The Digestive System. Purpose of digestive system: –Converts food into small molecules that can be used by cells!! –Why do the food molecules need to

The Digestive System

• Purpose of digestive system:– Converts food into small molecules that can

be used by cells!!– Why do the food molecules need to be

small??

– Four phases:• Ingestiondigestion absorption elimination

• Ingestion: process of putting food into your mouth

• Digestion: process of breaking food down– Mechanical: physical breakdown of large

pieces; increases surface area– Chemical: enzymes are used to break food

into smaller molecules

• Absorption: small molecules absorbed by cells in small intestine

• Elimination: removal of undigestable materials (like cellulose)

Mechanical vs Chemical

• Mechanical: grinding, tearing, peristalsis (churning action)….increases surface area for enzyme action

• Chemical: enzymes work to make larger molecules into smaller molecules (ex: starch-->simple sugars)

Your mouth does both!

•http://www.hns.org.uk/bio/index.php?option=com_content&view=article&id=123&Itemid=176

http://www.hns.org.uk/bio/index.php?option=com_content&view=article&id=123&Itemid=176

• Mechanical digestion is accomplished by chewing– Your teeth cut, tear, grind, and crush food

– Your tongue moves the food around so the tongue can work on it

• Chemical digestion of mouth– Enzyme=amylase

– Amylase begins to break down long starches forming sugars

– Saliva also has lysozyme….an enzyme that protects us against bacteria

• When you swallow the epiglottis covers the windpipe so that you don’t choke!

Esophagus

• Tube connecting throat to stomach• Peristalsis: rhythmic contractions of smooth

muscles that move food through the digestive system

Stomach

• Large muscular sac• Gastric glands release pepsin and HCl• Chemical digestion:

– Proteins--> smaller polypeptide chains

Another gland produces ______mucus_____________– o This lubricates so food can pass easier and

protects the stomach wall– o If acids erode the stomach wall and create a

sore it is called a peptic ulcer– o Now scientists know peptic ulcers caused by

Helicobacter pylori

• Mechanical digestion: smooth muscle churns and mixes food

– Chyme: mixture with an oatmeal-like consistency

Small Intestine

• Most digestion and all absorption• First part of SI= duodenum

– Mixes with fluids from the pancreas, the liver and the lining of the SI

• Pancreas: produces enzymes that break down carbohydrates, proteins, lipids and nucleic acids

– Also produces sodium bicarbonate…to neutralize stomach acid

• Liver and Gallbladder..help in the digestion of fats!

• Bile: emulsifies fats

• Bile is made in the liver and stored

(released) in the gallbladder

Absorption also occurs in SI

• Structure adapted for this function!

• Villi: fingerlike projections– Microvilli:tiny projections covering villi

Large Intestine

• Absorbs water from undigested material

• Bacteria found here help to produce Vitamin K• Concentrated waste material: feces

• Too much water absorbed: constipation

• If not enough water is absorbed: diarrhea

The Digestive System. Purpose of digestive system: –Converts food into small molecules that can be used by cells!! –Why do the food molecules need to

food molecules

small molecules

hclchemical digestion

digestion of fats

smaller molecules ex

larger molecules

stomach acidliver

small intestine elimination

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The Digestive System. Purpose of digestive system: –Converts food into small molecules that can be used by cells!! –Why do the food molecules need to

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