2 digestion and absorption

Question 1

what is pancreatic juice like

Answer 1

enzyme rich secretion, aqeuous alkaline secretion

Question 2

what are the ancillary organs required for digestion and absorption

Answer 2

liver, pacreas and gall bladder

Question 3

why does bicarbonate ions need to neutralise chyme

Answer 3

1. digestive enzyme activity (optimal at neural or slightly alkaline pH)
2. micelle formation (fat absorption)
3. protecting duodenal mucosa

Question 4

which ion does bicarbonate ions exchange with in the pancreas?

Answer 4

chloride ions

Cl- channels are absent in CF, so mucus plugs pancreas preventing natural release of enzymes

Question 5

Discuss carbohydrate digestion and absorption

Answer 5

1. Ingested as complex carbohydrate
2. digestion begins in mouth- salivary amylase (works at neutral or alkaline) activity stops in acidic stomach
3. digeston/ absorption cotinues in small intestine with pancreatic amylase splitting alpha 1,4 glycosidic linkages on chains larger than disaccharides

some salivary amylase is protected and embedded in food

Question 6

Carbohydrate enzymes located in brush border

Answer 6

Lactase- lactose to glucose and galactose

maltase- maltose to glucose and glucose

sucrase- sucrose to glucose and fructose

Question 7

Describe the digestion of carbohydrates by enzymes on brush border

Answer 7

• BB enzymes closely related to sodium pumps
• when sodium pump drag sodium into epithelial cells, this brings disaccharides in contact with enzymes
• glucose, fructose and galactose are then transported via glucose carriers into epithelial cells from apical membrane, then into basolateral membrane which then can diffuse into blood and transported to liver via portal vein
• sodium gradient is maintained by Na+/K+ ATPase

Question 8

What is the role of pepsin

Answer 8

Start of protein digestion and absorption in the stomach (15%)

pepsin activity stops when chyme interacts with alkaline pancreatic secretions

Question 9

Two major classes of pancreatic proteolytic enzymes? What is the fate of these enzymes?

Answer 9

1. Endopeptidases- cleaves interior peptide bonds
2. Exopeptidases- cleaves external peptide bonds

These enzymes are secreted into duodenum as inactive precursors trypsinogen (prevent autodigestion) converted to trypsin by enterokinase (brush border)

trypsin then activates other inactive precursors to digest peptides

Question 10

How are amino acids and di- and tripeptides absorbed?

Answer 10

Passive or faciliated diffusion

Question 11

which enzyme is most important in digesting fats?

what are its properties? what does this mean is digesting fats?

Answer 11

pancreatic lipase

water soluble, requires access to lipid site as fats are insoluble to water except some short chain FA

need to emulsify lipid droplets to increase surface area of lipid water interface – requires conjugated bile acids released from the gall bladder. products are mostly insoluble – absorbed by forming a micelle (bile salts). This process also important for absorption of fat soluble vitamins (A, D, E, K).

Question 12

what happens to fats once they are absorbed?

Answer 12

monoglyceride and free fatty acids are resynthesized into triglycerides, where they combine with protein, phospholipids and cholesterol to form a chylomicron. Chylomicrons are too large to enter capillaries and so are transported to the systemic circulation via the lymphatic system

Question 13

what are the controls of pancreatic secretions?

Answer 13

1. Vagus nerve. conditioned stimuli (cephalic phase)

presence of food in the stomach (gastric phase)

ACh also acts to potentiate the actions of secretin and cholecystokinin (CCK).

2. secretin (released in response to acid in duodenum) stimulates HCO3- production
3. cholycystokinin (CCK) stimulates enzyme rich secretion (released in response to presence of fat and protein in duodenum)

Pancreatic secretions can be reduced by sympathetic activation and by somatostatin.

Pancreas also has an important endocrine role by releasing insulin and glucagon.

Question 14

Xerostomia

Answer 14

dry mouth resulting from reduced saliva flow- symptom of various medical conditions

Question 15

Achlorhydria:

Answer 15

absence of HCl in gastric secretions

Question 16

pancreatic exocrine insufficiency

Answer 16

the inability of the pancreas to produce and/or transport enough digestive enzymes to break down food in the intestine and allow its absorption. It may be due to problems arising in the pancreas itself or problems outside the pancreas

Question 17

Lactase insufficiency

Answer 17

Intolerance to lactose (dairy products) produces osmotic diarrhoea and flatulence.

Question 18

Gluten enteropathy (coeliac disease)

Answer 18

gluten in diet (wheat, rye, barley) causes mucosal damage – decrease villi surface area for absorption. Increased delivery of nutrients to large intestine produces diarrhoea (osmotic) and flatulence.

Treatment – gluten-free diet.

Question 19

Pancreatitis

Answer 19

Acute – autodigestion of pancreas by secreted enzymes (can be due to blockage of pancreatic duct caused by bile duct stones). Alcohol binges.

Chronic – normally associated with alcohol abuse

Symptoms include steatorrhoea (fatty stools) due to fat malabsorption (lack of pancreatic lipase), and diabetes (lack if insulin).

No major effect on carbohydrate and protein digestion due to presence of additional digestive enzymes in small intestine.