T1 L5 Saliva & gastric secretions Flashcards
What are the functions of saliva?
Lubrication
Protection
Digestion - begins breakdown of carbohydrates & fats via a-amylase & lingual lipase
What is the function of lubrication?
Moistens mouth to lubricate food, which aids in swallowing
Facilitates movement of mouth & tongue for speech
Helps dissolve chemicals within food for presentation to taste receptors
What is the reason for saliva having a protection function?
Reduces adverse effects of oral bacteria
Alkalinity of fresh saliva neutralises acid produced by oral bacteria
Flow of saliva across teeth helps wash away bacteria
Contains additional substances that reduce bacterial growth
What are the first enzymes that begin the breakdown of carbohydrates & fats?
Alpha- amylase
Lingual lipase
What is Sjogren’s syndrome?
An autoimmune disease that destroys exocrine glands
Commonly affects tear & saliva production
Hallmark manifestations are dry eyes & mouth
What causes Xerostomia?
A lack of adequate saliva
Typically have dental caries & halitosis due to bacterial overgrowth
Difficult speaking or swallowing solid food due to inadequate lubrication
What type of protein is in serous secretions?
Ptyalin - hydrolyses starch
What type of protein is in mucous secretions?
Mucin - acts as lubricant
What are the 3 major salivary glands?
Submandibular glands
Parotid glands
Sublingual glands
What factors stimulate salivation?
Thought, smell or taste of food by conditioned reflexes & by nausea
What factors inhibit salivation
Sleep
Dehydration
Fatigue
Fear
How do efferent nerves reach the salivary glands?
Via glossopharyngeal & facial nerves
What type of receptors does acetylcholine act on?
Muscarinic receptors
What is the composition of gastric juice?
Water & electrolytes HCl Pepsins Mucus Intrinsic factor
What is the function of HCl in gastric juice?
Hydrolsis of fat & starch
Antiseptic kills contaminating microorganisms
Converts pepsinogens to pepsin
What is the function of pepsins in gastric juice?
Endopeptidases cleave peptide bonds for protein digestion
They are secreted as inactive pepsinogens & activated to form pepsins at a low pH
What is the function of mucus in gastric juice?
Water & mucin glycoprotein
Bicarbonate barrier
Protect surface epithelial cells from acid / pepsin erosion
What is the function of intrinsic factor in gastric juice?
Glycoprotein binds vitamin B12 for absorption in the ileum
What are the 2 major regions in the stomach?
Exocrine or glandular part consisting of funds & body or acid-secreting area
Endocrine or hormone secreting area portion located in the Antrum or gastric secreting area
What types of cells are found in the gastric mucosa?
Mucous cells Endocrine cells - D cells Chief cells Exocrine region Endocrine region
What is the function of endocrine D cells?
Secrete somatostatin which is a regulator of gastric release & gastric acid secretion
What is the function of chief cells?
Secrete pepsinogen which is converted by gastric acid to active form pepsin
What is the mechanism of gastric acid secretion by oxyntic cells?
H+ & HCO3- are generated inside the cells by carbonic anhydrase
H+ is pumped across luminal membrane
Cl-/HCO3- exchanger in basolateral membrane provides Cl- ions for HCl & HCO3-
How do gastric secretions protect against self digestion?
Lumen has a pH of below 2.0
Mucous layer of mucopolysaccharides & mucoproteins
Mucous viscosity generates mucosal barrier
Tight junctions between cells to stop acid entry into underlying tissue
What is gastritis?
Inflammation of gastric mucosa
Mostly caused by infection
Can be caused by smoking, alcohol, NSAIDs & chronic stress
If surface epithelium is acutely damaged it rapidly regenerates in a restitution process
What are proton pump inhibitors?
Potent inhibitors of H+/K+ ATPase pump on luminal surface of oxyntic cells
Omeprazole is an example, which binds irreversibly & inhibits H+ secretion
What are the 3 major stimulators of gastric acid secretion?
Gastrin
Histamine
Acetylcholine
How does gastrin control acid secretion?
Triggered by amino acids & peptides in the stomach
Stimulates secretion by increasing intracellular calcium ions
Predominantly secreted by antral G cells in pylorus & duodenum
Endocrine effect
Low pH inhibits release
How does histamine control gastric acid secretion?
Stimulates secretion by increasing cAMP Arises from mast-like cells ECL cells close to parietal cells Paracrine effect by local diffusion ECL cells are stimulated by gastrin & acetylcholine Local vasodilatation of arterioles
How does acetylcholine control gastric acid secretion?
Increases intracellular calcium ions
Secreted from postsynaptic vagal fibres innervating gastric mucosa
Acts on parietal & ECL cells to promote acid & histamine secretion
Acts on D cells to inhibit somatostatin release
What are the 2 major inhibitors of gastric acid secretion?
Somatostatin
Prostaglandins
Where is somatostatin secreted from?
Antral & oxyntic gland D cells
Pancreatic islet cells
How do prostaglandins inhibit gastric acid secretion?
Ez prostaglandin is produced in the stomach & is a physiologic antagonist of histamine at the oxyntic cell wall
Inhibits production of cAMP
From mucosal cells
What is autoimmune atrophic gastritis?
Antibody mediated destruction of gastric parietal cells
Causes hypochlorhydria & deficiency of IF
What are the 3 phases of regulation of gastric acid secretions?
Cephalic - sight, smell, taste, thought
Gastric - antral distention, protein content, pH above 4
Intestinal - intestinal gastrin, absorbed amino acids
