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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
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