Disorders of Lipid Metabolism

Question 1

How are triglycerides transported?

Answer 1

Via lipoproteins

Question 2

What are the two major lipoproteins?

Answer 2

• Chylomicrons (large and synthesised by enterocytes)
• Very low density lipoproteins (second largest and rich in triglyceride, synthesised by the liver)

Question 3

Name four major points about chylomicrons

Answer 3

1. largest lipoprotein and the richest in triglyceride
2. synthesised by enterocytes
3. secreted into lymph
4. transport lipid to tissues

Question 4

Why cant TG’s be transported via aqueous media

Answer 4

TG’s are hydrophobic

Question 5

What is lipolysis?

Answer 5

TG is broken down into glycerol and three NEFA’s

Question 6

What is the name of the enzyme that transfers TG via VLDL to tissues?

Answer 6

lipoprotein lipase

Question 7

What enzyme removes lipoprotein remnants from the liver?

Answer 7

hepatic lipase

Question 8

Why does Insulin inhibit ketogenesis?

Answer 8

Insulin increases the uptake of fatty acids
fewer fatty acids = less ketogenesis

Question 9

What are the four main disorders of lipid metabolism?

Answer 9

• Hyperlipaemia
• Hepatic lipidosis
• Pregnancy ketosis
• Acetonaemia

Question 10

What is the definition of hyperlipaemia in equids?

Answer 10

• Plasma TG is higher than 5mmol/ L
• causes an individual to become sick (low appetite)

opaque plasma

Question 11

What is the definition of hypertriglyceridaemia in equids?

Answer 11

• Plasma triglyceride will be higher than normal
• not sick or inappetent
• minimal plasma opacity

Question 12

What is the definition of severe hypertriglyceridaemia?

Answer 12

• Very high plasma TG
• subject may be sick due to another process but not hypertriglyceridaemia

Question 13

What are the clinical signs of ketosis in cattle

Answer 13

• Increase B-hydroxybuturate
• occurs in high yielding dairy cows
• occurs either in late pregannacy or early lactation
• any cow that is overconditioned (they become insulin resistant)

Question 14

What is type I ketosis in cattle?

Answer 14

• Occurs at peak lactation
• When glucose availability is low due to milk
• low glucose oxidation

Question 15

What is type II ketosis?

Answer 15

• Occurs immediately post-partum
• Cows are potentially insulin resistant

Question 16

What are the clinical features of pregnancy ketosis in sheep and goats?

similiar to type I ketosis

Answer 16

• Usually occurs in heavily pregnant does and ewes
• Older ewes
• May occur if there are multiple foetuses
• usually triggered by feed restrcition
• diseases in late pregnancy

Question 17

What are the characteristic features of hepatic lipidosis

Answer 17

• common cause of liver disease in cats
• especially affects overweight cats

Question 18

What is the structure of a lipoprotein?

Answer 18

• Outer phospholipid shell
• Apolipoproteins within the shell

Question 19

What pathway is inhibited by insulin?

Answer 19

Lipolysis

Question 20

What pathway is stimulated by insulin?

Answer 20

Lipogenesis

Question 21

What stimulates lipolysis?

Answer 21

• Catecholamines
• GH
• Cortisol
• TNF alpha

Question 22

What enzyme helps transfer TG to tissues?

Answer 22

Lipoprotein Lipase

stimulated by insulin and heparin

Inhibited by TNF alpha

Question 23

What are the clinical features of hyperlipaemia in equids?

Answer 23

They become insulin resistant

Question 24

What is primary hyperlipaemia?

Answer 24

Occurs without pre-existing disease

Negative energy balance?

Question 25

What is secondary hyperlipaemia?

Answer 25

occurs following a separate pre-existing disease condition

Negative energy balance

Question 26

What are the characteristic clinical features of ketosis in cattle?

Answer 26

• B-hydroxybutyrate is above 1.2 mmol / L
• High yielding dairy cows
• Late pregnancy/ early lactation
• Overconditioning- insulin resistant

Question 27

What are the characteristic features of hepatic lipidosis in cats?

Answer 27

• Most common cause of liver disease in cats
• especially affects overweight cats
• hepatic TG accumulation is prevalent,, hepatic ketosis also occurs and may cause a characteristic smell

Question 28

What are the characteristic features of seasonal pasture myopathy?

Answer 28

• Acute non-exertional rhabdomyolysis syndrome
• Affects healthy, grazing horses, ponies, donkeys, zebra
• Largely fatal
• Seasonal

Question 29

What is the structure of triglycerides?

Answer 29

Glycerol + Fatty acids = esterification
* Free fatty acids = non-esterified

Question 30

TG’s have to be packaged within…?

Answer 30

Lipoproteins

Question 31

What is the basic pathway of Lipid metabolism?

Answer 31

• TF in fat stores is then converted into NEFA and glycerol in the plasma
• In the liver they are re-converted into TG, ATP and ketones
• TG is then incorporated into VLDL
• Tissues extract NEFA from the VLDL
• remnants return to the liver

Question 32

What doesa lack of glucose promote?

Answer 32

• NEFA enters the mitochondria
• ketone synthesis occurs
• ketone is then used as a peripheral energy source, sparing glucose for mammary glands and foetus

Question 33

What enzyme removes TG remnants from the plasma?

Answer 33

Hepatic lipase

inhibited by TNF alpha

Question 34

What enzyme transfers TG within VLDL to tissues?

Answer 34

Lipoprotein lipase

Inhibited by TNF alpha

Question 35

How does insulin inhibit ketogenesis?

Answer 35

• If glucose is broken down the products of glucose oxidation block CPT1 activity and NEFA entry into the mitochondria
• therefore no ketogenesis occurs
• ketones are usally used as aperipheral energy source

Question 37

What is the pathophysiology of seasonal pasture myopathy?

Answer 37

• hypoglycin A from sycamore seeds and seedlings
• essentially blocks CPT1 (entry of NEFAS)
• blocks enzymes involved in B-oxidation
• MADD
• No ATP production via beta-oxidation