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SA gastro-intestine > S2) Physiology of the Gut > Flashcards

S2) Physiology of the Gut Flashcards

1
Q

Which three systems/mechanisms control the gut?

A
  • Autonomic nervous system
  • Enteric nervous system (in entire gut)
  • Hormones and paracrine substances
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2
Q

Identify the two neurons in the autonomic nervous system

A
  • Preganglionic neuron
  • Postganglionic neuron
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3
Q

Distinguish between the function of preganglionic and postganglionic fibres

A
  • The preganglionic fibre synapse with an autonomic ganglia outside the CNS
  • The postganglionic fibre synapse on peripheral effector organs
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4
Q

Which substances are released by postganglionic and preganglionic nerve fibres respectively?

A
  • All preganglionic fibres release Ach
  • Post ganglionic fibres release Ach, neuropeptides or noradrenaline
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5
Q

Describe the anatomical position of the sympathetic nerve fibres

A
  • Found at T5-L2
  • Pass through (paravertebral) sympathetic trunk without synapsing
  • splanchnic nerves synapse with pre vertebral (anterior to spinal chord) ganglia (renal)
  • mainly innervate blood vessels (constrict)
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6
Q

The SNS forms presynaptic splanchnic (abdominopelvic) nerves.

Identify them

A
  • Greater (T5-9)
  • Lesser (T10-11)
  • Least (T12)
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7
Q

The splanchnic nerves synapse with prevertebral ganglia and mainly innervate blood vessels.

Identify some of these prevertebral ganglia

A
  • Coeliac
  • Renal
  • Superior mesenteric
  • Inferior mesenteric
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8
Q

Identify the nervous structures of the parasympathetic system

A
  • Vagus nerve
  • Pelvic splanchnic nerves (S2-4)
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9
Q

Which substances do postganglionic nerve fibres release in the parasympathetic nervous system?

A
  • Acetylcholine
  • Peptides

I. Gastrin releasing peptide

II. Vaso inhibitory peptide

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10
Q

What do preganglionic fibres do in the parasympathetic nervous system?

A
  • Preganglionic fibres synapse in walls of the viscera
  • Innervate smooth muscle/endocrine and secretory glands
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11
Q

Compare and contrast the structures innervated by the PNS and SNS

A
  • Sympathetic nervous system: coeliac ganglia, superior mesenteric, inferior mesenteric
  • Parasympathetic nervous system:

I. Vagus nerve: oesophagus→transverse colon

II. Pelvic nerve: transverse colon→anal canal

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12
Q

Compare and contrast the ganglionic fibres of the PNS and SNS

A

- Sympathetic nervous system:

I. Short preganglionic fibres

II. Post ganglionic fibres extend to myenteric and submucosal plexuses

III. Noradrenergic

- Parasympathetic nervous system:

I. Long preganglionic fibres

II. Post ganglionic fibres extend to myenteric and submucosal plexuses

III. Cholinergic and peptidergic

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13
Q

The enteric nervous system is a division of the overall system.

Describe its role in the body

A
  • Can function completely independently (from brain)
  • Exists from oesophagus to anus
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14
Q

What are the two main plexuses in the enteric nervous system and where are the found?

A
  • Submucosal (Meissner’s) – submucosa
  • Myenteric (Auerbach’s) – in between circular and longitudinal muscle
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15
Q

What are the functions of the two plexuses in the enteric nervous system?

A
  • Submucosal (Meissner’s) – secretions and blood flow
  • Myenteric (Auerbach’s) – motility
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16
Q

What do the plexuses of the enteric nervous system communicate with?

A
  • Parasympathetic (vagus and pelvic nerves)
  • Sympathetic (prevertebral ganglia)
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17
Q

What are the two broad categories for gastro-intestinal hormones?

A
  • Gastrin family:

I. Gastrin

II. Cholecystokinin (CCK)

  • Secretin family:

I. Secretin

II. Gastric inhibitory polypeptide (GIP)

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18
Q

Describe the role of G cells in the secretion of gastrin

A
  • G cells in antrum of stomach
  • Increases gastric acid secretion
  • stimulated by protein breakdown and stomach wall stretching
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19
Q

Describe the role of I cells in the secretion of CCK (cholecystokinin - “bile” “sac” “movement”)

A
  • I cells in duodenum and jejunum
  • Increases pancreatic/gallbladder secretions

I. Stimulated by fat and protein

II. Gallbladder contracts and pancreas stimulated

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20
Q

Describe the role of S cells in the duodenum in the secretion of secretin

A
  • Stimulated by H+ and fatty acids
  • Increases HCO3 from pancreas/gallbladder to neutralise the chyme from stomach
  • Decreases gastric acid secretion
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21
Q

Describe the role of cells in the duodenum and jejunum in the secretion of GIP

A
  • Stimulated by sugars, amino acids and fatty acids
  • Increases insulin
  • Decreases gastric acid secretion
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22
Q

Describe visceral pain in accordance to the primitive gut tube divisions

A
  • Foregut structures: epigastric pain
  • Midgut structures: periumbilical pain
  • Hindgut structures: suprapubic/hypogastric pain
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23
Q

What are other sorts of pain that can be felt in the body and their associated conditions?

A
  • Right upper quadrant/right shoulder tip pain: gallstones
  • Back pain: pancreatitis/AAA
  • Retrosternal pain: oesophagus
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24
Q

Motility is the contraction and relaxation of the GI tract.

What is the purpose of this?

A
  • Moving things along
  • Mix contents
  • Grind contents
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25
Q

Almost all muscle in the gut is smooth muscle.

Which GI structures are composed of skeletal muscle?

A
  • Pharynx
  • Upper 1/3 of oesophagus
  • External anal sphincter
26
Q

Which two forms of smooth muscle are found in the gut?

A
  • Circular muscle
  • Longitudinal muscle
27
Q

Phasic contractions allow for motility in the gut.

Identify and describe its 2 forms

A
  • Periodic – propulsion and mixing
  • Tonic – constant level of contraction
28
Q

In which structures can you observe tonic contractions?

A
  • Upper stomach
  • Ileocaecal valve
  • Internal anal sphincter
29
Q

Another form of contraction is peristalsis.

Describe the 3 functions of this mechanism

A
  • Propel contents in one direction
  • Contraction proximal to contents
  • Relaxation distal to contents
30
Q

Another form of contraction is segmentation.

Describe the function and purpose of this mechanism

A
  • Contraction splits contents, then relaxes
  • To and fro movements that mix contents
31
Q

Another form of contraction is mass movement.

Where does this mechanism occur and what does it involve?

A
  • Occurs in distal colon
  • Rapid movement of contents into rectum
  • Gastrocolic reflex to expel residual waste
32
Q

Describe the role of the nervous system (SNS and PNS) in gut motility

A
  • Sympathetic stimulation (noradrenaline) – decreases motility
  • Parasympathetic stimulation (acetylcholine) – increases motility
33
Q

explain why the sympathetic nervous system slows down gut motility

A

→ it directs blood flow from the gut to other areas that require more blood during flight or fight

this reduced blood flow to gut will therefore slow done contractions

34
Q

Identify and describe three forms of motility problems which may arise

A
  • Paralytic ileus – loss of GI contractility
  • Achalasia – failure of LOS to relax (dysphagia)
  • Hirschsprung’s disease – lack of myenteric and submucosal plexuses
35
Q

Identify five substances which are secreted in the gut

A
  • Water
  • Acid/Alkali
  • Enzymes
  • Mucus
  • Waste products
36
Q

A fluid balance needs to be maintained between which 3 factors?

A
  • Ingested material
  • Secretions from the gut
  • Absorption
37
Q

Where are substances secreted from?

A
  • Saliva
  • Gastric
  • Intestinal: liver and pancreas
38
Q

What is the function of stomach acid secretion?

A
  • Innate barrier to infection
  • Prepares proteins for digestion
  • Activates enzymes
39
Q

What is the function of HCO3 secretions?

A

Neutralise the acid (food acidity and stomach acid)

40
Q

Describe how waste products are secreted

A
  • Mainly from liver
  • Done in bile
  • E.g. cholesterol and bilirubin*
41
Q

What three things do emulsifiers do?

A
  • Increase surface area of lipids
  • Aids digestion by lipases
  • Allows lipid break down products to be transported in the gut (micelles)
42
Q

Provide an example of an emulsifier

A

Bile salts

43
Q

Describe four functions of mucus secretions

A
  • Protects against acidic environment in stomach
  • Protects against bacteria in small intestine
  • Harbours bacteria in large intestine (provides partial food source)
  • Lubricates
44
Q

Which parts of the GI tract can one observe enzyme secretions?

A
  • Saliva
  • Stomach
  • Pancreas
  • Lining of intestine
45
Q

What role do enzyme secretions have in the GI tract?

A

Break down:

  • Protein (proteases)
  • Fat (lipases)
  • Carbohydrates (amylases)
46
Q

Identify 5 key gands in the GI tract where secretions come from

A
  • Acini of salivary glands
  • Acini of exocrine pancreas
  • Gastric glands (stomach)
  • Brunner’s glands (duodenum)
  • Intestinal glands (crypts of Lieberkuhn)
47
Q

Identify the three requirements for absorption

A
  • Movement across enterocyte e.g. apical membrane, cytosol, basolateral membrane
  • Active absorptive cells e.g. simple columnar cells
  • Small enough to absorb (mechanical breakdown and chemical digestion)
48
Q

Which three structures create a large surface area?

A
  • Permanent folds (plica circulares)
  • Villi
  • Microvilli (brush border)
49
Q

Identify some conditions which can reduce absorption

A
  • Diarrhoea
  • Malnutrition
  • Anaemia

I. Crohn’s disease

II. Coeliac disease

50
Q

Identify three types of substances that get absorbed in the body

A
  • Nutrients:

I. Carbohydrates, proteins, lipids

II. Water & Fat soluble vitamins

III. Bile salts

IV. Fe2+ and Ca2+

  • Electrolytes
  • Water
51
Q

Water absorption is passive and follows electrolytes/nutrients.

How does this occur after a meal?

A

Water uptake driven by nutrients coupled with Na+ (sodium co-transporters)

52
Q

Water absorption is passive and follows electrolytes/nutrients.

How does this occur in between meals?

A

Na+ + Cl- are absorbed (sodium/hydrogen & chloride / bicarbonate exchangers)

53
Q

Water absorption in the colon includes an additional mechanism so that stool can be desiccated.

Identify this

A

Epithelial Na+ channel (ENaC – identical to distal tubule of kidney)

54
Q

What is the peritoneal cavity?

A

The peritoneal cavity is the continous area (potential space) between the parietal peritoneum lining the abdominal wall and the visceral peritoneum surrounding the abdominal organs

55
Q

What does the peritoneal cavity normally contain?

A

The peritoneal cavity only contains a thin film of peritoneal fluid

56
Q

What are the two major divisions of the peritoneal cavity?

A
  • Greater sac: larger, comprises majority of peritoneal cavity
  • Lesser sac: smaller, aka omental bursa
57
Q

What is the connection between the two major divisions of the peritoneal cavity called?

A

The lesser sac is connected with the greater sac through the epiploic foramen (an opening in the lesser sac)

58
Q

What are the boundaries of the lesser sac?

A
  • Anterior: quadrate lobe of liver, stomach, lesser omentum
  • Posterior: left kidney, adrenal gland, pancreas
59
Q

The rectovesical pouch is an area in the peritoneal cavity where abnormal fluid can collect.

Where can it be found?

A

Rectovesical pouch is the pocket that lies between the rectum and the urinary bladder in human males

60
Q

The hepatorenal recess is an area in the peritoneal cavity where abnormal fluid can collect.

Where can this be found?

A

Hepatorenal recess is the space that separates the liver from the right kidney

61
Q

what are peritoneal ligaments?

A
  • double fold of peritoneum connecting viscera
  • eg: between the stomach and the liver

SA gastro-intestine (19 decks)

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