digestion Flashcards
what is the GIT?
alimentary canal that is continuous tube from the mouth to anus
What is the main function of the GIT?
Conveys food along GIT allowing it to be broken down into small molecules which can be ansorbed in the circulation
what is secretion?
the release of chemical substances to break down the food
how is motility related to digestion?
it involves the muscular activity which will propulse the food and allow for chemical breakdown and mixing of foods
what is the absorption aspect of digestion?
the transfer of nutrients into blood circulation
what is the role of GIT in homeostasis?
o Provide nutrients to the body which is needed for basic functions, regulation, growth & repair
what proportion of nutrients is absorbed by the GIT?
CHO 99%
FAT 95%
PROTEIN 92%
what properties of the GIT were observed in earth worms?
o Tubular nature
o Communication with the external environment at both ends
what is the length of the GIT in humans?
~4.5 m in adults
how much bigger is the GIT from the inside than the outside?
600x
what is the area covered by the GIT in adults?
200-250 m^2
what is the advantage of having such a large surface area in the GIT?
Great increase in area allows to obtain the ability to absorb nutrients in such an efficient way
how is the wall of the GIT divided?
into 4 functional layers
what are the layers that compose the wall of the GIT?
- serosa
- muscularis externa
- submucosa
- mucosa
what layer of the GIT is identified as being “thin, but though layer of connective tissue which surround the entire tube?”
serosa
what layer is o Continuous with the messenter, holds the GIT in place?
serosa
what type of fibers is the musculais externa composed of?
longitudinal fibers (outer layer) and circular fibers (inner layer)
what happens when the outer layer of the muscularis externa contracts?
GIT shortens
what happens when the inner layer of the muscularis externa contracts?
lumen will narrow
what part of the GIT is formed by striated muscles?
Top 1/3 of esophagus, oral cavity, pharynx and anal sphincter
in what layer are the lymphatic and blood vessels found?
submucosa
what is the mucosa layer composed of?
- muscularis mucosae
- lamina propria
- epithelial cells
what is muscularis mucosae?
smooth muscle
what is lamina propria?
loose connective tissue
what is the function of the epithelial cells?
secretory ; endocrine and exocrine gland
plays a role in absorption
does the ENS require input from the CNS?
NO
What is the ENS defined as?
• Independent, integrative nervous system
what is the main function of the ENS?
activities of muscular and secretory and absorptive elements of the GIT such as o Initiates o Programs o Regulates o Coordinates
what are the plexuses that form the GIT?
submucosal and myenteric plexus
what is a plexus?
collection of nerve cell bodies
where are sensory neurons receptors located?
receptors in mucosal/muscle layer
what do motor neurons in the ENS activate?
• Activate secretory cells, muscle cells and motor neurons (expand action of the neurons across the GIT wall)
although the plexuses are anatomically different in the ENS, do the function as one or multiple units?
function as a single unit
what does the myenteric plexus control?
smooth muscle
what does the submucosal plexus control?
controls glands of the endocrine cells
excitatory enteric neurons act on which receptors?
muscarinic receptors
what is released by excitatory enteric neurons?
ACh
inhibitory enteric neurons act on which receptors?
NANC (non-adrenergic/non cholinergic)
where do the sensory fibers in the cell bodies in plexuses receive information from?
they receive information from the gut chemo and mechanoreceptors
how is the stimulus transformed into a response?
stimulus sent to receptors then to nerve plexus then to muscle cells or gland to produce a response
what is the length of intra mural reflex
short
what do parasympathetic neurons reach the wall of the GIT as?
preganglionic fibers
what do preganglionic fibers synapse via?
• They synapse via nicotinic ACh receptors with enteric neurons
what does it result in the system in parasympathetic neurons
o Increases excitation in the system
what do sympathetic neurons reach the wall of the GIT as?
postganglionic fibers
what do postganglionic fibers synapse via?
• Synapses via NA receptors with enteric neurons
what effect is exerted by sympathetic neurons?
inhibitory effect thus causes vasoconstriction
what reflexes are permitted by sensory neurons?
long reflexes
give examples of some Non-GIT hormones?
o Growth hormones, thyroid hormones
what may non-GIT hormones influence?
growth and development of the GIT
can hormones be released by the GIT but influence activities outside of it?
yes, ex. grehlin increases appetide at the hypothalamic feeding center
generally what do GIT hormones regulate?
activities within the GIT
how does hormonal regulation of GIT actiity function?
diffusion of the endocrine system
what is the largest and most diversified endocrine system of the body
GIT endocrine system
how many hormones get released by the GIT?
~20-30
what is a endocrine cell that releases a hormone that functions on itself?
Autocrine
what is an endocrine cell that affects neighboring cells when releasing hormones?
paracrine cell
what is the endocrine effect?
hormones release and enter the blood stream to get to other regions
what type of hormones are the regulatory hormones of the GIT
Peptide hormones
what are regulatory hormones of the GIT released from?
mucosa
what is the pathway of the regulatory hormones of the GIT when released from the mucosa?
blood to liver to heart, through systemic circulation through out the body until they reach target cells
what happens when a hormone interacts in a synergistical manner with a NT?
they potentiate one another
what happens when a hormone interacts in a antagonistic manner with a NT?
they inhibit one another
when talking about muscular activity of the GIT, what layers are involved?
2 muscle layers of the muscularis externa
when referring to propulsion through the GIT; what does segmentation refer to?
rings of contraction causing for closing at different locations at different times
what is persistalsis?
circular muscles where the ring of the muscles moves along the wall of the GIT
how can the flow in the GIT be characterized?
- slow
- aboral
- little to no resistance
what is the other name given to the oral phase of swallowing?
volontary phase
what is carried out by the oral phase of swallowing?
food is transported from anterior mouth to the pharynx
what does swallowing involved?
Involves a series of reflexes coordinated in the deglutition center of the medulla oblongata via the cortex.
where is the pharynx located?
back of the throat
what senses the presence of the bolus in the pharyngeal phase?
sensory receptors
in the pharyngeal phase. how does food move down?
-reflexes causes it to move down
what happens when the bolus presses down on the epilottis?
reflexive contraction of the vocal cords and closure of the glottis and protect the lower airways
what occurs when swallowing?
apnea
what happes to the UES in the pharyngeal phase of swallowing?
it relaxes
what are deglutition reflexes?
a series of protective reflexes is initasatied by stimulation of afferent fibers in the pharynx
what signals the deglutition reflex?
the medulla
what is controlled by the deglutition reflex?
o Protective functions
o Relaxation UES
o Deglutition apnea
o Contraction of the pharyngeal muscles
what type of muscles composes the UES?
striated muscle
what innervates the UES?
somatic- Vagus N (X)
how is the UES when no food is present?
its contracted
what NT is released to ensure closure of the UES?
ACh
what is deglutition relaxation?
cessation of the impulse causes the muscle to relax
what happens to ACh in the deglutition relaxation phase
decreases
