L5 - Feeding and Osmoregualtion

Question 1

What are the 4 sections of the foregut?

Answer 1

Pharynx –> oesophagus –> crop –> proventriculus

Question 2

What organ consists the midgut?

Answer 2

The gastric caecae

Question 3

What are each lined with?

a) foregut
b) midgut
c) hindgut

Answer 3

a) cuticle
b) thin peritrophic membrane for protection
d) cuticle

Question 4

What are the guts like of very short lived insects?

Answer 4

Tube like

Question 5

What hormones cant insects synthesise which they must obtain from their diet or micro-organisms?

Answer 5

Sterols - used for moulting hormone

Carotenoids - used in visual pigments

Question 6

What are the 2 types of salivary gland insects can have?

Answer 6

labial or mandibular

Question 7

What is the function of the proventriculus

Answer 7

a grinding organ in some insects, can control the rate of food into the midgut

Question 8

What section of the gut is the main site for absorption?

Answer 8

Midgut

Question 9

In blood sucking insects, where is a lot of blood stored if they take a large meal at once?

Answer 9

a specialised portion of the midgut

Question 10

What are the sections of the hindgut in order?

Answer 10

malpighian tubules –> ilium –> colon –> rectum –> anus

Question 11

What are and what is the function of malpighian tubules?

Answer 11

Thin hair-like tubules found at midgut-hindgut barrier sphincter

Function is excretion

Question 12

Describe the general structure of the hindgut

Answer 12

Can be a straight tube, or modified into a fermentation chamber storing and harbouring micro-organisms that help in cellulose digestion

Question 13

Where are rectal pads found, how many of them are there, and what is their function?

Answer 13

6 rectal pads are embedded in the wall of the rectum.

These absorb water - in dry conditions they can absorb up to 90% of the water from the excretion

Question 14

What is the structure of the walls of the hind gut like?

Answer 14

Epithelium rests on the basal lamina. The walls contain both longitudinal and circular muscle for peristalsis

Question 15

What are the 3 basic types of insect mouthparts?

Answer 15

1) mandibulate - chewing and biting
2) Haustellate - lapping and sucking
3) Piercing

Question 16

What is the fat body?

Answer 16

Loose sheets/ribbons/lobes of cells lying in the body cavity (Haemocoel). These cells are in communication via gap junctions

Question 17

What are the functions of the fat body?

Answer 17

1) An energy store:
e. g.: Octopamine released from the brain mobilises fat to be metabolised during flight

2) Regulates blood sugar
- insects have insulin like peptide (Dilps) released from
- dietary amino acids activate TORC1 in fat cells - induces the production of Dilps

3) Synthesises major haemolymph proteins
e. g.: in females its used for a site of storage of vitellogenin

Question 18

What 3 ways can insects get rid of waste nitrogen?

Answer 18

1) Ammonia - is very toxic so must be excreted in a dilute form, or rapidly colletized (cocraches)
2) Urea - less toxic and more soluable, still requires water for elimination
3) Uric acid - not toxic, can be excreted dry and stored by most. It also has a high N:H ratio therefore less water used for excretion

Question 19

Describe the ‘general condition’ of the hindgut

Answer 19

1) Malpighian tubules absorb water, solutes and urate (uric acid) from the haemolymph in the body cavity
2) The rectum then reabsorbs water and solutes from the gut, leaving urate and precipitate behind to be excreted. Ions are then actively transported back (mitochondria positioned for this) water follows

Question 20

Describe the state of the hind gut in Liquid feeders

Answer 20

1) Distal MTs absorb water, solutes and urate/uric acid from the Haemocoel
2) Proximal MTs reabsorb water and solutes
3) Tubules are then flushed out and uric acid excreted because of the next blood meal

Question 21

What effects on the insect does a blood meal have?

Answer 21

A blood meal can be 10times the insects unfed weight, which can reduce flight speed from 15 to 3-4mph

In the tsetse fly, 40% of the meal is shed in 30mins. Mostly nutrient poor plasma, strong active transport mechanism in the epithelium of distal MTs

Diuretic hormones released in gut distension enables haematophagous (and probably also phytophagous) insects to deal with sudden large dietary loads

• After a blood meal, DH can increase water transport by x1000 in rohdnius
• after a Blood meal high ion concentration therefore

Question 22

Describe what happens in an insects gut in water stress?

Answer 22

During dry periods, water can be absorbed from the air by the rectum:

• distal regions of the MTs are wrapped around them
• ‘cryptonephridial system’

Ions are transported in high concentrations (mainly KCl) in the 6MTs. This draws liquid from the perirectal space and rectal lumen. This is then transported to free tubule and reabsorbed haemolymph or recycled in the rectum