upper gastrointestinal system physiology

describe the lips as part of the digestive system and what they are helpful in

• form opening

• help procure, guide, and contain food in mouth

• important in speech

• well-developed tactile sensation

what is part of the palate

• hard palate

• soft palate

• uvula

what does the hard palate do

forms roof of oral cavity and separates mouth from nasal passages

what does the uvula do

seals off nasal passages during swallowing

describe the tongue and what is helpful in

• forms floor of oral cavity

• composed of skeletal muscle

• movements aid in chewing and swallowing

• plays important role in speech

• taste buds

describe the pharynx and what is helpful in

• cavity at rear of throat

• common passageway for digestive and respiratory systems

• tonsils

where are the tonsils located and what are they made of

• within side walls of pharynx

• lymphoid tissue

what are the teeth responsible for

• chewing

• first step in digestive process

what is the approximate number of taste receptors

50

what is the approximate number of taste buds in the oral cavity and throat, most on upper tongue

10,000

how much saliva is produced a day

1-2 L

what is saliva produced by

by the 3 major pairs of salivary glands

what is the composition of saliva

• 99.5% H2O

• 0.5% electrolytes and protein (amylase, mucus, and lysozyme)

what is the basal amount of saliva produced per minute

• 0.5ml/min

• stimulated by constant low level parasympathetic NS

what is the max amount of saliva produced per minute

• 5ml/min

• e.g. sucking a lemon

what are the functions of saliva

• digestion

• lubricant

• swelling facilitated by moistening food

• antibacterial action

• solvent

• aids speech

• helps keep mouth and teeth clean

• rich in bicarbonate buffers

what does saliva digest

carbohydrates by salivary amylase

how does saliva provide lubrication

lubricant proceeded by mucus

how does saliva have antibacterial action

• lysozyme destroys bacteria

• saliva rinses away material that could serve as food source for bacteria

what sort of molecules is saliva a solvent for

molecules that stimulate taste buds

how does saliva aid speech

by facilitating movements of lips and tongue

what is the most complex reflex in the body

swallowing

what does swallowing do

moves food from mouth through pharynx into stomach

how is swallowing programmed

• sequentially programmed all-or-none reflex

• cant be stopped once begun

what are the 2 phases of swallowing

• oropharyngeal- 1 sec

• oesophageal- 5-9 secs

in the pharynx what is prevented from re-entering mouth, or entering nasal passages or trachea

bolus

what does the swallowing centre briefly inhibit

respiratory centre during swallowing

describe the structure of the oesophagus

• fairly straight muscular tube

• extends between pharynx and stomach

• sphincters at each end

what are the 2 types of sphincters

• pharyngoesophageal sphincter

• gastreoesophageal sphincter

what happens in the oesophagus

• peristaltic waves push food through oesophagus

• swallowing centre controls progression of wave

• secretions (mucus) are entirley protective

what are the 3 sections of the stomach

• fundus

• body

• antrum

what is the shape of the stomach

J shaped sac-like chamber between oesophagus and small intestine

what are the 3 main functions of the stomach

• store ingested food until it can be emptied into small intestine

• secretes HCl and enzymes that begin protein digestion

• mixing movements convert pulverised food to chyme

what is the pyloric sphincter

barrier between stomach and upper part of small intestine

what are the 4 aspects of gastric motility

• filling

• storage

• mixing

• emptying

describe filling for gastric motility

• involves receptive relaxation

• enhances stomachs ability to accommodate the extra volume pf food with little rise in stomach pressure

• triggered by act of eating

• mediated by vagus nerve

where does storage in regards to gastric motility take place

in body of stomach

where does mixing in regards to gastric motility take place

in antrum of stomach

what is emptying in regards to gastric motility largely controlled by

factors in duodenum

what factors in the stomach affect gastric emptying

amount of chyme in stomach is the main factor that influences strength of contraction

what factors in the duodenum affect gastric emptying

• fat

• acid

• hypertonicity

• distension

describe fat as a factor affecting gastric emptying in the duodenum

• fat digestion and absorption takes place only within small intestine

• when fat is already in duodenum, further gastric emptying of additional fatty stomach contents is prevented

describe acid as a factor affecting gastric emptying in the duodenum

un-neutralused acid in duodenum inhibits further emptying of acidic gastric contents until neutralisation can be accomplished

describe hypertonicity as a factor affecting gastric emptying in the duodenum

gastric emptying is reflexly inhibited when osmolarity of duodenal contents start to rise

describe distension as a factor affecting gastric emptying in the duodenum

too much chyme in duodenum inhibits emptying of even more gastric contents

what do factors of gastric emptying trigger

• neutral response

• hormonal response

what is neutral response mediated through and what is it collectively called

• mediated through both intrinsic nerve plexuses and autonomic nerves

• collectively called enterpgastric reflex

what does the hormonal response involve

involves release of hormones from duodenal mucosa collectively known as enterogastrones, inhibit gastric emptying

• secretin (produced by S cells)

• cholecystokinin (produced by I cells)

what are the 2 distinct areas of gastric mucosa that secrete gastric juice

• oxyntic mucosa- lines body and fundus

• pyloric gland area- lines the antrum

where are gastric pits located

at base of gastric glands

what are the 3 types of gastric exocrine secretors glands

• mucous cells

• chief cells

• parietal (oxyntic) cells

what do mucous cells line and secrete

• line gastric pits and entrance of glands

• secrete thin, watery mucus

what do chief cells secrete

enzyme precursor, pepsinogen

what do parietal cells secrete

HCl and intrinsic factor

what are the functions of HCl

• activates pepsinogen to activate enzyme pepsin and provides acid medium for optimal pepsin activity

• aids in breakdown of connective tissue and muscle fibers

• denatures protein by uncoiling

• anon with salivary lysozyme, kills most of the microorganisms ingested with food

what does the gastric mucosal barrier enable

enables stomach to contain acid without injuring itself

what do the gastric mucosal barrier cells line

line the stomach

what are the luminal membranes of the gastric mucosal cells impermeable to

• H+

• so HCl cant penetrate into the cells

• cells are joined together by tight junctions to prevent HCl form penetrating between them

what are other components of gastric juice

• pepsinogen

• mucus

• intrinsic factor

where is pepsinogen stored and in what conditions does it act optimally

• stored in zymogen granules of chief cells

• acts optimally in acid, breaking specific peptide bonds

what does HCl convert pepsinogen into

• pepsin

• which is autocatalytic

what does the mucus protect against

• protects mucosa against mechanical injury

• protects stomach wall from digestion by pepsin

what is intrinsic factor secreted by

• parietal cells

• essential for vitamin B12 absorption

what are the different phases of gastric emptying

• cephalic phase

• gastric phase

• intestinal phase

what is the cephalic phase

increased secretion of HCl and pepsinogen that occurs in response to stimuli acting in the head before food reaches stomach

what is the gastric phase

• begins when food actually reaches the stomach

• presence of protein increases gastric secretions

• presence of caffeine or alcohol

what is the intestinal phase

• inhibitory phase- acid, fat, hypertonicity, distension

• helps shut off flow of gastric juices as chyme begins to empty into small intestine

what can be absorbed because it is lipid soluble in the stomach

• alcohol

• aspirin§