Human Digestion

• This part of the life process of NUTRITION process by which an organism obtains and utilizes food

Food processing in four stages

1. Ingestion: taking in food2. Digestion: mechanical and chemical breakdown of

food so that it can be absorbed by the cells3. Absorption: cells lining the digestive tract take up

(absorb) small nutrient molecules4. Elimination: undigested material passes out of the

digestive tract

Human Digestion

Digestion ≡ 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 ones2.Chemical digestion – hydrolysis – the splitting of large insoluble molecules into 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

Examples of chemical Digestion

• Carbohydrates + water simple sugars ( e.g. glucose)

• Proteins + water amino acids• Lipids + water 3 fatty acids + glycerol

HUMAN DIGESTIVE SYSTEM

• Human digestive tract = GI (gastrointestinal) Consists of a one-way continuous tube (mouth to anus)

Mouth• Functions– mechanical digestion• teeth–break up food

– chemical digestion (saliva)• amylase enzyme–digests starch All that

in spit!

Mouth• 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

• Mouth: (oral cavity) ingests food

• Teeth: function in mechanical breakdown of food, increases surface area of food for enzyme action

• 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

HUMAN DIGESTIVE SYSTEM• Pharynx: food is pushed by tongue to back of throat, initiates

swallowing – food is now in the form of a bolus– Epiglottis: flap that prevents choking

• Esophagus: muscular tube that moves food from mouth to the stomach by process of peristalsis: – wave of muscular contractions that moves chewed food to

stomach

Swallowing (& not choking)

• Epiglottis ≡ flap of cartilage– closes trachea (windpipe) when

swallowing– food travels down esophagus

• Peristalsis ≡ involuntary muscle contractions to move food along

Stomach• Structure: muscular, expandable

bag• Functions–disinfect food•hydrochloric acid ≈pH 2–kills bacteria

–food storage•can stretch to fit ≈2L food

–Digestion: pepsin (enzyme) proteins A.A.

But the stomach is made out of protein!What stops the stomach from digesting itself?

mucus secreted by stomach cells protects stomach lining

stomachkills germs break up fooddigest proteinsstore food

Cardiacsphincter

Pyloricsphincter

mouthbreak up fooddigest starchkill germsmoisten food

Ulcers• Used to think all

ulcers were caused by stress–tried to treat

with antacids• Now know some

ulcers caused by bacterial infection of stomach–H. pylori bacteria–now treat with

antibiotics

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

Small intestine• Functions– digestion• digest carbohydrates–amylase from pancreas

• digest proteins–trypsin & chymotrypsin from

pancreas• digest lipids (fats)–bile from liver & lipase from

pancreas

This iswhere all thework is done!

Small intestine• Functions– absorption• nutrients move into body

cells by:–diffusion–active transport

This iswhere all thework is done!

Absorption in Small Intestines• Absorption through villi & microvilli– finger-like projections– increases surface area for absorption

SMALL INTESTINE6 meters long,but can stretchto cover a tennis court

small intestinesbreakdown food

- proteins- starch- fats

absorb nutrients

stomachkills germs break up fooddigest proteinsstore food

mouthbreak up fooddigest starchkill germsmoisten food

Pancreas: accessory organ• Produces digestive enzymes – digest proteins• trypsin, chymotrypsin

– digest starch• amylase

– digest lipids• lipase

• Produces buffers – buffers neutralize

stomach acidsmall

intestinepancreas

stomachkills germs break up fooddigest proteinsstore food

mouthbreak up fooddigest starchkill germsmoisten food

pancreasproduces enzymes to digest all foods

Liver & Gall Bladder: accessory organs

• Liver produces bile– Bile breaks down fats– gallbladder 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

bile contains colors from old red blood cells collected in liver =

iron in RBC rusts & makes feces brown

pancreasproduces enzymes to digest all foods

stomachkills germs break up fooddigest proteinsstore food

mouthbreak up fooddigest starchkill germsmoisten food

liverproduces bile

- stored in gall bladderbreak up fats

Large Intestines

• Functions to re-absorb water• use ≈ 9 liters of water every

day in digestive juices– if don’t reabsorb water

would die of dehydration

Large Intestines

• Function– 90% of water re-absorbed• not enough water re-

absorbed:–diarrhea–can be fatal!

• too much water re-absorbed:–constipation

• reabsorb by diffusion

You’ve got company!• Living in the large intestine is a community of helpful

bacteria– Escherichia coli: E. coli• digest cellulose–digests fruits & vegetables

• produce vitamins –vitamin K & B vitamins

• BUT generate gaseous (flatus) by-products of bacterial metabolism –Methane (CH4), hydrogen sulfide (H2S)

–STINKY! Everyone makes 1L to 2L daily

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 all foods

liverproduces bile

- stored in gall bladderbreak up fats

large intestinesabsorb water

Rectum

• Last section of large intestines– after the colon (s-shaped holding area)– eliminate feces through anus– what’s left over?• undigested materials– mainly cellulose from plants– called roughage or fiber – keeps everything moving & cleans out

intestines• masses of bacteria, mucus

So don’t forget to wash your hands!

Vermiform Appendix

Vestigial organVestigial organ

• Remnant from ancient grass-eating ruminant ancestor

Digestive Homeostasis Disorders• 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

• Diarrhea– opposite of constipation– associated with intestinal disturbances caused by infections or stress– prolonged diarrhea may result in severe dehydration

• Gall stones– small hard particles made of cholesterol which form & collect in gall bladder- may block the bile duct and cause pain

• Acid reflux -backflow of stomach contents upward into esophagus

• Appendicitis- inflammation of vermiform appendix