GIT secretio

exocrine and endocrine glands

exocrine out- secrete substances onto an epithelial surface by duct eg salivary, mammary, mucous

endocrine in- ductless glands of the endocrine system that secrete products directly into the blood eg pancreas, gonads

merocrine

secretory vesicles fuse with apical plasma membrane to release product into a duct

apocrine

scretory products released at apical cell surface in small membrane bound vesicles that enter into a duct

holocrine

secretory products accumulate in the secretory cells which then die and the entire cell and its secertory products are released into a short duct

saliva- what does it secrete, what is the pH, function, and what is it controlled by

• mucous

• amylase

• lingual lipase

• electrolyte solutions

• proteins and enzymes

• ph 6.5

• lubrication

• digestion

• volume varies among species

• autonomic parasympathetic control

stomach secretions

• including which cells secrete them

• what are these secretions stimulated by

• surface mucous cell secretes mucus

• mucous neck (found in gastric glands) cell secretes mucus

• parietal cell secretes hydrochloric acid and intrinsic factor

• chief cell secretes pepsinogen and gastric lipase (pepsinogen is a precursor to pepsin)

• g cell secretes hormone gastrin

• this is stimulated by acetylcholine, gastrin, histamine

what are the 3 phases of gastric secretion regulation?

cephalic

• conditioned reflex or sight/smell/taste of food

• via vagus, gastrin secretion and histamine

• increase stomach motility

• increase hcl and pepsinogen secretion

gastric

• stimulation of chemo and mechano receptors in stomach lead to release of gastrin and histamine

• local negative fedback loop operates if gastric pH is less than 3

intestinal

• presence of chyme in duodenum inhibits acid secretion and motility via release of secretin, gastric inhibirotry peptide and cholecystokinin

what should not be in the saliva

• blood

• glucose

regulatory peptides

• gastrin promotes growth of stomach mucosa

• enteroglucagon and cholecystokinin promote growth of intestinal mucosa

small intestine secretions

• exocrine

• endocrine

• effect of chyme

• exocrine cells- mucus, peptidase, sucrase, maltase, lactase, lipase, enterokinase

• endocrine cells- secrete cholecystokinin and secritin

greater the amount of chyme the greater the secretion (local reflex action from chemical and mechanical irritation from chyme)

intestinal secretions and what is the pH

• enterokinase (activates trypsinogen)

• carboxy and aminopeptidases

• maltase

• lactase

• sucrase

• lipase

• nucleases

• ph 7-8

brunner glands

• mostly secrete alkaline mucoid fluid, no enzyme

• designed to protect the small intestine mucosa from damage by stomach acid in first part of duodenum

function of the liver

• digestion (bile)

• metabolism

• production of bile, enzymes, hormones, cholesterol, triglycerides

• detoxification

• amino acid and protein synthesis

• storage of vitamins and minerals

• ammonia to urea

• blood clotting regulation

• breakdown of erythrocytes

• mainenance of blood temp and pressure

how is bile produced

• where from

• where does it secrete into and as what

• what is secreted from duct cells into bile

• from cholesterol in smooth ER of hepatocytes (also takes phospholipids and cholesterol from cell membrane)

• hydrophobic and hydrophilic sides

• secretes into canaliculi as sodium salts- draws water into bile by osmosis and electrolytes

• bicarbonate is secreted from duct cells into bile

• bile pigments are excreted through this route, main one is bilirubin

what is entero hepatic circulation

the circulation of biliary acids, bilirubin, drugs etc from liver into bile followed by entry into the small intestine, absorption by the enterocyte and transport back into the liver

exocrine secretios of the pancreas, the pH and what is this stimulated by?

• trypsinogen

• carboxy and aminopeptidase

• lipase

• amylase

• nucleases

• bicarbonate pH7-8

• stimulated by acetylcholine, cholecystokinin and secritin

general composition and characteristics of gi secretions

• water, ions, mucous, enzymes, hormones

• colour less, pale yellow (pH 1-3)

shape of gastric glands

• straight tubular

• branched tubular

what are pancreatic glands called

acinar

structure of salivary glands

compound acinar

mechanism of stomach secretions

production of HCl in parietal oxyntic cells