Macro and micronutrients: digestion

Question 1

What are the 3 macronutrients that we need in our diets to maintain homeostasis?

Answer 1

1 - carbohydrates

2 - proteins

3 - fats

Question 2

What is hydrolysis?

Answer 2

• breakdown of chemical bonds holding molecules together
• H+ and oxygen are added to the 1st carbon on one glucose
• the spare H+ from H2O is added to the 4th carbon on the 2nd gluocse
• the reactant is H2O which breaks down bonds in food

Question 3

Within carbohydrates, starch is held together by 2 forms of glucose polymers, what are these polymers called?

Answer 3

1 - amylose

2 - amylopectin

Question 4

Within carbohydrates, starch is held together by 2 forms of glucose polymers that hold carbohydrates together. Once of them is amylose, what is this?

Answer 4

• a polysaccharide made of α-D-glucose units
• bonded to each other through α(1→4) glycosidic bonds
• forms a linear structure

Question 5

Within carbohydrates, starch is held together by 2 forms of glucose polymers that hold carbohydrates together. One of them is amylopectin, what is this?

Answer 5

• polysaccharide made of α-D-glucose units
• bonded to each other through α(1→4 and 1→7) glycosidic bonds
• forms a branched structure

Question 6

What is the main enzyme in the oral cavity that begins digestion of carbohydrates in the oral cavity?

Answer 6

• α- amylase
• hydrolysis of α1-4 glycosidic bonds in starch
• forms maltose, maltotriose, and α–dextrins

Question 7

Maltose, maltotriose, and α–dextrins are the products of hydrolysis of α1-4 glycosidic bonds in the oral cavity. What is maltose?

Answer 7

• a sugar made out of two glucose molecules bound together

Question 8

Maltose, maltotriose, and α–dextrins are the products of hydrolysis of α1-4 glycosidic bonds in the oral cavity. What is maltotriose?

Answer 8

• a trisaccharide consisting of three glucose molecules linked with α-1,4 glycosidic bonds

Question 9

Maltose, maltotriose, and α–dextrins are the products of hydrolysis of α1-4 glycosidic bonds in the oral cavity. What are α–dextrins ?

Answer 9

• mixtures of linear α-(1,4)-linked D-glucose polymers starting with an α-(1,6) bond

Question 10

Does any starch digestion take place in the stomach and what dictates this digestion?

Answer 10

• no digestion in the stomach
• acid pH inhibits amylase

Question 11

Once starch reaches the small intestines, digestion begins again. There are 2 methods for starch to be digested in the small intestines, what are these?

Answer 11

1 - pancreatic secretions of α-amylase hydrolysis of α1-4 glycosidic bonds.

2 - enzymes present in the villi brush border

• maltase: hydrolysis of maltose
• sucrase: hydrolysis α1-4 glycosidic bonds and α1-6 glycosidic bonds

Question 12

Once carbohydrates have been digested sufficiencly in the small intestines, what is left that can be easily absorbed?

Answer 12

• glucose

Question 13

Once carbohydrates have been digested sufficiencly in the small intestines, glucose is the final product that can easily absorbed. How is glucose absorbed into the enterocytes at the apical (lumen surface)?

Answer 13

• use the Na+ / glucose transporter
• also called sodium-glucose co-transporter-2 (SGLT2)
• Na+ moves down concetration gradient
• glucose is taken against its concentration gradient

Question 14

Once glucose has entered the enterocytes, how does it leave and enter the blood stream?

Answer 14

• transporter called Glucose transporter 2 (GLUT-2)

Question 15

Why is the Na+ / K+ ATPase pump on the basolateral membrane important in glucose transport?

Answer 15

• Na+ is removed from enterocytes leaving a low Na+ concentration
• Na+ in lumen then moves down the concentration gradient into the enterocytes
• allows glucose to follow Na+

Question 16

In addition to providing energy for the body fats also serve an important process that helps vitamins to be absorbed. What are the vitamins that require fat to be absorbed?

Answer 16

• ADEK
• vitamins A, D, E and K

Question 17

Fat digestion begins in the oral cavity via mastication and a bolus formation, but what enzyme is responsible for the chemical digestion of fat in the oral cavity?

Answer 17

• lingual lipase.

Question 18

Lingual lipase is secreted in the oral cavity to begin fat digestion. Which salivary gland secretes lingual lipase?

Answer 18

• Ebner’s glands
• minor salivary glands located on both sides of your oral cavity
• back of your tongue

Question 19

Lingual lipase is secreted in the oral cavity to begin fat digestion by ebner’s glands located on both sides of your oral cavity at the back back of the tongue. What does lingual lipase do to triglycerides?

Answer 19

• hydrolyses triglycerides
• forms fatty acids and diglycerides

Question 20

Is lingual lipase still active in the stomach?

Answer 20

• yes

Question 21

In the stomach, in addition to lingual lipase that remains from the saliva, what other enzyme hydrolyses triglycerides into fatty acids and diglycerides?

Answer 21

• gastric lipase secreted by chief cells

Question 22

In the stomach lingual and gastric lipase are able to hydrolyse triglycerides into what?

Answer 22

• free fatty acids
• diaglycerides
• glycerides

Question 23

In fat digestion in the stomach the gastric contractions assist in mixing the contents. The diaglycerides also act as what that assists digestion?

Answer 23

• emulsifiers.

Question 24

The small intestines is is the primary site for absorption of fats. How does bile help with fat absorption and digestion?

Answer 24

• bile acts as an emulsifier
• emulsification ensures pancreatic lipase can access triglycerides
• also converts large fat globules into smaller fat globules

Question 25

Fats can be absorbed and transported across the micro-villi by 2 processes, what are these?

Answer 25

- transport in micelles - monoglycerides and fatty acids passively diffuse and via fatty acid transporter protein in plasma membrane

Question 26

Once fats are absorbed into the enterocytes of the small intestines, where are they transported to within the enterocytes?

Answer 26

- endoplasmic reticulum and latterly the Golgi - processed into triglyceride - triglycerides are then added to chylomicrons with cholesterol and lipoproteins

Question 27

Once fats have been processed inside the endoplasmic reticulum and golgi inside the enterocytes and processed into the chylomicrons, what happens to the chylomicrons?

Answer 27

- exocytosed via Golgi vesicles - exocytocic vesicles are transported to the basolateral aspect of the enterocyte into the lacteal (small lympharic vessels) - travel through lymphatics and into liver

Question 28

How are peptides held together to form proteins?

Answer 28

- peptide bonds

Question 29

What is the name of enzymes that are able to hydrolyse proteins and catalyse proteolysis?

Answer 29

- proteases

Question 30

Does protein digestion begin in the oral cavity or the stomach?

Answer 30

- stomach

Question 31

In the stomach, how does the low pH help with protein digestion?

Answer 31

- low pH denatures proteins - proteins are unfolded allowing access of enzymes

Question 32

In the stomach, once the low pH has denatured the proteins allowing access to peptide bonds, what does the stomach secrete to begin digestion and what cells secrete this?

Answer 32

- chief cells secrete pepsin - pepsin creates oligopeptide chains

Question 33

Once pepsin has hydrolysed proteins into oligopeptide chains, what enzymes in the small intestines continue the digestion of protein?

Answer 33

1 - trypsin 2 - chymotrypsin

Question 34

Once pepsin has hydrolysed proteins into oligopeptide chains, then enzymes trypsin and chymotrypsin continue the digestion of proteins. Are these pancreatic enzymes release in their active forms of trypsin and chymotrypsin?

Answer 34

- no as they may digest the pancrease - secreted as trypsinogen and chymotrypsinogen

Question 35

How are the inactive proteolytic enzymes trypsinogen and chymotrypsinogen activated in the small intestines to further digest proteins?

Answer 35

- enterokinase cleaves off amino acids from trypsin - phosphate is added making trypsin - trypsin can then activate other enzymes - enterokinase is a kinase secreted at the brush border mucosal membrane of the duodenum

Question 36

What do trypsin and chymotrypsin hydrolyse proteins into, that allows their absorption into the enterocytes?

Answer 36

- tripeptides - dipeptides - individual amino acids

Question 37

What ion is the absorption of amino acids dependent on?

Answer 37

- Na+ - Na+ binds to amino acids - sodium-dependent amino acid transporters undergo a confirmational change - Na+ and amino acid are deposited into enterocytes

Question 38

Once the amino acids enter the enterocytes do they all get transferred into the blood stream?

Answer 38

- no - some will remain to synthesis enzymes - the rest enter the blood stream at the baslateral membrane

Question 39

Bile is important for fat digestion, but it is also involved in the elimation of what waste products?

Answer 39

- biliruben from dead RBCs - cholesterol - drugs

Question 40

What are micronutrients?

Answer 40

- those that require only a small amount, hence micro - includes vitamins, minerals and trace elements