Lecture 24 Flashcards
(90 cards)
1
Q
What do we extract and absorb from food? What is the purpose of each of these?
A
- Metabolites for the growth and energy needs of the body.
- Fluid and electrolytes to replace losses
2
Q
The gastrointestinal system is (3):
A
- a long epithelium lined tube
- functional sections separated by sphincters
- connected to accessory exocrine glands
3
Q
What are the three sections of the small intestine in order?
A
duodenum
jejunum
ilium
4
Q
What are the names of the sphincters in the GI tract and where are they located?
A
- Upper oesophageal sphincter
- lower oesophageal sphincter
- pyloric sphincter
- sphincter of Oddi (helps move bile and juices from your pancreas into your small intestine)
- ileocecal valve
- anal sphincters
5
Q
What is gastrilation?
A
This forms the tube with a whole in the middle - you fold on yourself during development
6
Q
What are the names of the accessory exocrine glands?
A
- parotid salivary glands
- sublingual salivary glands
- submandibular salivary glands
- liver
- gall bladder
- pancreas
7
Q
What are the four layers of the GI tract called (in order from lumen, outwards)?
A
Mucosa
Submucosa
Muscularis externa
Serosa
8
Q
What three things make up the mucosal layer?
A
Epithelium
lamina propria
muscularis mucosa
9
Q
What is the purpose of the epithelium in the mucosal layer?
A
This is for secretion and absorption
10
Q
What is the lamina propria?
Thin layer of _______ tissue that forms part of the ________ linings known as the _________. It pushes into the ________. There are also _________ vessels going into the lamina propria for the transport of ___________
A
Thin layer of connective tissue that forms part of the moist linings known as the mucosa. It pushes into the microvilli. There are also lymphatic vessels going into the lamina propria for the transport of nutrients
11
Q
What is the muscularis mucosa and what is its purpose?
A
It is part of the mucosa and its job is to move the villi to bring the chyme into contact with the absorptive surfaces
12
Q
What are the two layers of the submucosa?
A
The major blood and lymphatic vessels and the submucosal nerve plexus
13
Q
What is the purpose of the submucosa?
A
This is to support the mucosa and to transport hormones and nutrients
14
Q
What is the purpose of the submucosal nerve plexus?
A
This is a network of interconnected neurons that will receive info about the goings on in the GI tact lumen from cells in the epithelial layer and can send regulatory messages to secretory cells in this layer
15
Q
What is a plexus?
This is a network of ________ neurons that communicate with the _______ plexus and the __________ nervous system.
A
This is a network of interconnected neurons that communicate with the submucosal plexus and the autonomic nervous system.
16
Q
What are the three layers of the muscularis externa?
A
- circular muscle
- myenteric plexus
- longitudinal muscle
17
Q
What is the purpose of the muscularis externa?
A
This is for controlling large gut motility patterns.
18
Q
What is the serosa?
A
This is the final layer of the GI tract
19
Q
What four things must the gut do?
- ________ the size of the ______ to allow _______
- deliver material to the site of _________
- ________ necessary _______ and _________ the rest
- act as a ______ to ________ and _______
A
- reduce the size of the food to allow absorption
- deliver material to the site of absorption
- absorb necessary material and excrete the rest
- act as a barrier to pathogens and disease
20
Q
What four mechanisms are involved in the function of the GI system?
A
- motility
- secretion
- digestion
- absorption
21
Q
What direction is secretion?
A
This is movement from the inside, across the epithelium to the lumen
22
Q
What direction is absorption?
A
This is from the lumen, across the epithelium to the inside of the body
23
Q
Describe the GI motility function
A
This moves food along the tact from mouth to the anus. It is also mixing and circulating the chyme to perform mechanical and chemical digestion.
24
Q
Describe the GI secretion function
A
eg. salt, water, enzymes
this is maintain an environment for digestive functions
25
Describe the GI digestion function
This is the mechanical and chemical process that breaks down food
26
Describe the GI absorption function
This is the uptake or re-uptake of nutrients, salts and water into the body
27
What do we want to regulate in the GI tract?
The composition of the lumen
28
There are control mechanisms that are governed by what? Describe this
They are governed by the volume and the composition of the intestinal lumen. We are trying to get the contents to a resting state.
28
There are control mechanisms that are governed by what? Describe this
They are governed by the volume and the composition of the intestinal lumen. We are trying to get the contents to a resting state.
29
Why is it important that we regulate the lumen of the GI tract?
So that we can have the right solutes and the right pH for the enzymes to do their job
30
What two things are the GI reflexes stimulated by?
stretch
| the chemical composition of the luminal contents
31
Describe the GI relflexes
Most of the GI __________ can be reflexed as the ENS acts _______ and has receptors to detect certain ________ (chemical and ________). It can send signals that have a direct effect on _______ of the _______ tract to change the _________ environment
Most of the GI neuroregulation can be reflexed as the ENS acts independently and has receptors to detect certain stimuli (chemical and stretching). It can send signals that have a direct effect on effectors of the GI tract to change the luminal environment
32
What is meant by the chemical composition of luminal contents that initiates a Gi reflex?
- osmolarity of chyme
- pH of chyme
- concentration of products of digestion in the chyme eg. amino acids, fatty acids
33
What do the stimuli in the GI tract act on?
mechano-, osmo- and chemoreceptors
34
What are the chemo and osmo receptors?
These are cells in the epithelial layer that communicate with the ENS and secrete their own hormones
35
What are external sensors?
eg. emotional states
36
What are the thee phases of stomach regulation?
- cephalic phase
- gastric phase
- intestinal phase
37
What is detected and what is prepared during the cephalic phase of stomach regulation?
detect: sense food, sight, smell and taste
prepare: the GIT lumen (by the CNS via the ENS
38
What is detected and what is prepared during the gastric phase of stomach regulation?
detect: distension, pH, nutrients
prepare: send signals via the ENS, CNS and hormones
39
What is detected and what is prepared during the intestinal phase of stomach regulation?
detect: stretch, acid, osmolarity, nutrients
prepare: ENS, CNS, hormones
40
GI tract neural regulation involves what two things?
- extrinsic reflexes involving the CNS
| - intrinsic (local) reflexes of the ENS
41
Describe the extrinsic reflexes involving the CNS
This is for regulation and co-ordination of GI function over long distances or to coordinate the GI response with emotional response
42
Describe the intrinsic (local) reflexes of the ENS as part of the GI tract neural regulation
This is regulation over cm - the receptors and responses are entirely local
43
Can the ENS act independently of the rest of the body?
Yes
| you can still get motility, excretion, absorption, with no impact from the CNS
44
What are the two neuron types in the GI tract innervation. Describe these
1. autonomic NS neurons: parasympathetic, sympathetic, motor and sensory which provides a route of interaction between the CNS and the ENS
2. Enteric NS neurons: sensory neurons (mechano/chemo), interneurons, efferent neurons (motor and secretory), interstitial cells of Cajal (pacemakers)
45
How does the ANS provide a route of interaction between the CNS and the ENS?
The CNS can regulate the ENS through the autonomic nervous system. The pathway/route from the CNS and ENS is part of the periphery. It acts through parasympathetic and sympathetic pathway (both afferent and efferent pathways)
46
What are the two structure of the ENS? What is the purpose of each of these?
- submucosal plexus which controls the mucosa (secretion, absorption and movement of villi)
- myenteric plexus which controls the muscularis (for motility)
47
What is in the submucosal plexus and the myenteric plexus?
There are
- sensory neurons
- efferent neurons
- Interstitial cells of Cajal
48
Describe the sensory neurons that are in the ENS
(some of which are interacting with enteroendocrine cells which detect luminal cotents)
eg. mechanoreceptors (which detect stretch and distension) and chemoreceptors (which feed info to the ENS) and these synapse with branches of the ANS that are arriving in the brain so they can convey info about the lumen of GI tract to the brain
49
Describe the efferent neurons of the ENS
These are secretory neurons sending messages to the secretory cells which might make acid, and motor neurons which send messages to the 3 muscle layers
50
Describe the interstitial cells of Cajal in the ENS
these are pacemakers setting the rate of contraction of GI smooth muscle
51
What is the purpose of the submucosal plexus?
To control the mucosa (secretion, absorption, movement of villi)
52
What is the purpose of the myenteric plexus?
it controls the muscularis
53
Describe the regulation of the GI tract by the CNS?
This is extrinsic (external) regulation. It mostly acts via the peripheral autonomic pathways and the ENS - it does not directly innervate GI structures
54
The CNS modulates the activity of the ENS. What are the exceptions to this?
- the upper structures involved in swallowing
- some blood vessels
- external anal sphincter
55
What is the effect of the parasympathetic NS on the GI tract?
This usually stimulates activity
56
What is the neurotransmitter and receptors involved in the parasympathetic activation of the GI tract?
ACh, detected by muscarinic receptors
57
What is the effect of the sympathetic NS on the GI tract?
Usually inhibits activity
58
What is the neurotransmitter and receptors involved in the sympathetic activation of the GI tract?
NA, detected by an α adrenergic receptor
59
We have the ability of the CNS to generate responses to both the _______ composition through long reflexes and _______ stimuli
luminal
| external
59
We have the ability of the CNS to generate responses to both the _______ composition through long reflexes and _______ stimuli
luminal
| external
60
The CNS can respond to both internal and external stimuli. What is meant by the internal and external stimuli?
- internal stimuli: luminal composition and volume
| - external stimuli: mood, thought, smell, sight
61
The ANS sensory pathways synapse in the layers of the ________ and then move to the ________. They are associated with three different areas as you go down the gut. What are these?
gut
brain
- upper part eg. the mouth, palate, pharynx, larynx, trachea, oesophagus and associated vessels and glands go through the cranial nerves
- the visceral organs located between the diaphragm and the pelvic cavity go through the posterior roots of the spinal nerves
- the organs in the inferior portion of pelvic cavity go through the posterior roots of the spinal nerves
62
The terminals of the ENs sensory neurons are located in all layers of the gut. They detect information regarding the duct and relay it to the CNS via the ANS. What so they detect information about?
- the nature of the luminal contents: pH, osmolarity, nutrient content (via interactions with the enteroendocrine cells), stretch/contraction
- painful stimuli
63
What are the two functions of the CNS?
- responses to external stimuli such as senses and emotions
| - responses to internal stimuli (GI luminal contents) via the long reflex path (gut to brain and back again)
64
Describe the long-reflex loop
Information from the GI tract lumen is transmitted through the ENS to the afferent branches of the ANS to the CNS and the CNS generates a response that is through the ANS to the ENS
65
How many neurons are in the ENS?
10^8
66
Is there interaction between the submucosal plexus and the myenteric plexus?
yes
67
In regards to the regulation of the ENS, there are receptors in the intestinal wall that respond to various stimuli (such as what?). Through local reflexes, the ENS regulates what?
- respond to various stimuli such as stretch, pH, osmolarity, products of digestion
- the ENS will send messages to modulate the smooth muscle of the secretory cells to respond to this stimuli
68
What are the stimulatory neurotransmitters in the ENS?
ACh and tachykinins (such as substance P, neurokinin A)
69
What are the inhibitory neurotransmitters in the ENS?
NO, VIP, ATP
70
What cell provides the link between hormones and neurons?
enteroendocrine cells
71
What do the enteroendocrine cells secrete?
They secrete CCK in response to peptides.
72
Describe enteroendocrine cells
They poke into the lumen of the small intestine and respond to changes in the luminal contents. They secrete into the blood vessels running into the lamina propria. They also come into contact with enteric nerves
73
What are endocrine cells regulated by?
intrinsic and extrinsic reflexes
74
The endocrine cells can be triggered to secrete hormones or pass messages onto the ENS as part of the GI luminal content, true of false?
True
75
What are the three kinds of endocrine action?
- endocrine
- paracrine
- neurocrine
76
What is the neurocrine mode of action?
This is when the neuron secretes a neurotransmitter that acts as a hormone
77
What type of hormones are the GI hormones?
These are peptide hormones that participate in feedback regulation of some aspect of luminal contents. The often regulate more than one cell
78
Potentiation is common for the Gi hormones. What does this mean?
This means that if more than one hormone is secreted that do the same thing, the effect is even bigger
79
GI hormones often regulate more than one cell. Give an example of this?
CCK:
| pancreas, gallbladder, sphincter of Oddi
80
GI hormones often have a trophic effect. What does this mean? Give an example
It means that is increases the size and the number of cells such as gastrin on the stomach mucosa
81
Where are the enteroendocrine cells located? Describe them
They are located in the epithelial layer. They are exposed to and respond to luminal contents (stretch and chemical composition). The basolateral pole has secretory ganules (hormones)
82
What does the Gi immune system do?
- barrier function
- active immune response
- modulator of GI tract
- responds to stuff
- releases stuff
- tolerance
83
What does the GI immune system respond to?
food antigens, pathogens, commensal/mutualistic bacteria
84
What doe the GI immune system release?
Inflammatory and other mediators that modulate GI function such as histamine, prostaglandins, leukotrines, cytokines
85
How is the epithelial layer acting as a barrier?
- cell shedding: the epithelium is replaced every days
- absorptive cells: these are near the surface and so come in contact with the intestinal contents, they have the shortest lifespan
- the secretory cells in the crypts or glands: outflow of fluid protects from infection as it stops things from entering the crypts (this protects the stem cells)
- stem cells
- paneth cells at the base of the crypts for immune purposes
86
What are some of the things involved in the GI immune system?
- mesenteric lymph nodes
- Peyers patches and range of immune cels
- intraepithelial lymphocytes patrolling the epithelia looking for pathogens
- B and T cells
- mast cells
- macrophages
- eosinophils
87
What is commensalism?
This is a relation between the individuals of two species in which one species obtains food or other benefits from the other without either harming or benefiting the latter.
88
What is mutualism?
This is the way two organisms of different species exist in a relationship in which each individual benefits from the activity of the other
