25 :o

Question 1

To increase efficiency of absorbtion of products from the GI tract into the body we have evolved…

Answer 1

Specialised structures that create a vast surface area for absorbtion

E.g
Villi
Microvilli (brush border)

Question 2

Sugars are highly _____ ______ and thus cannot simply _______ across _____ ________

Answer 2

Sugars are highly water soluble and cannot simply difffuse acrosss cell membranes

Question 3

For sugar to pass through the membrane they require…

Answer 3

Specific transporter proteins anchored in the membrane that form ‘pores’ in the membrane

Question 4

Two types of transport with transporter proteins for sugar

Answer 4

active transport - against a concentration gradient that needs energy from ATP

facilitative transport - passage down a concentration gradient

Conformational change ?

Question 5

Exapmple of glucose transporter - transport across the intestinal epithelia.. what does it involve ?

Answer 5

involves two glucose transporters
- SGLT 1 (sodium glucose linked transporter), a secondary active transporter
- GLUT 2, a facilitative transporter

Question 6

T he SGLT 1 and GLUT 2 membrane transporters
YAPPAGE
- Diagram + Na+ concentrations

Answer 6

SGLT1 = symport - symolatnaously transport
- co transport of sodium ions at the same time
- lower Na+ inside epithelial cell - allows it to move passsivly
- if this increases too much the transporter wont work
- second transporter system Na/K ATPase has evolved on the other side of the epithlieul cell (by the blood circulation)
- hydrolyses ATP bond to realise energy making it a pump system
- transports na to of the epitheliual cell and back transfers K+ ions
- conc of glucose inside cell will also therefore increase in conc in epithelial cell
- second glucose transporter (GLUT2) allows the glucose inside the epithelial cell to be transported with the gradient

Question 7

Glucose transport by SGLT 1 involves simultaneous transport of sodium ions - how does glucose make it from lumen into the blood capillaries??!!?!@?@?

Answer 7

Symport of glucose and Na+ into the epithelial cell from intestine lumen by SGLT1 increases the concentration of both in the cell

The Na+/K+ ATPase pumps the Na+ out of the epithelial cell to maintain low Na+ in the cell, that facilitates symport of glucose by SGLT1. Hence SGLT1 is considered to be an ‘active transporter’

Elevated glucose in the cell facilitates the transport by GLUT 2 to blood capillaries

Question 8

Na+/K+ - ATPase actively transports Na+ to maintain low [Na+] in epithelial cells

How many Na2+ out of the cell for how many K+ into the cell

Answer 8

• For every 3 Na+ transported out of the cell, 2 K+ are transported into the cell
• Hydrolysis of ATP and phosphorylation of the transporter, leading to conformational change, enabling the transport of the Na+, followed by the K+

Question 9

Other glucose transporters:

Answer 9

Once in the circulation glucose is taken up by tissues such as liver, muscle and brain via other glucose transporters
- such as GLUT 4 (muscle, adipose) and GLUT 3 (brain)

Ubiquitous - found in many sites

Question 10

Question 11

Very little aborbtion of peptides longer than…

Answer 11

4 amino acids long

Question 12

How are di and tri-peptides in the small intestine absorbtion? What happens after absorbtion? (Absorbtion of peptides )

Answer 12

by co- transport with H + ions via membrane transporter PepT1.

Absorbed di- and tri-peptides are further digested into individual amino acids by cytoplasmic peptidases and exported from the epithelial cells into the blood circulation.

Question 13

How absorbtion of amino acids form the gastrointestinal tract works? Na+-dependent carriers!!

Answer 13

Absorption from the lumen of small intestine by transepithelial transport

Semi-specific Na+-dependent transport system Na+-dependent carriers transport both Na+ and an amino acid

(Semi-specific means there isn’t a transporter for every individual amino acid - just the different classes)

Active transport Na+ out of the cell couples with K+ - uses ATP - to keep levels low

Amino acid leaved cell via facilitated transporter

At least six different Na+-dependent carriers:
- neutral AA
- proline and hydroxyproline
- acidic AA
- basic AA (Lys, Arg) and cystine

Question 14

Uptake of intact proteins from gastrointestinal tract Occurs only in….

Answer 14

…. A few circumstances, for example new born animals (or humans)

– such as uptake of immunoglobulins in colostrum milk – acquisition of passive immunity

Question 15

Question 16

Disorders of carbohydrate and protein digestion and absorption
- lactose intolerance

Answer 16

Lactase enzyme deficiency (genetic basis)

Lactose sugar is not hydrolysed and as a result continues down the GI tract and Causes bloating, flatulence and diarrhoea due to fermentation of lactose by intestinal bacteria

Need to avoid lactose in diet

Question 17

Examples of diseases affecting digestive organs

Answer 17

1. Pancreatitis leads to inappropriate activation of
   zymogens (proenzymes), resulting in “self digestion”
2. Stomach (or peptic) ulcers due to the breakdown of
   the mucosa which normally protects against protease
   action.
3. Cystic fibrosis causes malabsorption
4. Coeliac disease also causes malabsorption

Question 18

Pancreatitis leads to

Answer 18

inappropriate activation of
zymogens (proenzymes), resulting in “self digestion”

Question 19

Stomach (or peptic) ulcers occur due to

Answer 19

the breakdown of
the mucosa which normally protects against protease
action.

Question 20

Cystic fibrosis causes

Answer 20

malabsorption

• ion channel issue which results in the formation of a lot of material being generated that blocks up surfaces
• blocked pancreatic duct that prevents enzymes from entering the stomach

Question 21

Coeliac disease also cause

Answer 21

malabsorption

Question 22

Peptic ulcer

Answer 22

• protease pepsin causes an irritation

Question 23

Cystic fibrosis - what dos it cause, what does it block, how can it be aided?

Answer 23

Causes thick mucous secretions which block the pancreatic duct and secretion of pancreatic enzymes

Can be aided by taking supplements containing pancreatic enzymes ie ‘pancreatin’, a pancreas extract

Question 24

What is Coeliac disease? What happens to villi?

Answer 24

Disease of the small intestine
Body reacts against gluten protein present in wheat
Antibodies react with transglutaminase (can be detected in a blood test if u have elevated levels of IgA compared to transglutanmwe)
Villi flattened, nutrients not absorbed
Gastrointestinal symptoms

Question 25

Normal and coeliac-disease small-intestine mucosae

Answer 25

Question 26

Digestion of dietary nucleic acid polymers

Answer 26

DNA and RNA are subject to partial acid hydrolysis in the stomach

Intestinal endonuclease enzymes hydrolyse the phosphodiester bonds linking individual nucleotides

Exonuclease enzymes release individual nucleotides (nucleoside monophosphates)

Individual nucleotides are absorbed via nucleotide transporters

Question 27

General structure of DNA and RNA nucleic acid polymers and what happens in the stomach and intestine

Answer 27

Individual nucleotides are linked together by phosphodiester bonds in nucleic acid polymers.
Nucleic acid polymers consumed in the diet are partially hydrolysed by the acidic conditions in the stomach and subsequently by endo- and exo-nuclease enzymes in the intestine