Gastro 4

Question 1

What are the three regions of the pharynx and their roles?

Answer 1

A: The pharynx is divided into:

• Nasopharynx: Mainly an air passage lined with ciliated pseudostratified columnar epithelium; not directly involved in food passage.

• Oropharynx: Receives the food bolus from the oral cavity; lined by stratified squamous epithelium to withstand abrasion.

• Laryngopharynx: Directs food into the oesophagus while protecting the airway during deglutition.

Question 2

How is deglutition (swallowing) initiated and coordinated?

Answer 2

A: Deglutition begins voluntarily in the oral (buccal) phase when the tongue forms a bolus and propels it toward the oropharynx. It then becomes an involuntary reflex—the pharyngeal-oesophageal phase—where mechanoreceptors in the pharynx send sensory input via cranial nerve IX to the nucleus tractus solitarius (NTS) in the medulla. The NTS processes this input and activates the nucleus ambiguus (NA), which sends motor commands via cranial nerve X to coordinate the sequential contraction of the pharyngeal constrictor muscles and the relaxation of the upper oesophageal sphincter.

Question 3

What are the key anatomical features of the oesophagus and their functions?

Answer 3

A: The oesophagus is a muscular tube extending from the laryngopharynx to the stomach. Key features include:
• Upper Oesophageal Sphincter (UOS): Made of skeletal muscle, it prevents air from entering the oesophagus.

• Lower Oesophageal Sphincter (LOS): Composed of smooth muscle, it remains tonically contracted to prevent gastric reflux.

• Mucosa: Lined by stratified squamous epithelium for protection against abrasion.

• Oesophageal Glands: Located in the submucosa, they secrete mucus to lubricate the passage of food.

• Muscle Transition: The proximal oesophagus is skeletal muscle, transitioning to smooth muscle distally to facilitate peristalsis.

Question 4

How are peristalsis and food propulsion achieved in the oesophagus?

Answer 4

A: Food propulsion in the oesophagus is driven by peristaltic waves:

• Primary Peristalsis: Initiated by swallowing, it propels the bolus from the pharynx into the oesophagus.

• Secondary Peristalsis: Triggered by distension of the oesophageal wall, it clears residual food.
The coordinated activity relies on the intrinsic muscle layers, which transition from skeletal to smooth muscle along the oesophagus.

Question 5

How do neural control mechanisms ensure safe deglutition?

Answer 5

A: The deglutition reflex is coordinated by the interplay between the nucleus tractus solitarius (NTS) and the nucleus ambiguus (NA) in the medulla:

• NTS: Receives sensory input from the pharyngeal mechanoreceptors (via cranial nerve IX) and processes the information.

• NA: Sends out motor commands via cranial nerve X to the skeletal muscles, ensuring the timely contraction of pharyngeal constrictors and proper sphincter relaxation, while also briefly inhibiting respiration to prevent aspiration.

Question 6

The pharynx serves as a common pathway for both

Answer 6

food and air and is divided into nasopharynx, oropharynx, and laryngopharynx.

Question 7

Deglutition transitions from a voluntary phase to an

Answer 7

involuntary, reflex-mediated phase controlled by the NTS and NA.

Question 8

The upper oesophageal sphincter prevents air entry; the lower oesophageal sphincter prevents

Answer 8

reflux.

Question 9

Oesophageal peristalsis includes primary and secondary waves to

Answer 9

efficiently transport food.

Question 10

Sensory input from the pharynx via cranial nerve IX is essential to

Answer 10

trigger the swallowing reflex.

Question 11

Transition from skeletal to smooth muscle in the oesophagus facilitates

Answer 11

effective peristalsis.

Question 12

The oropharynx is the primary region where the food bolus enters the digestive tract.

Answer 12

A: True

Question 13

Deglutition is entirely a voluntary process.

Answer 13

A: False – It starts voluntarily but quickly becomes an involuntary reflex.

Question 14

The nucleus tractus solitarius (NTS) only receives sensory input and does not affect motor output during swallowing.

Answer 14

A: False – The NTS processes sensory input and helps coordinate motor commands via the nucleus ambiguus.

Question 15

The lower oesophageal sphincter (LOS) is normally relaxed to allow food reflux into the oesophagus.

Answer 15

A: False – The LOS is normally tonically contracted to prevent reflux.

Question 16

Secondary peristalsis is triggered by residual food distending the oesophageal wall.

Answer 16

A: True

Question 17

The pharynx is divided into the nasopharynx, ______, and laryngopharynx.

Answer 17

A: Oropharynx

Question 18

The involuntary phase of deglutition is coordinated by the ______ in the medulla.

Answer 18

A: Nucleus tractus solitarius (NTS)

Question 19

During swallowing, the ______ constrictor muscles contract to propel the food bolus through the pharynx.

Answer 19

A: Pharyngeal

Question 20

The ______ oesophageal sphincter prevents the backflow of gastric contents into the oesophagus.

Answer 20

A: lower

Question 21

Primary peristalsis in the oesophagus is initiated by the ______ phase of swallowing.

Answer 21

A: Buccal (or Voluntary)

Question 22

Which of the following correctly describes the transition in the oesophagus?
A) It remains entirely skeletal muscle from top to bottom.
B) It transitions from skeletal muscle in the proximal portion to smooth muscle distally.
C) It is composed entirely of smooth muscle.
D) It contains cardiac muscle in the distal segment.

Answer 22

A: B) It transitions from skeletal muscle in the proximal portion to smooth muscle distally.

Question 23

The sensory input that triggers the swallowing reflex is primarily transmitted by which cranial nerve?
A) Trigeminal (V)
B) Facial (VII)
C) Glossopharyngeal (IX)
D) Vagus (X)

Answer 23

A: C) Glossopharyngeal (IX)

Question 24

Which nucleus is responsible for sending the motor commands during deglutition?
A) Nucleus accumbens
B) Nucleus ambiguus (NA)
C) Dorsal motor nucleus
D) Red nucleus

Answer 24

A: B) Nucleus ambiguus (NA)

Question 25

The primary function of the upper oesophageal sphincter (UOS) is to: A) Prevent reflux from the stomach B) Prevent air from entering the oesophagus C) Secrete mucus for lubrication D) Initiate peristalsis

Answer 25

A: B) Prevent air from entering the oesophagus

Question 26

What distinguishes primary from secondary peristalsis in the oesophagus? A) Primary is voluntary; secondary is entirely involuntary. B) Primary is initiated by swallowing; secondary is triggered by oesophageal distension. C) Primary occurs in the upper oesophagus; secondary occurs in the lower oesophagus. D) Primary is mediated by smooth muscle; secondary is mediated by skeletal muscle.

Answer 26

A: B) Primary is initiated by swallowing; secondary is triggered by oesophageal distension.

Question 27

A patient with a brainstem lesion affecting the nucleus tractus solitarius (NTS) presents with severe dysphagia and frequent choking during meals. Question: How does damage to the NTS impact the swallowing process, and what complications may arise?

Answer 27

A: Damage to the NTS disrupts the processing of sensory signals from the pharynx, leading to uncoordinated or absent motor responses from the nucleus ambiguus. This impairs the swallowing reflex, causing dysphagia, increased risk of aspiration, and potential respiratory complications.

Question 28

An individual experiences chronic heartburn and regurgitation. Question: Which dysfunction in the oesophageal anatomy might be responsible, and what is the underlying mechanism?

Answer 28

A: Dysfunction of the lower oesophageal sphincter (LOS) may allow reflux of acidic gastric contents into the oesophagus, leading to chronic heartburn and regurgitation due to impaired sphincter contraction.

Question 29

A stroke patient shows impaired deglutition with aspiration pneumonia. Question: Which phase of swallowing is likely compromised, and what neural structures are implicated?

Answer 29

A: The pharyngeal-oesophageal (involuntary) phase is likely impaired. Lesions affecting the NTS or nucleus ambiguus can lead to inadequate coordination of muscle contractions, increasing the risk of aspiration and subsequent pneumonia.

Question 30

A patient reports difficulty initiating swallowing and describes a sensation of food “sticking” in the throat. Question: What could be the cause in terms of pharyngeal muscle function, and which muscles or neural inputs might be involved?

Answer 30

A: Impaired function of the pharyngeal constrictor muscles or disruptions in the neural input from the swallowing center (NTS and NA) may cause ineffective bolus propulsion, leading to a sensation of food sticking. This may result from neuromuscular disorders or lesions affecting cranial nerve IX or X.

Question 31

Pharynx:

Answer 31

The muscular tube divided into nasopharynx, oropharynx, and laryngopharynx; it serves as a common passageway for air and food.

Question 32

Deglutition:

Answer 32

The process of swallowing, which involves a voluntary buccal phase followed by an involuntary pharyngeal-oesophageal phase.

Question 33

Nucleus Tractus Solitarius (NTS):

Answer 33

A medullary center that receives sensory input from the pharynx and coordinates the swallowing reflex.

Question 34

Nucleus Ambiguus (NA):

Answer 34

A medullary nucleus that sends motor commands to the muscles involved in deglutition.

Question 35

Upper Oesophageal Sphincter (UOS):

Answer 35

A muscle ring in the proximal oesophagus that prevents air entry.

Question 36

Lower Oesophageal Sphincter (LOS):

Answer 36

A muscle ring at the distal oesophagus that prevents reflux of gastric contents.

Question 37

Peristalsis:

Answer 37

The wave-like contraction of the oesophageal muscles that propels food toward the stomach.

Question 38

Dysphagia:

Answer 38

Difficulty swallowing, often resulting from impaired neural control or muscle function in the deglutition process.