Digestive System chapter 24

Describe the mechanism used to make hydrochloric acid in the body. 6 steps

1. Carbon dioxide (CO2) diffuses into parietal cell 2. CO2 combines with H2O to form carbonic acid (H2Co3) This is catalyzed by carbonic anhydrase (CA). 3. H2CO3 dissociates into a bicarbonate ion (HCO3-) and a hydrogen ion (H+). 4. Bicarbonate ions are transported back into the bloodstream. An antiporter in plasma m. exchanges HCO3- for a chloride ion (CI-). 5. A H+-K+ pump moves H+ into the duct of the gastric gland and K+ into the parietal cell. 6. Chloride ions diffuse into the gastric gland duct.

What are the three types of neurons in the ENS?

1. Enteric sensory neurons that detect changes in chemical or mechanical changes. Enteric motor neurons stimulate or inhibit smooth muscle contraction and glandular secretion. Enteric interneurons connect enteric sensory and motor neurons.

What is the aqueous component of the pancreas?

1. What role does the HCO3- have? They neutralize the acidic chyme that enter small intestine from the stomach. 2. What are the functions of the enzymes trypsin, chymotrypsin and carboxypeptidase? digest proteins and are secreted in their inactive forms. 3. What is the function of amylase? Where else is amuylase found? Pancreatic juice contains amylase which continues the polysaccaride digestion initiated in oral cavity. 4. What is the function of lipase? a lipid-digesting enzyme. breaks down lipids into monoglycerides and free fatty acids. 5. What is the function of deoxyriboneclease and ribonuclease? enzymes that degrade DNA and RNA to their component nucleotides.

Describe lipid transport. Figure 24.30 pg 909

1. bile salts surround fatty acids and monoglycerides to form micelles. 2. micelles attach to plasma membrane of intestinal epithelial cells, and fatty acids and monoglycerides pass by simple diffusion into the intestinal epithelia cells. 3. within the cell fatty acids and monoglycerides are converted to triglycerides; proteins coat the triglycerides to form chylomicrons, which move out of cell by exocytosis. 4. the chylomicrons enter lacteals of villi and are carried through the lymphatic system to general circulation.

name the steps in transport of LDL into cells. figure 24.32 pg.911

1. cells have pits on the surface, which dontain LDL receptors. 2. LDL binds to the LDL receptors in the pits. 3. LDL bound to LDL receptors, is taken into the cell by endocytosis.

Name the steps in the transport of glucose across the intestinal epithelium. 4 steps figure 24.29 pg 908

1. glucose is absorbed by symport with Na+ into intestinal epithelial cells. 2. symport is driven by a sodium gradient established by a Na+ - K+ pump. 3. glucose moves out of the intestinal epithelial cells by facilitated diffusion. 4. glucose enters capillaries of intestinal villi and is carried through the hepatic portal vein to the liver.

describe the flow of bile and pancreatic secretions through the duct system of the liver, gallbladder and pancreas. (5 steps)

1. hepatic ducts, which carry bile from the liver lobes, combine to form the common heptic duct. 2. common heptic duct combines with the cystic duct from the gallbladder to from the common bile duct. 3.Common bile duct and pancreatic duct combine to form the hepatopancreatic ampulla. 4. hepatopancreatic ampulla emties bile and pancreatic secretions into the duodenum at the major duodenal papilla. 5. accessory pancreatic duct empties pancreatic secretions into the duodenum at the minor duodenal papilla.

describe control of pancreatic secretion. Figure 24.24 pg. 901 3 steps.

1. parasympathetic stimulation from the vagus nerve causes pancreas to release digestive enzymes. 2. secretin released from the duodenum stimulates the pancreas to release a watery secetion rich in bicarbonate ions. 3. cholecystokinin released from the duodenum causes the pancreas to release a secretion rich in digestive enzymes.

how is the defecation reflex regulated? 9 steps figure 24.27 pg. 905

1. thought or smell of food, distention and movement of chyme into duodenum stimulate gastrocolic and duodenocolic reflexes. 2. these reflexes stimulate mass movements in the colon, which propel the contents of the colon toward the recum. 3. distention of the rectum by feces stimulates local defecation reflexes. and cause contractions of the colon and rectum which move feces toward the anus. 4. local reflexes cause relaxation of the internal anal sphincter. 5. distention of rectum by feces stimulates parasympathetic reflexes. AP are propagated to the defecation feflex center located in the spinal cord. 6. AP stimulate contraction of the colon and rectum and relaxation of the internal anal sphincter. 7. AP are propagated through ascending nerve tracts to the brain. 8. descending nerve tracts from the brain regulate the defecation reflex center. 9. AP from the brain control the external anal sphincer.

Describe bicarbonate ion production in the pancreas. figure 24.23 pg. 901 5 steps.

1. water and CO2 combine (CA) to form H2CO3. 2. H2CO3 dissociates to form H+ and HCO3-. 3. H+ is exchanged for Na+ by anantiporter. Na+ is removed by the Na+-K+ pump. 4. HCO3- are transported intointercalated ducts in exchange for CI- which return to the lumen by a channel. Na+ and water folow the HCO3- into the ducts. 5. ions an dwater move through the intercalated duct toward the interlobular duct.

What are low-density lipoproteins made up of?

20% phospholipid, 10% triglyceride, 45% cholesterol and 25% protein.

What is high-density lipoprotein made up of?

30% phospholipid, 5% triglyceride, 20% cholesterol and 45% protein.

What are the four major cell types of the duodenum?

Absorptive cells - produce enzymes and absorb digested food. goblet cells - prduce a protective mucus. granular cells - help protect the interstinal epithelium from bacteria. endocrine cells - produce regulatory hormones. .

What is the role of acetylcholine and norepinephrine in the chemical regulation of the DS?

Acetylcholine stimulates and norepinephrine inhibits digestive tract motility and secretions.

Secretin secretion in the duodenum is stimulated by what? What are the secretory and motility effects of it?

Acidity of chyme. Decreases gastric secretion; stimulates pancreatic and bile secretions high in bicarbonate ions. Decreases gastic motility.

What is Secretion?

As food moves through the digestive tract, secretions are added to lubricate, liquefy, buffer, and digest the food.

What is the brush border?

Combined microvilli on the entire epithelial surface of the small intestine.

What do Mass movements do?

Contractions that move material in some parts of the large intestine. Mass movements extend over much larger parts of the digestive tract than peristaltic movements.

What is the ENS and what is it's function?

Extensive network of the submucosal and myenteric plexuses within the walls of the digestive tract. Network of neurons and neuroglial cells. contains more neurons than the spinal cord. Functions through local reflexes. parasympathetic division of the ANS through vegus and sympathetic nerves.

Cholecystokinin secretion in the duodenum is stimulated by what? What are the secretory and motility effects of it?

Fatty acids and peptides. Slightly decreases gastric secretion; stimulates pancreatic secretions high in D enzymes; Causes contraction of the gallbladder and relaxation of the hepatopancreatic ampullar sphincter. Strongly decreases gastric motility.

Where are mucous cells found and what is the function of the mucous cell within the gastric pit?

Found in surface and lining of pit. protect stomach wall from damage by acid and digestive enzymes. Produce an alkaline mucus that neutralizes the acid and is a barrier to the digestive enzymes.

Where are the chief cells found and what is their function?

Found interspersed in the deep parts of the glands. They produce pepsinogen.

Where are the endocrine cells found within the gastric pit and what is their function?

Found interspersed in the deep parts of the glands. They produce regulatory hormones and paracrine factors. several types of endocrine cells. Enterochromaffin cells produce histamine, which stimulates acid secretion by parietal cells. Gastrin-containing cells secrete gastrin, and somatostatin-containing cells secrete somstostatin, which inhibits gastrin and insulin secretion.

Describe the Storage of bile.

Hepatocytes can remove sugar from the blood and store it as glycogen. Hepatocytes help maintain blood sugar levels. When large amounts of sugar enter general circulation after a meal, the blood osmolality will increase, resulting in hyperglycemia. Blood from small intestine passes through the hepatic portal vein to the liver, where hepatocytes remove glucose from blood, store them and then secrete them back into the circulation when needed.

What is a gastric pit?

Indentations in the stomach which denote entrances to the tubular shaped gastric glands. They are deeper in the pylorus than they are in the other parts of the stomach.

Where is the Mucosa, what are it's layers and their functions?

Innermost tunic of the digestive tract Layers: mucous epithelium -- moist stratified squamous epithelium in the mouth, oropharynx, esophagus, and anal canal and simple columnar epithelium in the digestive tract. Lamina propria -- loose connective tissue Muscularis mucoaes -- epithelium extends deep into the lamina propria in many places to form intestinal glands and crypts.

What are the major functions of acid in the stomach?

Kills bacteria. Stops carbohydrate digestion by inactivating salivary amylase. Denatures many proteins so that proteolytic enzymes can reach internal peptide bonds. Provides proper pH for the activation and function of pepsin.

How are lipids absorbed and digested?

Lingual lipase digests a small amount of gastric lipase. Lipid droplets mix with bile salts in small intestine. Emulsification transforms large lipid droplets into smaller ones. Once lipids are digested, bile salts aggregate around the small droplets to form micelles. The hyrophobic ends of bile salts are directed towards free fatty acids, cholesterol, and monoglycerides at center of micelle. Hydrophilic ends are directed outward to water. When a micelle comes in contact with epithelial cells of small intestine, the lipid contents of the micelle pass by simple diffusion.

Describe the Synthesis of bile.

Liver can produce its own new compounds, including blood proteins like albumins, fibrinogen, globulins, heparin, and clotting factors, which are released into circulation.

Describe Bile Production

Liver produces and secretes about 600-1000 ml of bile each day. Bile has no digestive enzymes but neutralizes neutralize the acidic chyme and bring the pH up. Bile salts emulsify lipids and increase bile secretion through a positive-feedback system. 90% of bile salts are reabsorbed in theileum.. Neural and hormonal stimuli regulate secretion and release of bile. Bile secretion by the liver is increased by parasympathetic stimulation through the vagus nerve. Secretin also stimulates bile secretion.

What are Peyer patches?

Lymphatic nodules that are numerous in the mucosa and submucosa of the ileum. Initiate immune responses against microorganisms that enter the mucosa from ingested food.

Name all of the things that are secreted within the digestive tract.

Mucus - lubricates, coats and protects Water - liquifies food for easy digestion and absorption. Lipids -- secreted by liver Enzymes -- secreted by oral cavity, stomach, small intestine and pancreas break down large food molecules for absorption into intestinal wall.

How does mucus help in digestion?

Mucus is secreted along the entire digestive tract to lubricate the food and the lining of the tract. It also coats and protects the epithelial cells from mechanical abrasion, stomach acid, and digestive enzymes.

Where are mucous neck cells found and what is the function of the mucous cell within the gastric pit?

Near opening of gastric glands and in gastric glands. produce mucus.

How are carbohydates digested and absorbed?

Polysaccharides break down to disaccharides and monosaccharides. Carb digestion begins in oral cavity with partial digestion of starches by salivary amylase. Digestion continues in stomach until the food is well mixed with acid and inactivates salivary amylase. resumed in small intestine by pancreatic amylase. Disaccharidases bound to microvilli digest disaccharides into monosaccharides (glucose).

What is Elimination?

Process of waste by digestion are removed from the body. Primarily in large intestine water and salts are absorbed which changes material from liquefied to semi solid. Feces are eliminated from the digestive tract by the process of defecation.

Describe the Jejunum and the lleum.

Progressively smaller with a decrease in thickness and nubmer of circular folds and ville then duodenum. Major sites for nutrient absorption.

Describe the cephalic phase of stomach secretion.

Secretion of gastrin and histamine. 1. The taste, smell or thought of food or tactile sensations of food in the mouth stimulate the medulla oblongata. 2. Vagus nerves carry parasympathetic action p. to the stomach, where enteric plexus neurons are activated. 3. Postganglionic neurons stimulate secretion by parietal and chief cells and stimulate gastrin and histamine secretion by endocrine cells. 4. Gastrin is carried through the circulation back to the stomach where along with histamine, it stimulates secretion.

What is the ileocecal junction?

Site where ileum connects to the large intestine. Has a ring of smooth muscle called the ileocecal sphincter and one-way ileocecal valve, which allow intestinal contents to move from the ileum to the large intestine but ot in the opposite direction.

What is Mixing?

Some food is moved back and forth within the digestive tract to mix it with digestive secretions and help break it into smaller pieces.

large intestine does not participate much in any enzymatic break down or absroption of nutrients. What is its function?

The large intestine does reabsorb water and does take up some electrolytes. The large intestine also takes up vitamin K that is produced by the bacteria.

What is Propulsion?

The movement of food from one end of the digestive tract to the other. 24-36 hours for digestion.

What is Absorption?

The movement of molecules out of the digestive tract and into the circulation or into the lymphatic system. Pass out of digestive tract by diffusion, facilitated diffusion, active transport, symport, or endocytosis.

Describe Detoxification of bile.

liver forms a major line of defense by altering the structure of many harmful substances to make them less toxic or eliminate easier. Hepatocytes remove ammonia from the circulation and convert it to urea, which is less toxic than ammonia.

control of bile secretion and release figure 24.21

pg. 897

What does Peristalisis do?

propels material through most of the digestive tract by peristaltic waves in front and behind bolus. Each peristaltic wave travels the length of the esophagus in about 10 seconds.

How is protein absorbed and digested?

proteolytic enzymes produced in the pancreas produce small peptide chains which are broken down into tripeptides, dipeptides, and amino acids by peptidases bound to microvilli.

Nutrient Interconversion of bile.

the liver can convert some nutrients into others. an oversupply of amino acids can be regulated by hepatocytes breaking down the amino acids and cycle many of them through metabolic pathways so that they can be used to produce adenosine triphosphate, lipids, and glucose. Hepatocytes also transform substances that cannot be used by most cells into readily usable substances. combine ingested fats with chloine and phosphorus in the liver to produce phosphilipids.

What are intestinal glands?

tubular invaginations of the mucosa where epithelial cells are produced.

What is very-low-density lipoprotein made up of?

18% phospholipid, 60% triglyceride, 14% cholesterol and 8% protein

What is chylomicron made up of?

4% phospholipid, 90% triglyceride, 5% cholesterol and 1% protein.

What is chyme?

A semifluid material made from food that enters stomach and stomach secretions. chyme means juice.

What is Pepsinogen and it's function?

Breaks down protein in the stomach. Found in the chief cells.

What are carbohydrates, proteins, lipids broken down into?

Carbs to monosaccharides, proteins to amin acids, triglycerides

What are the three phases of stomach secretion regulation?

Cephalic, gastric and intestinal phase.

What is chemical digestion?

Digestive enzymes are secreted along the digestive tract. Organic molecules must be digested into their component parts before they can be absorbed by the digestive tract. Minerals and water and vitamins are not broken down before being absorbed.

Describe the secretion of the enzyme disaccharidases and peptidases.

Disaccharidases breaks down disaccharides to monosaccharides and peptidases which hyrolyze the peptide bonds between small amino acid chains.

Where are the parietal cells found and what is their function?

Found interspersed in the deep parts of the glands. They produce hydrochloric acid and intrinsic factor.

Describe the Gastric Phase

Greatest amount of gastrin secretion. 1. Distention of stomach stimulates mechanoreceptors (stretch receptors) and activates a parasympathetic reflex. AP generated by the mechanoreceptors are carried by the vagus nerves to the medulla oblongata. 2. The medulla increases AP in vagus nerves that stimulate secretions by parietal and chief cells and stimulate gastrin and histamine secretion by endocrine cells. 3. DIstention of stomach also activates local reflexes that increase stomach secetions. 4. Gastrin is carried through the circulation back to the stomach, where, along with histamine, it stimulates secretion.

Describe Phagocytosis of bile.

Hepatic phagocytic cells phagocytize "worn out" and dying red and white blood cells, some bacteria, and other debris that enters the liver through the circulation.

What is histamine?

Hormone produced in DS . Influence activity of nearby cells. Localized chemical regulators help local reflexes within the ENS control local digestive tract environments such as pH levels.

What is the myenteric plexus?

Much more extensive then the submucosal plexus and controls the motility of intestinal tract.

What are the four layers of the digestive tract?

Mucosa, submucosa, muscularis and serosa.

Name the five cell types within the gastric pit.

Mucous cell Neck cells parietal cells chief cells endocrine cells

What is a H+-K+ pump?

Often called a proton pump. Drugs that block the pump are used to lower gastric acid levels.

How are Proteins digested and absorbed?

Pepsin in stomach breaks proteins into polypeptide chains. Trypsin and other proteolytic enzymes from the pancreas produce smaller peptides. Peptidases, bound to the microvilli break down peptides. Amino acids, dipeptides, and tripeptides are absorbed by symport that is powered by Na+ or H+ gradients or by facilitedted diffusion. amino acids are transported to the liver, where the amino acids can be modified or released into the bloodstream. amino acids are actively transported into cells under the stimulation of growth hormone and insulin. amino acids are used as building blocks or for energy.

What is digestion?

The breakdown of large organic molecules into their component parts.

What are the islets of Langerhans? What hormones are produced here?

The endocrine part of the pancreas of pancreatic islets, or islets of Langerhans. Produces insulin and glucagon. Important in controlling the blood levels of nutrients.

What are the acini? What secretions arise from the acini?

The exocrine part of the pancreas is a compound acinar gland. The acini produce digestive enzymes.

What and where is the Serosa or Adventitia and what is it's function?

The fourth layer of digestive tract. visceral peritoneum. thin layer of connective tissue and a simple squamous epithelium. When outer layer is derived from adjacent connective tissue, the tunic is called the adventitia, they are found in the esophagus and retroperitoneal organs.

What is Mastication?

The process by which the teeth chew food in the mouth. Food must be broken down in order to be digested by enzymes.

What is defecation?

The process of feces elimination by digestive tract.

What is the Ville of the duodenum?

Tiny, fingerlike projections of the mucosa. covered by simple columnar epithelium and contains a blood capillary network and a lymphatic capillary called a lacteal.

What happens to create the alkaline tide?

When HCO3- are exchanged for CI- through an antiporter in the plasma membrane, and the CI- subsequently move into the cell. Results in an elevated blood pH in the veins that carry blood away from the stomach resulting in an alkaline tide.

What is lacteal?

Within the ville are lymphatic capillary.

What does deglutition do?

another term for swallowing, moves a mass of food or liquid called bolus from the oral cavity into the esophagus.

Why does secretin production in response to acidic chyme and its stimulation of bicarbonate ion secretion constitute a negative-feedback mechanism?

as the pH of the chyme in the duodenum decreases as a result of the presence of acid, secretin causes an increase in bicarbonate ion secretion, which increases the pH and restores the proper pH balance in the duodenum.

Name the functions and location of the Submucosa.

beneath the mucosa, a thick connective tissue layer containing nerves, blood vessels, lymphatic vessels, and small glands.

Name the parts of the large intestine.

cecum, colon,rectum, and anal canal.

What stimulates the gallbladder? What functions does the gallbladder have?

cholecystokinin and some vagal stimulation. water and electroytes are absorbed and bile salts and pigments become highly concentrated. Shortly after a meal, the gallbladder contracts and dumps large amounts of concentrated bile into the small intestine.

What are duodenal glands?

coiled, tubular mucous glands located in the submucosa of the duodenum.

What is the submucosal plexus?

consists of axons, scattered neuron cell bodies, and neuroglial cells. Axons extend to cells in epithelial intestinal glands, stimulating thier secretion. esophagus and stomach don't have a submucosal plexus.

Gastrin secretion in the stomach is stimulated by what? What are the secretory and motility effects of it?

distension of stomach, partially digested proteins, autonomic stimulation and ingestion of alcohol or caffeine. Increases gastric secretion causes a minor increase in gastric motility.

Where does intrinsic factor come from and what is its function?

glycoprotein produced by the parietal cells of the stomach, binds with vitamin B12, making the vitamin more readily absorbed in the ileum. B12 is important in DNA synthesis which leads to RBC production.

What is the role of gastrin and secretin?

help regulate many digestive tract functions, secretions of associated glands like liver and pancreas.

What are the five stomach secretions?

hydrochloric acid, gastrin, histamine, intrinsic factor, and pepsinogen.

Where is the muscularis and what are it's functions?

inbetween the submucosa and the serosa. consists of an inner layer of circular smooth muscle and an outer layer of longitudinal smooth muscle. Exceptions are upper esophagus and the stomach.

Describe the Intestinal phase

inhibits gastric secretions. 1. chyme in the duodenum (small intestine) with a pH less than 2 or containing fat digestion products inhibits gastric secretions by three mechanisms. (2-4) 2. Chemoreceptors in the duodenum are stimulated by H+ (low pH) or lipids. Actions potentials generated by the chemoreceptors are carried by the vagus to the medulla, where they inhibit parasympathetic action potentials decreasing gastric secretions. 3. local reflexes activated by H+ or lipids also inhibit gastric secretion. 4. Secretin and cholecystokinin produced by the duodenum decrease gastric secretions in the stomach.

How are lipids digested and absorbed?

lipase digests lipid molecules to form free fatty acids and monoglycerides. Emulsification occurs by bile salts. Micelles form around lipid digestion products and move to epithelial cells of small intestine by simple diffusion. free fatty acids are combined with a monoglyceride to form triglycerides. Proteins coat triglycerides, phospholipids, and cholesterol to form chylomicrons which enter lacteals in villi and are carried through lymph system to bloodstream. Triglycerides are stored in adipose tissue, converted to molecules or used as energy. LDL transports cholesterol to cells, and HDL transports it from cells to the liver.

What is mechanical digestion?

mastication and mixing of food.

What are Segmental contractions?

mixing contractions that occur in the small intestine.

What two plexuses form the enteric nervous system (ENS)? What is the functions of the ENS?

myenteric and submucosal plexuses. extremely important in controlling secretion and movement.

What is Hirschprung disease?

patients who lack a subset of enteric neurons.

label the histology of the liver figure 24.19

pg. 895

study blood and bile flow through the liver figure 24.20

pg. 896

How are carbs digested and absorbed?

polysaccharides are broken down into into monosaccharides by enzymes. Monosaccharides are taken up by intestinal epithelial cells by symport that is powered by a Na+ gradiant or ficilitated diffusion. Monosaccharides are carried to the liver and converted to glucose. Glucose is transported to the cells that require energy. Glucose enters the cells through facilitated dffusion. Insulin influences the rate of glucose transport. salivary amylase, pancreatic amylase.

What is bile and what is its function?

produced by the hepatocytes and consists primarily of metabolic by-products. neurtralizes and dilutes stomach acid and emulsifies lipids. Also helps neutralize acidic chyme and bring the pH up to a level at which pancreatic enzymes can function.

What is hydrochloric acid and its function?

produces the low pH of stomach's contents, between 1 and 3. Kills bacteria that is ingested.

What is the role of serotonin?

stimulates digestive tract motility. Produced by endocrine cells within digestive tract wall. 95% of serotonin is found in digestive tract. Drugs that release serotonin can affect digestive tract activity.

What is zymogen?

term for an inactive enzyme.

What is Ingestion?

the intake of solid for liquid food into the stomach.

What are the circular folds of the duodenum?

the mucosa and submucosa in a series of folds which run perpendicular to the long axis of the DT.

The absorptive and goblet cells migrate from the intestinal glands to cover the surface of the ________ and are eventually shed from it's tips.

ville