GI system Flashcards
functions
ingestion
motility
digestion
absorption
secretion
ingestion
food and liquid intake into oral cavity
motility
mechanical processing: swirling, mixing, churning, propulsive motions in tract along entire tube
compaction: dehydration of undigestable material + waste into feces (colon to anus)
digestion
chemical + enzymatic breakdown of sugars, lipids, + proteins into small molecules
secretion
acids, enzymes, + buffers are secreted by accessory organs (liver + pancreas)
help digestion
absorption
movement of molecules, electrolytes, vitamins, + water into ISF → blood vessels
carried from GI tract to liver = distributed to rest of body
excretion
elimination of undigested residue + waste products
GI tract
oral cavity (salivary glands) → pharynx → esophagus → stomach → small intestine (duodenum + jejunum + ileum) → large intestine → anus
accessory organs: liver, gallbladder, pancreas
exocrine tissue
secretions into GI tube (lumen)
endocrine tissue
secretions into surrounding connective tissue → circulation
histology of GI tube
4 layers found along entirety
- mucosa
- submucosa
- muscularis externa
- serosa
mucosa
epithelium (stratified at beginning + end; simple in middle for absorption
lamina propria
muscularis mucosa
lamina propria
connective tissue
has innervation + vasculature to support epithelium
glands + immune cells
muscularis mucosa
propels content of glands (in submucosa) into lumen
submucosa
connective tissue layer
conduit for vasculature, nerves, and lymphatics
immune cells, some exocrine glands, submucosal nerve plexus
muscularis externis
external muscle layer: (skeletal at ends, smooth in the middle)
- inner circular muscle = constriction
- myenteric plexus
- outer longitudinal muscle = propulsion
myenteric plexus
autonomic parasympathetic
innervates both smooth muscle layers
controls GI motility
serosa
simple squamous epithelium + connective tissue
serous membrane = produces watery fluid to lubricate peritoneal surfaces
abdominal quadrants
direct pain
vert + horiz planes intersect at umbilicus
RUQ + RLQ + LUQ + LLQ
RUQ
liver
gall bladder
duodenum
head of pancreas
transverse colon
right kidney
LUQ
stomach
spleen
pancreas (body + tail)
jejunum
transverse colon
left kidney
RLQ
ileum
cecum
appendix
ascending colon
LLQ
ileum
descending + sigmoid colon
abdominal regions
referred pain
two vertical midclavicular planes
horiz. subcostal plane (below ribs, along L1)
horiz. intertubercular plane (tubercles of iliac crests, along L5)
epigastric, umbilical, hypogastric
peritoneum
serous membrane lining peritoneal body wall + organs
parietal (line body wall) + visceral (line organs) layers
mesentery
2 layers of serosa around vasculature
allows vasculature to reach organs for absorption
omentum
layer of peritoneum folded on itself that contains more than vasculature + innervation
greater omentum
mesentery from greater curvature of stomach to transverse colon
large pouch in front of most organs below stomach
contains fat and immune cells in addition to blood, nerves, and lymphoid tissue
lipid deposition = temp control
immunological function → cells migrate to region of infection = first immune response in abdomen
lesser omentum
mesentery from lesser curvature of stomach to liver
intraperitoneal
organs that are within peritoneum = covered by visceral peritoneum
most of GI tube, liver
retroperitoneal
organs or structures found behind peritoneum
- in abdomen but not associated with GI = kidneys, ureters
- large vessels = aorta, inf vena cava
- anchoring organs = duodenum, pancreas, asc + desc colon
- pelvic organs below peritoneum
anchoring organs
abdominal aorta
supplies organs with vasculature
branches into:
- celiac trunk = foregut
- sup. mesenteric artery = midgut
- inf. mesenteric artery = hindgut
also branches to supply retroperitoneal organs
foregut
epigastric region: abd. esophagus to desc. duodenum
- vasc = celiac trunk
- innervation = celiac ganglia (T7-T9)
midgut
umbilical region: desc. duodenum to L colic flexure of transverse colon
- vasc = sup. mesenteric artery
- innervation = sup. mesenteric ganglia (T9-T11)
hindgut
hypogastric region: transverse colon to rectum
- vasc = inf. mesenteric artery
- innervation = inf. mesenteric ganglia (T11-L1)
celiac trunk
abd esophagus
stomach
spleen
liver
gallbladder
pancreas
duodenum
superior mesenteric artery
pancreas
duodenum
jejunum
ileum
cecum + appendix
asc + transverse colon
inferior mesenteric artery
desc + sigmoid colon
rectum
renal artery
kidneys
adrenal glands
gonadal artery
ovaries/testes
venous vasculature
similar to arterial but splenic vein instead of celiac
portal vein carries blood from GI tract to liver
veins from body wall organs drain into inf. vena cava
portal vein
receives blood from splenic vein + sup+inf mesenteric veins
oral cavity
stratified squamous epithelium = protection from stress
innervation = sensory analysis
mechanical digestion (teeth, tongue, palatal surfaces, cheeks)
saliva = mixed to lubricate + start enzymatic digestion
oral vestibule
space between lips, cheeks, + teeth
“entrance” to cavity
tonsils
lymph
- pharyngeal
- palatine
- lingual
tooth - crown
above gum line
- enamel
- dentin
- pulp cavity
tooth - neck
mucosa layer
gingiva
tooth - root
bone
periodontal ligament
cement
dentin
root canals = neurovascular bundle
periodontal ligament
fibrous tissue between bone + mucosa
gomphosis = articulation between maxilla/mandible + tooth
incisors
blade-like teeth
front of mouth
clip/cut food
canines
pointed teeth
side of mouth
tears/slash food
premolars
bicuspid
back of mouth
crush/mash/grind food
large surface area
molars
multi-cuspid
back of mouth
crush/grind food
large surface area
trigeminal nerve
sensory innervation of dentition
V2 → superior alveolar nerve = maxilla (upper)
V3 → inferior alveolar nerve = mandible (lower)
deciduous teeth
baby teeth = 20
no premolars
eruption 6-24 months
shed 6-12 years
permanent teeth
32 teeth
eruption 6-18 years (fully formed before)
skeletal muscles of tongue
innervated by CN XII
intrinsic + extrinsic
intrinsic tongue mm
shape of tongue
speech
3 orientations: sup/inf longitudinal, vertical, transverse
extrinsic tongue mm
swallowing + movement of tongue
4 mm: palatoglossus, styloglossus, hyoglossus, genioglossus
tongue surface
stratified epithelium covered by papillae → taste buds found throughout
taste: CNs VII (chorda tympani) + IX
general sensation: CNs V3 + IX
anterior 2/3 and posterior 1/3 are divided by terminal sulcus (associated with oropharynx)
salivary glands
exocrine glands with ducts into oral cavity
- serous = moistens food + contains enzymes
- mucous = lubricates passage of food
parotid
sublingual
submandibular
saliva
produced even without food = control bacteria population
contains
- amylase = initiation of CHO digestion
- buffers regulate oral pH
- antibodies for immune surveillance
dissolves chemicals = stimulate taste buds
stimulation of saliva
ANS
- parasymp. = stimulates secretion
- symp = inhibits secretion
presence of food + taste, sight, smell, thought
pharynx
stratified squamous epithelium
common passageway for food, liquid, + air
naso, oro, + laryngopharynx
ends at location of prox. esophagus + trachea
glands throughout = secretion of serous + mucous
innervated by CN X
pharynx muscles
palatal: (tensor + levator veli palatini) elevate soft palate during swallowing
pharyngeal constrictors (superior, middle, inferior → sequential contraction) + suprahyoid mm help elevate larynx + push bolus to esophagus
peristalsis
propulsion of bolus along tube
coordination of circular + longitudinal mm (opposite contraction)
circ = prevent movement in other direction
segmentation
churn + mix contents to breakdown
no directional movement
mechanical digestion
mainly circular muscle layer
esophagus
stratified squamous epithelium
passage to stomach
C6 - T7
~25 cm long
skeletal muscle at beginning, smooth muscle after
peristalsis carries bolus to cardiac sphincter
extra glands in submucosal layer = mucous secretion
innervated by CN X
prevention of reflux
lower esophageal sphincter
peristaltic clearance (prevent mvt back)
stratified squamous epithelium
submucosal glands
mucous from stomach
stomach
muscular sac that stores food temporarily
intraperitoneal in LUQ
supplied by celiac trunk = foregut
simple columnar epithelium
has extra layer of smooth muscle
chyme
viscous, acidic, soupy mixture
mixture of bolus and gastric juices formed in stomach
formed through mechanical breakdown (contractions of muscular wall = segmentation) + chemical digestion (actions of secreted acid and enzymes)
cardia
entrance of stomach from esophagus
proximal to heart
fundus
found in all muscular structures
dome-like superior portion of stomach
has cells that will stimulate others for contraction
usually empty
stomach curvatures
greater = outside → forms greater omentum
lesser = inside → forms lesser omentum
pyloric canal
tube shape
controls what enters small intestine
stomach wall
3 layers of smooth muscle = inner oblique, middle circular, outer longitudinal
simple columnar epithelium
gastric glands within mucosa
rugae in mucosa
surface mucus cells
produce thick mucus to protect from acid
mucus neck cells
produce more serous mucus
role in digestion → activation of acid and enzymes once mixed
parietal cells
secrete H+ and Cl- = HCl acid
digestion of tougher structures
chief cells
secrete digestive enzymes: pepsin + lipase
do not activate until mixed with mucus
G cells
enteroendocrine cells in fundus of stomach
release gastrin when food first enters stomach = stimulates other secretory cells
role in GI tract regulation
small intestine
longest part of GI tract (6-7m long)
found in all quadrants
specialized for absorption → circular folds, villi, + microvilli = ↑ SA
duodenum
25 cm; c-shaped; mainly in RUQ
beginning + end = intraperitoneal; middle = retroperitoneal
receives chyme from stomach; secretions of pancreas + liver
digestion of fat, proteins, + sugars
dual vasculature: anastomosis of celiac + SMA branches
Brunner’s glands
in submucosa of duodenum
provide abundant alkaline mucus to neutralize the acid contents entering from the stomach
hepatopancreatic ampulla
entrance of common duct from liver + pancreas into duodenum
pancreas
posterior to stomach, between duodenum + spleen
retroperitoneal
vasc: anastomosis of celiac + SMA branches (celiac → splenic artery) = foregut + midgut
endocrine + exocrine gland
secretes digestive enzymes + bicarbonate buffer
bicarbonate buffer
neutralizes acidic chyme from stomach
establishes alkaline pH for pancreatic digestive enzymes
venous drainage of pancreas
splenic vein to hepatic portal vein
islets of langerhans
endocrine secretions
closely associated with vasculature
alpha cells → glucagon
beta cells → insulin
delta cells → somatostatin
pancreatic acinus
acinar + centroacinar cells
exocrine secretion = pancreatic juice
neutralize acidic chyme, break down ingested material
acinar cells
secrete digestive enzymes (amylase, lipase, proteinase)
centroacinar (duct) cells
secrete bicarbonate buffer + regulate pre-enzyme release from acinar cells
pancreatic duct
carries exocrine secretions to duodenum
main duct merges with bile duct → enters duodenum at hepatopancreatic ampulla
liver
largest gland in the body
intraperitoneal
metabolic + secretory functions (endocrine + exocrine)
vasc: celiac trunk = foregut + hepatic portal vein
liver functions
metabolic regulation:
- carb, protein, + fat metabolism
- regulates circulating levels of everything absorbed by intestine
hematological regulation:
- destroys aged/damaged RBCs, cellular debris, + pathodens
- secretes plasma proteins into blood (osmotic concentration, nutrient transport, clotting system)
bile
water, ions, bilirubin, bile salts
required for digestion of lipids
synthesized + secreted by liver
stored in gallbladder
anatomy of liver
2 lobes
inf. vena cava passes posteriorly → L+R hepatic veins drain into
portal triad underneath R lobe → gallbladder
portal triad
hepatic artery + hepatic vein flow in
bile duct flows out
hepatic portal vein
carries deoxygenated nutrient-rich blood from GIT to liver
= all blood from intestines passes through liver before returning to heart
hepatic veins
carry metabolites from liver to inferior vena cava
lymphatic system
delivers large lipids directly to general circulation (drains into thoracic duct)
liver lobule
made up of hepatocytes = epithelial liver cells
surrounded by connective tissue (interlobular septum)
portal triad:
- bile canaliculi drain into bile duct
- central vein drains into hepatic veins
Kupffer cells
liver macrophages
line sinusoids
liver endocrine function
endocrine surface with fenestrated endothelium
takes substances from blood + secrete into blood
liver exocrine function
exocrine surfaces = epithelial tight junctions
face each hepatocyte
form small channels called canaliculi → bile is secreted into
gallbladder
storage of concentrated bile
cystic duct
bile enters gallbladder from common hepatic duct when ampulla is closed
bile duct
bile exits gallbladder to duodenum when ampulla is open
CCK
cholecystokinin
released by presence of chyme in duodenum
induces relaxation of sphincter + contraction of gallbladder → movement of bile into small intestine
jejunum
intraperitoneal (upper quadrants)
vasc = SMA + vein (midgut)
begins at duodenojejunal flexure
majority of nutrient absorption
thicker walls, larger diameter, + redder in colour than ileum (++ vasc)
larger + more plicae circulares
ileum
intraperitoneal (lower quadrants)
vasc: SMA + vein (midgut)
ileocecal valve = empties into large intestine
Peyer’s patches
aggregated lymphoid nodules in ileum
protection from colonic bacteria
SA of small intestine
↑ 600x by plicae circulares → villi → microvilli
= 2 million cm2 + absorptive area
absorptive cells
main epithelial cell
lots of microvilli
goblet cell
secrete mucus
promote movement along intestine
I + S cells
enteroendocrine cells in small intestine
release hormones to regulate other intestinal cells
paneth cells
variable secretions
determines gut flora
immunity = secretions kill some bacteria
absorption in small intestine
sugars → monosaccharides
proteins → amino acids
= absorbed into hepatic portal circulation
fats → fatty acids → chylomicrons → chyle
= absorbed into lacteals → lymphatic vessels → thoracic ducts
large intestine
1.5 m long; 7.5 cm in diameter
intraperitoneal: cecum, transverse, sigmoid
retroperitoneal: asc + desc, rectum
vasc: SMA + IMA = midgut + hindgut
reabsorbs water + electrolytes
absorbs vitamins produced by bacteria
compacts + stores feces
midgut
parts of small intestine
cecum → left colic flexure of transverse colon
hindgut
descending colon → rectum
teniae coli
longitudinal smooth muscle layer
merges together to form 3 stripes to assist propulsion along colon
haustra
pouches along large intestine that can expand
= contraction → segmentation (packaging of waste)
colon wall
simple columnar epithelium → no villi
mucosa = mucus glands (goblet cells)
lymphoid nodules in submucosa
rectum
simple columnar epithelium
15 cm
temporary storage of feces
entry into rectum triggers urge to defecate
anal canal
non-keratinized → keratinized stratified squamous epithelium (hard protein = protection)
internal sphincter = smooth muscle
external sphincter = skeletal muscle (levator ani: iliococcygeus + puborectalis)
