Digestive Tract II: Esophagus through Intestines
Rahul's Noteblog
Notes on Histology
Digestive Tract II: Esophagus through Intestines
A tube within a tube, in that there is slippage between the muscularis mucosa & muscularis externa. Fairly straight tube from pharynx to stomach. Most is intrathoracic but terminal 2-4 cm is below diaphragm. Food passes rapidly and there is no absorption. Stratified squamous mucosal. Muscularis mucosae fairly prominent when compared to other segments of the GI tract Submucosa has elastic fibers that contributes to lumen diameter change during swallowing. A few mucous esophageal glands in submucosa.
Upper 1/3 muscularis externa all skeletal Middle mixture of smooth & skeletal Lower 1/3 all smooth Esophagus
In lower esophagus, mucous glands in lamina propria are called cardiac glands due to their similarity to the cardiac region of the stomach.
Normal esophagus Barrett’s esophagus, islands of columnar epithelium in the esophagus Gastric reflux inflames columnar cells Ulcers can lead to scarring & narrowing of the lumen so that swallowing is almost impossible Stomach Ulcers
Musculature: Inner oblique Middle circular Outer longitudinal
Inner surface amplified by folds or rugae that flatten out when the stomach is full.
Rugae generally only have a core of mucosa but large ones may have a submucosal component.
Functions of Stomach:
1. Reservoir for food
2. Site for continuation of digestion
3. Kills bacteria & other live material
4. Blender for food
• Epithelial layer is highly invaginated to form gastric pits or foveloae which lead to gastric glands
• Pylorus Foveolae Foveolae are strictly mucous Broad shoulders with a tapering waist
Mucous cap cell UndifferentiatedStomach cell types Mucous Neck Oxyntic (parietal) Zymogen (chief) Enteroendocrine
Parts of gastric gland: Isthmus Neck Base Types of cells:
• Surface mucous cap cell (shaped like a chef’s cap)
• Undifferentiated cells in neck, can go up or down
• Mucous neck cells
• Parietal, oxyntic cells produce HCl & intrinsic factor, a glycoprotein necessary for absorption of vitamin B12. Stain like large fried eggs. Eosinophilic cytoplasm.
• Chief, zymogen cells produce pepsinogen that is changed to pepsin due to presence of HCl. Pepsin then cleaves protein. Basophilic.
Enteroendocrine cells modify adjacent cells by paracrine regulation. Basal secretions enter the lamina propria.
Apical canalicular trough of parietal cells increases area for HCl production.
Pump H+ ions into trough & combine with Cl- Abundant mitochondria
Fundus More than one gastric gland can tap into one foveola
Fundus Mucous Neck Parietal Chief Musc. mucosa.
Mucous cap cell lives 4-6 days Undifferentiated Stomach cell types Live > 2 days
Gastric glands are simple tubular but may branch. Surrounded by lamina propria. Longest ones crossed at base by mus. muc. Name glands based on ratio of foveolae to gland length.
Cardiac is kind of weak Fundus has funky glands Pylorus has puny glands Predominantly mucous Protects esophageal- gastric junction Produces most HCl & all pepsinogen. Short pits & long glands Shift back to mostly mucous & enteroendocrine Most parietals drop out. Deep pits & short glands.
Fundus Foveloa Gastric gland Mus. Muc.
Fundus Parietal Chief Mus. Muc.
Normal mucosa of mouse 8 min. after administration of 20 mM aspirin. Aspirin increases acid environ. & destroys mucous cap cells.8 min. after administration of 20 mM aspirin & 1mM HCl. Alcohol causes the same changes but slower.
Lesser curvature is main path for food Always exposed to acid Main site of ulcers Can be damaged with ingestion of drain cleaner Helicobacter pylori
Levels of amplification for absorption by the intestine
A. Lengthen,
B. Plicae circulares,
C. Villi,
D. Microvilli,
E. Glycocalyx
Small intestine is ~6-7 meters. Can remove up to 1/3. Large intestine forms a picture window that “frames” the small intestine. Plicae circulares (valves of Kerckring) have core of submucosa.
About 800 plicae. These are permanent and are present when the intestine is full. Spiral around 1/3 to 3 turns.
Villi 1/2 to 1.5 mm long Core of lamina propria, nerve, smooth muscle, single arteriole, capillary plexus, single venule & lymphatic (central lacteal) Each absorptive cell of a villus has ~3,000 microvilli. Small intestine: Completes digestion absorbs products of digestion to blood or lymph Produces hormones
Glands of intestine may occur as goblet cells (unicellular gland) or in lamina propria, mucosa, submucosa or external & connected by ducts.
Ground Zero Evagination = villus Invagination = crypt of Lieberkuhn
Cell types: Columnar absorptive cells (enterocytes) with microvilli and glycocalyx (PAS positive). Goblet cells, PAS positive, some consider them unicellular glands. Secretes mucin which hydrates with water to form mucous. Enteroendocrine cells. Two important factors are cholecystokinin and secretin.
Paneth cells are highly differentiated and never leave the crypt. Contain eosinophilic zymogen granules that produce lysozyme that digests cell wall of bacteria and regulates the natural bacterial flora of the intestine. M-cells (microfold cells) process antigen and associated region where basement membrane has ‘holes’ for interaction with lymphocytes Undifferentiated cells
Small Intestine cell types
• Cell life span:
• Esophagus 2-3 days
• Gastric 4-6 days
• Intestine 3-6, generally 6 days
• Paneth cells 30 days
Crypt cells
Colon,only crypts, no villi Duodenum Jejunum Ileum Villi Crypts
Duodenum 180 million crypts of Lieberkuhn Mucous glands of Brunner in submucosa that produce urogastrone, a gastric acid inhibitor. Secretions are alkaline (pH 8.1-9.3). Brings intestinal contents to optimal pH for pancreatic enzymes. Brunner’s tap into base of crypt.
Duodenum
Ileum with Peyer’s patches, M cells, etc. There are about 30 patches, visible with the naked eye. Mostly in submucosa but can project into mucosa.
Full circle: Antigen sampled by M cell & presented to lymphocytes in LP. Migrate to lymph nodes & circulate/ Exit at gut lamina propria. Develop into plasma cells. Secrete IgA into gut lumen. In lactating women contributes to milk.
Vessel plexus in submucosa supplies villi.
Prominent mucous cells produces a “mucous water slide” for fecal matter to surf out. Passively absorbs water. Elimination of residual foodstuffs. No important enzymatic activities, just left over from small intestine. Large intestine
Absorbs water. Prominent mucous cells produces a “mucous lubricant” for the forming fecal masses. Elimination of residual foodstuffs. No important enzymatic activities, just left over from small intestine.
Taenia coli thickened longi. layer of mus. ex.Haustra, out- pocketings caused by taenia
Appeddices epiploicae Plicae semilunares coli
Plicae semilunares coli
Few Few Most Cell types
Colon
Colon crypyts with (P) plasma & (E) enteroendocrine
Plicae tranversales recti in rectum support the fecal mass. Serosa covers caecum, appendix, transverse & sigmoid colon. Remainder are retroperitoneal.Rectal columns of Morgagni, mucous membrane.
Keratinized SS Mucosal SS = ectoderm (proctodeum)
Columnar = endoderm (hindgut) Pectinate line, embryonic division between endo. & ecto.
Muscularis mucosae terminates at junction of rectum and anus and lamina propria blends with submucosa. Skin around anus forms the zona cutanea and has no sweat glands but apocrine glands that secrete oily fluid related to sexual activity in lower animals. Circular smooth muscle of anal canal is thickened as the internal anal sphincter. External anal sphincter is skeletal muscle.
Hemorrhoids are dilations of the internal (above pectinate line) &/or external (below pectinate line) hemorrhoidal plexuses.
Appendix: no taenia coli, circumferrential lymphatic nodules with star shaped to obliterated lumen.
Additional Reading:
Basic Histology
1. Introduction to Histology
2. Basic Cell Physiology
3. Actin, Microtubules, and Intermediate Filaments
4. Mitochondria, Nucleus, Endoplasmic Reticulum, Golgi
5. Epithelium (Epithelial Tissue)
6. Connective and Adipose Tissue
7. Types of Cartilage
8. Osteogenesis
9. Nervous Tissue
10. Muscle Tissue
11. Cardiovascular System
12. Blood and Hematopoiesis
13. Lymphoid Tissue
14. Digestive Tract I: Oral Cavity
15. Digestive Tract II: Esophagus through Intestines
16. Liver, Pancreas, and Gall Bladder
17. Respiratory System
18. Integument
19. Urinary System
20. Endocrine System
21. Male Reproductive System
22. Female Reproductive System
23. Eye and Ear
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