Gastrointestinal secretions

major functions of GI secretions

chemical digestion, lubrication, signalling, protection, activation of enzymes, excretion of waste

what type of glands are salivary glands

exocrine because they secrete saliva onto an epithelial surface via ducts

name three pairs of major salivary glands

parotid glands, submandibular glands, sublingual glands

where are the minor salivary glands found

in the mucosal lining of the oral cavity, especially the lips, cheeks, and palate

composition of saliva

99.4% water, remaining 0.6%: mucins, electrolytes, antibodies, enzymes

functions of saliva

buffers keep pH around 7, keeps mucosa moist, protects against mechanical damage, aids speech, dissolves food chemicals for taste, begins carbohydrate digestion

which enzyme in saliva begins carbohydrates digestion

salivary amylase

what is xerostomia

a sensation of dry mouth caused by reduced saliva production

what symptoms can result from xerostomia

dysphagia, dental erosion, infections, altered taste and smell, cracked lips, difficulty speaking

how is salivation controlled

by the autonomic nervous system

what is the effect of parasympathetic stimulation on salivary glands

increases the volume of watery saliva secreted

what is the effect of sympathetic stimulation on salivary glands

alters saliva composition, increasing proteins such as amylase and IgA

what substances make up gastric juice

water, hydrochloric acid (HCI), pepsinogen, intrinsic factors, mucus

which stomach cells secrete hydrochloric acid

parietal cells

what are the functions of hydrochloric acid in the stomach

kills microbes, denatures proteins, activates digestive enzymes, creates acidic pH (1-3)

which stomach cells secrete intrinsic factor

parietal cells

why is intrinsic factor important

it is required for vitamin B12 absorption in the small intestine

what stomach cells secrete pepsinogen

chief cells

what activates pepsinogen into pepsin

low pH and hydrochloric acid

what is the function of pepsin

breaks peptide bonds during protein digestion

which stomach cells secrete gastric lipase

chief cells

what is the function of gastric lipase

digests short-chain triglycerides into fatty acids and monoglycerides

which cells protect the stomach lining from acid damage

mucous cells and mucous neck cells

how does mucus protect the stomach

it forms a protective alkaline barrier over the stomach epithelium

what are the two types of pancreatic secretion

exocrine secretions and endocrine secretions

how much pancreatic juice is secreted daily

approximately 1.2-1.5 litres per day

what is the role of bicarbonate in pancreatic secretions

neutralises acidic chyme entering the duodenum

what is the pH of pancreatic juice

approximately 7.1-8.2

what is the function of pancreatic amylase

digests starches/carbohydrates

what is the function of pancreatic lipase

digests fats

what do ribonuclease and deoxyribonuclease digest

RNA and DNA

why are pancreatic proteases secreted in inactive forms

to prevent the pancreas digesting itself

what activates trypsinogen into trypsin

enteropeptidase in the duodenum

which pancreatic enzymes are activated by trypsin

chymotrypsinogen and procarboxypeptidase

which pancreatic endocrine cells secrete insulin

beta cells

what stimulates insulin secretion

increased blood glucose

which pancreatic endocrine cells secrete glucagon

alpha cells

what stimulates glucagon secretion

low blood glucose

what are the actions of glucagon

stimulates glycogenolysis and gluconeogenesis

which pancreatic cells secret somatostatin

delta cells

what is the effect of somatostatin in the GI tract

inhibits gastrin release

which liver cells produce bile

hepatocytes

how much bile is produced daily

approximately 800-1000mL per day

what is the pH of bile

7.6-8.6

what substances are found in bile

bile salts, bilirubin, cholesterol, neutral fats, phospholipids, electrolytes

what are the functions of bile

lipid digestion and absorption, waste elimination, neutralises gastric acid, provides optimum pH for pancreatic enzymes

what is the function of gallbladder

stores and concentrates bile

how does the gallbladder concentrate bile

by absorbing water and ions

which duct does bile leave the gallbladder through

the cystic duct

which two structures produce small intestinal secretions

brunner’s glands, crypts of lieberkuhn

what do brunner’s glands secrete

mucus that protects the small intestine from stomach acid

what do goblet cells in the intestine secrete

mucus for lubrication and protection

what do crypt enterocytes secrete

large volumes of fluid added to chyme to aid digestion and absorption

approximately how much intestinal fluid is secreted daily

around 2 litres per day

how are small intestinal secretions mainly regulated

by local reflexes responding to chyme in the intestine

what are the three phases of digestive secretion control

cephalic phase, gastric phase, intestinal phase

what stimulates the cephalic phase

sight, smell, taste, thought of food

which cranial nerves are involved in the cephalic phase

facial nerve, glossopharyngeal nerve, vagus nerve

what happens during the cephalic phase

activation of salivary and gastric secretions in preparation for food

what stimulates the gastric phase

stomach distension, increased stomach pH, presence of food

what occurs during the gastric phase

increased gastric motility and gastric juice secretion

what provides negative feedback during the gastric phase

emptying of chyme into the duodenum causing reduced pH and distension

what begins the intestinal phase

entry of food into the small intestine

what effects does the intestinal phase have on the stomach

inhibits gastric motility, contracts pyloric sphincter, slows gastric emptying

which hormones are important during the intestinal phase

cholecystokinin (CKK) and secretin

what effect do CCK and secretin have on gastric secretions

they inhibit gastric secretion and motility