Digestion and Nutrition

1
Digestion and Nutrition

• Comparing digestive tracts

2
Heterotrophs Eat Preformed Foods

• The energy needed for routine metabolism
• The components to repair tissue or grow
• Carbohydrates - Amino acids
• Proteins - Nucleic acids
• Lipids
• Digestive system is an adaptation to a particular
  food source.

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A Gut is Complete or Incomplete

• Planarian/ Tapeworm
• Incomplete gut
• Contains only mouth, a pharynx intestine.
• Gastrovascular cavity is a sac with digestive
  enzymes.
• No specialized cells

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Earthworm Complete Gut

• System is a tube with a mouth and an anus.
• Different regions of tube have specialized
  functions.
• Digestion in intestines.
• Surface area increased by intestinal folds.
• Undigested passed out anus.

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Feeding can be continuous

• Called a filter feeder
• Constantly moving water carries in food.
• Cilia move food to mouth and stomach.
• Enzymes aid amoeboid cells in tract to complete
  digestion.

6
Feeding can be Discontinuous

• Mouth with jaws, teeth, and tongue.
• Esophagus leads to stomach.
• Requires storage area in gut due to occasional
  large consumption of food.

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Dentition Digestive Tract are Suitable to Diet

• Herbivores have teeth for crushing and grinding
  and long specialized digestive tract.
• Carnivores have pointed incisors and canine teeth
  to tear off pieces small enough to swallow have
  shorter digestive tract.
• Omnivores, including humans, have teeth for
  vegetable diet and a meat diet.
• Incisors (shearing) - Canines (tearing)
• Premolars and molars (grinding)

8
Humans Have a Complete Tract

• Functions of human digestion
• Ingestion receiving food and drink.
• Digestion mechanical chemical processes to
  break down food.
• Absorption nutrients from small intestine
  diffuse into cardiovascular lymphatic systems.
• Elimination indigestible waste removed

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Each part of digestive system has a specific
function
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Mouth Receives Food

• Mechanical digestion using teeth and tongue.
• Chemical digestion
• Three pairs of salivary glands
• Secrete salivary amylase, an enzyme to digest
  starch
• Taste buds primarily on tongue, but also surface
  of mouth and pharynx.
• Food chewed and mixed with saliva.
• Tongue pushes food back to pharynx.

11
Esophagus Conducts Food

• Esophagus and trachea (respiratory) joined in
  pharynx and then separate.
• Epiglottis covers opening to trachea.
• Muscles move bolus (food) through pharynx into
  esophagus.
• Esophagus is muscular tube that moves food to
  stomach by peristalsis.
• Peristalsis a series of contracting and
  relaxing muscle movements along a tube.

12
Stomach Stores Food for discontinuous feeding

• Walls contract to mix food with secreted gastric
  juices from gastric glands
• HCl lowers pH to 2 to stop amylase and promote
  pepsin enzyme.
• Pepsin produces peptides
• Mucous secretions for protection of stomach

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Structure of stomach

• Muscular outer wall.
• Epithelial walls dotted with gastric glands
• Gastric glands have 3 cell types
• Mucous cells protect stomach lining
• Chief cells that secrete pepsinogen
• Parietal cells that secrete HCl.
• Pyloric sphincter controls entry of chyme to
  duodenum.

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Small Intestine Absorbs Nutrients

• 4.5 meter muscular tube
• 3 sections
• Duodenum 25cm
• Receives chyme
• Digestive enzymes bi-
• Carbonate from pancreas
• Bile from liver gallbladder.
• 2. Jejunum
• 3. Ileum

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Small intestine specialized for absorption of
nutrients

• Surface of mucous membrane lining covered by
  ridges called VILLI.
• Microvilli are plasma membrane extensions of the
  villi.
• Increase surface area for absorption.

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Inside a Villi

• Contains blood vessels
• Sugar, amino acids, water into blood.
• Contains lymphatic vessel called lacteal.
• Lipids into lymph.
• Absorption involves ACTIVE TRANSPORT.

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Control of Digestive Juices

• Secretin produced in duodenal wall stimulates
  pancreas to secrete bicarbonate.
• Cholecystokinin (CCK) produced by duodenal wall
  to receive pancreatic juices bile
• Gastric Inhibitory Peptide produced by duodenal
  wall to stop action of gastrin.
• Gastrin produced by gastric glands increases
  mixing and secretion of enzymes.

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Two Accessory Organs
Pancreas
Liver
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Pancreatic Secretions

• Secretes pancreatic juice containing digestive
  enzymes and buffers into the duodenum by way of
  ducts (Exocrine).
• Secretes glucogon and the hormone, insulin, into
  the bloodstream (Endocrine).

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Liver is a Glandular Organ

• Large small intestines form hepatic portal vein
  leading to the liver.
• Numerous functions
• Detoxifies the plasma.
• Makes plasma protein.
• Destroys old blood cells to make bile.
• Produces bile to emulsify lipids.
• Stores glucose as glycogen breaks down for
  blood.
• Produces urea from amino groups ammonia.

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Large intestine absorbs water

• Follows small intestine
• Has four parts
• Cecum with appendix
• Colon
• Rectum last 20 cm.
• Anal canal ends at anus
• Feces is 75 water 25 solid matter

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Nutrition Affects Health

• Balanced diet includes all essential nutrients
  carbohydrates, lipids, proteins, vitamins and
  minerals.
• Vitamins are required for metabolic processes.
• Minerals are required for structure and function
  of specialized cells.
• Example hemoglobin requires Iron.