🪢 Endocrine System

Glandular System

👉🏻 Glandular system is otherwise called as secretary system and is divided in to two major groups based on the presence or absence of ducts.

Exocrine glands

• Glands with duct.

1. Salivary glands: Salivary glands are modified labial glands which secrete saliva and open beneath hypopharynx.
2. Mandibular glands: Secrete saliva in caterpillars when salivary glands are modified into silk glands. In queen bee it secretes queen substance.
3. Maxillary glands: Secretions are useful to lubricate mouth parts.
4. Pharyngeal glands: Secrete bee milk or royal jelly in nurse bee.
5. Stink glands (Repugnatorial glands): Secrete bad smelling substance. e.g. Stink bugs, bed bugs.
6. Pheromone glands: Found in abdominal terminalia of one sex and its secretions are released outside to attract opposite sex of the same species.
7. Wax glands: Dermal glands producing wax in bees and mealy bugs.
8. Sting glands: Modified accessory glands secreting venom in worker bees and wasps.
9. Lac glands: Dermal glands secreting resinous substance in lac insect.

Endocrine system

• Glands without duct.
• It consists of ductless gland that secretes chemicals called hormones, it released directly into haemolymph of insects.

  

• Insect endocrine system is structurally and functionally integrated with nervous system:

1. They secrete hormones which travel in the blood to various organs of the body coordinating their long-term activities.
2. Endocrine organs are of two types.
   • Neuro-secretory cells in the central nervous system
   • Specialized endocrine glands such as
     • Corpora cardiaca
     • Corpora allata
     • Prothoracic glands

Neurosecretory cells (NSC)

• These are typical neurons with secretory activity. They produce hormones which act directly on effector organs, or they may act on other endocrine glands which in turn are stimulated to secrete hormones.
• They occur in the mid region of brain and central nervous system. Their axons lead out from the brain, posteriorly, most often cross each other and emerge out of the brain to enter in to or lie opposed to the corpora cardiaca.
• The secretions of neurosecretory cells are called brain hormone or activator hormones.

Corpora Cardiaca (CC)

• It is small, paired structure known as neurohaemal organ. Major function is storage and release of hormones.
• They are paired structures, lying in close association with neurosecretory cells of brain. Each corpus cardiacum is transversed by neurosecretory axons from the brain.
• Neurosecretions from brain, on reaching corpus cardiacum, is stored and periodically released into the blood.

Corpora Allata (CA)

• They are glandular bodies, usually situated one on either side of the Oesophagous. They may be fused to a single median organ as in higher Diptera.
• Paired glands located behind corpora cardiaca.
• Each is connected with Corpus cardiac of the same side by a nerve which carries fibres from NSC.
• Under the influence of brain hormone, corpora allata secretes Juvenile hormone (JH) or neotenin
• It inhibit metamorphosis in young insects. Therefore, JH helps to keep the insect in young stage only.
• It is needed for egg maturation and functioning of male accessory glands.

Prothoracic Glands (PTG)

• They are two in number and placed mostly in thoracic region (near prothorax).
• It secrete moulting hormone (MH), called Ecdysone under the influence of brain hormone.
• Moulting hormone helps in insects in the initiation and process of moulting.
• Except in Thysanura (which moult as adults) and solitary locusts, the prothoracic glands break down soon after final moult to adults, so they are seen only in immature forms but not in adults.

- Insecta - Introduction: K.N. Ragumoorithi, V. Balasurbramani & N. Natarajan
- A General Textbook of Entomology (9th edition, 1960) – A.D. Imms (Revised by Professor O.W. Richards and R.G. Davies). Butler & Tanner Ltd., Frome and London.
- The Insects- Structure and Function (4th Edition, 1998) – R.F. Chapman. Cambridge University Press
- https://www.amentsoc.org/
- Researchgate
- Wikipedia