GI- Physiology- General Principles of Gastrointestinal Function Flashcards
How many sphincters in the GI system and what are they?
- Upper esophageal sphincter
- Lower esophageal sphincter
- Pyloric Sphincter
- Ileocecal sphincter
5&6. Internal and external anal sphincters
The and are responsible for chopping food into small pieces, lubricating it, initiating carbohydrate and fat digestion, and propelling the food into the esophagus.
mouth
oropharynx
The acts as a conduit to the stomach.
esophagus
The stomach temporarily stores food and also initiates digestion by churning and by secreting and acid.
proteases
The small intestine continues the work of digestion and is the primary site for the absorption of . The large intestine reabsorbs and
and also stores the fecal matter before expulsion from the body.
nutrients.
fluids
electrolytes
The glands and organs include the salivary glands, pancreas, and liver.
accessory
The secretes digestive enzymes into the duodenum, in addition to secreting to neutralize gastric acid.
pancreas
HCO3 -
The liver secretes which the gallbladder stores for future delivery to the duodenum during a meal. Bile contains bile acids, which play a key role in the digestion of fats.
bile
Review the layers of the GI system (this is the duodenum)
Describe and name the outermost layer of this cross section of the gut?
The serosa is an enveloping layer of connective tissue that is covered with
epithelial cells
squamous
Starting from the outside, what are layers 2 and 3 of the gut, describe these layers?
The muscle layer, the muscularis externa, includes two layers of smooth muscle. The inner layer is, whereas the outer layer is .
neurons are present between these two muscle layers.
circular
longitudinal.
Enteric
What are the Enteric neurons that are present between the 2 muscle layers of the muscularis externa (propria)?
Myenteric plexus
What nerve complex is responsible for peristalsis and where is it located in the gut?
Between the 2 layers of the muscularis externa (circular and longitudinal muscles) called the Myenteric plexus
What nerve plexus does not play a role in peristalsis and where is it located in the GI system?
submucosal plexus (Meissner’s plexus) between the circular muscle of the muscularis externa and the submucosa
The mucosa consists of the epithelial layer, as well as an underlying layer of loose connective tissue known as the lamina propria, which contains capillaries, enteric neurons, and immune cells (e.g., mast cells), as well as a thin layer of smooth muscle known as the .
muscularis mucosae.
The surface area of the epithelial layer is amplified by several mechanisms. Most cells have on their apical surfaces. In addition, the layer of epithelial cells can be evaginated to form villi or invaginated to form crypts (or glands). Finally, on a larger scale, the mucosa is organized into large folds.
microvilli
Review the diagram
How often is the lining of the gut replaced with the differentiation of stem/progenitor cells?
every 5 days
In the mouth, Digestion involves the conversion of dietary food nutrients to a form that the small intestine can absorb. For carbohydrates and lipids, these digestive processes are initiated in the mouth by salivary and lingual , respectively.
amylase (a-amylase/ptyalin)
lipase
Protein digestion is initiated in the by gastric .
stomach
proteases (i.e., pepsins)
Other than the mouth, lipid digestion also occurs in the .
stomach
Digestion of which food component does not occur in the stomach?
carbohydrates
Digestion is completed in the intestine by the action of both enzymes and enzymes at the of the small intestine.
small
pancreatic
brush border
Pancreatic enzymes, which include , , and , are critical for the digestion of lipids, protein, and carbohydrates, respectively
lipase
chymotrypsin
amylase
The enzymes on the luminal surface of the small intestine (e.g., brush-border disaccharidases and ) complete the digestion of and proteins.
dipeptidases
carbohydrates
Digestion by these brush-border enzymes is referred to as digestion.
membrane
The enteric nervous system is a “” with sensory neurons, interneurons, and motor neurons…
minibrain
Neurons of the ENS are primarily, but not exclusively, clustered in one of two collections of neurons in the plexus and the myenteric plexus
submucosal
The myenteric (or Auerbach’s) plexus is located between the and longitudinal muscle layers throughout the GI tract from the proximal end of the esophagus to the .
circular
rectum.
The submucosal (or Meissner’s) plexus is found in the submucosa only in the
and large intestine.
small
The ENS consists of circuits, interneuronal connections, and
neurons.
sensory
secretomotor
Sensory (or afferent) neurons monitor changes in luminal activity, including
(i.e., smooth-muscle tension), (e.g., pH, osmolality, levels of specific nutrients), and mechanical stimulation.
distention (stretch)
chemistry
These sensory (chemoreceptors and mechanoreceptors) neurons activate
, which relay signals that activate efferent neurons that in turn stimulate or inhibit a wide range of effector cells: smoothmuscle cells, epithelial cells that secrete or absorb fluid and electrolytes, submucosal blood vessels, and enteric endocrine cells.
interneurons
secretomotor
efferent secretomotor neurons stimulate or inhibit a wide range of effector cells: smooth muscle cells, cells that secrete or absorb fluid and electrolytes, submucosal blood vessels, and enteric cells.
epithelial
endocrine
The brain-gut axis is a bidirectional system that controls GI function via the ANS, GI , and the immune system…
hormones
neural control of the GI tract is a function of not only intrinsic nerves (i.e., the ENS) but also nerves that are to the GI tract composed of elements of both the and, to a lesser extent, the sympathetic nervous system and are under the control of autonomic centers in the .
extrinsic
parasympathetic
brainstem.
Review the diagram, secretions stimulate by the parasympathetic/sympathetic nervous system
parasympathetic
What are some things that can trigger the parasympathetic nervous system to activate secretion of the stomach and pancreas?
conditioned stimuli, smell, taste, chewing, swallowing, and hypoglycemia
What is the main neurotransmitter dropped off in both the presynaptics of the parasympathetic and sympathetic nervous systems of the gut?
acetylcholine
Postganglionic parasympathetic fibers use mainly as their neurotransmitter; however, many other neurotransmitters are also present. Parasympathetic stimulation— after one or more synapses in a very complex ENS network— increases secretion and
ACh
motility
The parasympathetic nerves also contain afferent fibers that carry information to autonomic centers in the from chemoreceptors, osmoreceptors, and mechanoreceptors in the mucosa. The loop that is initiated by these afferents, integrated by central autonomic centers, and completed by the parasympathetic efferents, is known as a reflex.
medulla
vagovagal
What do the duct and acinar cells secrete and where are they located?
pancreas
duct cells secret bicarbonate to neutralize stomach acid
acinar cells secrete digestive enzymes
ACh, peptides, and bioactive are the ENS neurotransmitters that regulate epithelial and motor function…
amines
Which neurotransmitter causes contraction of the smooth muscle in the wall of the GI tract, relaxes sphincters, increases saliva secretion, increases gastric secretion, and increases pancreatic secretion?
AcH (from cholinergic neurons)
Which neurotransmitter causes relaxation of the smooth muscle in wall of GI tract, contraction of sphincters, and also increases salivary secretion?
NE (from adrenergic neurons)
Which neurotransmitter comes from neurons of the enteric system and causes relaxation of the smooth muscle of GI system, increases intestinal secretion, and increases pancreatic secretion?
Vasoactive Intestinal Peptide (VIP)
What is the action of NO in the GI system and what is its source?
relaxation of the smooth muscle of gut and comes from the neurons of the enteric nervous system
What is the action of Gastrin-Releasing Peptide (GRP)?
What is another name for it?
What is it’s source?
increase gastrin secretion
Bombesin
Vagal neurons of gastric mucosa
What are neurons of the enteric nervous system that causes relaxation of the smooth muscle in the gut and decreases intestinal secretion?
Neuropeptide Y
What substance in cosecreted with ACh by neurons of the enteric nervous system and causes contraction of the smooth muscle of gut and increases salivary secretion?
Sustance P
Enkephalins (endogenous opiates) are from neurons of the
nervous system and cause of the smooth muscle of the gut and decrease/increase intestinal secretion
enteric
contraction
decrease
Though ACh works directly to contract the smooth muscle, it can work indirectly with which two transmitters to cause relaxation of the smooth muscle?
VIP
NO
What stimulates secretion of Gastrin, where does it come from, and what does it do?
What stimulates secretion of cholecystokinin, where does it come from, and what does it do?
What stimulates secretion of Secretin, where does it come from, and what does it do?
What stimulates secretion of Gastric inhibitory peptide, where does it come from, and what does it do?
What stimulates secretion of Motilin, where does it come from, and what does it do?
Review the diagram:
In addition to the “hard-wired” communications involved in sensory input and motor output, communication via the gut-brain axis also requires significant participation of the immune system. Neuroimmune regulation of both epithelial and motor function in the small and large intestine primarily involves cells in the of the intestine.
mast
lamina propria
What are the 3 main components of the gut-brain axis?
ENS
GI hormones
immune system
What redundancy permits fine tuning of the regulation of digestive processes and provides “backup” or “fail-safe” mechanisms that ensure the integrity of GI function, especially at times of impaired function (i.e., during disease).
substantial redundancy via three parallel components of the gut-brain axis (ENS, GI hormones, and immune system)
Review diagram of comparison of muscle types
