GI Anatomy🤮 Flashcards
1
Q
Describe the abdominal cavity
A
The abdominal cavity is separated from the thorax by the diaphragm. As we have learned, the diaphragm contains apertures that allow structures to pass between the thorax and abdomen.
2
Q
Describe the pelvic cavity
A
The pelvic cavity lies inferior to the abdominal cavity and is continuous with it.
3
Q
What is in the abdominal cavity
A
The abdominal cavity contains organs of the gastrointestinal tract (stomach, small and large intestine), the hepatobiliary system (liver and gallbladder), the urinary system (kidneys and ureters) and the endocrine system (pancreas and adrenal glands). The abdomen also contains the spleen (a haematopoietic and lymphoid organ) and of course the great vessels (abdominal aorta and inferior vena cava) and their branches.
4
Q
What is the abdominal wall made of?
A
The anterior, lateral, and posterior walls of the abdomen are composed of skin, subcutaneous tissue and muscles and their associated aponeuroses (flat tendons).
Five lumbar vertebrae contribute to the posterior wall of the abdominal cavity.
5
Q
What are the functions of the abdominal wall?
A
- protect the abdominal viscera
- increase intra-abdominal pressure (e.g. for defecation and childbirth)
- maintain posture and move the trunk
6
Q
Key bony landmarks that define the boundaries of the abdominal cavity
A
- Xiphisternum
- Costal margin
- Iliac crests
- Anterior superior iliac spines (ASIS)
- Pubic tubercles
- Pubic symphysis (a fibrocartilaginous joint).
7
Q
What are the four quadrants of the abdomen?
A
In clinical practice, the anterior abdominal wall can be described in terms of the four quadrants. These are the right upper and lower quadrants and the left upper and lower quadrants.
8
Q
What are the invisible lines that divide the abdomen into quadrants?
A
- a vertical line that runs down the midline through the lower sternum, umbilicus, and the pubic symphysis
- a horizontal line that runs across the abdomen through the umbilicus.
9
Q
Why do we have the nine regions of the abdominal cavity?
A
Because these regions are smaller than the four quadrants, using them allows us to be more precise when we are describing the site of a patient’s pain or the location of tenderness, a mass, a swelling, an injury or a lesion on examination
10
Q
What are the lines that divide the abdomen into nine regions?
A
- the right and left midclavicular lines, which extend vertically from the midclavicular point to the mid-inguinal point (halfway between the anterior superior iliac spine and the pubic tubercle)
- the subcostal line - a horizontal line drawn through the inferior-most parts of the right and left costal margins (through the 10th costal cartilage)
- the intertubercular line - a horizontal line drawn through the tubercles of the right and left iliac crests and the body of L5.
11
Q
List the central regions from superior to inferior
A
The central regions, from superior to inferior, are the epigastrium, the umbilical region and the suprapubic region (sometimes called the hypogastric region).
12
Q
List the right sided regions of the abdomen from superior to inferior
A
On the right, the regions from superior to inferior are the right hypochondrium, the right flank (sometimes called the right lumbar region) and the right iliac fossa.
13
Q
List the left sided regions of the abdominal cavity from superior to inferior
A
On the left, the regions from superior to inferior are the left hypochondrium, the left flank (sometimes called the left lumbar region) and the left iliac fossa.
14
Q
What is the transpyloric plane?
A
A horizontal line that passes through the tips of the right and left ninth costal cartilages. It lies halfway between the superior border of the manubrium and the pubic symphysis. It transects the pylorus of the stomach, the gallbladder, the pancreas and the hila of the kidneys.
15
Q
What is the transumbilical plane?
A
An unreliable landmark as its position varies depending on the amount of subcutaneous fat present. In a slender individual it lies approximately at the level of L3.
16
Q
What is the intercristal plane?
A
A horizontal line drawn between the highest points of the right and left iliac crests. It cannot be palpated from the anterior aspect of the abdominal wall. It is used to guide procedures on the back (e.g. lumbar puncture).
17
Q
What is McBurney’s point?
A
The surface marking of the base of the appendix. It lies two thirds of the way along a line drawn from the umbilicus to the right anterior superior iliac spine.
18
Q
What are the four pairs of muscles that comprise the anterolateral abdominal wall?
A
- External oblique (diagonally orientated fibres)
- Internal oblique (diagonally orientated fibres)
- Transversus abdominis (horizontally orientated fibres)
- Rectus abdominis (rectus = straight).
19
Q
What are the 3 sheets of muscle that are lateral to the rectus abdominis?
A
Fibres all run in different directions
* External oblique (EO) is most superficial. The fibres of EO run medially and inferiorly, towards the midline.
* Internal oblique (IO) lies deep to EO. The fibres of IO are orientated perpendicular to those of EO (they run medially and superiorly).
* Transversus abdominis lies deep to internal oblique. Its fibres are orientated horizontally.
20
Q
What do the EO, IO and transversus abdominis muscles do?
A
When these muscles contract together, they increase intra-abdominal pressure. Alone, the oblique muscles act as lateral flexors of the lumbar spine.
21
Q
What happens to the EO, IO and transversus abdominis anteriorly?
A
these muscles become aponeurotic (an aponeurosis is a flat tendon). The fibres of the aponeuroses fuse with each other, and, in the midline, they fuse with the aponeuroses of the opposite side, forming a tough midline raphe (= seam) called the linea alba (‘white line’). The aponeuroses of these muscles also form the rectus sheath, which encloses the rectus abdominis.
22
Q
What are the left and right rectus abdominis muscles made of?
A
Muscle segments interspersed with horizontal tendinous bands. When the muscle segments hypertrophy with exercise, they bulge either side of the tendinous bands and can be seen on the anterior abdominal wall as bulges – the ‘six-pack’. Rectus abdominis is a flexor of the lumbar spine.
23
Q
Where is the rectus abdominis?
A
Rectus abdominis lies within the rectus sheath. The anterior and posterior walls of the rectus sheath are formed by the aponeuroses of EO, IO and transversus abdominis.
* As it approaches the midline, the aponeurosis of IO splits into anterior and posterior layers.
* The EO aponeurosis and the anterior layer of the IO aponeurosis form the anterior wall of the rectus sheath.
* The posterior layer of the IO aponeurosis and the transversus abdominis aponeurosis form the posterior wall of the rectus sheath.
24
Q
Where is the transversalis fascia and the parietal peritoneum?
A
The transversalis fascia lies deep to transversus abdominis. Deep to the fascia lies the parietal peritoneum.
25
What is the inguinal ligament and ingual canal?
The most inferior part of the external oblique aponeurosis is attached to the anterior superior iliac spine laterally and the pubic tubercle medially, forming the inguinal ligament. Just above the inguinal ligament is the inguinal canal
26
What are the arteries of the anterior abdominal wall?
* musculophrenic artery, a branch of the internal thoracic
* superior epigastric artery, which is the continuation of the internal thoracic artery. It descends in the rectus sheath
* inferior epigastric artery, a branch of the external iliac artery. It ascends in the rectus sheath and anastomoses with the superior epigastric.
27
Where are the abdominal wall veins found?
The arteries are accompanied by deep veins. As well as an extensive network of superficial veins is found in the anterolateral abdominal wall.
28
Which nerves innervate the muscles and skin of the anterolateral abdominal wall?
● Thoraco-abdominal nerves T7 – T11. These are essentially the continuation of the intercostal nerves T7 – T11. These somatic nerves contain sensory and motor fibres.
● The subcostal nerve – this originates from the T12 spinal nerve (so called because it runs along the inferior border of the 12th rib).
● Iliohypogastric and ilioinguinal nerves – both are branches of the L1 spinal nerve.
29
What is the inguinal canal?
The inguinal canal is an oblique passageway through the muscles of the anterior abdominal wall and lies superior to the medial half of the inguinal ligament. It passes through each layer of the abdominal wall as it travels medially and inferiorly. The canal is about five centimetres long in the adult
30
Where can you find the inguinal canal?
It extends from the deep inguinal ring laterally (an aperture in the transversalis fascia) to the superficial inguinal ring medially (an aperture in the external oblique aponeurosis).
31
Describe the anterior border of the inguinal canal
● External oblique aponeurosis
● Laterally only: internal oblique aponeurosis
32
Describe the posterior border of the inguinal canal
● Transversalis fascia
● Medially only: medial fibres of the aponeuroses of the internal oblique and transversus abdominis (which are together known as the conjoint tendon).
33
Describe the roof of the inguinal canal
● Transversalis fascia
● Arching fibres of the internal oblique and transversus abdominis.
34
Describe the floor of the inguinal canal
Inguinal ligament (the lower border of the external oblique aponeurosis).
35
Describe abdominal hernias
A hernia is an abnormal protrusion of tissues or organs from one region into another through an opening or defect. Herniae of the anterior abdominal wall may occur if the muscles are weak or have been incised during surgery. A segment of the small intestine may protrude through a defect in the wall, forming a visible and palpable lump under the skin.
36
Describe laparotomy
This term describes the surgical opening of the anterior abdominal wall, undertaken for major operations where good access to the abdomen is needed. A midline sagittal incision of the linea alba involves minimal risk to nerves and muscles. Ideally, muscles are split, rather than cut. Where possible, keyhole surgery (laparoscopy) is performed, as it is associated with less post-operative pain, faster wound healing and a smaller risk of wound infection and post-operative hernia.
37
Describe Abdominal aortic aneurism
This is an abnormal swelling of the wall of the aorta. The affected portion of the wall becomes distended, but it is weak and prone to rupture. An aneurysm may be detected on abdominal examination, felt as a pulsatile mass in the midline of the abdomen. Examination of the abdomen must always include palpitation of the aorta, as detection can be lifesaving. Sudden rupture of an AAA carries an extremely high mortality rate.
38
What is an inguinal hernia?
An inguinal hernia is a protrusion of abdominal contents (normally part of the greater omentum or loops of small intestine) through the anterior abdominal wall into the inguinal canal. Inguinal hernias are indirect or direct.
39
What is an indirect inguinal hernia?
In an indirect inguinal hernia, intra-abdominal contents are forced through the deep inguinal ring and into the canal. The abdominal contents may even be forced along the canal and through the superficial ring. From here, the hernia may extend into the scrotum in males or into the labia majora in females. Indirect hernias are more common than direct hernias. They are more likely to get stuck in the canal and become ‘irreducible’. Potentially, herniated tissue can ‘strangulate’ and become ischaemic. This is a surgical emergency.
40
What is a direct inguinal hernia?
In a direct inguinal hernia, intra-abdominal contents are forced through the posterior wall of the inguinal canal (i.e. the relatively weak transversalis fascia) and directly through the superficial ring. The herniated abdominal contents do not pass through the deep inguinal ring in direct inguinal hernias. Although they are less common than indirect hernias, direct inguinal hernias are often easier to reduce.
41
Describe the parietal peritoneum
Parietal peritoneum lines the abdominal wall.
* It can be seen with the naked eye and is innervated by the somatic nerves that supply the overlying muscles and skin of the abdominal wall.
* Pain from the parietal peritoneum is usually sharp, severe, and well localised to the abdominal wall.
42
Describe the visceral peritoneum
Visceral peritoneum covers the abdominal viscera.
* It is adhered to the surface of the viscera and cannot be seen with the naked eye.
* The visceral peritoneum is innervated by visceral sensory nerves. These nerves convey ‘painful’ sensations back to the CNS along the path of the sympathetic nerves that innervate the organ / structure it covers.
43
Describe pain in the peritoneum
* Pain from the visceral peritoneum can be severe. It is usually dull and diffuse (i.e. it cannot be pinpointed to a specific location).
* ‘Painful’ sensations from the visceral peritoneum may be perceived as nausea or distension.
44
Describe the peritoneal cavity
Between the parietal and visceral peritoneum lies the peritoneal cavity. In a healthy abdomen, a thin film of peritoneal fluid lies in the peritoneal cavity. It allows the viscera to slide freely alongside each other.
The two layers of peritoneum are continuous with each other. The arrangement of the two layers mirrors the arrangement of the parietal and visceral pleurae.
45
What does intraperitoneal mean?
almost completely covered by peritoneum e.g. the stomach
46
What does retroperitoneal mean?
Some retroperitoneal organs are described as ‘secondarily retroperitoneal’. These organs were intraperitoneal in early development but came to be ‘stuck down’ onto the posterior abdominal wall.
47
What do the Mesenteries, Omenta, Ligaments and Folds have in common?
* They are all composed of peritoneum and connect organs to each other and to the abdominal wall.
* They may carry blood vessels, nerves, and lymphatics to the viscera.
* They contain a variable amount of fat; some are usually very fatty (the omenta).
48
What are mesenteries?
Mesenteries are folds of peritoneum that contain fat and suspend the small intestine and parts of the large intestine from the posterior abdominal wall. Arteries that supply the intestine (from the abdominal aorta) and veins that drain the gut (tributaries of the portal venous system) are embedded in the mesenteries.
49
What are the greater and lesser omenta?
The greater and lesser omenta are folds of peritoneum that are usually fatty and connect the stomach to other organs.
* The greater omentum hangs from the greater curvature of the stomach and lies superficial to the small intestine.
* The lesser omentum connects the stomach and duodenum (the first part of the small intestine) to the liver. The hepatic artery, the hepatic portal vein, and the bile duct (the ‘portal triad’) are embedded within its free edge.
50
What are ligaments connecting to the liver?
Ligaments are folds of peritoneum that connect organs to each other or to the abdominal wall. E.g:
* falciform ligament, which connects the anterior surface of the liver to the anterior abdominal wall
* the coronary and triangular ligaments, which connect the superior surface of the liver to the diaphragm.
51
What are peritoneal folds?
Peritoneal folds are raised from the internal aspect of the lower abdominal wall and are created by the structures they overlie, like carpet running over a cable. Sometimes they are difficult to see.
52
What is the median umbilical fold and where is it?
The median umbilical fold lies in the midline and represents the remnant of the urachus, an embryological structure that connects the bladder to the umbilicus
53
What are the medial umbilical folds and where are they?
Lateral to the median umbilical fold lie the medial umbilical folds. These represent the remnants of the paired umbilical arteries, which returned venous blood to the placenta in foetal life.
54
What are the lateral umbilical folds and where are they?
Lateral to the medial umbilical folds are the lateral umbilical folds. The inferior epigastric arteries lie deep to these peritoneal folds. They supply the anterior abdominal wall.
55
What are the greater and lesser sacs?
The peritoneal cavity is divided into two regions of unequal size.
* The smaller lesser sac (also called the omental bursa) is a space that lies posterior to the stomach and anterior to the pancreas.
* The larger greater sac is the remaining part of the peritoneal cavity.
* The greater and lesser sacs communicate with each other via a passageway that lies posterior to the free edge of the lesser omentum, the epiploic foramen (also called the omental foramen).
56
What does the gastrointestinal system develop from?
The gastrointestinal system develops from the embryonic gut tube which lies in the midline of the abdominal cavity, suspended from the posterior abdominal wall by the dorsal mesentery
57
What is the ventral mesentery and what does it become?
The ventral mesentery connects the stomach to the anterior abdominal wall. As the liver grows within it, the anterior part of the ventral mesentery becomes the falciform ligament and the posterior part becomes the lesser omentum.
58
Why is there a lesser sac and retroperitoneal organs?
During development, organs grow, migrate, and rotate towards their final positions. As they do so, they ‘pull’ their peritoneal attachments with them. Growth, migration, and rotation of organs during development is responsible for the formation of the lesser sac and results in some organs being ‘pushed’ onto the posterior abdominal wall and becoming retroperitoneal.
59
What is peritonitis?
Peritonitis describes infection and inflammation of the peritoneum. It may be localised (i.e. to the region of peritoneum adjacent to an inflamed / infected organ) or generalised (affecting the whole peritoneum). Peritonitis may be caused by inflammation of an organ (e.g. the pancreas) or rupture of a hollow viscus (e.g. the stomach or bowel). Rupture of the intestine allows faecal matter and bacteria to contaminate the peritoneum. Because the peritoneum has a large surface area and is semi-permeable, peritonitis can lead to sepsis and is hence a life-threatening condition. Peritonitis is extremely painful.
60
What are peritoneal adhesions?
In a healthy abdomen, a thin layer of peritoneal fluid allows the abdominal viscera to slide freely alongside each other. Adhesions are pathological fibrous connections between the parietal and visceral peritoneum. When the peritoneum is irritated (e.g. by infection) it produces fibrin which causes the parietal and visceral peritoneum to adhere to each other. These connections may become fibrous. They can cause chronic abdominal pain and they increase the risk of volvulus (twisting) of the intestine, because it can no longer move freely.
61
What is ascites?
Ascites is an increased volume of peritoneal fluid. It occurs secondary to other pathology, such heart failure, liver failure or intra-abdominal malignancy. The abdomen may become very distended, and it is very uncomfortable. An ascitic drain can be used to remove the fluid and relieve symptoms, but fluid will usually reaccumulate.
62
What are the three parts of the developing gut tube?
Foregut
Midgut
Hindgut
63
Where is the foregut?
oesophagus to halfway along the duodenum
64
Where is the midgut?
half way along the duodenum to
2/3 of the way along the transverse colon
65
Where is the hind gut?
2/3 of the way along the duodenum to the upper anal canal
66
What is the clinical relevance of the peritoneum?
Peritonitis – inflammation / infection of the peritoneum
Adhesions – fibrous connections between the parietal and visceral peritoneum Tethers organs to each other or to the abdominal wall.
Ascites – increased volume of peritoneal fluid.
67
Describe the abdominal aorta
Lies just to the left of the midline on the posterior abdominal wall.
Carries blood to the abdomen.
Bifurcates at L4/5 into the right and left common iliac arteries > supply the pelvis and lower limbs.
The aorta gives rise to paired and unpaired (single) branches in the abdomen.
68
What are the three unpaired branches of the abdominal aorta?
3 unpaired branches leave the anterior aspect of the abdominal aorta and supply the gut:
The coeliac trunk (axis) at T12 > supplies the foregut
The superior mesenteric artery at L1 > supplies the midgut
The inferior mesenteric artery at L3 > supplies the hindgut
69
Where does the coeliac trunk supply?
Supplies the foregut: oesophagus, stomach, first half of the duodenum, liver, gallbladder, pancreas, spleen.
70
What are the branches of the coeliac trunk?
Left gastric artery > supplies the stomach
Splenic artery > supplies the spleen, stomach and pancreas
Common hepatic artery > supplies the liver, gallbladder, stomach, duodenum
71
Describe the superior mesenteric artery (SMA)
Artery of the midgut. It leaves the aorta at the level of L1. Its branches supply the midgut structures: the second half of the duodenum, the small intestine, and the large intestine as far as (and including) the first two thirds of the transverse colon. Branches also supply parts of the pancreas.
72
Describe the superior mesenteric artery
Supplies the foregut: oesophagus, stomach, first half of the duodenum, liver, gallbladder, pancreas, spleen.
Coeliac trunk has 3 branches:
Left gastric artery > supplies the stomach
Splenic artery > supplies the spleen, stomach and pancreas
Common hepatic artery > supplies the liver, gallbladder, stomach, duodenum
73
Describe mesenteric ischaemia
Thrombus in a mesenteric artery (or one of its branches) leading to hypoperfusion of the segment of gut the vessel supplies. Can progress to infarction of the gut. Mortality is high.
74
Describe ulcers
Ulcers of the stomach and duodenum – may erode through nearly vessels and cause severe intra-abdominal bleeding.
75
Describe abdominal aortic aneurysm (AAA)
part of the wall of the aorta weakens and bulges / expands. Rupture has a high mortality – older people, sudden onset severe abdominal / back pain, rapid bleeding, circulatory shock.
76
Describe the systemic veins
Carry venous blood directly to the IVC – blood does not pass through the liver
E.g. renal veins, adrenal veins, hepatic veins
77
Describe the portal veins/ system
Carry nutrient-rich venous blood from the gut to the liver. Blood then enters the hepatic veins and returns to the IVC.
E.g. superior mesenteric and inferior mesenteric veins
78
Describe the portal system
The inferior mesenteric vein unites with the splenic vein.
The splenic vein unites with the superior mesenteric vein to form the hepatic portal vein.
The hepatic portal vein enters the liver. Blood is processed, nutrients removed, and the venous blood then enters the hepatic veins, which join the inferior vena cava.
79
Describe liver metastases from colon cancer
Cancers of the colon often metastasize to the liver because venous blood from the colon is carried first to the liver via the portal system.
80
Describe portal hypertension
High blood pressure in the portal system because of obstruction to flow through the portal vein or liver. Can lead to distended veins and bleeding at sites of portosystemic anastomoses
81
Where does the foregut start and end?
Starts: Distal oesophagus
Ends: Halfway along the duodenum (1st and 2nd parts of the duodenum are foregut)
82
Where does the midgut start and end?
Starts:Halfway along the duodenum (just distal to the entrance of the bile duct – 3rd and 4th parts of duodenum are midgut)
End: Junction of the proximal 2/3 of the transverse colon with the proximal 1/3 (first 2/3 of the transverse colon are midgut)
83
Where does the hindgut start and end?
Start: Distal 1/3 of the transverse colon
End: Upper anal canal
84
Arterial supply of the foregut
Coeliac trunk
85
Innervation of the ANS (symp/parasymp) of the foregut
S: Greater splanchnic n. (T5 – T9)
P: Vagus
86
Where is visceral pain in the foregut felt?
Epigastric region
87
Arterial supply of the midgut
Superior mesenteric artery
88
Innervation of the midgut
S: Lesser splanchnic n. (T10-11)
P: Vagus
89
Which artery supplies the hindgut?
Inferior mesenteric artery
90
Innervation of the Hindgut
S: Least splanchnic n. (T12 +/- L1) and lumbar splanchnic nerves
P: Pelvic splanchnics
91
Describe lateral folding in the embryo
Closure of the gut tube along its length except for a connection that remains between the midgut region and yolk sac – the vitelline duct > narrows and degenerates during gestation
Closure of the ventral body wall complete except at the connecting stalk > umbilical cord
92
Where is mesentery
Dorsal is all along behind the gut tube
in front it is only in the foregut
93
Describe the differentiation of the gut tube
The gut tube starts to differentiate whilst lateral folding is bringing the ventral body wall together.
Concentration gradient of retinoic acid starts to specify the different parts
Lowest levels cranially
Highest levels distally
Differential expression of transcription factors and genes along the tube specify how regions will develop.
94
What is included in the foregut?
Oesophagus
Stomach
First half of the duodenum (1st and 2nd parts)
95
What are the derivatives of the foregut?
Liver
Pancreas
96
What are the mesenteries of the foregut?
Dorsal mesentery
Ventral mesentery
97
Describe the development of the oesophagus
The lung bud appears at the ventral wall of the foregut in the 4th week – become separated from each other.
98
What is abnormal development of the oesophagus?
Oesophageal atresia -absence or narrowing of oesophagus
Tracheoesophageal fistula- abnormal connection between trachea and oesophagus
Because the oesophagus doesn't properly separate from the trachea
99
Describe the development of the stomach
This section of the gut tube starts to dilate in week 4
Changes shape due to different rates of growth of different parts
Changes position – rotates 900 clockwise around its long axis: brings the left side to lie anteriorly and the right side to lie posteriorly
Brings duodenum to the right
100
Describe development of the liver from 25 to 32 days
Liver bud is an outgrowth from the distal foregut - appears in week 3
Cells proliferate into the septum transversum (mesoderm)
Connection between the liver bud and foregut (duodenum) narrows > bile duct
101
Describe the development of the liver from 32 days onwards
Small outgrowth from the bile duct > gallbladder
As the liver grows, mesoderm of the septum transversum forms the falciform ligament and lesser omentum
102
What does the ventral mesentery split into?
lesser omentum – connects the liver to the stomach and duodenum
falciform ligament – connects the liver to the anterior abdominal wall
103
Describe development of the pancreas
Dorsal and ventral buds arise from the duodenum
Dorsal bud develops in the dorsal mesentery
Rotation of the stomach swings the ventral bud posteriorly
Dorsal and ventral buds fuse
104
Where is the final position of the stomach?
Rotation of the stomach brings its left side anteriorly and swings the duodenum to the right
A small space behind the stomach – the lesser sac – is formed
105
Where are the final positions of the mesenteries in the foregut?
The dorsal mesentery along the greater curvature bulges down and grows – the greater omentum. This becomes fixed to the mesentery of the transverse colon (and posterior wall).
Rotation alters the position of the mesenteries, omenta and peritoneal ligaments
106
Which organs become retroperitoneal during development?
Pancreas and duodenum, Ascending and descending colon
107
WHat are the 3 pairs of major salivary glands?
c 80% of salivary flow)
Parotid
Submandibular
Sublingual
108
Where are the minor salivary glands
Submucosa of oral mucosa – lips, cheeks, hard and soft palate, tongue
109
What is the structure of salivary glands?
Composed of two morphologically and
distinct epithelial tissue
– acinar cells around
– ducts - collect to form large
duct entering the mouth
Equipped with channels and
transporters in the apical and basolateral
membranes enabling transport of fluid
and electrolytes
i.e. just like any other secretory or
reabsorbing epithelia
110
Describe serous acini
Dark staining
nucleus in basal third
Small central duct
Secrete water + α amylase
111
Describe mucous acinus
Pale staining - ‘foamy’
Nucleus at base
Large central
duct
Secrete mucous (water + glycoproteins)
112
Which type of acini does each gland contain?
Parotid gland - serous acini
Submandibular – mixed and referred to as seromucous
Sublingual – mixed but more mucous acini
113
What are intralobular ducts?
An intralobular duct is a portion of an exocrine gland inside a lobule, leading directly from acinus to an interlobular duct
114
WHat are intercalated ducts
short narrow duct segments with cuboidal cells that connect acini to larger striated ducts
115
WHat are striated ducts and what do they look like
Major site for reabsorption of NaCl
striped.
Connect the intercalated ducts to the interlobular ducts. They are found in the salivary glands and the pancreas. They are characterized by the basal infoldings of their plasma membrane
116
Describe the hypotonic nature of the saliva
The ducts are NOT just a plumbing system.
Primary saliva – NaCl rich isotonic plasma-like fluid secreted by acini.
Electrolyte composition is modified in duct system.
Ducts secrete K+ and HCO3- and reabsorb Na+ and Cl-.
Epithelium of duct doesn’t allow any water movement so final saliva becomes hypotonic.
117
What are the borders of the parotid glands?
Superior – zygomatic arch
Posterior – external acoustic meatus and sternocleidomastoid muscle
Anterior – sternocleidomastoid muscle inferiorly, masseter muscle
118
What structures run through the parotid gland
Horizontally it has a triangular outline with apex on carotid sheath
External carotid artery + terminal branches
Retromandibular vein
Facial nerve + branches to muscles of facial expression
Parotid capsule very tough
119
Describe the lobes of the submandibular gland
Two lobes separated by mylohyoid muscle
Larger superficial lobe
Smaller deep lobe in floor of mouth
Submandibular duct (Wharton’s duct) begins in superficial lobe, wraps round free posterior border of mylohyoid, runs along floor of mouth and empties into oral cavity at sublingual papillae.
120
Describe the acini of the submandibular gland
Histology – mixed gland with serous and mucous acini.
Some serous acini arranged as a crescent-shaped groups of glandular cells at the bases of mucous acini referred to as serous demilunes
121
Describe the sublingual glands
Between mylohyoid muscle and oral mucosa of the floor of the mouth
No large duct – drains into submandibular (Wharton’s) duct and/or small ducts that pierce oral mucosa on the floor of the mouth
122
Where are the minor salivary glands found?
Concentrated in the buccal labial, palatal and lingual regions.
Also found at
superior pole of tonsils (Weber’s glands),
tonsillar pillars
base of the tongue (von Ebner’s glands - underlying circumvallate papillae).
123
What type of acini are in minor salivary glands
All minor salivary glands are mucous except serous glands of von Ebner
124
Ducts of msgs
Minor salivary glands lack a branching network of draining ducts
- each salivary unit has own simple duct
125
DEscribe the stimulation of salivary glands
Stimulation of parasympathetic nerves causes the production of a copious
flow of saliva while sympathetic stimulation selectively causes secretion of
protein and glycoprotein
126
What are the functions of saliva?
Lubricant for mastication, swallowing and speech
Oral hygiene - Wash
- Immunity – Antibacterial/antiviral/antifungal
- Buffer
Oral pH needs to be maintained at about pH 7.2 (but ranges from 6.2-7.4)
- bicarbonate/carbonate buffer system for rapid neutralisation of acids
Digestive enzyme
- Aqueous solvent necessary for taste
Dysfunction associated with oral pain, infections and increased risk of dental caries
127
Describe the rate and volume of production of saliva
Flow rate from 0.3 to 7ml per minute
Daily secretion of 800 – 1500ml in adults from major and
minor glands.
128
Describe the function of serous secretion
α amylase – starch digestion
129
Describe the function of mucous secretion
Mucins for lubrication of mucosal surfaces
130
What factors affect the composition and amount of saliva produced?
Flow rate
Circadian rhythm
Type and size of gland
Duration and type of stimulus
Diet
Drugs
Age
Gender
131
What is the general function of saliva?
-Secretion of proteins and glycoproteins in a
buffered electrolyte solution
-Major contributor to oral health
-Lubrication – mucous coat
-Mechanical cleaning – flow
-Buffering salts – neutralise acid
-Remineralisation – Ca 2+ and PO43-
-Defensive and digestive function - proteins
132
Describe proteins in saliva
3652 proteins and 12,562 peptides detected to date
51% of proteins and 79% of peptides also contained in plasma
133
What is defence in the mouth provided by?
a) The mucosa - physical barrier
b) Palatine tonsils – lymphocyte subsets + dendritic cells – immune surveillance and resistance to infection
c) Salivary glands – saliva washes away food particles bacteria or viruses might use for metabolic support
134
What is the link between saliva and immunity?
Salivary glands are surrounded by lymphatic system
– linked to thoracic duct and blood
Broad range of functional immune cells
Oral mucosa and glands have high blood flow rate
135
WHen do each of the glands produce saliva
Submandibular, sublingual and minor glands are
continuously active
Parotid – no measurable unstimulated secretion but becomes
main source of saliva when stimulated
136
What is unstimulated vs stimulated saliva?
Unstimulated saliva is dominated by SMG components
Stimulated has composition resembling parotid secretion
137
What is whole saliva?
salivary gland secretions, blood, oral tissues,
microorganisms and food remnants
means that saliva can be used for diagnosis
138
What are the different causes of salivary gland disease and dysfunction
Obstructive
Inflammatory
Degenerative
Drug side effects
Cancer
139
What is xerostomia and what are the most common causes?
dry mouth
May be a consequence of cystic fibrosis or Sjogrens syndrome
Most common causes – medication and irradiation for head and neck cancers
High prevalence of caries and Candida infections
140
Describe obstruction of the salivary glands
Saliva contains calcium and phosphate ions that can form salivary calculi (stones)
Most often in submandibular gland (c 80%)
Block duct at bend round mylohyoid [X] or at exit at sublingual papillae [X]
141
Describe inflammation of the salivary glands
Infection secondary to blockage
Mumps (viral infection)
Fever, malaise
Swelling of glands
Pain especially over parotid because capsule
does not allow much enlargement
142
Describe degenerative diseases of the salivary glands
Complication of radiotherapy to head and neck for cancer treatment
Sjogren’s syndrome
Mainly post-menopausal females
Also affects lacrimal glands
Rheumatoid arthritis may also be present
143
Describe drug side effects in relation to saliva
The most common dysfunction you will encounter
About 500 prescription drugs have a sympatheticomimetic effect
Act on NA receptors or
inhibit parasympathetic action at ACh receptors
144
Effects of salivary gland dysfuntion
If salivary output falls to < 50% of normal flow – patient experiences xerostomia (dry mouth)
Low lubrication – oral function difficult
Low (natural) oral hygiene – poor pH control
Accumulation of plaque =>Rampant dental caries, gingivitis and periodontal disease
Opportunistic infections esp. fungal infections (candida = thrush)
145
Describe salivary gland cancers
They are rare – only about 720 cases per year in the UK
80% of SGT are benign and so incidence of malignancies only around 1.2-1.3 cases per 100,000 of population or around 3% of all head and neck cancers
Circa 65% of the benign tumours are pleomorphic adenomas –
the most common type of SGT
Parotid – 70% of SGT
Submandibular – 10%
Sublingual – less than 1%
Minor glands – around 20%
BUT 50% of the tumours found in minor glands are malignant (20% in major glands)
AND tumours in sublingual almost always malignant
146
Describe the distal oesphagus
The oesophagus passes through the oesophageal hiatus in the diaphragm at the level of T10. The muscle around the hiatus functions as a sphincter that prevents reflux of stomach contents into the oesophagus. The abdominal segment of the oesophagus is less than 2 centimetres long.
147
Describe the blood supply to the distal oesophagus
The distal oesophagus is supplied by branches from the left gastric artery. Its venous drainage is towards both the systemic system of veins (via oesophageal veins that drain into the azygos vein) and to the portal venous system (via the left gastric veins). The distal oesophagus is thus a site of portosystemic anastomoses, which are clinically important. We will come back to portosystemic anastomoses in later sessions.
148
Describe the junction of the oesophagus and stomach
The oesophagus travels through the diaphragm at the level of T10 and is continuous with the cardia of the stomach.
149
Describe the fundus
Most superior part of the stomach
It lies superior to the level of entry of the oesophagus and is usually filled with gas.
150
Describe the body of the stomach
The largest part of the stomach
151
Describe the pyloric part, where it is and what it contains
The pyloric part is distal to the body. The pyloric antrum is wide and tapers towards the pyloric canal, which is narrow and contains the pyloric sphincter. The sphincter is a formed of circular smooth muscle. It regulates the passage of chyme into the duodenum.
152
What are the two curvatures of the stomach and where are they?
The right border of the stomach is the lesser curvature. The longer left border is the greater curvature.
153
Where is the stomach?
The stomach lies in the left upper quadrant, but its size and position are variable. It is covered with visceral peritoneum.
* Its anterior surface is related to the anterior abdominal wall, diaphragm, and left lobe of the liver.
* Its posterior surface forms the anterior wall of the lesser sac.
154
Describe the lesser sac
The lesser sac and the structures that form its posterior wall lie posterior to the stomach: these include the pancreas, left kidney and spleen.
155
What is the lesser omentum and it's free edge
* The lesser omentum connects the lesser curvature to the liver.
* The free edge of the lesser omentum contains the hepatic artery, hepatic portal vein and the bile duct.
* Posterior to the free edge is the entrance to the lesser sac.
156
Where is the greater omentum?
* The greater omentum hangs from the greater curvature.
157
What is the coeliac trunk and what does it supply?
The coeliac trunk is only a short stump; it divides into three branches close to the aorta. These are the left gastric artery, the common hepatic artery, and the splenic artery.
It supplies the organs of the foregut incl. stomach, 1/2 duodenum, liver, gallbladder, pancreas and spleen
158
Describe the left gastric artery
Runs along lesser curvature of the stomach
Anastomoses with the right gastric artery Arises from the coeliac trunk.
159
Describe the right gastric artery
Runs along the lesser curvature of the stomach and anastomoses with the left gastric artery
May arise from either the common hepatic artery or the hepatic artery proper.
160
Describe the left gastro-omental
Runs along the greater curvature of the stomach
Anastomoses with the right gastro-omental
Arises from the splenic artery
161
Describe the right gastro-omental
Runs along the greater curvature of the stomach
Anastomoses with the left gastro-omental artery
Arises from the gastroduodenal artery, a branch of the common hepatic artery.
162
Describe the hepatic portal vein and what other veins run into it
Right and left gastric veins and right and left gastro-omental veins drain into the hepatic portal vein (HPV). The hepatic portal vein is a large vein that carries nutrient-rich venous blood from the GI tract to the liver.
163
Describe parasympathetic stimulation of the stomach
The vagus nerve conveys parasympathetic fibres to the stomach. Parasympathetic stimulation promotes peristalsis and gastric secretion.
164
Describe the sympathetic innervation of the stomach
Sympathetic fibres are conveyed to the stomach via the greater splanchnic nerve. The greater splanchnic nerve is formed of preganglionic sympathetic fibres that leave spinal cord segments T5-T9 and pass through the sympathetic trunk without synapsing. The fibres synapse in prevertebral ganglia around the coeliac trunk. The postganglionic fibres travel to the stomach and inhibit peristalsis and secretion.
165
What is a hiatus hernia?
The abdominal oesophagus and upper part of the stomach may herniate through the oesophageal hiatus into the thorax. If contents of the stomach reflux into the oesophagus the patient may experience heartburn (a burning feeling in the chest after eating) and acid reflux (regurgitation of bitter fluid).
166
What is a gastric ulcer?
Mucous lines the internal wall of the stomach and protects the mucosa from the acidic stomach contents. A gastric (stomach) ulcer develops when the mucosal lining of the stomach breaks down. This is normally due to infection with Helicobacter pylori, which erodes the mucosal lining, exposing the muscular wall to gastric acid and enzymes. Erosion through the wall and into nearby blood vessels can result in catastrophic intra-abdominal bleeding.
167
What is pyloric stenosis?
This is a congenital malformation characterised by hypertrophy of the circular smooth muscle of the pyloric sphincter. It is more common in baby boys than girls and typically presents at approximately six weeks after birth. The typical presentation is of vomiting (sometimes projectile) after feeds, but the baby does not appear unwell and is hungry and willing to take more feeds. With continued vomiting, babies with pyloric stenosis become dehydrated and stop gaining weight. It can be treated surgically.
168
What is gastric cancer?
Primary cancer of the stomach may present late as some of the symptoms are non- specific. Symptoms include abdominal discomfort, early satiety (feeling full quickly), loss of appetite, nausea, weight loss, difficulty swallowing and indigestion.
169
What is the duodenum and where is it ?
The duodenum is continuous with the pylorus of the stomach. It is short and curved into a C-shape around the head of the pancreas. Most of the length of the duodenum is retroperitoneal.
170
What is the major duodenal papilla and where is it?
Approximately halfway along the internal wall of the duodenum is the major duodenal papilla. This is the opening of the bile duct and the main pancreatic duct into the duodenum.
171
Where does the duodenum develop from and what arteries is it supplied by?
The first half of the duodenum develops from the embryological foregut and is supplied by arterial branches from the coeliac trunk. The second half of the duodenum develops from the embryological midgut and is supplied by branches from the artery of the midgut – the superior mesenteric artery
172
Where are the jejunum and ileum
Both the jejunum and ileum are intraperitoneal and are ‘suspended’ from the posterior abdominal wall by the mesentery of the small intestine. The small intestine lies centrally in the abdomen; the jejunum lying in the left upper region and the ileum lying in the right lower region.
173
Where are the blood vessels that supply the jejunum and ileum?
Blood vessels that supply the small intestine (from the superior mesenteric artery) are embedded within the mesentery
174
Where do the jejunum and ileum develop from?
Both the jejunum and ileum are derived from the embryological midgut.
175
What is the function of the jejunum and ileum
The jejunum and ileum are the sites of nutrient absorption, so have a vast surface area: the small intestine is long, the mucosa is folded (plicae circulares), the mucosal folds bear villi and there are microvilli on the luminal surface of each epithelial cell
176
What's the visible difference between the jejunum and ileum?
The plicae are more pronounced in the jejunum. The internal ileum is characterised by Peyer’s patches, which are large submucosal lymph nodules.
177
What is Meckel's diverticulum?
Blind-ended diverticulum approximately one metre from the termination of the ileum. embryological remnant of the connection that was present between the midgut loop to the yolk sac. If it becomes inflamed, it may mimic an appendicitis (inflammation of the appendix). Up to 4% of ppl
178
Where is the ileocaecal junction and what does it connect?
The terminal ileum is continuous with the caecum - the first part of the large intestine – at the ileocaecal junction in the right iliac fossa.
179
What does the large intestine do?
Reabsorbs water from faecal material to form semi-solid faeces
180
Where is the large intestine?
It lies peripherally in the abdomen and some segments are retroperitoneal, and some are intraperitoneal
181
What are the different parts of the large intestine?
Caecum, appendix, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, and anal canal.
182
What is the visible difference between the small and large intestine?
The L. intestine is peripherally located, and larger calibre. The outer longitudinal muscle layer is organised into three bands – the taeniae coli. The inner circular muscle layer forms ‘bulges’ called haustra (or haustrations). The large intestine bears fatty tags called epiploic appendages (appendices epiploicae) that mark the point at which blood vessels penetrate the intestinal wall.
183
What is the caecum?
The caecum is the first part of the large intestine. It is a distended, blind-ended ‘pouch’. The caecum is covered by peritoneum but does not have a mesentery.
184
What is the appendix?
The appendix is a small diverticulum that arises from the caecum and contains lymphoid tissue. The surface marking of the base of the appendix is McBurney’s point. The appendix varies in length and the position of its tip is variable. The appendix is connected to the caecum by a small mesentery, the mesoappendix.
185
Describe the ascending colon
The ascending colon is continuous with the caecum. It runs vertically on the right side of the posterior abdominal wall in the right paracolic gutter. It is retroperitoneal (it is an example of a secondarily retroperitoneal organ).
186
What is the hepatic flexure?
The ascending colon makes a 90 degree turn left in the right upper quadrant, becoming continuous with the transverse colon. The ‘bend’ in the colon here is the hepatic flexure (sometimes called the right colic flexure).
187
Describe the transverse colon
The transverse colon is continuous with the ascending colon. It runs horizontally in the upper abdomen but often hangs inferiorly. It is intraperitoneal and is suspended from the posterior abdominal wall by the transverse mesocolon.
188
Describe the splenic flexure
The ‘bend’ in the colon here is the splenic flexure (sometimes called the left colic flexure). The splenic flexure is tethered to the diaphragm by the phrenicocolic ligament – we will come back to the clinical importance of this later when we look at the spleen.
189
What is the point where the midgut becomes the hindgut?
The transverse colon marks the transition point between the embryological midgut and embryological hindgut. The proximal (first) two thirds develop from the embryological midgut, whilst the distal (last) third develops from the embryological hindgut. This means that these two parts of the transverse colon are supplied by different blood vessels and nerves.
190
Describe the descending colon
The descending colon is continuous with the transverse colon superiorly and the sigmoid colon inferiorly. It runs vertically on the left side of the posterior abdominal wall in the left paracolic gutter. It is retroperitoneal (also secondarily retroperitoneal).
191
Describe the sigmoid colon
The sigmoid colon lies in the left lower quadrant and is named because of its sinuous shape. It is continuous with the descending colon superiorly and the rectum inferiorly. As the sigmoid approaches the midline, it makes a 90 degree turn inferiorly into the pelvis - this ‘bend’ is the rectosigmoid junction. The sigmoid colon has a mesentery - the sigmoid mesocolon - and is therefore intraperitoneal.
192
Where are the rectum and the anal canal?
The rectum lies in the pelvis and is retroperitoneal. It is continuous superiorly with the rectosigmoid junction (at the level of S3) and inferiorly with the anal canal.
193
Where does the superior mesenteric artery's branches supply?
Its branches supply the midgut structures: the second half of the duodenum, the small intestine, and the large intestine as far as (and including) the first two thirds of the transverse colon. Branches also supply parts of the pancreas.
194
What are the branches of the superior mesenteric artery and what do they supply?
* Jejunal branches – several branches to the jejunum
* Ileal branches – several branches to the ileum
* Ileocolic artery – supplies the caecum, appendix, and ascending colon
* Right colic artery – supplies the ascending colon
* Middle colic artery – supplies the transverse colon.
195
Where are the jejunal and ileal branches of the superior mesenteric and how do they supply the intestinal wall?
The jejunal and ileal branches are embedded in the mesentery of the small intestine. They anastomose with each other, forming ‘loops’ of arteries called arcades. From these arcades run the vasa recta (‘straight’ vessels), which supply the intestinal wall.
196
Where is the inferior mesenteric artery?
The inferior mesenteric artery is the artery of the hindgut. It leaves the aorta at the level of L3
197
What does the branches of the inferior mesenteric supply?
Hindgut structures: the distal third of the transverse colon, the descending and sigmoid colon, the rectum, and the upper part of the anal canal.
198
What are the major branches of the inferior mesenteric artery?
* Left colic artery – supplies the transverse colon and the descending colon
* Sigmoid branches – supply the sigmoid colon
* Superior rectal artery – the terminal branch of the IMA, which supplies the rectum.
199
What is the marginal artery?
Branches of the middle colic artery (from the SMA) and left colic artery anastomose along the distal third of the transverse colon and the splenic flexure forming the marginal artery
200
What arteries supply the rectum?
Middle and inferior rectal arteries which branch from the internal iliac arteries in the pelvis. The middle and inferior rectal arteries anastomose with branches of the superior rectal arteries.
201
Describe venous drainage of the intestines
Venous blood from the gut ultimately reaches the inferior vena cava (IVC) and is returned to the heart. However, venous blood from the gut contains absorbed nutrients, so it first enters the liver via the portal venous system before being returned to the heart via the IVC.
202
Describe the inferior mesenteric vein
The inferior mesenteric vein (IMV) accompanies the IMA and drains the hindgut. The inferior mesenteric vein ascends on the left side of the abdomen and typically drains into the splenic vein from the spleen. Venous blood from the rectum drains into both the portal system (via the IMA) and into the systemic system (via the internal iliac veins).
203
Describe the superior mesenteric vein
The superior mesenteric vein (SMV) accompanies the SMA and drains the midgut. The SMV ascends and unites with the splenic vein close to the liver (posterior to the neck of the pancreas) to form the hepatic portal vein.
204
Describe the hepatic portal vein
The hepatic portal vein enters the liver. After the nutrients are removed from the blood, it enters small hepatic veins, which unite within the liver to form two or three large hepatic veins that enter the IVC as it passes posterior the liver (hence the hepatic veins are within the liver and cannot be seen externally).
205
What nerves supply parasympathetic stimulation to the foregut and midgut?
Vagus nerves
206
What nerves provide parasympathetic stimulation to the hindgut?
Pelvic splanchnic nerves
207
How are splanchnic nerves formed?
By the axons of parasympathetic neurons that lie in the sacral spinal cord.
* The cell bodies of preganglionic parasympathetic neurons lie in sacral segments S2 – S4.
* The axons of these neurons leave the spinal cord and form the pelvic splanchnic nerves.
* The preganglionic axons synapse with a second neuron in a ganglion. The parasympathetic ganglia are located very close to, or even within, the walls of the viscera.
208
Where do the greater splanchnic nerves innervate?
The greater splanchnic carries fibres from T5 – T9 and innervates the foregut.
209
What are the stages of development of the midgut
1. Elongation (growth)
2. Physiological herniation (protrusion into the umbilical cord) – week 6
3. Rotation (around the axis of the superior mesenteric artery)
4. Retraction (back into the abdomen) – week 10
5. Fixation
210
Describe stage 1 (elongation) of development of the midgut
Elongation > formation of the primary intestinal loop
Connection to the yolk sac (the vitelline duct) is maintained, but narrows
211
What does the Cephalic limb of the primary intestinal loop give rise to?
Distal part of the duodenum
Jejunum
Part of the ileum
212
What does the caudal limb of the primary intestinal loop give rise to?
Distal part of the ileum
Caecum
Appendix
Ascending colon
Proximal 2/3 transverse colon
213
What is the caecal bud
develops into caecum
214
Describe stage 2 (physiological herniation) of the development of the midgut
The intestinal loops herniate into (i.e. move into) the umbilical cord in the 6th week
Why? The abdominal cavity is too small for the gut loops and the liver, which are both rapidly growing
During herniation, the gut loop starts to rotate
215
Describe stage 3 (rotation) of the development of the midgut
Rotation is 90degerees anticlockwise, as viewed from the front, around the axis of the superior mesenteric artery (SMA).
The first 90degrees of rotation occurs as the gut loop herniates.
This brings the caudal limb – which will form the more distal parts of the midgut, more cranially
216
What process happens alongside herniation?
Elongation continues: the part destined to become small intestine develops coils
The segment destined to become large intestine also elongates, but it doesn’t coil
217
Describe stage 4 (retraction) of the development of the midgut
Week 10, the gut loop returns to the abdomen – factors guiding are not fully understood
During this stage, the gut loop rotates a further 1800 anticlockwise
In total, the gut loop rotates approx. 2700 anticlockwise
218
How does retraction start to position the gut?
Jejunum returns first > left side. Followed by ileum > settles towards the right
Caecum returns last to the right upper quadrant
Caecum descends to right iliac fossa, thus ascending colon settles on the right
219
Describe stage 5 (fixation) of the development of the midgut
Some mesenteries come into close contact with the posterior abdominal wall and become fused / fixed to the posterior wall
They are considered ‘retroperitoneal’
Where this happens, a fascial layer – Toldt fascia – develops between the parietal peritoneum on the posterior body wall and the visceral peritoneum on the organ
220
What are the final positions and mesenteries of the Ileum and jejunum?
Some mesenteries come into close contact with the posterior abdominal wall and become fused / fixed to the posterior wall
They are considered ‘retroperitoneal’
Where this happens, a fascial layer – Toldt fascia – develops between the parietal peritoneum on the posterior body wall and the visceral peritoneum on the organ
221
Which organs of the abdomen are fixed (retroperitoneal?
Ascending colon
222
Which of the abdominal organs are mobile (intraperitoneal)?
Stomach, caecum, sigmoid colon
223
Describe the caecal bud and the appendix
Once the gut returns to the abdomen the caecal bud is first in the upper right quadrant
It descends to the right iliac fossa as the ascending colon lengthens – the appendix develops during descent
The appendix comes to lie in a variety of positions
224
What can some congenital anomalies occur with?
Gut rotation
Return of the gut loops to the abdomen
Mesenteries
225
What is omphalocele?
Midgut loop doesn’t return to the abdomen in the 10th week; remains in the umbilical cord
Gut is covered with a layer of amnion
High mortality – often associated with other congenital and chromosomal anomalies
Different from gastroschisis
226
Describe the formation of the hindgut
Extends as far as the upper anal canal.
The last part of the hindgut communicates with the cloaca.
Urorectal septum grows towards the cloacal membrane and separates the urogenital sinus from the cloaca.
227
Describe the formation of the anorectal canal
Ectoderm invaginates
> forms the anal pit
> lower part of the anorectal canal
Cloacal (anal) membrane ruptures
> upper and lower parts of the anal
canal become continuous with
each other
Because of their different origins, the upper and lower parts of the anal canal have different blood supplies and epithelia.
228
What are some congenital anomalies of the urorectal septum?
Urorectal fistula
Absence of connection between the rectum and anal pit as anal membrane hasn't broken down - imperforate anus
229
Where is the liver?
The liver is protected by the ribs and moves inferiorly with inspiration – the lowermost part of the liver may be palpable below the right costal margin in inspiration
230
What does the liver do?
All the products of digestion, except lipids, are transported to the liver from the gut via the hepatic portal vein. The liver also produces bile, which is transported to the gallbladder for storage. Bile emulsifies lipids in the chyme entering the duodenum from the stomach
231
What are the two surfaces of the liver and where are they?
* The diaphragmatic surface lies anterosuperior and is related to the inferior surface of the diaphragm.
* The visceral surface lies posteroinferior and is related to other organs.
232
What are the areas of the liver not covered with visceral peritoneum?
* bare area of the liver – a region on the posterior surface that lies in contact with the diaphragm
* the region where the gallbladder lies in contact with the liver
* region of the porta hepatis – where hepatic blood vessels and ducts of the biliary system enter and exit the liver (the equivalent of the hilum of the lung)
233
Describe the two anatomical lobes and what separates them
The liver is composed of two anatomical lobes – a large right lobe and a small left lobe. They are separated by the falciform ligament, which connects the anterior surface of the liver to the internal aspect of the anterior abdominal wall.
234
Describe the two accessory lobes of the lung and their placement
Two accessory lobes, the caudate and quadrate lobes, are located on the posteroinferior surface. These lobes do not represent the internal, functional organisation of the liver.
235
Describe the eight functional segments of the lung
Internally the liver is organised into eight functional segments. Each segment is served by its own branch of the hepatic artery and portal vein, and by its own hepatic duct.
236
How is the liver connected to different things?
The liver is connected to the:
* diaphragm by the coronary and triangular ligaments
* anterior abdominal wall by the falciform ligament
* stomach and duodenum by the lesser omentum.
237
Describe the portal triad
The hepatic artery, hepatic portal vein and the bile duct run together as the portal triad in the free edge of the lesser omentum. The portal triad and the free edge of the lesser omentum form the anterior boundary of the epiploic foramen; the entrance into the lesser sac (which lies posterior to the stomach).
238
Describe the two recesses in the liver
* The hepatorenal recess lies between the right kidney and the posterior (visceral) surface of the right side of the liver. Fluid flows into this space in the supine position.
* The left and right subphrenic recesses lie either side of the falciform ligament, between the anterosuperior surface of the liver and the diaphragm.
239
Describe the development of the liver
The liver develops from the embryological foregut. It grows from a tissue bud that develops in the ventral mesentery – a peritoneal fold in the upper abdomen that connects the stomach to the anterior abdominal wall. As the liver grows and migrates to the right side of the abdomen, its peritoneal attachments are pulled with it. The remains of the ventral mesentery form the lesser omentum and the falciform ligament. The peritoneal attachments of the liver anchor it to surrounding structures, including the diaphragm superior to it.
240
Describe the round ligament of the liver
The free edge of the falciform ligament contains the round ligament of the liver (the ligamentum teres). It is the remnant of the umbilical vein, which, in the foetus, carries oxygenated blood from the placenta to the foetus
241
Describe the ligamentum venosum
Another embryological remnant, the ligamentum venosum, lies on the posterior surface of the liver, in the groove between the caudate lobe and the left lobe of the liver. It is the remains of the ductus venosus, which in foetal life diverts blood from the umbilical vein to the IVC, thus shunting oxygen-rich blood to the heart and bypassing the liver.
242
Describe the arterial blood supply to the liver
The liver is supplied by the right and left hepatic arteries. These branches ultimately derive from the coeliac trunk.
* The coeliac trunk gives rise to the left gastric, splenic, and common hepatic arteries.
* The common hepatic artery gives rise to the gastroduodenal artery; after this point, the common hepatic artery is called the hepatic artery proper (HAP).
* The hepatic artery proper bifurcates into right and left hepatic arteries, which enter the liver at the porta hepatis.
243
Describe venous blood pathway out of the liver
Venous blood exits the liver via two or three large hepatic veins that lie within the liver – they are not visible external to the liver. They unite with the inferior vena cava as it passes posterior to the liver.
244
Describe the hepatic portal vein
Nutrient-rich venous blood that leaves the gut is transported to the liver via the hepatic portal vein, which receives blood from the superior and inferior mesenteric veins and the splenic vein.
245
Describe the innervation of the liver
The liver is served by the hepatic plexus, which is formed of parasympathetic fibres from the vagus nerves and sympathetic fibres. These fibres follow the paths of the hepatic vessels and ducts of the biliary tree. Because the liver is a foregut derivative, pain arising from it is referred to the epigastric region.
246
Describe the gallbladder
The gallbladder stores and concentrates bile. It lies on the posteroinferior (visceral) surface of the liver and lies close to the duodenum. The gallbladder has three parts, the fundus, the body, and the neck.
247
Describe the body of the gallbladder
The body forms the main part of the gallbladder which sits in the gallbladder fossa on the visceral surface of the liver
248
Describe the neck of the gallbladder
It tapers towards the neck, which communicates with the cystic duct
249
Describe the fundus of the gallbladder and it's
The fundus is the rounded end of the gallbladder, which typically extends to the inferior border of the liver The surface marking of the fundus of the gallbladder is at the tip of the 9th costal cartilage, at the point where the right midclavicular line intersects the right costal margin.
250
Bile is continuously produced by hepatocytes in the liver and is first excreted into small channels called bile canaliculi. The canaliculi drain into bile ducts of increasing calibre, which ultimately converge to form right and left hepatic ducts that exit the liver at the porta hepatis.
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Describe the hepatic ducts
* The left and right hepatic ducts converge to form the common hepatic duct.
* The common hepatic duct receives the cystic duct from the gallbladder. Distal to this point, the duct is called the common bile duct (or sometimes just simply the bile duct).
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Where does the common bile duct go?
* The common bile duct runs in the free edge of the lesser omentum.
* The common bile duct descends posterior to the superior part of the duodenum and posterior to the head of the pancreas.
* The common bile duct enters the duodenum
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Describe the involvement of the gallbladder in the release of bile
If bile leaving the liver is not needed for digestion, it enters the gallbladder via the cystic duct. When needed, bile flows from the gallbladder, via the cystic duct, to the common bile duct and duodenum. The spiral fold (spiral valve) lies at the junction between the gallbladder neck and the cystic duct.
254
Describe the arterial supply of the gall bladder
Blood supply is via the cystic artery, which typically arises from the right hepatic artery (variation exists).
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Describe venous flow away from the gallbladder
The gallbladder is drained by cystic veins that pass directly into the liver or join the hepatic portal vein.
256
Describe the innervation of the gallbladder
The gallbladder is innervated by parasympathetic and sympathetic fibres.
257
Describe referred pain and the gall bladder
* Visceral afferents from the gallbladder return to the CNS with the sympathetic fibres. Visceral pain from the gallbladder enters spinal cord levels T5 – T9 and is therefore referred to (i.e. felt in) the epigastrium.
* Gallbladder pain may also be referred to the right shoulder if gallbladder pathology (e.g. inflammation) irritates the diaphragm. The diaphragm is innervated by the phrenic nerve (C3-5). Spinal cord segments C3-5 also receive somatic sensory information from the skin over the shoulder. Therefore gallbladder pathology involving the diaphragm may be felt in the right shoulder.
* If gallbladder pathology irritates the parietal peritoneum, which is innervated by somatic nerves, pain is well localised to the right hypochondrium
258
Describe hepatomegaly
Hepatomegaly is enlargement of the liver. Causes include hepatitis (inflammation of the liver from various causes), malignancy, and heart failure. When the liver is enlarged, its inferior border becomes palpable inferior to the right costal margin.
259
Describe liver metastases
Although primary cancer of the liver does occur, most cancers of the liver are metastases from cancer elsewhere in the body. Because venous blood from the gut passes through the liver, bowel cancers often metastasize to the liver.
260
Describe cirrhosis of the liver
Cirrhosis is sometimes referred to as ‘scarring’ of the liver. It is caused by chronic excess alcohol consumption, chronic infection with hepatitis B or C, or a build-up of fat in the liver. Hepatocytes are destroyed and replaced with fibrous tissue. The liver becomes shrunken, hard, and nodular. Loss of hepatocytes impairs the function of the liver and liver failure may ultimately result.
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Describe portal hypertension
Portal hypertension is high blood pressure in the portal venous system. It results when blood flow through the liver and portal vein is obstructed (e.g. in cirrhosis of the liver).
262
Describe portosystemic anastomoses
Portosystemic anastomoses are communications between veins draining to the systemic circulation and veins draining to the portal circulation. For example, in the distal oesophagus, venous blood drains into both the systemic veins (via the azygos) and into the portal system (via the gastric veins). If flow in the portal system is obstructed, pressure in the portal system increases and blood is diverted from the portal veins into the systemic veins. The systemic veins become distended and varicose (in the oesophagus these are called oesophageal varices) and prone to rupture, which can result in catastrophic bleeding.
263
Describe gallstones
Gallstones are common in the UK population. They are mostly composed of cholesterol. They are often asymptomatic but cause symptoms when they migrate into the biliary tree and lodge there.
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Describe biliary colic
When a gallstone lodges in the cystic duct, contraction of the gallbladder against it causes severe pain termed biliary colic.
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Describe cholecystitis
If the stone moves back into the gallbladder, the pain eases. If it does not, and the stone becomes stuck, it blocks the flow of bile into the cystic duct and the gallbladder becomes inflamed (cholecystitis). Cholecystectomy is removal of the gallbladder. It is usually performed laparoscopically
266
Describe the main branches of the coeliac trunk
* The left gastric artery – supplies the distal oesophagus and lesser curvature of the stomach.
* The common hepatic artery – branches supply the liver, stomach, and duodenum.
* The splenic artery – branches supply the stomach, pancreas, and spleen
267
Describe the duodenum
The duodenum is the first and shortest part of the small intestine. It is continuous proximally with the pylorus of the stomach and distally with the jejunum. The pyloric sphincter regulates gastric emptying into the duodenum
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Where is the duodenum?
Most of the duodenum is retroperitoneal.
The duodenum forms a C-shape that cups the head of the pancreas
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What are the four parts of the duodenum?
* The duodenum is described in four parts. These are the superior (first), descending (second), the inferior (third) and the ascending (fourth) parts.
* The common bile duct, gastroduodenal artery and the hepatic portal vein lie posterior to the first part of the duodenum.
* The superior mesenteric artery lies anterior to the third part.
* The fourth part meets the jejunum at the duodenojejunal flexure
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Where do bile and digestive pancreatic secretions enter the duodenum?
Approximately halfway along the internal wall of the duodenum is a small elevation called the major duodenal papilla (papilla = nipple-like). This marks the point at which bile and digestive pancreatic secretions (‘pancreatic juice’) enter the duodenum. We will learn more about this shortly.
271
Describe the arterial supply of the duodenum
The first half of the duodenum is derived from the foregut and is supplied by branches of the coeliac trunk (the artery of the foregut). The second half is derived from midgut and is supplied by branches of the superior mesenteric artery (the artery of the midgut). Arterial branches that supply the duodenum are derived from the:
* gastroduodenal artery (from the common hepatic artery and hence the coeliac trunk)
* inferior pancreaticoduodenal arteries (from the superior mesenteric artery)
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Describe the venous drainage of the duodenum
Veins follow the arteries and are tributaries of the hepatic portal vein.
273
Describe the pancreas
The pancreas lies horizontally on the posterior abdominal wall at the level of L1 and is retroperitoneal. It does not have a capsule so in the cadaver its surface appears ‘bumpy’ rather than smooth.
* It forms from dorsal and ventral pancreatic buds which fuse during development.
* It is composed of four parts: the head, the neck, the body, and the tail.
* The uncinate process is a hook-like projection of the head of the pancreas.
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Describe the location of the pancreas
* The head is cupped by the C-shaped duodenum and the tail extends to the hilum of the spleen.
* The pancreas forms part of the posterior wall of the lesser sac.
* The splenic artery runs towards the spleen embedded in the upper border of the pancreas. The splenic vein lies posterior to the pancreas.
* The main pancreatic duct and the accessory pancreatic duct run within the substance of the pancreas.
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What is the function of the pancreas?
The pancreas has an endocrine and an exocrine function. It synthesizes and secretes insulin and glucagon. Insulin is released in response to high levels of glucose in the blood. The pancreas also produces pancreatic juice that contains digestive enzymes. Pancreatic juice is transported through main pancreatic duct and the accessory pancreatic duct to the duodenum. The main and accessory pancreatic ducts usually communicate with each other.
276
Describe the relationship between the main pancreatic duct and the bile duct
The common bile duct and main pancreatic duct merge at the hepatopancreatic ampulla (ampulla = dilation). The hepatopancreatic ampulla opens into the second part of the duodenum at the major duodenal papilla, which is located on the internal wall of the duodenum, about halfway along its length. The hepatopancreatic ampulla is surrounded by smooth muscle - the hepatopancreatic sphincter (sometimes called the sphincter of Oddi). Contraction of the sphincter prevents reflux of duodenal contents into the common bile duct and main pancreatic duct.
277
Where does the accessory pancreatic duct empty?
The accessory pancreatic duct empties pancreatic juice into the duodenum at the minor duodenal papilla, which lies just proximal to the major duodenal papilla
278
Describe the arterial supply of the pancreas
The pancreas is supplied by blood vessels derived from the coeliac trunk and blood vessels derived from the superior mesenteric artery:
* The splenic artery, a major branch from the coeliac trunk, runs along the upper border of the pancreas and gives rise to pancreatic arteries.
* The gastroduodenal artery (from the common hepatic artery and hence the coeliac trunk) gives rise to the superior pancreaticoduodenal arteries that supply the pancreas.
* The superior mesenteric artery gives rise to the inferior pancreaticoduodenal arteries that supply the pancreas.
279
Describe the venous drainage of the pancreas
Veins follow the arteries. The splenic vein drains the pancreas and unites with the superior mesenteric vein to form the hepatic portal vein posterior to the neck of the pancreas.
280
Describe spleen
The spleen is a haematopoietic and lymphoid organ that lies in the left upper quadrant, protected by ribs 9 - 11. It is covered with visceral peritoneum. It has several functions that include the breakdown of old red blood cells, the storage of red blood cells and platelets, and various immune responses, including production of IgG.
281
Describe the two surfaces and four borders of the spleen
* the diaphragmatic surface lies adjacent to the diaphragm
* the visceral surface lies in contact with the stomach, left kidney and colon. The splenic vessels enter and exit the spleen at the hilum on the visceral surface
* the anterior and superior borders are typically notched
* the posterior and inferior borders are smooth.
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What does it mean if you can feel the spleen?
A normal sized spleen is not palpable below the costal margin. If it is palpable, it is enlarged by at least three times its normal size.
283
Describe the arterial blood supply to the spleen
The spleen is supplied by the splenic artery, a branch of the coeliac trunk. The splenic artery runs along the superior border of the pancreas, embedded within it. The artery divides into approximately five branches at the hilum.
284
Describe the venous drainage of the spleen
Venous drainage is via the splenic vein, which runs posterior to the pancreas. It unites with the superior mesenteric vein to form the hepatic portal vein.
285
Describe a duodenal ulcer
Duodenal (peptic) ulcers are most common in the first part of the duodenum. A duodenal ulcer here may erode the duodenal wall and the gastroduodenal artery, which lies posterior to the first part of the duodenum, resulting in severe intra-abdominal bleeding.
286
Describe pancreatitis
Inflammation of the pancreas may be chronic or acute. Acute pancreatitis is a life-threatening condition. There are many causes, but in the UK, it is most commonly due to excess alcohol intake or impaction of a gallstone at the hepatopancreatic ampulla. In gallstone pancreatitis, impaction of the gallstone prevents pancreatic juice from leaving the pancreas and it starts to break down the pancreas (autolysis). It is extremely painful, typically causing pain that radiates to the back.
287
Describe pancreatic cancer
Cancer can affect any part of the pancreas and typically causes pain that radiates to the back. When it affects the head of the pancreas, it can obstruct the flow of bile in the bile duct. This leads to an accumulation of bile pigments in the blood and results in jaundice (yellowing of the skin).
288
Describe splenomegaly
Enlargement of the spleen is splenomegaly. Causes include infection (e.g. infectious mononucleosis, malaria), haematological malignancy (e.g. leukaemia) and portal hypertension. When the spleen enlarges, it does so towards the midline, in the direction of the right iliac fossa, because the phrenicocolic ligament prevents its direct descent towards the left iliac fossa.
289
Describe splenic rupture
The spleen is soft and highly vascular and is therefore vulnerable to blunt abdominal trauma or rib fractures that may puncture the spleen. Splenic haemorrhage is life-threatening and is managed by removing the spleen (splenectomy). The spleen is not essential for life, although patients are more prone to some bacterial infections after splenectomy.
