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The alimentary system > Motility of the GI tract > Flashcards

Motility of the GI tract Flashcards

1
Q

What are the 4 physiological processes the GI tract is involved in?

A

Motility
Secretion
Digestion
Absorption

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2
Q

Name some accessory glands in the GI tract

A

Salivary
Gall bladder
Pancreas
Liver

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3
Q

What are sphincters?

A

Made of smooth muscle
Separate parts of the GI tract from one another
Act as a valve of a reservoir

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4
Q

What is the common cause of most GI motility disorders?

A

Dysfunction of sphincters

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5
Q

Why is movement controlled along the gut?

A

Gut is an integrated system of different compartments
Food must be delivered at the appropriate time
Food must be delivered in the appropriate composition
Food must stay in the different compartments for the appropriate duration
Time and digestion are key components of this

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6
Q

What are the layers of the gut wall?

A

Mucosa
Submucosa
Muscularis externa
Serosa

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7
Q

Describe the structure of the mucosa

A

Epithelial layer
Lamina propria
Muscularis mucosa

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8
Q

Describe the structure of the submucosa

A

loose CT, large BVs, lymphatic vessels
Glands in some GI regions
Submucosal nerve plexus - Meissners plexus - regulates blood flow and secretion

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9
Q

Describe the structure of the muscularis externa

A

Thick muscle whose contraction contributes to major gut motility (segmentation and peristalsis)
Two substantial layers of smooth muscle cells: Inner Circular and outer longitudinal layer.
Myenteric nerve plexus

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10
Q

Describe the structure of the serosa

A

Connective tissue and connects to the abdominal wall, supporting Gi tract in the abdominal cavity. Several major structures enter through the serosa, including blood vessels, extrinsic nerves, and the ducts of the large accessory exocrine glands.

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11
Q

What is the intrinsic pathway of GI innervation?

A

The enteric nervous system

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12
Q

What is the extrinsic pathway of GI innervation?

A

The gut brain axis

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13
Q

What effect does parasympathetic control have on the GI tract?

A

Increases

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14
Q

What effect does sympathetic control have on the GI tract?

A

Decreases

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15
Q

When are spike potentials stimulated?

A

When slow waves reach a threshold

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16
Q

When are spike potentials stimulated?

A

When slow waves reach a threshold

Ca2+ channels open and allow entry into the smooth muscle cell. This triggers muscle contraction

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17
Q

What is the major function of the basic electrical rhythm?

A

Determine whether contraction can occur

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18
Q

The strength of contraction depends on…

A

The number of spikes

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19
Q

What does epinephrine do?

A

Inhibits muscle contraction

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20
Q

What neurotransmitter stimulates muscle contraction of the gut?

A

Acetylcholine

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21
Q

List the 3 types of gut motility

A

Segmentation
Tonic contraction
Peristalsis

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22
Q

What is migrating motor complex?

A

Pattern of motility that occurs about every 90 minutes between meals
Sweeps the stomach and small intestine of indigestible materials
Prevents bacterial overgrowth of the upper intestine

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23
Q

Migrating motor complexes may decrease when? What may this cause?

A

In radiotherapy patients

Bacterial overgrowth

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24
Q

What is paralytic ileus?

A

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

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25
Q

What is vomiting in terms of swallowing?

A

The reversal of the process

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26
Q

Name the 3 types of movement of the stomach

A

Receptive relaxation
Mixing
Emptying

27
Q

Where are the pacemaker cells in the stomach located?

A

Longitudinal layer of the greater curvature

28
Q

What is gastrin?

A

Hormone released in response to food in the stomach

29
Q

What is the enteric nervous system?

A

Controls the elaborate processes of the GI tract to ensure overall function is met.
Involves many neurons in the GI tract walls and several hormones

30
Q

Dysfunction is sphincters can lead to…

A

Many types of GI motility disorders including GERD, peptic ulcer disease and diarrhoea

31
Q

Describe the epithelial layer of the mucosa

A

Exocrine (secrete mucus and digestive enzymes) and endocrine (secrete hormones) gland cells

32
Q

Describe the lamina propria layer of the mucosa

A

small blood vessels(BVs), nerve fibers, lymphatic cells/tissue (GALT-gut associated lymphatic tissue) loose connective tissue(CT)

33
Q

Give the two main functions of the gut associated lymphatic tissue

A

Secretes antibodies to specific food or bacterial antigens

Triggers immunological reactions against them leading to mucosal inflammation and damage

34
Q

Activation in the GI immune system is involved in which diseases?

A

Inflammatory bowel diseases and coeliac disease

35
Q

Describe the muscularis mucosa layer of the mucosa

A

thin layers smooth muscle

responsible for controlling mucosal blood flow and GI secretion

36
Q

Give the effect of the intrinsic pathway

A

Increases gut motility

Secretion of digestive enzymes for absorption and digestion

37
Q

Describe the gut brain axis

A

The link between the sensory and motor neurons of parasympathetic and sympathetic supply

38
Q

Where are the intrinsic enteric neurons found?

A

In gut plexuses such as the submucosal (or Meissner’s plexus) and the myenteric (or Auerbach’s plexus)

39
Q

What is the basic electrical rhythm?

A

Smooth muscle cells display pacemaker activity – resting membrane potentials close to threshold - slow spontaneous depolarisation initiates contraction.

40
Q

How do excitatory transmitters work?

A

Excitatory transmitters often cause nonselective cation channels in the smooth muscle cells to open; the resting membrane potential is depolarized and more slow waves cross the threshold for the generation of a spike potential.

41
Q

How do inhibitory transmitters work?

A

Inhibitory transmitters often act by opening the K+ channels in smooth muscle cells, hyperpolarizing the membrane potential and preventing the slow waves from reaching threshold.

42
Q

Describe segmentation

A

Mainly small intestine, for mixing food with enzymes.
Closely spaced contractions of circular smooth followed by relaxation.
No net forward movement.

43
Q

Describe peristalsis

A

Longitudinal smooth muscle contracts first, followed half way through its contraction by the circular muscle. Longitudinal relaxes during latter half of circular contraction …leads to a progressive wave. Distension of gut by food is trigger for peristalsis. Net effect – propel food along GI tract

44
Q

What is paralytic ileus? State the signs and symptoms

A

Temporary cessation of gut motility caused by abdominal surgery or infection, inflammation, drugs and electrolyte abnormality. Signs and symptoms include nausea, abdominal distention, absent bowel sounds and vomiting.

45
Q

Upon swallowing what occurs in the oesophagus?

A 
The upper oesophageal sphincter briefly relaxes, allowing the food bolus to pass into the esophagus.
A contractile (peristaltic) wave sweeps down the oesophagus.
The lower oesophageal sphincter and the proximal stomach relax to allow the bolus to enter the stomach
46
Q

Does oesophageal muscle have pacemakers?

A

No- spontaneous contraction

47
Q

What are the 3 functions of the stomach which define the motility of the stomach?

A
  1. Storage. Ingest food faster than can be digested, aided by receptive relaxation.
  2. Physical and chemical disruption - mixing.
  3. Deliver resultant chyme to intestine at optimal rate – gastric emptying
48
Q

What regulates the mixing of the stomach?

A

Distension of stomach activates mechanoreceptors, ENS/extrinsic
Gastrin release in response to food in stomach also stimulates stomach motility

49
Q

An increase in … causes antral contractions and opening of the sphincter as peristaltic waves approach

A

Chyme

50
Q

Why is emptying of the stomach regulated?

A

To ensure optimal intestinal digestion

51
Q

Describe the enterogastric reflex and its function

A

Inhibits emptying and consists of complex hormonal and neural signals. It stimulates pyloric contractions and also increases tone of pyloric sphincter to prevent emptying, thereby preventing the upper small intestine from being overwhelmed by material from the stomach.

52
Q

Describe the hormonal pathway for gastric emptying

A

presence of fatty acids/monoglycerides in duodenum (not emulsified), Low pH –
stimulates release of hormones (e.g. Secretin, GIP (Gastric inhibitory Peptide), CCK Cholecystokinin

53
Q

Describe the neural pathway for gastric emptying

A

Via ENS and/or extrinsic nerves from duodenum to stomach wall

54
Q

What is dumping syndrome?

A

Rapid emptying of the stomach

Characterised by nausea, pallor, sweating, vertigo and syncope after eating

55
Q

What is gastroparesis?

A

Impaired/absent ability of the stomach to empty
Prevents proper digestion
Patients complain of early satiety (feeling of being full), abnormal bloating, and nausea.
Present in severely diabetic patients who develop autonomic neuropathy

56
Q

Describe the motility of the small intestine

A

Segmentation- multiple short contractions, frequency varies along a proximal to distal gradient. The decreasing gradient of BER frequency promotes the distal movement of intestinal chimes
Peristalsis- short contractions stimulated by both extrinsic and intrinsic factors
Villus movement- swaying and piston-like movements - to mix and to drain lymphatics of fat absorption

57
Q

Describe intestinal blind loop syndrome

A

Impaired peristalsis in the small intestine leading to abnormally high levels of bacteria causing diarrhoea and streahorreoa

58
Q

Describe the motility of the large intestine

A

Movements are slow and irregular

Mixing movements by segmentation or haustral shuffling

59
Q

What is the main role of the motility of the large intestine?

A

squeeze and roll to expose fecal material for reabsorption of water and electrolytes, and secretion of mucus to lubricate for expulsion

60
Q

Describe mass movement and gastric colic reflex of the large intestine

A

Mass movement occurs when segmental contraction of the left colon disappears and a simultaneous contraction of the right colon propels its content distally. Occurs several times a day but especially after meal – referred to Gastric colic reflex

61
Q

How is mass movement linked to defecation?

A

Propels faeces into rectum and distends stretch receptors to provoke defecation reflex

62
Q

Name the 2 sphincters which are normally contracted stating what type of control the body has on them

A

Internal anal sphincter - involuntary control

External anal sphincter - voluntary control – skeletal muscle

63
Q

What does afferent stimulation do to the internal sphincter?

A

Leads to parasympathetic signal to relax internal sphincter

64
Q

If voluntary relaxation of external sphincter does not occur via pudendal nerve…

A

Reverse peristalsis returns to colon

The alimentary system (21 decks)

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