lecture 25 Flashcards
Where are exocrine secretions produced?
Epithelia
Functions of mucus?
Protection and lubrication
aids mechanical digestion
Electrolyte solution functions?
Dilutes food and provides optimal pH
essential for chemical digestion of food
Which part of the GI tract has the lowest pH?
Stomach
Function if digestive enzymes?
essential for chemical digestion of food
aids absorption
A neutral pH secretion will have a large amount of what ions?
Bicarbonate, (HCO3-)
How much plasma is secreted a day?
3L
How many total secretions are there a day ?
~8L a day
How is 3L of plasma secretions turned into 8L of secretions?
reabsorption
How many pairs of salivary glands are there?
3 pairs
What are the names of the salivary glands?
Sublingual glands
submandibular glands
parotid glands
How much secretions do the salivary glands produce?
1.5L of fluid per day
Basal secretion vs stimulated secretion for salivary glands?
0.3mL/min vs 1.5ml/min
Which salivary gland produces the most saliva?
submandibular glands
Composition of Salivary secretion?
Mucus (lubrication)
Dilute solution of NaHCO3/NaCl (optimal pH)
Digestive enzymes
are salivary secretions essential?
no, not essential for survival
salivary secretions help with?
talking
chewing and swallowing
Hygiene
Digestion (taste)
what is Xerostomia?
dry mouth from reduced or absent saliva
Which system predominantly regulates salivary secretion?
Nervous system, though, smell or sight of food
How does the parasympathetic nervous system regulate salivary secretion?
stimulation of a large amount of fluid
Sympathetic nervous system causes what in the salivary glands?
small volumes of viscous fluid
How much secretions are made in the gastric system per day?
2-3L
what is the secretion rate of gastric secretion between meals?
15-30mL/h and mainly from surface mucosa cells
When eating which cells are producing gastric secretions?
Mucous cells Parietal cells (HCL) Chief cells (pepsinogen)
What activates pepsinogen?
HCL to produce pepsin
What are gastric secretions made up of?
Mucus
Intrinsic factor
pepsinogen
gastric acid
Function of intrinsic factor?
absorption of vitamin B12
Function of pepsinogen?
Inactive form of pepsin, once converted to pepsin by HCL starts digestion of proteins
Functions of gastric acid?
Dilutes food
Denatures proteins
activates pepsinogen
protection (kills bacteria)
Source of hydrogen ions for HCL?
dissociation of H2CO3+ (carbonic acid) into hydrogen ions and bicarbonate
How is H+ secreted into the stomach lumen?
through the H+-K+ATPase in the apical membrane of parietal cells
Source of chloride ions?
HCO3- is ejected into interstitial fluid via serosal membrane of parietal cells which provides transport for Cl- ions
How is Cl- transported to stomach lumen?
Diffuses across cell via Cl- channel in apical membrane
Regulation of gastric secretion?
Co-ordinated with arrival of food
Three phases of gastric secretion regulation?
Cephalic phase -head controls secretion
Gastric phase - stomach controls
Intestinal phase - intestine controls
Cephalic phase controls what percentage of the secretions?
20% of secretions
function of cephalic phase?
preparation for arrival of food
What stimulates cephalic phase of secretions?
Thought, smell, sight of food
chewing action and taste
How does Parasympathetic nervous system control cephalic phase?
Stimulates parietal cells, chief cells and goblet cells
stimulate secretion of hormone gastrin
What produces the hormone gastrin?
G cells
Function of gastric secretions?
ensures sufficient secretion to handle ingested food
What are the stimuli involved in gastric secretions?
Stretch/distention of the stomach wall
products of digestion stomach lumen
elevated pH
what is the local nervous reflex of gastric phase?
Enteric nervous system
External nervous reflex of gastric phase?
Parasympathetic nervous system
ENS and PSNS stimulate what to do with gastric phase?
Secretion
motility
gastric secretion
what detects elevated pH levels in stomach?
Chemoreceptors
What stimulates release of G cells?
Partly digested peptides
Function of intestinal phase?
Controls delivery to small intestine
What stimulates intestinal phase?
Distension of duodenum
arrival of acid chyme and lipids and carbohydrates
Intestinal phase is under what kind of regulation?
Hormonal and nervous
What hormones control intestinal phase?
GIP, CCK, secretin
What nerves regulate intestinal phase?
enterogastric reflex
hormonal and nervous regulation do what to intestinal phase?
Inhibition of secretion and motility
Pancreas is what kind of organ?
Endocrine and exocrine organ
How much does the pancreas secrete her day?
1-1.5L per day
what are the two components of pancreatic secretion?
Enzymes
alkaline fluid
What produces the enzymes in pancreatic fluid?
Pancreatic acing cells for chemical digestion
What produces alkaline fluid?
duct cells to neutralise acid
what enzymes are secreted by pancreas?
Lipolytic (lipase)
Amylytic
Proteolytic (trypsin, chymotrypsin)
Nucleolytic
Stimulation of pancreatic enzymes is done by?
Arrival of lipids and carbohydrates in duodenum stimulates cholecystokinin (CCK)
Function of pancreatic enzymes?
luminal chemical digestion of food
Where are inactive proteolytic enzymes activated?
in the duodenum
what are the enzymes that breakdown proteins?
Trypsin - trypsinogen
Chymotrypsin - chymotrypsinogen
carboxypeptidase - procarboxypeptidase
What activates proteins in small intestine?
Enterokinase or enteropeptidase converts trypsinogen to trypsin which converts the rest
how does enterokinase activate trypsinogen?
it cleaves the protein forming trypsin
what is alkaline?
a HCO3 rich fluid
What produces alkaline fluid?
Duct cells in pancreas
What stimulates secretion of alkaline fluid?
Arrival of acid chyme in duodenum
function of alkaline fluid?
neutralises acid chyme
creates optimum pH for pancreatic and intestinal digestive enzyme
What is optimal pH for pancreatic and intestinal digestive enzyme?
6.7-9pH
How much biliary secretions are there per day?
0.5L per day
what are products associated with digestion in liver?
Bile salts and HCO3- rich fluid
functions of bile salts?
Fat digestion
Functions of HCO3- rich fluid?
neutralises acid
functions of bile pigments?
excretion
Where is bile stored and concentrated?
In the gallbladder
When is bile delivers to duodenum?
When food is arrived
Initial delivery of bile is under what type of control?
hormonal control by CCK
Hormone CCK is produced in response to?
Products of digestion in duodenum which causes contraction of gall bladder and relaxation of hepatopancreatic ampulla
How does bile stimulate its own secretion?
enterohepatic circulation
what is enterohepatic circulation?
95% of bile is reabsorbed by ileum and transported back to liver in enterohepatic circulation
Where is 5% of the bile lost?
in feces
What does the presence of bile salts in the liver stimulate?
synthesis of further bile salts
How much does the small intestine secrete per day?
1.5L
What are the small intestine secretions?
mucus
isosmotic fluid
digestive enzymes
What is isosmotic fluid?
alkaline mixture of NaCl and NaHCO3
helps neutralise acid and dilutes
