Physiology of digestion and Absorption Lecture 2

Question 1

3 types of digestible carbohydrates

Answer 1

Polysaccharides (45-60%)
Oligosaccharides (30-40%)
Monosaccharides (5-10%)

Question 2

Examples of polysaccharides

Answer 2

Starch (plants) 
and glycogen (animals)

Question 3

Examples of oligosaccharides

Answer 3

Sucrose (table sugar)

lactose (milk sugar)

Question 4

Examples of monosaccharides

Answer 4

Glucose

Fructose

Question 5

What enzyme concerts starch to oligosaccharides

Answer 5

alpha amylase

Question 6

What enzymes converts oligosaccharides to monosacharites

Answer 6

Oligosacharidases

Question 7

What form of carbohydrates are absorbed

Answer 7

Monosacharides
Glucose
Fructose
Galactose

Question 8

What are oligosaccharidases

Answer 8

Intergal membrane proteins with a catalytic domain that faces the lumen of the Gi tract

break down oligosaccharides to monosaccharides

Question 9

What is lactose intolerance

Answer 9

Digestive problem resulting from in inability to actively digest lactose and convert it to a monosacharide

Caused by LACTASE insufficiency

Question 10

Types of lactase deficiency causing lactose intolerance

Answer 10

Primary lactase deficiency - lack of lactase persistence (lactase usually lost after weening but most have a gene to cause it to persist)

Secondary lactase deficiency - caused by damage to the proximal small intestine

Congenital lactase deficiency - rare autosomal disease - inability to digest lactose from birth

Question 11

Consequences of lactase insufficiency

Answer 11

Hypolactasia - lactose-containing food consumed causing the remaining lactase to be overwhelmed

bloating 
abdominal pain 
flatuence 
acidification of the colon 
Increased osmotic load- loose stool and diarrhoea

Question 12

Where does absorption of monosaccharides occur

Answer 12

Duodenum and jejunum

Brush border

Question 13

Glucose, galactose and fructose are all absorbed into enterocytes via secondary active transport true/false

Answer 13

False
glucose and galactose are absorbed via secondary active transport by SGLT1 with Na+

Frucose is absorbed by facilitated diffusion via GLUT5

Question 14

What must proteins be digested to to allow them to be absorbed

Answer 14

Oligopeptides

Amino acids

Question 15

How are proteins digested in the stomach

Answer 15

HCL begins to denature them

Pepsin cleaves proteins into peptides

Question 16

How are proteins digested in the duodenum

Answer 16

5 pancreatic proteases are secreted as proenzymes (not active) which act as endopeptases (break middle of chain) and exopeptases (break ends of chain)

Question 17

What proteases are secreted by the exocrine pancreas

Answer 17

Trypsin 
Chymotrypsin 
Elastase 
Procaroxypeptidase A 
Procaroxypeptidase B

Question 18

Where are additional proteases present other than in the pancreas

Answer 18

Brush border

Cytoplasm of enterocytes

Question 19

What are the 7 mechanism of protein absorption at the brush border

Answer 19

5- Na+ dependent co-transporters - secondary active transport

2 Na+ independent

Question 20

What are the 5 mechanism of protein absorption at the basolateral membrane

Answer 20

3 mediate efflux of amino acids and are Na+ independent

2 mediate influx (supply enterocytes own demand) and are Na+ dependant

Question 21

How are di- try- and tetra- peptides absorbed

Answer 21

Via H+ dependant mechanisms at brush border PepT1
Further hydrolyses into amino acids inside the enterocytes
The absorbed at basolateral membrane by Na+ Independant transport