What is the difference between mechanical and chemical digestion?
Mechanical digestion prepares food for chemical digestion, chews and mix's with saliva, churning of food in the stomach, segmentation of intestines rhythmic local constrictions of intestine, causes mixing improves absorption.
Chemical digestion breaks down complex food molecules into chemical building blocks, enzymes secreted into alimentary canal lumen.
Name the 4 tunics of the alimentary canal.
Mucosa, Submucosa, Muscularis Externa, Serosa
What are the different kinds of papillae? Which contain taste buds?
Filiform, Fungiform, Circumvallate. Fungiform and Circumvallate contain taste buds
What are the purposes of saliva? What digestive enzyme(s) does saliva contain?
The enzymes found in saliva are essential in beginning the process of digestion of dietary starches and fats. These enzymes also play a role in breaking down food particles entrapped within dental crevices, protecting teeth from bacterial decay. saliva serves a lubricative function. moistening food and helping to create a food bolus. This lubricative function of saliva allows the food bolus to be passed easily from the mouth into the esophagus. Saliva contains the enzyme amylase and is capable of breaking down starch into simpler sugars that can be later absorbed or further broken down in the small intestine. Salivary glands also secrete salivary lipase (a more potent form of lipase) to begin fat digestion. It also is initiation of swallowing, and protects the mucosal surfaces of the oral cavity from desiccation
What are the different parts of a tooth? The different layers?
Different parts- Crown, Neck, root.
Crown-projects into the oral cavity from the surface of the gingivae
Neck-marks the boundary between the crown and the root
Root- sits in a bony socket called an aveolus
The different layers are enamel, cementum, periodontal ligament, root canal.
Enamel- covers the dentin of the crown, contains calcium phosphate in a crystalline from, hardest biologically manufactured substance
Cementum-covers the dentin of the root and is less resistant to erosion than is dentin
Peridontal ligament- extends from dentin of the root to the bone of the aveolous
Root Canal- the pulp cavity receives blood vessels and nerves through the root canal, a narrow tunnel within the root of the tooth
Dentin-most of the tooth; tissue that is calcified and consists of tiny tubes
What are the different kinds of teeth? How many are there of each kind? Total?
Different kinds of teeth are incisors, cuspids, bicuspids, and molars. There are 8 incisors, 4 cuspids, 8 bicuspids, 12 molars. There are 32 total including wisdom teeth
How is smooth muscle organized in the intestines? In the stomach?
Stomach- columnar epithelium with goblet cells. To protect surface alkaline mucus and gastric pits. Muscularis externa has an additional layer that runs obliquely.
Intestines- circular folds, deep folds in mucosa and submucosa, bumps and grooves
Where are the 5 sphincters in the digestive tract? What is the role of each?
Gastroesophageal sphincter—Role is to allow food into stomach from esophagus and to prevent acid/food backflow from the stomach into the esophagus
Pyloric sphincter—Role is to keep food in the stomach so it has a chance to digest proteins, then it opens and allows the contents of the stomach (chyme) to enter the small intestine.
Sphincter of oddi—Role is to control the flow of digestive juices into the second portion of the duodenum
Internal anal sphincter—Role is the contract (involuntarily) to push feces toward external anal sphincter
External anal sphincter—Role is to contract (voluntarily) to prevent defecation
Where in the GI tract does starch digestion occur? What chemicals/enzymes are required?
Starch- (Amylase in the mouth and in the small intestine) The salivary glands, contains salivary amylase, an enzyme which starts the digestion of starch in the food.
Where in the GI tract does protein digestion occur? What chemicals/enzymes are required?
Protein- Gastric juice in the stomach starts protein digestion. Gastric juice mainly contains hydrochloric acid and pepsin. As these two chemicals may damage the stomach wall, mucus is secreted by the stomach, providing a slimy layer that acts as a shield against the damaging effects of the chemicals.
Where in the GI tract does fat digestion occur? What chemicals/enzymes are required?
Fat- Digestion of some fats can begin in the mouth where lingual lipase breaks down some short chain lipids into diglycerides. The presence of fat in the small intestine produces hormones that stimulate the release of pancreatic lipase from the pancreas and bile from the liver for breakdown of fats into fatty acids. Complete digestion of one molecule of fat (a triglyceride) results in 3 fatty acid molecules and one glycerol molecule.
Name and explain 2 reasons why the stomach environment is acidic. Why doesn't
the stomach digest itself?
The enzymes in the stomach have an optimum conditions, meaning that they work at a specific pH and temperature better than any others. The acid itself does not break down food molecules, rather it provides an optimum pH for the reaction of the enzyme pepsin and kills many microorganisms that are ingested with the food. It can also denature proteins. This is the process of reducing polypeptide bonds and disrupting salt bridges, which in turn causes a loss of secondary, tertiary, or quaternary protein structure. The parietal cells of the stomach also secrete a glycoprotein called intrinsic factor, which enables the absorption of vitamin B-12. Mucus neck cells are present in the gastric glands of the stomach. They secrete mucus, which along with gastric juice plays an important role in lubrication and protection of the mucosal epithelium from excoriation by the highly concentrated hydrochloric acid.
What are the different types of secretory cells in stomach glands? What does each produce/secrete?
Parietal Cells secrete Intrinsic Factor
Enteroendocrine cells produce a variety of hormones (secretin, gastrin, GIP, CCK, VIP)
Chief cells secrete pepsinogen
What are the three phases of gastric secretion? When does each occur?
The Cephalic phase, the Gastric phase, and the Intestinal phase.
occurs even before food enters the stomach, especially while it is being eaten. It results from the sight, smell, thought, or taste of food, and the greater the appetite, the more intense is the stimulation
is a period in which swallowed food and semidigested protein (peptides and amino acids) activate gastric activity. About two-thirds of gastric secretion occurs during this phase. Ingested food stimulates gastric activity in two ways: by stretching the stomach and by raising the pH of its contents. Gastric secretion is stimulated chiefly by three chemicals: acetylcholine (ACh), histamine, and gastrin.
the duodenum responds to arriving chyme and moderates gastric activity through hormones and nervous reflexes. The duodenum initially enhances gastric secretion, but soon inhibits it. Stretching of the duodenum accentuates vagal reflexes that stimulate the stomach, and peptides and amino acids in the chyme stimulate G cells of the duodenum to secrete more gastrin, which further stimulates the stomach
What structures does the small intestine have to increase surface area? Why have them?
Circular Folds- increases surface area available for absorbing nutrients, each circular fold contains intestinal villi and each villi is covered by epithelial cells whose exposed surfaces are covered with microvilli, this arrangement increases the total area for absorption by a factor of more than 600 to approximately 2 million.
What is the function of bile? Where does it come from?
Bile contains bile acids, which are critical for digestion and absorption of fats and fat-soluble vitamins in the small intestine. Many waste products are eliminated from the body by secretion into bile and elimination in feces. Bile is produced by the liver and is temporarily stored and concentrated in the gallbladder
What are the different parts of the colon?
The ascending colon, transverse colon, descending colon,and sigmoid colon. The ascending and descending colon are firmly attached to the abdominal wall. The transverse colon and sigmoid colon are suspended by mesenteries.
What are the differences between haustral contractions & mass movements?
Haustral contractions are slow segmenting movements that occur every 25 minutes. One haustrum distends as it fills, which stimulates muscles to contract, pushing the contents to the next haustrum.
Mass Movements- powerful peristaltic contractions, occur a few times per day in response to distenstion of the stomach and duodenum, these contractions begin at the transverse colon and push materials along the distal portion of the large intestine.
Why are changes in pH important for proper digestion? Explain using 2 different areas
of the GI tract to demonstrate your knowledge
pH plays a crucial role in a normally functioning digestive tract. In the mouth, pharynx, and esophagus, pH is typically about 6.8, very weakly acidic. Saliva controls pH in this region of the digestive tract. Salivary amylase is contained in saliva and starts the breakdown of carbohydrates into monosaccharides. Most digestive enzymes are sensitive to pH and will denature in a high or low pH environment. The stomach's high acidity inhibits the breakdown of carbohydrates within it. This acidity confers two benefits: it denatures proteins for further digestion in the small intestines, and provides non-specific immunity, damaging or eliminating various pathogens In the small intestines, the duodenum provides critical pH balancing to activate digestive enzymes. The liver secretes bile into the duodenum to neutralize the acidic conditions from the stomach, and the pancreatic duct empties into the duodenum, adding bicarbonate to neutralize the acidic chyme, thus creating of neutral environment. The mucosal tissue of the small intestines is alkaline with a pH of about 8.5
How is the pancreas involved in digestion?
By producing pancreatic alpha-amylase- enzyme that breaks down certain starches
Pancreatic lipase- breaks down lipids, releasing products like fatty acids that can be easily absorbed.
Proteolytic enzymes- breaks proteins apart, they are secreted as inactive proenzymes to protect the pancreas against the action of its own enzymes. The proenzymes become active once they are in the same duodenal lumen. The active enzymes include trypsin, chymotrypsin, carbodypeptidase, and elastase, Together they break down proteins
What is contained in the secretion from the acinar cells? What is its function?
Digestive enzymes, These cells of the pancreas that produce and transport chemicals that will exit the body through the digestive system. They are secreted in the duodenum where they assist in the digestion of food.
Why is release of a bicarbonate rich juice from the pancreas important for the digestive process? What stimulates its release?
The juices that come from the pancreas are responsible for breaking down fats, carbohydrates and proteins in chyme that comes from the stomach. The pancreas secretes a basic solution that neutralizes the acidic solution left over from the stomach. The juice provides an optimal environment for intestinal and pancreatic enzymes.
Secretin from intestinal cells stimulates the release.
Why produce mucus in the digestive tract?
Mucus protects the inner lining of the digestive system against abrasive objects. Mucus also provides a nice slippery surface so food slides more easily through each tract that breaks down the food. Mucus protects the inside of organs that produce acidic liquids—this keeps an organ from digesting itself.
Where does intrinsic factor come from? What does it do?
IF is a glycoprotein produced by parietal cells of the stomach. It is necessary for the absorption of vitamin B12 later on in the small intestine.
Describe the conditions of chyme leaving the stomach and entering into the small intestine. How does the small intestine respond? What is the function of each secretion released into the small intestine?
Chyme is composed of a highly acidic, viscous, soupy mixture. To offset the acidic conditions of chyme the small intestine relies on liver and pancreatic secretions for digestion and absorption. At the point of chyme leaving the stomach, carbohydrates and proteins are already partially digested, while lipids have not yet begun. The small intestine responds to the entrance of chyme by mixing the chyme with secretions via segmentation—pacemaker cells initiate contractions. Chyme leaves the stomach and enters the duodenum via the pyloric sphincter. Here, maltase breaks down maltose into glucose monomers and peptidases break down peptides into amino acids. Bile is then released from the gall bladder and enters the small intestine via the bile duct to aid in the digestion of fats into glycerol and fatty acids. The chyme then enters the jejunum where digestion continues and absorption begins (the jejunum is composed of many folds that increase its surface area and therefore improve absorption.) Glucose and amino acids are transported across the membrane by means of active transport (requires ATP) while glycerol and fatty acids require the help of carrier proteins (micelles-produced in the liver)) to enter the blood stream. Next, the chyme enters the ileum which is mainly responsible for the absorption of select nutrients. Once the chyme leaves the small intestine, most of the nutrients have been absorbed and only waste products and water remain.