Oesophagus and stomach Flashcards
What is key to remember about the G.I tract
Largely looks the same- same basic structure- the epithelium changes- but is always there
What is meant by digestion
Digestion is the process of breaking down macromolecules to allow absorption
What is meant by absorption
Absorption is the process of moving nutrients and water across a membrane
Describe the teeth
Adult humans have 32 teeth in total. 8 incisors 4 canines 8 premolars 12 molars The incisors and canines are used to bite and rip food into a manageable size for the mouth to handle. The premolars and molars are responsible for grinding it down into smaller pieces.
Describe the muscles in the oral cavity
Several muscles control the position of the jawbone (the mandible) and can widen or close the mandibular joint, as well as swing it side to side, or a combination of both. This will be explored more in year 2 but for now I just want to introduce you to the massater muscle. This is the largest jaw muscle, responsible for our biting action. If you clench your teeth you should feel it lateral to your clenched molars on both sides.
Describe the salivary glands
Small pieces of food are mixed with saliva, an aqueous secretion with digestive enzymes. Specifically, lingual lipase and salivary amylase, which for the first stage of fat and carbohydrate digestion respectively.
The mixing of food and saliva creates a bolus that can be swallowed into the stomach once it is the right size and consistency.
What are the two types of muscles found in the tongue
Intrinsic muscles - responsible for fine motor control of the tongue, such as enunciating specific sounds, or for moving food from one part of the mouth to another.
Extrinsic muscles - responsible for gross movements of the tongue, such as in, out, up and down. This is especially useful to assist mechanical digestion, by pounding the food bolus against the hard palate at the roof of the mouth.
What are the functions of the tongue
Key functions of the tongue include: speech, eating and taste (salt, sweet, bitter, sour, umami).
What are the components of the GI system
See diagram!
What 3 glands are present in the oral cavity
Parotid gland
Sublingual gland
Submandibular gland
Outline a basic plan of the gut wall
Mucosa- towards the lumen
Epithelium- type changes
Lamina propria (loose connective tissue)
muscularis mucosae- thin layer of muscle
Submucosa- connective tissue (contains nerve plexus and blood vessels)
Muscularis- smooth muscle (nerve plexus)- muscular structure for peristalsis
Serosa/epithelium- connective tissue (may have epithelium- holds gut to the body wall
What may be present in the mucosa and sub-mucosa
Mucosa- secretory glands (pancreas), GALT
Sub-mucosa- submucosal glands
Why are the structures in the submucosa important
Blood vessels- substrate for the gut- it should remove things from it
Why is mucus important in the alimentary system
Lubrication to allow the food bolus to pass down the G.I tract easily
Where can the oral cavity lead to and what are the consequences of this
Because the oral cavity leads to two different places (the lungs and the stomach) it is essential that we get food and air getting to their correct destinations.
What is the importance of the epiglottis and upper oesophageal sphincter
This is achieved by the epiglottis and the upper oesophageal sphincter. At rest, the oesophageal sphincter is tonically active and the epiglottis is in the upright position. These structures move during swallowing, with the epiglottis coming down to cover the entrance to the trachea as the bolus of food moves through the pharynx, and the upper oesophageal sphincter relaxes allowing it to flow into the oesophagus.
We need to be selective of what enters the lungs and what enters the G.I tract
Describe the differences between the oesophagus and trachea at rest
Trachea is patent- held open by cartilaginous rings
oesophagus is collapsed at rest
Describe the physiological anatomy of the oesophagus
§ Starts at C5 (throat) and ends at T10.
§ Structures located nearby include: trachea, aorta and diaphragm.
§ Trachea and pericardium are anterior.
§ Descending aorta is posterior and thoracic duct crosses posterior to oesophagus between T7 and T4.
Projects through thorax- pops through diaphragm at T10.
What can damage to the oesophagus cause
Damage to nearby structures (aorta, trachea, recurrent laryngeal nerve and vagus nerve)
its passage through the thorax places it in close proximity to key structures such as the heart, lungs and major blood vessels.
If the tube is ruptured it can cause major problems that are usually associated with a poor prognosis.
What is the key function of the oesophagus
Function: Conduit for food, drink and swallowed secretions from pharynx to stomach
No absorption takes place
Epithelium is crucial to its function
Describe the epithelium of the oesophagus
§ Non-keratinizing stratified squamous.
o Withstands ‘wear & tear’ in extremes of temperatures and textures.
o Lubricates with mucus glands.
Describe the oesophagus when there is no food in it
No food- oesophagus shuts off at both ends- the sphincters are tonically active at rest
The thorax has a negative pressure while the gut is slightly above atmospheric pressure so the sphincters act to restrict the escape of air/food/liquid from the stomach as it has a tendency to rise.
Positive pressure in stomach and negative pressure in oesophagus
Describe the differences between the upper and lower oesophageal sphincters
§ Upper oesophageal sphincter:
o Comprised of skeletal muscle only – this is controlled involuntary which is strange for skeletal muscle (detects eating food)
o Activated by the swallowing centre of the brain.
§ Lower oesophageal sphincter:
o Comprised of (skeletal muscle and) smooth muscle.
o Activated by the swallowing centre of the brain ( although to a lesser extent than the upper)
What are the two muscles in the upper oesophageal sphincter
Constrictor pharyngeal medius - which has commonality with the circular muscle layer of the GI tract
Constrictor pharynges inferior - which has commonality with the longitudinal muscle layer
What is the middle third portion of the oesophagus made up of
The middle third is a mixture of the two as the proportion of skeletal muscle tapers along its length.
What is key to remember about the muscles in the oesophagus
Despite the involvement of skeletal muscle, it is not under voluntary control.
Describe the components of the lower oesophageal sphincter
The internal component - which is built into the circular smooth muscle of the oesophageal wall
The external component - which is formed by the right crus of the diaphragm (voluntary control)
Describe peristalsis
Local effect responding to a food bolus
Nerve stimulus (food) causes circular muscle above the bolus to contract while causing the circular muscle below the bolus to relax (like a tube of toothpaste)
Independent of gravity
§ Longitudinal and circular layers of muscle exist.
Describe peristalsis in response to a big bolus
Contraction may not be large enough
May need a second peristaltic wave to ensure food passes down to the stomach (signal sent to brain)
Describe the epithelial change at the gastro-oesophageal junction
This lining exists all the way to the lower oesophageal sphincter, where the epithelial cells are arranged as simple columnar epithelia. This is to address the different conditions these epithelia need to tolerate (i.e. resistance against strong stomach acid). This epithelial change occurs within the sphincter along a jagged line called the z-line.
columnar are better adapted for secretion and absorption
