FOOD & DIGESTION DIGESTION

Functions of Digestive System Breaks down food into molecules Molecules are absorbed into blood and carried throughout the body Wastes are eliminated from the body

VIDEO

Parts of the digestive system

Task- 2.6 Draw and label the parts of the human digestive system.

Parts of the digestive system Two main parts: Alimentary canal – continuous coiled hollow tube Accessory digestive organs

Organs of the alimentary canal Mouth Pharynx Esophagus Stomach Small intestine Large intestine Anus

Accessory digestive organs Salivary glands Tongue Gall Bladder Liver Pancreas

Processes of the Mouth Mastication (chewing) of food Mixing masticated food with saliva Initiation of swallowing by the tongue Allowing for the sense of taste Slide 14.7 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Saliva Saliva helps break down starch into simple sugars. It also moistens the food allowing easier passage through the gastrointestinal tract. Saliva is secreted from glands found under the tongue and at the back of the mouth. The sight, smell, taste or even the thought of food will start to increase the amount of saliva secreted.

Pharynx Function Serves as a passageway for air and food Food movement is by alternating contractions of the muscle layers (peristalsis) Epiglottis shuts the air passage while swallowing.

Esophagus Runs from pharynx to stomach through the diaphragm Conducts food by peristalsis (slow rhythmic squeezing) Passageway for food only (respiratory system branches off after the pharynx) Slide 14.10 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Stomach Functions Acts as a storage tank for food Site of food breakdown Chemical breakdown of protein begins Delivers chyme (processed food) to the small intestine Slide 14.18 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Small Intestine The body’s major digestive organ Site of nutrient absorption into the blood Duodenum Attached to the stomach Curves around the head of the pancreas Slide 14.21 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Large Intestine Larger in diameter, but shorter than the small intestine Frames the internal abdomen Slide 14.28 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Functions of the Large Intestine Absorption of water Eliminates indigestible food from the body as feces Does not participate in digestion of food Slide 14.29 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Structures of the Large Intestine Colon Rectum Anus – external Body opening Slide 14.30b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Digestion Process by which the body breaks down food into small nutrient molecules

Two Kinds of Digestion Mechanical And Chemical

Mechanical Digestion Foods are physically broken down into smaller pieces. Begins when you take your first bite of food Your teeth are the first stage in mechanical digestion

Chemical Digestion Chemicals produced by the body break foods into smaller chemical building blocks. Begins in the mouth Accomplished by enzymes

What are enzymes? Catalysts speed up a reaction by providing an alternate path for the reaction(short cut route so that the reaction happens fast) Enzymes – protein that speeds up chemical reactions in the body. Enzymes are highly substrate specific. Names end with an ‘–ase’

Our food is made up of: Carbohydrates: Bread, Pasta, Potato Protein: Meat, Nuts, Lentils Fats: Butter, Milk Our body needs to digest them – turn them into a form that can be absorbed into the blood and used by cells. Enzymes make this possible.

Look closely at the 3 digestion equations: Enzymes that work on carbohydrates: Amylase + Starch Maltose Enzyme (in pasta, bread (a form of sugar that can be (in saliva) carbohydrate) absorbed by the body )

Enzymes that work on Proteins: Protease + Proteins Amino Acids Enzyme (eg. In meat, nuts) (the body can absorb (in stomach) them and use them)

Enzymes that work on Fats: Lipase enzyme + Fats Fatty Acids + Glycerol (secreted by pancreas) (Butter, Milk) (can be absorbed into body) http://www.youtube.com/watch?v=qDEVBMldiY8&feature=related Enzyme action animation

Task-2.8 Complete the table: Sl.No: Name of the enzyme Substrate Reaction it aids/ function Found in Carbohydrase Amylase Protease Lipase Peptidase Sucrase Pepsin Maltase lactase

What is digestion? Digestion is the breakdown of large insoluble molecules into smaller soluble molecules which can pass through the wall of the gut into the blood.

How does it start? Well first you chew something with your teeth. Which makes it have a larger surface area, then and enzyme in your saliva called amylase starts breaking the carbohydrate into sugar. The food is then pushed down the oesophagus to the stomach by PERISTALSIS. What’s that???

Peristalsis is the contraction and relaxation of the circular muscles in the wall of the gut. When the muscle relaxes the food drops down and when it contracts at the top the food at the bottom is pushed down

The food is then in the stomach, the food is churned around by more waves of peristalsis to make it into mush, and it mixes with gastric juice. Gastric juice contains and enzyme called Protease which breaks down, yup you guessed it, protein, into amino acids.

It also contains hydrochloric acid which kill bacteria and makes the optimum PH for this enzyme, meaning it will work at its best at a lower PH. The food is then released a little bit at a time into the duodenum, which is the first part of the small intestine. The duodenum DOES NOT produce any digestive juices, but has 2 poured into it! *Did you know the small intestine is 6m long?* Whoa that’s really long!

One of the juices comes from the pancreas One of the juices comes from the pancreas. Pancreatic juice, It contains carbohydrase, protease and lipase. What does each one do? The other digestive juice is call bile. Which is made by the liver and stored in a bag called the gall bladder. It is NOT AN ENZYME, but it neutralises the acid that was added in the stomach. This helps the small intestine work more effectively.

Bile also helps emulsify the fats. What’s emulsify mean? It means to make the fats into smaller blobs to make their surface area larger. So that the lipase can digest quicker.

The food is now a semi-liquid like a smoothie The food is now a semi-liquid like a smoothie! And it passes into the second part of the small intestine called the ileum. The walls of the ileum make a digestive juice which contains carbohydrase, protease and lipase.

These enzymes complete the digestion of fats to fatty acids, glycerol, (carbohydrate) to simple sugars and protein to amino acids. The ileum is specially adapted for absorption, passing digested food into the blood. It is very long to allow time for digestion.It has a very large surface area due to the presence of villi (finger like projections) and microvilli.

This allows rapid diffusion of the products of digestion This allows rapid diffusion of the products of digestion.Since villi walls are only one cell thick, this helps speed up the diffusion.

Each Villus has a blood vessel and a lymph vessel to carry the food away. All the food which cannot be digested ends up in the large intestine. It enters into the colon where most of the water is reabsorbed into the blood. The indigestible remains form a semi solid faeces which is stored in the rectum. Eventually it is passed out the anus.

Absorption Occurs after food has been digested. Process by which nutrient molecules pass through the wall of the digestive system into the blood

Summary of the phases of digestion Ingestion - this is the physical intake of foodstuffs into the gastrointestinal tract. Digestion - a series of physical and chemical processes which begin in the mouth, but take place mainly in the stomach and small intestine. Absorption - the passage of the digested food substances across the gastro-intestinal lining, or mucosa, into the blood and lymph. Elimination - the excretion, or elimination, of those food substances that cannot be digested (such as cellulose) or without any nutritional value in the faeces.

Some interesting facts on digestive system People do not have conscious control over the muscles in the oesophagus. Even if someone is upside down, the food will be passed on to the stomach. The stomach is an expandable sack made up of three different layers of muscles where the bolus will be churned for a few minutes or up to 2 or 3 hours. The duodenum is about 25 centimetres long and in the shape of a horse shoe. Fat can take from 3 to 5 hours to be broken down and absorbed. Dietary fibre aids peristalsis because it increases the bulk of the bolus or chyme being moved along. The villi have a surface area of about 30m2, this is equivalent to the size of a tennis court!

Task-2.8 Describe step wise the digestion of a chicken sandwich.