Unit 3: The Digestive and Respiratory Systems PDF

Unit 3: The digestive and respiratory systems 1. The nutrition function 2. Digestive system 2.1. The mouth: the beginning of digestion...

Unit 3: The digestive and respiratory systems 1. The nutrition function 2. Digestive system 2.1. The mouth: the beginning of digestion 2.2. Stomach: the gastric digestion 2.3. Intestinal digestion 2.4. Intestinal absorption 2.5. The large intestine 3. Respiratory system 3.1. Exchange of gases 3.2. Ventilation Think and answer? a. What is the function of the digestive system? And the function of the respiratory system? b. Name some organs of the digestive and respiratory systems. c. What are digestive enzymes? d. How are respiration and cellular respiration different? UNIT OBJECTIVES In this unit you will learn:  The anatomy of the digestive and respiratory systems  To the processes of transformation that foods undergo within the digestive system.  To distinguish between the cellular respiration and the processes of ventilation and gas exchange in the lungs.  To appreciate the importance of healthy habits related to digestive and respiratory systems.  The main diseases of the digestive and respiratory systems.  rd UNIT 3: The digestive and respiratory systems Biology and Geology (3 ESO) 1. Nutrition function Nutrition is the set of processes, which allow living beings obtain energy and matter to stay alive. Living means to be able to perform the vital functions (nutrition, interaction and reproduction) and elaborate its own matter in order to replace and repair the damaged parts of the organism. Nutrition is a complex function in which takes part several organ systems. Each one of them carries out part of the process and they depend on each other to complete it. These organ systems are: The digestive system. It processes and transforms food to obtain nutrients which cells are able to assimilate. The respiratory system. It obtains oxygen from air and expels carbon dioxide from the vital activity. The circulatory system. Its function is to distribute nutrients and oxygen throughout the body and collets the waste substances and carbon dioxide from cells. The excretory system. Its function is to expel the waste substances out of the body. ACTIVITIES 1.1. Nutrients are essential substances which living beings need to stay alive. Where can they find them? 1.2. What organ systems are involved in carrying oxygen to every cell of the body? And glucose? 1.3. Listen and indicate what body system related with the nutrition function is described: a. Digestive system b. Respiratory system c. Circulatory system d. Excretory system  rd UNIT 3: The digestive and respiratory systems Biology and Geology (3 ESO) 2. Digestive system a) Parts of the digestive system: The digestive system is formed by:  Digestive tract. It is a long tube differentiated in several parts: mouth, pharynx, oesophagus, stomach, small intestine, large intestine and anus. It is formed by three layers of tissue: mucosa (the internal layer, very folded and lined with glands), muscularis (the middle layer formed by two layers of smooth muscle) and serosa (the connective tissue layer that joins the digestive tract to other organs)  Digestive glands. They secrete digestive juices into digestive tube (salivary glands, gastric glands, intestinal glands, liver and pancreas) b) Digestive functions:  Ingestion. It is the entry of food into the digestive tract through the mouth.  Digestion. It is the transformation of food into simple nutrients which can be absorbed and used by cells. We can distinguish two types of processes: o Mechanical digestion. It includes physical transformations (cutting, crushing, mixing and kneading) to reduce the size and make easier the chemical digestion. o Chemical digestion It is the transformation of complex nutrients that are contained in food into simple nutrients through a chemical reaction. These transformations are carried out by enzymes, which are contained in digestive juices. Enzymes act as chemical scissors to cut the large molecules into small molecules that can be absorbed and used by cells.  Absorption. It is the pass of nutrients from the digestive tract to the blood or to the lymph.  Defecation. It is the expulsion of non-digested or non-usable parts of food (faeces). ACTIVITIES 2.1. Where do different digestive glands secrete their juices? 2.2. Why do you think it is recommendable chew the food well before swallowing it? 2.3. What are the differences between chemical and mechanical digestion? 2.4. Listen and indicate what part of the digestive system is described. a. b. c. d. e. f. g. h.  rd UNIT 3: The digestive and respiratory systems Biology and Geology (3 ESO) 2.1. Mouth: the beginning of digestion The food digestion begins in the mouth. There, mechanical and chemical processes take place. a) Mastication (Chewing) It is the crushing of food by teeth, helped by the tongue which changes the food from place to place. Teeth are hard structures compounded by calcium and fluorine, which are located within dental alveolus (tooth sockets) in the border of both mandibles. Their function is chewing food. There are four types of teeth. Each one of them has a particular function and shape. Their characteristics are summarised in the chart below: Type of Crown (shape) Roots Function Number (total) tooth INCISOR Flat and sharp 1 To cut 8 CANINE Conical and pointed 1 To tear 4 Wide and flat PREMOLAR 1 or 2 To crush and to grind 4 (2 protuberances) Wide and flat From 8 to 12 MOLAR 2 or 3 To crush and to grind (3 or 4 protuberances) (with wisdom teeth) Humans have two dentitions along their lives. Children have a set of teeth that fall out and are replaced by adult teeth (beginning at 6). These are called baby or milk teeth. These teeth are smaller than adult teeth and do not have roots. In addition, in children, molars are missing.  rd UNIT 3: The digestive and respiratory systems Biology and Geology (3 ESO) b) Insalivation It is the mix of food with saliva. Saliva is a digestive juice secretes by salivary glands. Humans have three pairs of them: parotid, submandibular and sublingual glands. Saliva is a liquid compounded by water, mineral salts, mucin (mucous substance) and enzymes (mainly salivary amylase or ptyalin, and maltase) The functions of saliva are: - To start the digestion of glucids (thanks to its enzymes) Salivary amilase Maltase Polysaccharides Disaccharides Monosaccharides (Ej: starch or glycogen) (Ej: maltose) (Ej: glucose) - To make easier swallow the food (thanks to its water and mucin) - To be disinfectant (thanks to its antibacterial compounds) The food bolus is each portion of food chewed, mixed with saliva and prepared to be swallowed. c) Deglutition (Swallowing) It is the pass of food bolus from the mouth to the oesophagus and then, to the stomach. We can distinguish three steps in this process: 1st) The tongue pushes food bolus into the pharynx (voluntary action) 2nd) When food bolus is in the pharynx, it activates a reflex (an involuntary action) that: o Closes choanae (openings that connect the mouth and the nasal passages) with the uvula. o Closes glottis (opening that communicates the pharynx with the larynx) with the epiglottis. 3rd) Food bolus passes into the oesophagus. It progresses through it thanks to peristaltic movements, circular contraction waves that progress from top to bottom of the oesophagus and force the food bolus into stomach (reflex act). ACTIVITIES 2.5. How many teeth have a human adult? And a child? 2.6. What is the function of the tongue in chewing? 2.7. Listen and indicate what digestive process carried out in the mouth is described: a. Mastication (chewing) b. Insalivation c. Deglutition (swallowing)  rd UNIT 3: The digestive and respiratory systems Biology and Geology (3 ESO) 2.2. The stomach: the gastric digestion The stomach is a J-shaped organ, located in the abdominal cavity beneath the diaphragm. The stomach is about 30 cm long and 15 cm wide at its widest point. It is very elastic and it can be up to 2 litres of capacity in an adult. The stomach has two openings. Both are sphincters. A sphincter is a circular muscle that acts as a valve, controlling the pass of substances from one place to another. o Cardia connects with oesophagus and prevents food bolus goes back. o Pylorus separates the stomach from the duodenum and prevents that non-digest food passes into the small intestine. The structure of the stomach wall is similar to the rest of the digestive tract, but it has three muscular layers (circular, longitudinal and an additional oblique muscle layer). Gastric digestion includes mechanical and chemical processes: a) Chemical processes They are made by gastric juice. This juice is produced by gastric glands that are located on the stomach mucosa (its innermost layer). The gastric juices contains mainly: - Hydrochloric acid (HCl) o It helps to disaggregate the food. o It activates pepsinogen because reduce the pH (about 2), making the chemical environment very acid. It is transformed in pepsin (active enzyme) o It destroys any bacteria or germs that could have entered with food. - Pepsinogen (inactive enzyme or precursor of the pepsin) - Mucin (protects the stomach from acid) The main function of gastric digestion is beginning the digestion of proteins. Pepsin breaks down long chains of amino acids (proteins) into short chains (peptides) b) Mechanical processes Stomach wall has peristaltic movements that mix food with gastric juice and grind and move it. The contraction waves close the pylorus when arrive to it. Only when food is very liquid and the gastric chemical digestion has finished, a very small portion of the stomach’s content passes into the duodenum in each train of waves. Chyme is the result of gastric digestion. It is an acid semi-liquid substance, which comes from the mixture of food bolus with saliva and gastric juice, and it is formed by partly digested glucids and proteins. ACTIVITIES 2.8. Why is pepsin secreted as an inactive enzyme (pepsinogen)? 2.9. What food will be more time in stomach, gherkins in vinegar or natural gherkins? Why? 2.10. Listen and find the six mistakes in the text: When the food bolus enters the throat, the gastric muscles relax. The food bolus stays there for between three and two hours. Here it mixes with gastric acid. The resulting mixture is called chyle. It is more solid than the food bolus.  rd UNIT 3: The digestive and respiratory systems Biology and Geology (3 ESO) 2.3. Intestinal digestion Intestinal digestion takes place in the small intestine thanks to several digestive juices: intestinal juice (produced by intestinal wall glands), pancreatic juice (produced by the pancreas) and bile (produced by the liver) a) Small intestine The small intestine is a long tube which is located within the abdominal cavity. It is about 7 m long and 2.5 cm in diameter. It is differentiated in three portions: - Duodenum. It is the initial portion, about 25 cm long. It connects with the stomach. The pancreas and the liver pour their secretions into it. - Jejunum. It is the middle portion, about 3 m long. - Ileum. It is the final portion, around 3 m long. It connects with the large intestine. The structure of the small intestine is similar to the rest of digestive tract but its mucosa has: - Intestinal glands that secrete intestinal juice. - Villi which are finger-like projections which increase the absorption surface area. a) Chemical processes Intestinal juice contains among other substances, enzymes to digest each type of nutrient (glucids, lipids and proteins) b) Mechanical processes The small intestine has also peristalsis to mix chyme with digestive juices and make advance food along it. b) Pancreas It is an elongated, pinkish and spongy-shaped organ which is located underneath and behind the stomach. It is a gland, which produces two types of secretion: - Hormones which control the sugar levels in blood (insulin and glucagon). - Pancreatic juice which has digestive function. Pancreas pours pancreatic juice into the duodenum. This juice contains water and: - Enzymes to digest every type of nutrient. - Sodium bicarbonate (neutralizes chyme acid and makes pH very alkaline, about 9, providing an optimal environment to enzymes work)  rd UNIT 3: The digestive and respiratory systems Biology and Geology (3 ESO) c) Liver It is the largest gland in the body. The liver is a brown-red organ divided into several lobes which is located on the right side of the stomach within the abdominal cavity. Liver has several important functions: - Storage glycogen (polysaccharide formed by many molecules of glucose) - Recycling of red blood cells which non-useful parts are excreted (bile pigments) - Detoxify blood. - Produce bile (digestive juice) It is connected with the gall bladder which stores bile. Bile is continuously produced in the liver but it is only poured into the duodenum when chyme is in it. Bile contains mainly: - Bile pigments (waste substances which are responsible for faeces colour) - Bile acids (they emulsify lipids, break down large fat drops into small ones which are easier to attack by enzymes) - Cholesterol Chyle is the result of intestinal digestion. It is a very liquid substance, which comes from the mixture of chyme with bile, pancreatic juice and intestinal juice, in which all nutrients are completely digested. ACTIVITIES 2.11. Give a reason to explain why: a. meals rich in fats usually provoke a heavy digestion. b. humans cannot feed only of vegetables and fruits. c. intestinal ulcers are produced in duodenum but neither in jejunum nor ileum. 2.12. Listen and complete the text: The ……………………. This is the largest ………………… in the body. It performs important functions, for instance, secreting …………………, stored in the ………………………, as part of the digestive function. Although bile does not contain digestive ………………………, it help us to digest ………………… (fats) by acting as a …………………………. The liver also performs other functions, such as storing ……………………, iron and some vitamins, in addition to eliminating toxic substances, such as ……………………, from the ………………………….  rd UNIT 3: The digestive and respiratory systems Biology and Geology (3 ESO) 2.4. Intestinal absorption Once digested, nutrients are in their simplest form and can be absorbed and used by cells. Absorption is the pass of nutrients from the digestive tract to blood or lymph capillaries, through absorptive cells of intestinal villi. - Monosaccharides and amino acids, mineral salts, water-soluble vitamins and water pass to blood - Fatty acids and glycerine, and fat-soluble vitamins pass to lymph Anyway, the simplest nutrients absorption, as water, mineral salts or alcohol, begins in the stomach. ACTIVITIES 2.13. Many sportspeople take glucose before a hard exercise to obtain extra energy. Why do you think they do not take other more energetic food, like bread or potatoes? 2.14. What kind of nutrients does not suffer any kind of transformation along the digestive system? Why?  rd UNIT 3: The digestive and respiratory systems Biology and Geology (3 ESO) 2.5. The large intestine The large intestine is a thick tube which is located into the abdominal cavity, surrounding the small intestine. It is about 1.5 m long and 6 cm in diameter. It is differentiated in three portions: - Cecum. It is the initial portion, separated from ileum by a valve. Joined to it, there is the appendix, a small blind prolongation. - Colon. It is the middle and largest portion. It is divided into: ascending, transverse descending and sigmoid colon. - Rectum. It is de final portion which ends in the anus, a double sphincter that controls defecation. The wall of the large intestine is similar to other parts of the digestive tract but: - The mucosa has a large number of mucus secrete cells but does not have any villi. - The longitudinal muscle layer is limited to three bands (teniae coli) that create pouches (haustra) along the colon. The remains of chyle which passes to cecum still contains a lot of water and mineral salts. These are absorbed meanwhile the mass goes through the colon forced by peristaltic movements of intestine wall. As a result, it forms faeces by progressive compacting of chyle remains. This process is so efficient thanks to symbiotic bacteria which live in our colon (gut flora). They help in the absorption of water and mineral salts and produces vitamins K and B12. ACTIVITIES 2.15. Why is it not recommendable to take antibiotics orally for a long time? 2.16. Listen and indicate if the following statements are true or false. a. T / F b. T / F c. T / F d. T / F