12. Alimentary Tract (Part 2) Flashcards
(153 cards)
1
Q
Summarise the 9 regions of the abdomen and the lines they are formed by.
A
- Transpyloric plane -> Horizontal line located midway between the suprasternal notch and the upper border of the pubic symphysis, approximately at the level of the lower border of the L1 vertebral body.
- Transtubercular plane -> Horizontal line located midway between the transpyloric plane and the upper border of the pubic symphysis, corresponding to the level of the iliac tubercles and the L5 vertebral body.
- Mid-clavicular lines
2
Q
Draw the 4 quadrants of the abdomen.
A
These quadrants are created by a vertical line along the mid-line, passing from the xiphoid process to the pubic symphysis, and a horizontal line passing through the umbilicus.
3
Q
Summarise what pain in each of the four quadrants of the abdomen may indicate.
A
4
Q
What is the peritoneal cavity?
A
- A potential space found between the parietal and visceral layers of the peritoneum.
- The smooth layers of the peritoneum permit free movement between the abdominal viscera and abdominal walls.
- Think of the peritoneum as the abdominal/pelvic equivalent of the pleura of the lungs or the pericardium of the heart
5
Q
What are the two types of peritoneum?
A
- Parietal peritoneum -> Lines the internal surface of the abdominopelvic wall and underside of the diaphragm.
- Visceral peritoneum -> Covers the outer surface of many organs and suspends them from the abdominopelvic wall.
6
Q
What is mesentery?
A
- A double layer of visceral peritoneum that suspends intra-peritoneal organs from the posterior abdominal wall.
- Blood vessels and nerves run within the mesentery to supply the intra-peritoneal organs.
7
Q
Summarise the innervation to the parietal and visceral peritoneum.
A
Innervation of the parietal and visceral peritoneum follows the same pattern as the pleura:
- Parietal peritoneum -> Innervated by the somatic segmental nerves innervating the skin of the abdominal wall, so sensation, including pain, pressure and temperature, is well localised.
- Visceral peritoneum -> Shares the same autonomic innervation as the viscera it surrounds. Sensitive to stretch and chemical irritation only, which is poorly localised.
8
Q
What is the transverse mesocolon?
A
The mesentery that suspends the transverse colon from the posterior abdominal wall.
9
Q
What is the sigmoid mesocolon?
A
- The mesentery that suspends the sigmoid colon from the posterior abdominal wall.
- Located within the left iliac fossa.
10
Q
What is the meso-appendix?
A
A tiny piece of mesentery attaching the appendix to the posterior abdominal wall.
11
Q
What is the retroperitoneum?
A
The organs that sit behind the parietal peritoneum and are therefore not entirely encased by peritoneum are described as retroperitoneal.
12
Q
What are primary and secondarily retroperitoneal organs?
A
- Primary retroperitoneal organs are those that developed and subsequently remained within the retroperitoneum.
- Secondarily retroperitoneal organs are those that developed initially within the intra-peritoneal compartment before retracting back to the posterior abdominal wall and the retroperitoneum before birth.
13
Q
What are the retroperitoneal organs?
A
The mnemonic “SADPUCKER” can be used:
- S = Suprarenal (adrenal) glands
- P = Pancreas (except tail)
- K = Kidneys
- A = Aorta/IVC
- U = Ureters
- E = (o)Esophagus
- D = Duodenum (2nd and 3rd parts)
- C = Colon (ascending & descending)
- R = Rectum
14
Q
What are the secondarily retroperitoneal organs?
A
Ascending and descending colon
15
Q
What is the greater and lesser sac of the peritoneal cavity?
A
The peritoneal cavity can be divided into the greater and lesser peritoneal sacs:
- The greater sac comprises the majority of the peritoneal cavity.
- The lesser sac (also known as the omental bursa) is smaller and lies posterior to the stomach and lesser omentum.
16
Q
Draw the position of the greater and lesser sacs of the peritoneal cavity in the axial section?
A
17
Q
Describe the position of the lesser sac and how it connects to the greater sac.
A
- Located behind the stomach
- Opens into the greater sac via the epiploic foramen (foramen of Winslow)
18
Q
A
19
Q
What are the two main compartments of the greater sac of the peritoneal cavity?
A
- Supracolic compartment -> Located superior to the transverse mesocolon and contains the stomach, spleen and liver.
- Infracolic compartment -> Located inferior to the transverse mesocolon and contains the small bowel loops, ascending and descending colon.
20
Q
What is the epiploic foramen?
A
The foramen connecting the greater and lesser sacs of the peritoneal cavity. It is found posterior to the stomach.
21
Q
A
22
Q
What are the pieces of mesentery in the peritoneal cavity you need to know?
A
- Small bowel mesentery
- Meso-appendix
- Transverse mesocolon
- Sigmoid mesocolon
23
Q
What are the peritoneal pouches?
A
The reflection of the parietal peritoneum onto the superior surfaces of the pelvic organs (bladder, uterus), creates pouches either side of these organs in which fluid can collect.
In males:
- Recto-vesical pouch -> Between the posterior surface of the bladder and the anterior surface of the inferior of rectum.
In females:
- Vesicouterine pouch -> Between the posterior surface of the bladder and the anterior surface of the uterus, descending adjacent to the anterior fornix of the vagina.
- Rectouterine pouch -> Between the posterior surface of the uterus and the anterior surface of the rectum.
24
Q
Describe gas under the diaphragm.
A
- Gas contained within the peritoneal cavity is called pneumoperitoneum.
- This is often caused by serious problems within the abdomen, including perforated bowel (due to conditions such as peptic ulcer disease, bowel obstruction, ischaemia, diverticulitis).
- It may also be caused by gas injected into the abdomen during operations.
- The gas is clearly seen on erect chest X-rays, where it collects under the domes of the diaphragm. Here, the gas collects between the parietal peritoneum of the abdominal wall and the visceral peritoneum covering the surface of the liver
25
What is the greater omentum? What are the important relations?
* A large, fatty fold of peritoneum that hangs from the greater curvature of the stomach to cover the anterior abdominal viscera like an apron.
* The greater omentum inserts into the transverse colon at its distal end.
* The greater omentum functions to isolate regions of infection and inflammation within the abdomen by wrapping around and sticking to affected areas.
26
What is the lesser omentum? What are the important relations?
* A smaller fold of peritoneum that runs from the lesser curvature of the stomach to the inferior edge of the liver.
* The free edge of the lesser omentum contains the portal triad of vessels: proper hepatic artery, common bile duct and the hepatic portal vein.
* Also forms the anterior border of the epiploic foramen.
27
What vessels does the lesser omentum contain?
The portal triad of vessels:
* Proper hepatic artery
* Common bile duct
* Hepatic portal vein
28
Describe the passage of the oesophagus.
* In the neck, the oesophagus follows the curve of the vertebral column, between the trachea and the vertebral bodies.
* Passes within the posterior mediastinum (**behind the heart**), anterior to the descending aorta, to the diaphragm.
* Enters the abdomen through the oesophageal hiatus of the **right crus of the diaphragm** just to the left of the mid-line, at the level of T10.
* It then has a short course in the abdomen to the gastro-oesophageal sphincter
29
Where does the oesophagus pass through the diaphragm?
* Right crus of the diaphragm just to the left of the mid-line.
* At the level of T10.
30
What types of muscle make up the oesophagus?
* Upper 1/3rd -\> Voluntary striated muscle
* Middle 1/3rd -\> Mix of striated and smooth muscle
* Lower 1/3rd -\> Smooth muscle
31
What are the three constriction points in the oesophagus?
1. Upper oesophageal sphincter – a constriction at the oesophageal origin, formed by the cricopharyngeus muscle.
2. Thoracic constrictions – two constrictions caused by the crossing of the aortic arch and the left main bronchus across the anterior surface of the oesophagus.
3. Lower oesophageal sphincter (diaphragmatic constriction) – after a short 1.25cm abdominal course, the oesophagus terminates at the cardial orifice of the stomach. The musculature of the diaphragm and acute angle of the oesophagus immediately above this gastro-oesophageal junction creates a physiological sphincter that can prevent reflux of gastric contents into the oesophagus.
32
33
Describe the arterial supply to the oesophagus.
* Thoracic part -\> Oesophageal arteries, arising from the thoracic aorta
* Abdominal part -\> Left gastric and left inferior phrenic artery
34
Describe the venous drainage of the oesophagus.
The inferior part of the oesophagus is drained by two venous systems:
* Portal circulation -\> Via the left gastric vein to the hepatic portal vein.
* Systemic circulation -\> Via the azygos vein to the superior vena cava.
These two connected venous systems create a porto-systemic anastomosis, which can become problematic in cases of portal hypertension.
35
The lower oesophageal veins connect the ... and ... veins.
Azygos and gastric
(This is a portal-systemic anastomosis that can become problematic in cases of portal hypertension)
36
Describe oesophageal varices.
* The presence of the porto-systemic anastomosis at the base of the oesophagus creates an intrinsic link between the pressures of the portal and systemic venous systems.
* In cases of portal hypertension, caused as a result of hepatic portal vein thrombosis and **liver cirrhosis**, the raised portal pressure is transferred into the systemic venous system, which cannot accommodate such increases in pressure.
* This causes the anastomotic venous system to distend and thin (oesophageal varices).
* These varices are prone to rupture, which can result in significant blood loss into the GI tract.
* Following rupture, the aim is to stop the bleeding through either endoscopic banding or injection of sclerotherapy to trigger venoconstriction.
* Once stabilised, the portal hypertension can be treated with the insertion of a transjugular intrahepatic porto-systemic shunt, relieving the pressure within the portal vein.
37
What are the different parts of the stomach?
* Fundus
* Body
* Pyloric region -\> Antrum, Canal, Sphincter
38
Where is the transpyloric plane?
* Halfway between the jugular notch and the superior border of the pubic symphysis.
* This is approximately at the level of the L1 vertebral body.
39
What structures are found in the transpyloric plane?
* Pylorus
* Root of transverse mesocolon
* Duodenum (D1)
* Gallbladder fundus
* Duodeno-jejunal flexure
* Hila of kidneys
* Hepatic and splenic flexures of colon
* 9th costal cartilage
* Neck of pancreas
* Origin of the SMA
* Termination of the spinal cord
40
Describe the innervation of the stomach.
* The stomach’s embryonic origin as a foregut structure means it is supplied by branches of the coeliac trunk and innervated by the coeliac plexus of nerves.
* Parasympathetic innervation to the stomach is supplied by the anterior and posterior vagal trunks of the vagus nerve.
* The sympathetic supply is supplied by the coeliac plexus, which receives input from T6-T9 nerve roots via the greater splanchnic nerve.
41
Describe the arterial supply to the stomach.
* Right gastric artery -\> From the common hepatic artery.
* Left gastric artery -\> From the coeliac trunk.
* Right gastro-omental artery -\> From the gastroduodenal artery, itself a branch of the common hepatic artery.
* Left gastro-omental artery -\> The largest branch of the splenic artery.
* Short gastric arteries -\> Small branches of the splenic artery.
42
Describe the venous drainage of the stomach.
Via veins running in parallel with the arteries, which ultimately converge on the hepatic portal vein.
43
At what level is the cardia of the stomach typically found?
T11
44
What are the relations of the greater and lesser omentum to the stomach?
* Greater omentum:
* Connects the greater curvature of the stomach with the transverse colon
* Lesser omentum:
* Connects the lesser curvature of the stomach to the porta hepatus and ductus venosus of the liver
* The free edge of the lesser omentum contains within it the common bile duct, hepatic artery and hepatic portal vein, forming the portal triad.
45
What is a hiatus hernia?
* Hiatus hernias occur when the viscera of the abdomen pushes into the thoracic cavity through the oesophageal hiatus of the diaphragm.
* This most commonly occurs in older patients, due to progressive weakening of the hiatus.
* Hernias may also result from congenital abnormalities of the diaphragm.
* Hiatus hernias are usually asymptomatic, but can cause chest pain, bloating and difficulty swallowing.
* Treatment is usually focused on relieving symptoms, but in severe cases, the defect may be surgically repaired.
46
What is pyloric stenosis?
* A relatively common condition seen in neonates where the circular muscle surrounding the outflow tract of the stomach (pyloric sphincter) becomes thickened.
* This results in obstruction of the outflow tract and forceful contractions of the stomach, which attempts to force ingested food through the stenosed orifice.
* Classically, newborns experience non-bloody projectile vomiting after most feeds, leading to poor weight gain, lethargy and malnutrition.
* Pyloric stenosis can be surgically treated with a Ramstedt’s procedure, in which the muscle is divided to open the outlet.
47
What are the different parts of the duodenum?
* D1 (superior part): 5cm proximal part, arising from the pylorus of the stomach, passing laterally to the right, before curving sharply inferiorly.
* D2 (descending part): passes from D1 to the inferior border of the L3 vertebral body, before turning sharply medially. The major duodenum papilla, into which the contents of the ampulla of Vater drains through (bile and pancreatic enzymes, via the common bile duct and pancreatic duct), is found in the wall of D2. The major duodenal papilla is surrounded by a muscular sphincter of Oddi, which controls the entry of these fluids into the duodenum.
* D3 (horizontal part): passes transversely to the left, crossing the mid-line.
* D4 (ascending part): passes superiorly until reaching the inferior edge of the pancreas. At this point, it curves and then terminates at the duodeno-jejunal flexure. This flexure is surrounded by a peritoneal fold called the ligament of Treitz.
48
Which side of the abdomen does the duodenum curve out to?
Right side
49
Between what vertebral levels is the duodenum?
L1 and L3
50
What demarcates the boundary between the foregut and the midgut?
The entry of the biliary and pancreatic ducts into the duodenum.
51
Where in the duodenum do the biliary and pancreatic ducts enter?
2nd (descending) part
52
What demarcates the point where the dudodenum becomes the jejunum?
* The ligament of Treitz (which joins the duodenum to the diaphragm).
* This is at the duodeno-jejunal flexure.
53
Describe the blood supply to the duodenum.
* First part -\> Coeliac artery
* Second part -\> Superior mesenteric artery
54
Draw the relations of the duodenum.
55
What is the sphincter of Oddi?
The smooth muscle that surrounds the end portion of the common bile duct and pancreatic duct. This muscle relaxes during a meal to allow bile and pancreatic juice to flow into the intestine.
56
What is the duodenal papilla?
* The point where the junction of the pancreatic duct and the bile duct enter the duodenum.
* Marks the transition between foregut and midgut regions of the GI tract.
57
Describe duodenal ulcers.
* Peptic ulcers are erosions of the mucosa of the GI tract, typically found within the stomach (gastric ulcers) or proximal duodenum (duodenal ulcers).
* The vast majority of ulcers are caused by extended NSAID use (e.g. ibuprofen) or Helicobacter pylori infection.
* Duodenal ulcers typically cause consistent burning epigastric pain, which is relieved by eating food.
* Perforation of duodenal ulcers may cause catastrophic bleeding into the GI tract, due to erosion into the gastroduodenal artery which is close by.
* To reduce the risk of progression of duodenal ulcers, patients are prescribed acid suppression medication, antibiotics for H. pylori infection and NSAIDs stopped.
58
What organs is the pancreas closely related to and why is this important?
* The communication between the pancreas, gallbladder and duodenum is clinically important.
* One of the most common causes of pancreatitis is the presence of gallstones within the distal biliary tree, just proximal to the duodenal papilla, blocking the common outflow.
* This results in a backlog of pancreatic juice into the parenchyma of the pancreas, causing auto-digestion, pancreatitis and ultimately tissue necrosis.
* Similarly, a procedure known as ERCP, used to remove gallstones impacted within the common bile duct via the duodenal papilla, can cause pancreatitis by releasing fragments of gallstones into the pancreatic ducts, which can trigger irritation and inflammation.
59
What are the parts of the small intestine apart from the duodenum?
* Jejunum
* Ileum
60
Compare the jejunum and ileum.
* Jejunum:
* Located in the left upper quadrant of the abdomen.
* Typically red in colour (darker than ileum).
* 2-4cm in diameter.
* Thick walled.
* Highly vascularised in comparison to ileum.
* Ileum:
* Located in the lower right quadrant of the abdomen.
* Typically pink in colour (lighter than jejunum).
* 2-3cm in diameter.
* Thin walled.
61
Compare the structure and length of the jejunum and ileum?
* Jejunum
* 2.5m
* Numerous mucosal folds
* Few Peyer’s patches (gut associated lymphoid tissue)
* Ileum
* 3.5m
* Smaller, less mucosal folds
* Large number of Peyer’s patches
62
What are taenia coli, haustra and epiploic appendices?
* Taenia coli -\> Longitudinal strips of smooth muscle on the outer surface of the large intestine. The taenia coli allow segments of the colon to contract independently.
* Haustra -\> The small pouches caused by sacculation, which give the colon its segmented appearance.
* Epiploic appendices -\> Peritoneum-lined protrusions of subserosal fat that arise from the surface of the large bowel.
63
Describe where the small bowel mesentry attaches.
Root of the mesentery:
* 15 cm.
* Lies obliquely across the posterior abdominal wall.
* Forms a line from the left of the vertebra L2 to the right sacroiliac joint.
64
What are the main parts of the large intestine?
* Caecum
* Appendiz
* Ascending colon
* Transverse colon
* Descending colon
* Sigmoid colon
* Rectum
65
Label this large intestine.
66
Describe the appearance of longitudinal muscle in the large intestine.
It is condensed into thin stripes called taeniae coli.
67
What are the puffy parts of the large intestine called?
Haustra
68
On which side of the body is the ascending colon?
Right
69
What prevents reflux from the caecum to the ileum?
Ileocaecal valve
70
Describe the position of the appendix of the large intestine.
It is at the start of the caecum, although the direction it points in is variable.
71
What is appendicitis and what are the symptoms? [IMPORTANT]
* It is inflammation of the appendix of the large intestine, usually due to infection
* Symptoms:
* Initial pain around the bellybutton due to the appendix being innervated by the T10 nerve root
* Pain later at McBurney's point
72
What are the main flexures of the large intestine that you need to know?
* Hepatic flexure
* Splenic flexure
73
Which parts of the large intestine are retroperitoneal and which are intraperitoneal?
* Caecum -\> Intraperitoneal
* Ascending colon -\> Secondary retroperitoneal
* Transverse colon -\> Intraperitoneal
* Descending colon -\> Secondary retroperitoneal
* Sigmoid colon -\> Intraperitoneal
* Rectum -\> Superior 2/3rd retroperitoneal
74
What are the folds in the rectum called? Describe them.
They are called the 'valves of Houston':
* 2 are on the left
* 1 is on the right
75
At what vertebral level does the rectum begin?
S3
76
Where is the anorectal junction?
It is at the point when the rectum pierces the pelvic floor muscles.
77
What is the rectal ampulla?
A dilated portion of the rectum.
78
Describe colon cancer.
* Colorectal cancer accounts for 15% of cancer related deaths in the Western World.
* More than 50% of cases occur within the rectum and sigmoid colon, usually after transformation of a benign polyp.
* Depending on where the tumour occurs, patients may experience a change in bowel habits, bleeding and abdominal pain from obstruction.
* Treatment options include surgical excision and chemotherapy
79
Compare the small and large intestine.
80
81
Describe a digital rectal examination.
* A DRE is a commonly performed examination in the hospital, used to screen for a variety of lower GI pathologies.
* When performing the examination, doctors assess the size and shape of the prostate in men, palpate for masses within the anal canal and assess anal sphincter tone.
82
What is the anal canal?
The anal canal connects the rectum to the anus, passing downwards and posteriorly.
83
What is the pubo-rectal sling?
The puborectal sling (part of the levator ani muscle group) surrounding the recto-anal junction kinks the anal canal forward, which functions as a sphincter.
84
Compare the muscles and innervation of the two anal sphincters.
Internal anal sphincter:
* Smooth muscle
* Autonomic control
External anal sphincter:
* Striated muscle
* Pudendal nerve (s2-S4) control
85
What are the anal cushions?
Submucosal tissue which assists the continence mechanism.
86
What are anal columns?
6 to 10 longitudinal mucosal folds in the anal canal.
87
What are anal valves?
Small valve-like folds at the lower ends of the anal sinuses in the rectum. They join the anal columns.
88
What is the pectinate line?
Indicates the junction of the superior part of the anal canal (visceral: derived from the embryonic hindgut), and the inferior part (somatic: derived from the embryonic proctodeum).
89
What is the perineal body?
* A fibro-muscular structure located in the midline of the perineum.
* Its exact location is the midline of the perineum at the junction of the anus and urogenital triangle in both females and males
90
What is the ischiorectal fossa?
The fat-filled wedge-shaped space located lateral to the anal canal.
91
Where is the boundary between the midgut and hindgut?
2/3rd of the way along the transverse colon
92
What are the three major arteries supplying the GI tract?
* Coeliac
* Superior mesenteric
* Inferior mesenteric
93
What organs does the coeliac artery supply?
Foregut derivatives:
* **Liver**
* **Stomach**
* **Proximal duodenum**
* Abdominal oesophagus
* Spleen
* Pancreas
94
What are the branches of the coeliac artery you need to know? Summarise what they supply.
* Common hepatic -\> Liver, duodenum, and pancreas.
* Left and right gastric (right from common hepatic) -\> Lesser curvature of stomach
* Left and right gastroepiploic arteries (left from splenic, right from common hepatic) -\> Greater curvature of stomach
Also worth knowing the splenic artery, since it gives rise to the short gastric arteries and left gastroepiploic artery.
95
What organs does the superior mesenteric artery supply?
Midgut derivatives:
* **Distal duodenum**
* **Small intestine**
* **Ascending and transverse colon** (proximal 2/3rds)
* Head of pancreas
* Caecum and appendix
96
What are the branches of the superior mesenteric artery you need to know? Summarise what they supply.
* Jejunal & ileal arcades -\> Anastamoses supplying the ileum and jejunum
* Ileocolic artery -\> Distal ileum, ceacum, appendix and proximal ascending colon.
* Appendicular artery -\> Appendix
* Right colic -\> Ascending colon
* Middle colic -\> Transverse colon
97
What organs does the inferior mesenteric artery supply?
Hindgut derivatives:
* **Descending colon**
* **Rectum**
* Sigmoid colon
* Distal 1/3rd transverse colon
98
What are the branches of the inferior mesenteric artery you need to know? Summarise what they supply.
* Left colic artery -\> Descending colon
* Sigmoid artery -\> Lower part of the descending colon, the iliac colon, and the sigmoid colon
* Superior rectal artery -\> Rectum (all mucosa)
99
Describe the blood supply to the rectum and anal canal.
* Superior rectal artery (from inferior mesenteric) -\> Supplies whole of the rectal mucosa and upper part of the anal canal, up to the dentate line
* Middle rectal artery (from internal iliac) -\> Supplies the muscle layers of the rectum
* Inferior rectal artery (from internal pudendal) -\> Supplies inferior parts of the rectum and anal canal
100
What is important to remember about the superior rectal artery?
* It arises from the inferior mesenteric artery.
* It supplies all the rectal mucosa.
101
What is important to remember about the superior rectal artery?
* It arises from the internal iliac artery.
* It supplies the muscle wall of the rectum.
102
What is important to remember about the inferior rectal artery?
* It arises from the pudendal artery
* It supplies the anal canal
103
Describe the anastamoses of the alimentary tract arteries.
* Anastomoses of the terminal branches of the superior mesenteric artery and inferior mesenteric artery form a continuous arterial arcade along the inner border of the large intestine, known as the marginal artery (of Drummond).
* Straight vessels, known as the vasa recta, pass from this artery to the colon itself within the mesentery.
* This anastomosis is critical to allow continued perfusion of territories supplied by the SMA or IMA should one of the arteries become occluded.
104
Describe the venous drainage of the GI tract.
* Venous drainage of the GI tract first passes through the portal venous system before reaching the systemic circulation, in order for products of digestion to be processed within the liver.
* In general, blood from foregut structures drain to the hepatic portal vein through the splenic vein.
* Midgut derivatives are drained by the superior mesenteric vein, which joins the splenic vein behind the neck of the pancreas to form the hepatic portal vein.
* Hindgut structures drain via the inferior mesenteric vein, which usually joins the splenic vein before the formation of the hepatic portal vein.
105
Describe the venous drainage of the rectum.
* Superior rectal vein -\> Drains into the hepatic portal system
* Middle and inferior rectal veins -\> Drain directly to the systemic circulation.
Anastomoses, known as the **rectal venous plexus**, form between the systemic and portal systems around the rectum.
106
Name the main sites of portal-systemic anastomosis in the GI tract.
* Rectum
* Oesophagus
* Paraumbilical region
* Retroperitoneum
107
Summarise the lymphatic drainage of the GI tract.
Drains to the **pre**-aortic lymph nodes (note that this is not para aortic like for the ovaries, etc.):
* Foregut derivatives -\> Drained by the coeliac nodes
* Midgut derivatives -\> Drained by the superior mesenteric nodes
* Hindgut derivatives -\> Drained by the inferior mesenteric nodes
108
Describe haemorrhoids.
* Haemorrhoids are highly vascular submucosal cushions which may swell, become itchy and bleed in response to hard stools and raised luminal pressures.
* The term “haemorrhoids” may be used to describe both normal, physiological anal cushions and pathological, engorged structures.
* External haemorrhoids are found below the dentate line, whilst internal haemorrhoids lie above the dentate line.
* Depending on the degree of bleeding and protrusion of the haemorrhoids, they may be surgically removed or endoscopically banded to reduce the risk of further bleeding.
109
Where may colorectal (bowel) cancer spread to?
* First to the **liver**
* Prior to distal spread, metastatic disease is often found in the local **lymph nodes** surrounding the bowel.
* Other common sites of metastasis include **peritoneum** and **vertebrae**.
110
Summarise the parasympathetic, sympathetic and somatic innervation of the GI tract, including ganglia.
Parasympathetic:
* Vagus nerve -\> To foregut and midgut
* Pelvic splanchnic nerves -\> To hindgut
Sympathetic:
* Coeliac ganglia (thoracic splanchnic sympathetic nerves) -\> To foregut
* Superior mesenteric ganglia (thoracic splanchnic sympathetic nerves) -\> To midgut
* Inferior mesenteric ganglia (pelvic sympathetic nerves) -\> To hindgut
Somatic:
* Pudendal nerve -\> To anal canal and external anal sphincter
111
Where are the parasympathetic ganglia of the GI tract found?
Within the walls of the GI tract, close to their terminal organs.
112
Describe the enteric nervous system.
* Myenteric plexus
* Located between the inner circular and outer longitudinal muscle layers of the GI tract
* Responsible for peristalsis
* Submucous plexus
* Located within the submucosa
* Responsible for glandular secretion and electrolyte transport across the mucosa
113
When does pain from the GI tract become more localised?
* Visceral afferent fibres travel with the autonomic fibres to diffusely terminate within the spinal cord.
* As such, sensation within the GI tract is poorly localised until the parietal peritoneum becomes involved.
* When the parietal peritoneum becomes involved, due to its innervation by the somatic nervous system, sensation becomes well-localised.
114
Describe the general distribution of referred pain from the GI tract.
In general, visceral sensory information is referred to the epigastric region for foregut structures, the umbilical region for midgut structures and the hypogastric region for hindgut structures.
115
Describe the afferent and efferent components of the vomiting reflex.
Afferent:
* Fear
* Pain
* Gastric irritation
Efferent (sympathetic, lower intercostal, phrenic and vagus nerves):
* Deep breath taken to avoid aspiration of vomit
* Increased salivation to reduce damage to teeth caused by stomach acid (parasympathetic innervation)
* Glottis closed, soft palate elevated and larynx raised, opening the upper oesophageal sphincter and closing off the nasopharynx.
* Sharp contraction of the diaphragm inferiorly to create negative pressure within thorax, causing the oesophagus and lower oesophageal sphincter to open.
* Abdominal wall muscle contraction to raise intra-abdominal pressure and expel stomach contents into the oesophagus and ultimately into the external environment.
116
Summarise the named nerves involved in the defecation reflex you need to know.
* Afferent: Pelvic plexus, Spinal cord centre
* Efferent: Sympathetic, Pudendal
117
Describe the afferent and efferent components of the defecation reflex.
This reflex is triggered on mass movement of faeces towards the rectum, initiated by high intensity contractions of the colon.
Afferent:
* Pelvic splanchnic nerves from rectum (S2-S4) -\> Detects sufficient distension of the rectum
Efferent:
* Contraction of the sigmoid colon and rectum
* Relaxation of the internal anal sphincter (triggered by parasympathetic fibres of pelvic splanchnic nerves)
* Contraction of the external anal sphincter (triggered by inferior rectal nerve, branch of the pudendal nerve)
This combination of events triggers an urge to defaecate, which is permitted on voluntary relaxation of the external anal sphincter. Expulsion is aided by the Valsalva manoeuvre, which raises the intra-abdominal pressure.
118
Summarise the named nerves involved in the vomiting reflex you need to know.
* Afferent: None named
* Efferent: Sympathetic, lower intercostal, phrenic, vagus
119
Draw the surface anatomy of the liver, gall bladder, pancreas and liver.
120
At what height is the liver found?
The right lobe of the liver is found deep to the 7-11th ribs, whilst the left lobe occupies the epigastric and left hypochondriac regions.
121
Describe the lobes of the liver.
Anteriorly you can see only 2 lobes:
* Right lobe
* Left lobe
Inferiorly, you can see 2 more lobes:
* Caudate (more posterior)
* Quadrate (more anterior)
122
Draw an anterior view of the liver.
123
Draw an inferior view of the liver.
Note: The anterior side is at the bottom of this diagram.
124
Which side of the liver is flatter?
Posterior
125
What is the porta hepatis and what is found there?
* A deep fissure seen at the inferior side of the liver
* The portal triad (hepatic artery proper, hepatic portal vein and common hepatic duct) enter and leave the liver parenchyma here
126
What separates the right and left lobes of the liver?
Falciform ligament
127
What separates the lobes of the liver on the inferior side?
Porta hepatis -\> It is sort of in the middle of all of the lobes.
128
What vessels run through the porta hepatis?
* Hepatic portal vein
* Hepatic artery
* Common hepatic duct
129
Describe the hepatic vasculature.
Blood supply:
* **Hepatic artery** and **hepatic portal vein** enter via the porta hepatis in the inferior liver
* They bifurcate into left and right branches and supply the liver (75% from hepatic portal vein, 25% from hepatic artery)
Blood drainage:
* **Hepatic veins** drain the liver and drain into the IVC at the superior end of the liver
130
Describe the functional segments of the liver.
* It can be divided into functional left and right lobes by drawing a line through the midline of the gallbladder and the inferior vena cava.
* This division results in the caudate and quadrate lobes being a part of the functional left lobe.
* The functional right lobe of the liver processes blood coming from the head of the pancreas, the pylorus and antrum of the stomach, and the midgut via the superior mesenteric vein.
131
Describe the position of the gall bladder.
* It is within the gall bladder fossa, on the inferior surface of the liver between the quadrate and right lobes.
* The fundus of the gall bladder is found posterior to the anterior end of the right 9th costal cartilage.
132
What is the function of the gall bladder?
To store and ultra-concentrate bile prior to its release during meals.
133
Describe liver cirrhosis.
Cirrhosis is the end-stage of liver fibrosis, which results in disorganised parenchymal architecture and impairment of liver function. Cirrhosis may be caused by chronic alcoholism or chronic hepatitis B/C infection. Biliary injury such as bile duct obstruction, primary biliary cirrhosis and primary sclerosing cholangitis may also result in liver cirrhosis. Symptoms are typically non-specific, and may include weight loss, fatigue and anorexia. With declining liver function, patients may become jaundiced and have ascites. Cirrhosis is considered irreversible and requires liver transplantation for a cure.
134
What can portal hypertension be caused by and what can it lead to?
* Portal hypertension is the most common, serious complication of liver cirrhosis
* It may cause GI bleeding through oesophageal/rectal varices at the sites of porto-systemic anastomoses, ascites, pulmonary hy- pertension and kidney injury.
* Portal hypertension may cause the re-canalisation of the obliterated paraum- bilical veins within the ligamentum teres and abdominal wall, resulting in the appearance of caput medusae around the umbilicus.
135
What are the ligaments of the liver essentially?
They are peritoneal attachments.
136
Name the peritoneal attachments of the liver you need to know.
* Falciform ligament -\> Remnant of the ventral mesentery of the foetus. Attaches the anterior surface of the liver to the anterior abdominal wall, dividing the liver into the left and right lobes. Its free edge contains the ligamentum teres (round ligament), a remnant of the umbilical vein.
* Triangular ligaments:
* Left triangular ligament -\> Attaches the posterior part of the superior surface of the left lobe of the liver to the diaphragm.
* Right triangular ligament -\> Passes from the posterior part of the bare area on the right side to the diaphragm.
* Coronary ligament -\> Attaches the superior surface of the liver to the inferior surface of the diaphragm.
* Lesser omentum -\> Passes from the lesser curvature of the stomach to the inferior surface of the liver. The portal triad is found within the free edge of the lesser omentum.
137
What is the ligamentum teres and where is it found?
* It is a remnant of the umbilical vein.
* It is found at the free edge of the falciform ligament.
138
Within what structure does the portal triad pass?
Lesser omentum
139
What is the clinical relevance of the ligamentum teres?
* The ligamentum teres is a remnant of the umbilical vein.
* Portal hypertension may cause the recanalisation of the obliterated veins within the ligamentum teres, resulting in the appearance of **caput medusae** around the umbilicus.
140
What is the bare area of the liver?
It is part of the right lobe, between the anterior and posterior folds of the coronary ligament.
141
Describe liver metastases.
* The most common form of liver tumour are metastatic deposits from primary tumours located elsewhere.
* 50% of all metastatic lesions within the liver are derived from GI tract malignancies.
* Other common primary tumours metastasising via the blood to the liver include the breast, lung, kidney and ovaries.
* The liver is a common site of metastatic disease due to its extensive, dual blood supply and relatively porous sinusoids, allowing the transport of malignant cells into the liver parenchyma
142
Describe the structure of the biliary tree.
* The **right** and **left hepatic ducts** unite to form the **common hepatic duct**
* After 6-8cm, the **cystic duct** from the gall bladder joins to the common hepatic duct to form the **common bile duct**
* The **main pancreatic duct** drains into the common bile duct as it reaches the level of the descending duodenum to form the Ampulla of Vater, which ultimately drains into the descending duodenum through the major duodenal papilla.
* Drainage is controlled by the **Sphincter of Oddi**.
143
Is it the common hepatic duct or common bile duct that runs via the lesser omentum? And which runs in the porta hepatis?
* Both run in the lesser omentum -\> First the common hepatic duct does. Then it becomes the common bile duct and continues running in the lesser omentum.
* Only the common hepatic duct runs in the porta hepatis
144
What is the function of the cystic duct?
Allows bile to move in and out of the gall bladder by communicating with the common hepatic duct.
145
What is Calot's triangle? What does it demarcate?
* A triangle formed by the cystic duct, common hepatic duct and inferior edge of the liver creates
* It demarcates the location of the **cystic artery** and Lund’s node, the sentinel lymph node of the gallbladder.
146
What does the cystic artery supply and what does it arise from?
* Supplies the gall bladder
* Arises from the right hepatic artery
147
Describe the innervation of the gall bladder.
* Coeliac plexus -\> Gives sympathetic and visceral afferent fibres
* Vagus nerve -\> Gives parasympathetic fibres
148
Where may pain from the gall bladder be referred to?
* If the gallbladder becomes infected, as in cholecystitis, involvement of the parietal peritoneum results in well-localised, sharp pain within the **right upper quadrant**
* This may be referred, via the phrenic nerve, to the **C4 dermatome**, due to diaphragmatic peritoneal irritation.
149
Describe the different locations in which gall stones can form and what the consequences of this are.
* Biliary colic:
* Gallstones within the cystic duct
* Pain in the right upper quadrant for 1-2 hours after meal
* Cholecystitis:
* Obstruction of the biliary tree, usually in cystic duct
* Pain may be constant and there is often signs of inflammation, such as fever and raised white cell counts. Pain in the right upper quadrant, radiating laterally beneath the right breast to the back.
* Choledocholithiasis:
* Gallstones within the common bile duct
* Prevents bile from draining into the duodenum, resulting in a backlog of bile into the liver and ultimately **jaundice**.
* Patients may also complain of pale stools and dark urine.
* Ascending cholangitis:
* Similar to choledocholithiasis, but with the presence of fevers and right upper quadrant pain.
150
Summarise the structure of the pancreas.
* Head -\> Sits anterior to the inferior vena cava
* Uncinate process -\> Separated from the pancreatic neck by the superior mesenteric artery and vein.
* Neck -\> Sits anterior to the origin of the hepatic portal vein.
* Body -\> Passes anterior to the abdominal aorta.
* Tail -\> Passes within the splenorenal ligament to reach the splenic hilum.
151
What are the endocrine and exocrine products of the pancreas and where do they drain?
* The exocrine products of the pancreas, including trypsinogen, chymotrypsinogen, carboxypeptidase, lipase and amylase, are drained from the parenchyma of the pancreas into the duodenum via the main pancreatic duct, which runs along the length of the pancreas.
* The endocrine units of the pancreas are the islet of Langerhans, which produce insulin, glucagon and somatostatin. These products drain directly into the bloodstream
152
Describe the blood supply of the pancreas.
* Head of pancreas:
* Superior pancreatico-duodenal arteries, from the gastroduodenal (from common hepatic, from coeliac artery)
* Inferior pancreatico-duodenal arteries, from superior mesenteric artery
* Remaining pancreas:
* Large splenic artery (from coeliac artery)
Note how the blood supply is split between the coeliac and superior mesenteric arteries.
153
Describe innervation of the pancreas.
* Sympathetic fibres from the coeliac plexus -\> Control blood flow
* Vagus nerve -\> Stimulates pancreatic enzyme and insulin release
