Lecture 19- Digestion 2

Question 1

What are the two areas in the stomach where lot of secretion happens?

Answer 1

-oxyntic mucosa= the part of the gastric mucosa in the antrum with a high concentration of glands (75%) -pyloric gland area

Question 2

What secretion happens in the oxyntic mucosa?

Answer 2

-have chief cells= pepsinogen -parietal cells= HCL, Intrinsic Factor -enterochomaffin-like cells =histamine

Question 3

What secretion happens in the pyloric gland area?

Answer 3

-different glands here, G cells and D cells in the lower part closer to the pyloric sphincter -G cells=gastrin -D-cells= somatostatin

Question 4

What is the gastric acid made up of and what is it for?

Answer 4

-HCL= 0.5% and lot of NaCl and KCl -pH 1-2 - key role in digestion of proteins, by activating digestive enzymes, and making ingested proteins unravel so that digestive enzymes break down the long chains of amino acids. -produced by parietal cells

Question 5

How does the secretion of gastric happen?

Answer 5

-in several steps -H+ and Cl- are secreted separately 1.Chloride and sodium ions are secreted actively from the cytoplasm of the parietal cell into the lumen of the canaliculus. This creates a negative potential of -40 mV to -70 mV across the parietal cell membrane that causes potassium ions and a small number of sodium ions to diffuse from the cytoplasm into the parietal cell canaliculi. 2.The enzyme carbonic anhydrase catalyses the reaction between carbon dioxide and water to form carbonic acid. This acid immediately dissociates into hydrogen and bicarbonate ions. The hydrogen ions leave the cell through H+/K+ ATPase antiporter pumps. 3.At the same time sodium ions are actively reabsorbed. This means that the majority of secreted K+ and Na+ ions return to the cytoplasm. In the canaliculus, secreted hydrogen and chloride ions mix and are secreted into the lumen of the oxyntic gland. stimuli:-Gastrin -Acetylcholine - Histamine

Question 6

What is pepsin?

Answer 6

-proteolytic enzyme (breaks down protein into peptides) -released in its inactive form by the chief cells=pepsinogen -is activated by HCl -the release of gastrin (hormone) and Actylcholine trigger the release of pepsinogen (as well as HCl)

Question 7

What triggers the release of HCl?

Answer 7

stimuli:-Gastrin -Acetylcholine - Histamine

Question 8

What is the gastric mucosal barrier?

Answer 8

-barrier of the stomach that allows it to contain acid -protection of the stomach= mucus coating but wouldn’t work long term, then tight junctions between the cells so the HCl can’t leak into the surrounding tissues -has three components: 1. A compact epithelial cell lining. Cells in the epithelium of the stomach are bound by tight junctions that repel harsh fluids that may injure the stomach lining. 2. A special mucus covering, derived from mucus secreted by surface epithelial cells and Foveolar cells. This insoluble mucus forms a protective gel-like coating over the entire surface of the gastric mucosa. The mucus protects the gastric mucosa from autodigestion by e.g. pepsin and from erosion by acids and other caustic materials that are ingested. 3.Bicarbonate ions, secreted by the surface epithelial cells. The bicarbonate ions act to neutralize harsh acids.

Question 9

What are the four phases in gastric acid secretion? names only

Answer 9

1.The basal phase 2.Cephalic phase 3.Gastric phase 4.Intestinal phase

Question 10

What happens in the basal phase of the gastric secretion?

Answer 10

-A small amount of acid is always being secreted into the stomach. The other three following phases increase the secretion rate in order to digest a meal

Question 11

What happens in the cephalic phase of the gastric secretion?

Answer 11

• Thirty percent of the total gastric acid secretions to be produced is stimulated by anticipation of eating and the smell or taste of food. This signalling occurs from higher centres in the brain through the Vagus Nerve. It activates parietal cells to release acid and ECL cells to release histamine. The Vagus nerve also releases Gastrin Releasing Peptide onto G cells. Finally, it also inhibits somatostatin release from D cells.

Question 12

What are the ECL cells?

Answer 12

Enterochromaffin-like cells -found in the gastric glands of the gastric mucosa beneath the epithelium, in particular in the vicinity of parietal cells -secrete Histamine -G cells are stimulated by the vagus nerve to release gastrin which stimulates the ECL cells to secrete histamine -histamine and gastrin stimulate the secretion of HCl

Question 13

What happens in the gastric phase of the gastric secretion?

Answer 13

-stimulated by food entering the stomach -About fifty percent of the total acid for a meal is secreted in this phase. Acid secretion is stimulated by distension of the stomach and by amino acids present in the food.

Question 14

What happens in the intestinal phase of the gastric secretion?

Answer 14

-Inhibitory : influenced by chyme entering duodenum -The remaining 10% of acid is secreted when chyme enters the small intestine, and is stimulated by small intestine distension and by amino acids. The duodenal cells release entero-oxyntin which acts on parietal cells without affecting gastrin -chyme is starting to be fed into the small intestine= measn fat and acid and high tonicity of material -strong feedback effect = secretes Secretin and CCK(Cholecystokinin) those are called enterogastrones(intestino stomach)- negative effects on the G cells, prietal and chief cells= dampening down of activity in the stomach and ENS and ANS

Question 15

What is the enterogastric reflex?

Answer 15

eneterogastric reflex= feeding into the ANS= slowing it down

Question 16

What stops/decreases the gastric secretion in the stomach?

Answer 16

-decrease in Protein & distension in stomach -Very high [H+] (=very low pH)=Accumulates as chyme levels fall in stomach -Enterogastric reflex & enterogastrones

Question 17

What is an enterogastrone?

Answer 17

-any hormone secreted by the mucosa of the duodenum in the lower gastrointestinal tract in response to dietary lipids that inhibits the caudal (or “forward, analward”) motion of the contents of chyme -secretin -cholecystokinin -gastric inhibitory peptide

Question 18

What digestion happens in the stomach?

Answer 18

-carbohydrate digestion continues=Salivary amylase continues to hydrolyze polysaccharides until low pH inactivates amylase -Protein digestion begins in antrum=Pepsin hydrolysis=beginning, not in individual amino acids yet

Question 19

Does nutrient and water absorption occur in the stomach?

Answer 19

-No nutrient absorption occurs -No water or electrolyte absorption occurs=Stomach epithelium impermeable to water & electrolyte transporters not present

Question 20

In what way is the pancreas a digestive accessory organ?

Answer 20

-secretews pancreatic juice containing digestive enzymes that assist the absorption of nutrients and the digestion in the small intestine. -These enzymes help to further break down the carbohydrates, proteins, and lipids in the chyme. -pancreas is exocrine and endocrine gland lot of glands connected ducts but those produce enzymes too

Question 21

What two types of cells make up the exocrine portion of the Pancreas?

Answer 21

-duct cells -acinar cells

Question 22

What do the acinar cells of the pancreas secrete?

Answer 22

-Digestive enzymes =Proteolytic enzymes =Pancreatic amylase = Pancreatic lipase

Question 23

What do the duct cells of the pancreas secrete?

Answer 23

-Aqueous, alkaline solution =High[NaHCO3] =Mechanism similar but opposite to Parietal cells

Question 24

What is trypsin?

Answer 24

-proteolytic enzyme -secreted in its inactive form trypsinogen by the acinar cells of the pancreas -is secreted into the small intestine= duodenum in its inactive form and then activated by an enzyme secreted by the wall of the duodenum enterokinase -trypsin then activates the other proteolytic enzymes released by the pancreas (chymotrypsin, elastase, and carboxypeptidase)

Question 25

What is lipase?

Answer 25

-an enzyme that catalyzes the breakdown or hydrolysis of fats (lipids) -secreted by the pancreas -converts triglyceride substrates found in ingested oils to monoglycerides and free fatty acids. -secreted in its final form -secreted into the duodenum

Question 26

In regulation of pancreatic exocrine secretion what happens when the is acid in duodenal lumen?

Answer 26

-acid in the duodenual lumen leads to secretin release from the duodenal mucosa (secretin carried by blood) =stimulates the pancreatic duct cells that secrete the aqueous NaHCO3 solution into the duodenal lumen= so more of it in the duodenum and pH goes up=more alkaline

Question 27

What is secretin?

Answer 27

• hormone that both controls the environment in the duodenum by regulating secretions of the stomach and pancreas, and regulates water homeostasis throughout the body -helps in regulating the pH within the duodenum by inhibiting gastric acid secretion by the parietal cells of the stomach, and by stimulating bicarbonate production by the centroacinar cells and intercalated ducts of the pancreas -not an enzyme as it’s acting locally so it’s paracrine

Question 28

In regulation of pancreatic exocrine secretion what happens when the are fat and protein in duodenal lumen?

Answer 28

-when fat and protein are present in the duodenum that stimulates the release of CCK from duodenal wall (carried by blood) to pancreatic acinar cells that are then stimulated to increase secretion of pancreatic digestive enzymes into the duodenal lumen and those then digest the fat and protein =that’s how the enzymes are triggered at exactly the right time when the food is arriving

Question 29

What is canine chronic pancreatitis?

Answer 29

-very common, the reasons for it not entirely clear -manifests with:Diarrhoea, weight loss, poor coat -also have Exocrine Pancreatic Insufficiency =Trypsin =Lipase =Amylase Can treat it with alterations in diet=can put enzymes into food to help the defficiency of the enzymes =low fat=not a good idea to overload them with energy rich food as it doesn’t have much lipase in the system =protein restriction=the same case with protein -dosgs fat,eat a lot and then start losing weight etc= sign of the pancreatitis

Question 30

What is splanchnic circulation?

Answer 30

-term for the blood circulation in the gut

Question 31

Where does the liver get its blood from?

Answer 31

1. Arterial blood which provides the liver with O2 supply and carries blood-borne metabolites for hepatic processing is delivered via the HEPATIC ARTERY 2.Venous blood draining the digestive tract is carried by the hepatic portal vein to the liver for processing and storage of newly absorbed nutrients =leaves via the HEPATIC VEIN -hepatic portal vein= connecting the small intestine to the liver -hepatic artery- connecting liver to the small intestine

Question 32

What does the liver do in digestion?

Answer 32

-pretty central role in digestion in general absorption= the material goes into the capillaries from the small intestine= these go first to the liver -we can have uptake of glucose in the small intestine and then in the blood goes to the liver= there can be stored as glycogen= very useful -other things absorbed as well -liver is like a factory for blood components (albumin) -can produce it as it has the amino acids coming in from the intestine in liver=dangerous poisons and alkaloids can be broken down (alcohol) -there is a limit to how much it can take, then it can damage liver= death of liver cells= problem

Question 33

What is bile and what does it do?

Answer 33

-hepatocytes produce bile -it is a mixture of water, bile salts, cholesterol, and the pigment bilirubin -When food containing fats reaches the duodenum, the cells of the duodenum release the hormone cholecystokinin (CKK) to stimulate the gallbladder to release bile. Bile travels through the bile ducts and is released into the duodenum where it emulsifies large masses of fat. The emulsification of fats by bile turns the large clumps of fat into smaller pieces that have more surface area and are therefore easier for the body to digest.

Question 34

What is bilirubin?

Answer 34

-pigment -made from worn out blood cells= gives bile the green colour -end product of hemoglobin

Question 35

Where is bile stored?

Answer 35

-gallbladder

Question 36

Do all animals have a gallbladder?

Answer 36

-no, horses don’t, not clear why

Question 37

What do duct cells of the liver secrete?

Answer 37

-H2O and bicarbonate(NaHCO3) -other inorganic salts

Question 38

What regulates bile secretion?

Answer 38

-rise in uptake of bile salts by liver -Fat=duodenum =CCK -stimulates the release of CCK

Question 39

How does emulsification of fat by bile happens?

Answer 39

-

Question 40

What does an Emulsification droplet look like?

Answer 40

-small droplets sucked in surrounded by lecithin and bile salt -much easier to handle by the membrane