The Structure and Function of the Upper GI Tract Flashcards
What are the two functions of chewing?
- a prolonged taste experience
- defence against respiratory failure
Name the two types of control that allow chewing.
- voluntary control
- reflex control
Where does voluntary control of chewing come from?
- somatic nerves act on the skeletal muscle of the mouth and jaw
Where does reflex control of chewing come from?
- the pressure of food against the gums, hard palate and tongue triggers mechanoreceptors, inducing a contraction of jaw muscles
Name the three pairs of salivary glands.
- parotid
- submandibular
- sublingual
List the components of saliva.
- water
- mucins
- alpha-amylase
- electrolytes
- lysozymes
Are the salivary glands exocrine glands or endocrine glands?
- exocrine glands
- as the exit into the mouth which is ‘outside’ of the body
Name the three types of bulbous alveoli found in the salivary glands.
- mucous
- serous
- mixed
What affects do the parasympathetic and sympathetic nervous systems have on salivary secretion?
- They are both stimulatory
Where does parasympathetic stimulation of salivary glands come from?
- cranial nerves XII and IX
What type of saliva is stimulated by the parasympathetic system?
- profuse, watery secretion
Where does sympathetic stimulation of salivary glands come from?
- either alpha-1 adrenoreceptors
- or beta-2 adrenoreceptors
What type of saliva is stimulated by sympathetic action on alpha-1 adrenoreceptors?
- a small volume of viscous salivary secretion with a high mucus content
What type of saliva is stimulated by sympathetic action on beta-2 adrenoreceptors?
- a small volume of viscous salivary secretion with a high amylase content
How does reflex control stimulate salivary secretions?
- via chemoreceptors and pressure receptors in the walls of the mouth and the tongue
- they respond to the presence of food in the mouth
On average, how long is an adult oesophagus?
- around 25cm
Name and describe the four layers of the oesophageal wall.
- mucosa - made up of stratified squamous epithelium
- submucosa - contains ducts and lubrication
- muscularis externa - superior third is skeletal muscle, while the inferior two-thirds are smooth muscle
- adventitia
How many sphincters are there in the oesophagus and where are they located?
- there are two sphincters
- there are situated at either end of the oesophagus
Name the phases of swallowing.
- oral phase
- pharyngeal phase
- oseopharyngeal phase
What is the oral phase of swallowing?
- where the bolus is pushed to the back of the mouth by the tongue
What occurs during the pharyngeal phase of swallowing?
- the presence of the bolus triggers reflex contractions of pharyngeal muscle
- this is coordinated by the swallowing centre in the medulla
- the soft palate is reflected backwards and upwards to close off the nasopharynx
What occurs during the oesopharyngeal phase of swallowing?
- propulsion of the bolus towards the stomach
- this triggers a peristaltic wave
What triggers the expansion of gastric rugae?
- stimulation via the vagus nerve
List the five primary functions of the stomach.
- temporary storage of indigested materials
- dissolve food particles and initiate the digestive progress
- control delivery of contents to the small intestine
- sterilise ingested materials
- produce intrinsic factor
Why is controlled delivery important?
- it prevents mass delivery which would increase tonicity and therefore affect osmosis
Which part of the stomach is responsible for controlled delivery?
- the pyloric sphincters
Describe the muscle at the top of the stomach.
- thin, stretchy, smooth muscle
Describe the muscle at the bottom of the stomach.
- thicker, more powerful muscle
- this is due to the presence of an oblique muscularis layer underneath the usual layers of the muscularis
