Biology Unit 2a "Nutrition & Digestion"
Food, Nutrients and Digestion ( chapter 8 )
1. The words nutrient and food are often used interchangeably. However from the Biologists perspective they have different meanings. "Food" refers to what we eat whereas "Nutrient" refers to the components of food we require. Nutrients are the substances that provide energy and materials for metabolic activity. ( Example: growth, repair, maintenance and regulation )
2. There are 6 nutrient groups. They are:
-1- protein -4- carbohydrates
-2- fats -5- vitamins
-3- minerals -6- water
Protein
- Food sources: meat, fish, poultry, milk, eggs, nuts, beans
- Function: growth, repair and maintenance of cells & tissues, enzymes, hormones
Carbohydrates - ( sugar, starch, fibre )
- Dietary sources: - sugar found in sweets
- starch found in breads, pastas, potato
- fibre found in fruits and vegetables
- Function: - sugars supply energy quickly
- starches supply energy slowly
- fibre aids in regularity ( reduces chances of cancer )
Fats
- Food source: butter, margarine, cooking oils, bacon, meat, cream
- Function: supply energy, gives food flavor, carries vitamins
Vitamins
- Function: co-enzymes; aid chemical reactions
Minerals
- Function: become incorporated in important molecules like proteins that are required,
For metabolism, growth repair.
Water
Function: transport, digestion, building material of cells
3. Physical v.s. Chemical Digestion
Physical digestion is like physical change. It involves the breakdown of large food particles into small food particles. But there is no chemical change. Human digestive system aids physical digestion with teeth, tongue, hard palate, grinding stomach, bile.
Chemical digestion is like chemical change. It involves the breakdown of large molecules into smaller molecules. Example: Protein - polypeptide - AA
Starches - sugars
Fats - fatty acids, glycerol
The major distinction to be made here is that there is a different molecule produced. The digestive enzymes produced by salivary glands, stomach, pancreas are responsible for chemical digestion.
4. The alimentary canal refers to the hollow tubes through which the food passes during digestion. ( mouth, pharynx, esophagus, stomach, small intestine, anus )
The digestive organs ( salivary, gastric organs, pancreas ) produce digestive enzymes that chemically digest food. Food does NOT pass through these organs.
Mouth - Responsible for some chemical and some physical digestion: teeth, hard palate,
Tongue and cheeks.
3 types of teeth:
-1- Incisors: cutting ( eg. cows, horses )
-2- Canine: tearing ( eg. dogs )
-3- Premolars & Molars: chewing
Salivary Glands produce Saliva which contains:
- Salivary Amylase: digests starch to smaller polysaccharides.
- Mucin: moistens food for swallowing
Pharynx:
Muscular portion of the throat responsible for swallowing.
Esophagus: Tube leading from the mouth to the stomach
- line with smooth muscle
- perislases pushes food along food tube ( Rhythmic contractions )
- no digestion occurs here
Cardiac Sphincter: Circular muscle at top of stomach
- controls food entering and leaving stomach
Pyloric Sphincter: Circular muscle at bottom of stomach
- controls food ( chyme ) leaving stomach to small stomach
Stomach:
- digests protein, stores food before digestion
- folds along lining of stomach called Rugel
Stomach ( Protein Digestion )
- food enters stomach through cardiac sphincter
( * Note on heart burn )
- when food enters stomach, stomach cells release gastrin into the blood stream, and stimulates gastric glands to release gastric juice into the stomach
- gastric juice contains HCl and pepsinogen. The pepsinogen then changes to pepsin which is able to digest protein into a chain or polypeptide chains.
Small Intestine:
- food ( chyme ) enters the small intestine through pyloric sphincter
- 3 parts:
1. Duodenum 2. Jejunum 3. Ileum
- most digestion occurs in duodenum and jejunum
Liver/Gall Bladder:
- liver produces bile; stored in gall bladder
- bile enters duodenum through common bile duct
- bile not an enzyme. It contains bile salts which cased fat emulsification
( i.e. Breaks up fat globules )
Pancreas:
- secretes digestive enzymes which are transported to duodenum through pancreatic duct
- Lipase breaks fat into fatty acids and glycerol
- Pancreatic Amylase: Starch - Maltose
- Trypsins: hydrolyzes, polypeptides and protein into smaller polypeptides
- Sodium Bicarbonate: increase pH so pancreatic enzymes can work
Small Intestine ( ... continued )
- Villi: finger like projections on the intestinal lining which extend into the hollow of the intestine
- Functions:
-1- increase surface area for increased absorption
-2- cells of Villi contain enzymes to digest disaccharides and polypeptides
Peptides: Polypeptides - Amino Acids
Maltase: Maltose - 2 glucose
Sucrose: Sucrose - glucose + fructose
Lactase: Lactose - glucose + galactose
Absorption:
- By this stage of digestion food has been converted to its simplest form:
-1- Amino Acids -2- Monosacharides
-3- Glycerol -3- Fatty Acids
- Nutrients then enter the capillaries which merge from the hepatic portal vein leading to the liver. From liver, blood circulates to the rest of the body bringing nutrients to the cells.
- Glycerol and Fatty Acids are absorbed by lacteals in the Villi and are distributed in the Lymphatic System.
Large Intestine:
- Undigested materials and water go into the large intestine from the small intestine
- 3 sections of large intestine ( colon )
- ascending colon
- transvers colon
- descending colon
- no digestion occurs in colon
- major function is to absorb water from the undigested materials
- the undigested material becomes solid called feces and is stored in the rectum and eliminated through the anus
- feces contain bacteria which makes vitamin B12 that humans need. A lack of this vitamin results in abnormal red blood cell and hemoglobin production
- * Note Mutualism
Rectum:
- stores and compacts feces into stool for elimination
- anal sphincter relaxes, muscles around rectum contract forcing feces out
5. The purpose of digestion is to breakdown food to the point where the required nutrients are small enough to be transported across the cell membranes and through the circulatory system..
Absorption
1. Food is cligested mechanically/physically so it will be small enough to manage in the digestive system AND to provide a larger surface area for Enzymes to act on.
Food is chemically digested into it's smallest nutrient components so it can be transported throughout the body by diffusion, osmosis, facilated diffusion and active diffusion.
Diffusion - requires small molecules, therefore digestion is needed.
Facilated Diffusion - requires specific chemical shape, like enzymes, therefore digestion is needed.
Active Transportation - requires specific shape
2. In the digestive system absorption of nutrients into the circulatory system involves different types of transport.
Examples:
Small Intestine:
- some simple nutrient molecules are absorbed by diffusion into villi
- Glucose and Amino acids are actively transported into villi
Large Intestine:
- ions actively transports into blood
- water fallows by osmosis
3. Absorbed nutrients reach the liver through the hepatic portal vein. The liver deals with the absorbed materials in 2 ways:
-1- Glucose is stored in the liver as glycogen for later use
-2- Toxic substances such as alcohol are chemically changed so they dissolve in blood and can be filtered out by kidney. ( cirrhosis of liver/connective tissue )
4. Once nutrients reach body cells they are used in one of two ways:
-1- undergo respiration to produce energy ( like glucose )
-2- are synthesized into chemical compounds for growth, repair, and maintenance of tissue.
5. Undigested material is stored in the rectum and eliminated through the anus
* Note * Importance of Cellulose/Roughage
- provides bulk, builds up feces faster, more bowel movements, therefore toxins in feces have less time to diffuse in to body, therefore less chance of
disease.