GI Flashcards
Food/nutrients do not become a part of the internal environment until …
absorbed into the blood or lymphatics
GI structure: 4 parts
upper, middle, lower and accessory
what makes up the upper GI ? what does it do?
mouth, esophagus, stomach
initial receptacle, initiation of digestion
what makes up the middle GI ? what does it do?
small intestine- duodenum, jejunum, ileum
most absorption and digestion processes occur
what makes up the lower GI ? what does it do?
cecum, colon, rectum
storage for elimination
what makes up the accessory GI ? what does it do?
salivary glands, liver, pancreas (an gallbladder)
produces secretions that aid in digestion
what is the mouths job in digestion?
entrance, mastication and directs food toward esophagus
physical characteristics of esophagus
10 in long, muscular and collapsible, sits behind trachea
epithelial layer to lubricate and protect its surface
esophagus: upper third vs lower third - what are they made up of?
Upper third is skeletal striated muscle gradually replaced with smooth muscle until smooth muscle completely covers the lower third
lower third: Peristalsis of smooth muscle helps to move food along tube
movements of small vs large intestine
small: break up food AND move it along
large: larger movements to move food along tract
what are the upper and lower sphincters of the GI tract?
upper: pharyngoesophageal
lower: gastroesophageal
where is the gastroesophageal sphincter located?
about 3cm above stomach
GI lower/gastroesoph. sphincter: when is it contracted vs relaxed?
- Remains contracted (tonic) causing an area of high pressure to keep contents in stomach
- Receptive relaxation when eating
the gastroesophageal sphincter aids in maintenance of what?
aids in maintenance of high pressure area around lower sphincter to prevent reflux
how does the gastroesophageal sphincter enter the diaphragm?
Passes through a “hiatus” (an entry) through the diaphragm into the stomach
what is a haital hernia?
haital hernia- protrusion of stomach up through this haitus for gastroesoph. sphincter - causes regurg of food contents from stomach
- the majority are gradual and asymp.
- if become symptomatic then one can consider sugery
what is the residual volume of the stomach? how much can it hold before intraluminal pressure rises?
50mL (how much usually stays in the stomach)
1000mL
what are the different portions of the stomach? entry, upper, main, lower and exit?
Entry is the cardiac orifice Fundus is upper portion Body is the main portion Antrum is the lower portion Pyloris is the exit
what is the pyloris?
exit of the stomach: a ring-like muscle that contracts, controls the rate of gastric emptying. The pyloric sphincter allows for controlled delivery of the acidic chyme to the duodenum
how long are each part of the small intestine?
duodenum: 10 inches
jejunum and ileum: 23 ft
how do bile and pancreatic enzymes get into the small intestine? what do they do there?
duodenum contains openings for the common bile and main pancreatic ducts
- bile and pancreatic enzymes enter to help aid in digestion, which takes place in the jejunum and ileum
function of the jejunum and ileum?
digestion and absorption of food
the duodenum helps ___ acidic chyme
alkalyze with bile and HCO3
when is the duodenum “ready” to receive food stuff/chyme from the stomach?
when it is alkalytic enough to receive the acidity
how long is the large intestine?
4.5-5ft
what are the parts of the large intestine?
cecum, colon, rectum and anal canal
what is the cecum?
Blind pouch at the junction of the ileum and the colon
where is the appendix?
The appendix arises from the cecum about 1 in (2.5 cm) from ileocecal valve
where is the ileocecal valve? what does it do?
Ileocecal valve (upper border of cecum) prevents fecal matter from back-flowing into the small intestine
what are the parts of the colon?
Ascending –> hepatic flexure–>transverse–>splenic (left colic) flexure –> descending–>sigmoid
what are the 4 layers of the GI wall?
mucosal (innermost lumen), submucosal, muscularis externa, peritoneum/serosa
What are 5 important jobs of the mucosal layer of the GI wall?
- Mucous lubricates and protects
- Secretion of digestive enzymes
- Absorption
- Barrier to noxious or pathologic organisms
- Contains the Lymphatics – first line of immune defense
what are the 3 sublayers within the first GI layer (mucosal)
3 parts innermost to outermost: Epithelium–>Lamina propria (connective tissue)–>muscularis mucosae (smooth muscle)
what is significant about the epithelial sublayer of the mucosal layer of the GI wall?
-Epithelial cells have rapid turnover rate of 4-5 days and are shed in stool: Rapid healing without scar tissue
2 kinds of muscle in the muscularis externa of the GI wall?
longitudinal and circular
submucosal layer of GI wall
Connective tissue layer
Blood vessels, nerves, and structures responsible for secreting digestive enzymes
what are the two main parts of the GI peritoneum?
two continuous layers: parietal (attached to abd. wall) and visceral (attached to organ wall)
what is the peritoneum of the GI? clinical importance?
Loosely covers the organs and the body cavity creating a peritoneal cavity (potential space)
Serous fluid creates an area of low friction
Ascites- an accumulation of fluid in the peritoneal space
what is the mesentary?
A double fold of peritoneum that encloses a portion or all of one abdominal organ attaching it to the abdominal wall
Contains BLOOD SUPPLY, NERVES, and lymphatic vessels supplying intestinal wall
what is the omentum?
double layer of peritoneum from stomach or proximal duodenum to adjacent organs or abdominal wall
what are the two parts of the omentum?
greater and lesser
what is the greater omentum? what does it do?
mobile, Double layer of peritoneum that folds down from the stomach to cover the transverse colon and folds of the intestines
Protects the intestines from cold or injury (fatty) and serves to contain infection or in response to inflammation (adhesions)
what is the lesser omentum? what does it do?
Connects the liver to the lesser curvature of the stomach
Really doesn’t do much
what do we worry about with the mesentary?
mesentaric infarctions - leads to hyperemic mesentary (very red) - out of proportion abdominal pain
3 main players in motility
- Enteric Nervous System Innervation
- ANS Innervation
- Intestinal Smooth Muscle
enteric nervous system: where is it? where does it come from?
Lies entirely within the walls of the gut; it’s the intrinsic innervation of the gut; a division of the autonomic nervous system
what is the intrinsic vs extrinsic innervation of the gut?
intrinsic: enteric nervous system
extrinsic: ANS (sympathetic and parasympathetic)
regulation of the two enteric system networks/plexus (myenteric and submucosal) are from what 3 things?
Regulation occurs by local influences, input from the ANS, and communication between the two
A system of ganglionic cells that extend along the length of the gastrointestinal wall.. is known at the what?
enteric nervous system
myenteric (aeurbach) plexus: location and purpose?
Located between the circular and longitudinal muscle layers
Mainly concerned with motility along the length of the gut (because it’s between two layers of muscle)
what are the two enteric networks/plexuses? which works along the entire length and which only some segments?
myenteric (auerbach)- entire length (small and large intestine)
submucosal (meissner) - segments
submucosal (meissner) plexus : location and purpose ?
Located between the mucosal layer and the circular muscle layer of the intestinal wall
Mainly concerned with controlling the function of each segment of intestinal tract
the submucosal plexus Integrates signals received from the mucosal layer into ____, _____ and _______
local control of motility, intestinal secretions, and absorption of nutrients
parasympathetic mainly supplied by what? stimulation = ?
vagus nerve ( w/ postganglionic neurons in myenteric nas submucosal plexuses) and the pelvic nerve
stimulation: excitatory: increased motility and secretions
what is the vagus vs pelvic nerve responsible for?
Vagus nerve responsible for parasympathetic innervation of: Stomach Ileum and Small intestine Cecum Ascending colon Transverse colon
Parasympathetic Fibers of the Pelvic nerve responsible for
Remainder of the colon
sympathetic stimulation of the gut is largely excitatory or inhibitory
inhibitory (decreased motility and secretions )
sympathetic stimulation of the GI through…
thoracic chain of the sympathetic ganglia
4 parts of thoracic ganglia
Celiac Ganglia, Superior mesenteric ganglia, Inferior mesenteric ganglia, and hypogastric ganglia
sympathetic control is largely mediated by altering the activity of ____, to do what 4 things ?
intramural neurons: Controls mucous secretion Reduces motility Enhances sphincter function Increases the vascular smooth muscle tone of the blood vessels that supply the GI tract
Movement of food particles along the alimentary canal is done through ______
Motion is influenced by_____, ______ and ______ influences
smooth muscle contraction
local, humoral, and neural
3 types of movements ?
Tonic movements
Rhythmic movements
Peristaltic movements
tonic movements
continuous movements that last min to hrs- occur at sphincters
rhythmic movements
intermittent contractions: churning food and presenting it to the surface area of the GI tract for max abs
peristaltic movements
rhythmic propulsive movements
force contents forward.
what is pacemaker-generated smooth muscle?
Involuntary muscle- its activity arises spontaneously or through the activity of the autonomic nervous system.
what does the “Greater tension development” for smooth muscle mean?
they can be stretched far.. unlike skeletal muscle where when theyre stretched too far, they lose the ability to contract
smooth muscle contraction is initiated by what?
influx of Ca+
smooth muscle is present in all of the GI tract EXCEPT what?
except pharynx, upper 1/3 of esophagus, and external anal sphincter
mechanoreceptors vs chemoreceptors of the GI tract, what does each monitor?
mechano: Monitor the stretch and distention of the gut wall; distention of the bowel is the main stimulus for relaxation of the sphincters of the gut
Chemo: Monitor the chemical composition of the GI contents (i.e. pylorus to duodenum)
what cranial nerves are part of the swallowing reflex?
CN 5,9,10 and 12 are part of swallowing reflex
trigem, glossopharyngeal, vagus, hypoglossal
The swallowing reflex is a rigid sequence of events that starts off ______, but becomes _______ as it reaches the pharynx
voluntary, involuntary
3 phases of swallowing
Three phases:
- Oral phase (voluntary) - food pushed to the back of the mouth where tongue lifts food to touch posterior pharynx
- Pharyngeal phase- epiglottis in place, bolus is moved backward through constrictive movements of the pharynx (swallow)
- Esophageal phase- walls stretch = peristalsis is initiated
swallowing reflex happens in the ____ of the brain, if a pt can’t swallow what might you worry about?
medulla/pons
-a stroke in this area
Pacemaker of the stomach is in the____ and peristalsis moves toward the _____, this contracts and occludes the ______ and sends the chyme back in the opposite direction.
middle/body
antrum
pyloris
(the churning of food stuff)
what kind of sphincter is the pyrolis?
physiologic
Hormonal mechanisms can also control gastric emptying in response to what?
pH, osmolar and fatty acid composition of the chyme
two hormones to regulate gastric emptying: what are they and what do they do?
Cholecystokinin (regulates the contraction of the gallbladder in order to secrete stored bile)
Glucose-dependent insulinotropic peptide (AKA gastric inhibitory peptide) increases insulin secretion and decreases H+ secretion
2 patterns of movement in the small intestine
peristalsis: move food along
segmental contractions: churn food and expose it to intestinal wall for absorption
Peristalsis starts in the duodenum at ____ and continues but slows down in the ileum to _____
(these are Smooth muscle contractions)
12/min
9/min
segmental waves/contractions are what type of muscle activity ?
Circular muscle activity
Stretch at the distal ileum causes…
ileocecal valve to relax and allows the fluid to enter the cecum.
colonic motility: two types of movements
haustrations and propulsive mass movements
haustrations
Caused by small segments of haustra (“sacculations”) which produce a “digging” type movement designed to introduce all the contents to the bowel wall.
propulsive mass movements
Propulsive movement caused by large segment constriction that moves the fecal matter forward
Normally initiates defecation.
defecation is controlled by ___ and ___ sphincters
internal and external
internal sphincter for defecation
involuntary
thickened smooth muscle inside anus
external sphincter for defecation
voluntary
striated muscle
two types of defecation reflexes
intrinsic myenteric reflex (mediated by enteric system)
and parasympathetic reflex
intrinsic myenteric reflex for defecation
Initiated by distention of rectum sends impulses to increase the peristaltic waves in descending & sigmoid colon and rectum
parasympathetic reflex for defecation
Nerve endings in the rectum are stimulated –>signals go to the sacral spinal cord and reflex back by way of the pelvic nerves to the descending & sigmoid colon, rectum and anus
Increase peristaltic waves and relax the internal sphincter.
external sphincter is controlled by…
pudendal nerve (S2-S4) which is controlled by the cortex (voluntary)
how does one control defecation- saving for “appropriate” times. ?
dont wanna poop: cortex inhibits the parasympathetic efferent impulses and constricts the external sphincter.
want to poop: Afferent impulses are easily fatigued – voluntary re-initiation of afferent impulses by abd contraction when more convenient to defecate
