(2) groups of organs compose digestive system
Gastrointestinal (GI) tract
Accessory digestive organs
Gastrointestinal (GI) tract
mouth, most of pharynx, esophagus, stomach, small intestine & large intestine
Accessory digestive organs
teeth, tongue, salivary glands, liver, gallbladder & pancreas
(6) functions of digestive system
ingestion
secretion of water, acid, buffers & enzymes into lumen
mixing & propulsion
digestion (mechanical & chemical)
absorption
defecation
(4) LAYERS of GI Tract
Mucosa
Submucosa
Muscularis
Serosa
Mucosa - inner lining
epithelium - protection, secretion & absorption
lamina propria - CT with blood & lymphatic vessels & MALT
muscularis mucosae - thin layer of folded smooth muscle
Submucosa
CT binding mucosa to muscularis
contains many blood & lymphatic vessels
submucosal plexus - network of neurons
Muscularis
voluntary skeletal muscle in pharynx, mouth, upper 2/3 of esophagus & anal sphincter
involuntary smooth muscle elsewhere
arranged in inner circular fibers & outer longitudinal fibers
myenteric plexus between muscle layers
Serosa
outermost covering of organs suspended in abdominopelvic cavity
also called visceral peritoneum
esophagus lacks serosa - has adventitia
Neural Innervation (2)
Enteric Nervous system
Autonomic nervous system
enteric nervous sytem
intrinsic set of nerves - "brain of gut"
neurons extending from esophagus to anus
(2) plexuses
- myenteric (GI tract motility)
- submucosal (controlling secretions)
Autonomic Nervous system
extrinsic set of nerves
Parasympathetic stimulation - increases secretion & activity by stimulating ENS
Sympathetic stimulation - decreases secretion & activity by inhibiting ENS
Peritoneum
divided into? (2)
largest serous membrane of body
parietal - lines wall of cavity
visceral (aka serosa) - covers organs
(5) major peritoneal folds
greater omentum
falciform ligament
lesser omentum
mesentery
mesocolon
Oral Cavity
formed by?
cheeks, hard & soft palates & tongue
Oral cavity proper
space from gums & teeth to fauces (opening between oral cavity & oropharynx)
(3) pairs of major salivary glands secrete most of saliva
parotid
submandibular
sublingual
Salivation controlled by?
parasympathetic stimulation
sympathetic stimulation
ANS
parasympathetic stimulation - promotes secretion
sympathetic stimulation - decreases salivation
Teeth - (3) major regions
crown
root
neck
Dentin of crown covered by ___
enamel
2 sets of teeth
deciduous (baby teeth)
permanent teeth
Mechanical Digestion in mouth
chewing
tongue, teeth, saliva
forms bolus
Chemical Digestion
salivary amylase - secreted by salivary glands acts on starches
inactived by stomach acid
lingual lipase - secreted by lingual glands of tongue acts on triglycerides
activated in acidic environment of stomach
Pharynx
(3) parts
food passes from mouth into pharynx
nasopharynx - respiration
oropharynx - digestive & respiratory
laryngopharynx - digestive & respiratory
Esophagus
secretes mucous, transports food - no enzymes produced, no absorption
Esophagus
1) mucosa
2) submucosa
3) muscularis
4) adventitia
1) protection against wear & tear
2) ---
3) divided into third
superior - skeletal
middle - skeletal & smooth
inferior - smooth
2 sphincters
(2) sphincters in esophagus muscularis
Upper esophageal sphincter (UES) - regulates movement into esophagus
Lower esophageal sphincter (LES) - regulates movement into stomach
Swallowing involves (3)
(3) stages
mouth, pharynx, esophagus
voluntary - bolus → oropharynx
pharyngeal - pharynx → esophagus
esophageal - esophagus → stomach
Stomach
(4) main regions
cardia
fundus
body
pyloric part - pyloric antrum, pyloric canal, pylorus
Stomach mucosa
gastric glands open into gastric pits
(3) types of exocrine gland cells
- mucous neck cells, parietal cells, chief cells (pepsinogen & gastric lipase)
G cell - endocrine cell - secretes gastrin
Muscularis of Stomach
additional 3rd inner oblique layer
Serosa
part of visceral peritoneum
Mechanical Digestion
mixing waves - creates chyme
Chemical Digestion
- gastric juice
parietal & chief cells
digestion of salivary amylase
inactivated by acidic gastric juice - activates lingual lipase (digest triglycerides into FAs & diglycerides)
Parietal cells- secrete HCl (kills microbes & denatures proteins)
pepsin secreted by chief cells (digests proteins)
gastric lipase splits triglycerides into FAs & monoglycerides
Pancreas
lies posterior to greater curvature of stomach
pancreatic juice secreted into pancreatic duct & accessory duct to small intestine
pancreatic duct joins __ ___ __ and enters ___ at ___ ___
common bile duct
duodenum
hepatopancreatic ampulla
Histology of Pancreas
99% of cells are acini
- exocrine
- secrete pancreatic juice
1% of cells are pancreatic islets (Islets of Langerhans)
- endocrine
- secretes hormones glucagon, insulin, somatostatin, pancreatic polypeptide
Liver
composed of (3)
heaviest gland of body
1) hepatocytes
2) bile canaliculi
3) hepatic sinusoids
1) hepatocytes
major functional cells of liver
secrete bile
2) bile canaliculi
exits liver as?
ducts between hepatocytes that collect bile
common hepatic duct → cystic duct from gallbladder → common bile duct
Hepatic Sinusoids
highly permeable blood capillaries recieving oxygenated blood from hepatic artery & deoxygenated blood from hepatic portal vein
Gallbladder
contraction of smooth muscle fibers eject contents of gall bladder into ?
cystic duct
Functions of Gallbladder
store & concentrate bile produced by liver until it is needed in small intestine
Hepatic Blood Flow
liver recieves blood from:
hepatic artery carrying oxygenated blood
hepatic portal vein carries deoxygenated blood
Small Intestine
(3) regions
duodenum
jejunum
ileum
Mucosa of Small Intestine
absorptive cells
goblet cells
intestinal glands
paneth cells
enteroendocrine cells
Submucosa of Small intestine
dudenal glands secrete alkaline mucus
Duodenum
recieves stomach contents, pancreatic juice & bile
neutralize stomach acid, emulsifies fats, pepsin inactivated by pH increase, pancreatic enzymes
Jejunum
most digestion & nutrient absorption occur here
Ileum
has peyers patch - clusters of lymphatic nodules
ends at ileocecal junction with large intestine
Special structural features of small intestine
circular folds - permanent ridge of mucosa & submucosa
causes chyme to spiral
Villi - contains arteriole, venule, capillary & lacteal
Microvilli - projections of absorptive cells
Brush Border Enzymes
inserted into plasma membrane of absorptive cells
Mechanical Digestion
governed by?
segmentations
myenteric plexus
localized mixing contractions
mix chyme & bring it in contact with mucosa for absorption
Chemical Digestion
1) carbohydrates
2) proteins
1) pancreatic amylase
a-dextrinase, sucrase, lactase, maltase in brush border
2) trypsin, chymotrypsin, carboxypeptidase & elastase from pancreas
aminopeptidase & dipeptidase in brush border
Lipid Digestion
emulsification by __ __ increases surface area
triglyceride digestion
bile salts
amphipathic - hydophobic & hydrophilic regions
Nucleic Acids
ribonuclease & deoxyribonuclease in pancreatic juice
nucleosidases & phosphatases in brush border
Absorption of:
1) Monosaccharides
2) Amino acids
1) facilitated diffusion or active transport
2) active transport
Large Intestine
(4) major regions
cecum
rectum
colon
anal canal
Large Intestine
ileocecal sphincter
ileocecal sphincter - between small & large intestine
Colon divided into (4)
ascending, transverse, descending & sigmoid
opening of anal canal (anus) guarded by ?
internal anal sphincter of smooth muscle & external anal sphincter of skeletal muscle
Anatomy of large intestine
Mucosa - mostly absorptive & goblet cells
no circular folds or villi
has microvilli
Submucosa
Muscularis - longitudinal muscle modified to form teniae coli
forms baustria - pouches
Large Intestine begins as __ & __ in lower right corner
cecum & appendix
Digestion of Large Intestine
1) mechanical digestion
2) chemical digestion
1) haustral churning
peristalsis
mass peristalsis
2) bacterial action, no enzymes
Anatomy of Anal Canal
anal columns
hemorrhoids
anal columns - longitudinal ridges seperated by mucus secreting anal sinuses
hemorrhoids - permanently distended veins
Defecation
stretching of rectum
intrinsic defecation reflex via myenteric plexus → muscularis contracts & internal sphincter relaxs
parasympathetic defecation reflex via spinal cord
stretching of rectum → sensory signals to spinal cord →splanchnic nerves return signals
Defecation occurs only if ?
external anal sphincter is voluntarily relaxed
abdominal contractions increase abdominal pressure as...
levator ani lifts anal canal upwards
feces will fall away
