CHAPTER 21Nutrition and Digestion

Nutrition->life process by which an organism obtains and utilizes food

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

Overview: Food processing occurs in four stages

1. Ingestion: taking in food

2. Digestion: mechanical and chemical breakdown of food so that it can be absorbed by the cells

3. Absorption: cells lining the digestive tract take up (absorb) small nutrient molecules

4. Elimination: undigested material passes out of the digestive tract

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

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

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)

The food and breathing passages both open into the pharynx The swallowing reflex moves food from the

pharynx into the esophagusAt 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

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

into the stomach

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-solvent2. mucus-lubrication3. pepsin- enzyme that begins chemical digestion of protein4. Hydrochloric acid ( HCl) - makes food acidic, (pH=2) activates pepsin

Food now in liquid form –chyme

NOT all digestion has occurred

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

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

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

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

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

Largeintestine(colon)

Smallintestine

Rectum

Anus

Endof smallintestine

Nutrientflow

Cecum

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

NUTRITION

Overview: A healthful diet satisfies three needs fuel for its activitiesraw materials for making the body’s own

moleculesessential nutrients that the body cannot make

Chemical energy powers the body

Once nutrients are inside cells, they can be oxidized by cellular metabolism to generate energyThis energy is in the form of ATP

Chemical energy powers the body

The energy a resting animal requires each day to stay alive is its basal metabolic rate (BMR)

Chemical energy powers the body

More energy is required for an active life Excess energy

is stored as glycogen or fat

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

Connection: Vegetarians must be sure to obtain all eight essential amino acids

The eight essential amino acids that adults require must be obtained from foodThey are easily

obtained from animal protein

They can also be obtained from the proper combination of plant foods

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

Diet can influence cardiovascular disease and cancer