Chapter 24: Digestive
What is emulsification?
bile salts break lipid droplets apart into smaller droplets.
In detail describe the gastric phase.
(AKA go for it) this stage produces the greatest volume of gastric secretions. The presence of food in the stomach initiates the gastric phase. The primary stimuli are distension of the stomach and the presence of amino acids and peptides in the stomach. Distension of the stomach wall, especially in the body or fundus, stimulates mechanoreceptors. Action Potentials generated by these receptors initiate reflexes result in acetylcholine release and the cascade of event that increase secretion, as in the cephalic phase. The presence of partially digested proteins, or moderate amounts of alcohol or caffeine in the stomach also stimulates gastrin secretion. When the pH of the stomach contents falls below 2, increased gastrin secretion produced by distension of the stomach is blocked. This negative-feedback mechanism limits the secretion of gastric juice.
What does bile contain and is the purpose of each product?
-bile salts -bile pigments -cholesterol -lipids -lipid-soluble hormones -lecithin
What are the major tunics of the digestive tract wall, listed from the inside to the outside?
1. Mucosa 2. submucosa 3. muscularis 4. serosa or adventia
Name the 4 types of cells found in the duodenal mucosa and state their functions.
1. absorptive cells- cells with microvilli that produce digestive enzymes and absorb digested food. 2. Goblet cells- produce a protective mucus 3. Granular cells (Paneth cells) may help protect the intestinal epithelium from bacteria. 4. Endocrine cells- produce may regulatory hormones (Secretin and cholecystokinin)
Name the 5 types of epithelial cells found in the stomach and describe them.
1. surface mucous cells: found on the surface f the gastric pit. They protect the stomach wall from being damaged by acid and digestive enzymes. They connect by tight junctions and provide and additional barrier that prevents acids and enzymes from reaching the deeper tissues. They are replaced rapidly. 2. Mucous neck cells-located near the openings of the glands and produce mucus. 3. Parietal cells- produce hydrochloric acid and intrinsic factor. 4. Chief cells- Produce the enzyme pepsinogen. They also produce the enzyme gastric lipase, which can digest lipids in the stomach. 5. Endocrine cells- produce regulatory hormones and paracrine factors. (Enterochromaffin cells- secrete histamine, Gastrin cells, and somatostatin cells.
Explain the 3 types of propulsion through the digestive tract
1. swallowing (deglutition) 2. Peristalsis: Propels material through most of the digestive tract. 3. Mass movement: contraction that move materials in the distal part of the large intestine to the anus
Blockage of the pancreatic duct prevent pancreatic enzymes from being delivered to the small intestine. What effect would you expect this to have on cholecystokinin and secretin levels in the blood?
Because the secretin is regulated by nutrients in the duodenum and parasympathetic nerves, a blockage of the pancreatic duct would not have an effect on cholecystokinin and secretin blood levels.
Where is the myenteric plexus located and what does it do?
Between the inner circular and outer longitudinal muscular layers. controls the motility of the intestinal tract.
What are gastric pits and gastric glands?
Gastric pits are found in the walls of the stomach that contain gastric glands that secrete mucus, hydrochloric acid, intrinsic factor, pepsinogen, and hormones.
Which two reflex trigger mass movements?
Gastrocolic- entrance/ distension of food into the stomach duodenocolic- produced by chyme entering (distension) duodenum
What is the purpose of hydrochloric acid in the stomach?
HCL is the acid of gastric juice. It produces the low pH (1-3) of the stomach's contents
Stomach secretions include
Hydrochloric acid, intrinsic factor, mucus, and digestive enzymes (pepsinogen and gastric lipase)
What is the purpose of bile?
It contains no digestive enzymes, but it pays a role in digestion because the bile salt neutralizes stomach acid and emulsifies lipids
How does water help in the digestive tract?
It liquefies the food, making it easier to digest and absorb. It moves into the intestine by osmosis.
What are the major duodenal papilla and the minor duodenal papilla?
Major: point of opening of the common bile duct and the pancreatic duct into the duodenum. Minor: Site of the opening of the accessory pancreatic duct into the duodenum.
List the muscles of mastication and the actions they produce. Describe the mastication reflex.
Temporalis: close the jaw, retracts the jaw, masseter: close the jaw, protraction of jaw medial pterygoid: close the jaw, excursion of jaw, protraction of jaw. lateral pterygoid: open the jaw, protraction of the jaw
Explain the difference in structure between the internal anal sphincter and the external anal sphincter.
The internal sphincter is at the superior end of the anal canal and is a smooth muscle ring. The epithelium is simple columnar The external sphincter is at the inferior end of the anal canal and is formed by a ring of striated muscular fibers. The epithelium if stratified squamous.
Name the parts of the pharynx involved with digestion. What are pharyngeal constictors?
The pharynx consists of 3 parts 1. nasopharynx, 2. oropharynx, and 3. laryngopharynx. Food is only transmitted through the oropharynx which than continues into the laryngopharynx, which extend to the esophagus. The epiglottis covers the larynx and keeps food out of the lungs. The posterior walls of the oropharynx and laryngopharynx consist of 3 muscles the superior, middle, and inferior pharyngeal constrictors
What are the hard and soft palates? Where is the uvula located?
The roof of the oral cavity is called a palate. the hard palate is the anterior bony part the soft plate is the posterior nonbony part consisting of skeletal muscle and connective tissue. The uvula is a located on the posterior portion of the soft plate.
Describe the movement of water through the intestinal wall.
Water moves in either direction across the wall of the small intestine by osmosis. Osmotic gradients across the epithelium determine the direction of this diffusion,
Triglycerides are broken down into
glycerol and fatty acids
What are lacteals?
lymphatic vessels in the wall of the small intestine that carries chyle from the intestine and absorbs fat.
What is the fauces?
opening to the pharynx or throat.
Disaccharidases and peptidases are enzymes secreted by the
stomach
What types of tissue are found in muscularis tunic?
the muscular layer. consist of an inner layer of circular smooth muscle and an outer layer of longitudinal smooth muscle
Describe in detail the intestinal phase.
(AKA slow down) This stage inhibits gastric secretions. It is initiated by acidic chyme entering the duodenum of the small intestine, which activates both neural and hormonal mechanism. Secretions are inhibited when the pH of the chyme entering the duodenum drops to 2 or below. In addition, when the chyme contains lipids digestion products, gastric secretions are inhibited. There are 2 hormones involved in the intestinal phase. 1. secretin (released in response to acidic solution in the duodenum. It inhibits gastric secretions by inhibiting both parietal and chief cells.) 2. Cholecystokinin (released in response to fatty acids, other lipids, and to a lesser degree protein digestion products in the duodenum and the proximal jejunum. In inhibits gastric secretion) The inhabitation of gastric secretion is also under nervous control. The enterogastric reflex consist of local reflex and a reflex integrated within the medulla oblongata that reduce gastric secretion. Distension of the duodenal wall, the presence of irritating substances in the duodenum, reduces pH, and hypertonic or hypotonic solutions in the duodenum activate the enterogastric reflex
In detail describe the cephalic phase?
(AKA: get started) it is the brain phase of stomach secretion. It is controlled by the CNS. It begins even before the bolus of food enters the stomach. Several type of stimuli (taste and smell of food, chewing and swallow, and pleasant thoughts of food) act on the centers within the medulla oblongata to influence gastric secretions. Action potentials are sent from the medulla oblongata alone parasympathetic neurons within the vagus (x) nerves to the stomach. Within the stomach wall, the preganglionic neurons stimulate the postganglionic neurons in the ENS. The postganglionic neurons, which are primarily cholinergic, stimulate secretory activity in the cells of the stomach mucosa. Parasympathetic stimulation of the stomach mucosa results in the release of the neurotransmitter acetylcholine, which increases the secretory activity of both the parietal and the chief cells and stimulate the secretion of gastrin and histamine from endocrine cells. The gastrin released into the circulation travels to the parietal cells, where it stimulates additional hydrochloric acid and pepsinogen secretion. In addition, gastrin stimulates enterochromaffin-like cells to release histamine, which stimulates parietal cells to secrete hydrochloric acid. Histamine acts as both local paracrine chemical messengers and a hormone in the blood to stimulate gastric gland secretory activity. Acetylcholine, histamine, and gastrin working together causes a greater secretion of hydrochloric acid than any of them do separately. Of the three, histamine has the greatest stimulatory effect. Drugs block the actions of histamine are used to lower acids levels.
Explain how tripeptides, dipeptides, and amino acids enter intestinal epithelial cells.
1. Basic, acidic, and neutral amino acids are transported into the epithelial cells by separate carrier molecules 2. Acidic and most neutral amino acids enter by support of Na= gradient. Basic amino acids enter the epithelial cells by facilitated diffusion. Dipeptides and tripeptides enter intestinal epithelial cells by H= symport mechanism analogous to Na+ symport. Once inside the cells, dipeptidase and tripeptidases split the dipeptides and tripeptides into their component amino acids. 3. Individual amino acids then leave the epithelial cells. 4. Amino acids then enter the hepatic portal system, which transport them to the liver. The amino acids may be modified in the liver or released into the blood stream and distributed throughout the body.
List the 3 parts of a tooth. What are dentin, enamel, cementum, and pulp?
1. Crown: part of the tooth exposed in the oral cavity and covered with enamel. 2. Neck: all region between the crown and root. 3. Root: Largest region of the tooth, anchors it to the bone. Dentin: bony material forming the mass of the tooth. enamel: hard substance covering the exposed portion of the tooth. cementum: layer of modified bone covering the dentin of the root and neck of a tooth, which helps anchor the tooth pulp: collection of blood vessels, nerves, and connective tissue.
Describe each of the functions involved in the normal functions of the digestive system. (There are 6)
1. Ingestion and mastication: Ingestion is the intake of solids or liquids through the oral cavity. Mastication is the process by which the teeth chew food in the mouth 2. Propulsion and Mixing: Propulsion is the movement of food forward through the digestive tract. Mixing is the movement of food back and forth in the digestive tract without forward movement. 3. Secretion: added to lubricate, liquefy, buffer, and digest the food as it moves 4. Digestion: the breakdown of large organic molecules into their individual components. 5. Absorption: movement of molecules out of digestive tract into the blood or into the lymphatic system. 6. Elimination: process by which waste products of digestion are removed from the body. Water and salts are absorbed in the largest intestine and the material turns from liquified to semisolid.
Digestive function of the oral cavity
1. Ingestion and mastication: solid food and fluids are taken into the digestive tract through the oral cavity. The teeth break food into smaller pieces. 2. propulsion and mixing. The tongue forms food into a bolus and pushes the bolus into the pharynx to begin the swallowing reflex. 3. digestion and secretion: mystification begins mechanical digestion of food. Amylase in the salvia begins carbohydrate (Strach) digestion. 4. absorption: some drugs can be absorbed across the oral mucosa.
What stimulates bile secretion from the liver?
1. Parasympathetic stimulation through the vagus nerves increases bile secretion from the liver 2. Two hormones released from the duodenum increase bile in the digestive tract: secretin and cholecystokinin. Secretin stimulates bile secretion from the liver, primarily by increasing the water and HCO3- content of bile 3. Cholecystokinin stimulates gallbladder contraction to release bile into the duodenum 4. Bile salts increase bile secretion through a positive feedback system. Over 90% of bile salts are reabsorbed in the ileum and carried in the blood by the hepatic portal circulation. Upon their return to the liver, the bile salts stimulate further bile secretion and are once again secreted into the bile. This recycling process reduces the loss of bile salts in the feces. Bile secretion into duodenum continues until the duodenum empties.
Describe the flow of blood to and through the liver. Describe the flow of bile away from the liver.
1. The hepatic artery carries oxygenated blood from the aorta through the porta hepatis of the liver. Hepatic artery branches become part of the portal triads. Blood from the hepatic artery branches enters the hepatic sinusoids and supplies hepatocytes in the hepatic cords with O2 2. The hepatic portal vein carries nutrient-rich, deoxygenated blood from the small intestine through the porta hepatis of the liver. Hepatic portal vein branches become part of the portal triads. Blood from the hepatic portal vein branches enters the hepatic sinusoids and supplies hepatocytes in the hepatic cords with nutrients 3.
Diagram the duct system from the liver, gallbladder, and pancreas that empties into the major duodenal papilla.
1. The right and left hepatic duct first unite to form a single common hepatic duct. 2. The cystic duct from the gallbladder joins the common hepatic duct to from the common bile duct. 3. Bile can flow from the gallbladder through the cystic duct into the common bile duct, or it can flow back up the cystic duct into the gallbladder. 4. The common bile duct joins the pancreatic duct at the hepatopancreatic ampulla, which is an enlargement where the two ducts merge. the hepatopancreatic ampulla empties into the duodenum at the major duodenal papilla. A smooth muscle sphincter surrounds the common bile duct where it enters the hepatopancreatic ampulla. 5. The accessory pancreatic duct empties pancreatic secretions in the duodenum at the minor duodenal papilla.
What enzymes are present in pancreatic juice? Explain the function of each.
1. Trypsin (trypsinogen) 2. chymotrypsin (chymotrypsinogen) 3. carboxypeptidase (procarboxypeptidase)
What are the events that occur with once the vomiting center of the medulla oblongata are stimulated?
1. a deep breath is taken 2. the hyoid bine and larynx are elevated, opening the upper esophageal sphincter 3. the opening of the larynx is closed. 4. the soft palate is elevated closing the connection between the oropharynx and the nasopharynx 5. the diaphragm and abdominal muscles are forcefully contracted, strongly compressing the stomach and increasing the intragastric pressure 6. the lower esophageal sphincter is relaxed. 7. the gastric contents are forced out of the stomach, through the esophagus and oral cavity, to the outside.
Describe the 3 tunics of the gallbladder wall.
1. an inner mucosa folded into rugae that allows the gallbladder to expand 2. muscularis, which is a layer of smooth muscle that allows the gallbladder to contract 3. outer covering of serosa
Name the 2 kinds of exocrine secretions produced by the pancreas. What stimulates their production, and what is their function?
1. aqueous component (rich in bicarbonate ions) actively secreted by columnar epithelial cells that line the smaller ducts of the pancreas. The HCO3- ions of the aqueous pancreatic juice neutralize the acidic chyme that enters the small intestine from the stomach. Stops pepsin digestion. and allows the functioning of pancreatic and brush-border enzymes. 2. enzymatic component helps digest lipids, proteins, and carbohydrates
Explain and give examples of the major functions of the liver.
1. bile production for digestion and excretion 2. storage of nutrients (glycogen, lipids vitamins (A, B12, D, E, and K) 3. processing of nutrients (can convert some nutrients into others) 4. detoxification (alters the structures of many harmful substances making them less toxic or easier to eliminate, and hepatic phagocytic cells {Kupffer cells}.) 5. synthesis of new molecules (plasma proteins {albumin, fibrinogen, globulins, heparin, and clotting factors.} and cholesterol synthesis)
Describe the 3 phases of regulation of stomach secretions?
1. cephalic (get started) when stomach secretions are increased in anticipation of incoming food. 2. gastric (go for it) when most of the stimulation occurs) 3. intestinal (slow down) during which stomach secretion decreases.
what are the circular folds, villi, and microvilli in the small intestine? What are their functions?
1. circular folds- the mucosa and submucosa form a series of folds, which run perpendicular to the long axis of the digestive tract 2. villi- tiny fingerlike projections of the mucosa, about 0.5-1.5mm in length. Each villus is covered by simple columnar epithelium and contains a blood capillary network and a lymphatic capillary (lacteal) 3. Microvilli- cytoplasmic extensions on the villi that increase the surface area. Combine microvilli on the entire epithelial surface from the brush border
Name and describe the 3 parts of the small intestine
1. duodenum 25cm long 2.jejunum 2.5m long (2/5) 3. ileum 3.5m long (3/5)
How is saliva protective?
1. large volume of saliva helps prevent bacterial infections in the mouth 2. saliva contains the proteins lysozyme and immunoglobulin bicarbonate ions in saliva act as a buffer to neutralize the acids produced by oral bacteria, protecting tooth enamel. 4. mucous in saliva helps protect the digestive tract from physical irritation and enzymatic digestion.
What are the 2 types of mixing contractions?
1. mixing waves: gentle contractions in the stomach that churn the food with gastric secretion 2. segmental contractions: mix food particles with digestive secretions in the small intestine by sequence of segmental contractions
List the regions of the digestive tract, from beginning to end.
1. oral cavity (tongue, teeth, and salivary glands) 2. pharynx 3. esophagus 4. stomach 5. small intestine (duodenum, jejunum, and ileum) accessory organs: liver, gallbladder, and pancreas 6. large intestine (cecum, colon, rectum, anal canal, and anus)
Name and give the location of the 3 largest salivary glands. What are the other types of salivary glands called?
1. parotid glands 2. submandibular glands 3. sublingual glands. the other types of salivary glands are the lingual glands, palatine glands, buccal glands, and labial glands
How does peristalsis work
1. peristaltic waves: muscular contractions consisting of waves of relaxation of the circular muscles in front of the mass of undigested food (chyme) 2. followed by a strong wave of contractions of the circular muscles behind the mass of chyme, which forces the bolus along the digestive tract.
Describe the movements in stomach
1. relatively weak contraction result in mixing waves which thoroughly mix ingested food with stomach secretions to form chyme 2. in the mixing wave, the more fluid part of the chyme is pushed back toward the pyloric sphincter, whereas the more solid center moves back toward the body of the stomach. 3. Stonger contractions results in peristaltic waves, which force the chyme toward and through the pyloric sphincter. The pyloric sphincter usually remains closed because of mild tonic contractions 4. Again, the more fluid part of the chyme is pushed toward the pyloric region, whereas the more solid center of the chyme squeezes past the peristaltic constriction back toward the body of the stomach. 5 Each peristaltic contractions sufficiently strong to cause partial relaxation of the pyloric sphincter and to pump a few milliliters of chyme though the pyloric opening and into the duodenum. Increased motility leads to increased emptying.
How is hydrochloric acid formed?
1. the process begins with H+ derived from CO2 and water, which enter the parietal cell from its serosal surface (the side opposite the lumen of the gastric pit) 2. Inside the cell, the enzyme carbonic anhydrase catalyzes the reaction between CO2 and the water to form carbonic acid. 3. Some of the carbonic acid molecules them dissociate to from H+ and HCO3-. 4.While H+ is pumped into the stomach lumen, HCO3- moves down its concentration gradient from the parietal cell into the extracellular fluid. During this process, HCO3- is exchanged for Cl- through an antiporter, which is located in the plasma membrane, and the Cl- subsequently moves into the cell. This results in and elevated blood pH in the veins that carry blood away from the stomach, called the alkaline tide. An alkaline tide normally occurs after eating a meal. 5. Drugs that block the proton pump are used to lower gastric level. The pump moves H= by active transport against a steep concentration gradient, and Cl- diffuses from the cell through ion channels in the plasma membrane. 6. Diffuse of Cl- into the gastric gland duct balances the positively changed H+ to reduce the amount of energy needed to transport the H+ against both a concentration gradient and an electrical gradient.
What types of tissue are found in the mucosa tunic?
3 separate layers 1. mucous epithelium, nonkeratinized stratified squamous epithelium in the mouth, oropharynx, esophagus, and anal canal and simple columnar epithelium in the remainder of the digestive tract. 2. loose connective tissue call the lamina propria 3. tinner outer layer of smooth muscle called the muscularis
Identify the mismatched pair of enzyme and substrate below. A. Carboxypeptidase-lipids B. Chymotrypsin-proteins C. Amylase-polysaccharides
A. Carboxypeptidase-lipids
How is the production of HCO3- in the pancreas similar to production of H+ in the gastric gland and how is it different.
Both processes require the enzyme carbonic anhydrase and the exchange of HCO3- and Cl- The major difference is that an alkaline solution is produced in the pancreas, whereas an acidic solution is produced in the stomach.
What is the function of HCO3- when it is secreted by the large intestine? Multiple Choice A. It aids in digestion of cellulose. B. It decreases the pH of feces, which are alkaline because of bacterial secretions. C. It increases the pH of the feces, which are acidic because of bacterial secretions. D. It aids in digestion of proteins.
C. It increases the pH of the feces, which are acidic because of bacterial secretions.
Describe the defecation reflex.
Combination of local and central nervous system reflexes initiated by distention of the rectum and resulting in the movement of feces out of the lower colon. 1. Distention of the rectum by feces stimulates local defecation reflexes that cause contractions of the large intestine and rectum, which moves feces toward the anus 2. Distention of the rectum stimulates parasympathetic reflexes. Action potentials are propagated to the defecation reflex center of the large intestine and rectum but causes relaxing of the internal anal sphincter. 3. Voluntary control of the external anal sphincter from motor nerve fibers contracts it or relaxes it, depending on whether defecation is initiated.
Describe the roles of the CNS in controlling the digestive system.
Control occurs when the reflexes are activated by stimuli originating either in the digestive tract or the CNS. action potentials are carried by sensory neurons in the vagus and sympathetic nerves to the CNS, where the reflexes are integrated. Reflex can be activated by sight, smell, or taste of food.
What two ligaments are attached to the liver?
Coronary ligament attaches the liver to the diaphragm. falciform ligament attaches the liver to the anterior wall.
Describe the enzymatic digestion of carbohydrates. List where each step of digestion occurs and the breakdown products of each step.
Digestion of carbohydrates begin in the oral cavity by salivary amylase. Digestion continues in the stomach until food is well mixed with acid, which inactivates the salivary amylase. It than continues in the small intestines by pancreatic amylase. The small intestines are mainly responsible for carbohydrate digestion
Describe the enzymatic digestion of proteins. List where each step of digestion occurs and the breakdown products of each step.
Digestion of proteins begins in the stomach. Pepsin secreted by the stomach catalyzes the cleavage of covalent bonds in proteins to produce smaller polypeptide chains. The digestion continues in the small intestine, the pancreas secretes proteases (trypsin, chymotrypsin and carboxypeptidase). Proteins are finally broken down into tripeptides, dipeptides, and amino acids by peptidases bound to the microvilli of the small intestine.
Describe the parts of the pancreas responsible for endocrine and exocrine secretions.
Endocrine: Pancreatic islets (islets of Langerhans) the islet cells produce 3 hormones: Insulin, glucagon, and somatostatin Exocrine: compound acinar gland. The acinar cells within the acini produce digestive enzymes.
Describe the roles of the ENS in controlling the digestive system.
Enteric nervous system: submucosal plexus and the myenteric plexus it is capable of controlling the complex peristaltic and mixing movements, as well as blood flow to the digestive tract. there are 3 major types of enteric neurons 1. enteric sensory: detect change in the chemical composition of the digestive tract contents or detects mechanical changes (stretch of the digestive tract walls) 2. enteric motor: stimulate of inhibit smooth muscles contraction and glandular secretion in the digestive system. 3. enteric interneurons: connect sensory and motor neurons.
What are the functions of the intestinal glands and duodenal glands?
Intestinal gland- tubular glands in the mucous membrane of the small and large intestines; also called crypts of Liberkuhn. The absorptive and goblet cells migrate from the intestinal glands to cover the surface of the villi and are eventually shed from its tip Duodenal glands: (Brunner glands) small gland that opens into the base of the intestinal glands; secretes a mucoid alkaline substance.
When and where are various ions absorbed?
Ions are mainly absorbed by active transport in the small intestine. Chloride ions move passively through the intestinal wall of the duodenum and jejunum following the positively charge Na+, but Cl- is actively transported from the ileum. Ca2+ is actively transported the entire length of the small intestine
What types of tissue are found in the submucosa tunic?
It is a thick layer of connective tissue. this layer contains nerves, blood vessels, lymphatic vessels, and small glands.
What does digestive mucus do?
It is secreted along the entire digestive tract, lubricates the food and the lining of the tract. The mucus coats and protects the epithelial cells of the digestive tract from mechanical abrasion, stomach acid, and digestive enzymes.
What is the function of the peritoneum?
Its secretes serous fluid that provides a lubricating film between the membranes allowing organs to move within the abdominal cavity with little to friction.
Describe the lesser omentum and the greater omentum .
Lesser: portion of the mesentery connecting the lesser curvature of the stomach and the proximal end of the duodenum to the liver and diaphragm. Greater: region of the mesentery extending as a fold from the great curvature of the stomach and the transverse colon over the small intestine.
Describe the enzymatic digestion of lipids. List where each step of digestion occurs and the breakdown products of each step.
Lipids include triglycerides, phospholipids, cholesterol, steroids, and fat-soluble vitamins. Lipase enzymes digest lipid molecules. Digestion starts in the oral cavity by lingual lipase, it then continues in the stomach by gastric lipase, and continues in the small intestines by pancreatic lipase. Lipase alone cannot completely digest lipid. Lipase works together with emulsification. emulsification breaks the large lipids into smaller lipids allowing lipase to cover a larger surface area.
What is the difference between mechanical digestion and chemical digestion?
Mechanical: mastication and mixing of foods. chemical: composed of digestive enzymes secreted along the digestive tract.
What is the mesentery? Name and describe the location of the mesentery in the abdominal cavity.
Mesentery is a continuous, double layer of epithelial tissue attached along its full length to the posterior abdominal wall. It holds the abdominal organs in place. there are 6 regions 1. mesentery of the small intestine 2. right mesocolon: 3. transverse mesocolon 4. left mesocolon 5. mesosigmoid: anchors sigmoid colon 6. mesorectum: anchors rectum
List the enzymes of the small intestinal wall and give their functions.
Mucus- protects duodenum from acidic chyme and intestinal wall from digestive enzymes Brush Border enzymes: Disaccharidases- breaks down disaccharides to monosaccharides Peptidases: break peptide bonds between amino acids of polypeptides Enterokinase: converts Trypsinogen to trypsin Sucrase: break apart sucrose into glucose and fructose Maltase: breaks part maltose into two glucose molecules Isomaltose: breaks apart isomaltose into 2 glucose molecules Lactase: breaks apart lactose into glucose and galactose
Match each enzyme with its function Enzyme: Pancreatic amylase Pancreatic lipase Trypsin Function: fat digestion digest protein polysaccharide digest
Pancreatic amylase: Polysaccharide digestion Pancreatic lipase: Fat digestion Trypsin: Digests protein
What kinds of movements occurs in the large intestine?
Peristaltic waves are largely responsible for the moving of chyme alone the ascending colon. In the transverse and descending colon mass movements (Forcible peristaltic movements of short duration, occurring only 3 to 4 times a day, which moves the contents of the large intestine) occur. Mass movements occur usually after a meal due to the presence of food in the stomach and duodenum.
Digestive function of the small intestine:
Propulsion and mixing: Segmental contractions mix the chyme, and peristaltic contractions move the chyme into the large intestine: Secretion: Bicarbonate ions from the pancreas and bile from the liver neutralize stomach acid to from a pH environment suitable from pancreatic and intestinal enzymes. Mucus provides lubrication, prevents digestion of the intestinal wall, and protects intestine from stomach acid Digestion: Segmental contractions aid mechanical digestion. Enzymes frog the pancreas and the lining of the small intestine complete the breakdown of food molecules. Bile salts from the liver emulsify lipids to allow lipid digestion. Absorption: The circular folds, villi, and microvilli increase surface area. Most nutrients are actively or passively absorbed. Most of the ingested water or the water in digestive tract secretions is absorbed.
Digestive function of the large intestine
Propulsion and mixing: slight segmental mixing occurs. Mass movements propel feces towards the anus, and defection eliminates the feces. Secretion: mucus provides lubrication; mucus and bicarbonate ions protect against acids produced by bacteria. Absorption: The first half of the colon absorbs salts, water and vitamins produces by bacteria. Elimination: The second half of the colon holds feces until they are eliminated
Digestive function of the pharynx.
Propulsion and mixing: swallowing moves the bolus from the oral cavity to the esophagus. materials are prevented from entering the nasal cavity by the soft palate and kept out of the lower respiratory tract by the epiglottis and vestibular folds. secretion: mucus provides lubrication.
What are the 2 kinds of movement of the small intestine? How are they regulated?
Segmental contractions mix the intestinal contents peristaltic contractions propel the intestinal contents along the digestive tract. Local mechanical and chemical stimuli regulate the motility. Smooth muscle contractions increase in response to distention of the intestinal wall. Solutions that are either hypertonic or hypotonic, solutions with a low pH, and certain products of digestion, such as amino acids and peptides, also stimulate contractions of a small intestine.
Describe the mechanism of absorption and the route of transport for water-soluble and lipid-soluble molecules.
Some molecules can be absorbed by diffusion, whereas others must be transported across the intestinal wall. Water, ions, and water-soluble digestive products, such as glucose and amino acids, enter the hepatic portal system and travel to the liver. Lipid-soluble molecules are coated with proteins and transported into lymphatic capillaries called lacteals and travel to the left subclavian vein, then travel in the blood to adipose tissue or to the liver.
What are the 3 phases of swallowing? Sequentially list the processes involved in the last 2 phases and describe how they are regulated.
Swallowing, also referred to as deglutition, is broken up into 3 phrases. 1. voluntary- a bolus of food is formed in the mouth and pushed by the tongue against the hard palate, until it is forced towards the posterior part of the mouth and into the oropharynx. 2. pharyngeal- a reflex is initiated by the stimulation of tactile receptors in the area of the oropharynx. Sensory action potentials travel through the trigeminal(V) and glossopharyngeal (IX) nerves to the swallowing center in the medulla oblongata. Initiating action potentials in the motor neurons, which pass through the trigeminal (V), glossopharyngeal (IX), vagus (X) and accessory (XI) nerves to the soft palate and the pharynx. This phase begins the elevation of the soft palate, which closes the passage between the nasopharynx and oropharynx. The pharynx elevates to receives the bolus of food from the mouth and moves the bolus down the pharynx into the esophagus. The superior, middle, and inferior sphincters contract in succession, forcing the food through the pharynx. At the same time, the upper esophageal sphincter relaxes, the elevated pharynx opens the esophagus, and food is pushed into the esophagus. 3. esophageal- muscles contractions in the walls of the esophagus occur in peristaltic waves. Gravity helps moved liquids, and watery food through the esophagus. As the waves and the food bolus approach the stomach, the lower esophageal sphincter in the esophagus relaxes. The presence of food in the esophagus stimulates the myenteric plexus, which controls the peristaltic waves. Food in the esophagus also stimulates tactile receptors, which send sensory impulses to the medulla oblongata through the vagus nerves. Motor impulses, in turn, pas along the vagal efferent fibers to the skeletal and smooth muscles within the esophagus, thereby stimulating their contractions and reinforcing the peristaltic contractions
Where is the esophagus located? Describe the tunics of the esophageal wall and the esophageal sphincters.
The esophagus expends from the pharynx to the stomach, lying in the mediastinum, anterior to the vertebrae and posterior to the trachea The esophagus consists of 4 tunics the mucosa, submucosa, muscularis, and adventitia. The esophagus differs from the rest of the digestive tract because it has skeletal muscle fibers in the superior 1/3, a mix of skeletal and smooth muscle fibers in the middle 1/3, and smooth muscle fibers in the inferior 1/3. The upper and lower esophageal sphincters regulate the movement of materials into and out of the esophagus.
What is the function of the gallbladder? What stimulates the release of bile from the gallbladder?
The gallbladders' function is to store and concentrate bile. It concentrates the bile but absorbing some of the water and electrolytes. Bile is released from the gallbladder by contractions stimulated by cholecystokinin and, to a lesser degree, by vagal stimulation.
Describe the parts of the large intestine.
The large intestine consists of 4 parts 1. cecum- meets with the small intestine at the ileocecal junction and extends inferiorly, it contains the vermiform appendix and its most inferior end. 2. colon- can be broken down into 4 parts, the ascending colon (extends superiorly form the cecum and ends at the right colic flexure), transverse colon (extends from the right colic flexure to the left colic flexure), descending colon (extends from the left colic flexure to the superior opening of the true pelvis), and the sigmoid colon (S-shaped tube that extends into the pelvis and ends at the rectum.) 3. rectum- straight muscular tube that begins at the distal end of the sigmoid colon and ends at the anal canal. 4. anal canal- Begins at the inferior end of the rectum with the internal anal sphincter and ends at the anus with the external anal sphincter.
Why must digested lipids be moved out of the intestinal epithelial cells into lacteals of the lymphatic system?
The lipids become surrounded with hydrophilic proteins inside the intestinal epithelial cells to form chylomicrons. Chylomicrons cannot move through the hydrophobic cell membrane by simple diffusion and are too large to move through a membrane transport protein. Consequently, they are packed into vesicles for exocytosis across the plasma membrane and into lacteals.
What are the functions of the lips and checks? What muscle forms the substance of the lips and of the checks?
The lips and checks help manipulating food for mastication. They also help form words when we speak. The lips are formed by the orbicularis oris muscle and tissue the muscles of the cheek are the buccinator muscle
Describe the lobes of the liver. What is the porta hepatis?
The liver consists of 4 lobes
Explain why the portal triad has both an artery and a vein, yet both have blood flowing in the same direction
The liver receives not only oxygenated blood via an artery, but also a second supply of blood via a vein. The second supply is from the hepatic portal vein, which has nutrient-rich, but oxygen-poor, blood from the small intestine. Both the hepatic artery and hepatic portal vein are following in the same direction in the portal triad because they are booth bringing essential oxygen and nutrients to the liver. The liver is the first stop for the portal blood before being reoxygenated because the liver is a metabolic center designed to store and process nutrients, as well as scan blood for pathogens. Blood does leave the liver, but it does so via the central veins, then into hepatic veins.
Name the substance secreted and absorbed in the large intestine.
The major secretion is mucus. Mucus is secreted by numerous goblet cells scattered along the length of the mucosa of the large intestine.
What is the role of microorganisms in the large intestine?
The microorganisms are referred to as normal microbiota of the gut. They synthesize vit k,
As the stomach fills, why does the pressure not greatly increase until maximum volume is reached?
The rugae flatten as the stomach volume increases, allowing the stomach to accommodate large amounts of food with little increased pressure.
Describe the parts of the stomach. List the tunics of the stomach wall. How is the stomach wall different from the esophagus wall.
The stomach is divided into 4 regions 1. cardia-opening 2. fundusleft of the cardia and superior to the cardiac opening. 3. body-largest part of the stomach which turns right creating the great curvature and the lesser curvature 4. pylorus- the body narrows to form a funnel-shape The stomach consists of 4 tunics the serosa (outermost layer), the muscularis which is broken into 3 layers (1. the outer longitudinal layer, 2. the middle circular layer, 3. inner oblique layer- helps generate strong contractions that physically break down ingested food into smaller particles.), the submucosa and the mucosa. The submucosa and mucosa are arranged in large holds called rugae that allows the stomach to stretch.
List the functions of the tongue. Distingue between intrinsic and extrinsic tongue muscles.
The tongue moves food in the mouth and, in cooperation with the lips and gums, holds the food in place during mastication. It also helps with swallowing and speech. Intrinsic muscle: are responsible for changing shape of the tongue, such as flattening and elevating it during drinking or swallowing. Extrinsic muscles: protrude and retract the tongue, move it from side to side, and change its shape.
What is the difference between the vestibule and the oral cavity proper?
The vestibule is the space between the lips or cheeks and the teeth. The oral cavity proper lies medial to the teeth
Where are the visceral peritoneum and parietal peritoneum found? Define and give examples of the retroperitoneal organs.
Visceral peritoneum covers the organs of the abdominal cavity parietal peritoneum covers the interior surface of the wall abdominal cavity retroperitoneal: non-mesenteric structures correlates to the parietal peritoneum and includes structures that are posterior to the mesentery such as the inferior vena cava, kidneys and ureters.
What chemical mechanisms regulate the digestive system?
acetylcholine, norepinephrine, serotonin
What are the 3 major ENS neurotransmitters
acetylcholine: stimulates norepinephrine: inhibits serotonin: stimulates
What is the submucosal plexus?
aka Meissner plexus: gangliated plexus of unmyelinated nerve fibers of the intestinal submucosa. Axons from the plexus stimulate the cells of the epithelial intestinal glands causing them to secrete. it controls the secretions of the digestive tract. the esophagus and stomach lack a submucosal plexus.
proteins breaks down into
amino acids
What are gallstones?
crystallization of cholesterol or calcium and bile salts if a gallstone passes and enters the cystic ducts if blocks the release of bile. If moves far enough down the duct it can also block the pancreatic duct, resulting in pancreatitis.
What makes up the portal triad
hepatic artery, portal vein, bile duct
Name the types of teeth.
incisors: cutting teeth canines: cuspid tooth premolars: bicuspid teeth. molars: tricuspid teeth; 3 posterior teeth of the dental arches.
What are the functions of saliva?
it has 3 functions 1. keeps oral cavity moist 2. protective 3. begins digestion
Describe the stimuli that stimulated the release of saliva. What nerves are involved?
it is stimulated by both the parasympathetic and sympathetic nervous systems, but more by the parasympathetic. Salivary nuclei in the brainstem increase salivary secretion by sending action potentials through parasympathetic fibers of the facial (VII) and glossopharyngeal (IX) cranial nerves in response to stimuli
Name the 2 kinds of stomach movements. How are stomach movements regulated by hormones and nervous control?
mixing waves: contractions that occur about every 20 seconds proceeding from the body of the stomach toward the pyloric sphincter. Peristaltic waves: forces chyme near the periphery of the stomach toward the pyloric sphincter The neural mechanisms that stimulate stomach secretions are also involved with increasing stomach motility; the major stimulus is distension of the stomach wall. The enterogastric reflex and the hormone cholecystokinin are major inhibitors of gastric motility.
Carbohydrates break down into
monosaccharides
What are permanent and deciduous teeth?
permanent (adult/secondary): the teeth of an adult mouth replace deciduous teeth at 5 years to 11 years old. deciduous teeth (primary/milk/baby): being coming in at 6 months of age until 24 months of age.
Digestive function of the stomach
propulsion and mixing: mixing waves churn material and stomach secretions into chyme. Rugar all the stomach to expand and store food. Peristaltic waves move the chyme into the small intestine. Secretion: Release of hydrochloric acid creates the acidic stomach environment. The acid kills most microorganisms and activates the precursor of the proteolytic enzyme pepsin. Mucus provides lubrication and prevents digestion of the stomach wall. Digestion: mechanical digestion occurs as food is churned in the stomach by mixing waves. Protein digestion begins as a result of the actions of hydrochloric acid and pepsin. Absorption: water alcohol and aspirin
Digestive function of the esophagus:
propulsion and mixing: peristatic contractions move the bolus from the pharynx to the stomach. The lower esophageal sphincter limits reflux of the stomach contents into the esophagus. secretion: mucus provides lubrication and protects the inferior esophagus from the stomach acid.
what are ezymes
proteins that act as catalyst.
How are gastric secretions inhibited? Whis is this inhabitation necessary?
secretin (released in response to acidic solution in the duodenum. It inhibits gastric secretions by inhibiting both parietal and chief cells.) Cholecystokinin (released in response to fatty acids, other lipids, and to a lesser degree protein digestion products in the duodenum and the proximal jejunum. In inhibits gastric secretion) It ensures that the acidic chyme entering the duodenum is neutralized, which is required for the digestion of food by pancreatic and brush-border enzymes in the intestine, and for prevention of peptic ulcer formation
What types of tissue are found in serosa and adventitia tunic?
serosa: part of the digestive tract located in the peritoneal cavity thin layer of connective tissue and a simple squamous epithelium adventitia: esophagus and the retroperitoneal organs connective tissue covering that blends with the surrounding connective tissue and is derived from adjacent connective tissue.
What is the difference between serous and mucous saliva?
serous portion of the saliva provides moistening, it also contains a digestive enzyme called salivary amylase, which breaks the covalent bonds between glucose molecules in starch and other polysaccharides to produce the disaccharides maltose and isomaltose. mucous portion contains large amounts of mucin that gives a lubricating quality to saliva
Intrinsic factor is secreted by the organ called the
stomach
What are hepatic cords?
strings of cells that radiate out from the central veins of each lobule like the spokes of a wheel. It is composed of hepatocytes, which are the functional cells of the liver.
In what tunics of the digestive tract are the submucosal and myenteric plexuses found? What are their functions?
submucosal plexus: submucosal tunic; controls secretions myenteric plexuses: muscularis tunic; control motility of the intestinal tract.
What are taeniae coli, haustra, and crypts?
taeniae coli- the incomplete longitudinal muscle layer that forms 3 bands haustra- sacs of the colon, caused by contractions of the taeniae coli, which are slightly shorter than the guts so that the latter is thrown into pouches crypts- pit like depression or tubular recess.
What is the function of the ileocecal sphincter?
the ileocecal sphincter is located between the ileum and the large intestine remains mildly contracted most of the time, when peristaltic waves reach it from the small intestine cause it to relax and allow the chyme to move from the ileum into the cecum. Closure of the sphincter facilitates digestion and absorption in the small intestine into the large intestine and prevents materials from returning to the ileum from the cecum
What is the primary function of the stomach?
to store and mix chyme
