large amounts of bile salts to the liver, its output of bile rises dramatically. Secretin, released by intestinal cells exposed to fatty chyme, also stimulates liver cells to secrete bile. When no digestion is occurring, the hepatopancreatic sphincter is closed and the released bile backs up the cystic duct into the gallbladder, where it is stored until needed. Although the liver makes bile continuously, bile does not usually enter the small intestine until the gallbladder contracts. -1. chyme entering the duodenum causes duodenal enteroendocrine cells to release cholecystokinin (CCK) and secretin 2. CCK and secretin enter the blood stream 3. CCK -> secretion of enzyme rich pancreatic juice secretin -> release of HCO3- rich juice 4. bile salts and secretin stimulate bile production 5. CCK causes the gallbladder to contact and hepatopancreatic sphincter to relax- bile enter duodenum 6. vagal nerve stimulates gallbladders to contract weekly (gastric and cephalic phases)

47. Describe the pathway pancreatic juice follows as it travels from acinar cells to the duodenum.

pancreas (acinar cells) -> main pancreatic duct (bile ducts enters)-> duodenum drains from the pancrease into the duodendum via the main pancreatic duct, this main duct connects with the bile duct. there is also a smaller accessory duct that empties directly into the duodenum.

65. Describe the composition of intestinal juice.

slightly alkaline & isotonic with blood plasma, largely water but it also contains some mucous, no enzymes bc they are in the brush border

36. How does gastrin help regulate gastric gland secretion?

stimulates parietal cells -hormonal control of gastric secretion is largely the province of gastrin. It stimulates secretion of enzymes and HCl by the stomach, and of hormones (mostly gastrin antagonists) by the small intestine

73. Describe the teniae coli and haustra.

teniae coli→three bands of smooth muscle teniae coli creates pocketlike sacs called→haustra within large intestine wall

2. Name and describe the general function of the accessory digestive organs.

the accessory digestive organs are the teeth, tongue, gallbladder, and a number of large digestive glands--the salivary glands, liver, and pancreas. the accessory digestive glands produce variety of secretions that help break down foodstuffs. -teeth: masticate (chew) -tongue: makes the bolus -teeth and tongue: mechanical digestion -salivary glands: start chemical digestion process because secrete salivary amylase which help swallowing -gallbladder:store bile -liver: make bile -pancreas: secrete enzyme-rich pancreatic juice which breaks down food; chemical digestion

55. What is the function of bile salts?

they emulsify fats, break them down into smaller pieces and distribute them throughout - physically separate/disperse large fat globules entering the small intestine→increases the surface area for enzymes to work on. - facilitate fat and cholesterol absorption, help solubilize cholesterol

44. Describe the composition of pancreatic juice.

water, electrolytes, and enzymes. a lot of bicarbonate ions (alkaline). -the high pH of pancreatic fluid helps neutralize acidic chyme entering the duodenum and provides the optimal environment for intestinal and pancreatic enzymes

54. Describe the composition of bile.

yellow-green alkaline solution containing bile salts, bile pigments, cholesterol, triglycerides, phospholipids, and other electrolytes. Of these, only bile salts and phospholipids aid the digestive process