Human Digestion

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Human Digestion

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

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Food processing 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

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Human Digestion

• Digestion 2 part process that changes food into
  a form useable by the body cells
• Mechanical digestion physical breakdown of
  large pieces of food into smaller ones
• 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

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Examples of chemical Digestion

• Carbohydrates water ? simple sugars ( e.g.
  glucose)
• Proteins water ? amino acids
• Lipids water ? 3 fatty acids glycerol

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HUMAN DIGESTIVE SYSTEM

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

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Mouth

• Functions
• mechanical digestion
• teeth
• break up food
• chemical digestion (saliva)
• amylase enzyme
• digests starch

All thatin spit!
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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!
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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

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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

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Swallowing ( not choking)

• Epiglottis flap of cartilage
• closes trachea (windpipe) when swallowing
• food travels down esophagus
• Peristalsis involuntary muscle contractions to
  move food along

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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
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mouth ?break up food ?digest starch ?kill
germs ?moisten food
Cardiac sphincter
Pyloric sphincter
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Ulcers
Free of H. pylori
Colonized by H. pylori

• 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
H. pylori
cell damaging proteins (VacA)
inflammatory proteins (CagA)
cytokines
helper T cells
?
?
neutrophil cells
white blood cells
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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!
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Small intestine

• Functions
• absorption
• nutrients move into body cells by
• diffusion
• active transport

This iswhere all thework is done!
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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
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mouth ?break up food ?digest starch ?kill
germs ?moisten food
stomach ?kills germs ?break up food ?digest
proteins ?store food
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Pancreas accessory organ

• Produces digestive enzymes
• digest proteins
• trypsin, chymotrypsin
• digest starch
• amylase
• digest lipids
• lipase
• Produces buffers
• buffers neutralize stomach acid

smallintestine
pancreas
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mouth ?break up food ?digest starch ?kill
germs ?moisten food
stomach ?kills germs ?break up food ?digest
proteins ?store food
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Liver Gall Bladder accessory organs

• Liver produces bile
• Bile breaks down fats
• gallbladder only stores bile
• thats 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
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mouth ?break up food ?digest starch ?kill
germs ?moisten food
stomach ?kills germs ?break up food ?digest
proteins ?store food
pancreas ?produces enzymes to digest all foods
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Large Intestines

• Functions to re-absorb water
• use 9 liters of water every day in digestive
  juices
• if dont reabsorb water would die of dehydration

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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

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Youve 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!
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mouth ?break up food ?digest starch ?kill
germs ?moisten food
stomach ?kills germs ?break up food ?digest
proteins ?store food
liver ?produces bile - stored in gall
bladder ?break up fats
small intestines ?breakdown food - proteins -
starch - fats ?absorb nutrients
pancreas ?produces enzymes to digest all foods
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Rectum

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

So dont forget to wash your hands!
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Vermiform Appendix

• Remnant from ancient grass-eating ruminant
  ancestor

Vestigial organ
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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