CHAPTER 21 Nutrition and Digestion

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CHAPTER 21Nutrition and Digestion

• Nutrition-gtlife process by which an organism
  obtains and utilizes food

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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

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Overview Food processing occurs in four stages

1. Ingestion taking in food
2. 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

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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

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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

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Examples of chemical Digestion

• 1. Carbohydrates water -gt simple sugars (glucose
  for instance)
• 2. Proteins water -gt amino acids
• 3. Lipids water -gt 3 fatty acids gylcerol

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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

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Mouth

• Functions
• mechanical digestion
• teeth
• break up food
• chemical 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!
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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

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The food and breathing passages both open into
the pharynx

• The swallowing reflex moves food from the pharynx
  into the esophagus
• Food is now in the form of a bolus

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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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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,
  (pH2) activates pepsin
• Food now in liquid form chyme
• NOT all digestion has occurred

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

• Used to think ulcers were caused by stress
• tried to control with antacids
• Now know ulcers caused by bacterial infection of
  stomach
• H. pylori bacteria
• now cure 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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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

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Liver Gall Bladder accessory organs

• Produces bile
• breaks up 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 proteins
starch
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Enzymes from the walls of the small intestine
complete the digestion of many nutrients
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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

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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
pancreas ?produces enzymes to digest proteins
starch
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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)
Small intestine
Endof smallintestine
Rectum
Anus
Nutrientflow
Cecum
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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 gases
• by-product of bacterial metabolism
• methane, hydrogen sulfide
• STINKY!

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 proteins
carbs
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Rectum

• Last section of large intestines
• 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

So dont forget to wash your hands!
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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