L24 (gut) Flashcards
1
Q
what is the role of the GI tract
A
The gastrointestinal tract takes in food, digests it to extract and absorb metabolites for the growth and energy needs of the body plus fluid and electrolytes to replace losses, and expel the remaining waste.
2
Q
describe the gastrointestinal system
A
A long epithelium lined tube
Functional sections separated by sphincters
Connected to accessory exocrine glands.
3
Q
describe how the GI tract forms
A
The embryo starts as a flat 3 layered disk, and during gastrulation that disk folds on itself and forms into a tube. Now you have a tube like embryo, this will eventually become the GI tract
4
Q
what lines the GI tract
A
epithelium
5
Q
what organs make up the GI tract
A
mouth pharynx esophagus stomach small intestine large intestine anus
6
Q
where are the sphincters located
A
between the GI tract and the accessory organs
7
Q
what are the sphincters of the GI system and where are they located
A
upper esophageal sphincter = between the pharynx and esophagus
lower esophageal sphincter = esophagus and stomach
pyloric sphincter = stomach and small intestine
sphincter of oddi = pancreas and small intestine
ileocecal valve = small and large intestine
anal sphincters
8
Q
what are the accessory organs of the GI tract
A
salivary glands
- sublingual
- submandibular
- parotid
liver
gallbladder
pancreas
9
Q
what are the layers of the GI tract (deep to superficial)
A
luman
epithelium (part of the mucosa)
mucosa
- lamina propria
- muscularis mucosa
submucosa
muscularis externa
serosa
10
Q
describe the mucosa
A
contain the epithelial layer as well as the lamina propria and the muscularis mucosa
This is an area of connective tissue with extracellular fluid (interstitial fluid) and that i the compartment of the body where nutrients and water first get absorbed into when they first get absorbed into the body
11
Q
what is the role of the muscularis mucosa
A
The muscularis mucosa can move villi to bring all of the chim into contact with the absorptive surfaces
12
Q
what is the role of the submucosa
A
it provides support for the muscosa
it has blood for transport of nutrients and hormones
it also has a submucosal neural plexus which is interconnected neurons which receives messages about what is going on within the epithelial layer and it can also send regulatory messanges to secretory and absorptive cells in this layer
13
Q
what does the submucosal layer contain
A
the submucosal plexis
14
Q
what is the role of the submucosal plexus
A
it also has a submucosal neural plexus which is interconnected neurons which receives messages about what is going on within the epithelial layer and it can also send regulatory messanges to secretory and absorptive cells in this layer
15
Q
describe the muscularis externa
A
controlling the large gut motility patterns therefore it contains 2 layers of muscle (3 in the stomach)
the muscularis externa consists of circular mussle , myenteric plexus, longitudinal muscle
16
Q
what does the myenteric plexus communicate with
A
submucosal plexus and the autonomic NS
17
Q
what is the role of the serosa
A
it is the outer sheath
18
Q
the overall function of the GI system is to take in food, digest it to extract and absorb
metabolites for the growth and energy needs of the body plus fluid and
electrolytes to replace losses, and expel the remaining waste
to do this the gut must…… (4 things)
A
- reduce size of food to allow absorption
- deliver material to site of absorption
- absorb necessary material & excrete the rest
- act as a barrier to pathogens and disease
19
Q
what are the mechanisms involved in the overall function of the GI tract
A
- Motility
- Secretion
- Digestion
- Absorption
20
Q
define motility
A
- Motility: Moves food along
the tract.
21
Q
define secretion
A
- Secretion: Maintain an
environment for digestive
functions. (Water, Salt, and
Enzymes)
22
Q
define digestion
A
- Digestion: Mechanical and
chemical processes that
break down food.
23
Q
define absorption
A
- Absorption: Uptake (or
reuptake) of nutrients, salts
and water into the body.
24
Q
what regulates the composition of the lumen
A
• Control mechanisms governed by volume and composition of
the intestinal lumen.
25
GI reflexes initiated by... (2 things)
Stretch
- distension of GI wall by volume of contents
Chemical composition of luminal contents such as..
- osmolarity of chyme
- pH of chyme
- concentration of products of digestion in the chyme
e. g., amino acids, fatty acids
26
Chemical composition of luminal contents causes GI reflexes. what are some examples of this
- osmolarity of chyme
- pH of chyme
- concentration of products of digestion in the chyme
e. g., amino acids, fatty acids
27
why is the GI tract regulated by reflexes
The enteric NS acts independently therefore it is a reflex which will send signal which will go directly to receptors which will change the luminal environment
28
what receptors get activated in GI tract regulation
another way the GI tract is regulated is through Stimuli acting on mechano-, osmo- and chemoreceptors
29
what is the controlled varable of homeostasis in the GI tract
the conditions in the GI tract lumen
30
what are the sensors for GI tract homeostasis
your special sensory
chemo,osmo, mechanoreceptors
Mainly these receptors in the gut but can also be from external receptors or emotions
31
what are the signal pathways in GI tract homeostasis
neural (CNS and ENS) and hormones
32
what are the effectors in GI tract homeostasis
GI tract smooth muscle (motility) and epithelial cells (secretion and absorption)
33
what is a controlled varable
something that you are trying to keep constant
34
what are the phases of gastric regulation
cephalic phase (preparative)
gastric phase (digestive)
intestinal phase (controlled release)
35
what cause the cephalic phase to start
detection of food through sight, smell or taste (special sences)
even thinking of food
36
what does the cephalic phase cause
it prepares the GIT lumen for food
secretions start (saliva, digestive enzymes, acid)
37
when does the gastric phase start
when distention, change of pH or nutrients are detected
38
what does the gastric phase do to prepare you for food
sends signals via ENS and CNS and hormones (eg gastrin)
39
when does the intestinal phase start
when stretch, acid, change in osmolarity and nutrients are detected in the small intestine
40
what prepares for the intestinal phase
ENS, CNS, hormones (eg CCK and secreatin)
41
why do we have phased regulation of the GIT
The GI tract has different functions
at different phases of digestion.
The regulation of the stomach changes to facilitate these different functions.
42
neural regulation of the GIT is rapid and precise. what does this involve (intrinsic vs extrinsic)
Extrinsic reflexes involving CNS
- regulation and co-ordination of GI function over long distances (eg gastrointestinal reflex
and complex behaviors such as swallowing
• Intrinsic (local) reflexes of enteric nervous system (ENS) = regulation over centimeters (local reflexes)
- eg gastroenteric reflex
43
what do autonomic neurons of the GIT consist of
parasympathetic, sympathetic, motor and sensory
44
what do the autonomic neurons provide for the GI tract
a route of interaction between the CNS and the ENS
45
what do ENS neurons consist of in the GIT
sensory (mechano and chemoreceptors)
- Feed information into the enteric ns and the autonomic nervous system
interneurons
```
effect neurons (motor and scretory)
- Might be cells that make acid ect. These also send messengers to the 3 muscle layers therefore they are motor neurons
```
intestinal cells of cajal (GI pacemaker cells)
- Set the rate of contraction of GI smooth muscle
46
ENS sensory neurons play what role
(these are mechano and chemoreceptors)
| - Feed information into the enteric ns and the autonomic nervous system
47
effect neurons in the ENS (motor and scretory) play what role
- Might be cells that make acid ect. These also send messengers to the 3 muscle layers therefore they are motor neurons
48
ENS intestinal cells of cajal (GI pacemaker cells) play what role
- Set the rate of contraction of GI smooth muscle
49
what are the 2 ENS Structures and what do they do
Submucosal plexus
- Controls the mucosa (secretion, absorption, movement of villi)
Myenteric plexus
- Controls the muscularus (motility)
50
• Extrinsic (external) regulation (I.e. by the CNS) mostly acts how??
via the peripheral autonomic pathways and the ENS. Does not directly innervate gastrointestinal intestinal structures
51
what is the role of extrinsic regulation
• Modulates the activity of the enteric nervous
| system
52
usually the extrinsic regulation modulates the activity of the enteric NS. what are some exceptions of this
why
* Upper structures involved in swallowing
* Some blood vessels
* External anal sphincter
this is because they are skeletal muscle structures therefore you have conscious control over them
53
the parasympathetic nervous system usually stimulates activity in the GI system. how does it do this
• Acetylcholine, detected by muscarinic receptors
54
the sympathetic nervous system is usually inhibitory in the GI system. why
• Noradrenaline, detected by α adrenergic receptors
55
what are some example of internal and external stiluli for regulation by the CNS on the GI tract
• Internal stimuli - luminal composition and
volume
• External stimuli - Mood, thought, smell, sight
56
describe the anatomy of the sympathetic and parasympathetic nervous system
* 2 neuron motor pathway
* Preganglionic neuron (cell body) in CNS
* Postganglionic neuron (cell body) in autonomic ganglia
```
sympathetic = short then long axon
parasympathetic = long then short axon
```
57
Both sympathetic and parasympathetic interact
| with.....
Afferent fibers of sensory ENS neurons
• Peripheral terminals of ENS located in all layers of gut
• Detect information regarding state of gut and relay it
(via autonomic NS) to the CNS
- Nature of luminal contents – pH, osmolality, nutrient content (interactions with enteroendocrine cells), stretch/contraction
- Painful stimuli
Efferent fibers of the ENS.
• Response in smooth muscle cells or epithelial cells
Exception: Upper structures involved in swallowing are directly controlled
(don’t have ENS neurons).
58
the solitary nucleus Is located on each side of the medulla oblongata. what information goes there and through which nerves
Mouth, palate, pharynx, larynx, trachea, esophagus, and associated vessels and glands = Cranial nerves V, VII, IX, and X
Visceral organs located between the diaphragm and the pelvic cavity = Posterior roots of spinal nerves T1–L2
Organs in the inferior portion of the pelvic cavity = Posterior roots of spinal nerves S2–S4
59
where is the solitary nucleus located
on either side of the medulla
60
how does information from the Mouth, palate, pharynx, larynx, trachea, esophagus, and associated vessels and glands get the the solitary nucleus
Cranial nerves V, VII, IX, and X
61
how does information from the Visceral organs located between the diaphragm and the pelvic cavity get to the soulitor nucleus
= Posterior roots of spinal nerves T1–L2
62
how does information from Organs in the inferior portion of the pelvic cavity get to the soltory nucleus
= Posterior roots of spinal nerves S2–S4
63
where are terminals of ENS sensory neurons located
in all layers of gut
64
what is the role of sensory ENS neurons
Detect information regarding state of gut and relay it to CNS via the Autonomic pathways
detect the nature of luminal contents – pH, osmolality, nutrient content (via interactions with enteroendocrine cells), stretch/contraction and painful stimuli
Exception: Upper structures involved in swallowing are directly controlled (don’t have ENS neurons).
65
the CNS has 2 functions in regulating the GIT. what are these
with examples
Function 1: Responses to external stimuli (Senses, Emotions) via ANS
- Sympathetic pathways = Reflexes that generally inhibit GI function. eg Noradrenaline, detected by α adrenergic receptors.
- Parasympathetic pathway = Reflexes that generally stimulate GI function eg Acetylcholine, detected by muscarinic cholinergic receptors.
Function 2: Response to internal stimuli (GI lumen contents)
the CNS has a Long Reflex Path – Gut to brain and back again!
66
describe the long reflex loop of the CNS in regulating the GIT
Long reflex loop where information from GI tract lumen is transmitted through the ENS to the afferent branches of the autonomic NS to the cns and then the CNS whill excert an effcet onthe enteric nervous system
Thesefore gut to CNS to gut
66
describe the long reflex loop of the CNS in regulating the GIT
Long reflex loop where information from GI tract lumen is transmitted through the ENS to the afferent branches of the autonomic NS to the cns and then the CNS will exert an effect on the enteric nervous system
Therefore gut to CNS to gut
67
the ENS consists of how many neurons
10^8 neurons
therefore it is comparable to spinal chord
```
Grouped into....
Submucosal plexus
• Secretory activity of epithelial and glands
Myenteric plexus
• Smooth muscle
Clearly interaction occurs
```
68
describe how the ENS is structured
Grouped into....
* Submucosal plexus which has secretory activity of epithelial and glands
* Myenteric plexus = Smooth muscle
there is a clear interaction between the plexi, autonomic NS, (CNS) and other receptors and effectors
ENS neurons are very short
69
describe the size of the ENS
there are many neurons in the ENS (10^8) but it is over a small distance
* Self contained system
* Short local reflexes over cm’s
70
describe the receptors of the ENS
* Receptors in intestinal wall
| * Respond to various stimuli eg Stretch, pH, osmolarity, products of digestion
71
the ENS acts through local reflexes. was do these reflexes effect
• Smooth muscle, secretory cells
72
what are the Stimulatory and Inhibitory neurotransmitters in the ENS
Stimulation = Acetylcholine and tachykinins (Substance P, neurokinin A etc)
Inhibitory = Mainly nitrous oxide – (also VIP, ATP)
73
what is the function of regulation of the GI tract by the ENS
Response to internal stimuli (GI lumen contents)
74
what is the role of receptors of regulation of the GI tract by the ENS
detect conditions in the GI tracts such as streach and chemical composition
75
how does the ENS response occur
through 2 short reflexes
76
what is the difference between the myenteric plexus and the submucosal plexus
Myenteric plexus
- Between longitudinal and circular muscle layers
- Motor neurons to smooth muscle
- controls motility
Submucosal plexus
- Between mucosa and circular muscle layers
- Secretomotor neurons to glands, epithelium, muscularis mucosa
- controls secretion
77
what is a hormonal neuron called
an enteroendocrine cell
78
what is the main difference between hormonal and neural control
• Hormones have a slow diffuse action
neurons are fast
79
where are the hormones of the GI tract secreted from
• Secreted by endocrine cells throughout the intestinal tract which is the Largest endocrine organ in
body
80
what is the largest endocrine organ in the body
the intestinal tract
81
what is the role of endocrine cells in the GI tract
• endocrine cells are exposed to luminal contents therefore they are able to respond to changes in luminal contents
endocrine cells are regulated by extrinsic and intrinsic reflexes.
82
what are endocrine cells in the GI tract regulated by
endocrine cells are regulated by extrinsic and intrinsic reflexes.
83
endocrine cells ave 3 main courses of action. what are these
endocrine = secretion of a hormone into the blood and then it acts on the target cell
paracrine = Diffusion to the target cell without the vasculature
neurocrine = When a neuron secretes a neurotransmitter that also acts as a hormone
84
most of the hormones in the GIT are what kind of hormone
peptide hormones
| Most of them as they are being generated by cells as part of the protein manufacture
85
what do GI hormones participate in
• participate in feedback regulation of some aspect of
luminal contents
• often regulate more than one cell e.g. CCK (pancreas, gallbladder and sphincter of Oddi)
* potentiation is common (even bigger effect when they are working together)
* e.g. CCK and secretin
* often have a trophic (growth) effect
* e.g. gastrin on stomach mucosa
86
what is an example where a GI hormone often regulate more than one cell
e.g. CCK (pancreas, gallbladder and sphincter of Oddi)
87
what is potentiation and what is a common example seen in the GI tract
this is common and is when an even bigger effect is seen when 2 hormones are working together
• e.g. CCK and secretin
88
what is an example of a hormone that has a trophic effect on the GI system
growth effect
• e.g. gastrin on stomach mucosa
89
what is the function of hormones in the GIT regulation
Function : Response to internal stimuli
| GI lumen contents
90
what are the receptors of the hormones involved in GIT regulation
Receptors : chemo, osmo, mechano receptors
91
where are Enteroendocrine cells located
Located in the epithelial layer, Exposed to and respond to luminal contents therefore are able to detect stretch and chemical composition
the basolateral pole of these cells have secretory granules
(hormones)
92
what is the immune function of the gut
There is a huge number of normal microflora in the gut (bacteria and virus that live in the gut that are beneficial to us)
There are also bacteria and virus that are pathogenic
Therefore the gut has the ability to get rid of the pathogens and leave the good ones alone
93
what does the GIT do to function as an immune system
Barrier function
- The physical barrier of the epithelia and some of the secretion like the mucus
Active immune response
Modulator of GI tract (and systemic) Physiology
Responds to...
Food antigens, pathogens, commensal/mutualistic bacteria (All foods are not part of the body therefore the immune system has the ability to respond to it)
Releases inflammatory and other mediators that modulate GI function
- eg Histamine, prostaglandins, leukotrines, cytokines
Tolerance
94
what does the immune system of the GI have the ability to respond to
Food antigens, pathogens, commensal/mutualistic bacteria (All foods are not part of the body therefore the immune system has the ability to respond to it)
95
the GI immune system has the ability to releases inflammatory and other mediators that modulate GI function. what are some examples of these
- eg Histamine, prostaglandins, leukotrines, cytokines
96
how often is the epithelium in the GI tract replaced
every 5 days
97
what cells are in the epithelial lining
Absorptive cells: near the surface: in contact with the intestinal contents
Secretory cells: in crypts or glands: Outflow of fluid
protects from infection
stem cells
Paneth cells: Immune
At the very base of the crips which secrete antimicrobial functions
98
the GI immune system is as large as the rest of the immune system
what does it consist of
• Mesenteric lymph nodes, Peyers patches & range of immune cells
• Intraepithelial lymphocytes, B & T cells, mast cells, macrophages,
eosinophils
99
All these sections of the immune system are interconnected and they can communicate with each other
1
100
what is commensalism
• Commensalism, is a relation between individuals of two species in which one species obtains food or other benefits from the other without either harming or benefiting
the latter.
101
what is mutualism
• Mutualism is the way two organisms of different species exist in a relationship in
which each individual benefits from the activity of the other.
