Digestive System Notes Digestion

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Digestive System Notes

Digestion: Process of changing complex solid foods into simpler soluble forms which can be absorbed by the body

Enzymes: Chemical substances that promote chemical reactions in living things although they themselves are unaffected by the reactions

Alimentary Canal: Digestive Tract or Gastrointestinal (GI Tract) consists of a mouth (Oral Cavity), Pharynx (Throat), Esophagus (Gullet), Stomach, Small Intestine, Large Intestine (Colon), and the Anus

30 Feet in Length (Slimy Mucus Lubricates and Insulates the GI Tract)

Accessory Organs: Tongue, Teeth, Salivary Glands, Pancreas, Liver, and Gall Bladder

4 Layers of the Digestive System

  1. Mucosa: Innermost Lining made up of Epithelial Cells

  2. Sub mucosa: Connective Tissue with Fibers, blood Vessels, and nerves

  3. Circular Muscle Layers

  4. Longitudinal Muscle Layers

Linings of the Digestive System

  1. Peritoneum: Serous Membrane made up of two layers

    1. Parietal ----- Outer Lining

    2. Visceral ----- Inner Lining

Peritonitis: Inflammation of the Peritoneum

  1. Mesentery: Attaches the Peritoneum to the posterior wall of the abdomen.

Small Intestines are attached to this layer. This is like a protective apron. Contains large amounts of fat called the Greater Omentum

The peritoneal structure between the liver and stomach is called the Lesser Omentum.

Functions of the Digestive System

  1. Bread Down Food Physically into smaller Pieces

  2. Change Food chemically to end products of fats, carbohydrates, and proteins

  3. Absorbs Nutrients into the Blood Stream Capillaries of the Small Intestines for use in the body

  4. Eliminate Waste Products of Digestion

Mouth: (Oral or Buccal Cavity) Lips: (Labia) Protects the Opening of the mouth. Roof has a hard and soft palate. Hard Palate is part of the Maxillary and Palatine Bones. Soft Palate is made from a moveable mucous membrane. Soft Palate separates the mouth from the nasopharynx

Uvula: Prevents food from entering the Nasal Cavity when Swallowing

Tongue: Attached to Four Bones (Hyoid, Mandible, Two Temporal Bones)

  1. Papillae: Epithelial Surface Projections (Taste Buds) are located here

    1. Bitter, Salty, Sweet, Sour

    2. Also Sensitive to Cold, Heat, and Pressure

    3. Majority of what we Taste is because we Smell it.

Salivary Glands:

  1. Parotid Gland: Formed on both sides of the Face, In front and below the ears. “Largest” of the Salivary Glands Secretes “Amylase” Enzymes

  2. Submandibular: Size of a Walnut Secretes Both “Mucin” and “Ptyalin”

  3. Sublingual: “Smallest” of the Glands found under the sides of the Tongue. Secretions consist mainly of “Mucus” and contains “No Ptylin”

Teeth: “Gingivae or Gums” support and protect the Teeth

2 Sets of Teeth over a Lifetime

  1. Deciduous: Baby Teeth (20) 2. Permanent: Adult Teeth (32)

    1. Incisors: Sharp Edges for Biting (4 x 4)

    2. Canines: Pointed for Tearing (2 x 2)

    3. Molars: Ridges for Crushing and Grinding (4 x 4) Adult (6 x 6)

    4. Premolars: (Adult Only): “Bicuspids” for Grinding (4 x 4)

    5. Wisdom Teeth: Last to Emerge (3rd Molars) around 17 – 25 Years Old

Structures of a Tooth

  1. Crown: Visible Portion of the Tooth

  2. Neck: Where the tooth enters the gum line

  3. Root: Embedded in the Alveolar Process of the Jaw

  4. Peridontal Membrane: Anchors the Tooth in Place

  5. Pulp Cavity: Contains the Nerves and Blood Supply of the Tooth

  6. Dentin: Surrounding the Pulp Cavity calcified

  7. Enamel: Dentin is covered with the hardest substance of the

Human body

Mastication: The Act of Chewing

Esophagus: Muscular Tube about 25 Centimeters or 10 Inches in Length.

Has 4 Layers (Mucosa, Submucosa, Muscular and External Serous Layer)

Stomach: Has Three Portions

  1. Fundus: Upper Part

  2. Body or Greater Curvature: Middle Section

  3. Pylorus: Lower Part

Rugae of the Stomach: Gastric Mucosa folds that increases the surface area of the stomach

Cardiac Sphincter: Controls passage of food into the stomach. Closest to the Heart

Pyloric Sphincter: Regulates food into the Duodenum (1st Part of the Small Intestine)

Pylorospasm: In Infants food isn’t completely digested and

Eventually is vomited

Gastric Juices: Mucosa contains millions of gastric glands which secrete digestive juices

  1. Enteroendocrine Glands: Secretes “Gastrin” which in turn stimulates cells to produce

“HCL (Hydrochloric Acid) and Pepsinogen”

  1. Parietal Cells: Produce HCL with converts Pepesinogen into “Pepsin” and

destroys Bacteria. Produces Intrinsic factors like absorption

of Vitamin B12 with Stops Pernicious Anemia

  1. Chief Type Cells: Produces Pepsinogen which convets to Pepsin. “Pepsin breaks

down Proteins into Protease and Peptone.

  1. Mucus Cells: Secrete Alkaline Mucus which helps to Neutralize the HCL Acid

  1. Rennin: Found in Infants and children, but not in Adults. Prepares milk

proteins for digestion by other enzymes

Small Intestine: Main absorption of food. Breaks down Protein using pepsin. It secretes digestive juices and is covered with villi, which absorbs the end product of digestion. Absorption is possible because of Villi. Each Villus contains a network of blood and lymph capillaries that absorbs nutrients. The Small Intestine has 3 parts.

      1. Duodenum: 12 inches and curves around the pancreas. Bile and

Pancreatic juices enter here and break down and emulsify fats. Pancreatic juices mainly Protease or Trysin breaks down protein to Ammino Acids. Amylase or Amylopsin which are secreated in the mouth continue to break down starches and carbohydrates into glucose. Lipase or Steapsin break down fats to fatty acids and glycerol. Pancreatic Juices also contains sodium bicarbonate which neutralizes the food content.

      1. Jejunum: 8 - 12 feet long

      2. Ileum: 10 – 15 feet long (Longest of the sections).

Pancreas: Feather shaped organ located behind the stomach. It is both an Exocrine and Endocrine gland

Exocrine Gland means it has a duct that carries away its secretions

Endocrine Gland means it is ductless and the secretions are emptied directly into the bloodstream.

Liver: Largest organ in the body, located below the diaphragm. The Portal Vein carries products of digestion from the small intestine to the liver.


  1. Manufactures Bile (Yellowish green digestive juices)

    1. Common Bile duct (Hepatic duct from the liver joins the Cystic Duct from the Gall Bladder) If this duct is blocked then Jaundice occurs which gives the skin and sclera of the eyes a yellow color.

  2. Produces and stores Glucose in the form of Glycogen

  3. Detoxifies alcohol, drugs, and other harmful substances

  4. Manufactures blood proteins

  5. Prepares Urea (Chief waste product of protein metabolism)

  6. Stores vitamins A,D, & B Complex

  7. Breaks down hormones no longer useful to the body

  8. Removes worn-out red blood cells and recycles Iron

Gall Bladder Small Green Organ in the inferior surface of the liver


  1. Stores and concentrates bile when it is not needed

  2. Bile is released when food high fat content is eaten

Large Intestine: Chyme a semi liquid food that enters here through an opening called the Ileocecal Valve. This valve permits the passage of chyme and prevents the backflow into the ileum.

  1. 5 feet long and 2 inches in diameter

  2. Lined with Haustra which are pockets that provide more surface area in the colon

  3. The Colon frames the abdomen

    1. Cecum

    2. Ascending Colon

    3. Transverse Colon

    4. Descending Colon

    5. Sigmoid Colon

    6. Rectum and Anus

  4. Cecum A blind pouch in the right abdomen. Attached to the Small Intestine at the Ileum.

  5. Appendix is located in the lower left of the cecum. Fingerlike projection. Safe house to store good bacteria for the intestines.

Anal Canal: Last portion of the large intestine

  1. Anus External opening ( 2 sphincter muscles keep this closed)

  2. Hemorrhoids Inflammation or enlargement of the rectal column veins

General Digestion

Bolus Soft, pliable ball of food

Peristalsis Muscular contractions of the digestive system, Segmented, rhythmic movements

Feces Remaining undigested food

Salivary Amylase and Ptyalin converts starches and carbohydrates into simple sugars. Saliva is affected by the nervous system. Just thinking about food causes the mouth to water or dry mouth occurs when you are nervous or frightened.

Deglutition: Swallowing involves constrictor muscles

Epiglottis: Covering of the windpipe when swallowing

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