Guts and Haemolymph Flashcards
Alimentary canal
Divided into 3 parts structurally with different embryological origins
1. Foregut
2. Midgut
3. Hindgut
Means they are different histologically (cell structure, interactions and how tissues are built)
Foregut structure
- transmits food from mouth to abdomen, lined with cuticle
- carries out food processing
- mouth part - pharynx
- oesophagus transporting food from pharynx to the abdomen
- have a crop (temporary food store)
- have gizzard/proventriculus - second mouth with strong musculature structure and sharp cuticular teeth (like set of jaws)
Midgut structure
•junction of midgut and foregut no more grinding
•caeca = extended tubes into haemocoel (increase SA?)
-tubes larger in herbivores?
•covered in microvilli to increase SA
•midgut length depends on insects food source
•swelling at end where Malpighian tubules found
Midgut = food digestion, secretion of enzymes (no cuticular barrier) and absorption of water
Hindgut structure
- lined with cuticle acting as a semi-permeable membrane
- cells lining are involved with water absorption
- squeezes as much water from food as possible before excretion
- counter-current system for water absorption
Insects other uses for the rectum…
- jet-propulsion system (in dragonfly larvae and some insects) to get away from predators
- some force air out to hiss and scare predators - cockroaches
- red flour beetles absorb water through air by sucking it into their rectum
Overcoming risks of no cuticle in midgut
- cover food in peritrophic membrane
- at junction of gizzard and midgut are a special group forming a continuous tube that secrete the membrane
- digested food carries on to haemolymph
- undigested food stays in membrane till excretion
- membrane made of cuticular proteins, with cross-links providing gaps for small molecules to pass, but not bigger ones like parasites etc.
Foregut modifications in blood-suckers
- have to suck blood against a pressure gradient
- blood is very viscous so don’t want their sucking structure to break, needs to be strong
- they have a siberial (or pharyngeal) pump which provides negative mechanical pressure in the structure
The process of blood-sucking
- Have 4 cuticular plates attached to powerful muscles
- The muscles contract making the plates expand
- Between the plates are pure resilin hinges in the pumps,
when they expand (muscles relax) = negative pressure and blood is drawn up
Malpighian tubules
- 1 cell thick wall
- internal surface is villate
- lie freely in body cavity bathed in haemolymph
- long thin, blind ended tubes, free-floating in haemolymph
- pump salts and water against their concentration gradient
- excretes N waste - as uric acid (crystalline form) = no water loss
- uric acid excreted into gut and passes through gut
Haemolymph
•body cavity - the haemocoel, is a cavity with an open circulatory system
•have a structure equivalent of heart involved in pumping
•any currents in body are mainly caused by insects moving
•haemolymph is only extracellular fluid with blood cells (haemocytes), nutrients salts and products of metabolic breakdown
-mainly involved in nutrient transport and defence
Haemocytes
- lots of different types
- some used in developmental stages of holometabolous insects - rebuilding tissues etc.
- different immune response depending on whether opportunistic pathogen (open wounds etc.) or parasitoids (lay eggs in insects)
- encapsulation response is major way of projecting from larger pathogens
Experiment mimicking parasitoid infection
- using a nylon insert to mimic the parasitoid egg
- encases it which kills the egg by melanising it
- can see when it has been encapsulated by taking it out and quantifying the encapsulation response
- externalises the egg by encapsulating it
