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GastroIntestinal > Anatomy 12 > Flashcards

Anatomy 12 Flashcards

1
Q

Where does the small intestine lie?

A

Lies centrally in the abdomen

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2
Q

What are the 3 parts of the small intestine?

A

Duodenum
Jejunum
Ileum

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3
Q

What is the duodenum?

A

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.

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.

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4
Q

What does the first half of the duodenum develop from?

A

Develops from the embryological foregut

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5
Q

What does the second half of the duodenum develop from?

A

Develops from the embryological midgut

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6
Q

What is the first half of the duodenum supplied by?

A

Supplied by arterial branches from the coeliac trunk

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7
Q

What is the second half of the duodenum supplied by?

A

Supplied by branches from the artery of the midgut – the superior mesenteric artery

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7
Q

What is the second half of the duodenum supplied by?

A

Supplied by branches from the artery of the midgut – the superior mesenteric artery

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8
Q

What are the jejunum and ileum?

A

The jejunum is continuous with the duodenum.
Both the jejunum and ileum are intraperitoneal and are ‘suspended’ from the posterior abdominal wall by the
mesentery of the small intestine.

Blood vessels that supply the small intestine (from the superior mesenteric artery) are embedded within the mesentery.

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.

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8
Q

What are the jejunum and ileum?

A

The jejunum is continuous with the duodenum.
Both the jejunum and ileum are intraperitoneal and are ‘suspended’ from the posterior abdominal wall by the
mesentery of the small intestine.

Blood vessels that supply the small intestine (from the superior mesenteric artery) are embedded within the mesentery.

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.

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9
Q

What are the jejunum and ileum derived from?

A

Embryological midgut

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10
Q

What are the jejunum and ileum the sites of, and what are adaptations of this?

A

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.

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11
Q

What are some internal differences between the jejunum and ileum?

A

The plicae are more pronounced in the jejunum.

The internal ileum is characterised by Peyer’s patches, which are large submucosal lymph nodules.

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12
Q

What is Meckel’s diverticulum?

A

The ileum bears a blind-ended diverticulum approximately one meter from its termination

It is the embryological remnant of the connection that was present between the midgut loop to the yolk sac.

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13
Q

What may Meckel’s diverticulum mimic when inflamed?

A

Appendicitis

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14
Q

What is the terminal ileum continuous with?

A

Continuous with the caecum - the first part of the large
intestine – at the ileocaecal junction in the right iliac fossa.

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15
Q

What does the large intestine do?

A

Reabsorbs water from faecal material to form semi-solid faeces

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16
Q

Where is the large intestine found?

A

Lies peripherally in the abdomen

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17
Q

What is the large intestine composed of?

A

Caecum
Appendix
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
Rectum
Anal canal

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18
Q

What makes the large intestine easier to identify than the small intestines in a cadaver?

A

It is peripherally located, and larger calibre

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19
Q

What is the outer muscle in the large intestine?

A

Longitudinal muscle layer is organised into three bands –
the taeniae coli

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20
Q

What does the inner circular muscle layer in the large intestine form?

A

Forms ‘bulges’ called haustra (or haustrations)

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21
Q

What does the large intestine bear?

A

Bears fatty tags called epiploic appendages (appendices epiploicae) that mark the point at which blood vessels penetrate the intestinal wall

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22
Q

What is the caecum?

A

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.

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23
Q

What is the appendix?

A

The appendix is a small diverticulum that arises from the caecum and contains lymphoid tissue.

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24
Q

What is McBurney’s point?

A

The surface marking of the base of the appendix

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25
Q

What is the appendix connected to the caecum by?

A

A small mesentery, the mesoappendix

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26
Q

What is the ascending colon continuous with?

A

Caecum

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27
Q

Where is the ascending colon found?

A

It runs vertically on the right side of the posterior abdominal wall in the right paracolic gutter

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28
Q

What is the ascending colon?

A

It is retroperitoneal (it is an example of a secondarily retroperitoneal organ).

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).

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29
Q

What is the transverse colon continuous with?

A

Ascending colon

The transverse colon makes a 90 degree turn inferiorly in the left upper quadrant, becoming continuous with the descending colon

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30
Q

Where is the transverse colon located?

A

It runs horizontally in the upper abdomen but often hangs inferiorly.

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31
Q

Is the transverse colon intraperitoneal or retroperitoneal?

A

Intraperitoneal

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32
Q

What is the purpose of the transverse mesocolon?

A

Suspends the transverse colon to the posterior abdominal wall

33
Q

What is the bend in the transverse colon?

A

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

34
Q

What does the transverse colon mark?

A

Marks the transition point between the embryological midgut
and embryological hindgut

35
Q

Where does the proximal (first) two thirds of the transverse colon develop from?

A

The embryological midgut

36
Q

Where does the distal (last) third of the transverse colon develop from?

A

The embryological hindgut

37
Q

What is the descending colon?

A

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).

38
Q

What is the sigmoid colon?

A

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.

39
Q

What is the rectum and anal canal?

A

The rectum descends inferiorly into the pelvis from the rectosigmoid junction and is retroperitoneal.

The rectum stores feaces until it is convenient to defecate.

The rectum is continuous inferiorly with the anal canal.

40
Q

What are the 3 large unpaired arteries that supply the gastrointestinal tract?

A
  • Coeliac trunk
  • Superior mesenteric artery (SMA)
  • Inferior mesenteric artery (IMA)
41
Q

Where does the coeliac trunk leave the aorta?

A

It leaves the aorta at the level of T12 and gives rise to branches that supply the foregut

42
Q

What branches supply the foregut?

A

Oesophagus
Stomach
First half of the duodenum
Liver
Gallbladder
Bile ducts
Pancreas
Spleen

43
Q

What is the superior mesenteric artery?

A

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.

44
Q

What is the inferior mesenteric artery?

A

Artery of the hindgut.

It leaves the aorta at the level of L3.

It is a smaller calibre vessel than the coeliac trunk and SMA.

Its branches supply the hindgut structures: the distal third of the transverse colon, the descending and sigmoid colon, the rectum, and the upper part of the anal canal.

45
Q

What is the superior mesenteric artery?

A

The SMA gives rise to several major branches that supply the midgut

46
Q

What are the major branches of the superior mesenteric artery?

A
  • 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.
47
Q

Where are the jejunal and ileal branches embedded?

A

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.

48
Q

What major branches does the inferior mesenteric artery give rise to?

A
  • 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 upper rectum.
49
Q

What forms the marginal artery?

A

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

Branches of the left colic and sigmoid arteries anastomose

50
Q

What is the lower rectum supplied by?

A

Supplied by blood vessels that originate from the internal iliac arteries in the pelvis.

51
Q

Explain the venous drainage system of the small and large intestine?

A

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.

52
Q

What does the inferior mesenteric vein do?

A

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.

53
Q

What does the superior mesenteric vein do?

A

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.

54
Q

What does the hepatic portal vein do?

A

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).

55
Q

What type of fibres innervate the midgut and hindgut?

A

Parasympathetic

56
Q

What are the foregut and midgut innervated by?

A

Innervated with parasympathetic fibres via the vagus nerve

57
Q

What is the hindgut innervated by?

A

Innervated with parasympathetic fibres via the pelvic splanchnic nerves.

These nerves are formed by the axons of parasympathetic neurons that lie in the sacral spinal cord.

58
Q

Where do the cell bodies of preganglionic parasympathetic neurons lie?

A

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.

The pelvic splanchnic nerves also convey parasympathetic fibres to the pelvic viscera

59
Q

Where do the preganglionic sympathetic fibres pass through?

A

From T5 – T12 pass through the sympathetic trunk (without synapsing) via the greater, lesser, and least splanchnic nerves

60
Q

Where do the greater splanchnic carry fibres to?

A

T5 – T9 and innervates the foregut

61
Q

Where do the least splanchnic carry fibres to?

A

T12 and innervates the hindgut

62
Q

What do the postganglionic sympathetic fibres form and inhibit?

A

Form visceral nerves that innervate the gut.
These fibres that inhibit peristalsis and secretions

63
Q

What are the sympathetic fibres?

A

Visceral motor fibres

64
Q

What do the visceral sensory fibres do?

A

Innervate the gut, which convey visceral sensory information from the gut to the CNS.

Such information usually does not reach consciousness, but painful sensations caused by ischaemia, distension or spasm do reach our conscious perception.

65
Q

Where does the foregut enter the spinal cord segment?

A

Foregut enter spinal cord segments T5 - T9

66
Q

Where does the midgut enter the spinal cord segment?

A

Midgut enter spinal cord segments T10 – T11

67
Q

Where does the hindgut enter the spinal cord segment?

A

Hindgut enter spinal cord segment T12.

68
Q

Where does the spinal cord receive somatic sensory information?

A
  • Segments T5 – T9 receive information from dermatomes T5 – T9 (upper abdomen and epigastrium).
  • Segments T10 – T11 receive information from dermatomes T10 – T11 (the umbilical region)
  • Segment T12 receives information from dermatome T12 (the suprapubic region).
69
Q

Where is pain in the abdominal viscera referred to the body wall?

A
  • epigastric pain suggests foregut pathology
  • central abdominal / umbilical pain suggests midgut pathology
  • lower abdominal / suprapubic pain suggests hindgut pathology
70
Q

What is appendicitis?

A

Inflammation of the appendix is appendicitis and is a common acute surgical presentation.

71
Q

Where does pain of appendicitis typically begin?

A

Typically begins in the umbilical region and is poorly localised

72
Q

What causes appendicitis?

A

The result of irritation of the visceral peritoneum (visceral
sensory afferents returning to spinal cord segment T10)

As inflammation progresses, the adjacent parietal peritoneum becomes involved.

This causes severe, well localised pain in the right iliac fossa (which is conveyed to the CNS via somatic nerves that innervate the body wall).

Therefore the history is of diffuse umbilical pain that ‘moves’ to the right iliac fossa.

Symptoms can vary, depending on where the tip of the appendix lies.

73
Q

Where is tenderness due to appendicitis maximal?

A

McBurney’s point

74
Q

What can rupture of the appendix lead to?

A

Peritonitis

75
Q

How is an appendicectomy usually performed?

A

Laparoscopy (‘keyhole’ surgery)

76
Q

What is mesenteric ischaemia?

A

Just like the coronary arteries, the mesenteric vessels may be occluded by a thrombus.

This results in ischaemia of the intestine which may progress to infarction.

Acute mesenteric ischaemia is a surgical emergency.

The gut must be revascularized and any sections of necrotic intestine must be removed.

Mortality is high, even when the condition is recognised and treated.

77
Q

What are two types of inflammatory bowel disease?

A

Crohn’s disease
Ulcerative colitis

78
Q

What is Crohn’s disease?

A

Crohn’s disease is characterised by inflammation of the gut mucosa.

It can affect any part of the GI tract but typically affects the small intestine.

Patients suffer with symptoms including abdominal pain, diarrhoea, bloody stools, weight loss and tiredness

79
Q

What is Ulcerative colitis?

A

Ulcerative colitis affects the colon and rectum. The mucosa becomes inflamed and ulcerated.

Patients suffer with abdominal pain, bloody diarrhoea,
weight loss and tiredness.

80
Q

What might need to happen if medications fail to control symptoms of inflammatory bowel disease?

A

The affected part of the gut may be removed

81
Q

What is colon cancer?

A

Cancer of the colon (often called bowel cancer) is common in the UK.

The main symptoms of colon cancer are a change in bowel habit, blood in the stools and abdominal pain or bloating.

Colonoscopy allows visualisation of the colon and biopsies can be taken if a mass is seen.

82
Q

What is volvulus?

A

Volvulus is twisting of the gut. It affects parts of the gut that are mobile (i.e. have a mesentery) and is most common at the sigmoid colon.

Twisting obstructs the passage of feaces and may cause ischaemia and infarction of the affected part of the gut.

GastroIntestinal (19 decks)

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