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 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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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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Digestion begins in the oral cavity

• The teeth break up food (mechanical digestion)
• Saliva moistens it
• Salivary enzymes begin the hydrolysis of starch
  (amylase) (chemical digestion)
• The tongue pushes the chewed food into the
  pharynx (throat)

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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
• At the same time, food is kept out of the
  trachea epiglottis is a flap that prevents
  choking
• Food is now in the form of a bolus

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The esophagus squeezes food along to the stomach

• Peristalsis in the esophagus moves food boluses
  into the stomach

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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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Connection Bacterial infections can cause ulcers

• evidence suggests that a spiral-shaped prokaryote
  causes many ulcers
• Helicobacter pylori growth erodes protective
  mucus and damages the stomach lining

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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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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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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 and elimination of feces
• rectum-last part of GI, feces eliminated through
  anus

Largeintestine(colon)
Small intestine
Endof smallintestine
Rectum
Anus
Nutrientflow
Cecum
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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

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NUTRITION

• Overview A healthful diet satisfies three needs
• fuel for its activities
• raw materials for making the bodys own molecules
• essential nutrients that the body cannot make

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Chemical energy powers the body

• Once nutrients are inside cells, they can be
  oxidized by cellular metabolism to generate
  energy
• This energy is in the form of ATP

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Chemical energy powers the body

• The energy a resting animal requires each day to
  stay alive is its basal metabolic rate (BMR)

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Chemical energy powers the body

• More energy is required for an active life
• Excess energy is stored as glycogen or fat

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Connection Body fat and fad diets

• The human body tends to store excess fat
  molecules instead of using them for fuel
• A balanced diet includes adequate amounts of all
  nutrients
• Fad diets are often ineffective and can be
  harmful

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Connection Vegetarians must be sure to obtain
all eight essential amino acids

• The eight essential amino acids that adults
  require must be obtained from food
• They are easily obtained from animal protein
• They can also be obtained from the proper
  combination of plant foods

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A healthful diet

• includes 13 vitamins
• Most of these vitamins function as coenzymes
• Essential minerals are required for many body
  functions
• A sound diet supplies
• enough raw materials to make all the
  macromolecules we need
• the proper amounts of prefabricated essential
  nutrients
• enough kilocalories to satisfy our energy needs

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Diet can influence cardiovascular disease and
cancer