lecture 25 Flashcards by Jack Pronk

Where are exocrine secretions produced?

Epithelia

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Functions of mucus?

Protection and lubrication

aids mechanical digestion

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Electrolyte solution functions?

Dilutes food and provides optimal pH

essential for chemical digestion of food

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Which part of the GI tract has the lowest pH?

Stomach

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Function if digestive enzymes?

essential for chemical digestion of food

aids absorption

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A neutral pH secretion will have a large amount of what ions?

Bicarbonate, (HCO3-)

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How much plasma is secreted a day?

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How many total secretions are there a day ?

~8L a day

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How is 3L of plasma secretions turned into 8L of secretions?

reabsorption

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How many pairs of salivary glands are there?

3 pairs

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What are the names of the salivary glands?

Sublingual glands
submandibular glands
parotid glands

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How much secretions do the salivary glands produce?

1.5L of fluid per day

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Basal secretion vs stimulated secretion for salivary glands?

0.3mL/min vs 1.5ml/min

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Which salivary gland produces the most saliva?

submandibular glands

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Composition of Salivary secretion?

Mucus (lubrication)
Dilute solution of NaHCO3/NaCl (optimal pH)
Digestive enzymes

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are salivary secretions essential?

no, not essential for survival

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salivary secretions help with?

talking
chewing and swallowing
Hygiene
Digestion (taste)

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what is Xerostomia?

dry mouth from reduced or absent saliva

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Which system predominantly regulates salivary secretion?

Nervous system, though, smell or sight of food

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How does the parasympathetic nervous system regulate salivary secretion?

stimulation of a large amount of fluid

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Sympathetic nervous system causes what in the salivary glands?

small volumes of viscous fluid

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How much secretions are made in the gastric system per day?

2-3L

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what is the secretion rate of gastric secretion between meals?

15-30mL/h and mainly from surface mucosa cells

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When eating which cells are producing gastric secretions?

Mucous cells 
Parietal cells (HCL)
Chief cells (pepsinogen)

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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