Digestive System description and function .ppt
- 1. THE DIGESTIVE SYSTEM THE DIGESTIVE SYSTEM © PDST Home Economics
- 2. Without food, water and oxygen, human beings could Without food, water and oxygen, human beings could not survive. not survive. The digestive system is a set of organs which change The digestive system is a set of organs which change what we eat into substances that can be used in the what we eat into substances that can be used in the body. body. These substances can be used for energy, growth and These substances can be used for energy, growth and repair. repair.
- 3. THE DIGESTIVE SYSTEM THE DIGESTIVE SYSTEM The The alimentary canal alimentary canal is a tube that runs from the is a tube that runs from the mouth to the anus mouth to the anus It is composed of the mouth, oesophagus, stomach, It is composed of the mouth, oesophagus, stomach, small intestine and the large intestine small intestine and the large intestine As food passes through the alimentary canal it is As food passes through the alimentary canal it is changed and the nourishment is taken into the blood changed and the nourishment is taken into the blood Waste passes out the end of the canal Waste passes out the end of the canal Certain organs and glands add juices to the canal at Certain organs and glands add juices to the canal at various points various points
- 4. Mouth Mouth 1. Chemical digestion (amylase 1. Chemical digestion (amylase converts starch to maltose converts starch to maltose) ) 2. Physical digestion (teeth break 2. Physical digestion (teeth break food down into smaller food down into smaller pieces) pieces) Oesophagus Oesophagus Connects mouth Connects mouth to stomach to stomach Stomach Stomach Liver Liver Produces Produces bile bile for the for the digestion of digestion of fats fats Gall Gall bladder bladder Stores bile Stores bile 1. 1. Holds the food for a while Holds the food for a while 2. 2. Physical digestion (food is Physical digestion (food is churned and mixed) churned and mixed) 3. 3. Chemical digestion (assisted Chemical digestion (assisted by HCl) by HCl) Pancreas Pancreas Produces digestive Produces digestive juices juices Small intestine Small intestine 1. Chemical digestion 2. Absorption of nutrients into blood Appendix Appendix Large intestine Large intestine (colon) (colon) 1. 1. Elimination of waste Elimination of waste 2. 2. Absorption of water Absorption of water Rectum Rectum Stores faeces Stores faeces Anus Anus
- 5. Food can be broken down (digested) in one of two Food can be broken down (digested) in one of two ways: ways: 1. 1. Physical Digestion Physical Digestion This is where large pieces of food are broken down This is where large pieces of food are broken down into smaller pieces of the same food into smaller pieces of the same food 2. 2. Chemical Digestion Chemical Digestion This is where food is broken down into a different This is where food is broken down into a different substance that can easily pass into the blood substance that can easily pass into the blood
- 6. Mouth Mouth The food is broken down by the teeth and mixed with The food is broken down by the teeth and mixed with saliva. saliva. Saliva is excreted by three pairs of glands: Saliva is excreted by three pairs of glands: • The parotid gland (below the ear) The parotid gland (below the ear) • The submandibular (under the tongue) The submandibular (under the tongue) • The sublingual (under the tongue) The sublingual (under the tongue) Saliva contains water, mucus and the enzyme salivary Saliva contains water, mucus and the enzyme salivary amylase. amylase.
- 7. Functions of Saliva Functions of Saliva It lubricates food with mucus, making it easier to It lubricates food with mucus, making it easier to swallow. swallow. It contains the enzyme salivary amylase, which acts on It contains the enzyme salivary amylase, which acts on cooked starch turning some of it into maltose. cooked starch turning some of it into maltose. It keeps the mouth and teeth clean. It keeps the mouth and teeth clean. The ball of food that leaves the mouth is known as a The ball of food that leaves the mouth is known as a bolus. bolus.
- 8. Functions of the Tongue Functions of the Tongue Taste Taste: it is covered with thousands of : it is covered with thousands of taste buds taste buds. . These are sensitive to These are sensitive to salt, sweet, sour and bitter salt, sweet, sour and bitter chemicals chemicals in food and drink. in food and drink. They help us enjoy food and drink and They help us enjoy food and drink and warn warn us when us when food, drink are off or inedible. food, drink are off or inedible. Chewing Chewing: the tongue aids chewing by moving the food : the tongue aids chewing by moving the food around the mouth, pushing it between the teeth and around the mouth, pushing it between the teeth and covering it with saliva, which contains enzymes that covering it with saliva, which contains enzymes that start the digestive process. start the digestive process. The food is turned into a partially digested mass known The food is turned into a partially digested mass known as a as a bolus bolus. . Swallowing: when the food is ready to travel to the Swallowing: when the food is ready to travel to the stomach, the tongue pushes it to the back of the mouth. stomach, the tongue pushes it to the back of the mouth.
- 9. Tongue Taste Centres Epiglottis Bitter Sour Salt Sweet Taste Buds Papillae
- 10. Oesophagus Oesophagus The food passes into the pharynx (a muscular tube The food passes into the pharynx (a muscular tube behind the mouth) and down the oesophagus. behind the mouth) and down the oesophagus. The epiglottis a small flap of cartilage blocks the The epiglottis a small flap of cartilage blocks the entrance to the larynx, this stops the food going down entrance to the larynx, this stops the food going down the wrong way and prevents choking the wrong way and prevents choking. .
- 11. Structure of the Oesophagus Structure of the Oesophagus & Functions & Functions It is a muscular tube. It is a muscular tube. It leads from the pharynx to the stomach. It leads from the pharynx to the stomach. Function Function To carry chewed food from the pharynx to the To carry chewed food from the pharynx to the stomach. stomach. Food moves along it by a muscular contraction known as Food moves along it by a muscular contraction known as peristalsis. peristalsis. The muscle fibres contract and relax which acts like a The muscle fibres contract and relax which acts like a wave on the tube, pushing the bolus forward. wave on the tube, pushing the bolus forward. It’s lining secretes mucus to lubricate the passage of It’s lining secretes mucus to lubricate the passage of food. food.
- 12. The Stomach Oesophagus Pyloric Sphincter Duodenum Body of Stomach Cardiac Sphincter
- 13. Stomach Structure Stomach Structure It is a J-shaped, elastic organ. It is a J-shaped, elastic organ. Food enters it from the oesophagus through the cardiac Food enters it from the oesophagus through the cardiac sphincter. sphincter. The cardiac sphincter, is a valve that stops back flow of The cardiac sphincter, is a valve that stops back flow of the stomach`s contents. the stomach`s contents. Food leaves the stomach through the pyloric sphincter Food leaves the stomach through the pyloric sphincter into the duodenum (first part of the small intestine). into the duodenum (first part of the small intestine).
- 14. The walls of the stomach is made up of layers of The walls of the stomach is made up of layers of muscle. muscle. It has an inner mucous membrane. It has an inner mucous membrane. This membrane has lots of folds. This membrane has lots of folds. When the stomach is full these folds stretch out, When the stomach is full these folds stretch out, enabling it to expand, then they contract when the enabling it to expand, then they contract when the stomach empties. stomach empties.
- 15. Functions of The Stomach Functions of The Stomach It digests protein through the action of enzymes. It digests protein through the action of enzymes. It churns food with the gastric juices. It churns food with the gastric juices. It helps lubricate the food by producing mucus. It helps lubricate the food by producing mucus. It absorbs alcohol. It absorbs alcohol. It kills bacteria by producing hydrochloric acid. It kills bacteria by producing hydrochloric acid.
- 16. Gastric Juices Hydrochloric acid neutralises bacteria and activates pepsin. Rennin is an enzyme that curdles milk protein in infants. Pepsin is an enzyme that breaks down proteins into peptones.
- 17. Structure of the Small Intestine It is seven metres long. It is divided into three parts: The duodenum The jejunum The ileum The walls has four layers: A muscular layer A layer containing blood vessels, lymph vessels, and nerves. A submucous layer, A mucous layer.
- 18. The inner wall is covered in villi, tiny hair like projections which increase the surface area for absorption. Each villi contain blood vessels and lymph vessels.
- 19. Functions of The Small Intestine Digestion Pancreatic juice is secreted into the duodenum and contains the following enzymes: Trypsin: converts proteins into shorter chains. Lipase: converts fats into fatty acids and glycerol. Amylase: converts starch into disaccharides. Bile: emulsifies fats (breaks them into smaller droplets). Intestinal Juices have the following enzymes: Maltase, sucrase, lactase: change disaccharides into monosaccharides. Peptidase: changes polypeptides into amino acids.
- 20. Absorption Digested food is absorbed through the villi walls. Fats, fatty acids and glycerol are passed into the lymph system. Amino acids and sugars pass along the portal vein to the liver.
- 22. What is the Large Intestine It deals with waste. It is about 1.5m long. It consists of the following: The caecum: a small pouch; the ileum empties its contents into the caecum through the ileo-caecal valve. The colon: ascending, transverse, descending colon. The appendix: narrow tube attached to the caecum. The rectum. The anus
- 23. Functions Whatever remains of the food, is passed into the large intestine To reabsorb water and vitamins left in digestive waste. It secretes mucus to help the movement of faeces. Short term storage of faeces in the rectum. Many bacteria live in the large intestine, they are harmless in the colon and may be useful e.g. produce Vitamin K. Defecation: peristalsis pushes waste along the colon and then it is passed out of the body.
- 24. ENZYMES ENZYMES An enzyme is a An enzyme is a biological catalyst biological catalyst A catalyst speeds up chemical reactions A catalyst speeds up chemical reactions Enzymes speed up biological reactions Enzymes speed up biological reactions All chemical reactions that take place in living systems All chemical reactions that take place in living systems require the action of an enzyme require the action of an enzyme
- 25. ENZYMES ENZYMES Digestive enzymes break food down into smaller, more Digestive enzymes break food down into smaller, more soluble substances soluble substances This allows the food to be absorbed into the blood This allows the food to be absorbed into the blood
- 26. ENZYMES ENZYMES An example of a digestive enzyme is An example of a digestive enzyme is amylase amylase Amylase is present in Amylase is present in saliva saliva Amylase chemically Amylase chemically breaks down starch breaks down starch
- 27. ENZYMES ENZYMES Amylase converts starch into a sugar called Amylase converts starch into a sugar called maltose maltose STARCH STARCH MALTOSE MALTOSE
- 29. ENZYMES ENZYMES The substance that an enzyme works on is known as its The substance that an enzyme works on is known as its SUBSTRATE SUBSTRATE The substance formed by the enzyme is known as its The substance formed by the enzyme is known as its PRODUCT PRODUCT Therefore Therefore starch starch is the is the substrate substrate for amylase and for amylase and maltose maltose is its is its product product
- 30. STAGES OF NUTRITION STAGES OF NUTRITION There are four stages in human nutrition: There are four stages in human nutrition: 1. 1. Eating Eating (also called “ingestion”) (also called “ingestion”) 2. 2. Digestion Digestion 3. 3. Absorption Absorption of digested food into the blood of digested food into the blood 4. 4. Elimination Elimination of undigested food (also called “egestion”) of undigested food (also called “egestion”)
- 31. STAGES OF NUTRITION STAGES OF NUTRITION Digestion changes food into a form that can enter the Digestion changes food into a form that can enter the blood blood Physical (mechanical) digestion breaks food down into Physical (mechanical) digestion breaks food down into smaller pieces smaller pieces Chemical digestion breaks food down into different, Chemical digestion breaks food down into different, more soluble substances more soluble substances
- 32. The contents of the alimentary canal are pushed The contents of the alimentary canal are pushed along by a rhythmic pulsing of the muscles of the along by a rhythmic pulsing of the muscles of the intestines intestines This is known as This is known as peristalsis peristalsis
- 33. TEETH TEETH An adult human has 32 teeth, 16 in either jaw An adult human has 32 teeth, 16 in either jaw The shape and size of the tooth varies with the job it The shape and size of the tooth varies with the job it has to do has to do There are four different types of tooth There are four different types of tooth
- 34. TEETH TEETH Incisors Incisors These These cut and bite food cut and bite food Canines Canines These These grasp and tear food grasp and tear food Pre-molars Pre-molars These These grind and chew food grind and chew food Molars Molars These also These also grind and chew food grind and chew food
- 36. TEETH TEETH The type of teeth that an animal has depends on what it The type of teeth that an animal has depends on what it eats eats A herbivore eats plant material and has very large A herbivore eats plant material and has very large incisors and molars incisors and molars A carnivore eats other animals and needs very large A carnivore eats other animals and needs very large canines canines An omnivore (e.g. humans) eats all kinds of food and An omnivore (e.g. humans) eats all kinds of food and needs and use all of the types of tooth equally needs and use all of the types of tooth equally