Anatomy of the Alimentary system 1 - Lecture 9

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1

Describe and identify the regions of the stomach, including that cardia, funds, body, pyloric part and its subdivisions

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Anterior relation

  • Liver and diaphragm

Posterior relation

  • omental bursa
  • structures of stomach bed

Cardia

  • Where oesophageal sphincter is located - food enters
  • Below the z-line of the gastro-oesophageal junction
    • Epithelium from stratified squamous to columnar
  • Fairly fixed region

Fundus - often filled with gas

  • Superior curvature of the organ
  • Above gesture-oesophageal junction

Body

  • Main central region

Pylorus - thicker region

  • Antrum
    • Bottom of stomach, proximal to pyloric sphincter
    • Can by shut off by pre pyloric sphincter
  • Canal
    • Opening between stomach and duodenum
  • Sphincter
    • Pyloric spincter
    • Level of transpyloric plane

2 curvatures present

  • Greater - on lateral border
  • Lesser - on medial border, made by oesophagus and proximal duodenum

2 notches

  • Cardiac - notch between oesophagus and fundus
  • Angular - notch in lower part of the lesser curvature
2

Describe the internal features of the stomach including its secretions

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Rugae ar internal longitudinal folds

  • When stomach distends these rugae disappear

Gastric emptying is regulated by its distension and endocrine secretions

Secretions

Fundus

  • Mucous neck cells - mucus gel layer
  • Parietal cells - HCl and intrinsic factor
  • Chief cells - Pepsinogen and gastric lipase
  • Endocrine cells - gastrin, CCK, secretin, histamine, serotonin

Cardia

  • Mucous neck cells
  • Endocrine cells

Pylorus

  • Mucous neck cells
  • Endocrine cells
3

Outline the regions of the gut including the fore, mid and hind gut, and how the regions are divided

The regions are divided based upon arterial supply

Foregut - Supplied by Coeliac trunk

  • Oesophagus
  • Stomach
  • Duodenum - to just below greater duodenal papilla
    • Opening of the pancreatic duct
  • Organs that develop in mesentaries
    • Liver
    • Pancreas
    • Gall bladder
    • Spleen

Midgut - Supplied by Superior Mesenteric Artery

  • Duodenum - from just below greater duodenal papilla
  • Jejunum
  • Ilieum
  • Caecum
  • Appendix
  • Ascending Colon
  • Right 2/3 of Transverse Colon

Hindgut - Supplied by Inferior Mesenteric Artery

  • Left 1/3 of Transverse Colon
  • Descending Colon
  • Sigmoid Colon
  • Rectum
  • Most of Anal Canal
4

Describe the greater omentum as a peritoneal attachment of the stomach

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The greater and the lesser omentum are folds of peritoneum that connect the stomach to other abdominal organs

Greater omentum

  • Double fold attached to the greater curvature of the stomach and 1st part of duodenum
  • Continuous with gastrosplenic ligament
    • Attaches stomach and spleen
  • Attached to Transverse Mesocolon

Appearance

  • Covers anterior surface of most abdominal organs though does not adhere
  • Mesothelium present on anterior and posterior surface
    • Shiny mesothelial contains fatty patches
    • Grainy appearance with translucent fat free regions
  • Accumulations of macrophages that form opaque 'milk spots' in unembalmed tissue

Development

  • Initially a 'bag-like' structure
  • Inner layers of mesothelium fuse to give single structure

Function

  • Protective via macrophages and other immune cells
  • Adheres to peritoneal damage and inflammation

Blood supply

  • R.Gastroepiploic vessels
    • Branch of gastroduodenal artery from the common hepatic artery from the coeliac trunk
  • L.Gastroepiploic vessel
    • Largest branch of splenic artery from the coeliac trunk
  • Both anastomose within the two layers of the anterior greater omentum along the greater curvature of the stomach
5

Describe the lesser omentum as a peritoneal attachment of the stomach

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Peritoneum that extends from lesser curvature of the stomach and 1st part of duodenum to posterior surface of liver

Where it attaches to the the stomach, between layers of the omentum run the L. and R. gastric arteries and veins

Free edge

  • Two layers are continuous on the R.border and form a free edge (not attached laterally)
  • Extends from duodenum to posterior liver
  • Hepatic artery, portal vein, lymph vessels, nerves and bile duct run through lesser omentum to the L. of the free edge
6

Describe what is meant by the Lesser Peritoneal Sacs/Omental Bursa

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Lesser Sac/Omental bursa

  • Cavity in the abdomen that is formed by the greater and lesser omentum
    • Posterior to stomach and lesser
  • Connected to the Greater sac by the omental foramen
    • Opening behind free edge of lesser omentum
  • Can contain considerable amounts of fat
  • Allows for movement and expansion of the stomach
7

Describe what is meant by the Greater Sac

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General cavity of the abdomen/peritoneum of the peritoneal cavity proper

Cavity inside peritoneum but outside lesser sac

Bounded by portal triad

  • Hepatic artery
  • Portal vein
  • Common Bile duct
8

Describe the stomach bed in terms of peritoneal sacs

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Posterior wall behind the omental bursa (behind the stomach)

Includes retroperitoneal structures

  • Upper pole of L.kidney
  • L.suprarenal
  • Diaphragm
  • Part of spleen
  • Pancreas
  • Part of transverse mesocolon
  • Splenic Artery
  • Splenic Flexture of the colon
9

Give a brief outline of the microstructure of alimentary tract proper, oesophagus to anus

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Mucosa

  • Epithelium
  • Glands
  • Lamina propria
  • Muscularis mucosa

Submucosa

  • Connective Tissue

External muscle

  • Inner circular
  • Outer longitudinal

Adventitia

  • Retroperitoneal organs

Serosa

  • Intraperitoneal organs
10

Describe the location and relationship of the oesophagus in the body

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Originates C6 - top of trachea

Descends through superior and posterior mediastinum

Descends through diaphragm 2-3cm from midline at T10 (posterior to central tendon)

Descends through R.crus to enter cardia of stomach at T11

Mediastinal relationships

  • Posterior to trachea - joins by fibroelastic membrane against tracheal muscle
  • Lateral then anterior to aorta
  • Anterior to vertebral column
  • T5 to inferior it is medial to thoracic duct, azygous and descending aorta
11

Describe features of the oesophagus, indulging its innervation, its walls and its attachments

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Oesophageal walls

  • Stratified non-keratised squamous epithelium
  • Mucous-secreting oesophageal glands in the submucosa
  • Oesophageal cardiac glands in the lamina propria
  • Outer Longitudinal and Inner Transverse muscles are separated by the myenteric plexus

Innervation

  • R. and L.vagus form a plexus which forms the R. and L. vagal trunks which descend through the diaphragm with the oesophagus into the lower abdomen

The abdominal oesophagus

  • ~1cm long
  • Runs in the groove on the posterior surface of the liver
  • Attached posteriorly to the diaphragm by the gastrophrenic ligament
    • Also attached to funds of stomach
12

Describe the venous drainage and arterial supply of the oesophagus

...

13

Identify and describe the contractions that occur along the oesophagus

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4 main constrictions due to the compression on the oesophagus by other structures

  1. At start where pharynx joins behind the cricoid cartilage = circopharyngeus
    • Only complete cartilage rig around trachea
  2. Level of arch of aorta as it crosses in front
  3. Level of the L.main bronchus as it passes in front
  4. Level of the diaphragm = oesophageal hiatus
    • Specialised circular muscle in the diaphragm wall acts as a lower sphincter
    • Maintained tone by myenteric plexus, relaxes during swallowing and vomiting
    • Muscle on R.crus forms external sphincter - tightens in inspiration or when intra-abdominal pressure increases
14

Identify and describe the oesophageal sphincters

...

15

Outline in general terms the dorsal and ventral mesenteries and related structures and relate them to embryological development

Early development

  • Entire abdominal gut tube was attached to the posterior body wall by the dorsal mesentary
  • Stomach and 1st part of duodenum are attached to the anterior body wall by the ventral mesentary

Ventral mesentary

  • Liver, biliary system and ventral pancreas
  • Anterior to the liver forms the liver supporting structure, the falciform ligament
  • Between the liver anteriorly and the stomach posteriorly will form the lesser omentum

Dorsal mesentary

  • Attaches abdominal organs to posterior wall
  • Forms mesentery, mesoappendix, transverse mesocolon and sigmoid mesocolon
  • Dorsal pancreas and spleen for within
  • Regions destined to be retroperitoneal it fuses with posterior wall (fixation of the intestines)

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