Lecture 24: INTRODUCTION AND MOTILITY Flashcards
What are the functions of the GI tract?
To obtain nutrients required fo growth and energy needs. Also replace fluid and salts lost in urine, faeces, breathing and sweating
What must be regulated?
The conditions of the intestinal lumen
Where are receptors found?
In the wall of the GI tract
What do the receptors respond to?
Stretch when food is in the lumen and change in composition
What may change in composition be?
pH, osmolarity, amino acids, sugars and fats
What are the effectors?
Smooth muscle and glands
What do the receptors stimulate?
Smooth muscle contractions and gland secretion
What regulates GI function?
Nervous and hormonal
What does the CNS do?
Coordinate activity over long distances fan modulate activity of the enteric nervous system
What does the parasympathetic nervous system do?
Stimulate motility and secretion
What does the sympathetic nervous system do?
Inhibit motility and secretion
What is the ENS made up of?
Submucosal plexus and myenteric plexus
What does the submucosal plexus do?
Regulate secretion
What does the myenteric plexus do?
Regulate motility
What is the ENS involved in?
Local reflexes (involuntary) such as peristalsis and segmentation
Where is the ENS?
Total self contained in the GI tract
What is the largest endocrine organ in the body?
GI tract
What function does the GI tract have?
Endocrine (blood) and paracrine (localised)
What are critical hormones in the GI tract?
Gastrin, gastric inhibitory peptide (GIP), secretin and cholecystokinin (CCK)
What are the functions of motility in the GI tract?
Movement at a controlled rate, mechanical digestion, mixing and exposure to absorptive surfaces
What does movement at a controlled rate involve?
Propulsion and storage
What does movement at a controlled rate aid?
Chemical digestion and absorption
What does mechanical digestion do?
Increases surface area
What is mechanical digestion essential for?
Chemical digestion
What does mixing aid in?
Chemical digestion
What does exposure to absorptive surfaces aid?
Absorption
What is the basis of GI motility?
Smooth muscle
What are the properties of smooth muscle?
Spontaneously active (contracts without external input)
What is frequency of smooth muscle contraction regulated by?
ENS
What is the frequency of contraction in the stomach?
3/min
What is the frequency of contraction in the duodenum?
12/min
What is the frequency of contraction in the ileum?
9/min