Digestion 1: Function & Structure Flashcards
What are the functions of the digestive system?
1) supply: water, electrolytes, nutrients to the body
2) motility: move materials from 1 part to another, remove waste
3) absorption
4) defense: prevent infection & autodigestion
majority of the lymphoid tissues is found…
scattered throughout the Gi tract
we have ___ and ____ at the back of the throat for defense
tonsils;
lymphoid tissues
GALT
gut associated lymphoid tissues
What structures make up the digestive system?
1) tubular GI tract: esophagus, stomach, small & large intestines
2) accessory organs: teeth, tongue, salivary glands, liver, gall bladder, pancrease
Purpose of the mouth
receptacle for food
what happens in the mouth?
- tongue: taste & guide food to pharynx
- teeth: mechanical digestion
- salivary amylase & salivary lipase (minimal digestion)
- forms bolus
what secretes saliva?
salivary glands
what does saliva contain?
- antibacterial factors
- mucus
- salivary amylase & salivary lipase
pharynx is located…
at the back of the throat
purpose of pharynx
push food into esophagus
___ protects the larynx during swallowing
epiglottis
the swallowing reflex begins at…
pharynx
what feature of the pharynx makes swallowing very easy?
epithelial walls are closely adherent to the sides, making the lateral surface very flexible
function of esophagus
moves food into stomach (peristalsis)
which muscles are present in the esophagus?
beginning: striated muscles (voluntary)
end: smooth muscles (involuntary)
sphincters of the esophagus
beginning: upper esophageal sphincter
end: lower esophageal sphincter
sphincters of the esophagus control…
movement of materials through the esophagus
esophagus passes through the ___. what are the implications?
thorax;
inhaling will suck food upwards -> this is prevented by the esophageal sphincters
functions of the stomach
- temporarily stores ingested food
- secretes enzymes for digestion
- mechanical digestion
- slowly empties chyme into small intestines
the entire GI tract has a layer of ____ and ___ muscle
circular;
longitudinal
stomach muscles
- circular layer
- longitudinal layer
- oblique muscle layer
exit of chyme into the small intestines is controlled by…
pyloric sphincter
the pyloric sphincter checks …. before allowing food to exit the stomach
- pH
- liquid content
- size of particles
…in chyme
sections of the small intestines
- duodenum
- jejunum
- ileum
how does food move forward in the small intestines?
- peristalsis
- segmentation
main area of digestion and absorption?
small intestines
most of the enzymes secreted in the small intestines break down ____
macromolecules
absorption of nutrients occurs passively // actively
passively, once the micromolecules are small enough
amount of absorption depends on…
time that is spent in small intestines
digestion in the small intestines is aided by secretions of…
- liver (via gall bladder) → bile salts
- pancreas → pancreatic enzymes, bicarb
liver is connected to gall bladder by…
common hepatic duct
gall bladder secretes things into the small intestines by…
common bile duct
entrance of material from gall bladder & pancreas to small intestines is controlled through…
sphincter of oddi
secretions of the pancreas & gall bladder is influenced by…
hormones
segments of the large intestines
- ascending colon
- transverse colon
- descending colon
- sigmoid colon
- rectum
how is fecal matter moved in the large intestines?
- segmentation
- mass movement
what happens in the large intestines?
- absorption of water & electrolytes
- storage of fecal material for expulsion
entrance to the large intestine is controlled by…
illeocecal VALVE (not sphincter)
the small intestine is large in ____, while the large intestine is large in ____
length;
diameter
how is excretion of poop controlled?
internal & external sphincters
muscles of the large intestine
- circular layer
- 1 strip of longitudinal muscle = taenia coli
All circular muscles gather along taenia coli, forming haustra (bulges)
bulges in the large intestine =
haustra
layers of the GI tract
- mucosa
- submucosa
- muscularis externa
- serosa
mucosa is made up of…
- epithelial walls
- lamina propria
- muscularis mucosae
lamida propria
thin layer of connective tissues that have fibroblas, myofibroblasts
muscularis mucosae
- waves the villi
- helps more mucus come out
submucosa is made up of…
- Thick, dense layer of connective tissue
- Blood vessels
- Embedded glands
muscularis externa is made up of…
longitudinal & circular muscles
- partial oblique muscle in stomach only
serosa layer is made up of…
mesentary system
2 components of the enteric nervous system
- submucosal plexus
- myenteric plexus
mesentary system
double membrane tissue that surrounds the GI tract and attaches it to the rear wall of abdominal cavity
specialized cells of the mucosa
- epithelial cells / transport cells (parietal, goblet, paneth cells)
- enteroendocrine cells
- exocrine cells (goblet cells, paneth cells)
epithelial cells in the mucosa are responsible for…
- secretion: acid, bicarb
- absorption: nutrients, water, vit
enteroendocrine cells
cells that secrete hormone in the GI tract
exocrine cells of the mucosa are responsible for…
secreting enzymes, mucus, anti-microbials, etc.
goblet cells
secrete mucus
paneth cells
secrete anti-microbial compounds
parietal cells
secrete HCl
where are paneth cells olcated?
at the bottom of the crypt
what cell is responsible for immunity/defense in the GI?
paneth cells
cells in the GI have a short // long lifespan?
short
what is used to replace cells in the GI? Where are they located?
stem cells;
bottom of crypt → move to top of crypt as it differentiates
ENS
enteric nervous system
neurons in the ENS
- sensory
- interneuron
- parasympathetic ganglia
- sympathetic postganglionic fibres
myenteric plexus
regulates motility
myenteric plexus is also known as…
Auerbach’s plexus
submucosal plexus is also known as…
Meissner’s plexus
submucosal plexus
regulates secretion and absorption
2 main networks of the ENS
- myenteric plexus
2. submucosal plexus
where is the myenteric plexus located?
between the circular & the longitudinal layer
where is the submucosal plexus located?
in the submucosa
How is the activity of the digestive system regulated?
short (ENS) & long (CNS) reflexes
receptors/sensors in the ENS
- mechanoreceptors: stretching of stomach
- chemoreceptors: sense digestion products
how does the stomach send information to the CNS (long reflex)?
vagus nerve
response from long reflex
- enhance secretion & motility
- change motility & secretion pattern
response from short reflex
- enhance secretion & motility
- change motility & secretion pattern
2 ways the ENS/CNS can be stimulated
- presence of food
2. cephalic phase of digestion (thinking/smelling/seeing food)
smelling food sends information to ___ receptors, which then sends info to ___
sensory;
the cephalic brain
how does the cephalic brain send information to secretory cells of the stomach & small intestines?
via neurons of the myenteric & submucosal plexus
release of insulin & glucagon is controlled by the short // long reflex?
long
parasympathetic control is divided into…
- cranial division (vagus nerve)
2. sacral division (Pelvis nerve)
PNS has what effect on digestion?
increase digestion
- increased motility & secretion
- relaxes sphincters
cranial division of PNS connects to…
- esophagus
- stomach
- small intestines
sacral division of PNS connects to…
- large intestines
2. rectum & anus
Steps of PSN control, starting with preganglion neurons and ending with NT secretion
- pre-ganglion neurons synapse on ganglionic neurons in ENS
2. post-ganglionic fibres secrete ACh
distribution of SNS control
evenly distributed throughout GI
SNS post-ganglionic fibres release…
noradrenaline
SNS generally has what effect on digestion?
- inhibit gut movement
- reduce secretions
- cause sphincters to contract
SNS pre-ganglionic fibres release…
ACh
the SNS pre-ganglionic fibres connects to…
prevertibral ganglia
- celiac
- superior mesenteric
- inferior mesenteric
what changes in the GI regulate activity?
Local factors → secretory & enteroendocrine cells
- pH
- physical / chemical stimuli
Hormones → secretion & motility patterns
Neural mechanisms (myenteric/submucosal plexus)
- short reflex: input from stretch & chemoreceptors
- long reflex: input from CNS
first layer of control in the ENS is by…
local stimuli
sweet taste receptors activate ___, which increase of ___ (this increases glucose uptake from intestinal lumen)
G-proteins;
incretins
GIP
glucose-dependent insulinotropic peptide
GLP-1
glucagon-like peptide
enterocytes
epithelial cells found in the GI tract
2 peptides which stimulates the release of insulin
1) GIP
2) GLP-1
Sweet taste receptor is…
dimer of T1R2 and T1R3
sweet taste receptors can be found…
- in the mouth
- on enteroendocrine cells in the stomach
INCRETINS
general term for GI hormones that stimulate insulin release
incretins are secreted by ___ cells
enteroendocrine
Where does incretins act?
goes through circulatory system → pancrease
local effect of incretin
influence local enterocytes:
- more Na/glucose transporters
- more glucose uptake
- bring more glucose to enterocytes
___ circulation = blood flow from heart to digestive system
splanchnic circulation
what vessels bring blood to and from the digestive system?
- hepatic artery / hepatic vein
- digestive tract arteries / hepatic portal vein
SPLANCHNIC
general term for internal orgains
PORTAL SYSTEM
circulatory system from 1 capillary bed to another
all blood from the digestive tract passes through the ____ before entering the ____ → ____
liver;
hepatic vein;
inferior vena cava
arteries leading to stomach
celiac artery (left & right gastric arteries)
arteries leading to small intestines
- superior mesenteric artery
- hepatic artery (→liver)
- small artery that goes to gall bladder
arteries leading to large intestines
superior & inferior mesenteric arteries
____ artery supplies blood to majority of the small & large intestines
superior mesenteric
___ arteries supply blood to most of the digestive system (though not a main force)
inferior mesenteric
capillaries in the villi is used for…
- gas exchange
- transport soluble nutrients
- transport water & electrolytes
what is used for fat absorption? where does it go?
central lacteal;
lymphatic system
LACTEAL
projections of the lymph system
function of hepatocytes
- remove potentially harmful agents
- filters & processes the blood
blood from the hepatic portain vein & hepatic artery pools in the ____ → _____ vein → drain into ______
sinusoid;
central;
hepatic vein
SINUSOIDS
slight enlargement of capillaries
bile exits hepatocytes through ___, which then drains into ___ and is stored in the gall bladder
bile canaliculi;
bile ductules
functions of the liver
- glucose & fat metabolism
- protein synthesis
- hormone synthesis
- urea production
- detoxification
- storage
liver sends … via the hepatic vein
metabolites to peripheral tissues
- glucose
- plasma proteins (albumin, clotting factors, angiotensionogen)
- urea
- vit D, somatomedins
- metabolites for excretion
liver sends … via the bile duct
things secreted into duodenum
- bile salts
- bilirubin
- water, ions
- phospholipids
…. enters the liver via hepatic portal vein
things absorbed from GI tract
- bilirubin
- nutrients
- drugs
- foreign substances
… enters the liver via hepatic artery
metabolites & drugs from peripheral tissues
- bilirubin
- metabolites of hormones & drugs
- nutrients
