3. The Digestive System - 40S Biology · 03/11/2019  · Digestive System a healthy digestive system is essential for good health converts food into raw materials that build and fuel

Digestive System

Objectivesknow the organs in the GI tract and the accessory organs within the digestive system

list the functions of the GI tract including the enzymes responsible for macro nutrient breakdown

understand the importance of nutrition for overall health and wellness

Digestive System

a healthy digestive system is essential for good health

converts food into raw materials that build and fuel our body’s cells

takes in food (ingestion), physically and chemically breaks it down (digestion), takes the nutrients to the bloodstream (absorption), removes the waste (elimination)

https://www.youtube.com/watch?v=Og5xAdC8EUI

Digestive System

organs can be separated into two main groups

alimentary canal (gastrointestinal tract GI)

accessory organs

Alimentary Canal

performs all digestive functions (ingest, digest, absorb, and elimination of waste)

considered a tube that is open at both ends

it includes the mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus

Accessory Organs

Salivary Glands: produce saliva which contains enzymes that break down carbohydrate (starch)

Teeth: used for mastication (chewing) along with the tongue that pushes the food back to the teeth for it to be broken down further

Gastric Glands: (in the stomach) secrete enzymes that start digestion of proteins

Liver: secretes bile that emulsifies fat and is stored in the gallbladder

Accessory OrgansGallbladder: bile is expelled from the gallbladder into the small intestine where it emulsifies fat

Pancreas: secretes enzymes into the small intestine for the digestion of carbohydrates, proteins and fats (trypsin, lipase and amylase)

Intestinal Glands: (in walls of small intestine) secrete enzymes to complete digestion of proteins and carbohydrates

TeethTeeth are needed to tear, rip, and chew food to physically break it into smaller pieces

Tooth decay can be an issue in the digestive process

Saliva is normally slightly alkaline.

When we eat, bacteria in our mouth feed on sugar and turn it into acid

The sugar starts to attack the enamel and wear it away

Tooth decay

Decay has started in the

enamel

Decay has reached the

dentine

Decay reaches the pulp

Decay has spread down to the nerve root

No pain Slight toothache Severe toothache

Excruciating pain!

MouthFood is crushed and ground up by teeth

The salivary glands make saliva which makes the food moist and easy for swallowing

Amylase enzyme (in saliva) breaks the carbohydrate starch down into glucose

Esophagus

Muscular tube that connects mouth to the stomach

Moves food called a bolus, by peristalsis

StomachStomach muscles contract and relax to mechanically break down the food

They also mix the food up with gastric juice and hydrochloric acid

The acid kills germs in the food

The gastric juice contains the protease enzyme pepsin to digest protein into amino acids

Food spends about 3-4 hours in here

The Small Intestine

The small intestine 3 enzymes to complete digestion:

Amylase breaks starch down into glucose

Protease breaks protein down into amino acids

Lipase breaks fats down into fatty acids and glycerol

Muscular tube about 6 m. long where digestion is completed

Has three main parts: Duodenum, Jejunum, Ileum

Connects stomach and the large intestine

http://www.youtube.com/watch?v=xu5jDCX2cHM

The Small IntestineIn the duodenum, the food is now a semi liquid, highly acidic mush called chyme

It needs to be neutralized and digestion needs to be continued

The digested food is diffused through the wall of the small intestine into the blood stream

To do this effectively, the small intestine needs to have a large surface area

This is achieved through villi

Large Intestine

Muscular tube through which indigestible materials are passed to the rectum for excretion.

GI Functionsthe alimentary canal or the gastrointestinal tract has 6 main functions

ingestion

propulsion

mechanical digestion

chemical digestion

absorption

defecation

Ingestion and Propulsion

Ingestion: voluntary process whereby food is placed into the mouth

Propulsion: food needs to be moved from one organ to another this movement is peristalsis

voluntary alternating waves of contraction and relaxation of muscles in the organ wall that squeeze food (bolus) along the tract

swallowing food is the first act of peristalsis

Mechanical Digestion

mechanical digestion: prepares food for further degradation by enzymes by fermenting them into smaller particles

mixing of the food in the mouth, churning of the food in the stomach and segmentation in the small intestine

segmentation is the lateral movement of food in the small intestine along the internal wall in order to mix the food with the digestive juices (can also be considered a part of propulsion)

Chemical Digestionchemical digestion: process in which large food molecules are broken down into their building blocks by enzymes

water is used in this process to break the bonds between the molecules and is a dissolving medium as well as a softening agent for food digestion

food group building blocks:

carbohydrates = simple sugars (monosaccarides) glucose, fructose, galactose

proteins = amino acids

lipids = fatty acids and glycerol

begins in the mouth where saliva breaks down starches into smaller parts

in the stomach, food is broken down by hydrochloric acid where proteins are broken down

in the small intestine fats emulsify by bile salts from the liver

Digestive Enzyme: Chart & Breakdown

Absorption

transport of digested products from the GI tract to the blood or lymph

in order for this to occur, digested food must enter the mucosal cells in the small intestine

food for our cells is absorbed in the small intestine glucose, amino acids, fatty acids, glycerol

in the large intestine re-absorption of water, vitamins and some minerals

https://www.youtube.com/watch?v=1sISguPDlhY

Eliminationoccurs in the large intestine

removal of undigested and indigestible food along with other waste products from the GI tract

Nutrition

a certain fraction of the nutrients we intake are converted to build cellular molecules and structures

most food are used as metabolic fuels, they are oxidized and transformed into ATP

ATP is needed by cells to drive their many activities

the energy value of foods is measured in units called kilocalories (kcal or Calories)

https://www.youtube.com/watch?v=VEQaH4LruUo

Nutritionnutrient: substance in food that is used by the body to promote normal growth, maintenance and repair

6 categories:

major nutrients (macros) include carbohydrates, proteins, lipids

minor nutrients (micros) include vitamins and minerals

water

Carbohydratescomprised of sugars and starches

most carbohydrates we ingest are derived from plants

most ingested carbohydrates cane digested by humans (sugars and starches) with the exception of the polysaccharide cellulose (fibre)

even though cellulose cannot be digested it plays a vital role in increasing the bulk of stool which aids in waste elimination (egestion)

Lipidscholesterol, phospholipids, but mostly triglycerides

saturated fats come from animal products (meat and dairy) along with select plant products (coconut)

unsaturated fats are present in seeds, nuts and most vegetable oils

Proteinsanimal products contain highest quality of proteins (complete proteins) that meet the body’s need for tissue maintenance and growth

legumes, nuts, and cereals provide proteins but they are considered incomplete because tea re low in one or more essential amino acids

when these incomplete proteins are ingested together as a variety, the combination can create complete proteins (Mexican diet of rice and beans)

Vitaminsorganic nutrients that are required in small amounts (A, B, C, D)

found in many food groups but no one food contains all the required vitamins

coenzymes because they act with an enzyme to accomplish a particular type of chemical reaction (catalysis)

Mineralsinorganic substances that include calcium, phosphorus, potassium, sulfur, sodium, chloride, and magnesium along with trace amounts of other types

come from vegetables, legumes, milk and some meats

these are used in metabolism

Metabolism

means change

refers to all chemical reactions that are necessary to maintain life

catabolism in which substances are broken down to simpler substances which can aid in ATP production

anabolism in which larger molecules and structures are built from smaller ones for storage purposes

https://www.youtube.com/watch?v=fR3NxCR9z2U&vl=en

Additional Resources

Internet Interactive Activity:

http://www.klbict.co.uk/interactive/science/

digestion2.htm Crash Course Metabolism Part 2: https://www.youtube.com/watch?v=kb146Y1igTQ