Week 9 (Insect) physiology Flashcards
pupation origin
from a ligation experiment (strangle to separate the larvae to 2 halves)
- Only the anterior pupates
When do both anterior and posterior pupate in ligation experiment?
- injection of molting hormone into posterior
- if the hormone is already released into haemolymph
brain removal effect on pupation
has endocrine effects.
Brain removal before release of hormone leads to no pupation
kissing bug - moving from a nymph stage to the next
needs to feed on blood
decapitation
head removal from body
decapitation effect on moulting
Decapitation early after a meal, the kissing bug will not undergo moulting.
- A critical period.
how to find source of hormone
for example, after removal of brain - implantation of specific body parts to
brain hormone
prothoracicotropic hormone (PTTH)
is PTTH released into the blood (insect)
parabiosis experiment: hormone is indeed effective on both insects.
Allow free flow of haemolymph between two decapitated insects.
- one decapitated before critical period
- one decapitated after critical period
parabiosis proves…
blood-borne hormone is responsible for metamorphosis induction.
how does PTTH control metamorphosis
using the larvae of the silkworm - if the brain is taken out
- the larvae doesn’t mature to the adult form
- reversible from implantation
Does hormone from implanted brain directly act on tissues?
development:
- anterior half - YES
- posterior half - NO
- posterior half + thorax - YES
PROTHORACIC GLAND = development
brain and prothoracic gland and further hormone action
brain releases PTTH and acts on prothoracic gland
- the gland releases another hormone.
what hormone does the prothoracic gland produce?
Ecdysone - steroid hormone
It acts directly on tissues and induce moulting.
how does ecdysone act molecularly?
As a steroid hormone, it diffuses easily into cells
- In its presence, the ultraspiricle will combine with the ecdysone receptor
- when ecdysone binds to the receptor complex
- translocate to nucleus and alter gene expression.
ecdysone effect on chromosome
decondense bands/regions of chromosome, allowing gene transcription
pulses of ecdysone will lead to transition to different stages of development
inhibitory hormone
what’s the inhibitory hormone that stops the transition from nymph to adult?
the juvenile hormone
- from corpus allatum
juvenile hormone effects
it will alter ecdysone-stimulated moults to a new larval instar
- in the last larval instar – JH will drop below a critical threshold due to inhibition
- in the absence of JH, the larvae will turn to an adult
small size of insect implication
Large surface to volume ratio
LARGE water FLUCTUATION - dehydrate/rehydrate
insect renal tubule
they don’t have pressure difference to do filtration.
act on haemolymph
They produce urine by secretion
type of cells in renal tubule (insect)
principal and stellate cells
generation of primary urine (principal cell)
- through an ATPase, H+ is pumped to the lumen
- with H+ gradient, K+ is brought out to the lumen
- K+ is also transported into the cell from the haemolymph
generation of primary urine (stellate cell)
- due to favourable electrochemical gradient, Cl- is also transported from haemolymph to lumen
- water follow by osmosis - aquaporin in stellate cells and between cells.
What is the Ramsay Assay?
It measures the secretory function of the insect renal tubule
- extract renal tubule and put into saline
- open a hole on the other end and investigate the lumen of the tubule.
kinin function in insect renal tubule
Enhance secretion:
Works in stellate cells, stimulate absorption of Cl-
cAMP function in insect renal tubule
Enhance section:
Works in principal cells, stimulate H+ ATPase, pump out H+ to create gradient for K+ to be pumped out.
finding the source of diuretic factor in insects
adding body parts to the ramsay assay apparatus: mesothorax ganglia releases diuretic hormone.
- the CNS increases secretion
- mesothorax increases secretion
which diuretic hormones act on insect principal cells?
diuretic hormone
serotonin
CAPs
what diuretic hormone act on stellate cells?
kinins
What sort of physical signal leads to insect diuresis?
A stretch receptor in the abdomen:
- releases sertonin and CRF (diuretic hormone)
- These hormones act on principal cells.
how does the insect recover water and electrolytes after secretion?
In the rectum:
- The chloride transport stimulating hormone (CTSH) will stimulate chloride transport out of the lumen.
- potassium will passively follow through electrical coupling - k+ channel
- water will diffuse out along with ion reabsorption
insect water conservation in extreme environments
beetle: buried kidney complex
tubules very close to rectum
- conserve water passed from ‘wet faeces’ from hindgut.
- taking water from rectum
water vapour absorption - insect
The beetle: countercurrent exchange system
Has a pump that pumps in K+ and Cl- into the renal tubule:
- high electrolyte concentration close to the rectum
- water content is high further away from rectum
- always a difference between water content and electrolyte concentration.
- water will be absorbed
