L7 Digestion and Excretion Flashcards
What is the fat body made of?
A network of mesodermal tissue forming loops surrounding the gut, bathed in hemolymph.
Formed of vacuolated, rounded or polyhedral modified haemocytes - called adipocytes and trophocytes.
Functions of the fat body
Stores and excretion of proteins, lipids and glycogen [excretion of uric acid].
Location of intermediary metabolism and detoxification processes.
removes waste from hemolymph, convert to uric acid and return to hemolymph.
What are 3 excretory substances and which do insects use?
Ammonia - v toxic, many aquatic orgs excrete ammonia
Urea - requires large amounts of water to excrete
Uric acid - eg birds & insects, can be excreted almost dry, is not water soluble.
Where are the malphigan tubules?
200-300 tubules, at the junction of mid and hind gut, very fine, project into hemolymph.Lumen is lined with microvilli
How is uric acid made?
Malphigan tubules actively pump cl- and K+, toxins, organic waste through ionic pumps into their lumen.
Causes decrease in water potential so water, sugars, AA passively move into the lumen.
This forms primary urine then in the ileum and colon mixes with food.
It is important to monitor and reabsorb water.
How does water reabsorption occur?
Rectal pads run in longitudinal groups along edge of rectum, contain chloride cells which helps with the reabsorption of water.
If low in water, CL- pumped out of chloride cell, to build an osmotic gradient so water flows to the hemolymph.
Feces almost totally dry. Small packages covered in peritropic membrane
Describe the foregut
FOREGUT: lined with cuticle, so lost at moulting.
Mouth
Salivary gland -lubricating and produces enzymes,
Pharynx -pharyngeal muscles move food along
Crop -enlarged area of gut for storage.
Proventriculus -[gizzard/gastric mill] lined with elaborate cuticle spikes. Sphincter muscles relax to allow food movement in and out.
Describe the midgut
MIDGUT-just celular epidermis, no cuticle. Fine microvilli, main site of absorption with many digestive enzymes.
Production of peritrophic membrane - mesh structure, not attached to midgut wall, grows around food and encases food.
Gastric caecum, Malphigan tubules
Describe the hindgut
HINDGUT- Cuticle lined, houses symbiotic microbes, Ileum -can be enlarged to form a fermentation chamber, Rectum, Anus
How can symbiotic microbes be aquired?
- Oral uptake - extracellular symbionts, young insects eat adults feces containing flora.
- Intracellular -transovarian uptake, incorporated into the egg
What happens in the gastric caecum?
Main site of absorption, Cells actively pump digested ions out of caecum into hemolymph causing an osmotic gradient so water follows, carrying products of digestion.
describe some variants of the gizzard
Sugarbag bee - proventriculus lined with 4 groups of hairs, separating nectar from pollen
Fleas - lined with v fine hairs
Cockroach - large sclerotized teeth interlock to grind food.
