Digestive System Flashcards
What are the four layers of the GI tract wall?
Mucosa, submucosa, muscularis externa, serosa
What are the main functions of the mucosa?
Secretion (mucus, enzymes, hormones), absorption of nutrients, and protection from pathogens
What are the three sublayers of the mucosa, and what are their functions?
Epithelium (secretes mucus, enzymes, and hormones; absorbs nutrients), lamina propria (contains blood and lymph vessels, provides immune defense via lymphoid tissue), muscularis mucosae (creates local movements to enhance secretion and absorption).
What cell types are found in the epithelial layer of the mucosa?
Goblet cells (produce mucus), enteroendocrine cells (secrete hormones), absorptive cells (specialized for nutrient absorption).
What does the submucosa layer contain?
Dense connective tissue with blood vessels, lymphatics, nerves, and glands.
Describe the role of the muscularis externa.
Responsible for peristalsis (propelling food along the tract) and segmentation (mixing food); contains inner circular and outer longitudinal muscle layers.
What is the significance of the circular muscle layer in the muscularis externa?
It thickens in certain areas to form sphincters, regulating the passage of material.
What is the serosa, and where is it found?
The outermost layer of the GI tract in intraperitoneal organs; it is formed by visceral peritoneum and provides protection and lubrication.
How does the histology of the esophagus differ from the rest of the GI tract?
The esophagus is lined with non-keratinized stratified squamous epithelium to resist abrasion and has an adventitia (instead of serosa) for structural attachment.
What are Peyer’s patches, and in which layer are they found?
Aggregated lymphoid nodules located in the lamina propria and submucosa of the small intestine (especially the ileum), protecting against pathogens.
How do the histological features of the stomach mucosa aid in its function?
The stomach mucosa has gastric pits and glands with specialized cells:
- Parietal cells (secrete HCl and intrinsic factor)
- Chief cells (secrete pepsinogen)
- Mucous cells (secrete mucus to protect the lining)
- Enteroendocrine cells (secrete hormones like gastrin).
What distinguishes the histology of the small intestine?
Modifications to increase surface area, including:
- Circular folds (plicae circulares)
- Microvilli (brush border with digestive enzymes).
- Villi (finger-like projections with lacteals for lipid absorption)
How does the large intestine’s mucosa differ from that of the small intestine?
It lacks villi but has a greater abundance of goblet cells for mucus secretion, facilitating fecal movement.
What are the main functions of the tongue?
Repositioning/mixing food, forming bolus, swallowing, speech, taste.
Name the types of papillae on the tongue and their functions.
Filiform (friction), fungiform (taste buds), vallate (taste buds in V-shape), foliate (taste buds on sides).
What is the role of the salivary glands?
Produce saliva for digestion, lubrication, and taste.
Describe the layers of the esophagus
Mucosa (stratified squamous), submucosa (mucus glands), muscularis externa (skeletal and smooth muscle).
What is the primary function of the oral cavity?
Initiates mechanical and chemical digestion; moistens food to form bolus for swallowing.
Describe the structural and functional significance of the hard and soft palates.
The hard palate forms a rigid surface for the tongue to press food against during chewing, while the soft palate closes off the nasopharynx during swallowing.
What is the role of the pharynx in digestion?
Propels food from the oral cavity to the esophagus through the oropharynx and laryngopharynx.
How is food prevented from entering the respiratory tract during swallowing?
The epiglottis closes over the larynx, directing food into the esophagus.
Explain the function of the gastroesophageal (cardiac) sphincter.
Prevents reflux of acidic stomach contents into the esophagus.
What is the role of the esophageal glands?
Secrete mucus to reduce friction and ease food passage.
Differentiate between the voluntary and involuntary phases of swallowing (deglutition).
The voluntary phase involves the tongue pushing the bolus into the oropharynx; the involuntary phase (pharyngeal-esophageal) is controlled by the medulla and pons, involving smooth muscle contractions.
Describe peristalsis in the esophagus.
Involuntary waves of contraction and relaxation of the muscularis externa that propel the bolus towards the stomach.
