Digestive System

• Digestive system consists of:

  • Digestive tract (alimentary canal) - starts from oral cavity to anus
  • Digestive glands
• • Digestive glands - (1) embedded directly from digestive organs and (2) forms accessory glands outside the digestive organ (ex. pancreas)
• Function:

  Digestion of food

  Absorption of digestive materials

  Excretion of undigested materials
• Digestion involves the mechanical action of the digestive tract and the chemical action of substances and enzymes
• • Mechanical action - cutting food into smaller sizes
  • Chemical action - transforming food into smaller particles using enzymes and substances
• Four layers: 

  1. Mucosa
  2. Submucosa 
  3. Muscularis 
  4. Serosa / Adventitia
• Identify the parts

  A) mucosa

  B) submucosa

  C) muscularis

  D) serosa

  
• Mucosa - has three structures: (1) Mucous epithelium (2) lamina propria, and (3) muscularis mucosae
• Mucous epithelium - in the lumen organ or the colon

  • Visible or well-defined in the esophagus up to the anus
  • oral cavity up to the pharynx - this layer is not well-defined
  • Varies depending on the structure (can be keratinized, stratified squamous, etc)
• Mucosa

  • Lamina propria mucous epithelium attached; loose connective tissue
• Mucosa 

  Muscularis mucosa / muscularis interna - muscle tissue; usually smooth muscle tissue

  • Outermost part of mucosa layer
  • Separates the mucosa to the submucosa 
• Large intestine - simple columnar epithelium
• What is this tissue?

  Large intestine - big goblet cells

  
• • Submucosa consists of glands and blood vessels
  • Dense irregular connective tissue 
• Between submucosa and muscularis layer are nerves called submucosal plexus
• MUSCULARIS

  Two types of orientation:

  1. Circular muscle layer - inner
  2. Longitudinal muscle layer - outer
• 1. Circular muscle layer - inner
  2. Longitudinal muscle layer - outer

  In between these muscle layer are nerves called myenteric plexus
• Intramural plexus consists of: submucosal plexus and myenteric plexus
• Intramural plexus consists of: submucosal plexus and myenteric plexus

  • Submucosal plexus - nerves in between the submucosa and muscularis layer
  • Myenteric plexus - nerves in between the two orientations of muscle layer 
  • Both functions for the contraction of the muscle in the digestive organ for peristalsis - facilitates bolus
• SEROSA

  Consists of connective tissue layer, mostly seen in the peritoneum

  • Serosa - thin sheet of loose connective tissue located within the abdominal cavity; directly attached to visceral peritoneum 
  • Adventitia - layer of connective tissue continuous of the surrounding tissue; ex. Esophagus 

  All the layers are found from the lower esophagus to anus 
• Identify the parts of the digestive tract

  A) muscularis externa

  B) submucosa

  C) mucosa

  D) villi

  E) lumen

  F) muscularis externa

  
• ORAL CAVITY (MOUTH)

  2 Regions:

  1. Vestibule - anterior to teeth and gums (lips) 2. Oral cavity proper rest of the mouth
• Nonkeratinized stratified squamous - internal surface of lips, cheeks, soft palate, and ventral surface of the tongue
• Keratinized stratified squamous - hard palate to the gums and vermillion zone of lips
• ORAL CAVITY (MOUTH)Glands:

  • Labial Glands (upper and lower lips)
  • Buccal Glands (cheek)
  • Palatine Salivary Glands (Hard palate)
• LIPS

  Outer part of lips: keratinized stratified squamous 

  Inside of lips: nonkeratinized stratified squamous
• Lips - skeletal muscle in nature (noticed when pouting since the movement is voluntary)

  Skeletal Muscle - striated Skeletal muscle
• Skeletal muscle are found in the lips and tongue
• Lips 

  Skeletal Muscle - striated Skeletal muscle

  Labial glands - consist of mucous cells
• TONGUE

  Stratified squamous epithelium
• • Tongue muscular organ that plays an important role in mastication, deglutition and speech
• Tongue 

  • Histologically made up of skeletal muscle (same as lips)

  Anterior forms protrusions called lingual papillae
• • lingual papillae 

  1. Circumvallate lingual papillae
  2. Filiform lingual papillae 
  3. Fungiform lingual papillae
  4. Foliate lingual papillae 
• Identify the parts

  A) fungiform lingual papillae

  B) filiform lingual papillae

  C) circumvallate lingual papillae

  
• ONLY vallate and foliate lingual papillae has taste buds
• Filiform papillae - Highly keratinized, stratified squamous

  • Most numerous and found all over the dorsal surface of the tongue
• Foliate papillae - non keratinized, stratified squamous with taste buds 

  • Poorly developed in adults; consists of parallel ridges and furrows on the sides of the tongue
• Vallate papillae - lightly keratinized (less than fungiform), stratified squamous, with taste buds

  • Arranged along the sulcus terminalis; largest but least numerous
• Type of lingual papillae?

  A) fungiform papillae

  
• Type of lingual papillae

  A) filiform lingual papillae