Chapter 6 Flashcards
5 major organs involved with digestion
the liver, gallbladder, pancreas, spleen, and stomach
Gastrointestinal Tract (GIT), other names:
alimentary tract or gut
continuous muscular tube that winds through the body from the mouth to the anus
GIT
Organs of the GIT
mouth, pharynx, esophagus, stomach, small intestines, large intestines, and anus
Accessory organs of GIT
teeth, tongue, gallbladder, salivary glands, liver, and pancreas
Food becomes less complex as it
goes through the GIT
activity of the GIT is controlled by
chemical and mechanical stimuli
chemical stimuli
pH levels or presence of certain substrates
mechanical stimuli
stretching of organs as digesta passes through
different mechano- and chemoreceptors are activated, glands within the GIT are either inhibited or activated resulting
in increase of digestive juices into the lumen or hormones into the blood
Smooth muscles are stimulated to
contract, thus mixing luminal contents (digesta and juices) and moving them through the GIT
gut’s brain
GIT’s nerve plexus, called enteric nervous system located in the walls of the GIT
Intrinsic nerve plexus
enteric nervous system
the intrinsic nerve plexus communicates with
the extrinsic nerve plexus, which is outside of the GIT and relays those signals to the central nervous system
Vagus nerve, pelvic nerves and sympathetic pathways
provide connections between the two plexus (intrinsic and extrinsic nerve plexus)
2 common NT that help facilitate signals during different types of autonomic responses
Acetylcholine relays parasympathetic signals, while epinephrine relays sympathetic signals
if the vagus nerve or sympathetic signals were severed, could the GIT function?
Yes because of “gut’s brain”
if the enteric nervous system were severed, would the GIT function?
the GIT would be in a lot of trouble
Gastric secretion, 3 phases:
phase 1: cephalic
phase 2: gastric
phase 3: intestinal
Cephalic phase
condition response, which means that it is an automatic response to certain triggers
examples of the cephalic phase
aroma, taste, sight, and even thoughts revolving food could, begins before food is ingested
primer stage that prepares stomach for the incoming digesta
cephalic phase
What is going on during the cephalic phase?
olfactory receptors and taste buds send sensory input to the hypothalamus, which then stimulates vagal nuclei of the medulla oblongata within the brain, less than 50% of the total response of gastric secretion
during depression
patients are not hungry and have a suppressed appetite, which inhibits cerebral cortex function related to stimulating the parasympathetic centers
Gastric phase
at least 50% of the total response, it can last from 3-4 hours
Gastric phase stimulus
stomach distension and the presence of food chemicals, & rising pH within the stomach
Stomach distension activates activate stretch receptors
which then signals the medulla to send parasympathetic signals via the vagus nerve to the stomach
The presence of food stimulus
G cells present in the stomach to release gastrin in the blood
An important hormone that stimulates gastric function
Gastrin
if pH becomes too excessive (pH<2)
the G cells are inhibited from releasing gastrin
too much acidity can cause
damage to the GIT, it is important that the body regulate the acidity produced within the stomach
Emotional stress (any stress) can
inhibit gastric secretions because of the subsequent increased sympathetic stimulation that would override the parasympathetic stimulation
Intestinal phase is made up of:
stimulatory and inhibitory components
“off switch” phase needed to inhibit gastric secretions
intestinal phase
as digesta leaves the stomach and enters the duodenum of the small intestines
there is an initial increase in stomach secretions
nutrients
lipids, carbohydrates and proteins
as nutrients enter the duodenum
intestinal cells release gastrin, G cells in the stomach are stimulated in the same way to release gastrin (from G cells)
Intestinal gastrin
will increase gastric secretions and gut motility, but short-lived
as duodenum stretches
enterogastrones are released in response to the duodenal destension and these hormones initiate the inhibitory component, thus triggering the enterogastric relfex
the same stimulus for a brief increase in gastric secretion is also the same stimulus that begins inhibiting the gastric secretions by
inhibiting vagal nuceli in the medulla (which sends parasympathetic signals) and inhibiting the pyloric sphincter, which simulate enterogastric reflex.
enterogastric reflex
A nervous reflex whereby stretching of the wall of the duodenum results in inhibition of gastric motility and reduced rate of emptying of the stomach. It is a feedback mechanism to regulate the rate at which partially digested food (chyme) leaves the stomach and enters the small intestine
Cells in the stomach
mucous neck cells, parietal cells, chief cells, and enteroendocrine cells
gastric glands
location of cells
gastric pits
location of gastric glands, mucosa layer of the gastric tissues
mucous neck cells
secrete mucous and help coat and protect the stomach lining from its acidic contents
parietal cells
secrete HCl acid as well as intrinsic factor
HCl acid
important for breakdown of foodstuffs
intrinsic factor
is required for vitamin B12 absorption in the small intestines
Vitamin B12
cannot be synthesized de novo in the body, yet it is still needed for brain and nervous system maintenance as well as red blood cell formation.
cheif cells
produce lipases and pepsinogen, an inactive form of pepsin
Lipases
breakdown fats
pepsinogen
breaks down proteins once it it has been activated by HCl acid into pepsin
enteroendocrine cells
releases hormones such as gastrin, somatostatin, and serotonin
different regions of stomach
fundus, cardia, body, pylorus
cardiac glands
located within the cardiac region where digesta enters the stomach from the esophagus, are important for mucus secretion
cardiac region contain
mucus neck cells as well as some endocrine cells
fundic glands
found in both the fundus and body, are important for HCl acid and pepsinogen production because the bulk of digesta break down would be occurring in the central portion
fundus and body region contain
parietal cells and cheif cells, mucous cells and endocrine cells
pyloric glands
concentrated near where the digesta exits the stomach and enters the duodenum, contain mucus neck cells and G cells primarily
gastrin stimulates
HCl secretion in the stomach and muscular contractions of the small intestines, its released from G cells
Lysozymes
released from the epithelial cells of the pylorus and is important because of its antimicrobial activity
2 acts of defense in the GIT
HCl acid and lysozyme
histamine
can act as a NT, & is released from enterochromaffin-like cells activate the parietal cells to release HCl
Serotonin
causes contraction of the stomach muscle, which aids in digestion
Somatostatin
stimulated by sympathetic nerve fibers, inhibits secretions of the stomach, pancreas, small intestines, and gallbladder
major inhibitor of gastrin and histamine
somatostatin
a paracrine in the stomach
somatostatin, because it signals cells in proximity
Liver
metabolism and regulation, produces bil
bile
alkaline substance that emulsify fats, digestion of lipids in the small intestine
metabolic role of the liver
it receives venous blood from the intestines carrying absorbed nutrients and thus, the liver can metabolize those nutrients.
the liver uses what to make bile?
cholesterol, triglycerides, phospholipids, electrolytes, bile salts, and bile pigments
where is bile stored?
the gallbladder until needed
Bile salts and phospholipids
are the only 2 substances of bile that specifically act on fat emulsification
when bile is needed what hormone is released?
cholecystokinin (CCK), it stimulates gallbladder contraction and sphincter of Oddi relaxation in order to released the bile into the duodenum
bile patheway
traverses through the Small Intestines, it can;
- -exit the body via fecal matter
- -be recycled by being reabsorbed in the ileum
enterohepatic circulation
recycled by being reabsorbed in the ileum in a process
if bile is recycled
the bile salts can be recirculated 2, or even 3 times during each meal
Pancreas
conjunction with insulin, the hormone released after consuming a meal that helps regulate our glucose levels
pancreatic juice
water, enzymes, and electrolytes
pancreas alkaline
pH 8, helps balance the more acidic secretions exiting the stomach
hormones acting on the pancreas?
secretin and CCK, stimulate pancreatic juice secretions
vagal stimulation in pancreas
initiate pancreatic juice release
during which phases would you suspect the greatest vagal stimulation on the pancreas to occur?
cephalic and gastric phase require vagal stimulation of the pancreas
the pancreas releases enzymes that
can breakdown every type of foodstuffs; amylases, lipases, nucleases, and proteases
amylases
break down starch
lipases
break down fats
nucleases
break down nucleic acids
proteases
break down protein
trypsin
is a protease released into the duodenum via the pancreatic duct through the ampulla of Vater
zymogen
released in inactive form
trypsinogen
inactive form of trypsin, once its released into the duodenum it comes into contact with the enteropeptidases of the brush border to be converted into its active form trypsin
trypsin can activate
its own and other inactive forms and proteases like; chymotrypsinogen and procarboxypeptidase into active forms chymotrypsin and carboxypeptidase
bile from the gallbladder
joins the pancreatic juices prior to entry into the duodenum.
Upon hormonal stimulation of CCK
the gallbladder contracts and releases bile into the cystic duct, the cystic duct joins the common hepatic duct to form the common bile duct, then going into the pancreas
bile is NOT released in the
pancreatic tissues, it joins the pancreatic duct
CCK also stimulates enzyme secretion
from the pancrease
Secretin
hormone that initiates bicarbonate is released from the pancreas
joining of the pancreatic duct and common bile duct
both bile and pancreatic juices are released together into the duodenum.
The enterogastrones, or intestinal hormones, that are released during the enterogastric reflex, include;
secretin, CCK, and vasoactive intestinal peptide (VIP), and are released in response to the presence of lipids, the promote secretions of the pancreas & gallbladder as well as inhibition
why is inhibition important in enterogastric reflex
because now that acidic chyme is entering the small intestines at a steady pace, we no longer need gastric secretions, nor would it be wise to have continued acidic secretions that could overload the small intestines
brush border
a densely packed layer of microvilli and enzymes that aid in completing the digestion of carbohydrates and proteins
intestinal glands secrete
approximately 1-2 L of intestinal juice per day, which aid in promoting the slightly alkaline environment (7.4-7.8 pH) of the intestines
intestinal juice
contains large
amounts of water and some mucus, but poor concentrations of enzymes
trigger for intestinal juice secretion
is acidic chyme
As the digesta traverses through the
small intestines
the foodstuffs become broken down and their nutrient values absorbed through the enterocytes and into the blood stream.
vasculature that carry nutrients to the liver
superior and inferior mesenteric veins
appendix
contains masses of lymphoid tissues that aid in immunity and contain bacteria which help recolonize the gut when needed.
Large intestines
absorb water, temporarily store residual digesta (~12-24 hours) before expelling it as fecal matter
bacterial flora in large intestines
result in the synthesis of B complex vitamins and vitamin K, & fermentation of indigestible carbohydrates (e.g. cellulose).
epiploic appendages
fatty “tags” that attach to the colon, and are especially concentrated in the distal regions of the colon.
-help cushion the colon, play a role in regulating metabolism, and may even carry some immune function
haustra
“bulges” in the colon that help to swish the residual digesta around to help reabsorb water and any last nutrients that may be present
teniae coli
longitudinal muscles that run along the midline of the colon and are especially prominent in the
transverse colon, help form haustra by its contraction
