(2.3) Anatomy - Foregut PDF

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Summary

The digestive tract, peritoneum, greater and lesser omentum, the aorta and the branches supplying the foregut, neurovasculature of the foregut, embryology, clinical imaging, endoscopy, clinical cases....

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(2.3) ANATOMY - Foregut 14 October 2020

14:20

Learning Objectives • Identify the oesophagus, stomach and duodenum in the virtual cadaver • Describe their position with respect to surface landmarks • Identify the internal and external features of these organs • Draw and label the branches of the coeliac trunk • Describe the blood supply of the oesophagus, stomach and duodenum • Distinguish between parietal and visceral peritoneum, and describe its function • Identify the greater omentum, and describe how it is formed

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Component parts of the foregut • Oesophagus • Stomach • Duodenum

Blood supply of the foregut • Branches of the coeliac trunk Innervation of the foregut

Lymphatic drainage of the foregut Peritoneal structures of the foregut • Ligaments/mesenteries/omenta • Greater omentum • Lesser omentum

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The Digestive Tract 14 October 2020

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Digestion begins when food enters the mouth.

In the oral cavity: Teeth = mechanical digestion Salivary glands = chemical digestion

The oral cavity then bifurcates into the trachea (anterior) + oesophagus (posterior) - a fibromuscular tube

The pharynx is separated into 3 cavities - Nasopharynx - Oropharynx - Laryngopharynx

The stomach secretes acid (chemical digestion), muscular contractions (mechanism) The duodenum absorbs nutrients In the large intestine, the waste is starting to be extracted

Rectum = straightening of the tube

Anus = waste is excreted. Controlled by internal and external sphincters.

Separations of the gut Each section is supplied by a different artery Gut tube Supplying artery Foregut

Coeliac trunk (3 branches)

Midgut

Superior mesenteric

Hindgut

Inferior mesenteric

Passage of structures through the diaphragm Inferior vena cava = T9-T10 Oesophagus = T10 Abdominal aorta = T12 this is also where the coeliac trunk originates

Anatomy of the stomach

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• 3 layers of smooth muscles • Epithelia secrete enzymes for chemical breakdown of food + bicarbonate neutralise stomach acid

The duodenum

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Peritoneum 14 October 2020

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What is it? A single layer of flattened mesothelial cells The space between the visceral and parietal peritoneum is known as the peritoneal cavity.

There are no organs in the peritoneal cavity. It is a sterile environment. Containing a peritoneal fluid which acts as a lubricant for peristalsis. The cavity is closed in males and open in females. In females - this space is open as the uterine tubes enter into it - therefore it is open to the external environment.

Intraperitoneal Completely covered by the peritoneum

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Stomach Jejunum Ileum Transverse colon • Sigmoid colon • Liver • Spleen

Peritoneum One piece of continuous sheath that forms around abdominal structure.

Sub peritoneal = below the peritoneum - reproductive organs

Retroperitoneal Organs which have been pushed back by the peritoneum - so they only have peritoneum on their anterior surface

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Ascending colon Descending colon Kidneys Aorta IVC

Restricted movement as held back to posterior wall

• The peritoneum suspends abdominal viscera within the abdominal cavity – Peritoneum reflects from viscera to body wall • The peritoneum connects abdominal viscera to other abdominal viscera i.e. reflects from viscera to viscera • Barriers/restrictions are formed by these connections - prevents spread of infection.

Parietal peritoneum = peritoneum which is NOT on the surface of organs lines the abdominal cavity

Visceral peritoneum = peritoneum on the anterior surface of organs

Mesentery = pinched off part of the peritoneum

The large intestine

The ascending + descending colons are retroperitoneal The transverse + sigmoid colons are intraperitoneal The mesocolon of the transverse and sigmoid colons is the part of the peritoneum which pinches at the edge of these organs. The mesocolon allows these structures to be mobile.

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Greater and lesser omentum 14 October 2020

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The greater and lesser omentum's are reflections (part of) the peritoneum Important terms • Omenta – double layer of peritoneum. Connects abdominal viscera to other viscera • Mesenteries - double layer of peritoneum. Connects abdominal viscera to walls • Ligaments - double layer of peritoneum. Connects abdominal viscera to walls AND other viscera

The greater omentum Starts from the greater curvature of the stomach, travels inferiorly and then comes back up on itself. Whilst doing this, it encapsulates part of the transverse colon - and then pinches off.

The lesser omentum Originates from the lesser curvature of the stomach. It is made up of the hepatogastric ligament (from liver to stomach) and the hepatoduodenal ligament (from liver to duodenum).

There is a small opening in the lesser omentum - which is a result of the rotation of the organs in this.

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Posterior view

There is a small opening in the lesser omentum - which is a result of the rotation of the organs in this.

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The Aorta + its branches suppling the foregut 14 October 2020

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The aorta • Very thick • Elastic • Gives off many branches - to supply all of the body

At the point of the diaphragm, the thoracic aorta becomes the abdominal aorta

Unpaired abdominal arteries

Branch of aorta

Further branches

Organs supplied

Coeliac trunk Splenic artery (supplies organs derived from the foregut)

Spleen Pancreas (tail)

Left gastric artery

Lesser curvature of stomach

Common hepatic artery Liver Gallbladder Pancreas (head) Parts of duodenum Greater curvature of stomach Superior mesenteric artery (supplies organs derived from the midgut)

Duodenum Pancreas Jejunum Ileum Ascending colon 2/3 transverse colon

Inferior mesenteric artery

Last 1/3 transverse colon Descending colon Sigmoid colon Superior 1/3 of rectum

The stomach receives blood supply from all 3 branches of the coeliac trunk

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• The lesser curvature of the stomach is supplied by the R+L gastric arteries • The greater curvature of the stomach is supplied by the R+L gastro-omental arteries

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Complete anatomy questions 1. What region of the stomach does the L gastric artery help to supply? Supplies Lesser curvature 2. What is the relation of the splenic artery to the pancreas? Supplies tail of pancreas 3. What is the relation of the splenic artery to the stomach? The splenic artery branch, the short gastric arteries, supply the fundus and the upper greater curvature of the stomach. 4. Why is the splenic artery tortuous? It lies over the stomach. When the stomach expands - the bendy structure and extra length allow it to move with the stomach and cause no damage.

Cross-sections

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Neurovasculature of the foregut 14 October 2020

16:40

Autonomic innervation of the foregut is either from: • Sympathetic nerves = arise from central parts of the spinal cord = splanchnic nerves • Parasympathetic nerves = arise from inferior parts of the spinal cord OR within the brainstem = vagus nerve

Parasympathetic innervation Arises exclusively from the brain stem

Via the vagus nerve • Large number of branches • Passes through the diaphragm • Enters a collection of cell bodies which lie around a key blood vessel The parasympathetic nerves pass through the coeliac ganglion - however they DO NOT synapse How do the nerves reach their targets? They pass along the branches of the coeliac trunk - supplying the organ - and this is where they synapse

Sympathetic innervation Arise from the spinal cord The sympathetic nerves will give off branches which will go to individual sympathetic chain ganglions - where they will either a) Synapse b) Pass through c) Pass out as another branch They are able to do this as the ganglions are connected via the sympathetic trunk

These branches then give off more branches - known as the thoracic splanchnic nerves (s.n.) • Greater s.n. • Less s.n. • Least s.n. The thoracic s.n. travel towards the coeliac ganglion where they synapse. The postsynaptic axons then continue along the blood vessels to innervate the organs of the foregut.

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Foregut embryology 14 October 2020

Foregut development

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1. Foregut starts as a straight tube 2. As it develops it rotates and expands, becoming the stomach and the first part of the duodenum 3. The ventral and dorsal mesogastrium form

4. As the foregut rotates, the D+V mesogastria rotate with it 5. The VM swings to the R - running along the lesser curvature of the stomach + 1st part of duodenum 6. The DM swings to the L - running along the greater curvature of the stomach + the underside of the duodenum

7. The liver develops in the VM - growing rapidly, pressing against the wall + obliterating the peritoneum on the ventral side - creating a space behind the stomach - the lesser sac. 8. The spleen also develops

3D view - looking from inferior

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Dorsal mesogastrium development

The dorsal mesogastrium hangs down over the transverse colon

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Dr James Nott - video on peritoneum

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Clinical Imaging 17 October 2020

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LO Identify oesophagus, stomach + duodenum in clinical images - x-ray, barium swallow, endoscopy

Oes

• Trachea is anterior to oesophagus • Spine is posterior to oesophagus

Sagittal view

coronal view

x-ray

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Barium swallow • Pt swallows fluid - which appears black on imaging - can spots oesophagus via contrast • Done in real time

Barret's oesophagus

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Endoscopy

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S

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Barium swallow

X-ray (plain film)

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Endoscopy

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Endoscopy 17 October 2020

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Uses a colonoscope/gastroscope/bronchoscope Can be twisted inside of the body Button for gas - inflates the valve + wash lens Can change the stiffness of the tube - making it less stiff to get around bends in the body Tip of the endoscope

Magnetic imager - (scope guide) It is very difficult to know where exactly the endoscope is in the body. Therefore, a magnetic imager acts a 'sat nav' in the body - to tell us where the endoscope is - in real time. After use - the endoscopes are cleaned in a machine.

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Cases 17 October 2020

09:05

Upper GI presentations

Case 1 • 46y/o overweight male • Stomach ulcer - 10yrs ago • Smoker • c/o Epigastric pain - no haemoptysis, no haematemesis (vomiting blood). Heartburn at night. • On physical exam - diaphoretic (sweating), anxious, moderate tenderness in mid epigastric area. No jaundice, no R UQ tenderness - liver/gallbladder N. • Negative blood stool - no GI bleeding • N vital signs - slightly tachycardiac (100bpm)

Unit 10 Week 2 Video 2

Perform an OGD - oesophago-gastric duodenaloscopy

Treatment = Benign appearance - however would take a biopsy

Case 2 • 48 y/o M • Haematemesis - bright red blood • PMH - dyspepsia • Taking tri-therapy for H.Pylori eradication • c/o epigastric discomfort + nausea - 1 week. Black stools (associated with GI bleed). Lightheaded when standing. No palpitations, no SOB. • BP 110/70 (standing), drops to 90/60 (sitting) and 110 pulse (sitting ). Indicates blood volume is not adequate - indicating a bleed. Temp + resp rate N. Perform an OGD

Treatment = use washer to clear up blood clot. Dual therapy - seal blood vessel. Use a metal clip to reduce bleeding. Spray compound - to seal. Main aim - stop bleeding.

Case 3 • 65 y/o F • Brief sxs - dark burgundy stools • Haematemesis • Naso-gastric tube was inserted - showed a continuous flow of red blood - despite gastric lavage (procedure which cleans out the contents of the stomach. As she is still bleeding after this, it shows there is an active bleed). • PMH - high BP, diabetes - takes ASA (aspirin) od prophylactically - can cause gastric irritation • BP 96/60, pulse 120pbm (high), RR 18 (N) • Urgent! Perform an OGD • Blood in stomach

Treatment = a) cauterising bleeding point - using electricity to heat tissue to stop a bleed. b) Injecting adrenaline = vasoconstrictor c) Using a clip d) Sealing compound e) Surgery

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Lower GI presentations Case 1 • F • Blood in stool • Abdo pain Scope inserted into rectum

Diagnosis = possibly IBD - colitis/Chron's disease Take biopsy

Case 2 • Polyps present in colon • Use cauterisation to remove head from the stalk - as this could develop into cancer On some occasions, when this is done, bleeding occurs as a blood vessel may exist in the stem of the polyp. Can then use an electric portery probe to seal up the area of the bleed. • Use forceps to collect the head - take for biopsy

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