gI motility Flashcards
Name the three main salivary glands and their relative contribution to saliva production
Parotid (25%)
Submandibular (70%)
Sublingual (5%)
What is the largest part of the small intestine?
Ileum
What are the three main methods of movement seen in the GI tract?
Propulsive movement, mixing movement and tonic contraction.
Describe propulsive movements?
Peristalisis (contraction of the muscle behind and dilation in front)
Describe tonic contractions
A large amount of skeletal muscle contracts simultaneously, for example in defecation.
What is the purpose of secretion throughout the GI tract?
Digestion and protection
What do digestive secretions contain?
Water (from plasma)
Electrolytes
Organic compound (bile salts, mucus etc)
What is the purpose of mixing movements?
To break down and give a larger surface area, for enzymatic attack
Describe the layers of the gut wall front he lumen outwards:
- Mucosa
- Muscularis mucosae
- Submucosal plexus
- Submucosa
- Circular muscle
- Myenteric plexus
- Longitudinal muscle
- Serosa
What are the major physiological functions associated with the mouth?
Lips: containment of food
Teeth: Chewing to break down food, stimulation of taste buds
Palate: Separates mouth from nasal passages
Tongue: Guides food and allows swallowing, contains taste buds
Pharynx: Common passageway for reparatory and digestive tracts.
Give 6 functions of saliva
- Lubrication
- Solvent
- Antibacterial
- Beginnings of complex carbohydrate digestion
- Neutralization of acid
- Facilitates sucking by infants
What does saliva contain that gives it is antibacterial properties?
Lysozyme, lactoferrin and antibodies
What does saliva contain that allows it to neutralise acid?
Bicarbonate
What are the two stages of saliva formation and where do they occur?
- Primary secretion by acinus
2. Secondary modification by the duct cells
How are the components necessary for primary secretion moved?
Active transport
What is the main purpose of the secondary modification stage?
A diluting stage.
Sodium and chlorine are removed to a large extent and potassium and bicarbonate are added but to a lesser degree.
There is no addition of water.
How much saliva do we usually produce whilst asleep, normally and during active salivation?
Sleep = 0.05 ml/min Rest = 0.5ml/min Active = 5ml/min
By what two neuronal reflexes int he rate of saliva production increased by?
- Simple reflex
2. Conditioned/acquired reflex
Describe the simple reflex for saliva production
Chemo/pressure receptors in mouth sense presence of food
Impulses are then sent via afferent nerves to the salivary centre in the medulla
This then sends impulses via extrinsic autonomic nerves (sympathetic and parasympathetic)
Salivary glands will increase production
Describe the conditioned reflex for saliva production
Though/smell of food is sensed in the cerebral cortex
This is then sent to the salivary centre in the medulla
This then send impulses via autonomic nerves
Salivary glands increase production
What is the dominant tone in normal saliva production? What receptor mediates this?
Parasympathetic.
M3 muscarinic acetylcholine receptors
Whate nerves are part of the parasympathetic stimulation of saliva?
Glossopharyngeal and facial
What is the consistency of the saliva in the parasympathetic response?
Large volume
Watery
Rich in enzymes
What nerves mediate the sympathetic response for salivary production? What receptor is the mediator of this?
Postganglionic fibres from superior cervical ganglia
Beta 1 adrenoreceptors
Describe the saliva seen in the sympathetic response
Small volume, thick, mucus rich
What are the two distinct stages in swallowing?
- Oropharyngeal phase
2. Oesophageal phase
What is swallowing?
Movement of the food from the mouth to the stomach
Describe the voluntary stages of the oropharyngeal swallowing stage
Bolus formed in mouth
Tongue forces bolus into pharynx
Pressure stimulates pharyngeal pressure receptors
Describe the involuntary actions involved in oropharyngeal swallowing
Afferent impulse sent to swallowing centre in medulla
Efferent signals release an “all or nothing” reflex sequence of muscle movements
Upper oesophageal sphincer opens
Food passes through pharynx and into oesophagus
What happens in the oesophageal swallowing stage?
The swallowing centre in the medulla oblongata triggered a primary peristaltic wave and closure of the upper oesophageal sphincter.
How is oesophageal swallowing mediated?
By skeletal muscle in the upper oesophageal and smooth muscle in distal regions.
It is co ordinated by the cholinergic neurones of the enteric nervous system
What kind of muscle fibres squeezed behind the bolus?
Circular fibres
What do the longitudinal fibres do?
They are in front of the bolus and the shorten the distance of travel
Why does the lower oesophageal spinchter close after the passage of the bolus?
To pprevent reflux
What happens when food becomes lodged?
Secondary peristaltic wave stimulated
Increases saliva production
What kind of epithelium lines the oesophagus?
Stratified squamous
What is the purpose of the mucus secretions from the oesophagus?
Lubricates passage
Protects epithelium from attack by enzymes and acid in gastric juice.
What drives the relaxation of the stomach?
Vagus nerve
What digestive juices does the stomach contain?
HCl and pepsin
What does the stomach do?
Mixes food with gastric secretions to make chyme
Which part of the stomach does the majority of the mixing?
The antrum (has a thicker smooth muscle layer and is highly contractile)
How much gastric juices does the stomach secrete each day?
2 litres
What are the folds in the stomach called?
Ruggae
Where do you find the pacemaker cells of the stomach?
The interstitial cells of canal in the funds of the stomach
What do gastric pacemaker cells do?
The establish a basal electrical rhythm which spreads over the stomach front he funds to the pyloric sphincter
How many excitations are produced each minute?
3
How is electrical rhythm allowed to spread across the stomach?
Gap junctions
es every excitation result in smooth muscle contraction?
No, you need an external stimulus to allow the potential to reach threshold (recognition of food by chemoreceptors)
What determines the escape of chyme throughout he pyloric sphincter?
The strength of the antral wave
What gastric factors govern the strength of the antral wave?
Gastric factors:
- Rate of emptying is proportional to volume of chyme in the stomach - Distension increases motility due to stretch of smooth muscle, stimulation of intrinsic nerve plexuses, increased vagus activity and gastrinincrease.
- Consistency of chyme: Emptying facilitates by finely divided, thick liquid chyme
How can the duodenum delay the emptying of the stomach?
- Neuronal response, “The enterogastric reflex” decreases astral peristaltic activity through signal from intrinsic nerve plexuses and the autonomic nervous system.
- Hormonal response: The release of enterogastrones (secretin, cholecysystokin) from the duodenum inhibits stomach contraction.
What fourstimuli within the duodenum drive the neuronal and hormonal responses?
Fat (delays emptying)
Acid (delays emptying)
Hypertonicity (carbohydrate and protein digestion are very osmotically active)
Distension
