General Anatomy and Processes

Functions:

  1. Ingestion

    1. Taking in food

  2. Digestion

    1. Mechanical and chemical breakdown of food for the body to use

  3. Absorption

    1. Taking in nutrients for the body

  4. Compaction

    1. Absorbing water and consolidating leftover into poo

Mechanical Digestion:

  1. Physical breakdown of food into smaller pieces

    1. Chewing/Mastication and the contraction of the stomach

    2. Exposes more of the food to the digestive enzymes

Chemical Digestion:

  1. Series of hydrolysis reactions to break up dietary molecules to their base forms

    1. Hydrolysis Reaction: A chemical process where water is used to cleave the bonds of complex molecules

  2. Polysaccharides → Monosaccharides

    1. Proteins → Amino Acids

    2. Nucleic Acids → Nucleotides

    3. Fats → Monoglycerides and Fatty acids

  3. By digestive enzymes secreted by the salivary glands, stomach, pancreas, and small intestine

  4. Occasional molecules can be digested as ingested: Vitamins, water, cholesterol, etc

Anatomy

  1. Mucosa/Mucous Membrane - Inner lining of digestive tract

    1. Made of loose connective tissue - lamina propria

    2. Made thin smooth muscle layer - Muscularis mucosae

      1. The two epithelium are simple columnar for most of the tract, but stratified squamous for from oral cavity to esophagus and lower anal cavity

      2. Where tract is exposed to more abrasive actions \

    3. Muscularis mucosae - Tenses mucosa = makes grooves for more surface area to touch food = better efficiency in digestion and absorption

    4. Has a MALT - Mucosa Associated Lymphoid Tissue - for lymphocytes and lymphatic nodules

  2. Submucosa - Thick layer of loose connective tissue

    1. Contains blood vessels, lymphatics, nerve plexus, and occasionally glands that secrete into the lumen

    2. Where MALT occasionally extends into

  3. Muscularis Externa - 2 layers of muscles near surface

    1. Inner layer cells encircle tract

    2. Outer layer cells run longitude

    3. Inner circle layers sometimes form thick valves (sphincters) to regulate passage through the tract

    4. Responsible for motility in pushing food through the tract

  4. Serosa - Thin areolar tissue layer

    1. Covered by simple squamous epithelium

    2. Starts in lower esophagus and ends right before the rectum

    3. Most of the esophagus and pharynx have no serosa, but have adventitia

      1. Adventitia - fibrous connective tissue layer

        1. Blends into neighboring connective tissue of other organs

Tract

  1. Produces multiple hormones

    1. Secreted into blood

    2. Stimulate distant portions of tract

    3. Gastrin and secretin

  2. Produces paracrine secretions

    1. Diffuse through tissue fluids

    2. Stimulate nearby target cells

    3. Histamine and prostaglandins

  3. Both stimulate digestive functions