lecture 24 Flashcards
Functions of the GI tract?
Obtain nutrients required for growth and energy needs
Replace fluid and salts
How do you lose fluid and salts?
Urine and faeces
sweating
Breathing
Where does ingestion occur?
At the mouth
Where does mechanical digestion mainly occur?
In the stomach
What is mechanical digestion essential for?
Chemical digestion, it breaks it down into smaller parts for chemicals
What is chemical digestion essential for?
Absorption of nutrients
What is motility involved in?
mechanical and chemical digestion
mixing exposure to absorptive surfaces
mixing
storage propulsion
What regulates motility and secretion?
CNS/ENS and Hormones
Receptors in the wall of GI tract respond to?
Stretch when there’s food in the lumen
Change of composition
Effectors are made up of?
Smooth muscle and glands
Effectors stimulate?
Smooth muscle contraction
gland secretion
What type of activity does the CNS regulate?
Long distance activities
PSNS regulates what?
Stimulation of motility and secretion
SNS regulates what?
Inhibition of motility and secretion
CNS modulates activity of what?
Enteric nervous system
Submucosal plexus is a part of what nervous system?
ENS
Submucosal plexus regulates what?
Secretion
Myenteric plexus is a part of what nervous system and regulates what?
ENS and regulates motility
ENS is involved in what kind of reflexes?
Local reflexes such as peristalsis and segmentation
What is the largest endocrine organ in the body?
GI tract
What is endocrine function?
release of hormones into the blood
What is paracrine function?
Control of hormones at a local level, so a small area of the GI tract
Critical hormones for hormonal regulation?
Gastrin
Gastric inhibitory peptide (GIP)
Secretin
Cholecystokinin (CKK)
Functions of motility in the GI tract?
Movement at a controlled rate
Mechanical digestion
Chemical digestion
Mixing
How does mechanical digestion aid chemical digestion?
By breaking down the apple and increasing the surface area of the apple
Mixing the enzymes with food particles
What helps with GI motility?
Smooth muscle rings that contract without external input
Frequency of contraction in stomach?
3 per minute
frequency of contraction of duodenum?
12 per minute
Frequency of contraction of ileum?
9 per minute
Strength of contractions are controlled by?
nervous and hormonal input
Migrating motor complex kicks in?
4hr after a meal and repeats every 2 hours until we eat again
Stomach and colon aid with what feeding motility pattern?
Storage
How do stomach and colon store things?
relaxation of smooth muscle allows volume to increase without change in pressure
What aids with the propulsion pattern?
Oesophagus
stomach
small and large intestine
Propulsion is involved with what form of digestion?
Peristalsis
Stomach does what form of mixing?
retropulsion
Small and large intestine do what form of mixing?
segmentation and peristalsis
What is peristalsis?
movement of food through the GI tract through contraction of smooth muscle
What is segmentation?
Occurs at a more local level to mix the food together
Main purpose of chewing?
reduce food size
Reducing food size helps with?
ingestion
Chewing helps with taste how?
Mixing the food with saliva
Swallowing initialed voluntary but proceeds?
Involuntarily or reflexly
Gastric motility functions?
Storage
Mechanical digestion
mixing
controlled delivery to duodenum
Storage and mechanical digestion mainly occur where?
Fundus and body of stomach
Mechanical digestion and mixing occur where?
antrum
What controls delivery to duodenum?
Pyloric sphincter
Fasting gastric motility shrinks stomach to?
~50mL in volume
Migrating motor complex patterns?
Occurs 4h after a meal and will continue until food is consumed
1h of inactivity followed by 50 minute of uncoordinated activity and 10 minutes of coordinated activity
Function of gastric motility when fasting?
House keeping:
residual secretions and undigested material is pushed through GI tract
Vagus nerves control what in the stomach?
Relaxation of the stomach and allows increase in stomach without large change in pressure
Where is propulsion initiated?
On greater curvature and spreads to antrum
When does propulsion occur?
first 60 minute following a meal
Mixing and mechanical breakdown is a combination of?
Peristalsis and closure of pyloric sphincter
Rate of gastric emptying matches?
Digestive capacity of intestine
What regulates gastric emptying?
Feedback of duodenum
Factors affecting gastric emptying?
Size of meal
composition of meal (fluid or solid)
High or low fat
When fatty, hypertonic, acidic chyme is detected in duodenum the responses are?
Chemoreceptors and stretch receptors trigger enterogastric reflex
duodenal enteroendocrine cells secrete enterogastrones
Enterogastric reflex responses?
Short reflex via enteric neurons
Long reflex via CNS centres
Function of small intestine motility?
Mixing with secretions from pancreas, biliary system and intestine
controlled movement
exposure of products of digestion to absorptive surfaces
Small intestine motility pattern between meals?
migrating motor complex
Small intestine motility pattern after meal?
segmentation for mixing and limited peristalsis
When is colon mass movement?
1-2 times a day following meals
what drives faeces into rectum and initiates defecation?
Peristaltic wave of colon
