upper GI physiology Flashcards
nerve supply
parasympathetic and sympathetic
parasympathetic nervous system
- 1 pair of cranial nerves (vagus- 10th cranial nerve)
- supplies GI tract
- increases muscle activity (peristalsis) via myenteric plexus and increases glandular secretions
sympathetic nervous system
arise from thoracic and lumbar regions
- decreases muscle activity and glandular secretion
5 functions of GI tract
ingestion, propulsion, digestion, absorption, elimination
ingestion
intake of food into the gi tract
propulsion
contents are mixed and moved along the gi tract
digestion
a process which breaks down food into simpler constituents
can be mechanical or chemical
absorption
products of digestion pass through the walls of the GI tract, into the blood and lymph to be used by body cells
- via active transport or passive diffusion
elimination
food which cannot be digested is removed from the body via faeces
mechanical digestion
- mastication - chewing
- physically breaking down food
- increases surface area, allowing more exposure to enzymes
chemical digesetion
food is broken down into small molecules by chemical enzymes excreted in the different parts of the GI tract
- enzymes are specific to the type of food molecule they are digesting
oral cavity physiological processes
- ingestion
- mechanical and chemical digestion
oral cavity teeth
- different shapes according to function
- cutting and chewing/ grinding
oral cavity tongue
- chewing - mixing food with saliva
- swallowing (deglutition)
salivary glands
parotid
submandibular
sublingual
parotid glands
- located on either side of the face just below the EAM
- ducts open into the mouth at the level of the second upper molar
submandibular glands
- located on either side of face under the angle of the mandible
- duct opens into mouth either side of the frenulum
sublingual glands
- lie under the mucus membrane of the floor of the mouth
- located In front of the submandibular glands
- numerous small duct open into the floor of the mouth
saliva
released via the parasympathetic nervous system
- reflex secretion - sight or smell or food
saliva consists of
water, mineral salts, antimicrobial substances, mucus
functions of saliva chemical digestion
- amylase will start to break down complex sugars
- this continues during swallowing
- action of amylase is degraded b strong acidic acid in stomach
functions of saliva - lubrication of food
- dry food can be moistened to be formed into a bolus for swallowing
function of saliva- cleaning and lubrication
- keeps mouth supple, prevents damage from abrasive food
function is saliva - non-specific defence
- antibodies and lysozymes deal with invading microbes
function of saliva
moistens dry food, to stimulate taste buds- chemical reaction
Deglutition- oral phase
- voluntary muscles of the tongue and cheeks push bolus backwards into pharynx
deglutition-pharyngeal phase
- reflex action
- propels food bolus into the oesophagus
- soft palate rises up closes nasopharynx
- tongue and pharyngeal fold block mouth
- larynx lifts up and forward, so opening is occluded by epiglottis - protecting the trachea
deglutition - oesophageal phase
- presence of bolus stimulates perstalsis
- bolus moves from oesophagus towards stomach
- lower oesophageal sphincter relaxes to allow bolus into stomach
peristalsis
- controlled via parasympathetic and sympathetic nervous systems
- occurs from oesophagus onwards
- contraction of smooth muscle behind bolus pushes it forward
- lubricated by mucus - reduces damage to mucosa by food
stomach 3 layers of muscle fibres function
- assist with churning/mixing/peristalsis
- propulsion and mechanical digestion
stomach mucosal layer function
- allow stomach to expand/contract
- consists of rugae
- increase surface area - for secretion of gastric juice and enteroendocrine
products - lubricated by mucus
the stomach
food is liquified into chyme
- chyme passes through the pyloric sphincter into the duodenum in short bursts
functions of the stomach
- chemical and mechanical digestion
- limited absorption
- preparation of iron absorption
- production and secretion of intrinsic factor needed to absorb B12
gastric juice 3 phases of secretion
- cephalic
- gastric
- intestinal
cephalic phase
- flow starts before food reaches stomach
- stimulated by reflex stimulation of parasympathetic nerves - sight / smell of food
gastric phase
stimulated by presence of food
enteroendocrine and duodenal secrete gastrin into the bloodn- stimulates gastric glands to produce more juice
intestinal phase
chyme reaches duodenum and triggers production of secretin and cholecystokinin
- these reduce secretion of gastric juice and reduce gastric motility, slowing stomach emptying
gastric juice consists of
- water
- mineral salts
- mucus
- hydrochloric acid
- inactive enzyme precursors
gastric juice functions
- liquifies food
- acidifies process/ stops action of amylase
- kills digested microbes
- digestion to proteins
the pancreas
- the exocrine pancreas produces pancreatic juice
- stimulated by presence of chyme in the duodenum
the pancreas consists of
water
mineral salts
specific enzymes
inactive enzyme precursors
pancreatic juice function
- digestion of proteins
- digestion of carbohydrates
- digestion of fats
bile consists of
- water
- mineral salts
- mucus
- bile salts
- bile pigments
- cholesterol
bile function
- emulsification of fats
- making cholesterol and fatty acids soluble
- excretion of bilirubin
secretion of bile and pancreatic juice
- duodenum secretes secretin and cholecystokinin - which stimulates the contraction of the gall bladder and relaxation of the hepatopancreatic sphincter
bile and pancreatic juice are expelled via…
hepatopancreatic ampulla
