Lecture 24: Introduction and Motility Flashcards
What are two functions of the GI system?
- obtain nutrients required for growth and energy needs
2. replace fluids and salt lost in sweating, breathing, urination
What is chemical digestion?
extracting nutrients to be made available for absorption
What is absorption?
selecting material we want and leaving behind waste
The purpose of regulation of the gastrointestinal function is to
regulate the conditions in the intestinal lumen to change composition of luminal components to create optimal conditions for absorption and digestion
The regulation of conditions in the intestinal lumen is carried out by
receptors in the GI tract
What two things do receptors in the walls of the GI tract respond to?
stretch (due to food in the lumen) and change in composition
What things could change when the composition changes?
pH, osmolarity, amino acids, sugars, fats
The receptors in the GI tact respond to changes (such as stretch or changes in composition) and innervate effectors. What are the effectors and what does innervation of them involve?
The effectors of them are smooth muscle and glands and innervation of them can cause smooth muscle contraction and gland secretion
How are the effectors (smooth muscle and glands) regulated?
through nervous and hormonal regulation
The central nervous system coordinates activity over ______ distances
long
The central nervous system consist of the parasympathetic nervous system and the sympathetic nervous system. Which of these stimulates motility and secretion and which one inhibits it?
The parasympathetic nervous system stimulates motility and secretion and the sympathetic nervous system inhibits motility and secretion
Does the central nervous system directly innervate the GI system?
No
instead, it modulates activity of the ENS which directly innervates the smooth muscle and glands
Give an example showing the importance of nervous regulation of the GI system
What does it come as a result of?
When food arrives in the stomach, we change motility in the small intestine so the food in the SI is moved along to the LI to make room for new food. This comes as a result of PNS activation and SNS inhibition
What two parts make up the ENS and what are these parts used for?
- submucosal plexus for regulation of secretion
- myenteric plexus for regulation of motility
The ENS is involved in _____ _______ over ______ distances
local reflexes
short
Give two examples of local reflexes controlled by the ENS
peristalsis and segmentation
The hormonal regulation of the GI system includes cells that have both ______ and ______ function
endocrine
paracrine
What is the role of endocrine cells and how does this differ to paracrine cells?
Endocrine cells secrete hormones into the blood whereas paracrine cells secrete hormones into the interstitial fluid
What are four critical hormones in the GI tract?
gastrin
gastric inhibitory peptide (GIP)
secretin
cholecystokinin (CCK)
What is the role of gastrin?
control of secretion in the stomach
Motility in the GI system involves
moving it through the system and mixing it up
What are the four functions of the motility in the GI tract?
- movement at a controlled rate
- mechanical digestion
- mixing
- exposure to absorptive surfaces
Why is it important that contents are moved through the system at an appropriate rate?
to aid chemical digestion and absorption
What two things contribute to motility and moving contents at an appropriate rate?
propulsion and storage
What is the importance of the mechanical digestion function of motility?
it increases surface area which is essential for chemical digestion
What is the importance of the mixing function of motility?
mixing with digestive enzymes to come in contact with a low pH and chemical composition so that the composition is optimal for digestion and absorption to occur
What is the importance of exposing contents to the absorptive surfaces function of motility?
it aids absorption
Motility is driven by _____ muscle (ie. ______ and ________ muscle)
smooth
circular and longitudinal
The smooth muscle involved in GI motility is _________ active
spontaneously
The smooth muscle involved in the GI motility is spontaneously active which means that it contract without an
external input