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1. motility
2. ingestion
3. mechanical processes
4. secretion
5. digestion: chemical processes
6. absorption
7. elimination (defecation)
structure of the gut wall
mucosa
epithelium
stratified squamous
simple columnar
presence of goblet cells
lamina propria
loose connective tissue
muscularis mucosae
smooth muscle
luminal modifications
villi
plicae
submucosa
loose connective tissue
muscularis externa
skeletal muscle
smooth muscle
serosa or adventitia
smooth muscle
functional syncytium
slow waves
interstitial cells of Cajal
tonic contraction
enteric nervous system
myenteric (Auerbach’s) plexus
submucosal (Meissner’s) plexus
parasympathetic
vagus n [cranial n X]
sacral splanchnic nn
sympathetic
postganglionic fibers from celiac, superior mesenteric, and inferior mesenteric ganglia
hormonal control
gastrin
cholecystokinin
secretin
gastric inhibitory peptide
motilin
movements
peristalsis
mixing
chewing (mastication)
swallowing (deglutition)
voluntary stage
pharyngeal stage
esophageal stage
stomach mixing & storage
stomach emptying
gastric factors → promote
duodenal factors → inhibit
hormonal feedback
intestinal activity
colonic activity
defecation
types of glands
goblet cells
crypts & pits
tubular glands
complex glands
stimuli for secretion
contact
autonomic nerves
hormones
salivary glands
parotid glands
serous secretion
parotid (Stenson’s) duct
submandibular glands
mixed (seromucous) secretion
submandibular (Wharton’s) duct
sublingual glands
mucous secretion
multiple ducts
gastric secretion
cells
mucous neck cells
chief cells
parietal cells
secretions
hydrochloric acid
pepsinogen
intrinsic factor
phases of gastric secretion
cephalic
gastric
intestinal
pancreatic secretion
α-amylase
proteases
trypsinogen --> trypsin
trypsin inhibitor
enterokinase
chymotrypsinogen --> chymotrypsin
procarboxypolypeptidase --> carboxypolypeptidase
lipases
bicarbonate ion
liver secretion
bile
intestinal secretion
Brunner’s glands
mucus
crypts of Lieberkün
mucus
watery fluid
brush border enzymes
peptidases
disaccharidases
lipases
colonic secretion
mucus
hydrolysis
carbohydrates 1 and sugars 2
types
monosaccharides
glucose
galactose
fructose
disaccharides
sucrose
lactose
maltose
isomaltose
α– vs. β–glycosidic linkages
glycogen
α-1,4-glycosidic bonds and α-1,6-glycosidic bonds
starch
amylose
amylopectin
cellulose
phycopolysaccharides
agar
carrageenans
alginate
fucoidan
enzymes used
salivary amylase
pancreatic amylase
brush border disaccharidases
sucrase, etc.
proteins and amino acids 3
enzymes used
pepsin in the stomach
enzymes acting in the small intestine
trypsin
chymotrypsin
carboxypolypeptidase
brush border enzymes
aminopeptidases
carboxypeptidases
dipeptidases
types
triglycerides
cholesterol
chemicals & enzymes used
bile salts
pancreatic lipases
nucleic acids
pancreatic ribonucleases
deoxyribonuclease in the small intestines
carbohydrates
cotransport with Na+
facilitated diffusion
enter the capillary bed in the villi
transported to the liver via the hepatic portal vein
proteins
similar to carbohydrates
fatty acids and monoglycerides
diffuse into intestinal cells
combine with proteins and extrude chylomicrons
enter lacteals
transported to systemic circulation via lymph
glycerol and short chain fatty acids
into the capillary blood in villi
transported via the hepatic portal vein
nucleic acids
active transport via membrane carriers
absorbed in villi
transported to liver via hepatic portal vein
electrolytes
most ions are actively absorbed along the length of small intestine
Na+ is coupled with absorption of glucose and amino acids
ionic iron is transported into mucosal cells where it binds to ferritin
anions passively follow the electrical potential established by Na+
K+ diffuses across the intestinal mucosa in response to osmotic gradients
Ca2+
related to blood levels of ionic calcium
regulated by Vitamin D and parathyroid hormone (PTH)
water
95% absorbed in the small intestines by osmosis
moves in both directions across intestinal mucosa
net osmosis occurs whenever a concentration gradient is established by active transport of solutes into the mucosal cells
water uptake is coupled with solute uptake
as water moves into mucosal cells, substances follow along their concentration gradients
autonomous smooth-muscle function
slow-wave potentials
regulation of digestion involves:
receptor activation
chemoreceptors
mechanoreceptors
osmoreceptors
mechanical and chemical stimuli
pH
presence of substrate in the lumen
distention
osmolarity
reflexes affect glands and movement
nerve plexuses near the GI tract initiate short reflexes
short reflexes are mediated by local enteric plexuses
myenteric plexus (Auerbach’s plexus)
submucosal plexus (Meissner’s plexus)
extrinsic nerves
long reflexes arising within or outside the GI tract
involve CNS centers and extrinsic autonomic nerves
vagus n
gastrin
stimulus: protein-rich chyme in stomach
gastro-colic reflex
secretin
stimulus: acidic chyme in duodenum
cholecystokinin
stimulus: fatty and protein-rich chyme in duodenum
| Questions for thought | ||
|---|---|---|
| 1. | Diagram and label the layers of the gut tube wall. Give a brief description of the function of each layer. | |
| 2. | List the enzymes involved in the digestion of complex carbohydrates to simple sugars; for each, note where it is secreted and what its particular action is. | |
| 3. | What is meant by the term hydrolysis? Explain, using real examples, how this process breaks macromolecules into their constituent monomers. | |
| 4. | Describe the enteric nervous system and how is it regulated by the autonomic. | |
| 5. | Explain the processes, in sequence, necessary for the digestion, absorption, and transport of fats. | |
| 6. | Briefly explain the functions of the liver and pancreas (exocrine and endocrine). | |
| 7. | Describe how hormones produced by the duodenal and gastric mucosa (naming them as appropriate) are used to regulate emptying of the stomach and secretion of digestive juices by the liver and pancreas. | |
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[ Anatomy & Physiology 2 syllabus ][
Anatomy & Physiology 3 syllabus ] [ Page created 1999-04-29 ][ Last updated 2009-02-26 ] [ Questions about this lecture? E-mail me ] |
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