Upper GI structure and function Flashcards
Why do we chew?
Prolong taste experience
Defence against respiratory failure
What are the 2 ways in which chewing is controlled?
Voluntary
Reflex
How is chewing voluntarily controlled?
Somatic nerved innervate skeletal muscles of mouth and jaw
How is chewing reflex controlled?
Contraction of jaw muscles causes pressure of food against gums, hard palate and tongue
Mechanoreceptors cause reflex inhibition of jaw muscles, reducing pressure
What are the 3 glands saliva is secreted by?
Parotid
Sublingual
Submandibular
What type of glands are salivary glands?
Exocrine
What is the structure of a salivary gland?
Mucous alveoli
Serous alveoli- secrete proteaeous secretions
Mixed alveoli- secrete both mucus and proteaeous secretions
What are the components of saliva?
Water Mucins Alpha amylase Electrolytes Lysozyme
What is the function of water in saliva?
Softens, moistens and dilutes particles
Solvent
What is the function of mucins in saliva?
Lubricant
What are mucins?
The protein component of saliva
Together with water, they form mucus
What is the function of alpha amylase in saliva?
Catalyses breakdown starch and glycogen to maltose and glucose
What is the function of electrolytes in the saliva?
Control tonicity/pH
What is the function of lysozyme in the saliva?
Bacteriocidal
How does lysozyme function?
Breaks up polysaccharide component of bacterial cell wall
How is salivary secretion controlled?
Para and sympathetic nervous systems
Reflex
How do the parasympathetic nerves control salivation?
Controlled by facial and glossopharyngeal nerves
When stimulated, they produce a profuse amount of watery salivary secretion
How do the sympathetic nerves control secretion?
Produce a small volume of thick salivary secretion
High mucus content controlled by alpha 1 adrenoceptors
High amylase content controlled by beta2 adrenoceptors
How do reflexes control salivation?
Presence of anything in the mouth activates pressure sensors to start producing saliva
Presence of specifically food activates chemoreceptors for salivary production
What is the oesophagus?
25cm conduit between mouth and stomach
What are the layers of the oesophagus wall?
Mucosa
Submucosa
Muscularis externa
Adventitia/serosa
What is the mucosa of the oesophagus lined by?
Non keratinised stratified squamous epithelium
How do submucosal cells complete their function?
Submucosal glands release secretions via ducts which act as lubrication
What is the structure of the muscular externa in the oesophagus?
Upper 1/3= skeletal muscle
Lower 2/3= smooth muscle
What are oesophageal sphincters?
Thickened rings of smooth muscle that regulate movement in and out of the oesophagus
What happens in the oral phase of swallowing? lol that sounds dirty
Bolus pushed to the back of the mouth by the tongue
What happens in the pharyngeal phase of swallowing?
Presence of bolus causes a sequence of reflex contractions of pharyngeal muscles
Soft palate reflected backwards and upwards to close of nasopharynx
What is the pharyngeal phase of swallowing coordinated by?
Swallowing centre in medulla
What happens as the bolus approaches the entrance to the oesophagus?
Upper oesophageal sphincter relaxes and epiglottis covers larynx
What happens once th bolus enters the oesophagus?
Upper oesophageal sphincter contracts
Propulsion of bolus to stomach by peristaltic wave
How long does it take for food to travel down the oesophagus?
About 10 seconds
What happens as the bolus nears the stomach?
Lower oesophageal sphincter relaxes and food is allowed to enter stomach
What is initiated by the arrival of a bolus in the stomach and relaxation of lower oesophageal sphincter?
Receptive relaxation of stomach
What is receptive relaxation of the stomach?
Vagal reflexes cause relaxation of thin elastic smooth muscle of gastric funds and body
What is special about the “stretch” of the stomach?
Muscle wall itself doesn’t actually stretch, folds are simply straightened out
No change in pressure on stomach wall
What are the functions of the stomach?
Temporary store of ingested material
Dissolve food particles and initiate digestive process
Control delivery of contents to small intestine
Sterilise ingested material
Produce intrinsic factor for vitae’s B12 absorption
What is the function of the pyloric sphincter and where is it located?
At the entrance to the duodenum
Controls delivery of material to the small intestine
What is the difference in musculature across the stomach?
Antrum contains thicker, more powerful smooth muscle
What is the serosa?
Connective tissue outer layer
What are the layers of the muscular externa?
Longitudinal outer layer
Circular middle layer
Oblique inner layer
What is special about the stomach submucosa and mucosa?
Contain folds (rugae) when empty and stretch as the stomach fills
What is on the lumenal surface of the stomach?
Surface mucus cells
Invaginations (gastric pits) feeding into gastric glands
What types of cell are present in gastric glands?
Mucus neck
Parietal cells
Chief cells
