BIOL 2P93 Lecture Notes - Ileocecal Valve, Cholecystokinin, Transport Protein

12 views2 pages
Absorption of Water Soluble Materials I
I. Introduction
a. Main fxn of intestinal secretions is to maintain acid/base balance
b. Intestines are presented w/ a considerable absorptive load every day
i. Highly efficient—absorbs ALL calories that pass (almost)
ii. Even absorbs the considerable fluid volume from endogenous sources
c. Functional Unit: villus & its associated crypt
i. cells at tip are enriched in surface-tethered hydrolytic enzymes & carriers
ii. cells in crypts secrete fluid to lumen
d. Main divisions of SI
i. Duodenum—receives gastric chime, pancreatic acinar secretions,
pancreatic ductal secretions, & bile; little absorption of nutrients but lots
of H2O absorption & pH is returned to 6-7
ii. Jejunum—major site of absorption
iii. Ileum—sim. to jejunum (absorption); at terminus is highly specialized for
absorption of ascorbic acid, bile salts, & IF/cobalamin complex
iv. Colon—begins at ileocecal valve; reclaims salt & H2O & stores feces
e. Epithelial jxns
i. Leaky epithelium—handle large volumes at high rates, less selective
ii. Tight epithelium—work more slowly, highly selective, & often show
absorptive/secretive behavior that’s under hormonal control.
II. Carbohydrate Digestion / Absorption
a. Salivary & pancreatic amylases—cleave α-1,4 linkages but cannot cleave α-1,6
b. Digestion is usually completed w/in the duodenum b/c it’s very rapid & simple
c. Sucrase & lactase hydrolyze sucrose & lactose to give monosaccharides
d. Hydrolases are usually in excess => rate limiting step is sugar transport
e. Glucose, Galactose, Fructose—products of carbohydrate metabolism
f. SGLT1—Na-coupled cotransport system present on brush border, transports
Glucose & Galactose
g. GLUT transporter—facilitated diffusion transporter; located on apical
membrane to transport fructose intracellularly
h. GLUT-related carrier—present on basolateral membrane & exports glucose to
blood *Fructose & galactose are converted to glucose in enterocytes*
III. Protein Digestion /Absorption
a. Pepsin—released in stomach; commences limited hydrolysis of protein
b. Pancreatic Proteases—main protein digesters; secreted in zymogen
i. Trypsinogen activated by enterokinase => trypsin
ii. Trypsin activates the other proenzymes
iii. Pancreatic proteases convert peptides to free aa
c. Amino acid transport systems
i. Not well understood; 6 have been classified
ii. Na-coupled AA transporters & Facilitated Diffusion transporters
IV. H2O & Salt Reabsorption
a. Salt reabsorption
Unlock document

This preview shows half of the first page of the document.
Unlock all 2 pages and 3 million more documents.

Already have an account? Log in

Get OneClass Notes+

Unlimited access to class notes and textbook notes.

YearlyBest Value
75% OFF
$8 USD/m
$30 USD/m
You will be charged $96 USD upfront and auto renewed at the end of each cycle. You may cancel anytime under Payment Settings. For more information, see our Terms and Privacy.
Payments are encrypted using 256-bit SSL. Powered by Stripe.