Physiology and pharmacology Flashcards
what additional layer of muscle is present in the stomach
oblique
what does circular muscle contraction do to the lumen
narrower and longer
what does contract of the longitudinal muscle do to the lumen
intestine becomes shorter and fatter
how does contraction and depolarization take place in the GI tract
- gap junctions allow spread of electrical current from cell to cell forming a functional syncytium
- hundreds of cells are depolarized and contract at the same time as a synchronous wave
- slow waves, rhythmical patterns of membrane depolarization and repolarization that spreads from cell to cell via gap junctions
what is slow wave electrical activity driven by
interstitial cells of Cajal-pacemaker cells interspersed between the smooth muscle cells
what is upstroke mediated by
voltage activated calcium channels
where are interstitial cells of cajal located
between the longitudinal and circular muscle layers in the submucosa
what is downstroke mediated by
voltage activated K+ cells
do all slow waves trigger contraction
no threshold for action potential must be reached
what does depolarization of smooth muscles do
bring the slow wave peak to threshold for opening of L-type voltage-activated Ca2+ channels
what does the Myenteric (Auerbach’s) plexus do
regulates motility and sphincters
what does submucous (Meisserner’s) plexus do
mainly modulates epithelia and blood vessels
is the ENS intrinsic or extrinsic to GI tissue
intrinsic it forms a complete reflex circuit that can operate independently but hormones and extrinsic nerves exert a strong regulatory influence
what do all preganglionic fibres release
acetylcholine
what do postganglionic fibres in sympathetic nervous system release
noradrenaline
what does parasympathetic innervation of GI tract do
- increase gastric, pancreatic and small intestine secretions, blood flow and smooth muscle contraction
- relax some sphincters, receptive relaxation of stomach
what does innervation of the parasympathetic nervous system do
- increase sphincter tone
- decreased motility, secretion and blood flow
what is another name for intrinsic reflex
local
what do local/intrinsic nerve reflexes do
cause peristalsis
what does the short reflex do
intestine-intestinal inhibitory reflex (local distension activates sensory neurone exciting sympathetic pre-ganglionic fibres that cause inhibition of muscle activity in adjacent areas
what does the long reflex do
gastroileal reflex (increase in gastric activity causes increased propulsive activity in the terminal ileum
what triggers peristalsis
distension of the gut wall
what happens in in the oral direction in peristalsis following altered activity of interneurones
altered activity of motorneurones
circular muscle contracts (release of ach and substance P)
longitudinal muscle relxes (release of VIP and NO from inhibitory motorneurone)
which 2 substances in the GI tract cause contraction of muscle in peristalsis
acetylcholine and substance P
what happens in the aboral direction in peristalsis following the altered activity of interneurones
altered activity of motor neurones
longitudinal muscle contracts (release of ACh and substance P from excitory motorneurone)
circular musces relaxes relese of VIP and NO from inhibitory motorneurone)
what is segmentation
mixing, churning movements
rhythmic contractions of the circular muscle layer that mix and divide luminal contents
where does segmentation occur
in the small and large intestine
what is segmentation in the large intestine called
haustration
what is colonic mass movement
powerful sweeping contraction that forces faeces into the rectum-occurs a few times a day
what is migrating motor complex
powerful sweeping contraction from stomach to terminal ileum
what are tonic contractions
sustained contractions
which organs have low pressure tonic contractions
organs with a major storage function eg stomach
where are high pressure contractions take place
sphincters
how many sphincters in the GI tract are there
6
what type of muscle is the upper oesophageal sphincter made of
skeletal muscle
if food become lodged in the oesophagus what is stimulated
a secondary peristaltic wave-more forceful than primary-locally triggered
increased saliva production
what is luminal digestion
digestion mediated by pancreatic enzymes secreted into the duodenum
give some examples of oligosaccharides
lactose and sucrose
what is membrane digestion
digestion mediated by enzymes situated at the brush border of epithelial cells
what makes up starch
amylose and amylopectin
what is branched amylose or amylopectin
amylopectin
what type of enzyme is alpha amylase
an endoenzyme
what does a amylase break down
linear internal a-1,4 linkages but not terminal a-1,4 linkages
can a amylase produce glucose
no
what can a amylase not break down
terminal a-1,4 linkages
a-1,6 linkages at branch points or a 1,4 linkages adjacent to branch points
what are oligosaccharidases
integral membrane proteins with a catalytic domain that face the lumen of the GI tract
what are the substrates of lactase
glucose and galactose
what are the substrates of sucrase
glucose and fructose
what is unique about isomaltase
it is the only enzyme that can split the branching a-1,6 linkages of a-limit dextrins
where does absorption of glucose, galactose and fructose occur
the duodenum and jejunum
what are glucose and galactose absorbed (specifically)
secondary active transport mediated by SGLTI
what is fructose absorbed by and how
fructose is absorbed by facilitated diffusion mediated by GLUT5
how is exit for all monosaccharides mediated
facilitated diffusion by GLUT2
what are enterocytes
tall columnar cells with a brush border
what are goblet cells
produce mucin to protect epithelium and lubricate passage of material
what are paneth cells
cells found at the base of the crypts of Lieberkuhn they have a defensive function and have a role in regulation of bacterial flora
what is contained within the muscularis externa of the stomach
an additional layer of muscle the oblique layer which helps with churrning. It is located internal to the circular layer
what happens in the transition from stomach mucosa to duodenal mucosa
the inner circular layer of smooth muscle is markedly thickened to form the pyloric sphincter
what project downwards inbetween the villi
crypts of Lieberkuhn
what doe the small intestine contain within its layers
Brunner’s glands in the submucosa
what does the jejunum distinctively have
tallest villi, located on permanent circular folds of the mucosa and submucosa, the plicae circularis
what does the ileum distinctivey have in it layers
lymphoid follicles called Peyer’s patches found in the submucosa and often extending into the lamina propria
where are the Brunner’s glands found and what do they do
when stimulated by the presence of chime they produce a thin, alkaline mucous to neutralise the chyme
what are the plicae circualaris
folds with finger like projections: the villi
where do the plicae circualris form from
mucosa and submucosa
which tissue type is present in large quanitites in the ileum
lymphoid
what are large aggregations of lymphoid tissue in the ileum called
Peyer’s patches
what are the two main types of cells found in the large intestine
absorptive cells: for removal of salts and thereby water
goblet cells: for the secretion of mucus to lubricate the colon
how are the cells arranged in the large intestine
in straight, tubular glands called crypts that extend down into the muscularis mucosa
how is the longitudinal muscle in the large intestine distinct
it is not continuous but is found in 3 muscular strips TENIAE COLI
what is the appendix
a blind ending hollow extension of the ceacum
what is the tissue like in the appendix
less crypts than the rest of the colon
circular arrangement of lymphoid tissue in the submucosa and often the lamina propria
what is the tissue in the anal canal like
stratified squamous epithelium
where does the ENS receive its input from
autonomic nervous system
what are the two parts of the ENS called
myenteric plexus and submucosa plexus
what does the submucosa plexus do
control the muscle of the muscularis mucosae and help regulate secretion in the epithelium
all carbohydrates must be converted to what for absorption
monosaccharides
what type of enzyme is amylase
an endoenzyme
which oligosaccharidase only has one substrate
lactase- breaks down lactose to glucose and galactose
how are glucose and galactose absorbed
by secondary active transport mediated by SGLT1
how is glucose absorbed
by facilitated diffusion mediated by GLUT5
how is exit for all monosacchardies mediated
by GLUT2
what are the four ways that a protein can be digested
by luminal enzymes, by enzymes on the brush border, by intracellular hydrolysis or the peptide is transported out of the enterocyte without intervening intracellular hydrolysis
what type of enzyme is pepsin
an endopeptidase
how many pancreatic proteases are present in the duodenum
5
what are the pancreatic enzymes found in the duodenum called
trypsin, chymotrypsin, elastase, carbopeptidase A and carbopeptidase B
