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Gastrointestinal > Oesophagus and Swallowing > Flashcards

Oesophagus and Swallowing Flashcards

1
Q

Which cells is the oesophagus composed of?

A

Fibromuscular tube (25cm) of striated squamous epithelium

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2
Q

Where in the body is the oesophagus located?

A

Lies posterior to the trachea

Begins at end of laryngopharynx and joins stomach a few cm from diaphragm (at the cardiac orifice of the stomach)

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3
Q

What is the role of the oesophagus?

A

Transports food to stomach (eating gullet)

Secretes mucus

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4
Q

What promotes the transport of ingested food into the stomach?

A

Highly coordinated muscular process;
contraction & relaxation of oesophagus to move food through GIT
Relaxation of the sphincters (UOS and LOS)

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5
Q

Describe the muscular structure of the oesophagus

A

Skeletal muscles surround the oesophagus below the pharynx (the upper third)
Smooth muscles surround the lower ⅔

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6
Q

Name the 2 oesophagul sphincters?

A

Upper oesophageal sphincter (UOS): striated muscle;

Lower oesophageal sphincter (LOS): smooth muscle;

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7
Q

Describe the features of UOS

A

Musculo-cartilaginous structure

Constricted to avoid air entering the oesophagus

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8
Q

Describe the features of LOS

A

acts as a flap valve
LOS = area of high pressure zone where it merges with the stomach
LOS has intrinsic and extrinsic components

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9
Q

What are the intrinsic components of the LOS?

A

Intrinsic component: oesophageal muscles; under neurohormonal influence;

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10
Q

What are the extrinsic LOS components?

A

Extrinsic component: diaphragm muscle (adjunctive external sphincter)

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11
Q

What is the consequence of malfunctioning of the intrinsic/extrinsic LOS components?

A

Malfunction of intrinsic and extrinsic components of lower oesophagul sphincter → GORD

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12
Q

What is GORD?

A

GORD - gastro-oesophagul reflux disease

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13
Q

What are the 3 components of the LOS?

A
  1. Thick circular smooth muscle layers and longitudinal muscles
  2. Clasp-like semi-circular smooth muscle fibres on the
    right side
  3. Sling-like oblique gastric (angle of His) muscle fibres
    on the left side
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14
Q

How are the semi circular smooth muscle fibres activated in the oesophagus?

A

Myogenic activity (some resting tone), but less ACh-responsive

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15
Q

Describe the functional features of the oblique gastric muscle fibres

A

Work in concert with clasp like-semi-circular smooth muscle fibres, help prevent regurgitation- responsive to cholinergic innervation

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16
Q

Explain how the Angle of His (oblique fibres) in infants may cause reflux

A

Angle of His is poorly developed in infants as it makes a vertical junction with stomach, hence why reflux is common in infants

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17
Q

What is the Angle of His (oblique angles)?

A

The acute angle created between stomach entrance (cardia), and oesophagus. It forms a valve, preventing reflux entering the oesophagus

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18
Q

What is the consequence of reflux into the oesophagus?

A

Reflux of duodenal bile, enzymes, gastric acid cause irritation of the oesophageal lining, inflammation and in extreme cases Barrett’s oesophagus

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19
Q

What are the components of the extrinsic LOS?

A
  1. Crural diaphragm

2. Pinchcock action of crural fibres

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20
Q

Describe the role of the crural diaphragm in the extrinsic LOS

A

Crural diaphragm encircles the LOS

Forms channel through which oesophagus enters the abdomen

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21
Q

Explain how the crural fibres produce the pinchcock action

A

Fibres of the crural portion of the diaphragm possess a “pinchcock-like” action => (extrinsic sphincter; diaphragmatic sphincter) - myogenic tone

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22
Q

What is the oesophagul innervation?

A

Involvement of cholinergic (i.e. via ACh) and non-cholinergic, NANC innervation in the control of tone of the lower oesophageal sphincter

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23
Q

Outline the neural control of the oesophagul sphincters

A

Acetylcholine, SP: contraction of intrinsic sphincters
NO and VIP: relax the intrinsic sphincters
Extrinsic / intrinsic sphincters work in concert to push food → stomach

24
Q

Describe the muscular and neural structure of the upper part of the oesophagus

A

Striated muscle; supplied by somatic motor neurons of vagus nerve without interruption
- Vagus nerve
- Splanchnic nerves (thoracic sympathetic
trunks)

25
Q

Describe the muscular and neural structure of the lower part of the oesophagus

A

smooth muscles;
Innervated by visceral motor neurons of vagus nerve with interruptions (-synapse with postganglionic neurons; cell bodies in oesophagus and splanchnic plexus)

26
Q

Which nerves encircle the oesophagus>

A

encircled by nerves of the oesophageal plexus

27
Q

What is the Dorsal vagal nucleus

A

cranial nerve nucleus for the vagus nerve in the medulla

28
Q

Where is the DVN located?

A

It lies under the floor of the 4th ventricle

29
Q

What is the role of the DVN?

A

Mostly serves parasympathetic vagal functions in the GIT, lungs and other thoracic and abdominal vagal innervations

30
Q

What is the nucleus Ambiguus?

A

where the cell bodies for the preganglionic parasympathetic vagal neurons that innervate the heart reside

31
Q

What is the role of the phrenic nerve?

A

Innervates the external & internal intercostal muscles and the diaphragm, it passing motor information to the diaphragm and receiving sensory information from it

32
Q

Where is the phrenic nerve located?

A

originates in the neck (C3-C5) and passes down between the lung and heart to the diaphragm

33
Q

How many phrenic nerves are there?

A

2, left and right

34
Q

What innervates the phrenic nerve ?

A

The phrenic nerve receives innervation from parts of both the cervical plexus and the brachial plexus of nerves

35
Q

What is the significance of the phrenic nerves?

A

Provide the only motor supply to the diaphragm as well as sensation to the central tendon. In the thorax, each phrenic nerve supplies the mediastinal pleura and pericardium

36
Q

What controls the contraction of the crural diaphragm?

A

Contraction of the crural diaphragm is controlled by the inspiratory centre in the brain stem and the nucleus of the phrenic nerve

37
Q

What innervates the crural diaphragm?

A

right and left phrenic nerves through ACh

38
Q

What causes the swallow reflex?

A

Excitation of receptors in pharynx (oesophageal peristalsis and relaxation)

39
Q

What is swallowing?

A

Swallowing is the coordinated opening and closing of the upper and lower oesophageal sphincters

40
Q

Outline how the swallowing reflex takes place

A
  1. The afferent stimulus travels to the sensory nucleus
    (nucleus solitarius, smaller upper inset).
  2. Programmed events from DVN + nucleus ambiguus
    mediate oesophageal peristalsis and sphincter
    relaxation via NO /VIP
  3. Efferent impulses pass to pharyngeal musculature and
    tongue
  4. Vagal efferent fibres communicate with myenteric
    neurons that mediate relaxation of LOS (larger lower
    inset).
41
Q

What are the functions of the oesophagus?

A

Swallowing (deglutition)

Conveys food and fluids from pharynx to stomach

42
Q

How is swallowing initiated?

A

Swallowing is triggered by afferent impulses in the trigeminal, glossopharyngeal and vagus nerves

43
Q

What causes swallowing to take place?

A

Efferent impulses pass to the pharyngeal musculature and the tongue
- trigeminal, facial and hypoglossal nerves
(tongue muscles)

44
Q

Which impulses are required to integrate for swallowing to occur?

A

DVN, NTS and NA

45
Q

Describe how swallowing is voluntarily initiated?

A

Voluntary action – collect material on tongue and push it backwards into pharynx (skeletal muscle, mucus membrane)

46
Q

Describe how swallowing is involuntarily initiated?

A

Waves of involuntary contractions push the material into oesophagus
Food moves from Mouth→oropharynx→laryngopharynx→oesophagus + stomach

47
Q

What reflex responses occur during swallowing?

A

Inhibition of respiration - nasopharynx closed off
Closure of glottis (around the vocal cords) by epiglottis
Prevents food from entering the trachea
Ring of peristaltic waves (4cm/sec) behind the material moves it towards the stomach

48
Q

What causes food to move along the GI tract?

A

Progressive muscular contractions and relaxations move the food towards the stomach and along the GIT

49
Q

What is swallowing difficulty caused by?

A

Swallowing difficulty (oropharyngeal dysphagia) is caused by:
- UOS inability to open
- Timing discoordination between UOS opening and
pharyngeal push of ingested bolus

50
Q

What is the purpose of secondary peristalsis?

A

allows any remnants of food to be moved on

51
Q

Explain how secondary peristalsis occurs

A

Relaxation of upper oesophageal sphincter (UOS) – food passes
UOS closes as soon as food passes
Glottis opens
Breathing resumes

52
Q

Explain how primary and secondary peristalsis occur to aid swallowing

A

Lower oesophageal sphincter opens + stays open throughout swallowing

LOS closes after material passed

A large food material does not reach the stomach after the first peristaltic wave

Stimulation of receptors upon distension of oesophagus lumen by the food → repeated waves of peristalsis (secondary peristalsis)

53
Q

How is gastric reflex prevented ?

A

LOS – closes after material has passed

“Pinchcock” effect of the diaphragmatic sphincter on the lower oesophagus

Plug-like action of the mucosal folds in the cardia

54
Q

What is the effect of the plug-like action of the mucosal folds?

A

Abdominal pressure acting on the intra-abdominal parts of the oesophagus

Valve-like effect of oblique entry of oesophagus into stomach – in adults only

55
Q

Explain how the UOS and LOS prevent gastric reflux?

A

form an opening when relaxed and closing completely when contracted
there is an anti-reflux barrier in the region of gastro-oesophageal junction

Gastrointestinal (18 decks)

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