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Module 104 - Nutrition, metabolism & excretion > T1 L4 Motility of GI tract > Flashcards

T1 L4 Motility of GI tract Flashcards

1
Q

What are the 4 functions of the GI system?

A

1) Digestion
2) Secretion
3) Absorption
4) Motility

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2
Q

Definition of secretion

A

Delivery of appropriate fluid & enzyme solutions

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3
Q

Definition of absorption

A

Nutrient molecules are transported into the circulatory system

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4
Q

Definition of digestion

A

Macromolecules in food are hydrolysed

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5
Q

Definition of enteric nervous system

A

Large intrinsic network of neutrons in the walls of the gastrointestinal tract

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6
Q

Definition of transit time

A

Time taken for food to reach each indicated point after ingestion

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7
Q

Sphincters

A

Structures that separate the digestive tracts from each other
Made if smooth muscle
Act as valve of a reservoir for holding luminal content before emptying into next segment

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8
Q

Dysregulation of sphincters

A 
GI motility disorders
Gastroparesis
Dumping syndrome
Achalasia
GERD
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9
Q

Dysregulation of GI motility or secretion

A

GERD
Peptic ulcer
Diarrhoea

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10
Q

General structure of gut wall

A

Mucosa
Submucosa
Muscularis externa
Serosa

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11
Q

Structure of mucosa

A

Epithelial layer with exocrine & endocrine gland cells
Lamina propria
Muscularis mucosa

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12
Q

What do exocrine gland cells in mucosa of gut wall do?

A

Secrete mucus & digestive enzymes

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13
Q

What do endocrine cells in mucosa of gut wall do?

A

Release GI hormones into the blood

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14
Q

What makes up the lamina propria?

A

Small blood vessels
Nerve fibres
Gut-associated lymphatic tissue which secretes antibodies to specific food or bacterial antigens & triggers immune response
Loose connective tissue

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15
Q

Structure and function of muscular mucosa?

A

Thin layers of smooth muscle

Control mucosal blood flow & GI secretion

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16
Q

Structure of submucosa

A 
Loose connective tissue
Large blood vessels
Lymphatic vessels
Glands
Submucosal nerve plexus - Meissners plexus
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17
Q

Structure of muscular externa

A

Thick muscle - 2 layers of smooth muscle cells. Inner circular & outer longitudinal
Myenteric nerve plexus - Auerbach’s, which lies between muscle layers & regulates motility

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18
Q

Structure & function of serosa

A

Connective tissue
Connects to abdominal wall & supports GI tract in abdominal cavity
Major structures enter through serosa - blood vessels, extrinsic nerves & ducts of large accessory exocrine glands

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19
Q

Myenteric (Auerbach’s) plexus

A

Controls gut motility
Found between circular & longitudinal muscle layers
Thin layer of ganglia, ganglion cells & inter-ganglionic nerve tracts
Innervates longitudinal & outer lamella of circular smooth muscle layers
Some neutrons have projections into adjacent muscle layers
Some are interneurons

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20
Q

Submucosal (Meissner’s) plexus

A

Intestinal absorption & secretion
Neuronal array found between submucosal layers & circular muscle
Neurons are functionally distinct
Appear to project to inner lamella of circular muscle layer
Innervate glandular epithelium, intestinal endocrine cells & submucosal blood vessels

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21
Q

Hirschsprung’s disease

A

Congenital absence of myenteric plexus, usually involving part of distal colon
Pathologic section of the large bowel lacks peristalsis & undergoes continuous spasm
Leads to functional obstruction & severe constipation

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22
Q

Intrinsic pathway

A

Innervation needed for motility & secretory action
Enteric nervous system
Consists of submucosal & myenteric plexus

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23
Q

Extrinsic pathway

A

Autonomic nervous system

Linked to CNS via sensory & motor nerves of parasympathetic & sympathetic nervous system

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24
Q

Sympathetic innervation

A 
Extrinsic pathway
Inhibits gut motility & secretion
Constricts sphincters
Preganglionic fibres from T8-L2
Postganglionic cell bodies in coeliac, inferior &  superior mesenteric, hypogastric ganglia
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25
Q

Parasympathetic innervation

A

Stimulates motility & secretions by increasing the activity of ENS neurons
Vagus nerve
Pelvic nerve

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26
Q

What does the vagus nerve supply?

A 
Oesophagus
Stomach
Small intestine
Liver
Pancreas
Cecum
Appendix
Ascending colon
Transverse colon
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27
Q

What does the pelvic nerve supply?

A

Remainder of colon via hypogastric plexus

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28
Q

Types of gastrointestinal movement

A

1) Segmentation
2) Tonic contraction
3) Peristalsis

29
Q

What is the function of segmentation?

A

Mixes food with enzymes
Mainly occurs in small intestines
Closely spaced contractions of circular smooth movements followed by relaxation
No net forward movement

30
Q

What is the function of tonic contraction?

A

Separation

31
Q

What is the function of peristalsis?

A

Propulsion

32
Q

What is the mechanism of peristalsis?

A

Longitudinal smooth muscle contracts
Circular muscle contracts
Longitudinal relaxes during latter half of circular contraction

33
Q

What is the migrating motor complex?

A

Pattern of motility that occurs every 90 minutes between meals
Intervals of strong, propulsive contractions which pass down the distal stomach & small intestine
Intrinsic property that doesn’t require external innervation

34
Q

What is the function of the migrating motor complex?

A

Sweeps the stomach of indigestible materials

35
Q

What is paralytic ileus?

A

Temporary cessation of gut motility that is commonly caused by abdominal surgery

36
Q

Causes of paralytic ileus

A

Infection or inflammation in abdominal cavity
Electrolyte abnormalities
Drug ingestion

37
Q

What are the signs & symptoms of paralytic ileus?

A

Nausea & vomiting
Abdominal distention
Absent bowel sounds

38
Q

What are the 3 stages of swallowing?

A

1) Voluntary stage
2) Pharyngeal stage
3) Oesophageal stage

39
Q

What is the voluntary stage of swallowing?

A

Bolus is formed in the mouth by mastication & passed into oropharynx
The tongue moves upward & backwards against the palate

40
Q

What is the pharyngeal stage of swallowing?

A

Involuntary passage of bolus through the pharynx into the oesophagus

1) Bolus stimulates mechanoreceptors in pharynx, which send impulses to deglutition centre in medulla oblongata & lower pons of brain stem
2) Returning imposes cause soft palate & uvula to move upwards & superior constrictor of pharynx contracts to close off nasopharynx
3) Larynx rises so epiglottis covers trachea
4) Respiration is inhibited
5) Bolus moves through oropharynx & laryngopharynx
6) upper oesophageal sphincter relaxes & bolus moves into oesophagus

41
Q

What is the oesophageal stage of swallowing?

A

Involuntary passage of bolus through oesophagus into stomach
Starts once bolus enters oesophagus
Peristalsis wave is initiated in pharynx & continues length of oesophagus to push bolus onwards

42
Q

What is the composition of the upper 1/3 of the oesophagus

A

Skeletal, striated muscle

43
Q

What is the composition of the lower 2/3 of the oesophagus?

A

Smooth muscle

44
Q

Achalasia

A

Condition characterised by dysphagia resulting from a failure of the lower oesophageal sphincter to relax leading to a functional obstruction.
Loss of peristalsis of oesophageal body
Unknown cause

45
Q

Gastro-oesophageal reflux disease

A

Occurs when lower oesophageal sphincter is incompetent & allows the flow of gastric juices & content back into the oesophagus
Gastric juices are corrosive to the oesophageal mucosa leading to the distal oesophagus becoming inflamed & ulcerated causing heartburn

46
Q

What are the 4 regions of the stomach?

A

Cardia - surrounds opening of oesophagus into stomach
Fundus - primary function is for storage
Body - inferior to fundus
Pyloric part

47
Q

What regions is the pyloric part of the stomach divided into?

A

Pyloric Antrum - connects to body of stomach
Pyloric canal
Pylorus - connects to duodenum

48
Q

What are the functions of the stomach?

A

Storage
Physical & chemical disruption - mixing
Deliver resultant chyme to intestine at optimal rate

49
Q

What is the reason for the stomach having a storage function?

A

Food is ingested faster than it can be digested

Mainly in the funds

50
Q

What is the movement of food through the stomach?

A

1) Bolus of food enters the stomach & funds & upper body relax to receive it
2) Through peristalsis, the distal stomach mixes the gastric contents with gastric secretions
3) The gastric chyme is slowly emptied into the small intestine
4) Peristalsis proceeds through the gastric antrum, the pyloric sphincter partially closes leading to retropulsion of astral contents as the Antrum contracts

51
Q

What is receptive relaxation in the stomach?

A

The increase in stomach pressure triggers dumping & reflux
After ingestion, the first movement is relaxation of muscle by an increase in fibre length without a change in tone
Mediated by vagus as part of the end of swallowing reflex
Pressure sensors maintain pressure at abdominal levels
Occurs in proximal motor unit - body & funds of the stomach

52
Q

What is mixing in the stomach?

A

Peristalsis through strong coordinated contraction of 3 muscle layers in the distal motor unit - pylorus & Antrum
Activity originates in mid stomach & spreads away distally
A little chyme enters duodenum but most of the contents are returned under pressure to the distal regions - retropulsion

53
Q

What is emptying in the stomach?

A

Terminal part - pyloric Antrum has thickened muscle layers
Pyloric sphincter controls exit
Increase in chyme In stomach induces antral contractions & opening of sphincter
Small amount of chyme is ejected into the duodenum & pyloric sphincter contracts
Liquids leave first, solids after a lag time for mechanical break up

54
Q

What is the enterogastric reflex?

A

Inhibits emptying & consists of complex hormonal & neural signals
Stimulates pyloric contractions & increases tone of pyloric sphincter to prevent emptying
Prevents upper small intestine being overwhelmed by material from the stomach

55
Q

What is the hormonal regulatory pathway for gastric emptying?

A

Presence of fatty acids/monoglycerides in the duodenum, low pH
Leads to release of hormones - secretin, GIP, CCK

56
Q

What is the neural regulatory pathway for gastric emptying?

A

Via ENS and/or extrinsic nerves from duodenum to stomach wall
Fear, anger, depression produce a change in gastric motor ability

57
Q

What are the symptoms of dumping syndrome?

A

Nausea, pallor, sweating, vertigo & fainting within minutes after a meal or ingestion of a hypertonic solution

58
Q

What is gastroparesis?

A

Impaired or absent ability of the stomach to empty
Occasionally observe in severely diabetic patients who develop autonomic neuropathy
Loss of vagal stimulation in the stomach impairs antral systole, which prevents proper digestion & emptying of stomach contents

59
Q

What are the symptoms of gastroparesis?

A

Early satiety
Abnormal bloating
Nausea

60
Q

What are the functions of the small intestine?

A

Mixing

Peristalsis

61
Q

How does the small intestine protect itself as it is exposed to hostile environments?

A 
The gut can develop non-immunological defence mechanisms:
Gastric acid secretions
Intestinal mucin
Epithelial cell permeability barrier
Gut peristalsis
62
Q

What is the consequence of impaired peristalsis in the small intestine?

A

Abnormally high levels of bacteria leading to diarrhoea and/or steatorrhoea

63
Q

What are the taeniae coli?

A

3 thick bands of longitudinal muscle in the large intestine

64
Q

What is the main role of the large intestine?

A

Squeeze & roll to expose faecal matter for reabsorption of water & electrolytes.
Secretes mucus to lubricate for expulsion

65
Q

What is the mechanism for defecation?

A

1) Mass movement propels faeces into the rectum
2) Faeces distend the stretch receptors which transmit signals to the spinal cord to provoke defecation reflex
3) Spinal reflex stimulates contraction of the rectum & relaxes internal anal sphincter
4) Impulses from the brain prevent defecation by keeping external anal sphincter closed
5) Defecation occurs once external anal sphincter relaxes

If voluntary relaxation of the external sphincter doesn’t occur via the pudenal nerve then reverse peristalsis returns material to colon

66
Q

What is the basic electrical rhythm?

A

Slow wave rhythm in gastrointestinal smooth muscle

67
Q

How is smooth muscle contraction initiated?

A

Calcium entry occurs during spike potentials, which are trigger if the peak of a slow wave depolarises the membrane to threshold potential
ENS determines when slow waves will produce spike potentials & give rise to a contraction

68
Q

What do inhibitory transmitters do?

A

Open potassium channels in smooth muscle cells
Hyperpolarise membrane potential to prevent slow wave reaching threshold
Regulates smooth muscle contraction

69
Q

What side effects do anticholinergic drugs causes?

A

Xerostomia
Constipation
Ileus
Nausea & vomiting

Module 104 - Nutrition, metabolism & excretion (31 decks)

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