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58 Cards in this Set
- Front
- Back
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What is the role of the GIT in homeostasis?
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Provide nutrients
->essential for functioning of all cells in the body |
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Describe in general terms how nutrients are made available from the external environment.
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External env't -> Food -> digestive system -> absorbable molecules -> Internal env't -> processed ->-> -> Cells -> Energy nand raw materials :Growth and repair or fct and regulation
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What is the lumen in the GIT?
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An extension of the external environment
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What is the GIT structure?
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Tubular in nature (mouth ->. ans)
Communication with External environment |
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What is the length of the adult of GIT?
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4.5 m (3x the size of a human)
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Internal surface area of the lumen that lines the GIT?
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200-250 m2
Inner surface area is 600x the outer surface area A lot of transport occurs in this area |
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What is the differentiation of the GIT?the lining of the abdomen
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Dif portions of the tube are specialized for certain fcts
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What are the ass't or accessory glands of the GIT?
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Salivary glands
Pancreas Liver Gall bladder |
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What is the wall structure of the GIT?
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Out to in:
Serosa Muscularis externa (contains 2 layers of smooth muscle: longitudinal fibres and circular fibres) Submucosa: loose CT, has nerves, vessels and lymphocytes Mucosa: muscularis mucosa, lamina propia, epithelial) |
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What is the serosa?
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Thin but tough layer of CT, continuous with the abdomen
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What are the longitudinal fibres?
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parallel to the digestive tract
Contraction makes the tube shorter |
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What are the circular fibres?
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Narrows lumen when it contracts
Around the circumference of the tube Perpendicular to the long axis (Inner layer of muscularis externa) |
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What are the longitudinal fibres?
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parallel to the digestive tract
Contraction makes the tube shorter (outer laer of muscularis externa) |
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Where is the smooth and striated muscle in the GIT?
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Striated muscle: Moiuth, pharynx, upper 1/3 of the esophagus, rectum
Smooth muscle: rest of the GIT |
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What are the circular fibres?
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Narrows lumen when it contracts
Around the circumference of the tube Perpendicular to the long axis |
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What is the muscularis mucosae?
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Smooth muscle
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What is the lamina propria?
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Loose CT
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Where is the smooth and striated muscle in the GIT?
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Striated muscle: Mouth, pharynx, upper 1/3 of the esophagus, external anal sphincter
Smooth muscle: rest of the GIT |
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What is the muscularis mucosae?
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Smooth muscle
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What is the lamina propria?
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Loose CT
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What is the fct of the epithelial layer?
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Absorbtion
Digestive juices Is both exocrine and endocrine |
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What are the fcts of the GIT?
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Convey food along the GIT
Allow disruption of food into small molec Small molec can be absorbed into circulation |
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What are the 3 activities of the GIT?
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1) Motility (muscular activity): propulsion and physical breakdown of the meal
2) Secretion (glandular activity): chemical breakdowns (digestion) 3) Absorption: Transfer to circulation |
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What is the digestive/absorptive efficiency?
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Carb: 99%
Fat: 95% Protein: 92% (very efficient processes) |
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What do the neural and hormonal mechanism integrate?
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Propulsive
Secretory Absorptive activities |
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What does the enteric innervation system (ENS) do?
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Critical to regulating all activities in the digestive tract
It is an independent, integrative nervous system Neural regulation |
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What are thee activities of the muscular and secretory elements of the ENS?
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Initiate
Program Regulate Coordinate |
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What makes up the ENS?
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Myenteric plexus (btw the longitudinal and circular muscle layers)
Submucosal Plexus ->these 2 plexuses work as a fctnal unit, includese sensory neurns, effector neurons and interneurons |
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What do the sensroy fibres do?
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Pick up info from the receptors in the muscle
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What do the effector neurons do?
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can cause secretion or contractile activity
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What do interneurons do?
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Allow relay of info from ganglion cells which synapse with smooth muscle cells, endocrine and exocrine cells and other ganglion cells
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What do the excitatory enteric neurons do?
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Release mostly ACh -> act on muscarinic receptors
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What do the inhibitory receptors do?
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Release NANC
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What does atropine do?
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Blocks ACh
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What happens when there's a stimulus in the lumen or gut wall?
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In the Gut Wall:
Acts on receptors (chemo,osmo, mechano-receptors) -> nerve plexus (activation of the sensory fibres in it) ->activation of smooth muscle or gland -> response (occurs in the lumen, not the gut wall) |
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What happens if the ENS is destoyed? The ANS?
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ENS: gut doesn't function
ANS: gut still fcts, but with difficulties |
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Describe the parasympathetic fibres.
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PRE-ganglionic fibres
Initiated in the CNS Enter wall and synapsewith enteric neurons, release ACh acting on nicotinic receptor in the GIT (ENS) No interruption of the fibre |
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Describe the sympathetic fibre.
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POST-ganglionic
Starts in CNS Synapse OUTSIDE the GIT wall Release noradrenalin in the GIT Influences of ANS are not in contact with muscle cells and glandular cells |
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Describe autonomic innervation of the gut wall for parasympathetic and sympathetic.
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Parasympathetic:
Vagus: originates in the medulla Pelvic nerves: distal portion of colon Sympathetic: Originates in the spinal cord Celiac ganglion Superior mesenteric ganglion Inferior mesenteric ganglion |
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Do the sympathetic or parasympathetic innervate secretory cells or muscle directly?
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No
The sympathetic and parasympathetic fibres are used to modify the activity of the enteric neurons |
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Where do sensory fibres in the ANS originate from?
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In receptors in wall musculature or epithelial
They carry info to medulla or spinal cord ->get integration of info within medullary and spinal cord |
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What effect does the gut have on the CNS, ANS and ENS?
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Gut keeps CNS aware if what is going on in the gut
ANS influences the activty of the ENS |
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How does the ANS modulate the activity of the ENS through the parasympthetic system?
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Parasympathetic reaches the wall of the GIT as PREganglionic fibres, synapsing, va nicotinic ACh receptors, with enteric neuron (excitatory and inhibitory) to exert an EXCITATORY effect. If it releases Ach that acts on muscarinic receptors, stimulates an excitatory response. If the enteric neuron releases NANC, the parasympathetic stimulates an inhibt response (cuz NANC is an inhibitor)
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How is the parasympathetic excitatory?
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Activates ACh release at nicotinic receptor to act on muscarinic receptor on smooth muscle cell (+)
Excites ACh acting on Nicotinic receptor that activate the NANC receptor that inhibits muscle cell from contracting (.: excite inhibitory effect) |
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How does the ANS modulate the ENS through the sympathetic system?
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Sympathetic:ACh reaches the wall of the GIT as POSTganglionic fibres, synapsing, via NA (noradrenalin, inhibitory), with enteric neurons (both excitatory and inhibitory) to exert and INHIBITORY effect
-Sympathetic also innervates smooth muscle in blood vessels in the wall, causes vaoconstriction |
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How is the sympathetic system inhibitory?
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Synapses outside the wall with nicotinic receptors
-Inhibits ACh release onto muscarinic receptors, thereore no (+) effect on muscle cells -Inhibits inhibitory reflex: inhibits the release of NANC, which is an inhibitory effect, therefore there is contraction of the muscle |
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Where else do inputs come from?
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Emotional states
Sight, smell, taste of food Act on the CNS Afferent neurons act on the CNS, and efferent neurons ome from the CNS to act on the nerve plexus |
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What do sensory neurons allow?
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Long reflexes
->integrate activity over longer distance along the gut |
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In general, what effect does the Parasympathetic have? The sympathwtic?
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PS: Excitatory (can also excite inhibitory neurons)
S: Inhibitory (may also inhibit inhibitory neurons) |
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Is it essential to have the ANS?
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No
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What is the Diffuse Endocrine System (DES)?
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Largest, most diversified endocrine system in the body
->secretory cell can act in autocrine fashion or paracrine or endocrine There is no whole endocrine organ, just many cells that secrete hormones |
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What are the different modes of regulation?
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Autocrine
Paracrine Endocrine |
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What are gut regulatory peptides?
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All peptides, no steroid H in the gut
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Where does the mucosa of the stomach and small intestine release gut regulatory peptides into?
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Portal blood-> liver ->systemic circulation (heart) and back to the digestive system to regulate its movements and secretion
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What stimnulates the release of the peptides?
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Nervous, chemical and mechanical stimnulation, coincident with the intake of food
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What are the targets of the gut regulatory peptides?
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Multiple targets that are excitatory or inhibtory
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What do gut regulatory peptides interact with?
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other gut regulatory peptides or NT
1) Can be synergistic: support each other 2)Antaganistically: one can excite and the other can inhibit |
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Summarize GIT regulation.
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1) **Short enteric (intramulral) reflexes: critical, main, final regulation. If this is destroyed, can't have any other regulation of the gut
2) Long extrinsic (ANS) reflexes: modulate, modify 3) Hormonal factors: modulate (increase or decrease) |
