1. Digestion & Absorption
The body’s breakdown and uptake of nutrients

2. We are what we eat! Biochemically, this is true
However, most of us don’t look like this guy
To build the body out of the materials in food, we must first break foods down

3. From Atoms to Organisms

4. Digestive System Terminology
Digestion: process of breaking food into components small enough to be absorbed by the body
Absorption: process of taking substances into the interior of the body
Gastrointestinal tract: hollow tube consisting of the mouth, pharynx, esophagus, stomach, small intestine, large intestine and anus
Transit time: amount of time it takes food to pass the length of the GI tract
Feces: body waste, including unabsorbed food residue, bacteria and dead cells

5. The Digestive System

6. Anatomy of the Digestive Tract
Gastrointestinal (GI) tract
Flexible and muscular
Path
Mouth → esophagus → stomach → small intestine → large intestine → rectum → anus
Lumen
Continuous
Considered outside the body

7. Digestive Secretions
Digestion inside the GI tract is assisted by digestive secretions
Mucus: viscous material produced by goblet cells
Moistens, lubricates and protects the GI tract
Enzymes: protein molecules that speed up chemical reactions
Enzymes are catalysts
In digestion, speed up breakdown of nutrients

8. Turning Digestion On Cephalic phase Gastric and intestinal phases
Sensory stimuli
Thoughts of food
Tasting and chewing
Gastric and intestinal phases
Presence of food in digestive organs sends signals to brain and the organs themselves
Both phases are mediated by nerves and hormones

9. Control of Digestion

10. The Mouth Process of digestion begins here 4 taste sensations
Mastication
Saliva
Enzymes
4 taste sensations
#5: savory or umami
Aroma, texture, and temperature
Movement to pharynx: swallowing reflex
Bolus
The Mouth

11. Pharynx and Epiglottis

12. Heimlich Maneuver

13. Passage Through the Esophagus

14. The Esophagus and Stomach
Muscular tube; passes through diaphragm
Two sphincters
Upper esophageal sphincter
Lower esophageal sphincter
Stomach
Storage, mixing, and digestion
Chyme
Pyloric sphincter

15. Large intestine (colon)
Small intestine
Three segments
Duodenum, jejunum, ileum
Common bile duct
Pancreas and gall bladder
Absorption!
Large intestine (colon)
Ileocecal valve
Absorption of water, some vitamins, & minerals
Rectum and anus

16. Structure of the Gut Wall

17. Absorption in the Small Intestine

18. Muscular Action of Digestion
Peristalsis
Circular and longitudinal muscles working together
Stomach action
Circular, longitudinal, and diagonal muscles
Pyloric sphincter: times the release of chyme
Sphincter contractions
Periodically open and close
Control pace of GI tract contents

22. Secretions of Digestion
Five organs
Salivary glands, stomach, pancreas, liver, small intestine
Secretions
Water
Enzymes
Protein facilitator of chemical reactions
Ex: Lipase, protease, carbohydrase (amylase)
Bile: emulsifies fat

23. Enzymes and Digestion

24. Secretions of Digestion
Saliva
Moistens food - what does this accomplish?
Protective role
Carbohydrate digestion
Gastric juice
Protein digestion
Mucus
Low pH (very acidic)

25. The pH Scale

26. Secretions of Digestion
Pancreatic juice
Released via ducts into duodenum
Enzymes act on all three energy-yielding nutrients
Contains sodium bicarbonate: neutralizes acidic chyme
Bile
Produced in liver
Stored in gallbladder

27. Signals and Secretions

29. Large Intestine
No further digestion occurs here, except bacterial breakdown of digestive residues
Slow transit
Water absorption
Some vitamin and mineral absorption
Undigested residues
Exercise intestinal muscles
Fibers: retention of water
Feces stored in rectum prior to defecation
2 sphincters: internal and external
Intestinal bacteria
Synthesize some B-vitamins and vitamin K
From fiber: short-chain fatty acids

30. Nutrient Breakdown in Digestion

31. Nutrient Absorption
Most absorption happens in the small intestine

32. Nutrient Transport Pathways
Bloodstream
Water-soluble nutrients, smaller products of fat digestion
Sugars, amino acids, small lipid molecules, water-soluble vitamins
Liver: the gatekeeper
Stores some nutrients; allows others to flow to rest of body
Lymphatic system
Larger fats and fat-soluble vitamins
Form large particles called chylomicrons
Lymphatic capillaries in small intestine are called lacteals

33. Absorption in Villi of Small Intestine

34. Absorptive Routes

35. The Vascular Route Vascular system Closed system of vessels Blood
Heart is the pump
Blood
Delivers oxygen and nutrients
Removes carbon dioxide and wastes
Blood flow
Special routing for digestive system
Hepatic portal vein

36. The Lymphatic Route Lymphatic system: one-way route No pump
Returns fluid in tissues to bloodstream
Houses immune cells
Chylomicrons: too large to enter capillaries
Taken up by lacteals
Bypass liver at first and enter bloodstream directly via thoracic duct

37. Health of the GI Tract: Gut Flora
Gastrointestinal bacteria – flora
species – about 10x the number of cells in the body! – totaling about 3 pounds
Most are beneficial
Probiotic bacteria: microorganisms that confer a benefit on host when consumed in adequate amount
Prebiotics: indigestible carbohydrates in some foods (fruits, vegetables, and whole grains) that support growth of healthy bacteria
Dysbiosis: imbalance of gut bacteria
What are some probiotic-containing foods?

38. Direct Immune Function of Probiotic Bacteria

39. Benefits of Healthy Gut Flora
Break down indigestible substances (fibers, complex proteins)
Improve digestion and absorption
Support health of intestinal tissues – growth, development, and nourishment of cells
Produce vitamin K and some B-vitamins
Improve lactose digestion in lactose-intolerant people
Prevent diarrhea related to antibiotic use; shorten duration of diarrhea from illness
Promote mucin production
Enhance immune function
Positively associated with healthy body weight
Evidence indicates that they may also alleviate constipation, reduce allergy symptoms, and reduce risk of colon cancer