A Tour of the Digestive A Tour of the Digestive SystemSystem

Where is the food now? The duodenum

How broken down is it?◦Physical digestion: Teeth and stomach churning broke it into

pieces Bile broke the fats into smaller globs

◦Chemical digestion: Salivary amylase: starch maltose Pepsin in stomach: protein peptides Pancreatic amylase: starch maltose Trypsin from the pancreas: protein

peptides Lipase from the pancreas: fats glycerol

+ fatty acids

What still needs to be broken What still needs to be broken down?down?

◦FATS?fats glycerol + fatty acids

◦PROTEINS?protein peptides want AMINO ACIDS

◦CARBOHYDRATES?starch maltose want GLUCOSE

◦NUCLEIC ACIDS?DNA / RNA nucleotides P + sugar + base

Digestive Enzymes from the Digestive Enzymes from the Interstitial glandsInterstitial glands

Maltase

MaltoseGlucose

Peptidase

PeptideAmino Acids

Cells in Small Intestine make Cells in Small Intestine make enzymesenzymesInterstitial glands…

◦Peptidases break down proteins Amino acids

◦Maltase breaks down maltose Glucose Other disaccharides are also broken

down, e.g. lactase breaks down lactose◦Nucleosidases breaks down

nucleotides P, sugar, N base

Inside the small intestineInside the small intestineIncreased

surface area:◦Large folds◦Villi stick

out from the folds

◦Microvilli stick out from the villi

~600m2 (size of a baseball diamond)

The VilliThe Villi

Outer wall

Inner wall

Pathway for Food

VilliVilliLayer of cells

around villi (epithelium)

Lacteal in the centre◦lymphatic vessel

Blood capillaries surround the lacteal

Absorbing nutrientsAbsorbing nutrientsFats enter the lacteal

◦Absorbed by lymphatic system

Glycerol

Fatty Acid

Fatty Acid

Fatty Acid

Lipase

Absorbing nutrientsAbsorbing nutrientssugars and amino acids

enter the blood ◦Capillaries join hepatic portal vein to the liver

How long is “food” here?

Up to 4 hours

A close up look at villiA close up look at villi

A Tour of the Digestive A Tour of the Digestive SystemSystem

Large IntestineLarge IntestineColon

◦~1.5m long◦3 parts:

ascending transverse descending

Rectum◦Last 20 cm

Anus◦Sphincter at the end

Caecum • pouch at the start of the large intestine

Appendix • a vestigial organ

(no current function)

What does the large What does the large intestine do?intestine do?Reabsorption of waterAbsorption of some vitaminsAlso contains:

◦bile pigments◦heavy metals◦billions of E. coli bacteria break down some indigestible food produce some vitamins, amino

acids, and other growth factors

Indigestion?Indigestion?Disorders in the large Disorders in the large

intestine and symptomsintestine and symptoms

http://www.youtube.com/watch?v=1ZIK6Ua20JA&feature=channel_page

http://www.youtube.com/watch?v=0yLPtYH6xfE

Overall review of digestion:http://www.youtube.com/watch?v=QtDgQjOGPJM