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AP Biology Notes: Digestive System

Updated on February 14, 2016

Types of Feeders

Suspension Feeders: obtain food by getting particles to flow into organism via water.

ex: Sea anenomies, killer whales, shrimp (and most Crustaceans)

Fluid Feeders: suck nutrient rich fluid from a living host

ex: mosquitoes, ticks, leeches

Bulk feeders: Feeders that eat/binge a big meal at one time, to last them several days/weeks

ex: snakes

Substrate feeders: live in or on their food

ex: caterpillars (eat leaves), earthworms (dirt), parasites

Types of Systems

  1. Open: Where blood mixes with hemocoel (body cavities) and mixes with the body's interstitial/lymph fluid. It drains into the body cavities and tissues, typically through holes such as sinuses.
    ex: less complex animals: cnidarians (jellies and sea anenomies), arthropods (insects, grasshoppers), invertebrates
  2. Closed: Blood travels through vessels and doesn't mix with lymph fluid or body cavities. Found in more complex animals
    ex: vertebrates (mammalia, reptiles, amphibians), annelids (worms)
  3. Incomplete: Digestion and excretion take place through 1 hole, which acts as both the mouth and anus
    ex: Jellies & anenomies (cnidaria), Platyhelminthes (flatworms), invertebrates
  4. Complete: Digestion and excretion take place through 2 separate holes: the mouth, digestion, and anus, excretion
    ex: vertebrates (animals: arthropods, annelids (worms), mammals, mollusks (crustaceans, like crabs)

Organ systems


  1. Liver: filters and processes blood as it circulates through body.
    -Metabolizes nutrients, detoxifies drugs & alcohol
  2. Small intestine: where 90% of food's digestion and absorption occurs; breaks down your carbohydrates
  3. Stomach: where food, like lipids and proteins, are broken down by acidic acids and churning, so nutrients may be extracted from food.
    -Gastric juice: mixture of mucus, HCl, and enzymes to break down and digest food
    -Mucus: coats inner lining of stomach to prevent acid from digesting the stomach itself.
    -Parietal cells: Intrinsic factor (a glycoprotein binding to B12 and other vitamins so that the small intestine can absorb it), and hydrochloric acid (HCl) which kills pathogenic bacteria in food and helps digest proteins by denaturing them
    -Pepsinogen: precursor to the digestive enzyme pepsinogen: break proteins down to amino acids (their building blocks)
    -Gastric Lipase (enzyme that digests fats by breaking off their fatty acid chain (triglyceride)
    -G cells: release the hormone gastrin, which signals the stomach to stretch during meals, and to stimulate the glands and muscles for digestion to begin
    -Secretin: hormone produced by Duodenum that promotes the production of pancreatic juices and acid neutralizing bile for increased digestion efficiency, and to protect stomach from being ingested by its acids
  4. Gallbladder: breaks down lipids
  5. Anus: where solid waste is excreted
  6. Ureters: carry urine to bladder
  7. Mouth: where your teeth (break down food into particles) and salivary glands (which secrete carbohydrate breaking-down enzymes) reside; begins digestion.
  8. Large Intestine: Absorbs water from indigestible food matter and transport indigestible matter to anus
  9. Pancreas: a narrow, half-foot long gland that lies posterior and inferior to the stomach to the left of its abdominal cavity. Secretes digestive enzymes and neutralizing enzymes (so stomach doesn't digest itself)
    -Amylase: breaks down large polysaccharides (sugars) like starches and glycogen, so they can be absorbed
    -Lipase: lipid (fats) digesting enzyme that breaks down triglycerides into monoglycerides (basic building blocks)
    -Ribonuclease & Deoxyribonuclease: enzymes that break down nucleic acids

  10. Chyme: thick, acidic liquid to break down food for digestion
  11. Gallbladder: releases bile to help break fats.
  12. Kidneys: Filter blood to remove waste products and excess fluid from the body.
    -Nephrons: ~1 million of them reside in kidneys; filter blood to produce urine
  13. Duodenum: tube down to small intestine; where nutrient absorption occurs

Video Resource

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