Digestive system Nutrition: It's a process by which a living organism ingests food, digest it, absorb it, assimilate it, and lastly egest it. Ingest Digest Absorb Assimilate Egest Ingestion: The intake of any substance (e.g.: Food or Drinks), through the mouth. 1|Page Biology / Chapter 7 Digestion Mechanical Mechanical Breakdown of food, without chemically changing it. Chemical Chemical Breakdown of partially digested food, and insoluble food. Chewing, grinding in mouth (Teeth, Tongue). Churning, mixing in stomach. Using enzymes and juices Peristalsis in all body parts, especially the Oesophagus. In mouth (salivary amylase) In stomach (Gastric Juices, HCl) In small intestine (Pancreatic juices and bile) 2|Page Biology / Chapter 7 Absorption Movement of the small food molecules and ions Through the walls of the small intestine into the blood. Assimilation Movement of digested food molecules Into the cells of the body, where they're used Therefore becoming part of the cell Egestion (Elimination, Excretion) Excreting food that has not been digested or absorbed. As faeces through the anus 3|Page Biology / Chapter 7 Alimentary Canal Structure Mouth Salivary glands Oesophagus Function Where food enters the alimentary canal and digestion begins Produce saliva containing amylase Muscular tube which moves ingested food to the stomach Stomach Muscular organ where digestion continues Pancreas Produces digestive enzymes Liver Gall bladder Produces bile Stores bile before releasing it into the duodenum Small intestine duodenum Where food is mixed with digestive enzymes and bile Small intestine ileum Where digested food is absorbed into the blood and lymph Large intestine colon Where water is reabsorbed Large intestine rectum Where faeces are stored Large intestine - anus Where faeces leave the alimentary canal 4|Page Biology / Chapter 7 Mouth (Buccal Cavity) Consists of teeth and tongue Digestion Mechanical The teeth cut, tear, grind, and crush the food, increasing its surface area. Chemical StarchSalivary Amylase Maltose sugar Happens at pH (7-7.5), which is alkaline Tongue mixes the food with the saliva forming it into a bolus. Then it's swallowed. Salivary amylase Saliva Water Mucus 5|Page Biology / Chapter 7 • Amylase catalyses: starch → maltose • Maltase catalyses: maltose → glucose The digestion of starch to glucose needs two enzymes Teeth: Contribute in the ingestion and mechanical digestion of food. Teeth Structure: 6|Page Biology / Chapter 7 Enamel The hard outer layer of the crown to protect dentine (Hardest substance in the body). Can be dissolved by acids Non-living outer layer Living layer with channels of cytoplasm. Dentine Hard but not as hard as enamel. Forms the bulk of the tooth Can be sensitive if enamel is lost. Contain nerves for sensitivity Pulp cavity Contain blood vessels for food and oxygen supply. Contain cells which divide to make dentine Extends from the crown to the tip of the root Bone like substance. Cementum Has fibres growing out of it to attach the tooth to the jawbone and to allow the tooth to move slightly when biting. Covering the root Not as hard as enamel 7|Page Biology / Chapter 7 Types of human teeth Incisor • • • Canine Molar & Premolar Incisor – for biting and cutting Canine – for holding and cutting Premolar and Molar - crushing and chewing Difference between carnivorous and herbivorous teeth 8|Page Biology / Chapter 7 Herbivorous Carnivorous Have teeth that are highly specialized for eating plants; because plant matter (cellulose) is often difficult to break down, Have teeth that are very different from herbivores'; because they have a different diet. Their molars are wider and flatter, designed to grind food, and aid in digestion. Their incisors are sharp for tearing plants, but they may not be present on both the upper and lower jaw. E.G.: White tail deer (has only lower incisors and a rigid upper jaw). Horses and cows have jaws that are capable of moving sideways. • Use its teeth to kill a prey item before eating it. The sharp incisors and pointed canine teeth are designed for both incapacitating and eating a meal . Canine tooth can be easily identified, as it is the longer, pointed tooth located on either side of the incisors. The molars are fewer in number; because so much of the work is done by the teeth in the front of the mouth. E.G.: Tigers, Lions, Cheetahs, Hyenas, Cougars, Foxes, Mountain lions, Coyotes, Hawks. During the lifecycle of a mammal he has 2 sets of teeth, milk teeth (deciduous teeth) which are 20, later on in his life they're replaced by permanent teeth which are 32, equally distributed in each jaw. 9|Page Biology / Chapter 7 Tooth Decay: • Tooth decay happens when the hard outer enamel of the tooth is damaged. This can happen when bacteria in the mouth convert sugars into acids that react with the enamel. Bacteria can then enter the softer dentine inside. Tooth decay can be prevented by: • Avoiding foods with a high sugar content. • Using toothpaste and drinking water containing fluoride. • Regular, effective brushing to prevent the build-up of plaque (a sticky layer on the teeth), which is an average of 3 times per day. • Dental check-ups. • Eat a balanced diet that contains Calcium and Vitamin D. Fluoride compounds may be added to toothpaste and public water supplies. Fluoride reduces tooth decay by: • • Reducing the ability of bacteria on plaque to produce acid. Helping to replace calcium ions and phosphate ions lost by tooth enamel because of acid attack. However, there are arguments against fluoridation of drinking water. For example: • Some people say that they should not be forced to consume fluoride. • Excessive fluoride can cause grey or brown spots on teeth. The Pharynx: • • Common passage between the respiratory and digestive systems. • The epiglottis; a flap of cartilage; stops the food from going down into the lungs and closes the end of trachea. Peristalsis: It's a process by which food is moved through the digestive system, by the help of two muscles in the gut wall 1. Circular muscles - which reduce the diameter of the gut when they contract. 2. Longitudinal muscles - which reduce the length of the gut when they contract. 10 | P a g e Biology / Chapter 7 • The muscles work together to produce wave-like contractions. These have a ‘squeezing action’ that pushes the bolus through the gut. Oesophagus: It's a muscular tube which transports food from the mouth to the stomach, by peristalsis. The stomach: • A muscular sac-like organ located on the left side of the upper abdomen, and is the widest organ in the alimentary canal. • The stomach muscles contract periodically, churning food to enhance digestion, while simultaneously secreting gastric juices including hydrochloric acid, pepsinogen, and mucus partially digesting fats and proteins, and changing them into chyme. • Hydrochloric acid is used for: 1. Killing bacteria 2. Provides the optimum pH for inactive pepsinogen to change into active pepsin. • Protein By Pepsin (Happens at pH=2) 11 | P a g e Polypeptides Biology / Chapter 7 • G.R.F: The stomach doesn't digest itself. 1. Pepsin is secreted in its inactive form (Pepsinogen) 2. Stomach secrets a protective layer of mucus from the goblet cells. The Small Intestine Duodenum • Jejunum ileum The small intestine is about (6.7 - 7.6m). Duodenum: • • • • The smallest part of the small intestine (23 – 28cm) Responsible for the absorption of nutrients from the already digested food. After food is digested in the stomach, it reaches the duodenum through pyloric sphincter. Ducts from the liver, gallbladder, and pancreas enter the duodenum to provide juices that neutralize acids coming from the stomach and help digest proteins, carbohydrates, and fats. Enzyme Substrate End-products Where produced Salivary amylase Starch Maltose Salivary glands Pepsin Lipase Protein Lipids (fats and oils) Polypeptides Fatty acids and glycerol Stomach Pancreas Pancreatic amylase Maltase Starch Maltose Maltose Glucose Pancreas Small intestine Pancreatic trypsin (Protease) Chymotrypsin Carboxpeptidase Protein Peptides then into amino acids Pancreas 12 | P a g e Biology / Chapter 7 • • • • • Proteases catalyse the breakdown of proteins into amino acids in the stomach and small intestine. Lipases catalyse the breakdown of fats and oils into fatty acids and glycerol in the small intestine. Amylase catalyses the breakdown of starch into maltose in the mouth and small intestine. Maltase catalyses the breakdown of maltose into glucose in the small intestine. In addition to that, sodium hydrogencarbonate salts are also being produced to neutralize the acidic chyme and create an alkaline medium. (7.5 pH) Bile (Gall): • • • • • • It's a greenish yellow alkaline (7-8 pH) watery secretion. Produced in the liver and passed to the gallbladder. It is stored in the gallbladder and move through the bile duct into the duodenum. The enzymes in the small intestine work best in alkaline conditions. It neutralises the (hydrochloric) acid - providing the alkaline conditions needed in the small intestine. It emulsifies (mechanical digestion) fats - providing a larger surface area over which the lipase enzymes can work, by breaking fats globules into small ones. Bile salts • Bile Sodium hydrogencarbonate Bile pigment 13 | P a g e Biology / Chapter 7 Jejunum: • • Connects the duodenum to the ileum. Partial digestion of food occurs in it, because of the enzyme secretion from the cells in the walls of the small intestine. Ileum: • • It's where complete digestion and absorption occur. The longest part of the small intestine (2-4 m) • The villi (one is called a villus) are tiny, fingershaped structures that increase the surface area. They have several important features: 1. Wall just one cell thick - ensures that there is only a short distance for absorption to happen by diffusion and active transport. 2. Network of blood capillaries - transports glucose and amino acids away from the small intestine in the blood. 3. Internal structure called a lacteal - transports fatty acids and glycerol away from the small intestine in the lymph. • Brush border enzymes are special enzymes found on the microvilli of the small intestine that complete digestion. • Absorption: The movement of completely digested food molecules and ions into the blood stream. 14 | P a g e Biology / Chapter 7 Chemical digestion in ileum: • Substrate Enzyme End result Maltose Maltase Glucose Peptides Peptidase Amino acids Emulsified fats Lipase Fatty acids Assimilation: The movement of digested food molecules into the cells of the body where they are used. The liver: • • • • • • The largest gland in the body. The bile secreting organ. Glucose is used in respiration to provide energy. Amino acids are used to build new proteins. In liver: Glucose Amino acids Glycogen (A complex [polysaccharide] carbohydrate used for storage) Proteins Deamination: This is the removal of the nitrogen-containing part of amino acids, by the liver, to form urea, followed by the release of energy from the remainder of the amino acid. Functions of the liver: (The 3D, 2SR) 1. 2. 3. 4. 5. 6. 7. Destruction of old red blood cells. Detoxification of drugs and alcohol. Deamination of excess amino acids. Secretion of bile for fat emulsion. Regulation of blood glucose level. Storage of iron and fat soluble vitamins (K,E,D,A) Regulation of body temperature. 15 | P a g e Biology / Chapter 7 The large intestine: Some Water • By the time the contents of the gut reach the end of the small intestine, most digested food and water has already been absorbed. • Except for Bacteria (living & dead) Undigested food (e.g.: cellulose from plants' cell walls) Cells (from the lining of the gut) • Functions: 1. The colon is the first part of the large intestine; it absorbs most of the remaining water, minerals and salts from the undigested food. 2. This leaves semi-solid waste material called faeces, which are stored in the rectum, the last part of the large intestine. Egestion (defecation) happens when these faeces pass out of the body through the anus. • Egestion: The passing out of food that hasn't been digested or absorbed as faeces through the anus. Pancreas: • To make digestive chemicals (enzymes) which help us digest food. Enzymes help to speed up your body's metabolic (biosynthesis) reactions. • To make hormones which regulate our metabolism. Hormones can be released into the bloodstream. They act as messengers, affecting cells and tissues in distant parts of your body. 16 | P a g e Biology / Chapter 7 About 90% of the pancreas is dedicated to making digestive enzymes. Cells called acinar cells within the pancreas produce these enzymes. The enzymes help to make proteins, fats and carbohydrates smaller. This helps the guts (intestines) to absorb these nutrients. The acinar cells also make a liquid which creates the right conditions for pancreatic enzymes to work. This is also known as pancreatic juice. The enzymes made by the pancreas include: • • • Pancreatic proteases (such as trypsin and chymotrypsin) - which help to digest proteins. Pancreatic amylase - which helps to digest sugars (carbohydrates). Pancreatic lipase - which helps to digest fat. Approximately 5% of the pancreas makes hormones which help to regulate your body's metabolism. • • • Insulin - which helps to regulate sugar levels in the blood. Glucagon - which works with insulin to keep blood sugar levels balanced. Gastrin - which aids digestion in the stomach. Types of Pancreatic Enzymes and Their Effects: Lipase Effects: Lipase works with bile from the liver to break down fat molecules so they can be absorbed and used by the body. Shortage may cause: • Lack of needed fats and fat-soluble vitamins. • Diarrhoea and/or fatty stools. Protease Effects: Proteases break down proteins. They help keep the intestine free of parasites such as bacteria, yeast and protozoa. Shortage may cause: • Allergies or the formation of toxic substances due to incomplete digestion of proteins. • Increased risk for intestinal infections. 17 | P a g e Biology / Chapter 7 Amylase Effects: Amylase breaks down carbohydrates (starch) into sugars which are more easily absorbed by the body. This enzyme is also found in saliva. Shortage may cause: • Diarrhoea due to the effects of undigested starch in the colon. Diarrhoea: • • From the diseases related to the digestive system is Diarrhoea; Diarrhoea is the loss of watery faeces The second largest cause of death among children after pneumonia, a person with severe diarrhoea can lose dangerous amounts of water and salts from their body causing their organs to stop working. Causes: • Not enough water is absorbed from the faeces. • By Cholera; Cholera is an epidemic infection that spreads through water and food, which is contaminated with the bacterium of an infected person. • Cholera bacterium is found in unhygienic places such as refugee camps. • Once the bacterium infects the intestine, it secretes the enterotoxin (a protein exotoxin that targets the intestines) from its external coating. The enterotoxin binds to a receptor (an organ which responds to external stimuli) on the cells of the lining of the small intestine. Part of the toxin then enters the intestinal cells. The toxin increases the activity of an enzyme that regulates a cellular pumping mechanism that controls the movement of water and electrolytes between the intestine and the circulatory system. This pump effectively becomes locked in the “on” position, causing the outflow of enormous quantities of fluid—up to one litre (about one quart) per hour—into the intestinal tract. All of the clinical manifestations of cholera can be attributed to the extreme loss of water and salts. 18 | P a g e Biology / Chapter 7 Treatment: • Treatment consists largely of replacing lost fluid and salts with the oral or intravenous administration of an alkaline solution of sodium chloride. For oral rehydration the solution is made by using oral rehydration salts (ORS)—a measured mixture of glucose, sodium chloride, potassium chloride, and trisodium citrate. The kidney: Filters initial urine from the blood, reabsorb water and nutrients, and secrete wastes, producing the final urine, which is expelled. Blood glucose level: Normal blood glucose level is 80-120 mg / 100 cc of blood Q1: When and what happens if the blood glucose level rises above normal? After eating a meal rich in carbohydrates. 1. Liver regulates blood glucose level. 2. Pancreas secrete insulin hormone. 3. Glucose Insulin Hormone Glycogen (to be stored in liver and muscles) In pancreas 4. Blood glucose level return to normal. 5. A negative feedback mechanism to stop correction order. (Pancreas stops secreting insulin) Q2: When and what happens if blood glucose level fall below normal? When fasting. 1. Liver regulates blood glucose level. 2. Glycogen is broken down by glucagon hormone secreted from pancreas. 3. Glycogen Glucagon Hormone In pancreas Glucose 4. Blood glucose level return to normal. 5. A negative feedback mechanism to stop correction order. (pancreas stops secreting glucagon) 19 | P a g e Biology / Chapter 7 Enzyme Name Aminopeptidase Source Small intestine Pancreatic Carboxypeptidase acinar cells Substrates Notes (if applicable) Products Amino acid at amino end of peptides Amino acids & peptides n/a Amino acid at carboxyl end of peptides Amino acids & peptides Activated from procarboxypeptidase by trypsin; optimum pH varies Chymotrypsin Pancreatic acinar cells Proteins Peptides Activated from chymotrypsinogen by trypsin; optimum pH 7.8 Gastric lipase Stomach chief cells Triglycerides Fatty acids & monoglycerides Optimum pH 4-5 Lactase Small intestine Lactose Glucose & galactose n/a Maltase Small intestine Maltose Glucose n/a Pancreatic amylase Pancreatic acinar cells Starches Maltose, maltotriose, αdextrins Optimum pH 6.7-7.0 Pancreatic lipase Pancreatic acinar cells Triglycerides emulsified by bile salts Fatty acids & monoglycerides Optimum pH 8.0 Pepsin Stomach chief cells Peptides Activated from pepsinogen by pepsin & HCl; optimum pH 1.5-1.6 20 | P a g e Proteins Biology / Chapter 7 Sucrase Small intestine Salivary amylase Salivary glands Trypsin 21 | P a g e Pancreatic acinar cells Sucrose Glucose & fructose n/a Starches Maltose, maltotriose (trisaccharide), α-dextrins Optimum pH 6.7-7 Peptides Activated from trypsinogen by enterokinase; optimum pH 7.8-8.7 Proteins Biology / Chapter 7