Lecture

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Lecture 9 Animal Nutrition and Digestion
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Key Concepts

• Animals are heterotrophic!
• Nutritional needs what animals get from food
• Food processing
• The human digestive system

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Animals are always consumers

• Only photosynthesis can convert solar energy to
  usable chemical energy
• Plants store chemical energy
• Animals eat plants (or other animals)
• .of course this is somewhat simplified. but NO
  animals are autotrophic

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Critical Thinking

• Why do we eat??? Specifically, what do we get
  from food???

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Critical Thinking

• Why do we eat??? Specifically, what do we get
  from food???

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Why we eat energy

• Animals generate ATP by aerobic respiration
• Main substrate is carbohydrates
• Fats are also used
• Proteins are used as a last resort
• Digestion converts consumed polymers to the
  monomers used in respiration

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Remember bioenergetics

• Managing the energy budget is essential to
  maintaining animal function
• ATP powers basal metabolism, other activities
  maintains homeostasis etc
• Animals must eat to make ATP

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Why we eat carbon skeletons

• Animals need organic carbon scaffolds to build
  our own organic molecules such as???

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Why we eat carbon skeletons

• Animals need organic carbon scaffolds to build
  our own organic molecules such as
• These are the 4 main categories of macromolecules
  common to all forms of life
• Animals cant make organic molecules from CO2

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Why we eat essential nutrients

• Molecules that animals cannot make at all
• Do not have the right biosynthetic pathways
• Must be eaten in pre-assembled form
• Some common to all animals some specialized
• Essential amino acids
• Essential fatty acids
• Vitamins
• Minerals

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Essential Amino Acids

• Most animals use the same 20 amino acids to make
  what???

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Essential Amino Acids

• Most animals use the same 20 amino acids to make
• Most animals can only synthesize about half
• Remaining amino acids must be consumed
• All animal proteins are complete contain all
  the essential amino acids
• All plant proteins are incomplete missing some
  of the essential amino acids

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Human vegetarian diets must mix plant groups to
obtain all essential amino acids
Grains and legumes mixed provide all essential
amino acids cultural traditions prevent protein
deficiencies
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Essential Fatty Acids

• Some unsaturated fatty acids cannot be
  synthesized
• Most animals (especially humans!) get adequate
  essential fatty acids from their diet
• We use fatty acids for????

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Essential Fatty Acids

• Some unsaturated fatty acids cannot be
  synthesized
• Most animals (especially humans!) get adequate
  essential fatty acids from their diet
• We use fatty acids for

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Vitamins

• Organic molecules used in small quantities
• Water soluble vitamins usually function as
  coenzymes
• Fat soluble vitamins function in nutrient
  absorption, as antioxidants, etc..
• Deficiencies are rare with an adequate, balanced
  diet

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Critical Thinking

• Which category of vitamin is more likely to
  accumulate and become toxic water soluble or
  fat soluble??? Why???

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Critical Thinking

• Which category of vitamin is more likely to
  accumulate and become toxic water soluble or
  fat soluble??? Why???

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Study table in text for a general under-standing
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Minerals

• Inorganic elements
• Some required in small amounts some in larger
• Requirements vary by taxon
• Many different functions
• Some metabolic some structural
• Know top 8 minerals and their main functions

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Mineral Functions???

• Calcium
• Phosphorous
• Sulfur
• Potassium
• Chlorine
• Sodium
• Magnesium
• Iron

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Some Mineral Functions

• Calcium
• Phosphorous
• Sulfur
• Potassium
• Chlorine
• Sodium
• Magnesium
• Iron

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Food Processing

• Ingestion
• Digestion

• Absorption
• Elimination

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Evolution of Compartmentalization

• Food digestion must be contained
• Why???
• Earliest containment structures are food vacuoles
• Sponges digest entirely intra-cellularly
• Most animals digest at least partly outside the
  cells
• Simplest body plans have a digestive sac with one
  opening
• More complex animals have a digestive tube with
  an opening for ingestion and one for elimination

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Evolution of Compartmentalization

• Food digestion must be contained
• Earliest containment structures are food vacuoles
• Sponges digest entirely intra-cellularly
• Most animals digest at least partly outside the
  cells
• Simplest body plans have a digestive sac with one
  opening
• More complex animals have a digestive tube with
  an opening for ingestion and one for elimination

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Evolution of Compartmentalization

• Food digestion must be contained
• Earliest containment structures are food vacuoles
• Sponges digest entirely intra-cellularly
• Most animals digest at least partly outside the
  cells
• Simplest body plans have a digestive sac with one
  opening
• More complex animals have a digestive tube with
  an opening for ingestion and one for elimination

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Sponges digest food in vacuoles that fuse with
lysosomes containing hydrolytic enzymes
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Evolution of Compartmentalization

• Food digestion must be contained
• Earliest containment structures are food vacuoles
• Sponges digest entirely intra-cellularly
• Most animals digest at least partly outside the
  cells
• Simplest body plans have a digestive sac with one
  opening
• More complex animals have a digestive tube with
  an opening for ingestion and one for elimination

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Jellies and flatworms start digestion in
gastrovascular cavities finish in food vacuoles
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Jellies and flatworms start digestion in
gastrovascular cavities finish in food vacuoles
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Evolution of Compartmentalization

• Food digestion must be contained
• Avoids digestion of body cells and tissues
• Earliest containment structures are food vacuoles
• Sponges digest entirely intra-cellularly
• Most animals digest at least partly outside the
  cells
• Simplest body plans have a digestive sac with one
  opening
• More complex animals have a digestive tube with
  an opening for ingestion and one for elimination

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Evolution of Compartmentalization

• Food digestion must be contained
• Avoids digestion of body cells and tissues
• Earliest containment structures are food vacuoles
• Sponges digest entirely intra-cellularly
• Most animals digest at least partly outside the
  cells
• Simplest body plans have a digestive sac with one
  opening
• More complex animals have a digestive tube with
  an opening for ingestion and one for elimination

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Critical Thinking

• The 2-hole tube body plan processes food
  sequentially no mixing of incoming food and
  outgoing waste
• Can you think of another advantage for the 2-hole
  tube plan???

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Critical Thinking

• The 2-hole tube body plan processes food
  sequentially no mixing of incoming food and
  outgoing waste
• Can you think of another advantage for the 2-hole
  tube plan???

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Tubular system allows for specialization and
efficiency

• Specialization based on habitat and diet
• Both divergent and convergent patterns have
  emerged
• All mammals have a cecum
• Both earthworms and birds have developed crops

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The Human Digestive System

• Relatively straightforward adaptations to an
  omnivorous diet
• Tube running from mouth to anus with specialized
  regions for food processing, absorption, and
  elimination of wastes
• Accessory glands supply lubrication, digestive
  enzymes and other secretions

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Oral cavity, pharynx and esophagus allow for
chewing and swallowing food

• Teeth cut and grind
• Tongue mixes and pushes bolus to back
• Saliva lubricates food, protects the mouth
  lining, buffers pH, kills bacteria, and begins
  the digestion of carbohydrates

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Oral cavity, pharynx and esophagus allow for
chewing and swallowing food

• Epiglottis tips down to direct food from pharynx
  to esophagus (so you dont breathe your food)

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Oral cavity, pharynx and esophagus allow for
chewing and swallowing food

• Peristaltic contractions in esophagus push food
  to stomach
• Food does not fall by gravity remember our
  quadruped ancestors
• Sphincter (ring) muscles also control passage of
  food

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Stomach continues the action

• Stores food (very folded and stretchy)
• Muscle contractions mix food
• Lining secretes gastric juice
• Very acidic (pH 2) hydrochloric acid dissolves
  cell matrices and denatures proteins in swallowed
  food also kills many ingested bacteria
• Pepsin begins protein hydrolysis
• Stomach lining protected from self-digestion by
  thick mucus and secretion of inactive pepsin
  precursor
• Controls passage of food into small intestine

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Stomach continues the action

• Stores food (very folded and stretchy)
• Muscle contractions mix food
• Lining secretes gastric juice
• Very acidic (pH 2) hydrochloric acid dissolves
  cell matrices and denatures proteins in swallowed
  food also kills many ingested bacteria
• Pepsin begins protein hydrolysis
• Stomach lining protected from self-digestion by
  thick mucus and secretion of inactive pepsin
  precursor
• Controls passage of food into small intestine

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Ulcers..

• Stomach lining replaces itself by mitosis about
  every 3 days
• Lesions still sometimes occur
• Ulcer risk factors???

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Ulcers..

• Stomach lining replaces itself by mitosis about
  every 3 days
• Lesions still sometimes occur
• Ulcer risk factors

Ouch!!
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Other animals can get ulcers, too

• From a students extra credit ?
• Causes include stress, diet, genetic
  abnormalities, microbial infections, very finely
  ground grains, heredity, bile reflux that
  destroys stomach lining

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Stomach continues the action

• Stores food (very folded and stretchy)
• Muscle contractions mix food
• Lining secretes gastric juice
• Very acidic (pH 2) hydrochloric acid dissolves
  cell matrices and denatures proteins in swallowed
  food also kills many ingested bacteria
• Pepsin begins protein hydrolysis
• Stomach lining protected from self-digestion by
  thick mucus and secretion of inactive pepsin
  precursor
• Controls passage of food into small intestine

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The Small Intestine

• Completes digestion and absorbs monomers
• Some absorption occurs in other parts of the
  digestive tract, but most in the SI
• More than 6m long
• Multiple levels of folding increase SA
• Surface area about 600m2!!
• Most digestion occurs in the first 25cm of the
  small intestine
• Enzymatic hydrolysis
• Most absorption occurs in the latter 5.75m of the
  small intestine

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Four levels of folding function to increase
surface area tube, interior folds, villi,
microvilli
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Increased surface area, especially of transport
epithelia, is a hallmark of large, complex,
multi-dimensional animals

• Factoids from humans
• Lungs have 100 m2 of surface area (almost 1/2 as
  big as room)
• Small intestine has surface area of a tennis
  court
• 80 km of tubules in a single kidney
• 100,000 km of blood vessels almost 3X
  circumference of earth

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The Small Intestine

• Completes digestion and absorbs monomers
• Some absorption occurs in other parts of the
  digestive tract, but most in the SI
• More than 6m long
• Multiple levels of folding increase SA
• Surface area about 600m2!!
• Most digestion occurs in the first 25cm of the
  small intestine
• Enzymatic hydrolysis
• Most absorption occurs in the latter 5.75m of the
  small intestine

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Pancreas secretes enzymes and bicarbonate liver
secretes bile
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Digestive enzymes and substrates
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Most digestion in duodenum (1st 25cm)
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The Small Intestine

• Completes digestion and absorbs monomers
• Some absorption occurs in other parts of the
  digestive tract, but most in the SI
• More than 6m long
• Multiple levels of folding increase SA
• Surface area about 600m2!!
• Most digestion occurs in the first 25cm of the
  small intestine
• Enzymatic hydrolysis
• Most absorption occurs in the latter 5.75m of the
  small intestine

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Monomers cross into epithelial cells, then into
interstitial fluid, then into the lymph or
bloodstream

• Some transport is facilitated, some active
• Each villus includes lymph and blood vessels

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Fat Digestion

• Fats are hydrophobic
• Bile salts emulsify large fat droplets into
  smaller droplets ? more surface area
• Lipase digestion produces fatty acids and
  mono-glycerides
• These monomers form into micelles

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Fat Absorbtion

• Micelles are tiny enough to diffuse into
  epithelial cells
• Monomers are recombined into fats in the
  epithelial cells
• Fats mix with cholesterol and are coated with
  proteins
• Resulting globules are transported into the
  lymph, and eventually into the blood (at shoulder
  ducts)

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Intestinal blood vessels drain directly into the
hepatic portal vein

• Nutrients get sent straight to the liver for
  metabolic processing

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Intestinal blood vessels drain directly into the
hepatic portal vein

• From the liver, the blood goes straight to the
  heart for distribution throughout the body

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Critical Thinking

• Where will the levels of blood sugar and other
  nutrients vary the most???

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Critical Thinking

• Where will the levels of blood sugar and other
  nutrients vary the most???

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Celiac Disease
Brandon Mizroch, 2008

• Celiac disease is a genetic autoimmune disease
  where the immune system has an adverse reaction
  to gliadin (a type of gluten protein in wheat)
• If the intestinal villi come in contact with
  gliadin, they are modified by a malfunctioning
  enzyme and the immune system attacks the villi
• This causes inflammation and flattening of the
  villi and blocks absorption

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Celiac (cont.)-Symptoms and Complications

• Blocking absorption causes malnutrition and
  serious complications
• In infants- failure to thrive/grow
• In adults
• Osteoporosis
• Severe weight loss
• Cognitive impairment/ delusions/ hallucinations
  (starving brain neurons)
• Severe vitamin deficiency syndrome
• Megaloblastic anemia (large, dysfunctional RBCs)
• Skin ulcers and atopic dermatitis

Brandon Mizroch, 2008
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The large intestine, AKA the colon

• Connected to SI at T junction
• Dead-end of T is the cecum
• Appendix extends off cecum
• Cecum functions as fermentation chamber in many
  animals, especially herbivores
• Human cecum is small, relatively functionless
• Appendix contributes to immune function, but is
  dispensable
• Appendix may function to repopulate intestines
  with beneficial bacteria after intestinal
  infections

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The large intestine, AKA the colon

• Remainder of LI is 1.5m
• Main function is to absorb water
• 7l of fluid is secreted into intestinal lumen
• Additional water is consumed in diet
• SI and LI together absorb 90
• Inflammation of LI reduces water absorption ?
  diarrhea
• LI also houses both commensal and mutualistic
  bacteria
• Live on undigested or unabsorbed materials
• Produce important vitamins (K, Bs, folic acid,
  biotin)
• Some produce stinky gasses as a byproduct of
  metabolism

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The large intestine, AKA the colon

• Final section of LI is the rectum
• Feces are produced as water is absorbed from
  waste organic materials
• Waste includes LOTS of bacteria cellulose
• 40 of the dry weight of feces is bacteria
• Feces are stored in the rectum
• When the time comes, feces are eliminated
  through the anus
• Sphincter muscles control elimination
• One is voluntary, one involuntary
• Some, but not complete control over defecation

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Review Key Concepts

• Animals are heterotrophic!
• Nutritional needs
• Energy
• Carbon skeletons
• Essential nutrients
• Food processing
• The human digestive system