Enteric Infection (GIT)

Question 1

What are the general outcomes of enteric infection?

Answer 1

Diarrhoea, leading to dehydration and malabsorption and death.

Malabsorption can lead to malnutrition, growth stunting. impaired immunity and cognitive impairment.

Question 2

Define diarrhoea, and what is classed as acute and chronic.

Answer 2

Diarrhoea is defined as increased stool frequency and increased water content of stools.

Acute = lasts less than two weeks

Chronic = longer than two weeks

Question 3

What are the main sites of water absorption ih the GIT?

Answer 3

80% of water is absorbed in the small intestine, and the rest is absorbed in the large intestine (lacks villi and folds)

Question 4

Describe the factors of water flux in the small intestine - those that promote secretion and absorption.

Answer 4

Secretion

1. Digestion of food into small molecules of high osmolarity draws water in
2. Activate secretion of electrolytes by enterocytes (chlorine pump, sodium pulled into lumen by increased chloride and water follows)

Absorption

1. Sodium dependent hexose transporter (Na-glucose coupled transporter, brings sodium into enterocyte, and water follows)

Question 5

How do oral rehydration solutions function?

Answer 5

Absorption of water is dependent on the sodium-dependent hexose transporter. Coupled transport of sodium and glucose brings water back into the enterocyte.

Thus, water absorption can be increased by presenting the enterocytes with more sodium and glucose. This is the basis of oral rehydration solutions.

Question 6

What are the 4 main mechanisms for diarrhoea?

Answer 6

1. Increased active secretion of electrolytes
2. Damage to brush border causing malabsorption of nutrients/electrolytes
3. Damage to brush border causing loss of disaccharidase activity
4. Altered motility, less time for water absorption.

Question 7

How do enterotoxins, cytotoxins and neurotoxins result in diarrhoea?

Answer 7

Enterotoxins - interfere with salt/water transport by enterocytes resulting in loss of water

Cytotoxins - damage ot cells of intestine

Neurotoxins - nervous system stimulation causing increased motility.

Question 8

What are the four classifications of diarrhoeal pathogenesis?

Answer 8

• Inflammatory
• Secretory
• Osmotic
• Motility related

Question 9

What type of diarrhoea does Vibrio cholerae cause, and describe the pathogenesis.

Answer 9

Vibrio cholera causes secretory diarrhoea through the action of enterotoxins.

Enterotoxins adhere to enterocytes and secrete toxin.

B subunit of the toxin binds toxin to receptors on enterocytes.

A subunit of toxin enhances adenyl cyclase activity = overproduction of cAMP = too much chlorine pumped into lumen, sodium follows.

Question 10

What is oral rehydration solution (ORS) therapy effective in diarrhoea caused by cholera?

Answer 10

ORS is effective as enterocytes are NOT DAMAGED by the toxin, allowing for absorption to occur.

Question 11

What disease does Shigella cause, and how does it do it?

Answer 11

Shigella causes bacillary dysentry (inflammatory diarrhoea).

Shigella induce M cells in SI to engulf them. Viral plasmids encode invasion plasmid antigens (IPAs) which induce inflammation.

Shigella can spread laterally though intestinal cells, and damages them in the process.

Question 12

What is dysentery?

Answer 12

Dysentery (caused by Shigella) is disease that involve stool that contains blood and pus from inflammatory damage.