CHAPTER 21Nutrition and DigestionNutrition->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 stages1. Ingestion: taking in food2. 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 Digestion~ a 2 part process that changes food into a form useable by the body cells

1. Mechanical digestion – physical breakdown of large pieces of food into smaller ones

2. Chemical digestion – hydrolysis – the splitting of large insoluble molecules in small, soluble molecules with the use of water and enzymes ( in other words; breaking complex molecules into simple ones)

The process of chemical digestion ( hydrolysis) is regulated by enzymes

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

Examples of chemical Digestion:

1. Carbohydrates+ water -> simple sugars (glucose for instance)

2. Proteins+ water -> amino acids 3. Lipids+ water -> 3 fatty acids +gylcerol

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

Mouth Functions

mechanical digestion teeth

break up foodchemical digestion (saliva)

amylase enzyme digests starch

mucus protects soft lining of digestive system lubricates food for easier swallowing

buffers neutralizes acid to prevent tooth decay

anti-bacterial chemicals kill bacteria that enter mouth with food

All thatin spit!

HUMAN DIGESTIVE SYSTEM 1. Mouth: (oral cavity)

ingests food 2. Teeth: function in

mechanical breakdown of food, increases surface area of food for enzyme action

3.Tongue: acts as a plunger to push food back into the throat (pharynx) taste buds are located on the surface of the tongue

mouthbreak up fooddigest starchkill germsmoisten food

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

pharynx into the esophagusFood is now in the form of a bolus

Swallowing (& not choking)

Epiglottis flap of cartilage closes trachea (windpipe) when swallowing food travels down esophagus

Peristalsis involuntary muscle contractions to move food along

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

stomachkills germs break up fooddigest proteinsstore food

sphincter

sphincter

mouthbreak up fooddigest starchkill germsmoisten food

Used to think ulcers were caused by stress

tried to control with antacids

Now know ulcers caused by bacterial infection of stomach

H. pylori bacterianow cure with

antibiotics

Ulcers

inflammation of stomach

inflammation of esophagus

Colonized by H. pylori

Free of H. pylori

white blood cells

cytokines

inflammatory proteins(CagA)

cell damaging proteins(VacA)

helper T cells

neutrophil cells

H. pylori

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

Liver & Gall Bladder ~accessory organs

Produces bilebreaks up fatsgallbladder only stores bile

that’s why you can have your gall bladder removed

bile contains colors from old red blood cells collected in liver =iron in RBC rusts & makes feces brown

pancreasproduces enzymes to digest proteins & starch

stomachkills germs break up fooddigest proteinsstore food

mouthbreak up fooddigest starchkill germsmoisten food

liverproduces bile

- stored in gall bladderbreak up fats

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

small intestinesbreakdown food

- proteins- starch- fats

absorb nutrients

stomachkills germs break up fooddigest proteinsstore food

mouthbreak up fooddigest starchkill germsmoisten food

pancreasproduces enzymes to digest proteins & starch

liverproduces bile

- stored in gall bladderbreak up fats

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 of feces

Largeintestine(colon)

Smallintestine

RectumAnus

Endof smallintestine

Nutrientflow

Cecum

You’ve got company! Living in the large intestine is a

community of helpful bacteriaEscherichia coli: E. coli

digest cellulose digests fruits & vegetables

produce vitamins vitamin K & B vitamins

BUT generate gases by-product of bacterial metabolism methane, hydrogen sulfide STINKY!

PEE-YOO!

stomachkills germs break up fooddigest proteinsstore food

mouthbreak up fooddigest starchkill germsmoisten food

small intestinesbreakdown food

- proteins- starch- fats

absorb nutrients

pancreasproduces enzymes to digest proteins & carbs

liverproduces bile

- stored in gall bladderbreak up fats

large intestinesabsorb water

Rectum Last section of large intestines

eliminate feces through anuswhat’s left over?

undigested materials mainly cellulose from plants called roughage or fiber keeps everything moving & cleans out

intestines masses of bacteria

So don’t forget to wash your hands!

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