6 functions of the digestive system/tract
ingestion
digestion
secretion
motility
absorption
defecation
structures of digestive tract from superior to inferior
mouth/oral cavity
oropharynx
laryngopharynx
esophagus
stomach
small intestine
large intestine/colon
rectum
colon
digestive regulation sphincters/muscles from superior to inferior
orbicularis oris
upper esophageal sphincter
lower esophageal sphincter
pyloric sphincter
ileocecal valve
internal anal sphincter
external anal sphincter
what does the upper esophageal sphincter separate
laryngopharynx and esophagus
what does the lower esophageal sphincter separate
esophagus and stomach
what does the pyloric sphincter separate
stomach and small intestine
what does the ileocecal valve separate
small intestine and large intestine
what does the internal anal sphincter separate
rectum and anus
what does the external anal sphincter separate
anus and external environment
ingestion definition
ingestion of macronutrients (carbs, proteins, and fats/lipids)
digestion definition
breakdown of macronutrients into micronutrients (can be chemical or mechanical)
secretion definition
secretions of enzymes, bile, H2O, acid, etc. are emptied into lumen of GI tract from accessory organs or cells lining organs/mucosa to perform CHEMICAL DIGESTION
motility definition
movement via smooth muscle contraction/relaxation
absorption definition
movement of micronutrients from GI tract into blood/lymph
defecation definition
elimination of waste products (feces)
4 main tissues of the digestive system
nonkeratinized stratified squamous epithelium
simple columnar epithelium
skeletal muscle
smooth muscle
locations of nonkeratinized stratified squamous epithelium
mouth/oral cavity
oropharynx
laryngopharynx
esophagus
anus (more external region)
function of nonkeratinized stratified squamous epithelium
protection against abrasion
locations of simple columnar epithelium
stomach
small intestine
large intestine/colon
rectum
anus (more internal region)
function of simple columnar epithelium
secretion and absorption
2 specific structures of simple columnar epithelium
goblet cells → mucus (protects against acidity)
microvilli → increase surface area and therefore absorption
locations of skeletal muscle
orbicularis oris
upper esophageal sphincter
external anal sphincter
what branch of nervous system is skeletal muscle innervated by
somatic NS
what branch of nervous system is smooth muscle innervated by
autonomic NS
locations of smooth muscle
lower esophageal sphincter
pyloric sphincter
ileocecal valve
internal anal sphincter
sympathetic NS effects on digestion
innervate smooth muscle and halts digestion, tonic contraction
parasympathetic NS effects on digestion
helps promote digestion, relax smooth muscles via vagus nerve (CN X)
locations of ingestion
mouth/oral cavity
locations of digestion
mouth/oral cavity
stomach
small intestine
large intestine (if leftovers)
locations of secretion
mouth/oral cavity → salivary glands
stomach → cells in mucosa
small intestine → liver, gall bladder, pancreas
large intestine → H2O
locations of motility
oropharynx/laryngopharynx (peristalsis)
esophagus (peristalsis)
stomach (peristalsis and segmentation)
small intestine (peristalsis and segmentation)
large intestine (peristalsis)
peristalsis
propulsion of contents along length of GI tract (→)
segmentation
locations of absorption
mouth/oral cavity
stomach
small intestine (majority)
large intestine (water balance)
4 layers of GI wall
mucosa
submucosa
muscular layer
serosa
mucosa
linine of the lumen
has epithelial cells
specific secretory/absorptive cells
capillary beds that receive absorbed nutrients (blood/lymph)
submucosa
connection b/w layers
areolar CT
continuation of blood and lymphatic vessels
submucosal plexus of enteric NS
what plexus innervates the submucosa
submucosal plexus of enteric NS
muscular layer
2 layers of muscle
inner: circular layer → contraction and decrease diameter of lumen (segmentation)
outer: longitudinal layer → contraction is key for peristalisis
myenteric plexus of enteric NS
what plexus innervates the muscular layer
myenteric plexus of enteric NS
what type of motility is the inner/circular layer of muscular layer responsible for
segmentation
reduces diameter of lumen
what type of motility is the outer/longitudinal layer of the muscular layer responsible for
peristalsis
what serous membrane lines the surface of digestive organs
visceral peritoneum
what serous membrane lines the abdominal cavity
parietal peritoneum
function of peritoneal folds
anchor organs and serve as a pathway for nerves and vessels
what are the 3 types of peritoneal folds
greater omentum
lesser omentum
mesentery
what is ingestion controlled by in the oral cavity/mouth
orbicularis oris and temporomandibular joint
what is the goal of mechanical digestion in the oral cavity/mouth
physically break down macronutrients to form a bolus that can be swallowed
absorbable nutrients of the 3 macronutrients
carbs → monosaccharides (ex. glucose)
proteins → amino acids
fats → fatty acids
what structures and muscles are involved in mechanical digestion in the mouth/oral cavity
palate/cheeks
lips, teeth, tongue/genioglossus (skl. muscle)
muscle of mastication/chewing
temporalis
masseter
goal of chemical digestion in the oral cavity/mouth
salivary glands secrete saliva through ducts into oral cavity to begin breakdown of macronutrients to micronutrients via enzymes
components of saliva
H2O, ions, mucus, lysozymes
salivary amylase
lingual lipase
what are lysozymes
enzymes that break down
what is the function of mucus and H20 in saliva
to moisten the food
where is salivary amylase secreted
oral cavity
where does salivary amylase act
oral cavity
where is lingual lipase secreted
oral cavity
where does salivary amylase act
stomach
what does salivary amylase do
acts on carbs
breaks starches/polysaccharides down into disaccharides
what is salivary amylase regulated by
Cl- stimulates salivary amylase
stomach acid stops it from acting
what does lingual lipase do
acts on fats
breaks triglycerides down into fatty acids and glycerol
what is lingual lipase regulated by
stomach acid stimulates lingual lipase
overall main goal of oral cavity
start carb digestion (enzymatic)
mechanical formation of bolus
tissue type of mucosal lining of hard palate
nonkeratinized stratified squamous epi
what two bones form the hard palate
maxilla (anterior) & palatine (posterior)
location of esophagus
in thoracic cavity
posterior to trachea
tissue type of mucosal lining of esophagus
nonkeratinized stratified squamous epi (protect)
tissue type of submucosal lining of esophagus
areolar CT
tissue type of muscular layer of esophagus
superiorly in upper e. sphincter → skeletal muscle
inferiorly in lower e. sphincter → smooth muscle
along length of esophagus for peristalsis → smooth muscle
what layer is in the esophagus differs from normal structure
there is no serosa, instead it is the adventitia
what is the tissue type in the adventitia of the esophagus
only areolar CT (no simple squamous like in other serosa layers)
main overall goal/function of esophagus
no digestion or absorption only motility/conduction
when the bolus is pushed to the ------- region of the oral cavity by the tongue, it causes ------- of the oropharynx (voluntary)
posterior; distension
receptors in the ------- detect the distention of the oropharynx
oropharynx
what is the control center for the “bolus reflex arc”
pons and medulla
5 responses of the “bolus reflex arc”
tongue and soft palate elevate
epiglottis depresses
upper esophageal sphincter
peristalsis
lower esophageal sphincter
why does the tongue and soft palate elevate in “bolus reflex arc”
closes off nasopharynx and nasal cavity
allows bolus to move through oropharynx
why does the epiglottis depress in “bolus reflex arc”
closes off larynx and airway
bolus moves into laryngopharynx
why does the upper esophageal sphincter relax in “bolus reflex arc”
bolus moves into esophagus (decrease somatic innervation)
in order for the upper esophageal to relax we have to decrease
somatic innervation
why does peristalsis occur in in “bolus reflex arc”
allow bolus to move down the esophagus
smooth muscle for peristalsis is innervated by what nervous system
parasympathetic NS
in order to increase peristalsis we would increase innervation from (sympathetic/parasympathetic)
parasympathetic
why does the lower esophageal sphincter relax in the “bolus reflex arc”
allows bolus to enter stomach
to relax the esophageal sphincter we have to
increase parasympathetic NS
decrease sympathetic NS
5 functions of the stomach
reservoir for food/liquids
mechanical digestion
chemical digestion
secretion of hormone gastrin in blood
absorption of H2O, ions, fatty acids, aspirin, and alcohol
what do surface and neck mucous cells secrete
secrete mucus
function of mucus secreted by surface and neck mucous cells
coat surface of mucosa for added protection
what do parietal cells secrete
intrinsic factor
Hydrochloric acid (HCl)
function of intrinsic factor secreted by parietal cells
helps with vitamin B12 absorption in the small intestine
function of HCl secreted by parietal cells
protein digestion and kill microbes
what do chief cells secrete
pepsinogen (inactive form of pepsin)
gastric lipase
what is the function of pepsinogen secreted by chief cells
once active as pepsin it helps with protein digestion
what is the function of gastric lipase secreted by chief cells
fat digestion
what do G-cells secrete
gastrin
what is the function of gastrin secreted by G-cells
stimulate stomach activity
contract lower esophageal sphincter
increase motility
stimulate parietal and chief cells
relax pyloric sphincter
chemical digestion overview in the stomach: carbs
no chemical digestion of carbs in stomach
chemical digestion overview in the stomach: proteins
proteins begin being broken down into peptides
pepsinogen (inactive) → pepsin (active) → +protein digestion
needs HCl to activate pepsinogen
chemical digestion overview in the stomach: fats
fats broken down into monoglycerides and free fatty acids
lingual lipase (HCl is needed to stimulate)
gastric lipase
what structures are on the apical surface of a parietal cell
H-K ATPase’s (proton pumps)
K+ channels
Cl- channels