24 Flashcards
Functions of GI tract
Obtain nutrients required for
• Growth
• Energy needs
Replace fluid and salts lost
• In urine & faeces
• Sweating
• Breathing
The enteric nervous system can act independently of the central and
autonomic nervous systems : True or False?
True
- own pace maker cells
- ability to regulate itself
How Conditions in intestinal lumen are regulated
Receptors in the wall of GI tract
- Respond to
- Stretch – food in the lumen
- Change in composition
- pH, osmolarity, amino acids, sugars, fats
Effectors are smooth muscle and glands
- Reflexes stimulated by receptors stimulate
- Smooth muscle contraction
- Gland secretion
Nervous and hormonal regulation of GI function
Nervous regulation oof GI function - Central Nervous system
Coordinates activity over long distances
- parasympathetic nervous system
- stimulates motility and secretion
- sympathetic nervous system
- inhibits motility and secretion
!modulates activity of enteric nervous system!
- no direct innervation of parasympathetic and sympathetic
Submucosal plexus - regulates secretion (little bit of absorbtion )
Myenteric plexus - regulates motility
Regulation of GI function - enteric nervous system ENS
- submucosal plexus - regulation of secretion
- myenteric plexus - regulation of motility
Involved in local reflexes
Totally self contained
Regulation of GI Function - Hormonal regulation
GI tract largest endocrine organ in body
- Endocrine and paracrine functions
Sensor cells are called enteroendocrine cells: (censors r on their microvili)
- they are Epithelial cells pretty much that :
- Detect luminal content
- Release hormones (on base) - target cells at a large distance — also can affect next door epithelial cells - PARACRINE EFFECT
Critical hormones:
- Gastrin
- Gastric inhibitory peptide (GIP)
- Secretin
- Cholecystokinin (CCK)
Which of the following best describes peristalsis?
A. Contraction of circular muscle ahead of food, relaxation of
circular muscle behind food and contraction of longitudinal muscle.
B. Relaxation of circular muscle ahead of food, contraction of
circular muscle behind food and contraction of longitudinal muscle.
C. Contraction of circular muscle ahead of food, relaxation of
circular muscle behind food and relaxation of longitudinal muscle.
D. Relaxation of circular muscle ahead of food, contraction of
circular muscle behind food and relaxation of longitudinal muscle.
B
Motility in the GI tract - tonic contratctuions definition
Tonic contractions - sustained contractions for minutes to hours (e.g. sphincters)
Motility in the GI tract- phasic contractions
- waves of contraction and relaxation, each wave lasting seconds (e.g perisralsis
Motility / motility pattern =
any pattern of contraction or relaxation
of GI tract smooth muscle.
- some motility patters are a combination of two or more simpler patterns (e.g retropulsion )
- sometimes relaxation can be motility pattern (e.g storage in the stomach)
Movement / Propulsion =
motility patterns that specifically move / propel GI contents along the tract.
What type of muscle in the GI
Smooth muscle
Properties of smooth muscle in GI motility
- spontaneously active
- contracts without external input
- contains pacemaker cells
- frequency of contraction is a property of the GI region
- stomach 3 per min
- duodenum 12 peer min
- ileum 9 per min
- strength of contraction regulated by nervous and hormonal input
Generalised motility patters - fasting
MIGRATING MOTOR COMPLEX:
- 4h after a meal
- repeats every 2h until eat again
- house keeping - helps clears undigested material
Generalised motility patterns - FEEDING
- storage
- stomach and colon
- relaxation of smooth muscle allows volume to increase without change in pressure (example of relaxation being a motility pattern)
- propulsion / movement
- esophagous, stomach, small and large intestine
- perisgtalsis
- mixing
- stomach
- retropulsion
- small and large intestine
- segmentation
- stomach
Yes
Chewing and swallowing
Chewing
Reduce size of food
Allows ingestion, reduces size Mixes with saliva – taste Voluntary – skeletal muscle Reflex control of strength, frequency / rhythm
Swallowing
Rapid transfer of material from mouth to stomach
Initiated at will, proceeds reflexivel
Gastric motility functions:
- Storage
- fundus and body of stomach - Mechanical digestion
- antrum - Mixing
- antrum - Controlled delivery to duodenum
- pyloric sphincter
Fasting gastric motility
Stomach shrinks to ≈ 50 ml in volume
Migrating motor complex:
- Occurs 4 h after a meal
- Continues until eat
- 2 h of inactivity
- 50 min uncoordinated activity
- 10 min coordinated activity
Functions:
- House keeping
- Removes residual secretions
- Removes undigested material
- Promotes epithelial cell turnover
Feeding gastric motility I
Storage
- Receptive relaxation & gastric accommodation
- Nervous regulation - vagus nerve
- Increase in volume with minimal change in pressure
- Fundus and body
Propulsion / Movement
- Peristalsis
- Initiated on greater curvature & spreads to antrum
- 3 contractions per min
- First 60 min following meal gentle
- 60 - 300 min more intense activity
Pressure in stomach gets maintained a little bit higher / lower then eosophagous
Lower
- stops acidic chyme from refluxing back up esophagous
Gastric acomindaytin
- when stomach stetches it activates receptors
- sends a message up to the CNS\
- starts relaxing rugae
- and u get more volume
- so u dont change pressi=ur
Feeding gastric motility II - mixing and breakdown
- Mixing and mechanical breakdown
- Retropulsion
- Combination of peristalsis and closure of the pyloric sphincter
Gastric emptying - result of motility
- combination of peristalsis and periodic opening/relaxation of the pyloric sphincter
- rate matches digestive capacity of intestines
- regulated by feedback from duodenum (receptors)
- factors affecting gastric emtyping … ?
Factors affecting gastric emptying
- Size of meal - larger the meal faster the emptying
- Composition of meal
- Fluids faster than solids
- Related to role of stomach in digestion
-Reduction in size of food particles, increase in surface
area of food
- Related to role of stomach in digestion
- Fats slow gastric emptying
- Fats difficult to digest and need support of bile salts - Acids slow gastric emptying
- Need to neutralize
- Fluids faster than solids
Function of small intestine motility
- Mixing with secretions from pancreas, biliary system (liver/gallbladder) and intestine
- Controlled movement / propulsion
- Exposure of products of digestion to absorptive surfaces
Small intestinal motility patterns
- Motility patterns
- Between meals
- Migrating motor complex
- Between meals
- After meal
- The main motility pattern - Segmentation for mixing and
exposure to absorptive surfaces
- Contributes to movement also - Some - peristalsis for propulsion
- The main motility pattern - Segmentation for mixing and
Colonic or large intestinal motility - functions
- Storage of faeces
Colonic or large intestinal motility
- large periods of inactivity
- Segmentation
- Exposure to absorptive surfaces
- Absorption of fluid and salt from faeces
- Mass movement (propulsion)
- 1-2 time a day following meals
- Peristaltic wave
- Drives faeces into rectum
- Initiates defecation
Yes
Uighur
