The Human Digestive System The Digestive System The digestive system: is a group of organs that take...
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Transcript of The Human Digestive System The Digestive System The digestive system: is a group of organs that take...
The Human Digestive System
The Digestive SystemThe digestive system: is a group of organs that
take in food and change it into a form the body can use. Digestion: is the changing large molecules into
smaller ones capable of being used by the cells in the body.
Cells need food for energy, growth and repair.Can be compared to a factory – materials are
transported to different locations and are changed at every stop.
The final product is quite different than the original.
Nutritional RequirementsHumans need to take in food for:
fuel = chemical energy raw materials = carbon source essential nutrients = animals cannot make
elements (N, P, K, Fe, Na, K, Ca...), NAD, FAD, etc.
Getting & Using Food Ingest
taking in foodDigest
Physical digestionbreaking up food into smaller pieces
chemical digestionbreaking down food into molecules small enough
to be absorbed into cellsenzymes
Absorbabsorb across cell membrane
diffusionactive transport
Eliminate undigested extracellular material passes out of
digestive system
Physical vs. Chemical Change
Food gets broken down as it passes through the digestive system in 2 ways1. Physical Change:
Large pieces are broken down into smaller ones. The food is still in the same form (only the size and
shape of the food particles change).Occurs through chewing, grinding and mixing.
2. Chemical Change:This occurs when food changes form so the body may
use it.Body chemicals are added to food to make this happen.These chemicals are called enzymes.
Digestion
Digestive SystemWater, vitamins, and minerals can be
used by cells so do not need to be changed
Fats, proteins, and carbohydrates cannot be used so they need to be broken down by enzymesEnzymes: are chemicals that speed up
the rate of changeThere are different kinds of enzymes for
different nutrients.
Human digestive systemAlimentary Canal
Digestive SystemMain organ passageway:
1. Mouth (includes salivary glands)2. Esophagus 3. Stomach4. Small intestine5. Large intestine6. Anus
Additional organs necessary: Pancreas, liver, and gallbladder all secrete enzymes into the small intestine.
Common processes & structures
Movement & Control peristalsis
push food along by rhythmic waves of smooth muscle contraction in walls of digestive system
sphinctersmuscular ring-like valves, regulate the passage of material between sections of digestive system
Accessory glandssalivary glands, pancreas, liver & gall bladdersecrete digestive juices (enzymes & fluid)
Swallowing (& not choking)
Epiglottis problem: breathe & swallow through same orificeflap of cartilagecloses trachea (windpipe) when swallowingfood travels down esophagus
Esophagus move food along to stomach by peristalsis (pushing of food
along by waves of smooth muscle contractions)
IngestionMouth
physical digestionteeth
breaking up foodchemical digestion
salivaamylase
o enzyme digests starchmucin
o slippery protein (mucus)o protects soft lining of digestive systemo lubricates food for easier swallowing
buffers o neutralizes acid to prevent tooth decay
anti-bacterial chemicals o kill bacteria that enter mouth with food
mouthbreak up foodmoisten food digest starchkill germs
StomachFunctions
food storagecan stretch to fit ~2L food
disinfect foodHCl = pH 2 so kills bacteriaHas a mucus layer to protect itself from enzymes and HCl
chemical digestionpepsin
enzyme breaks down proteinsAfter the stomach completes its
part in digestion the food is now in a liquid form called chyme.
But the stomach is made out of protein!What stops the stomach from digesting itself?
mucus secreted by stomach cells protects stomach lining
StomachA large muscular bag that has gastric juice (juices
given off by the lining of the stomach) that mixes and digests protein. The gastric juice is made of an emzyme (pepsin) and HCl that digests protein.
The walls are muscular and thick that churns and grinds up the food. Once the food is mixed with the digestive juices, it starts to look like a milk shake.
The partially digested food is squeezed out of the stomach in spurts and moves to the small intestine.
Food usually stays in the stomach for 4 – 7 hours.
stomachkills germs store food break up fooddigest proteins
cardiacsphincter
pyloricsphincter
mouthbreak up foodmoisten food digest starchkill germs
Small IntestineFunction
major organ of digestion & absorption chemical digestion
digestive enzymesabsorption through lining by diffusion
over 6 meters in length! small intestine has huge surface area = 300m2
(~size of tennis court)Structure
A hollow tube with finger-like projections called villi. Each villus contains blood vessels that carry digested
food.From the blood vessels the food is carried to body
cells.
Duodenum 1st section of small intestines
acid food from stomach mixes with digestive juices from accessory glands:
pancreas liver gall
bladder
PancreasMakes enzymes to digest:
FatsProteinsCarbohydrates
These enzymes pass from the pancreas to the small intestine through a small tube.
Pancreas also produces insulin to regulate sugars.
stomachkills germs break up fooddigest proteinsstore food
pancreasproduces enzymes to digest proteins, starch &
fat
mouthbreak up foodmoisten food digest starchkill germs
Liver Digestive System Functions
produces bilestored in gallbladder until neededbreaks up fats
Stores unused sugar
Circulatory System ConnectionCirculatory System Connection
bile contains colors from old red blood cells collected in liver =iron in RBC rusts & makes feces brown
bile contains colors from old red blood cells collected in liver =iron in RBC rusts & makes feces brown
pancreasproduces enzymes to digest proteins, starch &
fats
stomachkills germs break up fooddigest proteinsstore food
liverproduces bile
- stored in gall bladderbreak up fats
mouthbreak up foodmoisten food digest starchkill germs
Digestive EnzymesCarbohydrate Digestion:
Mouth Salivary glands
Small IntestinePancreas
Protein Digestion:Stomach
Enzymes and HClSmall IntestinePancreas
Fat Digestion:Small Intestine PancreasLiver
Bile
Digestive enzymes
Absorption by Small Intestines
Absorption through villi & microvillifinger-like projectionsincrease surface area for absorption
Absorption of Nutrients
Occurs through diffusion.Final forms of nutrients:
Carbohydrates (starches and sugars) = glucose
Protein = amino acidsFats = glycerine and fatty acids
small intestinesbreakdown all foods
- proteins- starch- fats- nucleic acids
absorb nutrients
stomachkills germs break up fooddigest proteinsstore food
pancreasproduces enzymes to digest proteins & starch
liverproduces bile
- stored in gall bladderbreak up fats
mouthbreak up foodmoisten food digest starchkill germs
Large intestines (colon)Function
re-absorb wateruse ~9 liters of water every
day in digestive juices> 90% of water reabsorbed
not enough water absorbed back to body odiarrhea
too much water absorbed back to bodyoConstipation
No nutrients are absorbed here
Rectum Last section of colon (large intestines)eliminate fecesundigested materials
extracellular wasteomainly cellulose from plantsoroughage or fiber
saltsmasses of bacteria
stomachkills germs break up fooddigest proteinsstore food
small intestinesbreakdown food
- proteins- starch- fats
absorb nutrients
pancreasproduces enzymes to digest proteins & carbs
liverproduces bile
- stored in gall bladderbreak up fats
large intestinesabsorb water
mouthbreak up foodmoisten food digest starchkill germs
AppendixVestigial organVestigial organ
Problems with the Digestive System
Ulcers A sore or hole inside either the stomach or small intestine.Caused by the stomach lining being digested or “eaten away”
by enzymes and stomach acids.The mucus layer helps prevent this but this can be damaged by
a bacterial infection called Helicobacter pylori thus resulting in an ulcer.
HeartburnCaused by stomach acids moving into the esophagus.This causes a burning feeling.The esophagus is lies behind the heart so it feels like the heart
is burning.Eating too much at once or too much acidic or rich foods can
cause acid to back up.
Digestive System - GlandsSalivary glands – secrete amylase for preliminary
starch digestion.Glands in the stomach lining – secrete mucus and
gastric juice (contains pepsin and hydrochloric acid) for initial protein digestion.
Liver – secretes bile to emulsify fats.Pancreas – secretes sodium bicarbonate to neutralize
stomach acids and enzymes to act on proteins (proteases), carbohydrates (amylase) and fats (lipases).
Walls of the small intestine – secrete juices that complete the digestion of carbohydrates, fats and proteins.
Lab ActivityStations
Activity 1: How long is the Digestive System?
Materials: 4 different balls of yarn
Description: Students are to cut pieces of different coloured yarn for each of the following measurements. Then they are to tie them together to show how long each piece of the digestive system is in reference to each other.
Esophagus 25 cmStomach 20 cmSmall Intestine 700 cmLarge Intestine 150 cm
Activity 2: DigestionMaterials:
Sugar CubesGranulated SugarClear cups filled with water
Description:Place a sugar cube in a cup of
water. Place about a teaspoon full of granulated sugar in the other cup of water. Observe.
Activity 3: Carbohydrate Digestion
Materials: Unsalted crackers
Description: Students chew 2 unsalted crackers for two minutes without swallowing.
Activity 4: Hands on Digestion
Materials: Meatball size of hamburgerOne plastic bag1 M HCLDigestive juice A (pepsin, trypsin, and water)Digestive juice B (bile salts, pancreatin
enzyme and water)
Description: Place hamburger, 3 eyedroppers full of HCL, 1 tbsp of Digestive juice A and 2 Tbsp of Digestive juice B in the plastic bag. Knead with your hands for 10 minutes (stimulates the stomach) and it will have been reduced to liquid with a definite odor.
Activity 5: How do villi aid the Small Intestine in absorption?
Materials:Paper towels4 cups of equal amounts of waterGraduated cylinder
Description: Compare how 1,2,3, then 4 paper towels absorb. Dip each paper towel into a cup of water (same amount of water in each cup). Record the volume of water left in each cup (using the graduated cylinder).
Activity 6: The Digestive System Story
Description: Assign each student as a part of the digestive system and one student as food. As the food student moves past each digestive system part, the student labelled as that part must describe what they are doing to the food.
Questions:What system in your body is the same length
as the completed piece of yarn?In Activity 2, what can you conclude must be
done to food before digestion occurs?What physical and chemical changes occurred
to the soda crackers?What caused the physical and chemical
changes to the crackers?Did you notice a taste change in the crackers?How is physical digestion simulated in Activity
4?
Questions continuedWhat evidence was there that chemical
digestion occurred in the hamburger?Which paper towel had the largest surface
area?What relationship can you see between the
largest surface area and how villi aid in absorption?
Using Activity 6, create a diagram to demonstrate the passing of food through the digestive system.