Digestive SystemDigestive System

AnnouncementsAnnouncements

Exams

Lab notes will be on reserve in library and on the web

Goals of the Digestive SystemGoals of the Digestive System

1. Extract nutrients from food

2. Transform nutrients into useful forms

Ex- oreo= glucose

3. Absorb nutrients and distribute them where they are needed

Functions of the Digestive Functions of the Digestive SystemSystem

Ingestion: intake of nutrients

Digestion: breakdown of large particles into smaller ones

Absorption: uptake of nutrient molecules

Defecation: elimination of undigested residues

Actions of the Digestive Actions of the Digestive SystemSystem

1. Motility- Breaks up food- Moves food through the GI tract (Peristalsis)- Mixes with digestive enzymes

2. Secretion- Release of enzymes and hormones for chemical

digestion and regulation

3. Membrane Transport- Absorption of nutrients from the tissues by the

blood and lymph for transport

Stages of DigestionStages of Digestion

Mechanical: physical breakdown of food

Chemical: digestive enzymes hydrolyze food particles to break larger molecules into smaller ones

Some nutrients are absorbed with out digestion– Vitamins, minerals, cholesterol, water

Anatomy of the Digestive Anatomy of the Digestive SystemSystem

Oral Cavity Pharynx Esophagus Stomach Pyloric Sphincter Small Intestine Large Intestine

Accessory OrgansAccessory Organs

Teeth Tongue Salivary Glands

Liver Gall Bladder Pancreas

Oral CavityOral CavityFunctions:

– A. Ingestion: cheeks lips and tongue mobilize food

– B. Digestion: Mechanical

– Mastication Chemical

– 3 salivary glands

– Digests some starches and fat

PharynxPharynx

Motility: pharyngeal constrictors force food down during swallowing

EsophagusEsophagus

Straight muscular tube about 1 foot long

Motility: muscular contraction moves food towards stomach

www.mywebmd.ca.com

Heartburn and the EsophagusHeartburn and the EsophagusHeartburn, “ acid reflux”, is caused by acid and food

going from the stomach into the esophagus

The diaphragm normally prevents acid reflux, in conjunction with the lower esophageal sphincter.

When this fails, the burning sensation felt is known as “heartburn”

May be linked to a rare type of cancer, adenocarcinoma

StomachStomach Muscular sac on the left

side of the peritoneal cavity

Functions: – Food storage – Mechanical digestion– Chemical digestion

Rugae in the StomachRugae in the Stomach

Rugae- folds in the stomach lining that allow it to expand with more food

How do we vomit?

http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion

Pyloric SphincterPyloric Sphincter

Ring of smooth muscle

Regulates the passage of material from the stomach into the duodenum

http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion

Digestion in the StomachDigestion in the Stomach

Mechanical Digestion:– Muscular contraction

Chemical Digestion:– Secretes digestive enzymes and HCl

Small IntestineSmall Intestine http://www.afns.ualberta.ca/bbo/1/ANATOMY/SI1.asp 2 meters long, 1 inch

in diameter, 5-6 meters in cadaver

Functions: – Chemical Digestion– Nutrient Absorption– Motility

Anatomy of the Small Anatomy of the Small IntestineIntestine

Duodenum (25 cm): 1. Receives stomach

contents, pancreatic juice and bile

2. Neutralizes stomach acid and pepsin

3. Pancreatic enzymes and bile take over chemical digestion

Fig 25.22

Anatomy of the Small Anatomy of the Small IntestineIntestine

Jejunum (2.5m)

Ileum (3.6 m)– Reabsorbs bile acids

Functions of the Small Functions of the Small IntestineIntestine

Motility: smooth muscle contract

Digestion: chemical enzymes received from the pancreas, liver and gall bladder

Nutrient reabsorption:microvilli increase surface area

Microvilli

Dynamic Human: MicrovilliDynamic Human: Microvilli

Large IntestineLarge Intestine

Functions– Motility

– Reabsorbtion of Water and Electrolytes

Symbiotic bacteria– Synthesis Vitamins B & K

Anatomy of the Large Anatomy of the Large IntestineIntestine

Transverse Colon: right to left

Ascending Colon: Descending Colon:

up the right side down the left side

Cecum: sac on Sigmoid Colon:

lower right side S-shaped

Anatomy of the Large Anatomy of the Large IntestineIntestine

Rectum: straight down Anal Canal: out the

body Appendix: hangs off

cecum– Important in Immunity

Enzymes Involved in Enzymes Involved in Chemical DigestionChemical Digestion

Saliva:– Amylase: breaks down starch– Lipase: breaks down fats when it enters the

stomach Low pH of the stomach activates the enzyme

Enzymes Involved in Enzymes Involved in Chemical DigestionChemical Digestion

• Stomach:• Digestive chemicals-

• HCL: activates enzymes, breaks up foods• Pepsin: digests proteins• Renin: digests milk

Pepsin FormationPepsin Formation

• Interactions between Cells• Chief Cells make pepsinogen• Parietal Cells make HCl• Pepsinogen is cleaved by HCl into Pepsin

Dynamic Human: Pepsin Dynamic Human: Pepsin FormationFormation

Enzymes Involved in Enzymes Involved in Chemical DigestionChemical Digestion

• Small Intestine• Two sources of

enzymes

• Liver and Gall bladder• Pancreas

Enzymes Involved in Enzymes Involved in Chemical Digestion in the Chemical Digestion in the

Small IntestineSmall Intestine• Liver secretes bile that is active in the small

intestine• Bile: aids in fat digestion and absorption

•Activates pancreatic enzymes

•Synthesized from cholesterol

•Bacteria in the small intestine use bilirubin to make your feces brown

• Gall bladder stores and concentrates bile

Gall StonesGall Stones

What is a gall stone?

How do they treat gall stones?

How is the gall bladder removed?

Enzymes Involved in Enzymes Involved in Chemical Digestion in the Chemical Digestion in the

Small IntestineSmall Intestine Pancreas: secretes pancreatic juice

1. Amylase: breaks down starch

2. Lipase: breaks down fats

3. Ribonuclease (RNAase): breaks down RNA

4. Deoxyribonuclease (DNAase): breaks down DNA

5. Zymogens: inactive enzymes that activate in the small intestine

Mechanism of AbsorptionMechanism of Absorption

Membrane Transport:– Nutrients pass through membrane surface– The greater the membrane surface area, the

greater the amount of nutrients that can be transported

Surface Area– Rugae– Microvilli

Final Destinations of Digestion Final Destinations of Digestion ProductsProducts

Starches bloodstream

Fats lymph vessels (lacteals)

Proteins bloodstream

Dynamic Human: Dynamic Human: VisualizationVisualization

Cat DissectionCat Dissection

Be able to locate and identify– Esophagus– Stomach– Small Intestine– Large Intestine

Ascending colon Transverse colon Descending colon

Also know accessory organs– Tongue– Teeth– Gall Bladder– Liver

ConclusionConclusion