Test Your Knowledge on Human Digestive Processes!

Study Notes

The first step of digestion is chewing or mastication, which involves moving the jaw and helps smear the food out over the tongue so that it can be fully tasted.
The salivary glands are located outside the oral cavity and secrete saliva into the mouth.
The saliva is mainly made of water, but it also contains salivary amylase, which is a digestive enzyme, and mucus which protects the oral mucosa from drying out.
The major salivary glands are the parotid glands, found in front of each ear, the submandibular or submaxillary glands, found under the mandible and the sublingual glands that sit beneath the tongue, under the floor of the mouth.
The salivary glands are innervated by the cranial nerves nine, five, and seven, and work together to move the jaw up and down, allow the teeth to grind and mechanically break down the food, and push the food between the teeth for extra grinding.
The trigeminal, facial, and glossopharyngeal nerves send information to the salivatory nuclei in the brain stem, which then send efferent information to the salivary glands.
The sight or smell of food can cause the secretion of saliva, which is based on learned behavior.
Saliva helps to lubricate the surfaces of the mouth and pharynx, making it easier for food to go down.
The digestive enzyme amylase begins breaking down carbohydrates found in foods like potatoes and rice when saliva mixes with them.
When the food is chewed and mixed with saliva, it creates a soft, mushy mass called a bolus.
The saliva also lubricates the surfaces of the mouth and pharynx, making it easier for the food to go down.
Swallowing is coordinated by muscles under both voluntary and involuntary control and can be broken into three phases; the oral phase, the pharyngeal phase, and the esophageal phase.
The oral phase begins with the voluntary movement of the tongue.
The pharyngeal phase of swallowing begins when this efferent information causes the soft palate and uvula to move upwards, closing the path to the nasopharynx so food cannot reflux up into the nasal cavity.
At the same time, it makes the epiglottis, which is a flap-like structure, move downwards and cover the larynx to prevent food from entering the trachea and respiratory tract.
Finally, the upper esophageal sphincter, which is a muscular ring that guards the entrance to the esophagus, relaxes, allowing the food bolus to slip through.