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
Function of the Stomach
Begins to break down food and store for release in the duodenum
Structure of the stomach
- Greater/lesser curvature- where greater/lesser omentum attaches, where vessels/anastomoses are.
- Cardia – region where oesophagus enters.
- Fundus – most superior part.
- Pyloric region – divided into antrum and canal – just before opening to duodenum. Contains pyloric sphincter, responsible for controlling release of food into duodenum. The Pyloric canal is the final part of the stomach before the pyloric sphincter.
Pyloric sphincter
Strong muscles which control the emptying of the stomach
Borders of the stomach
- Superior- Oesophagus and diaphragm
- Inferior- rest of GI tract
- Anterior- greater omentum and abdominal wall, left lobe of liver
- Posterior- left kidney, spleen, pancreas and blood vessels (abdominal aorta, IVC, superior mesenteric artery and vein)
Function of the stomach
- Controlled release of ingested food to the duodenum. Moves food to small intestine at a suitable rate.
- Mixing- mixes food with gastric secretions to form chyme. Contracts and churns food, it emulsifies food ready for the duodenum. Gastric secretions include: acid, pepsinogen (proenzyme for pepsin which breaks down protein), intrinsic factor (needed for absorption of B12).
- Storage- reservoir of ingested food, stores until can move to duodenum.
Duodenum
It is located in the first part of the small intestine. It is a C-shaped structure that continues from the stomach, it is close to the head of the Pancreas. Located at L1-L3. The last part of the Duodenum is the duodenojejunal flexure.
The duodenojejunal flexure
The border between the duodenum and the jejunum. It is peritoneum which is suspended from the suspensory ligament of the duodenum
Duodenal papillae
In the descending part of the duodenum. It is where the bile and pancreatic ducts enter into the duodenum. Contains the major and minor papillae. The minor papillae is where the accessory pancreatic duct drain. The major papillae is where the bile duct and pancreatic duct drain
Spleen
It is in the upper left quadrant between ribs 9 and 11. It is posterior to the stomach at the tail of the Pancreas. It is protected by the ribs due to the strong blood supply, because when they rupture it is very dangerous. Just below the diaphragm.
Structure of Spleen
1) Hilum- where blood vessels enter (splenic artery)
2) The posteromedial and inferior borders are smooth, whilst the anterior and superior borders contain notches
3) Superior and inferior pole
Splenomegaly
In enlargement of the spleen (known as splenomegaly), the superior border moves inferomedially, and its notches can be palpated. Causes of splenomegaly can be liver disease, leukemia, acute or chronic infection.
Functions of spleen
- Filters RBCs (removes/recycles old/damaged)
- It is a secondary lymphoid organ and is the site for maturation and storage of T and B lymphocytes, playing an important role in the synthesis of immunoglobulin G (IgG) by mature B-lymphocytes upon interaction with the T-lymphocytes.
Can you remove the Spleen
Yes- but leaves you more open to infection
The 3 major branches of the Coeliac trunk
The Common hepatic artery (liver), the Left gastric artery (stomach) and the Splenic artery (spleen).
Blood supply to the Spleen
Splenic artery
The 5 arteries that supply the stomach
Left gastric artery, right gastric artery, left gastro-omental/gastroepiplotic artery, right gastro-omental/gastrepiploic artery and the short gastric arteries. These are all branches of the coeliac trunk.
Left gastric artery
A direct branch of the coeliac trunk. Runs around the lesser curvature of the stomach. Gives off branches that supply the Oesophagus. Supplies the lesser curvature of the stomach.
Right gastric artery
Branch of proper hepatic which is a continuation of the common hepatic artery. Supplies lesser curvature of stomach, anastomosing with the left gastric artery
Left gastro-omental artey
Branch of the splenic artery, it supplies the greater curvature of the stomach which is where the omentum attaches.
Right gastro-omental artery
A branch of the gastroduodenal artery which is a branch of the common hepatic artery. Supplies the greater curvature of the stomach, anastomoses with the left gastro-omental artery
Short gastric artery
Branches of the splenic artery. It supplies the fundus of the stomach.
Venous drainage of the stomach
The veins mirror the arteries, all ultimately drain into the hepatic portal vein.
• Right gastro-omental vein – drains to superior mesenteric vein
• Short gastric vein and left gastro-omental vein – drain to splenic vein
•Splenic and superior mesenteric veins join to form the hepatic portal vein
• Left and right gastric veins – drain to hepatic portal vein
Blood supply to the duodenum
The Duodenum marks the transition from foregut to midgut. So, the duodenum is supplied by branches of both the coeliac trunk and the superior mesenteric artery.
Duodenum- Coeliac trunk
1) The right gastric artery
2) The right gastro-omental artery
3) Branches of the Gastroduodenal artery. The Gastroduodenal artery gives rise to the anterior and posterior superior pancreaticodudoneal arteries.
Duodenum- Coeliac trunk
The arteries that supply the duodenum from the coeliac trunk are the right gastric artery, the right gastro-omental artery and branches of the Gastroduodenal artery. The Gastroduodenal artery gives rise to the anterior and posterior superior pancreaticodudoneal arteries.
Duodenum- Superior mesenteric artery
The arteries that supply the duodenum from the SMA are both the anterior and posterior branches of the inferior pancreaticoduodenal artery.
Duodenum- Venous drainage
- Superior & inferior pancreatic duodenal veins
- Superior –> portal vein
- Inferior –> superior mesenteric vein
Blood supply to the Pancreas
In the foregut and midgut so is supplied by the Coeliac trunk and SMA
Pancreas- Coeliac trunk
1) Splenic artery
2) The Gastroduodenal artery gives rise to the anterior and posterior branches of the superior pancreaticoduodenal artery
Pancreas- SMA
The anterior and posterior branches of the inferior pancreaticoduodenal artery
Functions of the GI tract
- Oesophagus- passage of food, friction
- Stomach- mechanical and enzymatic
- Small intestine- Enzymatic and absorption
- Large intestine- absorbs water and storage function
Salivary glands
There are three main glands producing a mixture of serous and mucous secretions from serous cells and mucous cells.
Submandibular glands
70% of total salivary flow, it is a 4:1 ratio of serous:mucous
Parotid glands
25% of total salivary flow, it is a 20:1 ratio of serous:mucous
Sublingual glands
5% of total salivary flow, it is a 3:1 ratio of serous:mucous.
Salivary duct structure
It contains a main duct which branches into Lobar ducts which then branches into interlobular ducts and then striated ducts (ionic modification) and finally intercalated ducts. Contains an acinus which is a small cavity surrounded by secretory cells. In the acinus there is a serous demilune as the end of the mucous tubule which secretes mucus containing antimicrobial lysozyme’s. The Acinus cells drain into the intercalated ducts. Each lobe of the gland is made of lots of different lobues.
Salivary duct- Acinus cells
Surrounded by a basement membrane, made of Myoepithelial cells
Salivary ducts- Intercalated ducts
Made of low cuboidal epithelium
Salivary ducts- Striated ducts
Made of cuboidal to columnar epithelium
Salivary ducts- Intralobular ducts
Made of cuboidal to columnar epithelium
Salivary ducts- Interlobular ducts
Made of pseudostratified columnar epithelium
Salivary ducts- Lobar ducts
Made of columnar stratified epithelium
