L20: Secretions from Salivary glands and stomach Flashcards
what is the cephalic phase of secretion
the anticipation of food triggers autonomic and endocrine reflexes (increased saliva, gastric acid, gastrin and pancreatic enzymes) that prepare the GI tract
what are the 3 phases of secretions from salivary glands and the stomach
- cephalic: food anticipation
- gastric: mechanical stimulation of oral cavity + stomach
- intestinal phase: regulation of stomach emptying and digestion/abs in SI
at which secretory phase does 70% of HCl secretion in the stomach occur
gastric
what are the 4 salivary glands
parotid
mandibular
lingual
buccal
what is the composition and functionof saliva
composition: water, electrolytes, salivary proteins, urea (ruminants)
function: solvent for molecules to stimulate taste buds, food lubricant, keeps mouth clean, contains buffer, lysozymes and antitoxic proteins
what are lysozymes
antibacterial proteins that break down bacterial cell walls
salivary glands are ______ glands
acinar
what do salivary glands consist of
collecting ducts and acini
acini are the secretory unit
secretory unit of salivary glands are called ______ and they empty into ______
acini
collecting ducts
what is ptyalin (alpha amylase)
salivary enzyme for digestion of starches
what is the pH of saliva
6-7, ideal pH for activity of alpha amylase (ptyalin)
what is mucin
lubricant that facilitates swallowing and protects buccal surfaces
what ions are removed (reabsorbed) from saliva, what are added in (secreted)
Na and Cl are removed; K+ and bicarbonate are added
what is a salivary mucocele (sialocele)
painless swealling of neck or within oral cavity caused by a collection of saliva that leaked from a damaged salivary gland or duct and has accumulated in interstitial tissues
saliva osmolarity is determined by ______; saliva is hypotonic at ______ and close to isotonic at ______
flow rate
hypotonic - slow flow rates
isotonic - high flow rates
how does flow rate determine saliva osmolartity
at high flow rates, saliva is nearly isotonic due to less time for the modification of ions in the ducts (less removal of Na, Cl)
compared to at slow flow rates there is more time for removal of Na and Cl
what restricts osmotic reabsorption of water in acinar cells
tight junctions
salivary duct cells reabsorb ____ and _____ in exchange for H+ and HCO3
Na and Cl
is salivary protein concentration affected by flow rate
no
the parotid salivary glands consist of _____ cells, providing ______ to saliva
serous
proteins
the sublingual and submandibular salivary glands consist of a mixture of ____ and _____ cells
mucus (more glycoproteins) and serous cells
enzyme that initiates starch digestion in pigs and humans but not in carnivores or horses
alpha amylase (ptyaline)
what is lingual lipase
enzyme in young animals on a milk diet; initiates hydrolysis of triglycerides into diacylglyceride and a free fatty acid
in ruminants and other herbivores, saliva contains lysozymes and ______ proteins
antitoxic
what is tannin, how can saliva protect against it
plant defense mechainism - polyphenolic compounds in plants that have a bitter taste and negatively affect digestion in SI
some saliva have proteins that have antitoxic effects against phenolic compounds
_____ glands produce proline rich proteins which binds and neutralize tannin
parotid
do browsers or grazers have larger parotid glands and why
browsers (eat shrubs, leaves, bark, etc contain lots of tannnins) have larger parotid glands since they eat plants with higher tannin concentrations
what is the main purpose of saliva in ruminants
it is a buffer (pH 8) for VFAs which are constantly being produced by microbial activity
4 main components of gastric juice
HCl
pepsiongen
mucus
intrinsic factor
what does HCl do
- decreases pH of stomach
- activates pepsinogen
- aids in protein digestion
- kills bacteira
what does pepsinogen do
pepsin (active form) digests proteins
what is the purpose of mucus
protects gastric mucosa from corrosive actions of HCl
what is the purpose of intrinsic factor
needed for the absorption of vit B12 in ileum
the epithelium in the glandular region of the stomach contain what cell types
- chief
- parietal
- enteroendocrine
chief cells do what
convert pepsinogen into pepsin
what cells secrete HCl
parietal
what cells produce a substance with a protective function against acid and mechanical damage of the stomach
surface mucous cells
what are the stem cells of the stomach
mucus neck cells - thin mucus and are progenitor cells (stem)
what are the enteroendocrine cells of the stomach that produce hormones that regulate gastric secretion and motility
D-cells, G-cells, ECL cells
where is HCl formed and what does it require
gastric lumen by parietal cells, requires ATP
Cl is exchanged from bicarb producing an _______
alkaline tide
temporary increase in blood pH
what catalyzes bicarbonate formation from OH and CO2
carboanhydrase
when does an alkaline tide occur
after a meal
what are the functions of HCl
- activates pepsinogen
- aids in breakdown of CT and proteins
- kills microorganisms
what is the neural control of HCl secretion
PNS and ENS activate parietal cells via M3 receptors (activated by ACh via the cholinergic system)
what is the endocrine control of HCl secretion
secretions of gastrin from G-cells; gastrin binds to CCK-B receptors
secretion of histamine from ECL binds to H2 receptors
what is histamine released in response to
gastrin
what is gastrin released in response to
- small peptides in AA and stomach
- distension of stomach
- vagal stimulation
what are the intracellular mechanisms that mediate the activation of the H+/K+ ATPase
- the PNS (ACh) and gastrin through GPCRs that stimulate IP3/DAG which increase Ca+ concentration
- by histamine receptors mediating an elevation of cAMP concentration
- both Ca and cAMP stimulate the proton pump
what is the main source of histamine in the stomach
ECL cells (enterochromaffin-like)
what inhibits histamine and gastrin release in the stomach
somatostatin released locally (paracrine)
what cells are measuring the pH of the stomach and what pH triggers a negative feedback
G-cells
pH < 2
what things cause a downregulation of HCl production
- absence of food
- somatostatin and prostaglandin
what are the components of the gastric mucosal barrier
- compact epithelial cell lining
- gastric mucus covering
- bicarbonate secreted by surface epithelial cells
what is the purpose of the gastric mucosal barrier and what are the consquences of it being broken
- helps protect stomach epithelial lining against the acidic environment
- if barrier is broken, acid can diffuse across mucosa and damage the stomcah wall
what is a gastric ulcer and what can cause it
localized area of erosion of the mucosal layer
caused by: defect in mucosal barrier, hypersecretion of HCl and H.pylori
what are the therapeutic approaches for treating a gastric ulcer
- reduced acid production (vagotomy or proton pump inhibitor)
- stimulate re-epithelization
- H.pylori antiiotics
where are proenzyme pepsinogen stored
zymogen granules; are released by exocytosis upons stimulus
what is the function of pepsin
cleaves proteins to peptides at aromatic links
what things stimulate pepsinogen
- PNS (vagus n) acts on chief cells
- gastric acts on chief cells
- secretin from the duodenum stimulate chief cells
