BIO 201 Digestive System

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Last updated 4:10 AM on 7/30/26
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31 Terms

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Digestive System

Set of organs that breaks down food items into nutrients. Two types of organs include:

  • Organs of alimentary canal

    • aka gastrointestinal tract

  • Accessory organs

<p>Set of organs that breaks down food items into nutrients. Two types of organs include:</p><ul><li><p>Organs of alimentary canal </p><ul><li><p>aka gastrointestinal tract </p></li></ul></li><li><p>Accessory organs</p></li></ul><p></p>
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Accessory Organs of the Digestive System

  • Teeth

  • Tongue

  • Salivary Glands

  • Liver

  • Gallbladder

  • Pancreas

<ul><li><p>Teeth</p></li><li><p>Tongue</p></li><li><p>Salivary Glands</p></li><li><p>Liver</p></li><li><p>Gallbladder</p></li><li><p>Pancreas</p></li></ul><p></p>
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Organs of the Alimentary Canal (GI Tract)

  • Oral Cavity

  • Pharynx

  • Esophagus

  • Stomach

  • Small Intestine

  • Large Intestine

  • Anal Canal

<ul><li><p>Oral Cavity</p></li><li><p>Pharynx</p></li><li><p>Esophagus</p></li><li><p>Stomach</p></li><li><p>Small Intestine</p></li><li><p>Large Intestine</p></li><li><p>Anal Canal</p></li></ul><p></p>
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General Functions of the Digestive System

  1. Take food into the body and break it down into its component nutrients (Most Fundamental Function)

  2. Taking in water and electrolytes via diet & delivering them to the blood. (Fluid, electrolyte, and acid-base homeostasis)

  3. Ingesting vitamins & minerals

  4. Producing hormones

  5. Excreting metabolic wastes

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Six Basic Processes of the Digestive System

  1. Ingestion

  2. Secretion

  3. Propulsion

  4. Digestion

  5. Absorption

  6. Defecation

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Ingestion

Intake of food and water via the mouth.

  • Basic process of the digestive system

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Secretion

Release of mucus, enzymes, acid, and hormones by endocrine and exocrine glands to aid other digestive processes.

  • A basic process of the digestive system

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Propulsion

Movement of ingested food and liquids from one digestive organ to the next.

  • Basic process of the digestive system

  • Accomplished largely by peristalsis

  • Aided by mucus secreted by multiple organs

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Peristalsis

Rhythmic contractions of smooth muscle of the alimentary canal that helps with the propulsion of food and liquids.

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Digestion

Food Breakdown

  • Basic process of the digestive system

  • Two Kinds:

    • Mechanical Digestion

    • Chemical Digestion / Enzymatic Hydrolysis

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Mechanical Digestion

Physical breakdown of food into smaller pieces

  • Examples: chewing & mixing by muscles

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Chemical Digestion / Enzymatic Hydrolysis

Enzymes catalyze reactions that break chemical bonds

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Absorption

Nutrients move through the wall into blood or the lymphatic vessels.

  • Basic process of the digestive system

  • Water, electrolytes & vitamins also move into the bloodstream

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Defecation

Materials that are not digestable or usable by the body continue their transit through the alimentary canal until they exit the body as feces.

  • Basic process of the digestive system

  • A specialized form of propulsion

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Motility/Movement

A key process in every region of the alimentary canal. Includes:

  • Swallowing

  • Churning

  • Peristalsis

  • Defectation

Regulated by the nervous system

  • Autonomic Nervous System (ANS)

  • Enteric Nervous System (ENS)

Also regulatied by the endocrine system

  • Hormones

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Motility Using Skeletal Muscle

  • Oral Cavity

  • Pharynx

  • Superior Portion of the Esophagus

  • Last Portion of the Large Intestine

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Motility Using Smooth Muscle

All of the alimentary canal except for:

  • Oral Cavity

  • Pharynx

  • Superior Portion of the Esophagus

  • Last Portion of the Large Intestine

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ANS Regulation of the Digestive System

Known as long reflexes.

  • Must travel outside of the local digestive neurons to the CNS

  • Sympathetic Nervous System

    • Inhibits digestive processes

  • Parasympathetic Nervous System

    • Activity stimulates digestive processes

<p>Known as <strong>long reflexes</strong>.</p><ul><li><p>Must travel outside of the local digestive neurons to the CNS</p></li><li><p>Sympathetic Nervous System</p><ul><li><p>Inhibits digestive processes</p></li></ul></li><li><p>Parasympathetic Nervous System </p><ul><li><p>Activity stimulates digestive processes </p></li></ul></li></ul><p></p>
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ENS Regulation of the Digestive System

Known as short reflexes.

  • Reflex pathways are confined to local neurons

  • Self-contained branch of the ANS

  • Extends from the esophagus to the anus

<p>Known as <strong>short reflexes.</strong></p><ul><li><p>Reflex pathways are confined to local neurons</p></li><li><p>Self-contained branch of the ANS</p></li><li><p>Extends from the esophagus to the anus </p></li></ul><p></p>
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Histology of the Alimentary Canal

Organs follow the same general tissue patterns of other hollow organs:

  • Concentric layers of tissue surround a space called the lumen

  • Most regions contain four layers (tunics):

    • Mucosa: Inner Epithelium

    • Submucosa: Connective Tissue

    • Muscularis: Smooth Muscle

    • Serosa: Outer Layer of Connective Tissue

<p>Organs follow the same general tissue patterns of other hollow organs:</p><ul><li><p>Concentric layers of tissue surround a space called the <strong>lumen</strong></p></li><li><p>Most regions contain four layers (<strong>tunics</strong>):</p><ul><li><p>Mucosa: Inner Epithelium</p></li><li><p>Submucosa: Connective Tissue</p></li><li><p>Muscularis: Smooth Muscle</p></li><li><p>Serosa: Outer Layer of Connective Tissue</p></li></ul></li></ul><p></p>
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Mucosa

Inner epithelial layer of the alimentary canal.

  • Contains three components:

    • Layer of epithelium faces the lumen

    • Thin layer of loose connective tissue called lamina propria

    • Thin layers of smooth muscle known collectively as the muscularis mucosae

<p>Inner <strong>epithelial </strong>layer of the alimentary canal.</p><ul><li><p>Contains three components:</p><ul><li><p>Layer of epithelium faces the lumen</p></li><li><p>Thin layer of loose connective tissue called <strong>lamina propria</strong></p></li><li><p>Thin layers of smooth muscle known collectively as the <strong>muscularis mucosae </strong></p></li></ul></li></ul><p></p>
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Lamina Propria

Middle layer of mucosa between epithelium and mucosal muscle.

  • Houses blood and lymphatic vessels, glands, and mucosa-associated lymphoid tissue (MALT)

<p>Middle layer of mucosa between epithelium and mucosal muscle.</p><ul><li><p>Houses blood and lymphatic vessels, glands, and mucosa-associated lymphoid tissue (MALT)</p></li></ul><p></p>
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Muscularis Mucosae

Outermost layer of the mucosa between the lamina propria and the submucosa.

  • Contractions facilitate release of secretions into the lumen

  • Increases contact of materials with mucosa

<p>Outermost layer of the mucosa between the lamina propria and the submucosa.</p><ul><li><p>Contractions facilitate release of secretions into the lumen</p></li><li><p>Increases contact of materials with mucosa </p></li></ul><p></p>
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Submucosa

A layer of connective tissue between the mucosa and muscularis layers of the alimentary canal.

  • Composed of dense irregular connective tissue with blood and lymphatic vessels as well as submucosal glands

  • Houses submucosal plexus and MALT Tissue

<p>A layer of connective tissue between the mucosa and muscularis layers of the alimentary canal.</p><ul><li><p>Composed of <strong>dense irregular connective tissue </strong>with blood and lymphatic vessels as well as <strong>submucosal glands</strong></p></li><li><p>Houses submucosal plexus and MALT Tissue</p></li></ul><p></p>
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Submucosal Plexus or Meissner’s Plexus

Nerve clusters in the submucosa that are a part of the ENS.

  • Regulate secretion and blood flow

<p>Nerve clusters in the submucosa that are a part of the ENS.</p><ul><li><p>Regulate secretion and blood flow</p></li></ul><p></p>
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MALT Tissue of Submucosa

  • Prevents ingested microbes from crossing the GI tract wall

  • Peyer’s Patches in distal small intestine

<ul><li><p>Prevents ingested microbes from crossing the GI tract wall</p></li><li><p>Peyer’s Patches in distal small intestine </p></li></ul><p></p>
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Muscularis Externa

A thick, smooth muscle layer found in most of the alimentary canal. Composed of two layers:

  • Inner circular layer of smooth muscle

  • Outer longitudinal layer of smooth muscle

  • Also houses the myenteric plexus (Auerbach’s plexus)

<p>A thick, smooth muscle layer found in most of the alimentary canal. Composed of two layers: </p><ul><li><p><strong>Inner circular layer</strong> of smooth muscle</p></li><li><p><strong>Outer longitudinal layer</strong> of smooth muscle </p></li><li><p>Also houses the myenteric plexus (Auerbach’s plexus)</p></li></ul><p></p>
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Myenteric (Auerbach’s) Plexus

Nerve clusters of the ENS are found in the muscularis externa layer of most of the alimentary canal.

  • Regulate the motility of the muscularis externa

<p>Nerve clusters of the ENS are found in the muscularis externa layer of most of the alimentary canal.</p><ul><li><p>Regulate the motility of the muscularis externa</p></li></ul><p></p>
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Serosa (Visceral Peritoneum)

The outer layer of connective tissue found in the organs of the alimentary canal that are surrounded by the peritoneal cavity.

  • Composed of simple squamous epithelial tissue and loose connective tissue

  • Supports the digestive organs and anchors them to surrounding structures

<p>The outer layer of connective tissue found in the organs of the alimentary canal that are surrounded by the peritoneal cavity.</p><ul><li><p>Composed of <strong>simple squamous epithelial tissue</strong> and<strong> loose connective tissue</strong></p></li><li><p>Supports the digestive organs and anchors them to surrounding structures</p></li></ul><p></p>
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Adventita

The outer connective tissue layer found in the organs located outside the peritoneal cavity within the alimentary canal.

  • Composed of dense irregular connective tissue

  • Supports digestive organs and anchor them to surrounding structures

<p>The outer connective tissue layer found in the organs located outside the peritoneal cavity within the alimentary canal. </p><ul><li><p>Composed of <strong>dense irregular connective tissue</strong></p></li><li><p>Supports digestive organs and anchor them to surrounding structures </p></li></ul><p></p>
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Epithelium of Mucosa (Stomach → Large Intesine)

Simple columnar epithelium with copious goblet cells that secrete an alkaline mucus.

  • Mucus coats the epithelium and protects surrounding tissues from ingested food and chemicals secreted by digestive organs.

  • Regenerative epithelial cells that have a high rate of mitosis allow the mucosa to replace epithelial cells as they undergo apoptosis and are sloughed off in the alimentary canal

<p><strong>Simple columnar epithelium</strong> with copious <strong>goblet cells</strong> that secrete an alkaline mucus.</p><ul><li><p>Mucus coats the epithelium and protects surrounding tissues from ingested food and chemicals secreted by digestive organs.</p></li><li><p><strong>Regenerative epithelial cells </strong>that have a high rate of mitosis allow the mucosa to replace epithelial cells as they undergo apoptosis and are sloughed off in the alimentary canal</p></li></ul><p></p>