6. Motility of the GI Tract Flashcards
3 phases of DEGLUTITION/SWALLOWING
- ORAL
- PHARYNGEAL
- OESOPHAGUS
is PHASE 1 (ORAL) of DEGLUTITION voluntary or involuntary
VOLUNTARY
is PHASE 2 (PHARYNGEAL) of DEGLUTITION voluntary or involuntary
INVOLUNTARY
is PHASE 3 (OESOPHAGEAL) of DEGLUTITION voluntary or involuntary
INVOLUNTARY
what happens in PHASE 1 DEGLUTITION
ORAL:
- Food BOLUS formed by MASTICATION
- TONGUE moves UP and BACKWARD
Muscles in TONGUE are CONTROLLED by which CRANIAL NERVE
12 - HYPOGLOSSAL
what happens in PHASE II DEGLUTITION
PHARYNGEAL:
- SOFT PALATE RISES
- EPIGLOTTIS CLOSES (down)
- PHARYNX CONTRACTS
- UPPER OESOPHAGEAL SPHINCTER (UOS) RELAXES (opens oesophagus)
RECEPTORS of the PHARYNX that detect the food and send signals to Brain Stem to UOS to RELAX (and all actions of pharyngeal phase)
TACTILE/DISTENSION RECEPTORS
- MECHANORECEPTORS
What happens in PHASE III DEGLUTITION
OESOPHAGEAL:
- UOS CONTRACTS (reflex after food enters stomach, so oesophagus closed again to prevent gastric reflux)
- Bolus moved by PERISTALSIS
- LOWER OESOPHAGEAL SPHINCTER (LOS) RELAXES and opens (LOS is smooth muscle)
CRURAL DIAPHRAGM role in DEGLUTITION
- (skeletal) MUSCLE that SURROUNDS LOS (sling around it)
CONTRACTS to OPEN, so food can pass into stomach
REFLEXES and NERVES used to OPEN LOS
VAGAL REFLEX and VAGAL PHRENIC REFLEX
VAGUS NERVE - VAGAL AFFERENT to BRAIN STEM
VAGAL EFFERENT to LOS
PHRENIC NERVE to CRURAL DIAPHRAGM
how does the PHRENIC NERVE stimulate the CRURAL DIAPHRAGM to CONTRACT and OPEN the LOS
- STIMULATES ACETYLCHOLINE RELEASE
how do VAGAL EFFERENT FIBRES cause RELAXATION of LOS
- VAGAL EXCITORY FIBRES (VEF) switched OFF
(no Ach release) - VAGAL INHIBITORY FIBRES (VIF) switched ON
-> release VASOACTIVE INTESTINAL POLYPEPTIDE (VIP) and NITRIC OXIDE (NO)
therefore relax LOS
to RELAX LOS, VAGAL INHIBITORY FIBRES are SWITCHED ON and RELEASE:
VIP (VASOACTIVE INTESTINAL POLYPEPTIDE)
& NO (NITRIC OXIDE)
what causes PERISTALTIC CONTRACTIONS in the STOMACH
PACEMAKER ZONE
- in FUNDIC region (fundus)
order of GASTRIC MOTILITY (how food passes in stomach)
- FUNDUS : PACEMAKER ZONE for PERISTALSIS - mix and churn
- CORPUS (body) : ACID SECRETIONS
- ANTRUM : MUSCULAR PUMP - contracts vigorously to further mix
- PYLORIC SPHINCTER: OPENS when PRESSURE in PYLORIS INCREASES
-> food to duodenum
4.
the ANTRUM of the STOMACH has what ROLE
MUSCULAR PUMP
- contracts vigorously to further mix food before it goes to small intestine
the CORPUS (body) of the STOMACH has what ROLE
ACID SECRETIONS
where is the PACEMAKER ZONE in the STOMACH
FUNDUS
what is RETROPULSION in the STOMACH
when PYLORIC SPHINCTER is still CLOSED, food PUSHED BACK and there is MORE MIXING
which part of the STOMACH acts as a MUSCULAR PUMP
ANTRUM
what are the PACEMAKERS of the GUT
INTERSTITIAL CELLS of CAJAL
(ICC CELL NETWORK)
(in the circular and longitudinal muscle layers of gut wall and submucosa)
(have gap junctions)
what do the INTERSTITIAL CELLS of CAJAL allow for in the GUT
SLOW WAVE MECHANISM conducted to smooth muscle
-> SMOOTH MUSCLE CONTRACTION
(ACTION POTENTIALS)
what causes DEPOLARIATION of membranes and hence ACTION POTENTIALS in the GUT (depolarisation pacemaker currents)
CALCIUM INFLUX (Ca2+)
by L-TYPE CA2+ CHANNELS
where does the BASAL ELECTRICAL RYTHM (BER) of the GUT originate and what happens to result in CONTRACTIONS
- In ICC
- when SPIKE POTENTIALS occur at MAXIMUM DEPOLARISATION of BER due to Ca2+ ENTRY
-> results in contraction
what causes HYPERPOLARISATION/REPOLARISATION in BER
OUTWARD K+ CURRENTS
(delayed)
ACTION POTENTIAL FREQUENCY can be INCREASED and DECREASED by which NEUROTRANSMITTERS
ACH - INCREASE
NORADRENALINE - DECREASE
I
what are the 4 PHASES of the MIGRATING MYOELECTRIC COMPLEX (MMC)
I - QUIESCENCE
II - RANDOM CONTRACTIONS
III - BURST of CONTRACTIONS (MAXIMUM AMPLITUDE and DURATION)
IV - RAPID DECREASE of CONTRACTIONS
Where does MMC Initiate / Occur
79% in ANTRUM of STOMACH (initiates here)
29% in DUODENUM
how much of MMC Occurs in the DUODENUM
29%
2 INTESTINAL MOVEMENTS that take place to move food
- SEGMENTATION
- PERISTALTIC REFLEX
what is SEGMENTATION in INTESTINES
ALTERNATE CONTRACTION and RELAXATION of ADJACENT SEGMENTS
Back and forth movement
- causes thorough MIXING of food contents
fine digestion into SMALLER components that can be ABSORBED
as BOLUS passed through INTESTINES what is it RECOGNISED BY to trigger PERISTALSIS
DISTENSION / STRETCH
->RELEASES 5-HT (5-hydroxytryptamine) (serotonin)
when DISTENSION/STRETCH recognises BOLUS and RELEASES 5-HT what is the SIGNAL PATHWAY
signals in Intrinsic PRIMARY AFFERENT NEURONS (IPAN)
(TK/ACH)
-> along INTERNEURONES (ACH)
EITHER
-> EXCITORY MOTOR NEURONES (ACH/TK)
OR
-> INHIBITORY MOTOR NEURONES (VIP/NO)
how are the 2 ends of the BOLUS described as it passes through INTESTINES
ORAD (BEHIND, Mouth end)
CAUDAD (IN FRONT, Tail end)
which END of the BOLUS CONTRACTS in INTESTINES
ORAD
what happens in CAUDAL END of the BOLUS in the INTESTINES
RELAXATION of CIRCULAR SMOOTH MUSCLE
what stimulates ASCENDING CONTRACTION of CIRCULAR SMOOTH MUSCLE in the ORAD end of the INTESTINES (behind bolus)
PRIMARY AFFERENT NEURONES -> INTERNEURONES (RELEASE ACH)
-> EXCITORY MOTOR NEURONES
RELEASE ACH / TK (tachykinin)
causes contraction
what do EXCITORY MOTOR NEURONES RELEASE to cause CONTRACTION of INTESTINES SMOOTH MUSCLE (circular)
ACh / TK
what causes DESCENDING RELAXATION of the CIRCULAR SMOOTH MUSCLE at the CAUDAD end of INTESTINES (in front of bolus)
PRIMARY AFFERENT NEURONES -> INTERNEURONES (ACH)
-> INHIBITORY MOTOR NEURONES
RELEASE VIP (vasoactive intestinal polypeptide)
/ NO (nitric oxide)
- RELAXING FACTORS
what RELAXING FACTORS are RELEASED by INHIBITORY MOTOR NEURONES to cause RELAXATION of INTESTINES SMOOTH MUSCLE in front of bolus
VIP / NO
PERISTALTIC REFLEX in INTESTINES has 2 actions
- ASCENDING CONTRACTION
- DESCENDING RELAXATION
DISTENSTION / STRETCH in the INTESTINES as BOLUS passes causes RELEASE of:
5-HT (SEROTONIN)
name of the SEGMENTATION action in the LARGE INTESTINE
HAUSTRATION
- mixing, absorption and stool formation
Strong PERISTALTIC WAVES SHIFT the INDIGESTIBLE MATERIAL in the COLON (LARGE INTESTINE) TOWARDS RECTUM. called:
MASS MOVEMENTS
MASS MOVEMENTS in the COLON are STIMULATED by
FOOD IN STOMACH and food in DUODENUM
(new food entering)
STRETCH of the RECTUM causes:
REFLEX:
COLON CONTRACTS to PUSH more indigestible material, RECTUM CONTRACTS
INCREASE PRESSURE
INTERNAL ANAL SPHINCTER RELAXES
RELEASE of what RELAXING FACTORS cause the INTERNAL ANAL SPHINCTER to RELAX
VIP (Vasoactive Intestinal Polypeptide)
& ATP
EXTERNAL ANAL SPHINCTER is under what CONTROL
SOMATIC - VOLUNTARY
(striated muscle)
- RELAXES by PUDENDAL NERVE
MASS MOVEMENTS initiate what REFLEX
DEFAECATION REFLEX
what NERVE CONTROLS EXTERNAL ANAL SPHINCTER
PUDENDAL NERVE (S2-S4)
how is MOTILITY LEVEL in the COLON (LI) and RECTUM compared to SMALL INTESTINE
LOWER MOTILITY
(4-6 waves per min)
