Class Notes (835,292)
Canada (509,072)
UOIT (1,700)
Biology (294)
BIOL 1840U (44)

Role of Hormones in Digestion I

3 Pages
Unlock Document

BIOL 1840U
Peter Cheung

Role of Hormones in Digestion I. Introduction a. Four types of control systems i. Neuronal—CNS & enteric NS ii. Hormonal—acts via hormones in circulation iii. Paracrine—acts on adjacent cells iv. Lumicrine—hormones released from 1 cell into gut lumen to affect another cell (like paracrine but further acting) b. Endocrine system—diffuse in GI; due to many different organs c. Hormones—released from cells in small amounts; affect target cells thru circulation i. six GI hormones: gastrin, CCK, secretin, GIP, GLP, motilin d. Peptides—regulate GI fxn via non-hormonal mechanisms; not delivered thru circulation i. Somatostatin—paracrine regulating peptide ii. GRP (gastrin-releasing peptide)—neurocrine regulation of enteric nervous system; released from enteric nerves in response to a meal iii. Also lumicrine regulation via peptides e. Feedback Loops—key inregulating hormonal function; mainly negative i. Most hormones have >1 negative (or positive) feedback loop ii. Stimulus (food/ pH / distension) => hormone secretion => changes in upstream & downstream GI system II. Response to a Meal a. Cephalic Phase i. Initiated in anticipation of a meal, smell/taste of food & controlled by neuronal pathways (parasympathetic & vagal) ii. Limited amounts of digestive secretions enter gut iii. What happens: ↑ salivary flow; small ↑ [Gastrin] in lumen & serum; small ↑ CCK & secretin secretion; stomach relaxes b. Gastric Phase i. Initiated by food in the stomach ii. Major hormone is Gastrin iii. What happens: ↓ saliva secretion; ↑ gastrin secretion; ↑ pancreatic enzyme secretion c. Early Intestinal Phase (Digestive Phase) i. Initiated by chyme entering the duodenum ii. Major hormones are CCK & secretin as well as incretins (GIP & GLP) iii. What happens: GB contracts => bile release; ↑ CCK, ↑ secretin, ↓ gastrin, ↓ gastric acid output, ↑ pancreatic enzyme secretion d. Late Intestinal Phase i. Initiated by chyme entering ileum => gradual return of activity to interdigestive state ii. Mobility pattern shifts => MMC (migrating myoelectric complex) 1 iii. What happens: ↓ luminal levels of all digestive secretions; ↑ volume of GB (as liver ↑ production); e. Interdigestive Period (Fasting) i. Secretory cells replenish stores; GB concentrates bile; salivary glands secrete at basal rate; MMC characterizes motor activity of gut III. Gastrin a. Structure i. Made as preprohormone (preprogastrin) which is cleaved => progastrin which is cleaved => gastrin ii. 2 major human forms: 1. G-34—predominant in duodenum; ½ life = 10 min; involved in growth of GI epithelium & preparation of duodenum 2. G-17—predominant in antral stomach; ½ life = 3 min; involved in regulation of acid secretion during a meal b. Storage—in G cells in antrum of stomach (& duodenum) c. Release i. Stimulated by peptides, amino acids, & Ca in stomach ii. Inhibited by low pH (<2.5) & somatostatin iii. GRP (released from enteric nerves) => potent effect (↑ gastrin) d. Cellular Targets i. CCK-B receptor—serpentine 7-transmembrane domain, GPCR ii. Binds to. . . 1. Gastric parietal cells— ↑ HCl secretion 2. Enterocromaffin-like cel
More Less

Related notes for BIOL 1840U

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.