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Digestive Tract, OSPE, Not the same, Serosa covers GIT parts in the…
Digestive Tract
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Main Organs
Oral CavityFunctions
- Taste sensation.
- Grinding of food through the actions of the teeth, tongue, and palatal surfaces.
- Lubrication by mixing with mucus and saliva.
- Limited digestion of carbohydrates and lipids
Following must work together
- Teeth
- Tongue
- Salivary glands
- Parotid
- Sublingual
- Submandibular
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Floor covered by thin and vascular layer of mucosa supported by geniohyoid and mylohyoid muscles while the tongue rests on it.
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Upper jaw is called as such, and mandible is the lower jaw
Swallow
Buccal phase
- Bolus pushed against hard palate
- Retraction of tongue pushes bolus to oropharynx and assists in raising soft palate, sealing off nasopharynx
- Bolus moves to oropharynx and bolus begins moving to stomach
Pharyngeal Phase
- Bolus comes into contact with palatoglossal arch and palatopharyngeal arch, as well as posterior pharyngeal wall.
- Elevation of larynx and folding of epiglottis directs bolus past the closed glottis
- Uvula and soft palate block passage to nasopharynx
Oesophageal phase
- Pharyngeal muscles forces bolus through entrance of oesophagus
- Bolus pushed to stomach by peristalsis
Bolus Enters Stomach
- Lower oesophageal sphincter opens
- Bolus continues to stomach
Pharynx
- Common passageway for solid food,
liquids, and air.
- Has stratified squamous epithelium
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Esophagus
- Muscular tube that starts from the pharynx and descends through the thoracic cavity to end into stomach.
- Always collapsed unless food is passing through.
- Located posterior to trachea and anterior to vertebral column.
- The opening between oesophagus and stomach is controlled by oesophageal sphincter (also known as cardiac sphincter).
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Stomach
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Body
Lesser Curvature
Lesser Omentum
- Connects to visceral surface of liver
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Greater Curvature
Greater Omentum
- Responsible for fighting infections
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Pylorus
- Pyloric Antrum
- Pyloric Canal
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Layers
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Inner surface - rugae
- Folds allow expansion of stomach
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Small intestine
- Longest part of GIT tract (about 6.7m).
- Main part of enzymatic digestion occurs at small intestine due to presence of enzymes (mostly secreted from pancreas not small intestine).
- Majority of nutrients are absorbed within small intestine.
- The absorption process takes about 3-6 hours
- Has Plica Circularis (Circular folds on the inner surface) to increase surface area, along with villi and microvilli
Duodenum
- Can be further subdivided into 1st, 2nd, 3rd and 4th parts
- Pancreatic enzymes reach small intestine through the 2nd part of duodenum and then it’s mixed with the chyme (partly digested food).
- Receives bile from Liver & Gallbladder
Brunner’s gland in the submucosa is the most significant feature in the duodenum
- It neutralises the acidic medium so that the food is suitable for the rest of the intestine
Jejunum
- About 2.5m long
- Compared to ileum, the mesentery here has less arcades (the curved blood vessels that look like an arc)
- Mesentery has longer vasa recta (the straight blood vessels arising from the arc)
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Ileum
- About 3.5m long
- Mesentery has more arcades (the curved blood vessels that look like an arc)
- Mesentery has shorter vasa recta (the straight blood vessels arising from the arc)
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Layers
Villi
- Increases surface area for absorption
- Crypts are the space between villi
- Paneth cells below villi
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Big intestine
- Identified by Haustrations (bulges and depressions)
- Appendices epiploicae (omental appendices, fat droplets)
- Taeniae coli (long linear muscle along the large intestine)
- Can see on histological image
- Lined by columnar epithelium &
numerous goblet cells to aid movement of food
Caecum
- Ileocecal junction & appendix
Ascending colon
Right Colic Flexure
Transverse colon
Left Colic Flexure
Descending colon
Sigmold colon
- 1 more item...
Appendix
- Extension from the cecum and its function is unknown.
- Receives blood supply from appendicular artery and vein.
- Appendicectomy is the removal of the appendix in case of its inflammation.
- Absence of villi
- Many lymphatic follicles
Appendicitis
- Acute inflammation of the appendix, and is the most common cause for acute, severe abdominal pain.
- The abdomen is most tender at McBurney’s point. This corresponds to the location of the base of the appendix.
- The condition is seen more commonly in older children and young adults, and is uncommon at the extremes of age. The disease is seen more frequently in the West and in affluent societies.
- If the appendix is not removed, it can rupture resulting in peritonitis, which is fatal
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Main Histology Features
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Serosa
- Outermost layer of the gut.
- It is a serous membrane lined by simple squamous epithelium.
- This layer is nothing but visceral peritoneum that covers most parts of the gastrointestinal tract and extends over the abdominal wall to form parietal peritoneum.
- Large blood vessels, lymphatics, and nerve trunk run through serosa
In some places where a peritoneal covering is absent (e.g. thoracic part of the oesophagus, duodenum, etc.) the outermost layer is called Adventitia.
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OSPE
Surface anatomy
Right hypochondrium (RHC)
- Liver and gall bladder
- Duodenum of the small intestine
- Right kidney
- Hepatic Flexure of Colon
Epigastric region
- Liver
- Stomach
- Pancreas
- Duodenum of the small intestines
- Part of spleen
Left hypochondrium (LHC)
- Stomach
- Top of the left lobe of the liver
- Left kidney
- Spleen
- Tail of the pancreas
- Parts of the small intestine
- Transverse colon
- Descending colon
Right lumbar region
- Gallbladder
- Right kidney
- Part of the liver
- Ascending colon.
Umbilical region
- Duodenum, the jejunum, and the ileum.
- Transverse colon
- Bottom portions of both the left and right kidney.
Left lumbar region
- Descending colon
- Left kidney
- Part of the spleen
Right Iliac (Inguinal)
- Appendix
- Cecum
- Right iliac fossa
Pubic (hypogastric) region
- Part of the sigmoid colon,
- Anus
Left Iliac (Inguinal)
- Descending colon
- Sigmoid colon
- Left iliac fossa
Oral CavityFunctions
- Taste sensation.
- Grinding of food through the actions of the teeth, tongue, and palatal surfaces.
- Lubrication by mixing with mucus and saliva.
- Limited digestion of carbohydrates and lipids
Following must work together
- Teeth
- Tongue
- Salivary glands
- Parotid
- Sublingual
- Submandibular
-
Floor covered by thin and vascular layer of mucosa supported by geniohyoid and mylohyoid muscles while the tongue rests on it.
-
-
-
Upper jaw is called as such, and mandible is the lower jaw
Swallow
Buccal phase
- Bolus pushed against hard palate
- Retraction of tongue pushes bolus to oropharynx and assists in raising soft palate, sealing off nasopharynx
- Bolus moves to oropharynx and bolus begins moving to stomach
Pharyngeal Phase
- Bolus comes into contact with palatoglossal arch and palatopharyngeal arch, as well as posterior pharyngeal wall.
- Elevation of larynx and folding of epiglottis directs bolus past the closed glottis
- Uvula and soft palate block passage to nasopharynx
Oesophageal phase
- Pharyngeal muscles forces bolus through entrance of oesophagus
- Bolus pushed to stomach by peristalsis
Bolus Enters Stomach
- Lower oesophageal sphincter opens
- Bolus continues to stomach
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- Serosa covers GIT parts in the peritoneal cavity.
- Adventitia covers GIT parts that are NOT in the peritoneal cavity.
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Aids digestion by mixing the food thoroughly with the stomach juices by "twisting and turning" the stomach
Key Functions of Stomach
- Mechanical digestion
- Due to the presence of three layers of muscles, stomach is able to turn and mix the food into Chyme
- Enzymatic digestion
- Protein digestion by Pepsin which is activated in acidic environment (Chief cells or Zymogenic cells)
- Neutralization of any bacteria by HCL (Hydrochloric acid) (Parietal cells)
- Oesophageal reflux or Heartburn
- Absorption
- Alcohol, sugar, salt, water and drugs
- Container and reservoir for food
- Stomach is distensible due to the presence of rugae and can store the food for up to 4 hours
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Innervation:
- Parasympathetic (from vagus nerve)
- Sympathetic (from celiac plexus)
Drains into the gastric and gastro-omental lymph nodes found at the curvatures that drain in the celiac lymph nodes
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Generally, rectum is similar to colon except for:
- A continuous coat of longitudinal muscle is present.
- There are no taenia coli.
- Peritoneum covers the front and sides of the upper one-third of the rectum; and only the front of the middle third. The rest of the rectum is devoid of a serous covering.
- No appendices epiploicae
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