DIGESTIVE SYSTEM

Digestion: process by which food and drink are broken down into smallest parts so that body can use them to build and nourish cells and provide energy Why is digestion important? Our food and drink must be changed into smaller molecules of nutrients before they can be absorbed into the blood and carried to cells throughout the body.

What nutrients do organisms need and Why? MACROMOLECULES Carbohydrates for short and long-term energy Carbohydrates for short and long-term energy Fats/Lipids for long-term energy Fats/Lipids for long-term energy Proteins for building organisms own proteins (performing important cellular functions, growth & repair) Proteins for building organisms own proteins (performing important cellular functions, growth & repair) If starving, proteins can be used for energy, but that is not their primary function If starving, proteins can be used for energy, but that is not their primary function Nucleic acids are synthesized by the organism, they are not usually obtained by feeding (function of nucleic acids is to store genetic information) Nucleic acids are synthesized by the organism, they are not usually obtained by feeding (function of nucleic acids is to store genetic information)

Organization of Complexity Tissue: A group of cells that works together to perform a specialized task Organs: A structure composed of different tissues specialized to carry out a specific function Organ system: A group of organs that work together to perform a specialized function   Cell The smallest structural unit of an organism that is capable of independent functioning, 

Digestive System

TISSUES OF THE STOMACH

4 Stages of Food Processing INGESTION (nutrients IN) INGESTION (nutrients IN) DIGESTION (break down of larger molecules into smaller molecules) DIGESTION (break down of larger molecules into smaller molecules) ABSORPTION (from intestine into blood) ABSORPTION (from intestine into blood) EGESTION, EXCRETION, ELIMINATION (wastes OUT) EGESTION, EXCRETION, ELIMINATION (wastes OUT)

Types of digestion 1) 1) Physical/Mechanical Digestion: is the physical breakdown of food by chewing, crushing in the mouth and grinding in the stomach. This is done primarily to increase surface area for exposure to digestive chemicals.

2) Chemical digestion: which is the breakdown of food by chemical substances such as bile, acids, and enzymes. This process starts in the mouth (saliva contains amylase), continues in the stomach (secretes acid and enzymes) and is completed in the small intestine.

ENZYMES Are proteins Are proteins Are catalysts (chemicals that speed up the rate of a reaction without being consumed themselves) Are catalysts (chemicals that speed up the rate of a reaction without being consumed themselves) Function best at a specific pH and temperature Function best at a specific pH and temperature Are highly specific for their substrate Are highly specific for their substrate Eg. Maltase catalyzes the hydrolysis of maltose into 2 glucose, but NOT the breakdown of Lactose, which would be catalyzed by lactase Eg. Maltase catalyzes the hydrolysis of maltose into 2 glucose, but NOT the breakdown of Lactose, which would be catalyzed by lactase

Optimal Temperature & pH

ENZYME ANIMATION hill.com/sites/ /student_vie w0/chapter2/animation__how_enzyme s_work.html hill.com/sites/ /student_vie w0/chapter2/animation__how_enzyme s_work.html

OPEN TUBE Two openings: one mouth & one anus Two openings: one mouth & one anus

Human Digestive System

Organs of Digestive System Animation hill.com/sites/ /student_view0/ chapter26/animation__organs_of_digestio n.html hill.com/sites/ /student_view0/ chapter26/animation__organs_of_digestio n.html hill.com/sites/ /student_view0/ chapter26/animation__organs_of_digestio n.html hill.com/sites/ /student_view0/ chapter26/animation__organs_of_digestio n.html

DIGESTIVE TRACT MOUTH A. Teeth - physical break down of food B. Saliva secreted by 3 pairs of salivary glands Contains the enzyme amylase, which begins chemical digestion of starch C. Tongue helps mix food and saliva, moistens (lubricates) food and forming it into a ball (bolus) so it can be easily swallowed.

Esophagus (passage way) A. A. Entire length is lined with muscles that contract in a wave like action called peristalsis. Peristalsis helps push food down towards your stomach. This is why you can even swallow food while hanging upside down!!! B. B. Many small glands are located in the back of the -throat and in the walls of the esophagus. These produce mucin, a lubricant that eases the travel of food to the stomach.

C. A valve or sphincter, called the cardiac sphincter is located at the end of the esophagus. It ensures that food that has entered the stomach can not move back into the esophagus (if it does it is- called reflux or heart burn)

Stomach (storage and digestion of proteins) J-shaped storage and digestive organ. Entrance to the stomach is through the cardiac sphincter, exit through the pyloric sphincter Consists of three (3) layers of muscle - churning aids physical breakdown. Churns food into "chyme" Acid environment (pH 2) due to hydrochloric acid (HCI). This kills bacteria and activates enzymes. Eg pepsinogen -> becomes pepsin (digests proteins)

Small intestine most chemical digestion occurs here therefore most enzyme activity occurs here Purpose is to complete chemical digestion (pH 8) and to absorb nutrients into blood (amino acids & monosaccharides) or lymph (fatty acids & glycerol). it is approximately 6-7 metres long composed of three sections: duodenum, jejunum, ileum Unabsorbed material exits via the ileo-cecal valve which opens into the large intestine

The entire surface is covered with finger like projections called villi which in turn are covered with smaller projections called microvilli – increase surface area for absorption Amino acids & monosaccharides are absorbed into the capillaries, but fatty acids and glycerol are absorbed into the lacteal, part of the lymphatic system, eventually they too enter the circulatory system

Large intestine Large intestine Purpose is to re-absorb water and to remove indigestible waste e.g. fibre Purpose is to re-absorb water and to remove indigestible waste e.g. fibre 7 litres of water/day are reabsorbed 7 litres of water/day are reabsorbed Waste/feces becomes more solid as it is moved along due to peristalsis Waste/feces becomes more solid as it is moved along due to peristalsis If peristalsis occurs too quickly, water cannot be reabsorbed into the body and remains in the feces causing diarrhea. If peristalsis occurs too quickly, water cannot be reabsorbed into the body and remains in the feces causing diarrhea. If peristalsis occurs too slowly, too much water may be removed resulting in constipation. If peristalsis occurs too slowly, too much water may be removed resulting in constipation. Colon is home to many beneficial bacteria like E. coli, which allow us to absorb certain vitamins Colon is home to many beneficial bacteria like E. coli, which allow us to absorb certain vitamins

Accessory Organs STOMACH

3 Accessory organs aid chemical digestion in the small intestine 1) Pancreas Many enzymes are made here which enter the small intestine through the common bile duct. These include lipases, proteases (trypsin, chymotrypsin, carboxypeptidase), carbohydrases (maltase, lactase) and lipases. It secretes bicarbonate, a base which neutralizes the stomach acid. It also produces insulin and glucagon which are hormones (NOT DIGESTIVE ENZYMES), that travel through the blood and aid in managing blood-sugar levels.

2) Liver The liver produces bile salts, a soapy emulsifier that breaks large globules of fat into smaller ones, thereby increasing surface area for lipase enzymes to act. 3) Gall bladder Attached to the liver, it stores bile until signaled to release it into the bile duct. It then travels through the common bile duct together with pancreatic juices into the small intestine.

HOMEWORK HOMEWORK Read pages 56 to 58 Read pages 56 to 58 See powerpoint on wiki See powerpoint on wiki Complete the Handout (see table 2.1 on page 65) Complete the Handout (see table 2.1 on page 65) Answer page 63 #1 - 5, Answer page 63 #1 - 5,