Bloodmeal digestion

Question 1

How can antibiotics sterilise flies?

Answer 1

By meaning they do not get enough nutrients for egg development (rely on symbionts for some vitamins)

Question 2

How are symbionts involved in susceptibility of infection?

Answer 2

They aid in digestion of blood meal to release D glucosamine which competitively inhivits lectins secreted from tsetse flies which helps in establishing a tryp infection (lectins kill tryps).

Question 3

What are the problems produced by blood-feeding?

Answer 3

• Weight due to large vol of blood reduces mobility
• Osmotic pressure of blood
• Toxicity due to iron in blood (forms superoxide radicals which damage midgut)

Question 4

How is the blood meal prevented from being too large?

Answer 4

Midgut stretch receptors which stop overfilling

Question 5

How can insects get more blood from a single meal?

Answer 5

Diuresis- excreting water using an NaCl pump into the urine as it feeds.

Question 6

How does the insect get around the difference in osmotic pressure of blood?

Answer 6

Secretes proteins to reduce osmotic pressure. E.g. secretes coagulants to make blood rubbery as it is taken up

Question 7

How can insects negate the toxicity of iron in blood?

Answer 7

PM surrounds blood meal and protects against superozide radicals.
Haem binding proteins (haemazoin, ferritin, glutathione transferase), antiozidant enzymes to deal with superoxide radicals.

Question 8

What are the types of cell found in the gut

Answer 8

• Exocrine and regenerative cells
• Microvillar boarder for absorption
• Digestive epithelial cells.

Question 9

How does the apical end of the midgut differ from the rest?

Answer 9

Cells stretched, microvilli lost here.
Formed of epithelia cells with lots of preformed digestive enzymes in secretory vessels ready for blood meal (up-regulation regulates transcription upon blood uptake).

Question 10

What is the PM made of?

Answer 10

Mesh of mucopolysaccharides (chitin). Is a semipermeable membrane- diffusion and directional transport.

Question 11

How does the PM protect against pathogens?

Answer 11

Physical barrier. Anchors antimicrobial peptides protecting against escaping pathogens.

Question 12

How does the PM aid digestion?

Answer 12

Provides a concentration gradient of enzymes so can access the blood meal from the outside going inside.

Question 13

What are the two types of PM? Which species have either?

Answer 13

Type I: bag- synthesised by all cells along midgut (mosuitos)
Type II: syntehisesd by specialist cells in the proventricular region to form a blind ended tube. (tsetse)

Question 14

What do triatomines produce instead of a PM?

Answer 14

An extracellular memrbane layer comprised of an extracellular coating, rather than a chitinous PM.

Question 15

How does chitin protect against destruction of the midgut epithelium?

Answer 15

Binds chitin binding proteins which protects against destruction of the midgut epithelia by proteinases?

Question 16

What does a distension of the midgut cells due to a blood meal result in?

Answer 16

Increase in DNA replication and translation of proteins such as trypsin

Question 17

How does a blood meal get formed into eggs?

Answer 17

Protines absorbed through the PM by themidgut cells and assimilated into the haemolymph and ultimately eggs.

in addition to this, triacylglycerol is stored in the fat body which also provides nutrients to make eggs.

Question 18

How do the digestive enzymes differ in diptera vs hemiptera (bugs)?

Answer 18

Diptera: early and late trypsins adn chymotrypsins

Hemiptera: cathepsins (endosomal enzymes) because there was an ancestral history of feeding on seeds which have lots of proteinase inhibitors.

Both have minor components of lipases and glycosidases.

Question 19

Where are digestive enzymes produced?

Answer 19

Digestive epithelial cells in midgut.

Question 20

When/why are leish sensitive to trypsin attack? How does it overcome this?

Answer 20

Targeted during transition from amastigote to procyclic promastigote as they are remodelling their LPG coverage at this point so it is not completely over the surface.

Suppresses digestion by suppressing trypsin expression in the vector. Also aids because nutrients stay around for longer and parasites can take advantage of this.

Question 21

How is trypsin expression modulated by leishmania infection?

Answer 21

Changes the expression profile to switch from early to late trypsins which reduces efficiency of digestion.

Reduction in trypsin one expression (late trypsin) in unfed infected flies.

Also tryp 2 upregulated and tryp 1 downregulated during infectoin.