Digestion and absorption of fat

Question 1

Which vitamins are fat soluble?

Answer 1

Vitamins A, D, E, K are fat soluble

Question 2

What does vitamin A deficiency lead to?

Answer 2

night blindness, corneal drying. corneal degeneraion and blindness, impaired immunity, hypokertosis, keratosis pilaris

Question 3

What does vitamin A overdose lead to?

Answer 3

hair loss, nausea, jaundice. irritability, vomiting, blurry vision, headaches, muscle and abdominal pain

Question 4

What are the sources of vitamin D?

Answer 4

sunlight can be used to generate vitamin D3 in the skin of animals

Dietry sources of vitamin D3 include egg yolk, fish oil and a number of plants

Question 5

What does vitamin D deficiency lead to?

Answer 5

Impaired bone mineralisation, rickets in children and osteomalacia in adults, osteoporosis. Maybe linked to cancer

Question 6

What are the sources of vitamin E/ tocopherol?

Answer 6

vegetable oils- palm oil, sunflower, corn, soybean and olive oil

Question 7

What does vitamin E deficiency lead to?

Answer 7

neurological problems due to poor nerve conduction

Question 8

What are the sources of vitamin K?

Answer 8

various foods in the diet but also produced by intestinal bacteria

Question 9

What is vitamin K involved in ?

Answer 9

carboxylation of specific glutamate residues in proteins to form Gla- residues- usually involved in binding calcium

1. Blood coagulation
2. bone metabolism
3. vascular biology or deposition of insoluble calcium salts in the arterial vessel walls

Question 10

What are the three essential fatty acids and what are their importance?

Answer 10

Linoleic acid

Linolenic acid

Arcidonic acid

• essentialbecause they cannot be derived endogenously, must be obtained from diet
• Important in a plethora of cellular and organ processes
  
  • formation of healthy cell membranes
  • developement and functioning of the brain and nervous system
  • production of Eicosanoids
  • regulating blood pressure, blood viscosity, vasoconstriction, immune and inflammatory response

Question 11

What are the symptoms of essential fatty acid deficiency?

Answer 11

• Hemorrhagic dermatitis
• skin atrophy
• scaly dermatitis
• dry skin
• weakness
• impaired vision
• tingling sensations
• mood swings
• edema
• high blood pressure
• high triglycerides
• hemorrhagic folliculitis
• hemotologic disturbances
• immune and mental deficiencies
• impaired growth

Question 12

What are 3 main forms of cosumed dietry fat?

Answer 12

tryiglycerides- 90%

phospholipids- 5%

Cholesterol (0.5g)+ lipovitamins- <5%

Question 13

Where does endogenous lipids in the GI lumen come form and what does it contain?

Answer 13

Bile

contains:

• Phospholipids
• unesterified cholesterol
• membrane lipids from desquamated cells
• lipids derived from dead colonic bacteria

Question 14

Summarise the digestive process

Answer 14

Lipid hydrolyis in the aqueous milieu of the intestinal lumen

catalysed by lipases

the products of lipolysis diffuse through the aqueous content of the intestinal lumen and enter the enterocyte for processing

Question 15

How and where does emulsification take place?

Answer 15

1. Food preparation
2. chewing and gastric churning allows mixing lingual and gastric juices
3. squirting of gastric contents into the duodenum
4. intestinal peristalsis mixes luminal contents with pancreatic and biliary secretions

These mechanical processes reduce the size of the lipid droplets and increases their ratio of SA to V

Question 16

What prevents these lipid particles from coalescing?

Answer 16

• coating the emulsion droplets with membrane lipids, denatured protein, dietry polysaccharides, products of digestion, biliary phospholipids and cholesterol
• The polar groups (hydrophilic) of the phospholipids project into the water; this prevent coalescence of the emulsion particles
• The core of the emulsion particle is composed of triglyceride, which also contains cholesteryl esters and other non polar lipids

Question 17

What happens in the mouth and stomach in terms of lipid digestion?

Answer 17

• Lipid digestion begins in the mouth, mediated by lingual lipase
• In stomach, both lingual lipase and gastic lipase (chief cells in response to gastrin/Ach) digest large amounts of lipid
• Lingual and Gastric lipase release a single fatty acid from triglycerides, leaving behind intact disaccharides
• The released long chain fatty acids are insoluble at acidic pH and remain in the core of triglyceride droplets
• medium and short chain fatty acids are ionised at acidic gastric pH, remain in solution and are passively absorbed across the gastric mucosa into portal blood
• 15 % fat digestion in stomach

Question 18

What happens in terms of fat digestion in patients with pancreatic insufficency- e.g. CF?

Answer 18

extended lingual and gastric lipase activity in the duodenal lumen partly alleviates fat malabsorption

Lingual lipase has a low pH optimum. Patients with CF has a low pH in the duodenum, thus lingual lipase can remain active through the stomach into the duodenum

Question 19

What happens once the fatty acids generated in the stomach reaches the duodenum?

Answer 19

Trigger the release of CCK from I cells in duodenal mucosa

CCK stimulates

• The flow of bile into the duodenum by gallbladder contraction and relaxation of the sphincter of Oddi
• The secretion of pancreatic enzymes, including lipases and esterases

Question 20

What is pancreatic lipase and what are the requirements for the full lipolytic activity of pancreatic lipase?

Answer 20

Pancreatic lipase is the major lipolytic enzyme which effectively digests all dietry triglycerides not hydrolysed in the stomach

Full lipolytic activity requires

1. Colipase- essential for ligand binding conformation
2. Alkaline pH
3. Bile salts
4. Fattty acids