Digestive
System
I. Digestion : breaking down of food materials for use by
body cells
A.Overview
of the digestive process
1.
Ingestion:
2.
Secretion:
3.
Mixing & propulsion:
4.
Digestion:
a.
mechanical digestion
i.
chewing
ii. churning
b. chemical digestion
5.. Absorption:
6.
Defecation:
B.
Layers of the GI Tract
1.
four layers
a.
mucosa
made
of three layers
a.
epithelium
b.
lamina propria
c.
muscularis mucosae
b.
Submucosa
c.
muscularis
two layers- inner
circular fibers & outer longitudinal fibers
d.
serosa
visceral
peritoneum
II. GI Tract:
A. Mouth &
Associated Structures
1.
lips and cheeks
2.
teeth
dentin
four types of teeth
i.
incisors
ii.
canines
iii.
premolars & molars
3. tongue:
tastebuds
papillae
i.
filiform papillae
ii.
fungiform papillae
4.
salivary glands: secrete saliva
a.
three pairs open into oral cavity
i.
parotid glands
ii.
sublingual glands
iii.
submandibular glands
b.
composition of saliva (pH 6.35-6.85)
i.
99.5% water
ii.
0.5% solutes:
a.
salts
b.
mucin
c.
lysozyme
d.
salivary amylase
e. lingual lipase:
c.
functions of saliva
5.
physiology of digestion in the mouth
a.
mechanical digestion
bolus
b.
chemical digestion
D.
pharynx
E.
esophagus
peristalsis
heartburn
F.
Stomach
composed of
a.
cardia -
b.
fundus
c.
body
d.
pylorus
e.
pyloric sphincter
rugae
has 3 layers of muscle (not just 2)
mucosa is composed
of simple columnar epithelial cells
a.
cells extend down into the lamina propria to form gastric pits
b.
three kinds of exocrine gland cells in the pits
mucous neck cells
chief (zymogenic) cells - pepsinogen
parietal cells
physiology of
digestion and absorption in the stomach
a. mechanical digestion
chyme
b.
chemical digestion
protein
digestion begins here
regulation
of gastric secretion - three phases
a.
cephalic phase
b.
gastric phase
c.
intestinal phase
G.
accessory structures emptying into small intestine;
three organs (pancreas, liver, gall bladder) important in chemical
digestion
1.
pancreas
pancreatic
juice:
water, salts, sodium bicarbonate, several enzymes (trypsin: protein
digestion; enzymes used in nucleic acid digestion)
2.
liver
lobule
hepatocytes
Bile
- contains water, bile salts, bile acids, cholesterol, bile pigments, several
ions, and lecithin (a phospholipid)
bilirubin
stercobilin
functions
of the liver
i.
carbohydrate metabolism
ii.
lipid metabolism
iii.
protein metabolism
iv.
removal of drugs and hormones
v.
excretion of bilirubin
vi.
synthesis of bile salts
vii.
storage
viii.
phagocytosis
ix.
activation of vitamin D
3.
gall bladder
hepatic
duct
cystic duct
common bile duct
H.
small intestine
Important
site of absorption
anatomy:
i.
composed of 3 sections
a.
duodenum
b.
jejunum
c. ileum
ii.
circular folds
iii.
ileocecal valve
iv.
structure of mucosa :
a.
villi
b.
microvilli
c.
glands
physiology of
digestion
a.
mechanical digestion - 2 types
i.
segmentations
ii.
migrating motility complexes ( MMCs):
b.
chemical digestion:
i.
carbohydrate digestion
ii.
protein digestion
iii. lipid digestion
iv.
nucleic acid digestion:
a.
ribonuclease
b.
deoxyribonuclease
physiology of
absorption
a.
carbohydrate absorption
b.
protein absorption
c.
lipid absorption
micelles
d.
water absorption
I.
large intestine
1. anatomy
a.
ileocecal valve
b.
appendix
c.
colon
i.
ascending
ii.
transverse
iii.
descending
iv. sigmoid
d.
rectum
e.
anus
2.
mucosa layer differs from small intestine
3.
muscularis
haustra
4.
physiology of digestion
a.
mechanical digestion
haustral churning
peristalsis
mass
peristalsis
b.
chemical digestion
bacteria
B vitamins and
vitamin K
5.
water absorption and feces formation
6.
defecation