Midgut Flashcards
1
Q
What comprises the midgut
A
Distal duodenum, jejunum, ileum, cecum, appendix, ascending colon, and proximal 2/3 of transverse colon
2
Q
Length of the small bowel
A
6.5m
3
Q
Length of the duodenum
A
25cm
4
Q
Most common site of duodenal ulceration
A
D1
5
Q
Intraperitoneal part of duodenum
A
Proximal 2-3cm
6
Q
Course of D1
A
- Ascends from pylorus
- Connected to liver by hepatoduodenal ligament
- 5cm long
7
Q
Course of D2
A
- Descending (L1-L3)
- Curves around head of pancreas
- Posterior to transverse colon
- Anterior to right kidney
8
Q
Point of entrance of bile and pancreatic ducts
A
- Medial aspect of D2
- Major duodenal papilla
9
Q
Junction of foregut and midgut
A
Major duodenal papilla
10
Q
Course of D3 (what does it cross and what is it crossed by)
A
- Inferior (L3)
- Runs horizontally over IVC, aorta and L3
- Crossed anteriorly by SM vessels and root of mesentery
- 10cm long
11
Q
Course of D4
A
- Ascending (L3-2)
- At the DJ flexure the intestine leaves the posterior abdominal wall and acquires a mesentery
12
Q
When does the small bowel acquire a mesentery
A
The DJ flexure
13
Q
How can the DJ flexure be identified at surgery
A
By the ligament of Treitz (descends from crus of diaphragm)
14
Q
Outline the blood supply of the duodenum
A
- Proximal to ampulla = gastroduodenal and superior pancreaticoduodenal
- Distal to ampulla = inferior pancreaticoduodenal (branch of SMA)
15
Q
Position of pancreaticoduodenal arteries
A
Lie in the curve between the descending duodenum and head of pancreas and supply both
16
Q
Point of anastomosis between superior and inferior pancreaticoduodenal arteries
A
Between point of entry of bile duct and junction between D2 and D3
17
Q
Venous drainage of the duodenum
A
Follow the arteries to eventually reach portal vein
18
Q
Outline the lymphatic drainage of the duodenum
A
- Anterior vessels = drain into pancreaticoduodenal and pyloric nodes
- Posterior vessels = superior mesenteric nodes
19
Q
Colour difference between jejunum and ileum
A
- Jejunum = deeper red
- Ileum = paler pink
20
Q
Vascularity difference between jejunum and ileum
A
- Jejunum = greater
- Ileum = less
21
Q
Difference in vasa recta and arcades between jejunum and ileum
A
- Jejunum = long vasa recta with fewer arcade loops
- Ileum = short vasa recta with many short arcade loops
22
Q
Difference in lymphoid nodules (Peyer patches) between jejunum and ileum
A
- Jejunum = few
- Ileum = many
23
Q
Contents of the mesentery
A
- Superior mesenteric vessels
- Lymph nodes draining small intestine
- Autonomic nerve fibres
24
Q
Outline blood supply of jejunum and ileum
A
SMA via:
- Jejunal arteries
- Ileal arteries
25
Level of SMA origin
L1
26
What leads to the formation of the hepatic portal vein
1. SMV
| 2. Splenic vein
27
What are the specialised lymphatic vessels in the intestinal villi called
Lacteals
28
Which 3 groups of lymph nodes does lymph pass through within the mesentery
1. Juxta-intestinal nodes
2. Mesenteric lymph nodes
3. Superior central nodes (located along proximal SMA)
29
Role of plicae circulares
Cause the chyme to spiral around the bowel to increase absorption time
30
What are contained within the crypts of Lieberkuhn
- Undifferentiated cells that replace enterocytes
- D-cells - produce somatostatin
- S-cells - produce secretin
- N-cells - produce neurotensin
- Enterochromaffin cells
31
What activates pancreatic trypsinogen
Enteropeptidase/Enterokinase from the brush border
32
Volume of small bowel secretions
2-3L/day
33
How are carbohydrates absorbed
- Glucose and galactose via Na+ co-transporter
| - Fructose is absorbed independent of Na+
34
Role of pancreatic lipase
Break down fat droplets into monoglycerides and free fatty acids
35
How are micelles formed
From combination of monoglycerides/FFA and bile salts
36
How are fats absorbed into the venous circulation
In the form of chylomicrons via lacteals
37
Where does fat absorption primarily occur
Jejunum
38
Daily protein requirement
0.8-1.5g/day
39
Where are amino acids primarily absorbed
Upper small bowel
40
How are amino acids absorbed
Na+ co-transporter (similar to glucose and galactose)
41
Where does water absorption mainly occur
Jejunum
42
What are the fat soluble vitamins
A, D, E, K
43
How are fat soluble vitamins absorbed
Absorbed with the micelles during fat absorption
44
What are the water soluble vitamins
B, C
45
Where is vitamin C absorbed
Jejunum
46
Where is vitamin B absorbed
- B12 in the ileum
| - Remaining B vitamins freely diffuse across enterocyte membrane
47
Where is iron absorbed
Duodenum (and jejunum)
48
What form is iron absorbed in and how is it changed to this
- Fe2+
| - Gastric acid converts it
49
How is iron absorbed
Via the transport protein transferrin
50
How is calcium absorbed
Via calcium-binding proteins in the intestinal cells
51
Where does calcium absorption occur
Duodenum and proximal jejunum
52
What are the 3 types of movement in the small intestine
1. Segmentation
2. Peristalsis
3. Migrating motility complex
53
Describe peristalsis of the small bowel
1. Longitudinal muscle contracts
| 2. Midway through the circular muscle also contracts
54
When do migrating motility complexes occur
During periods of fasting and involve contraction of the entire length of bowel
55
Describe the ileogastric reflex
Distension of the ileum reduces gastric motility
56
Describe the gastroileal reflex
Increases in gastric secretion or contractility increases ileal motility
57
What protects the duodenum from ulceration
HCO3 secreted from Brunner's glands in the pancreas
58
Outline the physiological effects of duodenal resection
- Ulceration of small bowel (duodenum is more resistant)
- Malabsorption (iron, calcium, phosphate)
- Dumping
59
Outline the physiological effects of terminal ileal resection
- Bile salts in the colon raises risk of malignancy
- Gallstones
- B12 deficiency
- Poor water reabsorption
60
Define a fistula
Conduit between two epithelial surfaces
61
Most common cause of small bowel ischaemia
Embolic or thrombotic occlusion of the SMA
62
Cause of chronic bowel ischaemia
Atherosclerosis
63
Cause of embolic bowel ischaemia
- Post-MI
| - AF
64
Most likely site of emboli in small bowel ischaemia
- Lodge at the branch of the middle colic artery
| - Spares the first part of the jejunum as the jejunal arteries are proximal to this
65
Most likely site of thrombotic small bowel ischaemia
Origin of the SMA at the aorta
66
GOLD standard investigation for small bowel ischaemia
Mesenteric angiography
67
Management of SMA embolus
Arteriotomy and embolectomy
68
Management of SMA thrombus
Aortomesenteric bypass
69
Causes of non-occlusive mesenteric ischaemia
- CCF
- MI
- Arrhythmia
- Hypovolaemia
- Sepsis
- Post cardiac surgery
70
Define a high output fistulae
3-4L fluid lost per day
71
Management of high-output fistulae
1. IV fluids
| 2. TPN until fistula closes or is surgically closed
72
Clinical features in chronic intestinal ischaemia
- Post-prandial abdominal pain
- Fear of eating
- Weight loss
73
Describe the features of Peutz-Jeghers syndrome
- Melanin spots around the lips, buccal mucosa, anal mucosa
- Numerous hamartomatous polyps throughout the bowel (classically the jejunum)
- Pedunculated polyps
74
Most likely site of carcinoid tumour
Terminal ileum
75
Describe carcinoid syndrome
1. Carcinoid tumour secreting vasoactive substances
| 2. Tumour has metastasised to the liver
76
Diagnosis of carcinoid syndrome
1. CT
2. Small-bowel follow-through
3. Urinary 5-HIAA levels
77
Symptoms of carcinoid syndrome
- Flushing
- Intractable diarrhoea
- Bronchospasm
78
Outline the management of carcinoid tumours
- <1cm and asymptomatic = local excision
| - >2cm = small-bowel resection and lymphatic clearance
79
Outline the management of carcinoid syndrome
Palliative resection, palliative liver resection, chemotherapy, subcutaneous ocreotide
80
Primary blood supply of the omentum
Gastro-epiploic
81
Blood supply of Meckel's diverticulum
Viteline artery
82
What method can be used to confirm enterocutaneous fistulas
Methylene blue
83
Origin of the spleen
Mesenchymal tissue
