Digestive System Anatomy Quiz

Gastrointestinal Tract Histology - Lecture 1

• The digestive system comprises the digestive tract and associated glands.
• The digestive tract includes the oral cavity, esophagus, stomach, small intestine, large intestine, rectum, and anus.
• Associated glands include the salivary glands, liver, and pancreas.
• The functions of the digestive system include obtaining molecules for growth, maintenance, and energy from ingested food.
• Large molecules (proteins, fats, carbohydrates, and nucleic acids) are broken down into smaller molecules for absorption, primarily in the small intestine.
• Water, vitamins, and minerals are also absorbed.
• The tract has a protective lining acting as a barrier between the lumen contents and the body's internal environment.

Histological Structure of the Foregut

• This lecture focuses on the histological structure of the oral cavity, pharynx, and esophagus.
• The oral cavity contains stratified squamous epithelium lining the lips, teeth, tongue, and palate.
• The hard palate is keratinized, while the soft palate and cheeks are non-keratinized.
• The oral mucosa differs in structure based on location and function.
• The lips exhibit three surfaces with varying epithelial features.
• Internal layer: thick non-keratinized mucosa with minor salivary glands.
• Vermilion zone: very thin keratinized stratified squamous epithelium. Transitional area. Lacks salivary and sweat glands, rich in sensory innervation and capillaries. Gives the lips pink color
• External surface (skin layer): thin skin. With epidermal and dermal layers, sweat glands, and many hair follicles with sebaceous glands.
• The tongue is a mass of striated muscle covered by mucosa. The lower surface is smooth, and the dorsal surface is irregular with papillae (filiform, fungiform, foliate, and vallate).
• Taste buds are ovoid structures found within the stratified epithelium on the tongue's surface.
• Taste buds contain gustatory cells (receptor cells) with microvilli that project into the taste pore. Three cell types are identified: gustatory, supportive, and basal stem cells. They are not restricted to papillae but also scattered across the tongue's dorsal and lateral surfaces.

Pharynx

• The pharynx is a transitional space between the oral cavity and respiratory and digestive systems. It acts as a passageway and forms an area between the area nasal region and larynx.
• The epithelium lining the pharynx changes, stratified squamous non-keratinized in areas connecting to the esophagus, and ciliated pseudostratified columnar in areas closer to the nasal cavity.
• Mucous salivary glands are present within the lamina propria (connective tissue).

Esophagus

• The esophagus is a muscular tube positioned behind the trachea.
• The outermost layer (adventitia) is continuous with the trachea's adventitia, anchoring the esophagus in the body.
• The esophageal mucosa is lined with stratified squamous non-keratinized epithelium.
• Mucous glands are present in the mucosa, especially in the lower esophagus (called cardiac glands), and are similar in structure to the glands in the cardiac portion of the stomach.
• The submucosa includes mucus-secreting glands.
• The muscularis externa consists of skeletal muscle in the upper third (involved in swallowing) and smooth muscle in the lower two-thirds (involved in peristalsis).
• The esophagus functions in transporting food from the mouth to the stomach, preventing retrograde flows of stomach contents via peristaltic contractions and esophageal sphincters (upper and lower).

Stomach

• The mucosa in the stomach changes dramatically in histology when compared to the esophagus. Namely, the epithelium transitions from non-keratinized stratified squamous to simple columnar epithelium.
• The lamina propria in the stomach contains tubular cardiac, gastric, and fundic glands.
• The muscularis mucosae in the stomach is thin and two-layered.
• Submucosa in stomach does not contain glands, unlike the esophagus.

Additional Diseases

• Hirschsprung disease: absence or injury to plexus in the digestive tract's enteric nervous system. This causes motility issues and may include dilated section(s).
• Chagas disease (trypanosomiasis): caused by Trypanosoma Cruzi, leading to GIT complications.

References

• Junqueira's histology
• Chapter 5 (specific chapter listed in references slide)