Digestion of Carbs, Proteins and Fat

Question 1

What are the features of the salivary glands?

Answer 1

The acinar is the cuboidal epithelial gland lining the salivary which has a characteristic and bulbous test tube shape.

Question 2

What occurs in the mouth?

Answer 2

Salivary gland releases lingual lipase for breakdown of trialglycerol (esp for neonates) and amylase for breakdown of starch. Teeth break food into a bolus which is pushed by the tongue to the back of the mouth.

Question 3

What are Ebner’s glands?

Answer 3

Ebner’s glands are on the dorsum of the tongue in the lamina propria. These secrete a serous solution containing lingual lipase between the sublingual papillae at the base of its invaginations. This is important for milk fat digestion by neonates.

Question 4

What occurs in the stomach?

Answer 4

In the stomach, the chief cells release pepsinogens which become cleaved in the presence of gastric acid to form pepsin. Gastric acid and pepsin digest proteins, gastric lipase digests lipids.

Question 5

How does emulsification of fat occur?

Answer 5

The churning action of the stomach is responsible for the emulsification of fat into smaller droplets at 37 degrees Celsius.

Question 6

How are proteins digested in the small intestine duodenum?

Answer 6

Trypsin cleaves other pepsinogen precursors such as chymotrypsinogen, proelaste, procarboxypeptidase, proaminopeptidase for digestion of dipeptides

Question 6

How are proteins digested in the small intestine duodenum?

Answer 6

Trypsin cleaves other pepsinogen precursors such as chymotrypsinogen, proelaste, procarboxypeptidase, proaminopeptidase for digestion of dipeptides

Question 7

Where and how are proteins absorbed?

Answer 7

Proteins can only be absorbed in the form of dipeptidase and free amino acids. Amino acid carriers such as the Na+/K+ ATPase transports this inside for absorption into the intestinal mucosa cells of the small intestine.

Question 8

What is glycaemic index?

Answer 8

Glycaemic index measures blood glucose levels following a meal. Foods with high GI such as ice cream and jasmine rice will increase insulin and blood glucose levels and reduce digestion. Foods with a low GI such as non-starch polysaccharides like wheat and oats will not cause fluctuations in blood glucose which will remain stable.

Question 9

Why are non-starch polysaccharides useful in diet?

Answer 9

It adsorbs onto bile, which can cause cancer. It adsorbs onto cholesterol which reduces cholesterol levels. via excretion.

Question 10

What does the non-starch polysaccharide form when fermented?

Answer 10

It produces propanyroate and butyrate. Butyrate has an anti-proliferative effect to prevent cancer and propanoate reduces hunger.

Question 11

What are the differences in absorption of different nutrients in the body?

Answer 11

Alcohol-. 100%
Carbs -> 99%
Fat -> 95%
Protein-> 92%

Question 12

How does the pancreas contribute to digestion?

Answer 12

The pancreatic acinar cells secrete pancreatic lipase, phospholipase A2 and cholesterol ester hydrolyse into the pancreatic duct which is deposited into the small intestine.

Question 13

What is the process of fat digestion in the stomach?

Answer 13

Trialglycerol -> gastric lipase -> dialglycerol which frees one fatty acid
Dialgylcerol -> pancreatic lipase -> 2-monoalglycerol
2-monoalglycerol -> cholesterol ester hydrolase -> glycerol (this is the slowest reaction)

Question 14

Why is the digestion of fats incomplete?

Answer 14

Cholesterol ester hydrolase reaction to digest monoalgycerol to glycerol is the slowest

Question 15

How are bile salts produced?

Answer 15

Bile is produced in the liver from the breakdown of cholesterol in hepatocytes in the form of bile acid
Cholesterol-> Bile acid
The conjugation of Bile acids with glycine and taurine to make it more polar and association with salty ions NA+ or K+ -> Bile salt.

Question 16

What are bile salts?

Answer 16

Bile salts are involved in solubilising the fat droplets for absorption into the aqueous small intestine. The bile salts are powerful biological detergents which disrupt the hydrophilic and hydrophobic interactions. It is composed mainly of 97% water then bile salts and bile pigment.

Question 17

How is a micelle formed?

Answer 17

The micelle has a spherical amphipathic structure of hydrophilic heads and hydrophobic tails in the core. When bile salts bind to the emulsified fat droplets, it orientates its hydrophobic region facing the core and the hydrophilic side facing the shell.
This prevents steric hindrance when crossing the membrane which is the slowing of chemical reactions.

Question 18

What is the role of co-lipase?

Answer 18

Colipase anchors the lipase to prevent disassociation following bile salt binding. During this phase, there is no release of fatty acids.

Question 19

What are lipoproteins?

Answer 19

Lipoproteins are a carrier molecule composed of proteins bound to lipids for the transport of hydrophobic lipids across an aqueous medium. For micelles, this is the small intestine.

Question 20

How are chylomicrons formed?

Answer 20

Once micelles are absorbed inside the intestinal cells, it passes from the endoplasmic reticulum to the Golgi apparatus. As it travels, the micelles form bonds with trialglycerol and phospholipids and are re-esterified with free fatty acids in order to assemble into a chylomicron lipoprotein. A structural component called an apolipoprotein is also synthesised which stabilises the chylomicron.

Question 21

What are chylomicrons?

Answer 21

An ultra-low density lipoprotein which transports lipids to the body tissues.

Question 22

How are chylomicrons distributed?

Answer 22

The chylomicron moves to the basolateral EC membrane of the enterocytes of the jejunum. It is too big to enter the capillaries so leaves by exocytosis into the mesentery lymphatic node of the lymphatic system. It moves into the thoracic duct where some of the fat is removed when distributed to the peripheral tissues. Remaining is deposited into the subclavian vein to enter blood circulation. The rest is taken up by the liver for metabolism into bile acids to be recirculated.

Question 23

How can fat distribution to tissues be reduced?

Answer 23

To prevent the release of chylomicrons into the lymphatic circulation, blocking protein synthesis will cause accumulation of the fat droplets

Question 24

What is the difference in lipoprotein fat distribution?

Answer 24

Chylomicrons transport protein to tissue via the plasma. LDL, VDL and HDL transport fat in the plasma to tissues.

Question 25

What are VLDL?

Answer 25

Very low-density lipoproteins- synthesised in the Liver and is responsible for the transport of fat to the peripheral tissues. Once fat is depleted it forms IDL (Intermediate density lipoprotein)

Question 26

What is LDL?

Answer 26

Low density lipoproteins- formed from IDL, High content in the blood plasma and delivers fat and fat soluble vitamins to the tissues

Question 27

What is HDL?

Answer 27

High density lipoproteins are produced in the liver and intestine with a disc like shape.=. It responsible for transporting excess cholesterol to the liver to be metabolised into bile acid for absorption and excretion in the intestinal tract. They have a disc like shape

Question 27

What is HDL?

Answer 27

High density lipoproteins are produced in the liver and intestine with a disc like shape. It responsible for transporting excess cholesterol to the liver to be metabolised into bile acid for absorption and excretion in the intestinal tract.

Question 28

What is cholelithiasis?

Answer 28

Gall stones are when bile storage in the gall bladder hardens. It forms because the chemical composition of the bile salt is imbalanced with excess cholesterol. When gall stones are present in the gall bladder, it is called a cholelithiasis.

Question 29

What are the risk factors for gall stones?

Answer 29

Caucasian, female, overweight, high starch and cholesterol/low fibre diet.

Question 30

What is the structure of fat?

Answer 30

Fats have the same composition of a trialglycerol structure in butter, cooking oil and margarine. This is three acyl chains bonded to a glycerol molecule via an ester bond.

Question 31

What are the cellular sources of fat in food?

Answer 31

Phospholipids in cell membranes.
Cholesterol in cell membranes
Cholesterol esters in adipose stores within animal cells.

Question 32

What are the sources of fat in the diet?

Answer 32

Milk products like milk, cheese, butter, margarine and cooking oils. Another source of dietary fat intake is the w3 and w6 essential fatty acids linoleic acid

Question 33

What are the benefits of omega 3?

Answer 33

Omega 3 is derived from fatty fish, green vegetables like kale and vegetable oil. It is a polyunsaturated fatty acid which has an anti-inflammatory effect. It is involved in regulation of blood clotting, formation cellular brain membrane and BP.

Question 34

What are the benefits of omega 6?

Answer 34

Omega 6 is derived from vegetable oils, meat, poultry, and soybean. It produces inflammatory mediators.

Question 35

What are the benefits of fat?

Answer 35

We derive 40% of our energy intake from fats. Fats are essential for the absorption of Vitamin A, D, E and K.