Digestive system 2

How is gastric secretion regulated

Through vagus nerve stimulation and hormones

Acetylcholine: increases gastric activity

Sympathetic stimulation decreases gastric activity

Enzyme and HCL plus most small intestine secretions gastrin antagonists

Describe the cephalic reflex phase of gastric secretion

Conditioned salivation at the thought, aroma, sight, and taste of food

Describe the gastric phase of gastric secretion

Stimulated by distension, peptides, low acidity, and gastrin

Low PH inhibits gastrin secretion (between meals)

However, when food enters stomach, PH rises, releases gastrin which triggers HCL/enzyme release, PH drops

Describe the intestinal phase of gastric secretion

Partially digested food enters small intestine causing brief gastrin release

What are the inhibitory effects of the intestinal phase of gastric secretion

Chymes with H+, fats, peptides, irritating substances cause inhibition

Describe the enterogastric reflex

Three reflexes act to

Inhibit vagal nuclei in medulla

Inhibit local reflexes

Activate sympathetic fibers  tightening of pyloric sphincter  no more food entry to small intestine

 Decreased gastric activity  protects small intestine from excessive acidity

What hormones (enterogastrones) are released during the intestinal phase

Secretin, Cholecystokinin, vasoactive intestinal peptide

All inhibit gastric secretion

If small intestine is pushed to accept too much chyme, then dumping syndrome occurs

Describe what occurs during gastric contractile activiy

Peristaltic waves move toward pylorus

Distension and gastrin increase force of contraction

Most vigorous near pylorus

How does Regulation of gastric emptying work

As chyme enters duodenum receptors respond to stretch/chemical signals

enterogastric reflex and enterogastrones inhibit gastric secretion and duodenal filling

How does Carb rich chyme move vs Fatty chyme

Carb rich Chyme: moves quickly through duodenum

Fatty chyme: remain in duodenum for 6 hours or more

Describe vomiting and its triggers/consequences

Caused by extreme stretching, intestinal irritants, spicy food, bacterial toxins, excessive alcohol, certain drugs

Chemical/sensory impulses: emetic center of medulla

Excessive vomiting: causes electrolyte and acid-based imbalance (alkalosis)

Describe the 3 small intestine subdivisions

Duodenum: bile duct and main pancreatic duct, with entry controlled by hepatopancreatic sphincter

Jejunum: extends from duodenum to ileum

Ileum: joins at large intestine at ileocecal

What are the circular folds (pilae circulaes) of the digestive tract

Permanent folds force chyme to slowly spiral through lumen more nutrient absorption

Describe the Vili

Extensions of mucosa, capillary bed, and lacteal for absorption

Describe Microvilli aka brush border

Contain enzymes for carbohydrates and protein digestion

Peyer’s Patches purpose

Protect distal part of digestive tract against bacteria

What is intestinal juices purpose

Secreted in response to irritation of mucosa

Facilitates transport and absorption of nutrients

Describe the Liver and Gallbladder role in digestion

Liver: only digestive function is bile production (bile is a fat emulsifier)

Gallbladder: main function is bile storage

Describe the contents of Bile alkaline solution

Bile salts: cholesterol derivatives and function in emulsification and absorption

Bilirubin: pigment formed from heme

Describe the Gallbladder function in depth

Stores bile

High cholesterol/not enough bile salts: gallstones

Muscular contractions release bile via cystic ducts

Bile stimulated by: secretin from intestinal cells exposed to HCL and fatty chyme

Describe what hormones cause gallbladder contraction

Cholecystokinin mostly but also from intestinal cells exposed to fatty chyme and vagus stimulation

CCK also causes secretion of pancreatic juice

Describe pancreas’s endocrine and exocrine functions

Endocrine: pancreatic islets secrete insulin and glucagon

Exocrine: secrete pancreatic juice (alkaline solution which neutralizes chyme) to duodenum via main pancreatic duct

Describe the enzymes of the pancreas

amylase, lipase, nucleases secreted in active form but require ions or bile for optimal activity

Proteases secreted in inactive form

How does regulation of pancreatic secretion work (3 types)

CCK induces secretion of enzyme rich pancreatic juice

Secretion causes secretion of bicarbonate rich juice

Vagal stimulation causes release of pancreatic juice

Describe sementation

Most common motion of small intestine

Moves toward ileocecal valve

wanes in late intestinal fasting phase