S2) Physiology of the Gut Flashcards Preview

Y2 SEM 3: Gastro-intestinal System > S2) Physiology of the Gut > Flashcards

Flashcards in S2) Physiology of the Gut Deck (59)
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Which three systems/mechanisms control the gut?

- Autonomic nervous system

- Enteric nervous system

- Hormones and paracrine substances 


Identify the two neurons in the autonomic nervous system

- Preganglionic neuron

- Postganglionic neuron


Distinguish between the function of preganglionic and postganglionic fibres

- The preganglionic fibre synapse with an autonomic ganglia outside the CNS

- The postganglionic fibre synapse on peripheral effector organs 


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

- All preganglionic fibres release Ach

- Post ganglionic fibres release Ach, neuropeptides or noradrenaline


Describe the anatomical position of the sympathetic nerve fibres

- Found at T5-L3

- Pass through (paravertebral) sympathetic trunk without synapsing 


The SNS forms presynaptic splanchnic (abdominopelvic) nerves.

Identify them

- Greater (T5-9)

- Lesser (T10-11)

- Least (T12) 


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

Identify some of these prevertebral ganglia

- Coeliac 

- Renal 

- Superior mesenteric

- Inferior mesenteric


Identify the nervous structures of the parasympathetic system

- Vagus nerve

- Pelvic splanchnic nerves (S2-4) 


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

- Acetylcholine

- Peptides

I. Gastrin releasing peptide

II. Vaso inhibitory peptide 


What do preganglionic fibres do in the parasympathetic nervous system?

- Preganglionic fibres synapse in walls of the viscera

- Innervate smooth muscle/endocrine and secretory glands


Compare and contrast the structures innervated by the PNS and SNS

- 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 


Compare and contrast the ganglionic fibres of the PNS and SNS

- 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 


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

Describe its role in the body

- Can function completely independently (from brain)

- Exists from oesophagus to anus


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

Submucosal (Meissner’s) – submucosa

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


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

Submucosal (Meissner’s) – secretions and blood flow

- Myenteric (Auerbach’s) – motility 


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

- Parasympathetic (vagus and pelvic nerves)

- Sympathetic (prevertebral ganglia) 


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

Gastrin family:

I. Gastrin

II. Cholecystokinin (CCK)

- Secretin family:

I. Secretin 

II. Gastric inhibitory polypeptide (GIP)


Describe the role of G cells in the secretion of gastrin

- G cells in antrum of stomach

- Increases gastric acid secretion 


Describe the role of I cells in the secretion of CCK

- I cells in duodenum and jejunum

- Increases pancreatic/gallbladder secretions

I. Stimulated by fat and protein

II. Gallbladder contracts and pancreas stimulated 


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

- Stimulated by H+ and fatty acids

- Increases HCO3 from pancreas/gallbladder

- Decreases gastric acid secretion 


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

- Stimulated by sugars, amino acids and fatty acids

- Increases insulin

- Decreases gastric acid secretion 


Describe visceral pain in accordance to the primitive gut tube divisions

Foregut structures: epigastric pain

- Midgut structures: periumbilical pain

- Hindgut structures: suprapubic/hypogastric pain


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

- Right upper quadrant/right shoulder tip pain: gallstones

- Back pain: pancreatitis/AAA

- Retrosternal pain: oesophagus


Motility is the contraction and relaxation of the GI tract.

What is the purpose of this?

- Moving things along

- Mix contents 

- Grind contents


Almost all muscle in the gut is smooth muscle.

Which GI structures are composed of skeletal muscle?

- Pharynx

- Upper 1/3 of oesophagus

- External anal sphincter 


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

- Circular muscle 

- Longitudinal muscle


Phasic contractions allow for motility in the gut.

Identify and describe its 2 forms

Periodic – propulsion and mixing

- Tonic – constant level of contraction


In which structures can you observe tonic contractions?

- Upper stomach

- Ileocaecal valve

- Internal anal sphincter 


Another form of contraction is peristalsis.

Describe the 3 functions of this mechanism

- Propel contents in one direction

- Contraction proximal to contents

- Relaxation distal to contents


Another form of contraction is segmentation.

Describe the function and purpose of this mechanism

- Contraction splits contents, then relaxes

- To and fro movements that mix contents