1. Digestion, Absorption, and Transport
Chapter 3

2. Digestion Breaking down foods into nutrients Challenges of digestion
Prepare for absorption
Challenges of digestion
Tasks of the mouth
Diaphragm
Steady movement
Lubrication of food
Digestive enzyme functions

4. Anatomy of the Digestive Tract
Gastrointestinal (GI) tract
Flexible and muscular
Path
Mouth → esophagus → stomach → small intestine → large intestine → rectum → anus
Lumen
Inner space within GI tract, continuous from one end to the other

5. Anatomy of the Digestive Tract
Mouth
**Process of digestion begins**
Mastication-process of chewing
Fluids help dissolve food so tongue can taste it
Four basic taste sensations (sweet, sour, bitter, & salty)
Aroma, texture, and temperature
Pharynx- passed through when food is swallowed
Short tube that’s shared by both digestive system and respiratory system
Epiglottis closes to bypass entrance to lungs to prevent choking
Bolus
After a mouthful of food has been chewed and swallowed

6. Anatomy of the Digestive Tract
Esophagus
Two sphincters muscles at each end
Upper esophageal sphincter-opens during a swallow
Bolus slides down the esophagus which passes through a hole in diaphragm to stomach
Lower esophageal sphincter-at entrance to stomach closes behind the bolus so that it proceeds forward and doesn’t slip back up into esophagus
Stomach
Retains bolus in upper portion
Movement of bolus
Little by little food is transferred to lower portion, adds juices and grins it to a semi-liquid called Chyme
Pyloric sphincter
Stomach releases chyme through which opens into the small intestine (SI) then closes

7. Anatomy of the Digestive Tract
Small intestine-
Common bile duct-at beginning of SI chyme bypasses which is dripping fluids complements of
Pancreas and gall bladder
Chyme travels down SI thru three segments:
Duodenum, jejunum, and ileum (10feet of tubing coiled within abdomen)
Large intestine (colon)
remaining contents arrive at Ileocecal valve (beginning of LI); lower right side of ab
Withdrawal of water
Leaving semisolid waste held till time to defecate
Rectal muscles relax and two sphincters of anus open and allows passage of waste

8. Muscular Action of Digestion
Peristalsis
Circular and longitudinal muscles working together
Wavelike muscular contractions of the GI tract that pushes its contents along
Rate and intensity of contractions vary
Factors that may interfere with peristalsis
Stress, medicines, medical conditions
Stomach action
Circular, longitudinal, and diagonal muscles
Three sets of muscles work to force chyme downward from passing duodenum of SI
Timing the release of chyme
Chyme is churned and forced down, hits pyloric sphincter, and remains in stomach
Stomach releases gastric juices
Chyme is liquefied, no longer resembles food
Segmentation
Contraction of circular muscles in small intestine
Mix chyme
Promote contact with absorption cells

10. Secretions of Digestion
Breakdown of food into nutrients requires secretions from five different organs
Salivary glands, stomach, pancreas, liver, small intestine
Secretions enter GI tract at various points along the way, bringing abundance of
Water
Enzymes (Ch.6)
Protein facilitator of chemical reactions making, breaking apart, changing arrangement or exchanging parts of molecule
As a catalyst enzyme remains unchanged
Hydrolysis-a chemical rxn involving the addition of water to break down a molecule into smaller parts

11. Secretions of Digestion
Saliva
Moisten food for easy passage
Protective role
Teeth and lining of mouth, esophagus, and stomach from damage
Contains water, salts, mucus, and enzymes that initiate CHO digestion
In stomach, gastric glands secrete gastric juice
Mixture of water, enzymes, and hydrochloric acid (HCL)
Acts primarily in protein digestion
Heartburn seen with reflux
Prevents bacterial growth *& kills most bacteria
Mucus
To protect stomach from HCL
Thick, slippery, white substance that coats cells
pH units
Measurement determining strength of acid
Gastric pH = below 2

12. Secretions of Digestion
By time food leaves stomach, digestion of CHO, fat, pro has begun & action gains momentum in SI
There pancreas contributes digestive juices
The pancreatic juice
Released via ducts into duodenum
Enzymes act on all three energy nutrients
Sodium bicarbonate
Basic/alkaline (opposite of stomach acid)
Neutralizes acidic chyme
Bile flows into duodenum
Liver-continuously produces bile
Gallbladder-squirts bile as fat arrives in duodenum
Not an enzyme, emulsifier-brings fats into suspension in water so that enzymes can break down

13. Secretions of Digestion

14. The Final Stage
At this point, CHO, fat, pro have been digested and ready to be absorbed
Vitamin and mineral absorption
Undigested residues (some fibers)
Not absorbed & continue thru the digestive tract, carrying some minerals, bile acids, additives, and contaminates out of body.
Retention of water seen in fiber is responsible for consistency of stools
Colon
Intestinal bacteria
Ferment some fibers, producing water, gas, and small fragments of fat that provide E for cells of colon
Recyclable materials colon itself retrieves
Water and dissolved salts

15. Absorption Small intestine
Traps and absorbs majority of nutrient molecules
Ten feet long
Absorption techniques
Simple diffusion
Facilitated diffusion
Active transport

16. Absorption

17. Anatomy of the Absorptive System
Folds in SI contain Villi
Small fingerlike projections
Select and regulate nutrients absorbed
Microvilli-
Tiny, hair-like projections on each cell of every villus that can trap nutrient particles and transport them into cells
Crypts
Tubular glands that lie between the intestinal villi and secrete intestinal juices into the SI
Goblet cells
Cells of GI tract (and lungs) that secrete mucus

18. Preparing Nutrients for Transport
Nutrient molecule crossed cell of villus, enters bloodstream or lymphatic system
Bloodstream
Water-soluble nutrients and smaller products of fat digestion
Guided to the liver where fate and destination will be determined
Lymphatic system
Larger fats and fat-soluble vitamins are insoluble in water
Larger molecules cluster together with special proteins forming chylomicrons
Bypass liver at first bc chylomicrons cannot pass into capillaries

19. Delivers a nutrient Once it has entered the bloodstream
Circulatory System
Delivers a nutrient Once it has entered the bloodstream

20. The Vascular System Or blood circulatory, closed system of vessels
Blood flows continuously
Heart serving as a pump
Blood
Delivers oxygen and nutrients
Removes carbon dioxide and wastes
Blood flow
Special routing for digestive system
Liver

21. The Lymphatic System
One-way route for fluid from the tissue spaces to enter the blood
No pump; lymph circulates between the cells of the body and collects into tiny vessels
Lymph-clear, yellowish fluid similar to blood, except it contains no red blood cells or platelets; transport fat & fat-soluble vit to bloodstream
Fluid moves from one portion of body to another as muscles contract and create pressure here and there
Much of lymph collects in thoracic duct
Thoracic duct opens subclavian vein which allows entry into bloodstream
Nutrients in lymphatic vessels
Bypass liver at first

22. Health and Regulation of GI Tract
GI tract health depends on adequate nutrition
Gastrointestinal bacteria – flora
Most are not harmful, but actually beneficial
Factors influencing bacteria presence
Diet – probiotics (pro=for; bios=life): living microorganism found in foods and dietary supplements that when consumed in sufficient quantities are beneficial to health
GI health benefits include alleviate diarrhea, constipation, inflammatory bowel disease, ulcers, enhance immune function, etc
Digestion of fibers and complex proteins
Vitamin production

23. Health and Regulation of GI Tract
Homeostasis
Survival depends on body conditions staying about the same
If something causes conditions to change too much, body must “do something” to bring back to normal
Homeostatic regulation
Body’s regulation of digestion is example
2 intricate and sensitive systems coordinate all the digestive and absorptive processes:
Hormonal or endocrine system
Nervous system
As food travels through the GI tract, it either stimulates or inhibits digestive secretions by way of messages that are carried from one section of GI tract to another by hormones and nerve pathways

24. The Digestive System at Its Best
Sensitive and responsive to environment
Immunity against intestinal diseases
Defense against foreign invaders
Health of digestive system
Healthy supply of blood
Lifestyle factors
Sleep, physical activity, state of mind
Types of foods eaten
Balance, moderation, adequacy, and variety