Lipid digestion, absorption and transport

Question 1

name the structural components of lipids and lipid classification

Answer 1

• COOH (carboxyl group)
• Steroids - ring structure that doesn’t contain enough hydroxyl groups to make them water soluble
• phospholipids
• triglyceride
• fatty acids

Question 2

why are lipids hydrophobic?

Answer 2

• are made up of ring structure - steroids which do not contain enough hydroxyl groups to make them water soluble

Question 3

what are phospholipids

Answer 3

• made up of 2 fatty acids and a phosphate group
• major component of the cell membrane

Question 4

what is the main dietary neutral fat

Answer 4

triglyceride/ treacly glycerols (TAG)
- made up of 3 carbon backbone and 3 fatty acids

Question 5

what are the major components of all types of fats

Answer 5

fatty acids

Question 6

what are 3 types of fatty acids

Answer 6

saturated
monounsaturated
polyunsaturated

Question 7

what is a saturated fatty acid

Answer 7

has maximum possible number of hydrogen atoms attached to every carbon atom
- ‘saturated’ with hydrogen atoms and all of the carbons are attached to each other with single bonds

Question 8

what are unsaturated fatty acids

Answer 8

• a pair of hydrogen atoms in the middle of a chain is missing creating a gap that leaves two carbon atoms connected by a double bond rather then a single bond
• chain has fewer hydrogen atoms- unsaturation

Question 9

what is a monounsaturated fatty acid

Answer 9

a fatty acid with one double bond because it has one gap

Question 10

what are polyunsaturated fatty acids

Answer 10

fatty acids having more than one gap are called polyunsaturated

Question 11

what type of fatty acids are present usually in foods of animal and plant origin

Answer 11

in animal origin- a large proportion of fatty aces are saturated
in plant origin and some seafood- large proportion of fatty acids are monounsaturated and polyunsaturated

Question 12

which types of food are saturated fats found in

Answer 12

• butter, cheese,while milk, ice cream, lard and fatty meats
• found in some vegetable producs such as coconut, palm and palm kernel oil
• saturated fats are solid at room temperature
• raise your cholesterol

Question 13

where do monounsaturated fats come from

Answer 13

seeds or nuts such as avocado, olive, peanut and canola oils
- may reduce total cholesterol and LDL cholesterol
- liquid at room temperature

Question 14

where do polyunsaturated fats come form?

Answer 14

vegetables, seeds or nuts such as corn safflower,sunflower,soybean, cotton seed and sesame seed oils
- lower cholesterol
- use them in place of saturated fats
- ;liquid at room temperature

Question 15

how are trans fats made?

Answer 15

• vegetable oils are processed or hydrogenated into shortening and stick margarine
• sources of trans fats include snack foods, baked foods and fired foods made with ‘ partially hydrogenated vegetable oil’

Question 16

what are the 7 functions of lipids?

Answer 16

• fat is one of the body fuels for energy, it serves as a source of energy once calories form carbohydrates are used up
• fat helps the body absorb important fat-soluble vitamins (Vitamins, A,D,E,and K)
• fat supports key body processes such as acting as biosynthetic precursors (steroid hormones form cholesterol)
• fat cushions internal organs and protects them from being damaged (kidneys are shielded with fat in fed state)
• the fat layer below the skin also insulates the body from heat loss
• fat plays a vital role in maintaining healthy skin and hair
• Fat (phophsolipids) form part of the myelin sheath around nerve and nervous tissue including brain and spinal cord

Question 17

how many calories does each gram of fat provide

Answer 17

9 calories

Question 18

what health problems is associated with excessive dietary fat?

Answer 18

obesity, diabetes, cancer,hypertension and atherosclerosis

Question 19

what is the FDA advice for fats and energy intake

Answer 19

not more than 35% of energy intake should come from fat. Saturated fat should not make up more than 10% of the total fat intake

Question 20

what is the daily value for total fat?

Answer 20

65g per day
based on a 2,000 calorie diet

Question 21

what does Omega 3-fattya acids (20 carbons) from fish protect?

Answer 21

protect against atherosclerosis. American heart association recommends 2-3 fish meals per week
- fish supplements should be avoided because they may contain concentrated toxins accumulated by the fish

Question 22

describe lipid digestion

Answer 22

• oral cavity : lingual lipase and chewing
• stomach - lingual lipase and gastric lipase split triglyceride into diglycerides and fatty acids , only 30% break down occurs after 2-4 Hours in stomach
• lingual lipases and gastric lipases are also known the acidic lipases as their activity is stimulated and increased by an acidic environment
• Small intestine - acid chyme stimulates mucosa cells to release a hormone (choleocytsokinin) which stimulate gall bladder and pacreas to release bile and digestive enzymes respectively

Question 23

what does bile help in breaking down fats

Answer 23

bile salts help emulsify fat droplets thus increasing their surface area exposed for digestion and pancreatic lipase breaks down triglycerides and diglycerides to 2- monoglycerides and fatty acids

Question 24

how does emulsification of lipids occur?

Answer 24

Bile salts/ acids are secreted from the gall bladder and contain cholesterol
- bile salts/acids have hydrophobic and hydrophilic side
- the hydrophobic side attaches itself to the lipid and emulsifies it increasing the surface area that can be acted upon by pancreatic lipase

Question 25

name the different enzymic digestions of lipids in small intestine

Answer 25

- triglyceride uses pancreatic lipase to break down to 2 FA and 2-monoacylglycerol (2 FA from carbon 1&3 are removed leaving 1 FA attached to carbon 2 of the glycerol) - cholesterol ester is broken down by cholesterol ester hydrolase to cholesterol and fatty acid - phospholipids is broken down by phospholipase A2 to lysophospholipid + fatty acid which uses lysophosplipase to form glcyerolphosphoryl base + fatty acid

Question 26

what medication is used to treatment of obesity

Answer 26

-Orlistat or Xenical - inhibits action of pancreatic lipase which inhibits digestion and absorption of lipid (only 30% of lipid intake)

Question 27

how are lipids absorbed

Answer 27

- as fatty acids are released from TAGs by digestion, they retain their association with bile acid and complex with other lipid to form structures called micelle. - this will make them have a water soluble coat that will aid their transport into the mucosal lining of the intestines - the ingest containing the micelles approach the brush border of the intestinal lining cells the lipid,monoglycerides and micelles are taken up by the epithelaila cells enterocytes

Question 28

describe lipids absorption

Answer 28

- the micelles and phospholipids enter the enterocytes via simple diffusion - if fats are not absorbed properly as is seen in some medical conditions, a persons stool will contain high amounts of fat - if fat malabsopriton persist the condition is known as steatorrhea

Question 29

what is steatorrhea

Answer 29

- fats not absorbed properly - result from diseases that affect absorption such as Crohn's disease and cystic fibrosis - higher solubility - enter brush border by simple diffusion

Question 30

how are lipids transported

Answer 30

- triglycerides are reassembled inside enterocytes and are combined with apoproteins, phospholipids and cholesterol to form CHYLOMICORNS - CHYLOMICORNS are lipoprotein particles made of apoproteins,triglycerides ,phospholipids and small amount of cholesterol - chylomicrons are packaged into vesicles in the Golgi apparatus - they leave the intestinal cells basolateral border by exocytosis

Question 31

what to chylomicrons do

Answer 31

- help transport lipids into lymph vessels n the intestine Calle the central lacteal, they are transported through the lymph vessels and enter the blood circulation via the thoracic duct

Question 32

determine the classes of lipoproteins

Answer 32

Chylomicrons formed in intestine Glycoproteins - mixture of lipids and proteins Classified according to the density High density- high protein density

Question 33

describe the composition of the different lipoproteins

Answer 33

Question 34

where are chylomicorsn assembled

Answer 34

intestinal mucosal cells

Question 35

what is the largest lipoprotein

Answer 35

chylomicrons with diameters of 75-600 nm - lowest protein to lipid ratio - lowest density

Question 36

where are chylomicrons synthesised and secreted by

Answer 36

chylomicrons are synthesised by absorptive cells of the intestinal lining and are secreted by these cells into the lymphatic system which joins the blood circulation at the subclavian or by the jugular vein.

Question 37

where is the primary destination in peripheral areas for cholymicrons

Answer 37

- Their primary destinations in peripheral areas are heart muscle, skeletal muscle, adipose tissue, and lactating mammary tissue. -The transfer of triglycerides and cholesteryl esters to the tissues depletes the lipid-protein aggregates of these substances and leaves remnant chylomicrons, which are eventually taken up by the liver. The lipid and protein remnants are used to form VLDL and LDL, described later

Question 38

what are VLDL - very low density lipoproteins

Answer 38

- synthesised by liver - analogous to the chylomicrons secreted by the intestine - deliver triglycerides, cholesterol esters, and cholesterol to peripheral tissues - VLDL largely depleted of its triglyceride content in these tissues and gives rise to an intermediated density lipoprotein remnant which is returned to the liver in the blood stream

Question 39

what are low density lipoproteins (LDL)

Answer 39

- derived form VLDL and IDL in the plasma - contain a large amount of cholesterol and cholesterol esters - role is to deliver these 2 forms of cholesterol to peripheral tissues = almost 2/3 if cholesterol and its ester found in plasma is associated with LDL

Question 40

describe HDL- high density lipoprotein

Answer 40

- lipoproteins of this class are the smallest and the highest protein - to lipid ratio - the resulting high density gives this class its name -HDL plays primary role in the removal of excess cholesterol from cells and returning it to the liber , where it is metabolised to bile acids/sakts -LDL and HDL together are the major factors in maintain the cholesterol balance of the body - Because of the high correlation between blood cholesterol levels and atheroscleroisis, high ratios of HDL to cholesterol correlate well with lower incidence of this disease in humans

Question 41

what are health implications of LDL

Answer 41

- carries cholesterol form liver tot he cells around the body where its needed, if level of LDL in the blood is too high, can form fatty deposits in the arteries and damage their linings - increases risk of coronary heart disease and stroke, LDL is called bad cholesterol

Question 42

what is good cholesterol ?

Answer 42

- HDL - helps removes other forms of cholesterol form the blood stream -higher levels of HDL cholesterol are associated with a lower risk of heart disease example: Omega 3 and fish oils are of LDL type and highly recommended to lower risk of CVS

Question 43

how is hyperlideamia treated?

Answer 43

Natural way of treatment of increased blood cholesterol levels: - Lowering fat intake and increasing fiber intake. - Cholesterol absorption is aided by an increase in dietary fat components and is hindered by high fiber content. This is the reason that a high intake of fiber is recommended to decrease blood cholesterol. - Foods high in fiber such as fresh fruits, vegetables, and oats can bind bile salts and cholesterol, preventing their absorption and carrying them out of the colon as waste .

Question 44

how are statins used to treat hyperlipidaemia?

Answer 44

- cholesterol is synthesised in the liver by a HMG CoA reductase enzyme - statins act by competitively inhibiting HMG-CoA reductase, the first and key rate limiting enzyme of the cholesterol biosynthetic pathway - Statins mimic the natural substrate molecules, HMG-CoA and compete for binding to HMGCoA-R enzyme