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FUNCTION OF DIGESTION. SBI3U Section 10.1 Pg 402-410. Organic Molecules. Organic molecules are carbon based molecules that are bonded to hydrogen and possibly other atoms such as oxygen, sulfur and nitrogen. . Macromolecules.

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function of digestion



Section 10.1

Pg 402-410

organic molecules
Organic Molecules
  • Organic molecules are carbon based molecules that are bonded to hydrogen and possibly other atoms such as oxygen, sulfur and nitrogen.
  • Macromolecules are molecules that are made up of subunits (monomers) of organic molecules and are known as macronutrients. They provide energy to our bodies, regulate cellular activities, build and repair tissue.
  • Energy released from macromolecules is used to maintain the bodies metabolism (all of the chemical reactions that occur in an organism)
four major categories of macronutrients
Four major categories of macronutrients
  • Carbohydrates, Lipids, proteins and Nucleic acids are the four major essential nutrients
  • They are nutrients that cannot be made by the body and must be obtained from food
  • Are macromolecules that always contain carbon, hydrogen and oxygen usually in a ration of 1C:2H:1O
  • Provide short-term or long-term energy storage for organisms
  • Monosaccharides
    • Single sugars
    • Eg. Glucose, fructose, dextrose




    • Combination of two monosaccharides
    • Eg. Sucrose, lactose, maltose


  • Polysaccharides
    • Consist of many linked monosaccharides
    • Eg. Glycogen (stored form of energy made up of glucose subunits), amylose (starch), cellulose
  • Insoluble in water
  • Fats, Oils and Waxes (depending on the state at room temperature)
    • Made of triglycerides (glycerol and three fatty acids)
    • Glycerol + fatty acids are condensation reactions

Lipids store 2.25 times more energy per gram than other macromolecules and can function as energy storage molecules or form the membrane that separates a cell from its external environment (phospholipid)

  • Made of chains of amino acids joined together by peptide bonds .These chains are called polypeptides.
  • A peptide bond is a covalent bond that is created when a carboxyl group of one amino acid reacts with the amino group of another amino acid
  • There are 20 different amino acids (8 are essential)
  • Each amino acids has an amino group, a carboxyl group and a unique portion called the R-Group
nucleic acids
Nucleic Acids
  • The food we consume contains the nucleic acids DNA and RNA
  • Recall that DNA and RNA are made up of purines adenine and guanine and pyrimidines cytosine , thymine in DNA and uracil in RNA
  • Our bodies break down the DNA and RNA from food into their constituent nucleotides which are then used to construct our own DNA and RNA
  • Macromolecules (carbohydrates, proteins and lipids) are broken down by the body by a process called hydrolysis
  • During hydrolysis a water molecule is added to the macromolecule and breaks the chemical bonds that hold the monomers together
  • These monomers can now be absorbed by the cells lining the small intestine
  • Enzymes are protein molecules secreted by cells in the digestive tract and act as catalysts there by increasing the rate of hydrolysis
role of minerals and vitamines
Role of Minerals and Vitamines
  • Minerals and vitamins are inorganic(minerals) and organic(vitamins) substances that enable chemical reactions to occur and aid in tissue development, growth and immunity.
  • Organic molecules required in tiny amounts by an organism
role of water in the body
Role of Water in the Body
  • Makes up two thirds of the bodies mass
  • Water transports dissolved nutrients into the cells that line the small intestine, flushes toxins from cells, lubricates tissues and joints, forms essential body fluids like blood and mucus, regulates body temperature and eliminates waste materials through sweating
the four stages of food processing
The four stages of Food Processing
  • The role of the digestive system is to break food down into small, soluble units that can be used by cells
  • Digestion occurs in the following four stages
  • Ingestion – the taking in or eating of food
  • Digestion – the breakdown of food by mechanical and chemical processes into molecules small enough for cells of the body to absorb
  • Absorption – the transport of the products of digestion from the digestive system into the circulatory system, which distributes them to the rest of the body
  • Elimination – the removal of undigested solid waste matter from the body
the human digestive system

The human digestive system


Section 10.2

Pg 411-418

  • Mouth starts mechanical digestion
    • Teeth grind and cut food
  • Saliva starts chemical digestion
    • Salivary amylase breaks down amylose into disaccharides
  • After chewing, tongue forms a ball from the food, called a bolus
  • Is a hollow muscular tube that transports each bolus of food to the stomach through a series of wave-like muscular contractions called peristalsis
  • The opening of the esophagus lies next to the opening of the windpipe(trachea) which carries air to the lungs
  • When eating the trachea is closed by a valve called the epiglottis to prevent food from going down the wrong tube
  • The entrance to the stomach is controlled by a ring of muscle called the esophageal sphincter which is normally closed to prevent stomach acid from flowing up the esophagus
  • Muscular and J-shaped
  • Mechanical digestion (contractions of muscle to churn food)
  • Chemical digestion (gastric juices that contain HCl, salts, enzymes, water and mucus)
  • During the chemical and mechanical digestion the food is broken up and mixed with the gastric juices to form a thick liquid called chyme
  • At the lower end of the stomach a valve called the pyloric sphincter keeps the food in the stomach when closed
  • Mucus is secreted by stomach cells to protect stomach from gastric juices
  • The enzyme pepsin activates once gastric juices are secreted and helps digest long polypeptides (proteins) into shorter polypeptides
  • A network of nerves that surround the stomach initiate stomach contractions that release partially digested food into the duodenum of the small intestine
small intestine anatomy
Small Intestine Anatomy
  • Divided into three components:
    • Duodenum
    • Jejunum
    • Ileum
  • 6-8 meters long
  • 1.5” in diameter
  • Digestion is completed in the small intestine and nutrient macromolecules are broken up into their component molecules (monomers)
small intestine
Small Intestine
  • The walls of the small intestine are lined by folds that greatly increase the surface area through which nutrients can be absorbed
  • The folds are covered by tiny finger like projections called villi which are in turn covered by brush like micro-villi
  • Duodenum - Is a U shaped tube that is responsible for the breakdown of food in the small intestine by using enzymes
  • Jejunum- Breaks down the remaining proteins and carbohydrates so the end products can be absorbed into the bloodstream
  • Ileum- absorbs nutrients and pushes the remaining undigested material into the large intestine
pancreas and gall bladder
Pancreas and Gall bladder
  • Are referred to as Accessory Organs because they are not part of the alimentary canal but are connected to the canal by ducts
  • The pancreas secrets pancreatic fluid (which contains enzymes) and bicarbonate (which alters the pH of chyme from strongly acidic(pH 1) to weakly basic(pH 8)) into the duodenum
  • The weakly basic chyme allows enzymes in the pancreatic fluid to work more efficiently
  • Bile is produce by the liver and stored in the gall bladder, it is then released by the gall bladder into the duodenum and helps to break up fats
factors that affect enzyme action
Factors that Affect Enzyme Action
  • The rate at which an enzyme function is dependent on temperature and PH
  • If the temperature is too low then there will be less energy added to the reaction thus reducing the rate and if the temperature is too high then the enzymes molecular structure will be effected and thus change its properties thus reducing the rate of reaction
absorption in the small intestine monosaccharides
Absorption in the Small Intestine (Monosaccharides)
  • Monosaccharides are absorbed into the bloodstream through the lining of the small intestine
  • They are then transported to the liver and converted into glucose
  • Glucose in carried from the liver to all parts of the body through the circulatory system and is used as a source of energy
  • Excess glucose is then converted to glycogen for storage in the liver until the body needs it for energy
absorption in the small intestine amino acids
Absorption in the Small Intestine (Amino Acids)
  • Amino acids are carried from the small intestine to the liver by the bloodstream
  • They are converted sugars or used in energy releasing chemical reactions
  • Some amino acids are carried by the circulatory system to the cells of the body where they are used to make enzymes and other proteins
absorption in the small intestine glycerol and fatty acids
Absorption in the Small Intestine (Glycerol and Fatty acids)
  • Glycerol and fatty acid molecules are absorbed into the cells of the small intestine and reassembled to form triglycerides
  • The triglycerides are then coated with protein to make them water soluable
  • Once in the bloodstream the protein coating is removed and the triglycerides are broken down by lipase enzymes back to glycerol and fatty acids and provide energy to the cells
the large intestine
The Large Intestine
  • The remaining unabsorbed material from the small intestine moves into the large intestine
  • The large intestine absorbs any excess water from the remaining material
  • Anaerobic bacteria (do no live in the presence of oxygen) living in the large intestine break down undigested food further producing vitamines which are absored into the blood stream
  • The left over matter(feces) is then eliminated through the anus