GIT - Lecture 1 Flashcards
What is the function of the GI tract?
conveys food along GIT, allowing it to be broken down into small molecules which can be absorbed into the circulation
What are the 6 activities that happen in the GI tract?
- INGESTION
- SECRETION
- MOTILITY
- DIGESTION
- ABSORPTION
- DEFECATION
What is secretion?
chemical breakdown of food
What is motility?
muscular activity
What is digestion a property of?
secretion and motility
Is secretion endocrine or exocrine?
both
The activities of the GI tract are aimed at maintaining…
homeostasis
What is the function of GIT?
to turn food into absorbable molecules
Why is it important that the GIT turns food into absorbable molecules?
because it is used by cells for growth and repair as well as function and regulation
What % of carbohydrates can we digest?
99%
What % of fats can we digest?
95%
What % of proteins can we digest?
92%
Which 3 activities of the GIT are highly coordinated?
propulsive, secretory and absorptive activities
What 2 factors describe the GIT?
- Tubular Nature
- Communication with External Environment at Both Ends
What are the contents of the luminal cavity considered as?
extracellular space
What is the GIT length longer than?
the length of the human
What is the length of the GIT tract in a normal adult?
4.5 m
What gives the GIT its length?
muscle tone
length of internal surface area ___ length of external surface area
larger than
What makes the internal surface of the lumen longer than the external surface?
both invaginations (inpushings and outpushings)
How much larger is the lumen than the outer wall of the GIT?
600x
What is the length of the lumen equal to in an adult?
200-250 m^2
What are the primary organs of the GIT?
- mouth
- esophagus
- stomach
- small intestine
- large intestine
- rectum
What are the secondary organs of the GIT?
- salivary glands
- liver and gallblader
- pancreas and spleen
What are the 4 main layers of the GIT?
- mucosa
- submucosa
- muscularis externa
- serosa
In some places in the GIT, the serosa is sometimes continuous with the…
peritoneum
What kind of tissue is the serosa?
thin, tough connective tissue
What are the 2 layers of muscle that make up the muscularis externa?
- longitudinal fibers
- circular fibers
Whether or not the muscle is smooth or striated depends on…
where we take a cross-section of the GIT
What kind of muscle makes up the muscularis externa if we take a cross-section in the esophagus and rectum?
striated muscle
What kind of muscle makes up the muscularis externa if we take a cross-section in the majority of the GIT?
smooth muscle
What happens to the GIT when longitudinal fibers contract?
it shortens
What happens to the GIT when circular fibers contract?
it narrows
What kind of tissue is the submucosa?
loose connective tissue
What does the submucosa contain?
lymphatics and blood vessels
What are the 3 layers of the mucosa?
- muscularis mucosae
- lamina propria
- epithelial layer
What kind of muscle is the muscularis mucosae?
smooth muscle
What kind of tissue is the lamina propria?
loose connective tissue
What kind of cells are found in the epithelial layer of the mucosa?
epithelial and glandular cells
What nervous system is a branch of the autonomic nervous system?
enteric nervous system
Where do all of the neurons of the enteric nervous system reside?
within the walls of the GIT
Does the enteric nervous system operate independent or dependently?
independent
What kind of system is the GIT?
integrative and independent
What 4 things does the ENS do to the activities of muscular and secretory and absorptive elements of the GIT?
initiates, programs, regulates, coordinates
What plexus is found beneath the muscularis mucosae?
submucosal plexus
What plexus is found beneath the circular muscle?
myenteric plexus
Though anatomically distrinct, the 2 plexuses of the GIT behave as ___ functional unit
one
What are the 2 plexuses of the GIT?
submucosal and myenteric
What do the plexus’ of the GIT contain for reflex arcs? (3)
- sensory neurons
- motor/effector neurons
- interneurons
Sensory neurons have receptors at the level of the…
mucosa or muscle
What can sensory neurons of the GIT respond to?
stretch receptors, chemoreceptors, osmoreceptors
What do the motor/effector neurons activate?
secretory and muscle cells
What do the interneurons of the GIT connect?
sensory neurons and motor neurons to integrate signals over longer distances
What does the ENS consist of?
ganglion cells
What do ganglion cells of the ENS synapse with? (3)
- smooth muscle cells
- endocrine and exocrine cells
- other ganglion cells
What are the 2 types of enteric neurons?
excitatory and inhibitory
What do excitatory enteric neurons release?
ACh
What do excitatory enteric neurons act on?
muscarinic receptors
What do inhibitory enteric neurons release?
NANC transmitters like NO
Where do enteric sensory fibers have cell bodies in?
in plexuses
Where do the sensory fibers of the enteric system get information from? (2)
gut chemoreceptors and mechanoreceptors
What is ACh blocked by?
atropine
What does the ultimate activity of the ENS depend on?
the algebraic sum of influences
What is stimulus sensed by in the gut wall?
chemoreceptors, osmoreceptors, mechanoreceptor
What do chemoreceptors, osmoreceptors and mechanoreceptors signal through after being activated?
nerve plexus
Where do the nerves go after moving through the nerve plexus?
smooth muscle or gland cell
Why is it called short, enteric reflexes?
made up of neurons within the enteric nervous system
What is the pathway of short, enteric reflexes?
- stimulus
- chemoreceptors, osmoreceptors, mechanoreceptor
- nerve plexus
- smooth muscle or gland cell
- response
Where does the ENS receive modulatory input from?
the ANS
The ANS can only impinge on the ___ of the ENS
neurons
Will the CNS ever synapse on the muscles or glandular cells of the GIT?
no, it will impinge on the enteric neurons and then through the system, the muscle is activate
Where does parasympathetic innervation of the GIT come from?
CNS
Is the preganglionic innervation excitatory or inhibitory? What kind?
nicotinic excitatory
What do the preganglionic neurons of the CNS release on the ENS neurons?
ACh
Where does sympathetic innervation of the GIT come from?
CNS
Is the postganglionic innervation excitatory or inhibitory? What kind?
noradrenaline NA inhibitory
What do the postganglionic neurons of the CNS release on the ENS neurons?
NA
What nerves provide parasympathetic innervation to the GIT?
- vagus nerve
- pelvic nerves (distally)
What nerves provide sympathetic innervation to the GIT?
- celiac ganglion
- superior mesenteric ganglion
- inferior mesenteric ganglion
Sympathetic neurons also innervate smooth muscle in blood vessels, causing ___.
vasoconstriction
Sensory neurons allow for “___ ___”
long reflexes
Parasympathetic input -> ___ of blood vessels
dilation
Sympathetic input -> ___ of blood vessels
constriction