24 - Digestive System

What is the digestive tract?

gastrointestinal/GI tract, alimentary canal, tub (mouth → anus)

• includes oral cavity, pharynx, esophagus, stomach, small/large intestine

What are accessory organs of the digestive system?

tongue, teeth, salivary glands, pancreas, liver, gallbladder

What are functions of the digestive system?

ingestion & mastication, propulsion & mixing, secretion, digestion, absorption, elimination

What are characteristics of propulsive movements?

swallowing, peristalsis, mass movements in intestine

What is deglutition?

swallowing, moves food/liquid bolus from oral cavity → esophagus

• partially voluntarily & automatic

What is peristalsis?

moves material through tract

• contraction behind bolus

• relaxation in front of bolus

What are mass movements in instestine?

3-4 contractions t/o day → push into distal area of colon

What are the 2 major types of mixing?

• mixing waves in stomach

• segmental contractions in SI

  • goal = get homogenous mix

How does the digestive system secrete?

lubricates, liquefies, digests

• use mucus, water, enzymes

What are the 2 types of digestion?

• mechanical → chew, muscular segmentation

• chemical → acids & enzymes

What is absorption?

movement from tract into blood/lymph

What is elimination?

waste products/feces removed from body through defecation

What are peristaltic waves?

muscular contractions consisting of a wave of relaxation of circular muscles in front of bolus

What follows peristaltic waves?

wave of strong contraction of circular muscles behind bolus

• force bolus along digestive tract

• proximal contract, distal relax

• 1st - wave of relaxation, 2nd - wave of contraction

How do peristaltic waves travel?

each wave travels length of esophagus in 10 sex

• waves in small & large intestines travel only short distances

How do segmental contractions work?

1. bolus/mass of chyme start position

2. alt contract & relax in adjacent areas

3. mass of chyme/bolus spread out in both directions/dilutes

How is the enteric NS involved in segmental contractions?

feel stretch, find bolus center squeeze & split

What are the 4 layers of mucosa?

mucous epi, lamina propria (loose CT), muscularis mucosae, submucosa

What is mucous epithelium?

• nonkeratinized stratified squamous epi → mouth, oropharynx, esophagus, anal canal

• simple columnar → rest of GI tract

What is muscularis mucosae?

smooth muscle

Where does mucosa extend into?

lamina propria in places to form intestinal glands or crypt

What are specialized cells of the digestive tract?

• mechanoreceptors to control peristalsis

• chemoreceptors for chemical digestion

What is submucosa?

thick CT layer w/ nerves, BVs, lymphatics, small glands

What is the submucosal plexus?

Meissner plexus → network of neurons & glial cells of enteric NS

• control release of intestinal gland secretions

What lacks the submucosal plexus?

esophagus & stomach

What is the muscularis?

2-3 layers of smooth muscle

• circular & longitudinal layers

• has myenteric plexus

What is the myenteric plexus?

Auerbach plexus, b/w circular & longitudinal layers of muscularis

• controls movements along GI tract

• interstitial cells w/in

What are the interstitial cells of the myenteric plexus?

form network of pacemakers to promote rhythmic contractions

What is the enteric nervous system made of ?

submucosal & myenteric plexuses

What is serosa?

CT, visceral peritoneum present

What is adventitia?

outer layers derived from adjacent CT

What is local nervous regulation of the digestive system?

enteric nervous system, coordinates peristalsis, regulates local reflexes

What is general nervous regulation of the digestive system?

CNS → sight, smell, taste can trigger reflexes

• mainly parasymp

• symp → inhibits muscle contraction, secretion, & blood flow to digestive tract (shuts down)

Why does sympathetic stimulation shut down digestion?

reroutes blood & E to necessary muscles → neural & blood flow

What are major ENS NTs?

• Ach → stim

• NE → inhibits

• serotonin → stim digestive motility, 95% body’s serotonin found there, satiety = feel good

Which hormones are produced in the digestive tract?

gastrin, secretin

What is peritoneum?

double layered, continuous watery/serous membrane

• visceral & parietal

What is visceral peritoneum?

covers organs

What is parietal peritoneum?

covers interior surface of body wall

What is retroperitoneal peritoneum?

some organs covered on only 1 surface → behind peritoneum

• ex → kidneys, pancreas, duodenum

• lines body wall, sneaks behind them/organ & rejoin body wall

What is peritonitis?

inflammation of peritoneum

• incomplete dx → only says inflammation, need to address cause

What are mesenteries?

2 layers of mesothelium w/ thin layer of loose CT b/w → single continuous organ

• 1 big 2 layer thing wrapping around things then rejoining

• make pathway for VLAN to go to diff organs

What is the mesenteric root?

point where mesentery attaches to posterior abdominal wall

How is the mesentery useful?

routes for vessels & nerves to pass from body wall to organs → parietal peritoneum

What are the 6 regions of the adult abdominal mesentery?

LI → R & L mesocolon, transverse mesocolon, mesosigmoid, mesorectum

SI’s mesentery

What is the mesentery of the small intestine?

mobile, attaches portions of jejunum & ileum to post abdominal wall

What is the R mesocolon?

ascending, anchors R side of colon → up R from cecum

What is the transverse mesocolon?

b/w hepatic & splenic flexures

What is the L mesocolon?

descending, anchors L side of colon

What is the mesosigmoid?

mobile & fixed, attached to sigmoid colon

What is the mesorectum?

anchors rectum

What are omenta?

folds of peritoneum that support organ, large hanging & folded, come back up

• greater & lesser

What is the greater omentum?

double fold of mesentery that connects greater curvature of stomach & transverse colon

What is the lesser omentum?

connects lesser curvature of stomach & proximal part of duodenum to liver & diaphragm

What is the omental bursa?

cavity b/w 2 layers of mesentery of greater omentum

What is the vestibule?

space b/w lip/cheeks & alveolar processes w/ teeth

What is the oral cavity proper?

medial to alveolar processes → where tongue is

What lines the oral cavity?

moist non-keratinized stratified squamous epithelium

• X waterproof

• cheek, esophagus, down full tract

What are lips/labia?

orbicularis oris muscle w/in

• exterior → keratinized stratified squamous epithelium, thin, blood in dermis = red/pink color

• thickness of dermis = color

What is the labial frenulum?

mucous fold, extends from alveolar processes of maxilla & mandible to upper & lower lips respectively

What are cheeks?

lateral walls of oral cavity

• buccinator muscles → flatten

• buccal fat pads → rounds out cheek profile

What is the palate?

separates nasal & oral cavities

What is the hard palate?

anterior, supported by maxilla & palatine bone

What is the soft palate?

posterior, skeletal muscle & CT, behind

What is the uvula?

projects from posterior of soft palate → part of reflex

What are fauces?

posterior boundary of oral cavity

• cross through to throat/nasopharynx

• like chonae

What are palatine tonsils?

in lateral walls of fauces

What is the tongue?

muscular w/ free anterior surface & attached posterior surface

• covered w/ moist stratified squamous epithelium

What are intrinsic tongue muscles?

change shape

What are extrinsic tongue muscles?

protrude/retract tongue, move side to side

What is the lingual frenulum?

attaches tongue inferiorly to floor of oral cavity

What is the terminal sulcus?

groove dividing tongue into anterior 2/3, posterior 1/3

What is the anterior tongue (2/3)?

papillae → some have taste bud on them, never in

What is the posterior tongue (1/3)?

X papillae, few scattered taste buds

• lingual tonsil → lymphoid tissue embedded in posterior surface

• near epiglottis

What is dentition?

involved in mastication & speech, distributed in 2 dental arches

What are the 2 sets of teeth?

• primary/deciduous/milk → childhood

• permanent/secondary → adult (32)

What are the types of teeth in each dental arch?

• incisors (2) → med & lat

• canines (1)

• premolars (2)

• molars (3)

  • PICM 2213

What is the crown of the tooth?

enamel covered, has cusps

What is enamel?

outermost layer of anatomical structure of the tooth, providing protection and strength.

• non-living, acellular, protective

• protect against stomach acid coming up from esophagus

What are cusps?

part of crown, points

What is the neck of a tooth?

enameled part below gum line

What is the root of a tooth?

anchors tooth in bone

What is dentin?

living, cellular, calcified tissue

• in root → covered by cellular bone-like structure that helps hold tooth in socket

What is pulp cavity?

filled w/ BVs, nerves, CT, lymphatics

• pulp of root = root canal

• helps feed area w/ blood supplt

What are periodontal ligaments?

hold tooth in socket

What is gingiva?

dense fibrous CT covered by stratified squamous epi

• blocks things from getting out

What is mastication?

chewing

• incisors/canines → bite/cut

• premolars & molars grind

What is the mastication reflex?

MO controls basic movements involved in chewing

• desc pathways from cerebrum provide conscious control

• initiate chewing control → then switch to voluntary

What are the salivary glands?

3 pairs of multicellular glands → parotid, sublingual, submandibular

What is the parotid gland?

largest, serous/gradual leaking, anterior to ear

• parotid duct → crosses masseter, penetrates buccinator, enters oral cavity adj to 2nd upper molar

What is the submandibular gland?

mixed, more serous than mucous

• post half of inf border of mandible

• duct enters oral cavity on either side of lingual frenulum (tissue holding tongue to bottom of mouth)

• watery liquid, starts on sides, lower part of cheek

What is the sublingual gland?

smallest, mixed → mucous > serous (pulls up from bottom)

• each has 10-12 ducts that enter floor of oral cavity

• food drops into fluid → become bolus to push down esophagus

What salivary glands are additional?

numerous small coiled tubular glands

• lingual → deep to tongue epi

• palatine → palate

• buccal → cheeks

• labial → lips

How are salivary glands built?

compound acinar/grape line cells → mixed, serous, mucous

• release both serous & mucous fluid → produce saliva

What are the digestive functions of saliva?

• salivary amylase → starch/simple sugars

• lingual lipase → lipid digestion

• helps form bolus (combine w/ mucus) for swallowing

What causes saliva production?

parasymp input through CN VII & IX

• higher brain centers can respond to smell, thoughts, sight of good

How can saliva help prevent bacterial infxn?

washes surface, bicarb ions, lysozyme, IgA

How do bicarbonate ions in saliva act?

act as buffer to neutralize acids made by oral bact

• reduces harmful effects of bact acids on tooth enamel

Which antibacterial proteins does saliva have?

lysozyme & IgA → both have antibacterial effects

• protect against oral bact & overgrowth during traveling down

How does mucous help protect?

helps protect digestive tract from physical irritation & enzymatic digestion