DigestionDigestionINGESTIONINGESTIONDIGESTIONDIGESTIONPERISTALSISPERISTALSISABSORPTIONABSORPTIONDEFECATIONDEFECATIONBio 391Bio 391

2.9 – 2.112.9 – 2.11

Answer: QUESTION #1

DIGESTION breakdown of large food molecules into smaller ones

Why is it necessary?

MECHANICAL• Physical change• Breaking food into smaller

parts by ripping, churning• Increases surface area• TEETH tear & crush• STOMACH churns• BILE separates• Gizzard grinds

CHEMICAL• Chemical change• Enzymes break bonds of food

molecules

• Enzymes are made and used by organs– Not always the same

• Each enzyme is specific to a type of macromolecule– Carb, fat or protein

Where does digestion occur?EXTRACELLULAR

• Alimentary canal / GI tract• Most animals, us too• More complex = 1 way• Carnivore vs. herbivores

– Venus fly trap– Bread mold

INTRACELLULAR

• Inside the cells• Plants – make own food,

process within same cell• Single-celled organisms and

simple animals

– Hydra

Why specialized? Why specialized?

Human Anatomy

1. Mouth• Physical digestion• Chemical digestion– Saliva, salivary glands– Starts carbohydrate digestion– Amylase• Starch complex smaller sugars (maltose)• Saliva’s pH at 6.0-7.4

– Short time in mouth lots left undigested

– Answer Q#2

2. Esophagus & Epiglottis

• Esophagus connects mouth to stomach– Peristalsis – wavelike

contrxns force food down– Mucus secreted

• Epiglottis– “trap door” prevents food

“going down the wrong way”

3. Stomach Q4, Q5• Physical digestion• Chemical digestion

– Presence of food triggers gastrin release• Hormone, controls juice prodxn

– Gastric juice• HCl + mucus + pepsinogen• pH 1.0 – 3.5• Pepsinogen pepsin once in acid

(inactive) (active)– Protein digestion begins– Proteins polypeptides

• Chyme• Mucus lining• Sphincters

4. Small Intestine Q3• All digestion completed, nutrients absorbed• S.I. secretions– Secretin – presence of acid stimulates SI cells to release hormone

to pancreas via blood stream• Stimulates pancreas to release NaHCO3

– Carbohydrases (ex: maltase)• Carbo digestion completed• Maltose glucose• Left over starch glucose

• Liver & Gallbladder– Adds bile to the mix

• Emulsifies fats

S. I. Digestion via pancreatic secretions• Pancreas adds pancreatic juice– Shifts pH from acidic to basic – WHY?– Protein digestion completed• Trypsinogen trypsin

(inactive) (active)– Polypeptides amino acids

– Fat digestion completed• Lipases

– Lipids fatty acid + glycerol

– Pancreatic amylase• Carbo’s (maltose) glucose

S.I. AbsorptionS.I. Absorption• Large surface area– Villi & Microvilli– Capillaries enter each

5. Large Intestine• Waste condensation– Water absorption– Feces

• Bacterial symbionts– Synthesize vitamins– Vitamins absorbed

• Also has villi• Diarrhea &

constipation• Undigested food leaves

through anus– Cellulose, fiber, etc.

DISORDERS• Heartburn stomach acid enters esophagus

because of weak cardiac sphincter• Peptic Ulcer Hole in stomach wall caused

by Helicobacter pylori. The pain is caused by the acid.

• Diarrhea Not enough water is absorbed• Constipation Too much water is absorbed• Diabetes Glucose cannot enter cells of

body very well, therefore glucose cannot get turned into energy!!

Diabetes• 6th killer in America (and rising)• Pancreas cannot produce insulin or the body

does not use it properly• Insulin is a hormone that decreases the

amount of sugar in the blood by helping it enter the cells of the body.– Glucose does not enter cells easily, insulin must

“act like a butler” and bind to a cell membrane protein to help it in.

SUMMARY QUESTIONS

• What are the 2 types of digestion?• Where does digestion begin?• Where does MOST digestion happen?• Where do nutrients enter the rest the of the

body? (i.e. leave the GI tract)

Where does Digestion occur?What Nutrient is Digested?

ORGAN TYPE OF DIGESTION NUTRIENT DIGESTED

MouthMechanical

Chemical

StomachMechanical

Chemical

Small Intestine Chemical

ENZYMES OF DIGESTION

ENZYME SITE OF ACTION SITE of PRODUCTION NUTRIENT DIGESTED

Amylase

Pepsin

Lipase

Amylase

Trypsin

Peptidase

Maltase

Sucrase

Lactase

OTHER SUBSTANCES INVOVLED IN DIGESTION

SUBSTANCE SITE OF ACTION ACTION

Saliva Moistens Food

MucusEsophagus, Stomach

Sm. & Lg. Intestines

Gastrin (H)

Hydrochloric Acid (HCl)

Helps breakdown food

Kills bacteria

Secretin (H)

Sodium bicarbonate

Bile

Bacteria