8.1 - Anatomy: Overview of the Digestive Tract Flashcards
What does the digestive tract consist of? (8)
What are the accessory organs of digestion? (6)
Digestive tract: mouth, pharynx, oesophagus, stomach, small intestine, large intestine and rectum.
Accessory organs of digestion: teeth, tongue, salivary glands, liver, gallbladder and pancreas.
- What does the oesophagus connect?
- Where does it originate and extend to?
- At what spinal level does it pass through the diaphragm? What hole?
Oesophagus
- Muscular tube that conveys food from pharynx to stomach.
- It originates at the inferior border of the cricoid cartilage (C6) and extends to the cardiac orifice of the stomach (T11).
- Passes through the diaphragm at T10 via oesophageal hiatus.
- ~25cm long
What is the structure of the esophagus?
What are the 4 physiological constrictions of the esophagus (anatomical relations)?
The anatomical relations of the oesophagus give rise to four physiological constrictions in its lumen – it is these areas where food/foreign objects are most likely to become impacted. They can be remembered using the acronym ‘ABCD‘:
- Arch of aorta
- Bronchus (left main stem)
- Cricoid cartilage
- Diaphragmatic hiatus
What is the vasculature of the esophagus?
Cervical part: inferior thyroid artery.
Thoracic part: oesophageal branches of descending aorta.
Abdominal part: oesophageal branches of the left gastric artery and the inferior phrenic artery.
Thoracic
The thoracic part of the oesophagus receives its arterial supply from the branches of the thoracic aorta and the inferior thyroid artery (a branch of the thyrocervical trunk).
Venous drainage into the systemic circulation occurs via branches of the azygous veins and the inferior thyroid vein.
Abdominal
The abdominal oesophagus is supplied by the left gastric artery (a branch of the coeliac trunk) and left inferior phrenic artery. This part of the oesophagus has a mixed venous drainage via two routes:
- To the portal circulation via left gastric vein
- To the systemic circulation via the azygous vein.
What is the innervation of the esophagus?
Esophagus - Innervation
The oesophagus is innervated by the oesophageal plexus, which is formed by a combination of the parasympathetic vagal trunks and sympathetic fibres from the cervical and thoracic sympathetic trunks.
Two different types of nerve fibre run in the vagal trunks. The upper oesophageal sphincter and upper striated muscle is supplied by fibres originating from the nucleus ambiguus. Fibres supplying the lower oesophageal sphincter and smooth muscle of the lower oesophagus arise from the dorsal motor nucleus.
What is the lymphatic drainage of the esophagus?
Lymphatics
The lymphatic drainage of the oesophagus is divided into thirds:
- Superior third – deep cervical lymph nodes.
- Middle third – superior and posterior mediastinal nodes.
- Lower third – left gastric and celiac nodes.
3 clinical significances of the esophagus?
- Barrett’s oesophagus refers to the metaplasia (reversible change from one differentiated cell type to another) of lower oesophageal squamous epithelium to gastric columnar epithelium. It is usually caused by chronic acid exposure as a result of a malfunctioning lower oesophageal sphincter.
- Esophageal varices - portal hypertension
- Esophageal carcinoma
What are the 4 parts/main anatomical divisions of the stomach?
What is the transpyloric plane? What level is it at?
- Cardia – surrounds the superior opening of the stomach at the T11 level.
- Fundus – the rounded, often gas filled portion superior to and left of the cardia.
- Body – the large central portion inferior to the fundus.
- Pylorus – This area connects the stomach to the duodenum. It is divided into the pyloric antrum, pyloric canal and pyloric sphincter. The pyloric sphincter demarcates the transpyloric plane at the level of L1.
What are the greater and lesser curvatures of the stomach?
- Which arteries supply each curvature?
- Which ligament is the lesser curvature attached to?
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Greater curvature – forms the long, convex, lateral border of the stomach.
- Arising at the cardiac notch, it arches backwards and passes inferiorly to the left.
- It curves to the right as it continues medially to reach the pyloric antrum.
- The short gastric arteries and the right and left gastro-omental arteries supply branches to the greater curvature.
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Lesser curvature – forms the shorter, concave, medial surface of the stomach.
- The most inferior part of the lesser curvature, the angular notch, indicates the junction of the body and pyloric region.
- The lesser curvature gives attachment to the hepatogastric ligament and is supplied by the left gastric artery and right gastric branch of the hepatic artery.
What is the gastrohepatic ligament?
- What does it connect?
- Functions?
- Contents?
- What is the lower end continuous with?
What are the 2 sphincters of the stomach?
- What marks the transition point between the esophagus & stomach?
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Inferior Oesophageal Sphincter
The oesophagus passes through the diaphragm through the oesophageal hiatus at the level of T10. It descends a short distance to the inferior oesophageal sphincter at the T11 level which marks the transition point between the esophagusand stomach (in contrast to the superior oesophageal sphincter, located in the pharynx). It allows food to pass through the cardiac orifice and into the stomach and is not under voluntary control.
Pyloric Sphincter
The pyloric sphincter lies between the pylorus and the first part of the duodenum. It controls of the exit of chyme (food and gastric acid mixture) from the stomach.
In contrast to the inferior oesophageal sphincter, this is an anatomical sphincter. It contains smooth muscle, which constricts to limit the discharge of stomach contents through the orifice.
Emptying of the stomach occurs intermittently when intragastric pressure overcomes the resistance of the pylorus. The pylorus is normally contracted so that the orifice is small and food can stay in the stomach for a suitable period. Gastric peristalsis pushes the chyme through the pyloric canal into the duodenum for further digestion.
What is the vasculature of the stomach?
Stomach: right and left gastric arteries (anastomose along lesser curvature) and right and left gastro-omental arteries (anastomose along greater curvature).
Arterial Supply
- The arterial supply to the stomach comes from the celiac trunk and its branches. Anastomoses form along the lesser curvature by the right and left gastric arteries and along the greater curvature by the right and left gastro-omental arteries:
- Right gastric – branch of the common hepatic artery, which arises from the coeliac trunk.
- Left gastric – arises directly from the coeliac trunk.
- Right gastro-omental – terminal branch of the gastroduodenal artery, which arises from the common hepatic artery.
- Left gastro-omental – branch of the splenic artery, which arises from the coeliac trunk.
The veins of the stomach run parallel to the arteries. The right and left gastric veins drain into the hepatic portal vein. The short gastric vein, left and right gastro-omental veins ultimately drain into the superior mesenteric vein.
What is the parasympathetic & SNS innervation of the stomach?
- Parasympathetic nerve supply arises from the anterior and posterior vagal trunks, derived from the vagus nerve.
- Sympathetic nerve supply arises from the T6-T9 spinal cord segments and passes to the coeliac plexus via the greater splanchnic nerve. It also carries some pain transmitting fibres.
Which omenta connect to the stomach?
2 Clinical Significances of the stomach?
- GORD
- Hiatus Hernia - when a part of the stomach protrudes through the esophageal hiatus of the diaphragm into the chest