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GB > 10. Digestion and Absorption of Lipids and Iron > Flashcards

10. Digestion and Absorption of Lipids and Iron Flashcards

1
Q

What lipid digestion occurs in the mouth?

A

Mastication
Emulsification
Lingual lipase

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2
Q

What do lingual and gastric lipase act on?

A

TAGs with short to medium fatty acid chains

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3
Q

What emulsifies lipids in the duodenum?

A

Bile salts

Peristalsis

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4
Q

How does pancreatic lipase degrade lipids?

A

Binds to the surface of the droplet in the presence of pancreatic colipase
Complex spreads out over the surface of the droplet
TAGs are hydrolysed to monoacylglycerol and fatty acids

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5
Q

What is the function of cholesterol esterase?

A

Hydrolyses cholesterol esters to cholesterol and free fatty acids

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6
Q

What increases the activity of cholesterol esterase?

A

Bile salts

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7
Q

What is the function of phospholipase A2?

A

Digests phospholipid to lysophospholipid by removing a fatty acid

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8
Q

What activates phospholipase A2?

A

Trypsin

Requires bile salts for optimum activity

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9
Q

What is the function of lysophospholipase?

A

Removes remaining fatty acid at C1

Leaves a glycerylphosphoryl base

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10
Q

What do the products of fat digestion form?

A

Mixed micelles

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11
Q

What is contained in a mixed micelle?

A

Bile salts
Free fatty acids
Free cholesterol
2-monoacylglycerol

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12
Q

How do mixed micelles assist in the absorption of lipids by enterocytes?

A

Hydrophilic surface of micelles facilitates transport of hydrophobic lipids across the brush border membrane

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13
Q

Where are fatty acids and monoglyceride transported?

A

Endoplasmic reticulum

Used to synthesise TAGs

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14
Q

What are new TAGs grouped with to form chylomicrons?

A 
Cholesterol esters
Free cholesterol
Phospholipids
Vitamins
Apo B48
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15
Q

How do new chylomicrons enter circulation?

A

Go to golgi apparatus
Extruded from golgi into exocytotic vesicles
Transported to the basolateral aspect of enterocyte
Vesicles fuse with the plasma membrane
Undergo exocytosis
Chylomicrons are dumped into the extracellular space and enter the lymph

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16
Q

What does normal absorption of lipids and fat soluble vitamins depend on?

A

Bile salts
Normal pancreatic function
Normal intestinal cells

17
Q

What conditions can result in mal-absorption syndromes?

A 
Pancreatic insufficiency
Inadequate mucosal surface
Inflammatory states
Infection
Surgery
Cystic fibrosis
Disaccharidase deficiency
18
Q

What are some symptoms of malabsorption states?

A 
Weight loss
Weakness
Failure to thrive in infants
Steathorrhoea
Intestinal discomfort
Diarrhoea
Vitamin deficiencies
19
Q

How can malabsorption states be detected?

A 
Endoscopy/biopsy
Serum enzymes (pancreatitis)
20
Q

How much iron is contained in the body?

A

2-4g

21
Q

What is the average intake of iron?

A

20mg/day

22
Q

What happens when iron levels drop?

A

Storage iron is mobilised first
Haemoglobin synthesis is impaired
Chronic deficiency results in microcytic hypochromic anaemia

23
Q

What is haemosiderosis?

A

Accumulation of ferritin and hemosiderin

Leads to free radical generation

24
Q

What is haemochromatosis?

A

Progressive hemosiderosis
Results in organ damage
Associated with mutation in HFE gene

25
Q

How can iron overload be treated?

A

Repeated phlebotomy

Iron chelator

26
Q

Name an iron chelator

A

Desferrioxamine

27
Q

What change does iron undergo in the stomach?

A

Fe+++ reduced to Fe++

Favoured by low pH and reducing agents (ascorbic acid)

28
Q

What change does iron undergo in the small intestine?

A

Iron dissociates from haem
Fe++ oxidised to Fe+++
Taken up by mucosal cells

29
Q

What transporter moves haem in the enterocyte?

A

Haem Carrier Protein 1

30
Q

What releases Fe++ from haem? (haem iron)

A

Haem oxidase

31
Q

What reduces Fe+++? (non-haem iron)

A

Duodenal cytochrome B

32
Q

What transports Fe++ into the enterocyte? (non-haem)

A

Divalent Metal Transporter 1 (DMT1)

33
Q

What is cytosolic iron stored as?

A

Ferritin

34
Q

What transports iron across the basolateral membrane?

A

Ferroportin

35
Q

What converts Fe++ back to Fe+++ in the enterocyte?

A

Hephaestin

36
Q

What does Fe+++ bind to for transport around the body?

A

Transferrin

37
Q

What reduces iron absorption?

A 
Tannins
Oxalate
Phytate
Inorganic phosphates
Phosphate-containing antacids
38
Q

How does iron enter a cell?

A

Endocytosis via a transferrin receptor
CURL is formed
Fe+++ is released and stored in ferritin in the cytoplasm of the cell
Apotransferrin (transferrin without iron) is recycled to the surface

39
Q

Which state is most iron stored in?

A

Fe+++

Stored in ferritin as FeOOH crystals

GB (15 decks)

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