digestive system
function is to break down food/drink into smaller units of absorbable nutrients which are used by your own body to generate energy
alimentary canal
structures form long tube that break down food (usually 24 hours: mouth, pharynx, esophagus, stomach, small intestine, and large intestine
accessory digestive organs
participate in digestive process but food does not pass through these structures; tongue, salivary glands, liver, gallbladder, and pancreas
ingestion
put food into mouth; extracellular process
propulsion
movement of food through canal; extracellular process
peristalsis
an organized contraction and relaxation of smooth muscle layers that propels food through the alimentary canal in one direction
mechanical digestion
physical break down of food particles; extracellular process
segmentation
contractions of smooth muscle move chyme back and forth within canal to allow mixing and further break down
chemical digestion
enzymes break down food particles; extracellular process
absorption
particles (sugars, fatty acids, etc) transported from canal into blood and lymph capillaries
defecation
indigestible products eliminated from body as feces; extracellular process
lumen
inside space of tubular structure
mucosa
innermost layer of alimentary canal and lines the lumen; has three sublayers
submucosa
second innermost layer of alimentary canal; higher concentration of collagen fibers for more support, highly vascularized, glands, submucosal nerve plexus
muscularis externa
second outermost layer of alimentary canal; two layers of smooth muscle (circular and longitudinal) and myenteric nerve plexus
serosa (visceral peritoneum)
outer surface of alimentary canal
epithelium
sublayer of mucosa; continuous with many digestive glands and functions include mucus production, absorption, protection, etc.
lamina propria
sublayer of mucosa; loose areolar connective tissue, capillary rich (absorption), MALT
MALT
mucosa associate lymphoid tissue; provides defense against bacteria
muscularis mucosa
sublayer of mucosa; thin layer of smooth muscle specializes in localized movements
submucosal nerve plexus
control of muscle cells, glandular secretions, etc
circular musclaris externa
inner layer, typically squeezes tube
longitudinal musclaris externa
outer layer, typically shortens tube; peristalsis and segmentation
serous membrane
simple squamous epithelium within a loose areolar connective tissue
adventita
fibrous CT that forms outer layer of esophagus (does not have serosa)
myenteric nerve plexus
controls peristalsis and segmentation; within muscularis externa
nerve plexuses
allow for localized response within visceral organs
oral cavity
chemical and physical digestion; stratified squamous epithelium and no muscularis externa or serosa/adventita
lips
margin between skin and oral cavity; not as keratinized as skin
teeth
accessory digestive organs
heterodont dentition
different shapes of teeth for different jobs
deciduous teeth
20 total erupt typically between ages 6 months to 6 years
permanent teeth
32 total that gradually deciduous
mandible
jaw
incisors
four pairs with one root; surface good for cutting and shearing food
canines
two pairs with one root; surface good for holding and tearing
premolars
four pairs with at least two cusps and 1 or 2 roots; rounded broad surface for grinding
molars
six pairs with four to five cusps and two to three roots; grinding surface
crown
portion of tooth above the gumline
neck
portion of tooth contained within gum tissue
root
portion of tooth contained within bone
pulp
layer of tooth composed of loose areolar CT, provides nutrients and sensation, odontoblasts
odontoblasts
create dentin
dentin
largest layer of tooth; collagen and minerals, no cells or blood vessels, harder than bone
enamel
layer of tooth that is 99% calcium; no cells or blood vessels, ameloblasts
ameloblasts
create enamel
cementum
layer of tooth that anchors tooth into place; calcified connective tissue similar to bone
cementoblasts
continually replace cementum
periodontal ligaments
dense connective tissues that attaches cementum of tooth to bony socket
cavity
enamel and dentin erode when plaques made of sugars and and bacteria form on teeth; bacteria feed on sugars and produce acids that demineralize tooth surface
root canal
when pulp of canal is infected nerves and blood vessels are removed; pulp is removed and filled
tongue
skeletal muscle covered in keratinized stratified squamous epithelium; moves food, helps mix with saliva to form bolus
filiform papilla
rough surface of tongue
fungiform and circumvallate papilla
contain taste buds
lingual frenulum
fold of mucosa layer that connects tongue to floor of mouth
tongue tied
lingual frenulum extends too far forward, tip of tongue can’t move and speech is difficult
salivary glands
accessory digestive organs; exocrine glands, produce saliva (cleans teeth, taste, digestive enzymes, mucus), serous and mucous cells
mucous cells
secrete mucus, lubricant
serous cells
secrete digestive enzymes
parotid gland and duct
largest contains serous cells, furthest away (longer ducts) more of a watery secretion
submandibular gland
approximately 50/50 serous to mucus cells; ducts open lateral to lingual frenulum
sublingual gland and duct
mucous cells with several shorter ducts that empty below tongue
pharynx
connects oral cavity to esophagus and nasal cavity
oropharynx
stratified squamous epithelium
laryngopharynx
stratified squamous epithelium
esophagus
stratified squamous epithelium; connects pharynx to stomach, mucous glands in submucosa and mucosa secrete mucus to lubricate as bolus of food passes through
upper muscularis externa of esophagus
skeletal muscle
middle muscularis externa of esophagus
mix of skeletal and smooth muscle
lower muscularis externa of esophagus
smooth muscle
stomach
mechanic and chemical digestion takes four hours to turn food into chyme, absorbs primarily water and drugs; simple columnar epithelium, abundant mucous cells
rugae
folds of mucosa that increase surface area and allow stomach to expand
sphincters
thickened regions of muscularis externa
cardiac sphincter
prevents food from moving back to esophagus
pyloric sphincter
controls release of chyme into duodenum
oblique muscularis externa
innermost; exists only in the stomach
gastric pits
regions where epithelium pushes dow into gastric gland
gastric gland
connected to lumen through gastric pit; specialized cells
mucous neck cells
parietal cells
produce/secrete HCl which destroys bacteria and gastric intrinsic factor which helps with absorption
gastric intrinsic factor
absorption and transportation of vitamin B12
chief cells
produce/secrete pepsinogen
enteroendocrine gland
releases hormones; ex. gastrin signals both parietal and chief cells
pepsin
breaks down proteins in food; created when pepsinogen (chief cells) and HCl (parietal cell) mix which is stimulated by gastrin
undifferentiated stem cells
found at junction between gastric pits and gastric glands
gastric fistula
abnormal connection between stomach and skin that left open hole into stomach
small intestine
simple columnar epithelium; 9 to 15 ft long where most absorption and chemical digestion occurs, chyme moves through peristalsis and segmentation
duodenum
shortest (5%) and busiest part of small intestine; receives chyme from stomach, digestive enzymes from pancreas and bile from liver/gallbladderj
jejunum
where majority of absorption occurs; 40%
ileum
longest portion (55%); absorption also occurs here and drains into large intestine
gallbladder
stores bile and breaks down fat; sphincters relax to let bile in; right below the right lobe of the liver
pancreas
empties directly into duodenum and adds digestive enzymes; pancreatic juices neutralize chyme
hepatopancreatic sphincter
the final control ‘valve’; controls bile and pancreatic juices
plicae circulares
easily visible folds of mucosa and submucosa in the small intestine
villi
folds of mucosa in small intestine and muscularis mucosa is responsible for localized movements; lamina propria, capillaries, lacteals
lacteals
transports fats that are too large to enter capillaries
enterocytes (absorptive cells)
transports nutrients across, majority of epithelial cells; protein pumps and endocytosis
protein pumps
move sugars, amino acids, etc
endocytosis
moves macromolecules
goblet cells
secrete mucus on to lumen to protect epithelium