Case 10- Blood supply Flashcards
The amount of blood that enters the liver
- Arterial blood enters liver (25%) from the heart through the hepatic arteries (oxygen).
- Venous blood enters liver (75%) from the digestive system via the portal veins (nutrients).
The portal system
The portal system has gas exchange with the blood but then will put nutrients in it, so its oxygen poor but nutrient rich. The veins will carry the blood into a portal vein, this will go to the second capillary bed within the liver. There are two capillary beds within the portal system. Within the second capillary bed the nutrients will be removed from the blood. The blood then enters the venules and then the venous system, where it is returned to the heart.
Portal venous system summary
When a capillary bed pools into another capillary bed through a vein without going to the heart first. Both capillary beds and the blood vessels that connect them are considered part of the portal venous system
What forms the portal vein
The superior mesenteric vein (SMV) joins the splenic vein to become the portal vein, under the neck of the pancreas. The inferior mesenteric drains into the splenic vein
Where is the portal vein contained
Within the hepatoduodenal ligament
The portal vein
The hepatic portal vein carries nutrient rich blood to the porta hepatis of the liver. The hepatic portal vein drains into left and right branches. Veins of the digestive organs and the IMV also drain into the portal vein
Portal systemic anastomoses
Connections between the veins of the portal venous and the veins of the systemic venous system.
The 5 portal systemic anastomoses
- Paraumbilical region- between the Paraumbilical veins and the veins of the anterior abdominal wall
- Rectal region- between the superior rectal veins and the inferior rectal veins.
- Oesophageal region- between the oesophageal branch of the left gastric vein and the oesophageal tributaries of the Azygos system.
- Retroperitoneal-between the tributaries of the mesenteric veins and the portal and retroperitoneal veins
- Intrahepatic- within the liver.
Caput medusae
Visible blood vessels. As a result of varices due to portal hypertension. More common in the paraumbilical region
What causes portal hypertension
Disruption to hepatic vasculature, such as a tumour or scarring (cirrhosis), which restricts blood flow. Because the veins don’t have valves in the portal system you get backflow of blood. The blood returns to the systemic system without any of the nutrients being removed. The blood will re-enter the systemic system at the portal systemic anastomoses, through the collateral routes. This shunting of blood into the collateral vessels at the portal systemic anastomoses will cause swollen veins (varices). If the varices rupture they can cause a haemorrhage.
The foregut
Liver, pancreas, gallbladder, spleen, stomach, superior part of the duodenum. Supplied by the Coeliac trunk which arises from T12
Midgut
Rest of the small intestine, part of the large intestine up to 2/3 of transverse colon. Supplied by the superior mesenteric artery which arises from L1
Hindgut
Rest of the large intestine. Supplied by the inferior mesenteric artery which arises from L3
What vessels does the coeliac trunk give off
The Splenic artery (spleen), left Gastric artery (stomach) and the common hepatic artery. The common hepatic artery divides into the left and right common hepatic artery.
What vessels supply the Liver and gallbladder
1) The Liver is supplied by the left and right hepatic arteries
2) The gallbladder is supplied by the cystic artery ( a branch of the right hepatic artery)
3) The hepatic and cystic arteries are derived from the coeliac trunk
The Oesophagus
The oesophagus begins at C6 and runs to T11, it is around 25cm and is a continuation of the Laryngpharynx. Where it enters the stomach is known as the gastro-oesophageal junction. Has longitudinal muscle on the outside and circular muscle on the inside, this helps with peristalsis.
Anatomical constrictions of the Oesophagus
Where the Oesophagus is compressed 1- Junction with pharynx (C6) 2- Where crossed by the aortic arch 3- Where crossed by the left main bronchus 4- At oesophageal hiatus (T10)
Why are the anatomical constrictions important
In accidental poisonings like a child consuming cleaning product, there is more likely to be damage around these areas where the cleaning products move more slowly which will be at the anatomical constrictions
Hiatus hernia
A hiatus hernia is where the stomach pushes through the hiatus into the thorax. Can happen when the diaphragm gets weaker. It goes through the oesophageal hiatus and results in gastric reflux.
Types of Hiatus hernia’s
- Sliding hiatus hernia- when the junction pushes up into the thorax
- Rolling hiatus hernia- the junction stays where it is but the top part of the stomach forces itself into the hiatus.
Anatomical relations to the Oesophagus
- Superior- Continuous with laryngopharynx.
- Inferior- through diaphragm to stomach.
- Posterior- vertebral bodies, more inferiorly it moves left to lie anterior to the abdominal aorta.
- Anterior- in the neck it’s the trachea. In the thorax it’s the arch of aorta, left main bronchus, pulmonary artery and left atrium.
Blood supply to the Oesophagus
- In neck: inferior thyroid artery (from thyrocervical trunk, from subclavian)
- In thorax: branches from thoracic aorta (bronchial and oesophageal branches)
- In abdomen: branches from inferior phrenic (first branch abdominal aorta) and left gastric arteries (from coeliac trunk from abdominal aorta at T12)
Venous drainage of the Oesophagus
- Neck: Inferior thyroid vein
- Thorax: Azygous system (azygous and hemiazygous veins, intercostal and bronchial veins – oesophageal veins drain to these)
- Abdomen: Into hepatic portal venous system via left gastric vein
- Oesphageal blood vessels from above/below diaphragm pass through oesophageal hiatus
Oesophageal varices
When there are problems in the hepatic-portal system like in portal hypertension it will be more difficult to drain the deoxygenated blood into the hepatic portal system. This will make the GI tract more dependent on vessels that drain straight into the portal system like the Azygos system. This can result in portal-systemic anastomoses as more blood then normal is draining through them. Oesophageal varices can cause bleeding when they rupture. These can develop in the Oesopageal veins. This is because it is more distal.
Innervation of the Oesophagus
Supplied by the left and right vagus nerve. The Vagus nerves start dividing rapidly to form the vagus plexus which surrounds the oesophagus. Near the diaphragm the vagus nerves start to condense together forming two distinct nerves, the anterior and posterior vagal trunk. This supplies parasympathetic nerve supply.
Function of the Oesophagus
It conducts food from the oral cavity down to the stomach, it does this through Peristalsis. When we swallow we get subsequent contractions of the pharyngeal constrictor muscles. Prevents passive diffusion of food and bacteria out of the oesophagus as its lined with stratified squamous mucosa
How the Oesophagus prevents gastric reflux:
- Physiological- lower oesophageal sphincter (not a true sphincter), it is a region of higher pressure where the oesophagus and stomach connect preventing gastric reflux. There is unidirectional peristalsis and gastric emptying.
- Anatomical- the sling like fibres of the oesophageal hiatus. The acute angle of the gastro-oesophageal junction (angle of His).
The Stomach
Within the left upper quadrant, under the ribs. It is ‘J shaped’. Contains rugae (folds) allowing stretch
