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Gastrointestinal > Session 2 - Physiology and Development > Flashcards

Session 2 - Physiology and Development Flashcards

1
Q

Describe the neuronal structure of the autonomic nervous system?

A 
The cell bodies reside in the CNS.
Each pathway = 2 neurones
-Preganglionic
-Postganglionic
(Preganglionic synapse with post ganglionic)
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2
Q

Which neurotransmitters are released by the pre and post ganglionic fibres of the ANS?

A

Pre ganglionic = Ach

Post ganglionic = Ach, Neuropeptides & Norepinephrine

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3
Q

Describe the presynaptic splanchnic nerves and their roots.

A

Greater (T5-9)
Lesser (T10-11)
Least (T12)

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4
Q

Which ganglia do the splanchnic nerves synapse with?

A

With Pre-vertebral ganglia

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5
Q

What is the main effect of sympathetic nerves of the GI?

A

To control blood flow to the various organs.

E.g. fight/flight to reduce blood flow to the GI

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6
Q

Where do parasympathetic nerves originate from?

A

Cranial-sacral outflow.
Nerves come from cranium.
And from the sacrum.

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7
Q

Which parasympathetic nerves innervate the gut?

A

Vagus nerve - main

Some pelvic splanchnic nerves (S2-4)

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8
Q

How do the sympathetic and parasympathetic nervous system affect the guy differently?

A

Sympathetic
Reduce blood flow, slow gut activity. (Shut down)

Parasympathetic
Stimulates the gut - causing digestion/ movement.

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9
Q

Where do parasympathetic fibres synapse?

A

Long pre-synaptic, synapse at the organ (viscera)

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10
Q

Which part of the gut do the left and right vagus nerves give parasympathetic innervation to?

A

Left Vagus = Anterior

Right Vagus = Posterior

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11
Q

What is a ganglion?

A

A collection of nerve cell bodies, in the sympathetic nervous system, the nerves usually synapse here.

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12
Q

What is the enteric nervous system?

A

A division of the nervous system.
Exists from oesophagus to anus.
Can operate independently.

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13
Q

Which are the two major plexuses of the enteric nervous system?

A

Submucosal (Meissner’s)
-submucosa

Myenteric (Auerbach’s)
-In between circular and longitudinal muscle

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14
Q

What does the submucosal plexus control?

A

Local blood flow/ secretions etc in epithelial area.

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15
Q

What does the myenteric plexus control?

A

Muscular control / motility

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16
Q

What are enteroendocrine cells?

A

The many cells of the GI tract that secrete hormones.

Often within crypts.

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17
Q

What are enterochromafin like cells?

A

Cells that secrete histamine in GI

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18
Q

How do hormones from the GI go on to affect the organs of the GI?

A

Released into portal circulation
Through liver
Into systemic circulation
Then affect the target organs (in GI)

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19
Q

What is the function of cholecystokinin?

A

Stimulates gall bladder to contract, pancreas to release enzymes and relaxes sphincter to allow the products to be secreted in the gut.

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20
Q

What is the function of Gastrin?

A

Secreted by G-cells in antrum of stomach.

Increases gastric acid secretion.

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21
Q

Which two hormones are in the Gastrin family?

A

Gastrin

Cholecystokinin

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22
Q

Which two hormones are in the Secretin family?

A

Secretin

Gastric inhibitory polypeptide

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23
Q

Where is secretin secreted? What is it’s function?

A

S cells in duodenum.
Stimulated by H+ and fatty acids.
Increases HCO3 secretion from pancreas/gall badder.
Decreases gastric acid secretion.

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24
Q

What is the function of gastric inhibitory polypeptide (GIP)?

A

Increases insulin secretion, decreases gastric acid secretion.

From cells in duodenum/jejunum

Stimulated by sugars, amino acids, fatty acids

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25
Q

Why would a case of appendicitis initially cause central abdominal pain?

A

Visceral peritoneum becomes distended/inflamed.
Visceral peritoneum hasn’t got its own sensory nerve supply.

Afferent sensory nerve follows splanchnic nerves to the roots.

In appendicitis - least splanchnic nerve (T10-11 - small intestine to transverse colon)

Body makes assumption that pain is from T10 dermatome, and thus gives midline pain.

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26
Q

Why would pain in appendicitis eventually cause localised pain in the Right iliac fossa?

A

As appendix becomes more distended/ inflamed, it may come into contact with parietal peritoneum.
This has somatic innervation, which can localise pain better.

27
Q

What are the layers of muscle which allow gut motility?

A

Circular muscle
Longitudinal muscle

Contractions to move contents

28
Q

What are periodic and tonic contractions?

A

Periodic contractions are physical (fast/ short) that move and mix contents.

Tonic contractions are a constant level of contraction (minutes/hours) e.g. upper stomach

29
Q

What is peristalsis?

A

Propulsion of contents in one direction, with contractions proximal to the contents.

30
Q

What is segmentation (motility)?

A

Contraction splits contents, then relaxes.

These to and fro movements mix contents.

31
Q

What is a paralytic ileum?

A

Temporary impairment of movement of gut contents (following GI surgery)

Functional obstruction - not real obstruction

32
Q

What is Hirschprung’s disease?

A

Lack of myenteric and submucosal plexuses.
Causes functional obstruction, as muscles cannot contract properly.

(In newborns, first faeces may not be passed)

33
Q

Why is mucus vital for a functional GI?

A
  • Protects against acidic environment in stomach.
  • Protect against bacteria in small intestine (contains antibacterial compounds)
  • Harbours bacteria in large intestine.
  • Lubricates contents
34
Q

How is the large surface area in the GI formed?

A

Permanent folds (plicae circulates) [SA x3]
Villi [SA x 10]
Microvilli [SA x20]

35
Q

How is the last small amount of water removed from the contents in the colon?

A

ENaC channels

Desiccate the stool (dry it out) so as little water as possible is lost.

36
Q

What is the gut tube? Describe its structure.

A

The endoderm lines tube, running the length of the body, containing blind pouches at the head and tale, with an opening at the umbilicus.
It has a splanchnic mesoderm covering.

37
Q

What are the embryonic divisions of the gut?

A

Foregut, midgut and hindgut.
Foregut and hindgut begin as blind diverticula.
Midgut has opening at first, is continuos with the yolk sac.

38
Q

Which structures are derivatives of the foregut?

A
  • Oesophagus
  • Stomach
  • Pancreas, liver & Gall bladder
  • Duodenum (proximal to bile duct entrance)
39
Q

Which structures are derived from the midgut?

A
  • Duodenum (distal to bile duct entrance)
  • Jejunum
  • Ileum
  • Caecum
  • Ascending Colon
  • Proximal 2/3 of transverse colon
40
Q

Which structures are derivatives of the hindgu?

A
  • Distal 1/3 of transverse colon
  • Descending & sigmoid colon
  • Rectum
  • Upper anal canal
  • Internal lining of bladder and urethra
41
Q

How does the embryonic development affect blood supply?

A

Arterial supply to each embryonic segment from a distinct branch of the abdominal aorta.

42
Q

Which blood vessels supply which parts of the gut?

A
  1. Celiac trunk: foregut
  2. Superior Mesenteric artery: midgut
  3. Inferior Mesenteric artery: Hindgut
43
Q

Which exceptions in the gut have mixed blood supply?

A
  1. Duodenum:
    Proximal to entry of bile duct = branches of celiac trunk
    Distal = branches of Superior mesenteric artery
  2. Pancreas:
    Head = branches of Celiac trunk AND Superior Mesenteric artery.
44
Q

What is the intra-embryonic coelum?

A

The cavity formed when the embryo folds, surrounded by mesoderm, containing the gut tube.
It is eventually gives rise to the thoracic and abdominal cavities.

45
Q

What does the membrane lining the whole intra-embryonic cavity specialise into through development?

A
  • Pericadrium
  • Pleural membrane

also
- Peritoneum & peritoneal cavity
(peritoneal membrane lines abdominal cavity, and invests the viscera)

46
Q

How are mesenteries formed in the embryo?

A

Primitive gut is suspended in intraembryonic coelum.

  • Splanchnic mesoderm surrounds the new gut.
  • Mesentery formed by a condensation of this mesoderm.
47
Q

Where do mesenteries suspend the parts of the gut tube from?

A
  • Doral mesentery = suspends entire gut tube from dorsal body wall.
  • Ventral mesentery = ONLY in the region of FOREGUT.
48
Q

How are the peritoneal sacs organised in the body?

A

Dorsal and ventral mesenteries in foregut region divide cavity into left and right.

Left sac - contributes to the Greater sac.
Right sac - contributes to the Lesser sac.
(comes to lie behind stomach)

49
Q

How are the greater and lesser omentum formed in the embryo?

A

Greater omentum.

  • Formed from the dorsal mesentry
  • First structure seen when abdo cavity opened anteriorly.

Lesser Omentum.

  • Formed from the ventral mesentery
  • Free edge conducts the portal triad
50
Q

What developmental process forms the greater omentum?

A

The folding of the stomach.
The ventral and dorsal mesenteries are flexible, and move witht he development of the stomach, forming this greater omentum.

51
Q

What is the infracolic compartment? What does it contain?

A

Infracolic = lies below the transverse mesocolon, contains Small intestine, ascending and descending colon.

52
Q

What is in the supracolic compartment?

A

Lies above the transverse mesocolon, contains stomach, liver and spleen.

53
Q

What is a peritoneal reflection?

A

A change in direction.
E.g. - from parietal peritoneum to mesentery.
- from mesentery to visceral peritoneum.

54
Q

What are retroperitoneal and secondary retroperitoneal structures?

A

Structures NOT suspended within the abdominal cavity.

Retroperitoneal = were never in peritoneal cavity, no mesentery.

Secondary = began development in peritoneum, had mesentery, BUT, with growth/development, mesentery is lost (fusion at posterior wall).

55
Q

What happens developmentally in the foregut in the 4th week?

A

A respiratory diverticulum forms in the VENTRAL wall of the foregut (at junction of pharyngeal gut)

  • respiratory primordium (ventrally)
  • Oesophagus (dorsally)
56
Q

How are respiratory and GI tracts separated? What can go wrong?

A

diverticulum separated by tracheoesophageal septum.

Abnormal positioning (1/3000 live births) can happen. Could give blind-end oesophagus, or fistulae.

57
Q

How does the liver develop in the embryo?

A

Appears as a liver bud.

contribution from endoderm of foregut, and also from developing diaphragm

58
Q

How is the liver connected to the abdominal wall?

A

By ventral mesentery.

The falciform ligament!

59
Q

Where does the pancreas develop?

A

Partly in the ventral, and partly in the dorsal mesentery.

60
Q

Which two folds of peritoneum hold the liver?

A 
Lesser omentum (between liver and stomach)
Falciform ligament (between liver and anterior wall of abdomen)
61
Q

What gives the duodenum its C shape?

A

Rotation of the stomach.

62
Q

What type of organ is the duodenum? Why?

A

Secondarily retropetitoneal.
Rotation of stomach pushes duodenum to right, then against the posterior abdominal wall, where most of it loses its mesentery.

63
Q

What are the two secondary retroperitoneal structures of the foregut?

A

Duodenum (except duodenal cap)

Pancreas

64
Q

What are fusion fascia?

Why is this important.

A

Where two layers of fascia fuse, e.g. when a peritoneal structure becomes retroperitoneal.

Structures can become mobilised, by freeing up the fusion fascia. (don’t have to enter retroperitoneum)

Gastrointestinal (9 decks)

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