L5 - smooth muscle Flashcards
functions of GIT
digestion, absorption , secretion and motility
where can you find the skeletal muscle in the GIT
Pharynx, upper third of oeso and external anal sphincter
types of SM in GIT
PHASIC AND TONIC
what is phasic muscle
conttract and relaxed in seconds
- in oeso, stomach antrum and small intesine
function of phasic muscle
empties food rapidly into intestine
what is tonic muscle
contraction sustanined for longer
function of tonic muscle
keeps the sphincters closed to carefully control the movement of the food and chyme
how is smooth muscle controlled by controlling APs
- the cells are electrically coupled with pacemaker cells
- when an AP occur inthe pacemaker cells, it’s transmitted throughout the muscle sheet of the cells
what factors leads to depolarisation of pacemaker cells
- stretching
- ACH
- PNS
what factors leads to hyper depolarisation of pacemaker cells
-NA and SNS
What happens when the amplitude of the depolarisation reaches threshold ?
- AP conducted, causing Ca ion inlfux and contraction of the smooth muscle
- the force of the contraction is proportional to the freq of AP and Ca conc
mechanism of Ca in SM contraction
- Ca2+ influx leads to calcium binding with calmodulin to make calmodulin-Ca complex
- the complex activates the inactive myosin light chain kinase into active one
- ATP phosphorylates the myosin and ATP is converted into ADP in that process
- myosin - P binds with actin and becomes phosphorylated through ATP to initiate contraction
how to stop contraction ? just a guess tho
the myosin is dephosphorylated by MLCP phosphostase
- Ca ions uptake by the SAR in the muscle cell to restore the intracellular Ca levels
innervation of the GIT
- extrinsic nerves of the ANS
- intrinsic nerves of the ENS
what does ENS controls in the digestive system
-motility, secretion and blood flow
what plexi is ENS made up of
-myenteric plexus and submucous plexus
what happens if myenteric plexus is activated
-increases tonic contraction, intensity and rate of contractions
what happens if submucousal plexus is activated
increases secretory activity and modulates intestinal absorption
- controls secretion and blood flow
pathway of the activity in the ENS
- sensory neuron>interneuron>motor neuron> smooth muscle in GIT
types of motor neurons in ENS
- excitatory - contracted
- inhibitory - relaxed
types of enteric sensory neurons
- mechano reception so produces a contractile response if stretched
- chemo reception - detects chemical stimuli like low pH or FAs
which gangelionic fibres does extrinsic PNS innervation conducted by
pregangelionic fibres ]
-
what nerve innervates the upper organs in the digestive system
vagus nerve for oeso, stomach, small intestine aand upper third of large intestine
what nerve innervates the lower organs in the digestive system
lower 2 thirds of large intestine, rectum and anus
