1. CHAPTER 21 Nutrition and Digestion
Nutrition->life process by which an organism obtains and utilizes food

2. OBTAINING AND PROCESSING FOOD
Animals ingest their food in a variety of ways
Animal diets are highly varied
Herbivores are plant-eaters
Carnivores are meat-eaters
Omnivores eat both plants and other animals

3. Overview: Food processing occurs in four stages
Ingestion: taking in food
Digestion: mechanical and chemical breakdown of food so that it can be absorbed by the cells
Absorption: cells lining the digestive tract take up (absorb) small nutrient molecules
Elimination: undigested material passes out of the digestive tract

4. HUMAN DIGESTIVE SYSTEM
consists of
1. alimentary canal (GI gastrointestinal tract)
~ continuous one way food tube (mouth to anus)
2.accessory glands
~pancreas, liver, & gallbladder

5. HUMAN DIGESTIVE SYSTEM
When food is swallowed, it is moved through the alimentary canal by peristalsis
Peristalsis is rhythmic muscle contraction in the walls of the digestive tract
Ringlike sphincter muscles regulate the passage of food

6. Digestion begins in the oral cavity
The teeth break up food (mechanical digestion)
Saliva moistens it
Salivary enzymes begin the hydrolysis of starch (amylase) (chemical digestion)
The tongue pushes the chewed food into the pharynx (throat)

7. The food and breathing passages both open into the pharynx
The swallowing reflex moves food from the pharynx into the esophagus
At the same time, food is kept out of the trachea; epiglottis is a flap that prevents choking
Food is now in the form of a bolus

8. The esophagus squeezes food along to the stomach
Peristalsis in the esophagus moves food boluses into the stomach

9. The stomach mechanically churns food into liquid and further chemically digests some of the food by secreting gastric juice
The stomach mixes food with gastric juice:
1. water-solvent
2. mucus-lubrication
3. pepsin- enzyme that begins chemical digestion of protein
4. Hydrochloric acid ( HCl) - makes food acidic, (pH=2) activates pepsin
Food now in liquid form –chyme
NOT all digestion has occurred

10. Connection: Bacterial infections can cause ulcers
evidence suggests that a spiral-shaped prokaryote causes many ulcers
Helicobacter pylori growth erodes protective mucus and damages the stomach lining

11. The small intestine is the major organ of chemical digestion and nutrient absorption
Alkaline pancreatic juice neutralizes stomach acids
Its enzymes digest polysaccharides, proteins, nucleic acids, and fats
Bile emulsifies fat droplets for attack by pancreatic enzymes
It is made in the liver and stored in the gall bladder

12. Enzymes from the walls of the small intestine complete the digestion of many nutrients

13. Absorption
The lining of the small intestine is folded and covered with tiny, fingerlike villi
Villi increase the absorptive surface
Nutrients pass through the epithelium of the villi and into the blood
The blood flows to the liver
The liver can store nutrients and convert them to other substances the body can use
Center of villi contains lymph vessel called lacteals which absorb fatty acids

14. The large intestine reclaims water
Undigested material passes to the large intestine, or colon
Water is absorbed
Feces are produced
Absorption of vitamins produced by bacteria that live in LI
Storage and elimination of feces
rectum-last part of GI, feces eliminated through anus
Large intestine (colon)
Small
intestine
End of small intestine
Rectum
Anus
Nutrient flow
Cecum

15. Some Digestive Homeostasis Disorders
1. Constipation– person has uncomfortable or infrequent bowel movements results from sluggish peristalsis that allows excess water to be removed from feces (fecal matter hardens)- may result from insufficient fiber in diet
2. Diarrhea– opposite of constipation– associated with intestinal disturbances caused by infections or stress– prolonged diarrhea may result in severe dehydration
3. Gall stones– small hard particles made of cholesterol which form & collect in gall bladder- may block the bile duct and cause pain
4. acid reflux -backflow of stomach contents upward into esophagus
5. appendicitis- inflammation of appendix

16. NUTRITION Overview: A healthful diet satisfies three needs
fuel for its activities
raw materials for making the body’s own molecules
essential nutrients that the body cannot make

17. Chemical energy powers the body
Once nutrients are inside cells, they can be oxidized by cellular metabolism to generate energy
This energy is in the form of ATP

18. Chemical energy powers the body
The energy a resting animal requires each day to stay alive is its basal metabolic rate (BMR)

19. Chemical energy powers the body
More energy is required for an active life
Excess energy is stored as glycogen or fat

20. Connection: Body fat and fad diets
The human body tends to store excess fat molecules instead of using them for fuel
A balanced diet includes adequate amounts of all nutrients
Fad diets are often ineffective and can be harmful

21. Connection: Vegetarians must be sure to obtain all eight essential amino acids
The eight essential amino acids that adults require must be obtained from food
They are easily obtained from animal protein
They can also be obtained from the proper combination of plant foods

22. A healthful diet includes 13 vitamins
Most of these vitamins function as coenzymes
Essential minerals are required for many body functions
A sound diet supplies
enough raw materials to make all the macromolecules we need
the proper amounts of prefabricated essential nutrients
enough kilocalories to satisfy our energy needs

23. Diet can influence cardiovascular disease and cancer