GI tract Flashcards
What are the organs that makeup the GI tract ?
- mouth
- pharynx
- salivary glands
- oesophagus
- stomach
- pancreas
- liver
- gallbladder
- small intestine
- large intestine
What is meant by exocrine secretions ?
secretions out of the body
What is the exocrine secretions and functions of the mouth, pharynx and salivary glands ?
- salt and water
- mucus
- amylase
- chewing
- swallowing reflex
- moistens, lubricates and digests polysaccharides
What is the exocrine secretions and functions of the oesophagus ?
- mucus
- lubricates contents
- peristaltic waves
What is the exocrine secretions and functions of the stomach ?
- HCl
- pepsin
- mucus
- food solubilisation
- kills microbes
- digests proteins
- lubrication
What is the exocrine secretions and functions of the pancreas ?
- enzymes
- bicarbonate
- digests carbohydrates, fats and proteins
- neutralises HCl
What is the exocrine secretions and functions of the liver ?
- bile salts
- bicarbonate
- organic waste products
- solubilises water insoluble fats
- neutralises HCl
- elimination of waste
What is the exocrine secretions and functions of the gallbladder ?
- no exocrine secretions
- storage and concentration of bile
What is the exocrine secretions and functions of the small intestine ?
- enzymes
- salt and water
- mucus
- food digestion
- maintain fluidity
- lubrication
What is the exocrine secretions and functions of the large intestine ?
- mucus
- lubrication
How much water is ingested and lost overall per day from the body ?
ingested = 2 litres per day
lost = 100 ml per day lost in faeces
How much water is secreted through saliva and what is the pH ?
- 1.5 litres per day
- pH 6.8 - 7
How much water is secreted through gastric secretions and what is the pH ?
- 2.3 litres per day
- pH 1.5 - 3
How much water is secreted through bile and what is the pH ?
- 500 ml per day
- pH 7.8 - 8
How much water is secreted through pancreatic juices and what is the pH ?
- 1 litre per day
- pH 8 - 8.4
How much water is secreted through intestinal secretions and what is the pH ?
- 1.5 litres per day
- pH 7 - 7.4
How much water is reabsorbed into the body and where does this take place ?
small intestine = 8 - 8.5 litres per day
colon = 0.4 - 1 litre per day
How long does the food remain in the mouth ?
30 seconds - 1 minute
How long does the food remain in the oesophagus ?
8 - 12 seconds
How long does the food remain in the stomach ?
1 - 3 hours
How long does the food remain in the small intestine ?
4 - 6 hours
How long does the food remain in the colon ?
10 - 20 hours
How long does the food remain in the rectum ?
20 - 100 hours
Describe the nervous system in relation to the gut
- the gut has its own nervous system known as the enteric nervous system
- the Myenteric plexus or Auerbach’s plexus is located in the muscularis externa and it is largely motor in function
- the submucosal plexus or Meissner’s plexus is located in the submucosa and is mainly sensory in function
- parasympathetic innervation to the gut increases motility
- sympathetic innervation to the gut decreases motility
Describe the basic histological features of the gut
- innermost layer = mucosa
consists of simple squamous non keratinised epithelium, lamina propria and muscularis mucosa - next layer = submucosa
contains the submucosal plexus - next layer = muscularis externa
consists of longitudinal and circular muscle
contains the myenteric plexus - outermost layer = serosa
this is a connective tissue layer
What are the 3 main phases of swallowing ?
1) oral
2) pharyngeal
3) oesophageal
Describe the oral phase of swallowing
- voluntary
- chewing and rolling of the tongue
- stimulates mechanoreceptors on the soft palate
- initiates the involuntary phase
Describe the pharyngeal phase of swallowing
1) raising of the soft palate allows for contraction of the superior constrictor muscles to stop food from the nasopharynx
2) initiation of peristaltic contractions - pushes the food bolus to the upper oesophageal sphincter
3) raising of the larynx closes the epiglottis
4) deglutition apnoea - inhibition of respiration
Describe the oesophageal phase of swallowing
- continuation of the peristaltic wave down the oesophagus pushes the food bolus down
- secretion of mucus from glands in the oesophageal submucosa lubricates the oesophagus - happens in response to pressure from the food bolus
- peristaltic wave relaxes the lower oesophageal sphincter allowing food to enter the stomach
Describe the structure of the upper third of the oesophagus
- largely striated muscle
- peristalsis is organised from the brainstem
Describe the structure of the lower third of the oesophagus
- largely smooth muscle
- peristaltic wave is largely innervated by the enteric nervous system
Describe the upper oesophageal sphincter
- composed of striated muscle
- innervated by the cranial nerves
Describe the lower oesophageal sphincter
- barrier between the stomach and oesophagus
- composed of smooth muscle
- innervated by the enteric nervous system
Summarise pressure changes in the oesophageal phase of swallowing
- at rest the UES is closed
- relaxation causes the UES to open
- contraction will cause food to be pushed down the oesophagus
- relaxation of the LES causes food bolus to move down and the LES opens
Describe the gastric motor functions
- the stomach has a basic electrical rhythm - slow phasic contraction ~ 3 contractions per minute
- the orad region of the stomach has tonic contraction only
What happens in the pacemaker region of the stomach ?
- the basic rhythmic contraction is initiated here
- slow waves are initiated here
What causes the initiation of slow waves ?
- caused by smooth muscle cell depolarisation
- triggers action potentials
- causes mechanical contraction
Describe postprandial movements in the small intestine
- villi cause small sweeping movements and mix acidic chyme and neutralised chyme
- pendular movements allow contraction and relaxation of longitudinal muscles causing sections of the small intestine to shorten and lengthen
- segmentation movements cause contraction and relaxation of circular smooth muscles
- peristaltic waves propel food along the small intestine
Describe the peristaltic reflex
- stimulation of stretch receptors
- widens the path ahead of the bolus and narrows the path behind
- inhibitory neurones can cause an area of receptive relaxation
