DIGESTIVEDIGESTIVESYSTEMSYSTEM

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 What nutrients do organisms need and Why?and Why?

MACROMOLECULESMACROMOLECULES CarbohydratesCarbohydrates for short and long-term for short and long-term energyenergy Fats/LipidsFats/Lipids for long-term for long-term energyenergy ProteinsProteins for building organisms own proteins for building organisms own proteins

(performing important (performing important cellular functions, cellular functions, growth & repairgrowth & repair)) If starving, proteins can be used for energy, but that is If starving, proteins can be used for energy, but that is

not their primary functionnot their primary function Nucleic acidsNucleic acids are synthesized by the organism, are synthesized by the organism,

they are not usually obtained by feeding they are not usually obtained by feeding (function of nucleic acids is to store genetic (function of nucleic acids is to store genetic information)information)

Organization of ComplexityOrganization 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

CellThe smallest structural unitof an organismthat is capableof independent functioning,

Digestive SystemDigestive System

TISSUES OF THE STOMACHTISSUES OF THE STOMACH

4 Stages of Food Processing4 Stages of Food Processing

INGESTIONINGESTION (nutrients IN) (nutrients IN)DIGESTIONDIGESTION (break down of larger (break down of larger

molecules into smaller molecules)molecules into smaller molecules)ABSORPTIONABSORPTION (from intestine into blood) (from intestine into blood)EGESTION, EXCRETION, ELIMINATIONEGESTION, EXCRETION, ELIMINATION

(wastes OUT) (wastes OUT)

Types of digestionTypes of digestion

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.

ENZYMESENZYMES

Are proteinsAre proteins Are catalysts (chemicals that speed up the rate of Are catalysts (chemicals that speed up the rate of

a reaction without being consumed themselves)a reaction without being consumed themselves) Function best at a specific pH and temperatureFunction best at a specific pH and temperature Are highly specific for their substrateAre highly specific for their substrate Eg. MaltEg. Maltasease catalyzes the hydrolysis of maltose catalyzes the hydrolysis of maltose

into 2 glucose, but NOT the breakdown of into 2 glucose, but NOT the breakdown of Lactose, which would be catalyzed by lactLactose, which would be catalyzed by lactasease

Optimal Temperature & pHOptimal Temperature & pH

ENZYME ANIMATIONENZYME ANIMATION

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_enzymes_work.html

OPEN TUBEOPEN TUBETwo openings: one mouth & one anusTwo openings: one mouth & one anus

Human Digestive SystemHuman Digestive System

Organs of Digestive SystemOrgans of Digestive SystemAnimationAnimation

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter26/animation__organs_of_digestion.html

DIGESTIVE TRACTDIGESTIVE TRACTMOUTH A. Teeth - physical break down of

food B. Saliva secreted by 3 pairs of

salivary glandsContains 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. 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. 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, C. A valve or sphincter, called the called the cardiac cardiac sphinctersphincter is located at is located at the end of the the end of the esophagus. It esophagus. It ensures that food that ensures that food that has entered the has entered the stomach can not stomach can not move back into the move back into the esophagus (if it does esophagus (if it does it is- called reflux or it is- called reflux or heart burn) 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 intestineLarge intestine Purpose is to re-absorb water Purpose is to re-absorb water

and to remove indigestible waste and to remove indigestible waste e.g. fibre e.g. fibre

7 litres of water/day are 7 litres of water/day are reabsorbed reabsorbed

Waste/feces becomes more Waste/feces becomes more solid as it is moved along due to solid as it is moved along due to peristalsis peristalsis

If peristalsis occurs too quickly, If peristalsis occurs too quickly, water cannot be reabsorbed into water cannot be reabsorbed into the body and remains in the the body and remains in the feces causing feces causing diarrheadiarrhea..

If peristalsis occurs too slowly, If peristalsis occurs too slowly, too much water may be removed too much water may be removed resulting in resulting in constipation.constipation.

Colon is home to many Colon is home to many beneficial bacteria like beneficial bacteria like E. coliE. coli, , which allow us to absorb certain which allow us to absorb certain vitaminsvitamins

Accessory OrgansAccessory Organs

STOMACH

3 Accessory organs aid chemical 3 Accessory organs aid chemical digestion in the small intestine 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.

HOMEWORKHOMEWORKRead pages 56 to 58Read pages 56 to 58See powerpoint on wikiSee powerpoint on wikiComplete the Handout (see table 2.1 on Complete the Handout (see table 2.1 on

page 65)page 65)Answer page 63 #1 - 5, 8 - 13Answer page 63 #1 - 5, 8 - 13