Section 2

Question 1

When does the cephalic phase of digestion begin, and what stimuli initiate it?

Answer 1

The cephalic phase of digestion begins before food enters the mouth, initiated by thoughts, sights, and smells of food stimulating the cerebral cortex and appetite centers in the brain. This activation triggers the parasympathetic system.

Question 2

How does the activation of the parasympathetic system contribute to the cephalic phase of digestion, and what is its main purpose?

Answer 2

Activation of the parasympathetic system, via the vagus nerve, stimulates gastric secretions in the stomach during the cephalic phase of digestion. This phase serves an anticipatory role, preparing the stomach before food arrival.

Question 3

What structures are involved in the oral phase of digestion, and what are their functions?

Answer 3

The oral phase of digestion involves the palate, tongue, pharynx, and teeth.

• The palate separates the oral cavity from the nasal cavity and permits breathing while chewing.
• The tongue, made of voluntarily controlled skeletal muscle, aids in chewing, swallowing, and speech, and contains taste buds.
• The pharynx connects the nose and mouth to the esophagus, serving as a common pathway for the digestive and respiratory systems.
• Teeth, external bones embedded in the jaw, are used for chewing (mastication) and mixing food with saliva.

Question 4

What is the composition of saliva, and what are its major proteins?

Answer 4

Saliva is primarily composed of water (99.5%) and contains electrolytes, enzymes, and proteins (0.5%). Its major proteins include amylase, mucus, and lysozyme.

Question 5

What is the function of amylase in saliva?

Answer 5

Amylase, found in saliva, begins the digestion of carbohydrates by breaking down polysaccharides into the disaccharide maltose.

Question 6

How does mucus in saliva contribute to digestion?

Answer 6

Mucus in saliva moistens food, facilitating swallowing.

Question 7

What role does lysozyme play in saliva?

Answer 7

Lysozyme, an enzyme in saliva, exhibits antibacterial properties and can destroy certain bacteria.

Question 8

How does saliva contribute to taste perception?

Answer 8

Saliva is important for taste perception, as only molecules dissolved in saliva or another water source can activate taste buds.

Question 9

What are the additional functions of saliva beyond digestion?

Answer 9

Saliva lubricates the tongue and lips, aiding in speech, and contains bicarbonate buffers to neutralize acids from food and bacteria in the mouth.

Question 10

How do the sympathetic and parasympathetic nervous systems influence salivation?

Answer 10

Both the sympathetic and parasympathetic systems stimulate increased salivary secretion, but they produce different types of saliva.

The parasympathetic system produces a fast flow of watery saliva rich in enzymes, while the sympathetic system produces a smaller volume that is thicker and rich in mucus.

Question 11

Why is there a perception of a dry mouth during stressful situations?

Answer 11

Strong sympathetic output in stressful situations leads to smaller volumes of saliva being produced, resulting in the perception of a dry mouth.

Question 12

What are the two types of salivary secretion reflexes?

Answer 12

Salivary secretion can be increased by two types of reflexes: simple salivary reflexes and conditional salivary reflexes.

Question 13

How do simple salivary reflexes occur?

Answer 13

Simple salivary reflexes occur when chemoreceptors and mechanoreceptors in the oral cavity respond to the presence of food.

Activation of these receptors sends information to the salivary center located in the brainstem, which then sends impulses via extrinsic autonomic nerves to the salivary glands to promote increased salivation.

Question 14

What triggers conditional salivary reflexes?

Answer 14

Conditional salivary reflexes, known as the “mouth watering” reflex, occur when thinking about, seeing, smelling, or hearing the preparation of food one enjoys.

This learned response is triggered by the pleasure of eating, activating the cerebral cortex to stimulate the salivary center.

Question 15

What is swallowing, and what phases of digestion does it encompass?

Answer 15

Swallowing is the process of moving food from the mouth down through the esophagus and into the stomach. It is included in both the oral and esophageal phases of digestion.

Question 16

Is swallowing a voluntary or involuntary process?

Answer 16

Swallowing is voluntarily initiated when a bolus or liquid is forced to the back of the mouth by the tongue. However, once initiated, swallowing becomes an involuntary response coordinated by 25 pairs of muscles.

Question 17

How is the swallowing reflex initiated and coordinated?

Answer 17

When the bolus exerts pressure on the pharynx, it triggers a complicated reflex coordinated by pressure sensors in the pharynx, sending signals to the swallowing center in the medulla of the brainstem. Efferent signals from the swallowing center control the timing of muscle activation necessary for swallowing.

Question 18

What is the significance of swallowing being an “all-or-none” event?

Answer 18

Swallowing is an all-or-none event, meaning that once initiated, it cannot be stopped.

Question 19

What are the two phases of swallowing, and how long does the oropharyngeal phase typically last?

Answer 19

Swallowing occurs in two phases, with the first phase being the oropharyngeal stage, which is very rapid and lasts around one second.

Once it enters the pharynx, it must be directed to the esophagus and prevented from entering other openings

Question 20

How is the bolus prevented from entering other areas during the oropharyngeal phase of swallowing?

Answer 20

In the mouth, the tongue positions against the palate to prevent food from coming back into the mouth.

In the nasal passages, the uvula elevates and blocks the nasal passages.

In the respiratory passages, the respiratory center in the brainstem is inhibited, preventing movement of air. Additionally, the larynx elevates, and the vocal folds tighten to prevent food from entering the trachea.

Question 21

What occurs during the esophageal phase of swallowing?

Answer 21

During the esophageal phase of swallowing, the upper esophageal sphincter (UES) closes, the oropharyngeal structures return to their normal position, and the inhibition on breathing is removed. The swallowing center activates a primary peristaltic wave that moves from the beginning to the end of the esophagus.

Question 22

What occurs during the esophageal phase of swallowing?

Answer 22

During the esophageal phase of swallowing, the bolus is forced ahead of a peristaltic wave down to the stomach. If the bolus does not make it with the primary peristaltic wave, the distension of the esophagus initiates a secondary, more forceful peristaltic wave. These peristaltic waves relax the lower esophageal sphincter (LES) to allow the bolus into the stomach.

Question 23

What initiates the secondary peristaltic wave?

Answer 23

The secondary peristaltic wave is initiated by the distension of the esophagus, not from the swallowing center, but rather from the intrinsic nerve plexus.

Question 24

What functions does mucus serve in the esophagus during swallowing?

Answer 24

Throughout the esophagus, mucus is secreted to lubricate it for easier movement of the bolus and as a protective layer from gastric juices.

Question 25

Why does the lower esophageal sphincter (LES) remain tightly contracted, except during swallowing?

Answer 25

The LES remains tightly contracted, except during swallowing, to prevent the reflux of acidic stomach contents into the esophagus, a condition known as gastric reflux.

Question 26

The thought, sight, smell, and taste of food stimulates cerebral cortex:

a) cephalic phase
b) esophageal phase
c) oropharyngeal phase

Answer 26

a) cephalic phase

Question 27

The uvula elevates and blocks the nasal passages:

a) cephalic phase
b) esophageal phase
c) oropharyngeal phase

Answer 27

c) oropharyngeal phase

Question 28

The upper esophageal sphincter (UES) closes and the inhibition on breathing is removed:

a) cephalic phase
b) esophageal phase
c) oropharyngeal phase

Answer 28

b) esophageal phase

Question 29

The larynx elevates and the vocal folds tighten to prevent food from entering the trachea:

a) cephalic phase
b) esophageal phase
c) oropharyngeal phase

Answer 29

c) oropharyngeal phase

Question 30

Anticipatory in preparing the stomach for the arrival of food:

a) cephalic phase
b) esophageal phase
c) oropharyngeal phase

Answer 30

a) cephalic phase

Question 31

Peristaltic waves relax the lower esophageal sphincter (LES) and allow the bolus into the stomach:

a) cephalic phase
b) esophageal phase
c) oropharyngeal phase

Answer 31

b) esophageal phase