Regulation of the GI tract - secretion

Question 1

Digestion depends on extensive well regulated secretion of digestive juices. What aids this?

Answer 1

• epithelial cells within the walls of the stomach/intestine
• discrete large glands situated outside the tract - salivary gland, liver and pancreas

Question 2

In order to aid enzymes present in the tract what do digestive juices have?

Answer 2

• digestive juices have a composition and pH that is well adapted to the characteristic of the enzymes in that part of the tract

Question 3

What makes up digestive secretions?

Answer 3

• water (98%)
• ions
• mucus
• enzymes

(Wallace must ingest edam)

Question 4

What are the 4 functions of saliva?

Answer 4

• lubrication
• antibacterial effect
• enzymic digestion
• pH regulation

Question 5

How does saliva lubrication aid digestion?

Answer 5

• contains mucin which facilitates chewing and swallowing

Question 6

What are the antibacterial substances in saliva?

Answer 6

• lysozyme and antibodies present in saliva

Question 7

How does saliva enzymic digestion aid in digestion?

Answer 7

• amylase breaks down starch

Question 8

How does saliva help pH regulation?
what is Ruminants pH?

Answer 8

• bicarbonate neutralises acid produced by bacteria
• pH = 8.2

Question 9

Saliva secretion is under control by what?

Answer 9

• saliva secretion is entirely under neural control (automimic - parasympathetic)

Question 10

Epithelial cells in the stomach produce what?

Answer 10

• Epithelial cells produce a mucus which is viscous and high in bicarbonate

Question 11

What are the 4 types of cells found in the glandular part of the stomach?

Answer 11

• mucin producing cells
• parietal cells
• chief producing cells
• endocrine cells

(my people can eat)

Question 12

What are the functions of mucin producing cells, parietal cells and chief cells?

Answer 12

• mucin producing cells produce alkaline mucus
• parietal cells produce hydrochloric acid
• chief cells produce pepsinogen (inactive zymogen for pepsin)

Question 13

What are the 3 types of endocrine cells found in the glandular region of the stomach? what layer are they found in?

Answer 13

• G-cells which produce gastrin
• ECL-cells which produce histamine
• D-cells which produce somatostatin
• all of these cells found within the epithelial layer

Question 14

What is the purpose of intrinsic factors within the stomach?

Answer 14

• Intrinsic factors help to ensure absorption of B12 in the stomach

Question 15

How does somatostatin impact G cells?

Answer 15

• somatostatin has a negative impact on G-cells
• the more somatostatin produced, the fewer G cells there are

Question 16

What are the 3 phases of gastric secretion?

Answer 16

• cephalic phase
• gastric phase
• intestinal phase

Question 17

Describe the cephalic phase

Answer 17

• normally elicited by sight, smell, and taste of food.
• entirely mediated by the vagus nerve

Question 18

Describe the gastric phase

Answer 18

• elicited by the presence of food in the stomach
• mediated via neural reflexes and hormones

Question 19

Describe the intestinal phase

Answer 19

• initial stimulatory effect, followed by an inhibitory effect
• mediated via neural reflexes and hormones

Question 20

During the intestinal phase of gastric secretions there is initially a stimulatory effect followed by an inhibitory effect why is this?

Answer 20

• to ensure the secretions are not continuous

Question 21

The pancreas has both exocrine and endocrine functions what are these functions?

Answer 21

• exocrine - products are pancreatic juices
• endocrine - products are insulin, glucagon, somatostatin

Question 22

Pancreatic juices have an aqueous components and an enzymic component - what do these components do?

Answer 22

• aqueous component - alkaline due to a high concentration of bicarbonate stimulated by secretin
• enzymic component - digestion for all major classes of foodstuffs

Question 23

Proteases digest proteins what are the three proteases produced by the pancreas? give their inactive forms and active form

Answer 23

• trypsinogen > trypsin
• chymotrypsinogen > chymotripsin
• procarboxypeptidase > carboxypeptidase

Question 24

What is the function of alpha amylase?

Answer 24

• to digest starch

Question 25

Lipases digest fats, what are the 3 lipases produced by the pancreas?

Answer 25

- triacylglycerol hydrolase - cholesterol ester hydrolase - phospholipidase A2

Question 26

What are the key points about the cephalic phase of pancreatic secretions?

Answer 26

- cephalic phase increases in association with feeding - its mediated by the vagal nerves that run into the glands - affected by gastrin secretion in the stomach

Question 27

What are the key points about the gastric phase of the pancreatic secretions?

Answer 27

- increases in association with feeding - mediated by the vagal nerves to the glands and gastrin secretion in the stomach

Question 28

when does the intestinal phase of pancreatic secretion begin?

Answer 28

- when chyme enters the duodenum

Question 29

How is the intestinal phase of pancreatic secretion mediated?

Answer 29

- mediated by secretin and CCK release

Question 30

What is the function of secretin?

Answer 30

- inhibits gastrin release from G cells - inhibits response of parietal cells to secretagogues - stimulates pancreas to produce bicarbonate rich fluid - increase production of bile by the liver

Question 31

What is the function of CCK?

Answer 31

- inhibits secretions from parietal cells - stimulates pancreas to increase enzyme secretion

Question 32

The liver receives what type of blood?

Answer 32

- both arterial and venous blood

Question 33

What is the role of the liver in digestion?

Answer 33

- it has hepatocytes that produce bile which are important in fat digestion - it handles nutrients absorbed from the intestine and regulates their release into the blood - ( other functions not directly associated with processing nutrients)

Question 34

Bile which is produced by hepatocytes is excreted into what?

Answer 34

- bile canaliculi (common bile duct)

Question 35

where is bile stored when there is no digestion occurring?

Answer 35

- the gall bladder

Question 36

When digestion starts the gall bladder slowly contracts, sphincter of Oddi relaxes - how does this control the release of bile?

Answer 36

- when the sphincter is relaxed bile is released into the small intestine - when its contracted there is no bile released

Question 37

What does bile contain?

Answer 37

- 95% water - bile acids - cholesterol - phospholipids - bile pigments (Bilirubin)

Question 38

How are primary bile acids made?

Answer 38

- synthesised from cholesterol in the hepatocyte

Question 39

How are secondary bile acids formed?

Answer 39

- when primary bile acids undergo dihydroxylation by bacteria in the small intestine

Question 40

How are bile salts formed?

Answer 40

- primary + secondary bile acids conjugate with an amino acids (taurine/glycine)

Question 41

What is the function of bile salts?

Answer 41

- bile salts are more water soluble than bile acids and act as detergents to emulsify lipids - they form spherical micelles which are important in digestion and absorption of fats

Question 42

How do bile acids recirculate back to the liver?

Answer 42

- by enterohepatic circulation

Question 43

How is bile and bicarbonate production increased?

Answer 43

- acidic duodenal contents stimulate secretin which in addition to increasing bicarbonate from the pancreas and production of bile

Question 44

What happens when fat is detected on CCK producing cells?

Answer 44

- stimulates CCK - opens the sphincter of Oddi - more bile is released into the small intestine

Question 45

Is neural stimulation important in bile production?

Answer 45

- NO