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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