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What is Digestion and the Digestive System? Digestion: “The chemical breakdown of large organic molecules into smaller units that can pass across plasma membranes” Digestive System: “Alimentary canal and associated organs that secrete chemicals into the canal” What animals need for digestion 4 steps must occur before a substance becomes available to the cells of an animal: 1. Ingestion of food • Food source from environment captured and taken into an animal’s mouth. ACTIVITY Rules PAW YOU – Your species can only use your paws to pick up your food source (Clips) SNOUT – Your species must have both hands behind your back and can only pick food source up with your snout (straw) PARTIAL SIGHT – Your species can only look at the roof, at all times LUCKY – No adaptations. Enjoy! What animals need for digestion 2. Mechanical Breakdown of the ingested food Broken down into Large pieces Smaller pieces This process is important as it increases the Surface Area : Volume ratio of the food for enzyme activity. The greater the surface area for enzymes to act, the faster the digestion. Mechanical Breakdown of Food Jaws and Teeth Jaws surround the mouth and are opened/closed by muscles Jaws move the teeth (bony appendages) to break food into pieces Most living vertebrae have teeth of some kind (except birds) One exception Short Beaked Echidna • It has a short snout that it uses to break into ant and termite nests. • It catches these ants and termites with its ‘sticky’ tongue • It then chews its food through two horny plates at the back of its mouth. • ***Which adaptation represented this best in the ‘fantales game??’ Mechanical Breakdown of Food There are four different types of teeth found in most mammals: 1. 2. 3. Incisors – located at the front of the mouth are usually used to get food into the mouth Canines – Pointed teeth which pierces and tears through food Premolars & Molars – have ridged surfaces to grind the food so it is easy to swallow. What animals need for digestion 3. Secretion of various digestive enzymes onto the food Step 1: enzymes and secreted onto the food source Step 2: enzymes act on and breakdown organic molecules into smaller units to enable them to cross cell membranes Step 3: This energy and matter acted on by the enzymes is able to cross the cell membranes and is available for use. What animals need for digestion 4. Absorption of Digested Food The organic molecules pass over the cell membranes and line the digestive tract and then pass into the body fluids. DRAW THE DIGESTIVE SYSTEM Draw and label the following organs within the body: Small Intestine Anus Oesophagus Pancreas Gall Bladder Mouth Large Intestine Rectum Stomach Liver Digestive System MOUTH OESOPHAGUS LIVER STOMACH GALL BLADDER LARGE INTESTINE APPENDIX ANUS PANCREAS SMALL INTESTINE RECTUM The mouth The beginning of the digestive system Both mechanical and chemical breakdown occurs Food is ground into smaller pieces with the teeth While this is occurring, saliva is released from the salivary glands, which mixes with the food, which turns the food soft and easy to swallow Amylase WHAT IS IT?? Enzyme which is found in saliva Acts on starch molecules and breaks them down into smaller chains. Once the food turns into a rounded chuck, bolus, which sits at the back of the mouth and waits for the individual to begin the swallowing process. The Oesophagus Soft muscular tube About 20 – 23 centimetres long in an adult. It secretes mucus, and transports food from mouth to the stomach Food moves down oesophagus by muscular movements and not gravity. This is called “Peristalsis” Page 109 The Stomach Mechanical and Chemical breakdown process continues Empty – size of large banana (volume = 50 ml) When food is swallowed – stretches to 1.5 L volume As the stomach stretches it activates nerve endings in the cell wall which secretes gastric juice. Gastric Juice Mixture of mucus, enzymes, hydrochloric acid and water. Different cells in the stomach wall secrete these different elements. The gastric juice mixes with the churning food and saliva to create chyme. Just like a yummy milkshake!!! Stomach Continued The gastric juice contains hydrochloric acid and the inactive form of the enzyme pepsin. (Pepsinogen) The hydrochloric acid creates a highly acidic environment (pH 2) which activates the pepsinogen into pepsin. Pepsin Acts on peptide bonds between amino acids This leads to the beginning of protein digestion. Time in the Stomach Food stays in the stomach for 1 – 4 hours The more carbohydrates in a meal, the quicker it leaves the stomach The more fat in a meal, the longer it must stay in the stomach. Meals high on protein are in the stomach for longer than carbohydrates but less that fats. Time in the stomach Short Time Carbohydrates Long Time Proteins Fats Hormones in the Stomach During digestion in the stomach, hormones, are produced in the stomach wall These hormones are transported to body parts such as the pancreas and the gall bladder This signals to these organs that food is in the stomach and will be travelling to the short intestine soon. The Small Intestine The waves that churn the food in the stomach, forces amounts of food out of the stomach and through a muscular opening called the pyloric sphincter The small intestine is about 6.2 metres long and 2.5 centimetres in diameter. Food stays in the small intestine for about 3 – 6 hours The Small Intestine Digestion in the SI is able to occur through enzyme secretion from the intestine wall as well as secretions from the 3 organs that lead into the SI – pancreas, liver & Gall Bladder. Cystic Fibrosis is a disease where thick mucus blocks the bile duct which stops pancreatic enzymes from entering the small intestine. Page 111 Figure 5.20 Parts of the Small Intestine The small intestine has three main parts – Duodenum, Jejunum and the ileum.
