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Questions and Answers
What type of epithelium lines the mouth?
Nonkeratinized Stratified Squamous
Which region of the stomach contains the gastric pits?
The large intestine consists of appendix, colon, rectum, and anal canal. It is characterized by the absence of Plicae circulares and ___
villi
Match the following respiratory passages with their corresponding epithelium type:
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Clara cells are present in both terminal and respiratory bronchioles.
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What is the main function of Septal cells in the alveoli?
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What do Type II Alveolar or Type II Pneumocytes secrete that spreads over the alveolar surface?
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What is constantly renewed and prevents collapse of the alveoli during expiration?
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Alveolar Macrophages are responsible for cleaning the alveoli of invading microorganisms and inhaled particulate matter.
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Study Notes
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Histology of the Gastrointestinal Tract
- The digestive system is composed of the mouth, pharynx, esophagus, stomach, small intestine, and large intestine
Layers of the GI Tract
- Mucosa:
- Epithelium
- Lamina propria
- Muscularis mucosae
- Submucosa:
- Submucosal plexus (Plexus of Meissner)
- Muscularis:
- Myenteric plexus (Plexus of Auerbach)
- Serosa
Histology of the Oesophagus
- Mucosa: stratified squamous non-keratinized epithelium
- Submucosa: contains Meissner's plexus and oesophageal glands
- Muscularis externa: upper 1/3 skeletal fibres, middle 1/3 mixed fibres, lower 1/3 smooth fibres
- Adventitia: loose areolar connective tissue
Histology of the Stomach
- Cardiac region:
- Mucosa: simple columnar epithelium, mucous secreting cardiac glands in lamina propria
- Submucosa: connective tissue
- Muscle layer: inner circular, outer longitudinal
- Serosa: simple squamous epithelium
- Fundic region:
- Mucosa: simple columnar epithelium, presence of gastric glands in lamina propria
- Cells of fundic region: mucous neck cells, parietal cells, chief cells, enteroendocrine cells, undifferentiated cells
- Submucosa: contains blood vessels, lymphatics, and Meissner's plexus
- Muscularis externa: inner oblique, middle circular, outer longitudinal layer
- Serosa: consists of surface layer of flattened mesothelial cells
- Pyloric region:
- Mucosa: pyloric glands in lamina propria, deeper gastric pits extending half the thickness of mucosa
- Muscle layer: inner circular (thickened to form pyloric sphincter), outer longitudinal layer
- Submucosa and Serosa: same as in fundic part
Histology of the Small Intestine
- Divided into duodenum, jejunum, and ileum
- Mucosa:
- Characteristic features: plicae circularis, villi, microvilli, goblet cells, crypts of Lieberkuhn
- Glands are lined by columnar cells, goblet cells, Paneth cells, and enteroendocrine cells
- Submucosa: contains blood vessels, lymphatics, and Meissner's plexus
- Muscularis externa: outer longitudinal and inner circular layers of smooth muscle
- Serosa/Adventitia: same as in stomach
Histology of the Large Intestine
- Consists of appendix, colon, rectum, and anal canal
- Mucosa:
- Absence of plicae circularis and villi
- Presence of microvilli and crypts of Lieberkuhn
- Presence of goblet cells in large number
- Submucosa:
- Blood vessels and lymphatics
- Muscularis externa:
- Inner circular layer - thin compared to small intestine
- Outer longitudinal layer - forms taenia coli
- Adventitia: appendices epiploicae (peritoneum forms pouch-like processes filled with fat)
Histology of the Respiratory System
- Conducting part: nasal cavities, pharynx, trachea, bronchi, and their intrapulmonary continuations
- Respiratory part: lungs
- Histology of trachea:
- Mucosa: pseudostratified ciliated columnar epithelium
- Submucosa: loose connective tissue, tracheal glands, blood vessels, and ducts
- Cartilage and smooth muscle layer
- Adventitia: fibroelastic tissue
- Histology of bronchi:
- Principal bronchus: same as trachea
- Secondary/lobar bronchus: irregular hyaline cartilage, pseudostratified ciliated columnar epithelium
- Tertiary/segmental bronchus: columnar epithelium, patches of cartilage
- Histology of bronchioles:
- Terminal bronchiole: columnar epithelium, no cartilage, smooth muscle layer, Clara cells present
- Respiratory bronchiole: cuboidal epithelium, no mucous glands, smooth muscle layer
- Cells seen in the respiratory passages:
- Goblet cells
- Non-ciliated serous cells
- Basal cells
- Cells of Clara
- Brush cells
- Argyrophil cells
- Lymphocytes
- Alveoli:
- Total area - 75 square meters
- Total capillary surface area - 125 square meters
- Separated by interalveolar septum
- Contain an network of capillaries, supported by reticular and elastic fibers, occasionally fibroblasts, macrophages, and mast cells
- Pneumocytes:
- Type I: squamous epithelial cells, form the lining of 90% of the alveolar surface
- Type II: secretory cells, produce pulmonary surfactant
- Macrophages or dust cells:
- Derived from monocytes
- Phagocytose inhaled particulate matter
- Migrate from septum to alveolar surface and are carried to the pharynx through sputum
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Description
Learn about the histology of the digestive system, including the layers of the mucosa, submucosa, and muscularis, and the different parts of the gastrointestinal tract.
