READ ME / 1: Structure of the GI tract and motility Flashcards
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What is the purpose of the GI system?
Absorb nutrients from food ingested from the external environment
What is ingested food called once it passes into the stomach and is partially digested?
Chyme
The small intestine absorbs basic nutrients.
What does the large intestine absorb?
Fluids (water) and electrolytes
What is a hormone, apart from insulin and glucagon, produced by the pancreas?
Somatostatin
What does the exocrine liver produce?
Bile
What is stored within the gall bladder?
Bile
What is bile’s function?
Fat digestion
What is motility (in terms of the GI tract)?
The movement of food down the tract
Which kind of muscle is most involved in motility?
Smooth muscle
Where in the GI tract is skeletal muscle found?
Mouth
Pharynx
Upper oesophagus
…
External anal sphincter
By which process do enzymes digest complex molecules into smaller, absorbable units?
Hydrolysis
How many layers of muscle are found in the muscularis externa?
Two
What are the two layers of muscle found within the GI tract wall?
Muscularis mucosae (on the inside)
Muscularis externa (on the outside)
What are the two types of muscle found within the muscularis externa?
Circular muscle
Longitudinal muscle
How does circular muscle contraction affect the dimensions of the GI tract?
Narrower and longer
How does longitudinal muscle contraction affect the dimensions of the GI tract?
Shorter and wider
What are the special properties of the muscularis externa in
a) the colon
b) the stomach?
a) Longitudinal layer has three bands (teniae coli)
b) Muscularis external has circular, longitudinal AND oblique layers
Which kind of junction connects GI smooth muscle cells?
Gap junctions (allows passing of ions –> electrical currents) between each cell
Similar to that of the heart, which kind of smooth muscle cells trigger contractions in the GI tract?
Pacemaker cells
In the GI tract, spontaneous electrical activity occurs as (slow / fast) waves.
slow
What are the GI tract’s pacemaker cells called?
Interstitial cells of Cajal (ICCs)
ICCs are found in both muscle layers of the muscularis externa - what are these muscle layers called?
Circular layer
Longitudinal layer
Uptake of ions through which channel triggers smooth muscle contraction in the GI tract?
Ca2+ channels
Efflux of ions through which channel triggers the downstroke of a smooth muscle repolarisation?
K+ channels
Force of contraction in the digestive tract is related to the (intensity / number) of action potentials.
number
Some molecules inhibit the contraction of smooth muscle by __ the downstroke, i.e causing hyperpolarisation.
abolishing
Do all slow waves trigger a contraction of smooth muscle?
No - dependent on other stimuli
What name is given to the collection of nervous tissue found within the GI tract?
Enteric nervous system
Nerves of the enteric nervous system tend to join together and form ___.
plexuses
The enteric nervous system is (extrinsic / intrinsic).
intrinsic
Which arm of the autonomic nervous system is responsible for regulating GI function?
Parasympathetic
What does parasympathetic stimulation of the GI tract cause?
Increased secretion
Increased blood flow
Increased smooth muscle contraction
to aid in the digestion of food
What does parasympathetic stimulation cause in the GI tract?
Relaxation of smooth muscle
What is the neurotransmitter for parasympathetic preganglionic nerve fibres?
Acetylcholine
What does sympathetic stimulation cause in GI tract sphincters?
Increased tone i.e holds them shut
What is peristalsis?
Sequential contraction and relaxation of smooth muscle moving food aborrally
What stimulus triggers peristalsis?
Distension of the gut wall by a bolus
What molecules trigger relaxation of smooth muscle?
VIP
Nitric oxide
What is the name given to the mixing, churning movements of the GI tract which mix lumenal contents together?
Segmentation
In the muscularis externa, which muscle layer contraction causes segmentation?
Circular layer contraction (narrower and longer)
Which large contraction, occuring a few times a day, sweeps faeces into the rectum?
Colonic mass movement
Which sphincter opens to allow swallowing?
Upper oesophageal sphincter
Which sphincter relaxes to allow food to enter the stomach?
Lower oesophageal sphincter
Which sphincter opens to allow the passage of chyme from the stomach to the duodenum?
Pyloric sphincter
Which sphincter regulates flow from the ileum of the small intestine to the caecum of the large intestine?
Ileocaecal valve
There are two anal sphincters - what are they called?
What is the main difference between them?
Internal and external anal sphincters
The external anal sphincter is skeletal - voluntary.
The GI tract has 6 sphincters. Divide them into two categories: voluntary and involuntary.
Voluntary: Upper oesophageal sphincter, External anal sphincter
Involuntary: Lower oesophageal sphincter, Pyloric sphincter, Ileocaecal valve, Internal anal sphincter
Can swallowing be voluntarily stopped once it has started?
No - all or nothing reflex
Which type of receptor triggers the swallowing reflex?
Mechanoreceptors
Which structure prevents food from entering the trachea?
Epiglottis
Which cranial nerve supplies smooth muscle in the oesophagus?
Vagus nerve CN X
