ndSBI3UI-02 DIGESTIVE SYSTEM QUIZ REVIEW September 30, 2021 What is the digestive system and why is it important? The digestive system is made of the Gastrointestinal tract, and 3 accessory organs; liver, pancreas and gallbladder Importance: The body needs nutrients to work properly and be healthy. These nutrients are proteins, fats, carbohydrates, lipids, nucleic acids, vitamins and water ● Proteins break down amino acids ● Fat breaks into fatty acids and glycerol ● Carbohydrates break simple sugars SUMMARY ● 4 major categories of macromolecules that contain essential nutrients needed to maintain life: carbohydrates, lipids, proteins, and nucleic acids ● Hydrolysis breaks down macromolecules Important Definitions Chyme: semi- pasty food mixed with gastric juice produced in stomach that’s been thoroughly mixed Rugae: folded lining (contains villi) in stomach that increases SA dramatically. - Important to absorb nutrients efficiently System Order Ingestion, Digestion, Absorption, Excretion Organs and their Functions Mouth: food transports from mouth to esophagus. ○ epiglottis folds over windpipe preventing food and drink to cause choking ○ Tongue, teeth, soft palate, hard palate How does it work? salivary glands make saliva to moisten food, so it moves more easily through your esophagus. **There are 6 salivary glands ● Salivary glands produce amylase - breaks down starch into simple sugars. ● Salivary glands produce lingual lipase - breaks down lipids Esophagus: Brain signals esophagus and peristalsis begins. ○ Peristalsis contracts and relax bolus down tube ○ Under tonic control, very dependant on nerves ○ Cardiac/esophageal sphincter opens to allow bolus go down stomach How does it work? Peristalsis. - Circular muscle contracts behind bolus and pushes bolus forward - Longitudinal muscle contracts ahead of bolus Stomach: muscle contractions churn bolus and gastric juice, which is then broken down into chyme ○ Pyloric sphincter regulates chyme movement to small intestine How does it work? Glands in stomach lining make stomach acid and enzymes that break down food. Stomach muscles mix food with these digestive juices. Small Intestine: makes digestive juice mixing bile and pancreatic juice to breakdown protein, carbs and fat ○ ○ Absorbs water and digest nutrients into bloodstream FIRST SECTION: Duodenum (90% of digestion) ● Chyme is pushed into the U-shaped duodenum ● Villi has blood supply to absorb nutrients ○ SECOND SECTION: Jejunum ● ○ Breaks down remaining proteins and carbohydrates ILEUM: absorbs nutrients and pushees undigested material into Large Intestine Large Intestine: Includes appendix, cecum (first part), colon, rectum ○ absorbs water, and changes liquid waste into stool ○ Colon absorbs 90% water ○ Colon’s bacteria helps produce B&K vitamins, folic acid, etc. How? Peristalsis moves stool into rectum. Rectum & Anus: rectum stores stool until pushed out of anus during bowel movement Pancreas- produces hormones and secretes pancreatic juice to digest macromolecules - Delivers digestive juice to S.I through ducts (tube) Gallbladder- stores bile Liver- Produces bile and helps break down RBCs. Helps break down fat by **Bile ducts carry bile from liver to gallbladder (storage) or S.I (use) Process Definition Part of digestive tract where process occurs Chemical digestion Enzymes & liquids break down macromolecules into smaller pieces. The macromolecule's energy and matter regulates metabolism. Small intestine. Mechanical digestion Teeth break down food into small pieces. - Canine teeth to tear - Premolars to chew Mouth. Sphincters ESOPHAGEAL SPHINCTER: ● At the end of the esophagus, a ring- like muscle relaxes and lets food pass into ● stomach This sphincter stays closed to keep food from flowing back up PYLORIC SPHINCTER: ● ● The valve at the end of the stomach Controls flow of chyme Role of Water 70% of the body. The seven roles of water are. ● ● ● ● ● ● ● Forms blood Detoxification Lubricates tissue and joints Eliminates waste Transports Maintains body temperature Produces mucus and bodily fluids Carbohydrates Made of hydrogen, carbon & oxygen ○ Provides short or long term energy storage ○ TWO MAIN TYPES: Simple sugars and polysaccharides ○ Disaccharides/ double sugars- made of 2 simple sugars ● ● Polysaccharides- large molecules made of simple sugars Monosaccharides- carbohydrate hydrolysis’ final products ○ Water- soluble & immediately absorbed by blood Fibre Fibre cannot be digested ● Stimulates growth of beneficial bacteria and mucus secretion causing faster and easier chyme flow ● Rich fibre diets associated with lower cholesterol and reduced risk of heart disease and certain cancers Gastric Secretions Chemicals released by cells of stomach ○ Fe3+ cannot be absorbed ■ Therefore, stomach acids oxidizes Fe3+ into Fe2+ Intrinsic Factor - Protein secreted by stomach - Binds vitamin B12 - Essential because without Vitamin B12, you cannot form HEMOGLOBIN Hemoglobin: a large protein composed of 4 chains (2 alpha, 2 beta) that transports oxygen - Can be injected or orally taken if necessary *Hydrolysis: chemical reaction that breaks down macromolecules with water molecule - reverse reaction of condensation Emulsification The process of breaking down fat to help enzymes digest & pass through the cell membrane ○ Process: Bile salts form a cage around fat molecule ○ Inside cage= polar Outside cage= non- polar Condensation Two molecules form together as one. (Disaccharide + water) Glucose Important energy molecule. (a sugar) ● ● Hypoglycemia: when glucose (concentrated) level is too low ○ Means blood sugar is low ○ The hormone glucagon breaks down big sugars as glucose Hyperglycemia: when glucose (concentrated) level is too high ○ Tells pancreas to release insulin to process glucose properly Peptide Bonds Bonds that connect 2 amino acids. Condensation occurs when peptide bonds connect 2 amino acids Disorders Abdominal adhesions: ○ Scar- like tissue bands that form inside abdomen ○ Causes organ surfaces to stick together which can twist, pull, kink or compress intestines and other organs ○ Can cause complications such as intestinal obstruction or blockage ○ A severe and long lasting issue where the stomach contents come back into Acid reflux: esophagus GI Tract anatomic problems: ○ Lower GI tract may be in wrong place, or shaped abnormally ENTEROKINASE: an enzyme that operates on trypsinogen to form into trypsin (inactive to active) DIAGRAMS How hydrolysis breaks down molecules: Mineral and Vitamins: Small Intestine: The Human Digestive System Consists of the Digestive Tract (a.k.a the GI tract or gastrointestinal tract) ● Is a muscular tube that extends from the mouth to the anus ● Order: Mouth, Esophagus, Stomach, Pancreas, Liver, Gallbladder, Small Intestine, Large Intestine (colon), and Rectum Mouth (INGESTION) ● The primary role of the mouth is to digest food by reducing its size ● Includes the tongue, teeth, hard and soft palate ● Three sets of salivary glands (*6 salivary glands in total) that secrete saliva: parotid, sublingual and submaxillary ● The tongue contains taste buds to recognize different flavours and it also moves food around while chewing (mixes food particles with saliva) ● Uvula: prevents food from entering the naso-pharynx Digestion in the Mouth ● There are two types of digestion in the mouth: mechanical and chemical digestion ● Mechanical digestion by chewing (mastication); teeth bite, tear, and grind food ○ Teeth have 4 quadrants: physical breakdown of food, type of teeth depends on food source. ○ Molars: grind food ○ Premolars: tear and grind food ○ Canine: tear food ○ Incisors: bite and cut food ● Salivary glands produce saliva: chemical digestion of carbohydrates by amylase ● Saliva contains the enzymes amylase and lingual lipase: amylase breaks down carbohydrates (starches) in your food and lingual lipase breaks down lipids. ● How does it work? salivary glands make saliva to moisten food, so it moves more easily through your esophagus. Esophagus (MOVEMENT OF FOOD TO STOMACH) ● Esophagus: the muscular tube through which food passes from the mouth to the stomach ● Brain signals esophagus and peristalsis begins. ● Peristalsis: wave-like series of muscular contractions in the esophagus ● Food exiting the mouth forms into a bolus - the bolus passes the epiglottis to prevent choking ● Peristalsis occurs: contraction and relaxation of the smooth muscle moves the bolus down to the stomach ● The cardiac/esophageal sphincter opens up to allow the bolus of food to enter the stomach ● Once the ‘digested’ food enters the esophagus - peristaltic motion propels the food toward the stomach ● About 3 cm before the juncture of the esophagus and the stomach, the circular muscle layer functions as a broad lower esophageal sphincter, also known as the gastroesophageal sphincter ○ The sphincter is usually in a tonically constricted state ○ A healthy gastroesophageal sphincter prevents the backflow (reflux) of stomach contents into the lower esophagus. ● As you chew your food, your tongue helps mould and smooth the food into a soft mass, called a bolus. The tongue then pushes the bolus to the back of your mouth. When you swallow, the bolus enters the top of the esophagus. Once the ‘digested’ food (bolus) enters the esophagus, peristaltic motion propels the food (bolus) towards the stomach. The opening of the esophagus lies next to the opening of the windpipe, or trachea, which carries air to and from the lungs. To prevent the food (bolus) from going down the wrong tube and choking you when you swallow, the opening of the trachea is closed by a valve (flap-like tissue) called the epiglottis when you swallow. ● Epiglottis: a valve or a ‘flap-like tissue that closes/covers the opening of the trachea to prevent food from going down the wrong tube and choking you when you swallow. ● Esophagus does not secrete enzymes ● Some diseases: Acid reflux, Bulimia (acid damages lining of esophagus), Cancer Peristalsis in Detail ● Involves two muscles: circular muscle and longitudinal muscle ● Circular muscle is the inside layer, longitudinal muscle is the outside layer ● STEP 1: Contraction of circular muscles behind the food mass (bolus) ● STEP 2: Contraction of longitudinal muscles ahead of the food mass (bolus) ● STEP 3: Contraction of the circular muscle layer forces/pushed the food mass (bolus) forward (towards the stomach) The Stomach (DIGESTION AND SOME ABSORPTION) ● Muscle contractions in the stomach churn and mix the bolus with gastric juice: a combination of water, mucus, HCl acid, and enzymes (e.g. pepsin) ● The bolus is chemically broken down into a solution called chyme ● The pyloric sphincter regulates the movement of chyme into the small intestine ● After food in the stomach has become thoroughly mixed with the stomach secretions, the resulting mixture that passes down the gut is called chyme. The appearance of chyme is that of a murky semifluid or paste. ● How does it work? Glands in stomach lining make stomach acid and enzymes that break down food. Stomach muscles mix food with these digestive juices. ● Rugae: folded lining (contains villi) in stomach that increases surface area dramatically. Allows the expansion of the stomach. ○ Important to absorb nutrients efficiently ● Mucus: protects the stomach from HCl and pepsin ● Diseases: Ulcer, acid reflux Gastric Secretions ● The gastric glands produce around 2 - 3 L of gastric juice per day ● Stomach acid (HCL acid) has many functions: ○ Activates enzymes such as pepsin and lingual lipase ○ Breaks up connective tissues and plant cell walls ○ Converts ingested Fe3+ into Fe2+, which can be absorbed and used to make hemoglobin ○ Contributes to nonspecific disease resistance by destroying most ingested pathogens Pepsin and Gastric Lipase ● Zymogens are secreted inactive enzymes that are later activated by the removal of the required amino acids from the proteins. ● The chief cells secrete a zymogen called pepsinogen ○ ● In the presence of HCl acid, pepsinogen is converted to pepsin. The enzymes gastric lipase and lingual lipase (produced in the salivary glands) digest 10-15% of the dietary fat in the stomach. The remainder is digested in the intestines. Intrinsic Factor ● The parietal cells of the stomach also secrete a glycoprotein called the intrinsic factor. The intrinsic factor is essential for the absorption of vitamin B12. Without vitamin B12, hemoglobin cannot be synthesized and pernicious anemia develops. ● The secretion of intrinsic factor is the only indispensable function of the stomach ● Binds to vitamin B-12 ● Hemoglobin: a large protein composed of 4 chains (2 alpha, 2 beta) that transports oxygen in your blood from the lungs to the tissues ○ Can be injected or orally taken if necessary Pancreas ● The pancreas secretes pancreatic juice containing enzymes into the duodenum to digest carbohydrates, lipids, and proteins. ● The pancreas delivers the digestive juice to small intestine through ducts (small tubes) ● The fluid from the pancreas contains bicarbonate (HCO3-) and neutralizes the acidic pH of chyme from the stomach (1 →8) ● The pancreas also produces digestive enzymes ● The pancreas secretes around 1.2-1.5 L of pancreatic juice ● The pancreatic zymogens are trypsinogen, chymotrypsinogen, and procarboxypeptidase. ● When trypsinogen is secreted into the intestinal lumen, it is converted to trypsin (active enzyme) by enterokinase (active enzyme), which is secreted by the mucosa of the small intestine. ● Trypsin also converts chymotrypsinogen and procarboxypeptidase into chymotrypsin (active enzyme) and carboxypeptidase (active enzyme). ● Pancreatic amylase →digests starch ● Pancreatic lipase →digests fat ● Ribonuclease and Deoxyribonuclease →digests RNA and DNA respectively ● HCO3- →neutralizes the acidic pH of chyme from the stomach (from strongly acidic (pH 1) to weakly basic (pH 8)). This produces conditions in which the enzymes in the pancreatic fluid can work most efficiently. The Liver ● The liver produces bile, which is stored in the gallbladder ● Bile salts in bile aid in the physical breakdown of larger lipids into smaller fat droplets, which allows more surface area for further digestion ● The liver also helps break down old red blood cells. ● The liver also digests some vitamins ● Bile ducts carry bile from your liver to your gallbladder for storage, or to the small intestine for use. Gallbladder ● The bile salts produced by the liver are stored in the gallbladder ● The bile salts are released by a hormone ● Gallbladder stores bile between meals. When you eat, your gallbladder squeezes bile through the bile ducts into your small intestine. Small Intestine ● Absorption of monosaccharides, amino acids, glycerol and fatty acids occurs ● The small intestine is equipped with folds and little finger-like projections called villi, which increase the surface area for absorption ● The duodenum is the first section of the small intestine ● The jejunum is the second/middle section of the small intestine. Absorption of nutrients occurs here. ● The ileum is the last stop (and the longest section) of the small intestine. It has fewer villi. Its function is to also absorb nutrients, as well as to push the remaining undigested material into the large intestine. ● makes digestive juice which mixes bile and pancreatic juice to complete the breakdown of proteins, carbohydrates and fats Emulsification The process of breaking down fat to help enzymes digest & pass through the cell membrane ○ Process: Bile salts form a cage around fat molecule ○ Inside cage= polar Outside cage= non- polar ○ Takes place in the small intestine The Colon (Large Intestine) ● Absorption of water (90% of the water is absorbed) ● Bacteria that reside in the colon help produce B and K vitamins, folic acid, etc. ● Includes appendix, cecum (first part), colon, rectum ● absorbs water, and changes liquid waste into stool ● How? Peristalsis moves stool into rectum. Anus and Rectum ● Rectum is the lower end of the large intestine ● The remaining matter forms feces ● The feces are stored in the rectum ● The brown colour is from the breakdown of bilirubin from red blood cells ● The odour is from bacterial gases ● The feces are eliminated through the anus (or pushed out of anus) during a bowel movement Accessory Organs ● The liver, pancreas and gallbladder are not part of the digestive tract itself, but they are connected to the digestive tract by ducts. They have a role in digestive activities. Because of this close association with the digestive tract, they are referred to as accessory organs. (An accessory is something that aids or provides support to something else.) Fluids produced by the accessory organs are essential to the process of digestion. Fibre ● Fibre cannot be digested ● Adds bulk to your stool ● Stimulates the growth of beneficial bacteria and the secretion of mucus in your intestines making it faster and easier for chyme to flow ● Diet rich in fiber associated with lower cholesterol and a reduced risk of heart disease and certain cancers Diseases ● Peptic ulcer: a sore on the lining of the stomach or duodenum, most commonly caused by infection with the bacteria Helicobacter pylori ● Acid reflux:
