Digestion

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Digestion

• Chapter 41 AP Biology

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Animals Are Heterotrophs

• They canNOT make organic compounds from inorganic
  compounds like plants can.
• They must INGEST organic compounds by eating food
  made of organic compounds.

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What are Essential Nutrients?

• Materials that must be obtained in their
  assembled form because the animal cannot assemble
  them from other raw materials.
• Of the 20 amino acids needed by humans, about
  half of them must be obtained in their
  assembled state. We cant make them using
  other components.
• essential fatty acids some of these are
  required to make phospholipids.
• Vitamins organic molecules required in very
  small amounts. 13 are essential.
• Minerals inorganic substances required in very
  small amounts.
• calcium, phosphorus, iron
• used as cofactors

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Feeding in Animals - What they eat

• Herbivore
• Carnivore
• Omnivore

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Feeding in Animals How they eat

• Suspension feeders also called filter feeders
  strain particles from water

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Feeding in Animals How they eat

• substrate/deposit feeders - live on/in their
  food supply

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Feeding in Animals How they eat

• fluid feeders suck fluids from others

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Feeding in Animals How they eat

• bulk feeders most animals

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Processes involved in Obtaining Nutrition

• Ingestion
• Digestion
• Absorption
• Elimination

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Process 1 - Ingestion

• Ingestion act of eating taking in food

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Process 2 - Digestion

• Digestion - breaking down food into molecules
  small enough to be absorbed.
• Large macromolecules must be broken down into
  smaller molecules that can be used.

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Process 2 Digestion

• Macromolecules (proteins, fats, carbos.) consumed
  in food are not DIRECTLY usable by an animal.
• too big to pass across cell membranes
• type of macromolecule in food may not be exactly
  what is needed by the animal consuming the food.

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Process 2 - Digestion

• Digestion cleaves macromolecules into their
  component MONOMERS which the animal can use to
  make its own molecules.
• Polysaccharides and disaccharides gt simple sugars
  
• fats gt glycerol and fatty acids
• proteins gt amino acids
• nucleic acids gt nucleotides

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Process 2 - Digestion

• Remember breaking of macromolecules is achieved
  by hydrolysis reactions

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Process 3 - Absorption

• the animals cells take up the small molecules
  (monomers) made during the digestion process.

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Process 4 - Elimination

• undigested material passes out of the body.

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Types of Digestion

• Intracellular digestion - digestion within a
  single cell
• Simplest digestive compartments are food
  vacuoles.
• food vacuoles cellular organelles in which
  hydrolytic enzymes break down food without
  digesting the cell itself.
• typically occurs after engulfing food by
  phagocytosis.
• food vacuoles fuse with lysosomes which contain
  the enzymes.
• Sponges use this method. (also protists, but
  protists are not animals)

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Intracellular Digestion
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Types of Digestion

• Extracellular digestion break down of food
  within a chamber (gut) outside of (but surrounded
  by) cells.
• 2 Types
• Incomplete (more simple/primitive)
• Complete (more complex/advanced)

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Types of Extracellular Digestion

• Incomplete digestive sac with single opening.
• Simple/primitive
• Mouth and gastrovascular cavity present
• No Anus
• both digestion and distribution of nutrients to
  the body
• advantage of any gut (digestive cavity) is it
  allows the animal to devour larger prey than can
  be taken into a single cell.
• Phylum Cnidaria (the Hydra, for example)
• Phylum platyhelminthes (the flatworms)

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Incomplete Digestive System Phylum Cnidaria
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Types of Digestion

• complete digestive system (alimentary canal)
• most animals
• tract between two openings mouth and anus
• assembly line digestion is possible
• mouth gt pharynxgt esophagusgt cropgt gizzardgt
  intestine gt anus

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Mammalian Digestion - Fundamentals

• Alimentary canal
• The tube from mouth to anus through which
  food passes
• Mouth
• Pharynx
• Esophagus
• Stomach
• small intestine
• large intestine
• anus

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Mammalian Digestion - Fundamentals

• accessory glands
• secrete digestive juices
• Include
• salivary glands
• Pancreas
• Liver
• gallbladder

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Mammalian Digestion - Fundamentals

• Movement
• peristalsis - rhythmic waves of muscle
  contraction (smooth muscle) push food along.
• Involuntary

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Mammalian Digestion - Fundamentals

• sphincters
• junctions between organs of the alimentary canal
  
• regulate the passage of material from one part
  of the tube to the next.

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The oral cavity

• Physical digestion
• chewing (mastication)
• heterodont dentition specialized teeth for
  various purposes
• Incisors - cutting
• Canines - tearing
• Premolars grinding
• Molars - grinding

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The Oral Cavity

• Chemical digestion - secretion of saliva
• buffers to lower acidity and prevent tooth decay
  
• antibacterial agents
• digestion of carbohydrates begins here
• amylase enzyme which hydrolzyes starch and
  glycogen
• products are smaller polysaccharides and a
  disaccharide (maltose)
• the bolus food ball made by mixing of food w/
  saliva by the tonuge.

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Oral Cavity
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The pharynx

• throat
• intersection b/t esophagus and windpipe
  (trachea)
• at swallowing, top of windpipe moves up
• opening (glottis) covered by the epiglottis (a
  cartilaginous flap)
• guides food to esophagus

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Pharynx
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The Esophagus

• swallowing passes food into esophagus (voluntary)
  
• peristalsis moves it down (involuntary)

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The Stomach

• located below the diaphragm
• Folds (rugae) and elasticity allow expansion to 2L

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The Stomach

• epithelium secretes gastric juice
• juice contains HCl
• pH of about 2
• acid kills bacteria and breaks apart matrix which
  holds cells together in tissues that are eaten.
• juice contains pepsin
• enzyme that begins break down of proteins
• breaks peptide bonds to make smaller polypeptides
• works best in strongly acid environment (unusual
  for enzymes)

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The Stomach

• Cell types in stomach all found in structures
  called gastric pits
• chief cells secrete pepsinogen (inactive form
  of pepsin)
• parietal cells secrete HCl
• mucus is also secreted to protect the stomach
  from being digested.

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The Stomach

• Food leaves the stomach in the form of an acidic
  substance called chyme
• The openings at either end of the stomach are
  controlled by muscles
• cardiac sphincter
• pyloric sphincter

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The Small Intestine

• longest section of alimentary canal (6 meters)
  (small due to diameter)

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The Small Intestine

• Most enyzme digestion of food macromolecules
  occurs here
• duodenum is the first foot or so of the small
  intestine
• acidic chyme from the stomach mixes with
  digestive juices from the pancreas, liver,
  gallbladder and glands of the intestinal wall.
• pancreas
• makes several enzymes
• secretes bicarbonate which neutralizes the acid
  in the chyme
• without neutralizing the acid, the digestive
  enzymes here would not work
• liver
• lots of functions
• bile production is big digestive function
• bile is stored in gallbladder
• bile has no enzymes but does break down fats
• bile contains pigments that are eliminated with
  the feces

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Duodenum
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Detail on enzymatic digestion in small intestine

• Carbohydrates
• digestion was begun in the mouth with salivary
  amylase
• pancreatic amylase continues breakdown of
  starch/glycogen
• enzyme maltase breaks down maltose (a
  disaccharide) into two molecules of glucose
• sucrase breaks down sucrose
• lactase breaks down lactose

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Detail on enzymatic digestion in small intestine

• proteins
• Small intestine completes work begun by pepsin in
  the stomach
• enzymes that break large polypeptide chains into
  smaller ones
• trypsin and chymotrypsin
• enzymes that break off one amino acid at a time
• carboxypeptidase breaks an amino acid at the
  carboxyl end
• amino peptidase breaks an amino acid at the
  amino end
• dipeptideases are attached to the intestinal
  lining and split small peptides
• enteropeptidase is an enzyme that activates
  certain enzymes secreted by the pancreas

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Detail on enzymatic digestion in small intestine

• Nucleic Acids
• nucleases break down nucleic acids into
  nucleotides
• others break down nucleotides into their
  components (sugars, phosphates, bases)

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Detail on enzymatic digestion in small intestine

• Fats
• fats hard to digest insoluble in water
• bile salts from gallbladder secreted into the
  duodenum emulsify fat. (make tiny droplets)
• lipases are enzymes that then break down the fat
  molecules

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The Small Intestine

• Digestion is completed in the duodenum of the
  small intestine
• absorption of most nutrients occurs in the
  jejunum (middle region) and ileum (end region) of
  the small intestine
• villi and microvilli are folds of the small
  intestine that increase surface area for
  absorption

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Jejunum and Ileum
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Small Intestine villi and microvilli
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Large Intestine (colon)

• Major function is to reabsorb water that has
  entered the digestive tract.
• Also to move feces to the end of the tract for
  elimination.
• Lots of bacteria live in large intestine
• lots of E.coli
• generate gases
• generate useful vitamins (K, many B vits.)

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Large Intestine (colon)
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Adaptations of Digestive Systems

• Dentition different teeth for different diets

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Adaptations of Digestive Systems

• Length of digestive tract
• long herbivore (plant matter hard to digest)
  shorter carnivore
• long tracts allow more time for digestion more
  surface area for absorption
• tadpole/frog classic example
• Tadpole long tract herbivore cellulose
  tough to digest
• Frog shorter tract carnivore
  meats/proteins easier to digest

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Adaptations of Digestive Systems

• Symbiosis many herbivores house microorganisms
  in a pouch (cecum) which aid in digestion.
• Ruminants cattle and sheep