CHAPTER 21 Nutrition 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 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

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 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

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-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

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 Large intestine (colon) Small intestine End of small intestine Rectum Anus Nutrient flow 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 activities raw materials for making the body’s own molecules essential 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 energy This 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 food They 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