5.21 The structure of the sting mechanism and how this mechanism operate to penetrate human skin and deliver the venom Flashcards
Which honeybee castes possess a sting?
Worker and Queen
When does a queen honeybee typically use her sting?
Queens usually use their sting against other queens or if mishandled by beekeepers.
What is unique about the queen’s ability to sting?
Unlike workers, a queen can survive after using her sting.
What anatomical structure houses the sting in honeybees?
The sting is housed in the sting chamber formed from abdominal segments A8 and A9.
What produces the venom in honeybee stings?
The venom (or acid) gland produces the venom, which is ejected when the sting is used.
What additional gland contributes to the sting in queen honeybees?
Hormones from the Dufour’s (or alkaline) gland also empty into the sting chamber in the queen.
How is the structure of the sting described?
Each side of the sting is an identical mirror image made from 3 interlocking plates:
* Oblong plate (which is fixed)
* Triangular plate (moves)
* Quadrate plate (moves)
What happens when a bee prepares to sting?
The bee curves its abdomen using sclerite muscles to ensure the sting enters the skin at 90 degrees.
What muscles are involved in forcing the lancets and stylet out during a sting?
Protractor muscles contract to force the lancets and stylet out of the A7 segment.
What is the function of the barbs on the lancet?
The barbs prevent the sting from being removed from the skin.
What happens to the bee after it stings?
The bee will die within a few days and cannot sting again.
How does the queen’s sting differ from that of a worker bee?
The queen’s sting has fewer barbs and firmer (more robust) internal connections, allowing her to remove it without damage.
What is the role of melittin in honeybee venom?
Melittin causes blood cells and mast cells to rupture, initiating an inflammatory response.
How much venom is injected with each sting?
Each sting injects about 0.1mg or one thousandth of a gram of venom.
What is venom composed of?
Melittin
phosphoridiase
hyaluronidiase
histamine
acid-phosphate
Venom consists of a number of chemicals that generally cause an inflammatory response:
* Melittin makes up around 50% of the venom; it is a protein that causes blood cells and mast cells to rupture.
* The rupture releases histamine and heparin, initiating the inflammatory response and preventing blood clotting.
* Phospholipase A works alongside melittin to break down cell membranes at the sting site, destroying cells and causing pain.
* Hyaluronidase breaks down the glue that holds cells together, causing tissue damage.
* Other substances include those that prevent melittin or enzymes from being broken down and histamine, which enhances the inflammatory response.
What comprises the shaft of the sting?
The shaft comprises the lancets and a stylet which expands into the bulb via an umbrella valve for each lancet.
What is the function of the umbrella valve in the sting?
The valves push/propel the venom down through the bulb to as their corresponding lancet moves down/forward. This forces the venom into the venom channel and into the victim.
What does the venom sac do?
The venom sac holds the venom and is connected to the bulb.
What are poison glands and what is their role?
Poison glands (acid glands) secrete the venom into the sac.
What is the function of the Dufour gland?
The Dufour gland (alkaline gland) opens to the sting chamber to lubricate the stylet and to possibly neutralise any leaked venom.
How does a bee position itself before stinging?
Before stinging, the bee positions itself perpendicular to the victim by contracting ventral sclerites and extending dorsal sclerites.
What controls the action of the sting?
The action of the sting is controlled by two muscles (Protractor and Retractor) attached to either side of the fixed oblong and quadrate plates
Where does the 1st muscle attach?
Q
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q
Where does the 1st muscle attach?
A
a
The 1st muscle from the rear of the quadrate attaches to the front of the oblong plate.
Where does the 2nd muscle attach?
The 2nd muscle from the front of the quadrate attaches to the rear of the oblong plate.
What happens when the 1st muscle contracts?
When the 1st muscle contracts, the articulation between the oblong and triangular plates moves, driving the ramus which pushes the lancet into the victim.
How does the 2nd muscle function in relation to the 1st muscle?
The 2nd muscle works antagonistically with the 1st muscle so when it contracts the lancet is withdrawn.
Bee Venom - Melittin (protein) effects
50% of venom
* Breakdown membrane of blood and mast cells (mast cells are a form of white cell which have a role in the immune system)
* Histamine and serotonin released by mast cells
* Lowers blood pressure and respiration
Bee Venom - Phospholipase A effects
Breaks down cell membrane
Pain
Toxicity; synergistic with melittin
Bee Venom - Hyaluronidase effects
<3%
* Hydrolyzes connective tissue; opens up passages between cells for other components
* Not toxic to humans
Bee Venom - Acid phosphate effect
Involved in allergic reaction, possibly nausea
Bee Venom - Histamine effect
Itching
Pain
Not toxic, mast cells release far more histamine
