DIGESTIVE SYSTEM

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DIGESTIVE SYSTEM

• The digestive system ingests, digests, and
  absorbs nutrients for use by all body cells.

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The Key Processes

• Digestion process of food break down
• enzymatic hydrolysis
• intracellular breakdown within cells (sponges)
• extracellular breakdown outside cells (most
  animals)
• alimentary canals (digestive tract)
• Absorption cells take up small molecules
• Elimination removal of undigested material

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The Mouth

• Receives food and begins digestion. Made up of
• Cheeks and Lips
• -contains muscles associated with chewing
• Tongue
• -handles food and contains taste buds
• Palate
• - closes the opening to the nasal cavity during
  swallowing
• Teeth
• - mechanically break food into smaller pieces,
  increasing the surface area exposed to digestive
  actions

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Salivary Glands

• Secrete saliva
• Moistens food
• Helps bind food particles
• Begins chemical digestions of carbohydrates
• Makes taste possible
• Helps cleanse the mouth
• Include serous cells that secrete digestive
  enzymes including amylase and mucus cells that
  secrete mucus.

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Pharynx and Esophagus

• Pharynx the passage way intersection for both
  the digestive and respiratory system.
• - involuntary reflex actions move food from
  pharynx to esophagus
• - includes epiglottis flap like structure at
  back of tongue near entrance to trachea
• Esophagus muscular tube that conducts food from
  the pharynx to the stomach.
• - circular muscle fibers at the distal end of the
  esophagus help prevent regurgitation of food from
  the stomach

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Stomach

• The stomach stores food and performs preliminary
  digestion (moves food into small intestine).
• Cells Mucous cells chief cells that secrete
  Pepsinogen and Zymogen Parietal cells which
  secrete HCl.
• Gastric Secretion
• gastric juice contains
• Pepsin a protein splitting enzyme that digests
  almost all types of protein
• Hydrochloric acid regulates the pH of stomach
  needed for the creation and function of pepsin
• Intrinsic factor aids in Vitamin B-12 absorption
• Mucus provides protective layer on inside
  stomach wall
• Regulation of Gastric Secretions
• - controlled by nerve impulses and the hormone
  gastrin

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Accessory Organs

• Include
• Pancreas secretes a digestive juice called
  pancreatic juice
• -Pancreatic Juice
• - pancreatic amylase breaks down carbohydrates
• - pancreatic lipase breaks down fats
• - nucleases break nucleic acid into nucleotides
• Liver
• Carbohydrate metabolism
• Lipid metabolism
• Protein metabolism
• Blood filtering
• Detoxifies blood
• Stores glycogen, iron, and vitamins
• Secretes Bile
• Bile- a yellowish-green liquid that contains bile
  salts
• Helps with the digestion of fat molecules
• Gall Bladder secretes and stores bile (accessory
  organ of the liver).

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Small Intestine

• The small intestine receives secretions form the
  pancreas and liver, completes nutrient digestion,
  absorbs the products of digestion, and transports
  the residues to the large intestine.
• Parts of the small intestine Duodenum, Jejunum,
  and Ileum.
• Structure of intestine wall
• lined with villi which increase surface area
  aid with absorption
• Secretion
• Mucus and digestive enzymes enzymes split
  molecules of carbohydrates, proteins, and lipids.
• Regulation of small intestine secretion
• Gastric juice, chyme, and reflexes stimulated by
  distension of small intestine wall stimulate
  secretion

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Small Intestine

• Absorption
• Enzymes on microvilli
• Villi absorb monosaccharides, amino acids,
  fatty acids, and glycerol
• fat molecules enter the lacteal of the villi
• fatty acids enter blood capillaries of villi
• Movements
• - ileocecal vavle controls movement of the
  intestinal contents from small into large
  intestine

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Large Intestine

• Parts
• Cecum Rectum
• Anal Canal
• Colon
• divided into ascendin, transverse, descending,
  and sigmoid portions
• Major function is water reabsorbtion
• Functions
• secretes mucus
• absorbs water and electrolytes
• forms and stores feces
• Feces
• consist mostly of water, undigested material,
  electrolytes, mucus, and bacteria
• stored in rectum and pass through the two
  sphincters (one voluntary and one involuntary) to
  the anus

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Hormones that Regulate Digestion
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References

• Campbell, N.A., J.B. Reece, L.G. Mitchell.
  1999. Biology. 5th Edition. Menlo Park, CA
  Pearson-Benjamin/Cummings.
• Shier, David, Butler Jackie, Ricki Lewis. 1998.
  Essentials of Human Anatomy and Physiology. 6th
  Edition. Boston, MA McGraw-Hill.
• AP Biology Glenbrook South High School. 26
  October 2006. 29 October 2006 k.k12.il.us/Academics/gbssci/bio/apbio/Lecture/lec
  ture.htm.
• Massengales Biology Place. 29 October 2006.
  h.htm.
• Massengales Biology Place. 29 October 2006.
  m.