Digestive System Past Paper PDF

Digestive System Why do humans need to eat? Animals are Heterotrophic A heterotroph is an organism that cannot produce its own food. Therefore, it needs to get nutrition from other sources of organic carbon. In other words, it needs to feed from another organism Animals are Heterotrophic In general,...

Digestive System Why do humans need to eat? Animals are Heterotrophic A heterotroph is an organism that cannot produce its own food. Therefore, it needs to get nutrition from other sources of organic carbon. In other words, it needs to feed from another organism Animals are Heterotrophic In general, animals fall in three categories Carnivores Herbivores Omnivores ✓ Eat other animals ✓ Eat mainly autotrophs ✓ lions, sharks, hawks, spiders, snakes ✓ Regularly consume animals and plants or algae ✓ giraffes, guinea pigs, cows, elephants, deer ✓ humans, pigs, bears, racoons, cockroaches (plant, algae, etc) The main stages of food processing are ingestion, digestion, absorption, and elimination Ingestion is the act of eating. Digestion is the process of breaking food down into molecules small enough to be absorbed. o Mechanical (physical) digestion increases the surface area of food for faster chemical digestion o Chemical digestion is the process of enzymatic hydrolysis, which splits bonds in molecules with the addition of water Absorption is the uptake of nutrients by the digestive tract Elimination is the passage of undigested material out of digestive tract Mechanical Digestion - Teeth Mechanical digestion starts in the mouth with the help of Teeth. Vertebrate dentition (shape and number of teeth) varies greatly among the different groups. Mammals can have 4 types (shapes) of teeth (incisors, canine, premolars and molars). Cheek teeth is a terminology that includes both premolars and molars. Some animals grow new teeth during their entire life. However, mammals only have two sets of teeth during its life: deciduous teeth (milk/baby teeth) and permanent teeth (adult teeth). Interesting fact, many animals only have one shape of teeth. Mammalian Dentition: Herbivore x Carnivore x Omnivore Human dentition Mechanical Digestion - Peristalsis peristalsis peristalsis Oral cavity chemical digestion Incisors are sharp and blade-like for tearing and grinding food. Incisors are sharp and blade-like for tearing and grinding food. False Peristalsis is rhythmic contractions of skeletal muscles. Incisors are sharp and blade-like for tearing and grinding food. False Organs specialized for sequential stages of food processing form the mammalian digestive system. gastrointestinal tract (GI tract) peristalsis. Organs specialized for sequential stages of food processing form the mammalian digestive system Mammalian accessory organs ✓Tongue - Shape food into a bolus and provides help with swallowing. ✓Salivary Glands - Secrete saliva into the oral cavity ✓Pancreas - Secrete enzymes into the duodenum (small intestine) ✓Liver and Gall Bladder - Liver produces bile, and gall bladder stores and secretes it into the duodenum Oral Cavity 2. Salivary glands deliver saliva to lubricate food. Teeth help in mechanical digestion by breaking food into smaller particles (chewing). mechanical digestion chemical digestion salivary amylase ✓ Salivary amylase: ✓ Lingual lipase: lingual lipase. Pharynx and Esophagus pharynx esophagus Stomach esophageal sphincter ✓Esophageal sphincter by the stomach ✓ pepsin gastric juice produced chyme hydrochloric acid Stomach ✓ mechanical digestion Pyloric Sphincters regulate chyme entry into the small intestine The stomach has accordion-like folds and a very elastic wall (organ can stretch to accommodate about 2 litres of food and fluid) Gastric rugae are a series of ridges produced by folding in the stomach When food enters, these rugae unfold and become stretched (thereby expanding the stomach) Stomach Cells Parietal cells secrete hydrogen (H+) and chloride (Cl-) ions, separately Chief cells secrete inactive pepsinogen, which is activated to pepsin when mixed with hydrochloric acid in the stomach ✓Pepsin breaks peptide bonds and cleaves proteins into smaller polypeptides Mucous cells (or goblet cells) secretes mucus, which protects stomach lining from gastric juice Besides activating pepsinogen into pepsin, HCl also kills invading bacteria Small Intestine small intestine ✓ Duodenum ✓ Jejunum ✓ Ileum Small Intestine Duodenum ✓ Chyme from the stomach mixes with digestive juices from the pancreas, liver, gall bladder, and small intestine itself. Pancreatic secretions zymogens pro-enzymes pancreas Zymogens or pro-enzymes are dormant (non-functional) enzyme precursors ✓ ✓ ✓ Enzymatic hydrolysis in the human digestive system Bile is produced by the liver and acts emulsifying fat bile liver gall bladder emulsifies mechanical digestion. chemical digestion By Onkar Bains, with modifications by Vinicius Cavicchioli Azevedo Liver Functions Besides bile production, the liver has several functions: ✓ Detoxifies the blood to rid it of harmful substances such as alcohol, drugs and environmental toxicants ✓ Stores some vitamins and iron ✓ Stores glucose as glycogen ✓ Converts glycogen to usable sugar when the body’s sugar (glucose) levels fall below normal ✓ Breaks down hemoglobin as well as insulin and other hormones ✓ Converts ammonia to urea ✓ Destroys old red blood cells By Onkar Bains, with modifications by Vinicius Cavicchioli Azevedo Small Intestine Jejunum ✓ Hydrolysis of nutrients is continued while most of the carbohydrates and amino acids are absorbed through the intestinal lining. Ileum ✓ The ileum is the last part of the small intestine and here the bile salts and vitamins are absorbed into the bloodstream. The undigested food is sent to the colon from the ileum via peristaltic movements of the muscle. Absorption in the small intestine – villi and microvilli villi microvilli By Onkar Bains lacteal chylomicrons By Onkar Bains hepatic portal vein Absorption in the large intestine colon cecum large intestine appendix By Onkar Bains Absorption in the large intestine feces rectum By Onkar Bains, with modifications by Vinicius Cavicchioli Azevedo The pH of gastric juice in the stomach is about 2 due to the formation of HCl. Where does this formation of HCl occur? The pH of gastric juice in the stomach is about 2 due to the formation of HCl. Where does this formation of HCl occur? In the stomach lumen Gall bladder secretes bile in the duodenum to emulsify (mechanical digestion) fat and assist in chemical digestion of lipids Salivary amylase is an enzyme produced in the stomach to help break down carbohydrates. Salivary amylase is an enzyme produced in the stomach to help break down carbohydrates. False Salivary amylase is an enzyme produced in the salivary glands to help break down carbohydrates The pancreas produces digestive enzymes that are released into the ileum. The pancreas produces digestive enzymes that are released into the ileum. False The pancreas produces digestive enzymes that are released into the duodenum The liver and pancreas are parts of the gastrointestinal tract. The liver and pancreas are parts of the gastrointestinal tract. False The liver and pancreas are accessory organs Regulation of digestion by specific hormones - Gastrin Hormones are chemical signals that travel in bloodstream to affect function of a target organ gastrin Gastrin ✓ Production of gastric juice ✓ Growth of gastric mucosa By Onkar Bains Regulation of digestion by specific hormones - CKK and Secretin Chyme (an acidic mixture of partially digested food) eventually passes from the stomach to the duodenum This triggers cells lining the wall of duodenum to release the hormones cholecystokinin (CCK) and secretin into the bloodstream CCK triggers: ✓ the gall bladder to contract so that bile can be released into the duodenum via bile duct ✓ the pancreas to secrete digestive pancreatic juices into duodenum By Onkar Bains Regulation of digestion by specific hormones - CKK and Secretin Secretin triggers pancreas to secrete HCO3 ions into duodenum so that chyme is neutralized - If chyme is rich in fats, the high levels of secretin and CCK released act on stomach to inhibit peristalsis and secretion of gastric juices, thereby slowing digestion By Onkar Bains Glucose homeostasis insulin glucagon o Insulin insulin Insulin molecule Glucagon molecule glucagon Glucose homeostasis in humans Glucose homeostasis - Critical Thinking Question Glucose homeostasis D. Secretin When secretin and CCK are released at high levels they inhibit stomach contractions D. When food enters the stomach, gastrin (a hormone) is released to stimulate the production of gastric juices. Nutrition Nutrition: Carbohydrates Carbohydrates are present in food in the form of sugars, starch, and fiber. Fruits, vegetables, milk, and honey are natural sources of sugars. Monosaccharides: ✓ Glucose ✓ Fructose Disaccharides: ✓ Lactose (milk sugar) ✓ Sucrose (table sugar) After being absorbed from the digestive tract all sugars are converted to glucose ✓Glucose is the preferred direct energy source in cells. Plants store glucose as starch, Animals store glucose as glycogen Nutrition: Fiber Includes various undigestible carbohydrates derived from plants Food sources rich in fiber include beans, peas, nuts, fruits, and vegetables Technically, fiber is not a nutrient for humans ✓Cannot be digested ✓Soluble fiber combines with bile acids and cholesterol in the small intestine and prevents them from being absorbed Nutrition: Proteins Adequate protein formation requires 20 different types of amino acids Adults require 8 from the diet, children require 9, and they are know as essential amino acids ✓Some foods, such as meat, milk, and eggs, provide all 20 (complete) ✓Vegetables supply one or more essential amino acids, but are deficient in at least one ✓Vegetarians and vegans should combine plant products to provide all the essential amino acids Nutrition: proteins Kids also need Arginine Nutrition: Lipids Fat, oils, and cholesterol Essential for the storage and activity of fat-soluble vitamins A, D, E and K Provide energy at nine calories per gram. fat storage is essential to protect your internal organs and to help insulate against cold temperatures Saturated fats (solids at room temperature) usually come from animals ✓Butter and meats, such as marbled red meats and bacon, contain saturated fats ✓Palm oil and coconut oil are high in saturated fats http://www.nature.com/nature/supplements/insights/lipids/index.html Diet and Obesity Too many calories from any source contributes to body fat. ✓Increases risk of obesity and associated illnesses Type 2 diabetes and cardiovascular disease are often seen in people who are obese. Nutrition: Vitamins Organic compounds the body is unable to produce, but are required for metabolic purposes Must be obtained externally Water or fat soluble Some vitamin deficiencies can have a dramatic effect on health Antioxidants ✓Cellular metabolism generates free radicals that carry extra electron ✓Vitamins C, E, and A are believed to defend the body against free radicals Nutrition: Vitamins Nutrition: Minerals Inorganic essential nutrients that must be obtained from food. They help in structure and regulation and are considered co-factors. Which statement is NOT true? B. Vitamins are required in small quantities for bodily function. C. Some amino acids can be synthesized by the body, while others need to be obtained from diet. A. Vitamins come in two categories: fat-soluble and watersoluble. Which statement is NOT true? A. Essential nutrients can be synthesized by the body. B. Vitamins are required in small quantities for bodily function. C. Some amino acids can be synthesized by the body, while others need to be obtained from diet. A. Vitamins come in two categories: fat-soluble and watersoluble. Essential nutrients must be acquired from diet Which substance carbohydrates usually contain that the body cannot break down? A. Protein B. Amino acids C. Starch Which substance carbohydrates usually contain that the body cannot break down? A. B. C. D. Protein Amino acids Starch Fiber Fibers are undigestible D. Vitamin D Meats have more carbohydrates than fruits. Meats have more carbohydrates than fruits. False Meats have more protein than fruits Fibres cannot be digested (1 mark) but combine with bile acids and cholesterol, preventing cholesterol from being absorbed (1 mark). Minerals help in the formation of body structures. They can also act as co-factors of enzymes, helping in metabolism (1 mark). Examples include calcium, phosphorus, sodium, chlorine, potassium, magnesium, iodine, and iron (1 mark for any two of this list).