DIGESTIVE SYSTEM Flashcards
(45 cards)
What are the functions of the digestive system
Nutrition
excretion/defecation
fluid and electrolyte control (large intestine)
immune function
What is motility
The propulsion of food through the gut
Describe the walls of the gut tube
Lumen
Mucosa (villi)
Submucosa (CT)
Smooth muscle layer
Describe the smooth muscle layer of the gut walls
1st: inner circular smooth muscle, constrict diameter
2nd: longitudinal layer of smooth muscle, shorten length
What does it mean that the components of the digestive system are electrically discrete
Only once the stomach has finished contraction will the small intestine start to be electrically excited.
What is peristalsis
Occurs when a bolus travels down the oesophagus by constriction behind it and shortening in front of it
What are the skeletal muscle sphincters of the GI tract
Upper oesophageal: top of oesophagus
External anal: at anus
What are the smooth muscle sphincters of the GI tract
Lower oesophageal: bottom of oesophagus
Pyloric: bottom of stomach
Sphincter of oddi: where pancreatic and bile ducts merge
Ileocecal: end of ileum
Internal anal: at anus
What are the 4 parts of the nervous system of the GI tract
Sensory nerves: Chemo- and mechano- receptors
Autonomic nerves: Activate glands and smooth muscle
Somatic motor nerves: Activate skeletal muscle
Enteric nerves: Activate glands and smooth muscle
Describe the 2 plexuses of the enteric system
Myenteric plexus: Between circular and longitudinal muscle layers, entire length of gut, controls motility because of its location
Submucosal plexus: In submucosal CT. Only in some parts of gut, controls secretion from glands and absorption of nutrients.
What are the general patterns of Ach and NO in the GI tract
Ach = excitatory (motility and secretion)
NO = inhibitory (relaxation of smooth muscle
Explain how the different components of the GI nervous system are activated
Sensory mechanoreceptors detect bolus and project to CNS
Activates efferent somatic nerves for skeletal function (swallowing and shitting)
Activates efferent autonomic nerves to release neurotransmitter for smooth muscle contraction and mucous secretion (lubrication)
Activates enteric system which has same function as parasympathetic ANS but are activated straight from stretch receptors NOT the CNS
Explain the innervation of smooth muscle sphincters
Innervated by both autonomic and enteric systems
Sympathetic activation contracts circular smooth muscle to keep sphincter closed
Parasympathetic and intrinsic inhibitory nerves of the myenteric plexus cause opening
What are the 2 types of contractions that can occur in the small intestine and how are they triggered
Segmenting/mixing contractions
Peristaltic contractions
Stretch caused by eating triggers parasympathetic to increase GI motility
Explain segmenting/mixing contractions
Localised constrictions that slowly occur to breakdown food blobs into mixed, smaller blobs. Ensure digestion
Explain the movements of peristaltic contractions in SI
Replace mixing contractions after most digestion has occurred
Move about 60 cm each contraction to push remains into large intestine
also prevent overgrowth of bacteria
stop when meal enters the stomach because eating triggers mixing contractions for digestion
called migrating myoelectric complex (MMC)
Explain how small intestine peristaltic contractions are activated
Increase in chyme pH: acidity decreases due to mixing contractions signalling for new contraction
Increase [motilin] in plasma which is usually inhibited by feeding
Modulation by ENS and ANS
Explain the longitudinal muscle of the large intestune
Specialised into three strips called teniae coli
As these contract, bulbs on surface form called haustra
Haustra are thus forms by the activation of myenteric nerves and the activation of circular smooth muscle
What are the 2 types of large intestine contractions
Mixing/haustral contractions
Mass movements
Explain a mixing/haustral contraction
Slow segmenting movements occurring every 25 minutes
one haustrum distends as it fills with chyme, stimulates the muscle to contract moving on contents
Explain a mass movement
Peristaltic contractions where a constrictive ring forms and there is a loss of haustra
Long (about 30 secs, 3-4 per day)
Facilitated by gastrocolic and duodena-colic reflexes
As stomach and SI fill, triggers parasympathetic nerves of LI to clear colon by mass movement ready for next meal
Explain activation of the rectum in defecation
Triggered by mass movement of faeces from sigmoid colon to rectum
activation of rectal wall stretch receptors which activate parasympathetic nerves and ENS for relaxation of internal anal sphincter, rectal contraction and mucous secretion
Outline constipation
passing of hard and incomplete stools <2/week
Cause: poor motility or obstruction (blocking) of LI.
Treatment: eating fibre or laxative or manual evacuation
Outline Diarrhea
Rapid movement of fecal matter through LI
Organic cause: inflammation of LI
Functional cause: Damage to muscle nerves
Osmotic cause: e.g. lactose intolerance, no enzymes to break down, increased solute in LI attracts water
Treatment: look at underlying cause
