4.3. Dietary Nutrients and Absorption - Fat

Question 1

What is most ingested fat in the form of?

Answer 1

A Triacylglycerol

Question 2

What are Triacylglycerol’s found in?

Answer 2

A Water-Insoluble Large Lipid-Droplet (Large Fat Droplet)

Question 3

What forms a Triacylglycerol?

Answer 3

1 x Glycerol Molecule attached to 3 x Stearic Acid Molecules

Question 4

Why is Digestion of a Triacylglycerol slow?

Answer 4

As Digestion can only occur at the Surface of the Droplets

Question 5

What is done to increase the Rate of Digestion?

Answer 5

Emulsification occurs

Question 6

What is Emulsification?

Answer 6

The process of dividing the Large Lipid Droplet into Smaller Lipid Dropelets

Question 7

What is the Advantage of Emulsification?

Answer 7

It increases the Total Surface Area, so Digestion can proceed at a faster rate

Question 8

What Enzyme is responsible for the break down of Triacylglycerol?

Answer 8

Pancreatic Lipase

Question 9

What does Triacylglycerol break down into, under the influence of Pancreatic Lipase?

Answer 9

1 x Monoglyceride

2 x Stearic Acids (Fatty Acids)

Question 10

What is required for Emulsification to Occur?

Answer 10

1. Mechanical Disruption via the Mixing of the Luminal Contents
2. An Emulsifying Agent via an Amphipathic Molecule

Question 11

What is the Process of Mechanical Disruption?

Answer 11

The Turning of the Large Lipid Droplets into Small Lipid Droplets

Question 12

What allows for the Mixing the Luminal Contents?

Answer 12

The Contraction of Smooth Muscle

Question 13

What is the Function of the Emulsifying Agent?

Answer 13

To prevent the reformation of the Large Lipid Droplets

Question 14

What does the Emulsifying Agent consist of?

Answer 14

1. Bile Salts

2. Phospholipids

Question 15

What are Phospholipids?

Answer 15

Amphipathic Molecules

Question 16

What are Amphipathic Molecules?

Answer 16

Molecules with one Polar and one Non-Polar end

Question 17

What are the Non-Polar portions of the Amphipathic Phospholipids associated with?

Answer 17

The interior portion of the Droplets

Question 18

Which part of the Amphipathic Phospholipids are exposed to the Water Surface?

Answer 18

The Polar (charged) Portions

Question 19

What is the function of the Polar (charged) Portion of the Amphipathic Phospholipids?

Answer 19

To repel other Small Lipid Molecules (Which are also covered in Bile Salts) - preventing the formation of a large lipid molecule

Question 20

Does Emulsification alone speed up the digestion of Fats enough?

Answer 20

No

Question 21

What is done to enhance the speed of Digestion of Fats?

Answer 21

Micelles are formed

Question 22

What do Micelles consist of?

Answer 22

1. Bile Salts
2. Monoglycerides
3. Stearic Acids (Fatty Acids)
4. Phospholipids

Question 23

What are Micelles?

Answer 23

These are very similar to Emulsified Droplets, only much smaller (4-7µm in diameter)

Question 24

Is the Surface of the Micelles Polar (Charged) or Non-Polar (Uncharged)?

Answer 24

Polar (Charged)

Question 25

Is the Core of the Micelles Polar (Charged) or Non-Polar (Uncharged)?

Answer 25

Non-Polar (Uncharged)

Question 26

What acts on the Emulsion Droplets to form the Micelles?

Answer 26

Pancreatic Lipase

Question 27

How does the Pancreatic Lipase form the Micelles?

Answer 27

1. The Pancreatic Lipase causes the Splitting of the Triacylglyceride into the Monoglyceride and the 2 Free Fatty Acids, within the Emulsion Droplet
2. After these are split, they are released from the Emulsion Droplet
3. These are then surrounded by Bile Salts and Phospholipids to form the Micelles

Question 28

What is the relationship between the Micelles and the Free Fatty Acids / Monoglycerides?

Answer 28

There is a dynamic equilibrium between the Micelles created and the Free Fatty Acids / Monogycerides in the lumen - They are being broken down and reformed as needed

Question 29

How do the Free Fatty Acids (Stearic Acids) get into the Intestinal Epithelium?

Answer 29

Most of these are are stored in Micelles whilst the supply of Free Fatty Acids / Monoglycerides are constantly being replenished

Question 30

Are the Micelles themselves absorbed?

Answer 30

No, they are broken down and the Free Fatty Acids / Monoglycerides are absorbed

Question 31

How do the Free Fatty Acids / Monoglyecrides enter into the Epithelium of the Intestinal Lumen?

Answer 31

Via Diffusion - No Transporter is needed

Question 32

Why is no Transporter Protein needed for the Free Fatty Acids / Monoglyecrides?

Answer 32

Due to their Non-polar (Uncharged) Nature

Question 33

What happens to the Free Fatty Acids / Monoglyecrides after they enter into the Intestinal Epithelium?

Answer 33

They enter into the Smooth Endoplasmic Reticulum (sER)

Question 34

What happens to the Free Fatty Acids / Monoglyecrides in the Smooth Endoplasmic Reticulum of the Intestinal Epithelial Cells?

Answer 34

They are transformed back into Triglycerol

Question 35

What transforms the Free Fatty Acids / Monoglyecrides into Triglycerol?

Answer 35

The Enzymes present

Question 36

What happens to the Triglycerol once formed in the Smooth Endoplasmic Reticulum?

Answer 36

They are emulsified by Amphipathic Molecule to form a Vesicle and are then processed by the Golgi Apparatus

Question 37

What happens to the Triglycerol once entered into the Golgi Apparatus?

Answer 37

1. They are converted into Chylomicrons

2. They are transported and Exocytosed into the Lumen

Question 38

What are Chylomicrons?

Answer 38

Extracellular Fat Droplets

Question 39

What do Chylomicrons contain?

Answer 39

1. Phospholipids
2. Cholesterol
3. Fat-Soluble Vitamins

Question 40

Can Chylomicrons pass through the Capillary Basement Membrane?

Answer 40

No

Question 41

What do the Chylomicrons pass between?

Answer 41

Endothelial Cells, called Lacteals