Insects: Internal Anatomy and Physiology Review PDF

**INSECTS** **INTERNAL ANATOMY AND PHYSIOLOGY** Phylum: Arthropoda Class: Insecta Common traits - - - **Facts and Figures about Insects** - - - - - - **DIGESTIVE SYSTEM** - - - Divided into three regions: foregut, midgut, and hindgut **Foregut or stomodeum**...

**INSECTS** **INTERNAL ANATOMY AND PHYSIOLOGY** Phylum: Arthropoda Class: Insecta Common traits - - - **Facts and Figures about Insects** - - - - - - **DIGESTIVE SYSTEM** - - - Divided into three regions: foregut, midgut, and hindgut **Foregut or stomodeum** Anterior most region includes the Buccal cavity, the esophagus, and the crop primary function is to begin the breakdown of food particles and transport them to the next region, the midgut ectodermal in origin Internal cuticular lining is present Foregut consists of: - - - - **Midgut or mesentron** - - - - **Structure present in midgut:** - - - - - \- ectodermal in origin **Hindgut is differentiated into three regions** - - - - - - - - - - - - - **EXCRETORY SYSTEM** - **Excretion** - - **Malpighian Tubules** - - - - **Nitrogenous excretion** - - - - - - **Respiratory System** - - **Organs of Respiration** **Spiracles** - - - **Tracheae:** invaginations of the epidermis and thus their lining is continuous with the body cuticle **Tracheloes:** less than 1 μm in diameter and they end blindly and closely contact the respiring tissues **Respiration Process**  **CIRCULATORY SYSTEM** - - **DORSAL VESSEL** - - - Hemolymph flows posteriorly and is returned to the heart via ostia (small slits in the heart region of the dorsal vessel designed for hemolymph uptake) **NERVOUS SYSTEM** - **NEURON** - Dendrites: receive stimuli Axon: transmits information, may have lateral branches called collateral **Types of Neurons (On structural basis)** Monopolar: neuron with a single axon Bipolar: neuron with a proximal axon and a long distal dendrite. Multipolar: neuron with a proximal axon and many distal dendrites. **Types of Neurons (Functional basis)** Sensory neuron: It conducts impulse from sense organs to central nervous system (CNS). Motor neuron: It conducts impulse from CNS to effector organs Interneuron (association neuron): It inter-links sensory and motor neurons. **Ganglion** - dense cluster of interconnected neurons that process sensory information or control motor outputs **Ganglia**- cell bodies of interneurons and motor neurons are aggregated with the fibers inter connecting all types of nerve cells to form nerve centers **CENTRAL NERVOUS SYSTEM** Insects have a relatively simple central nervous system dorsal brain is linked to a ventral nerve cord Nerve cord consists of paired segmental ganglia **STOMODAEAL NERVOUS SYSTEM** **Frontal nerves:** arise near the base of the tritocerebrum and link the brain with a frontal ganglion **Frontal ganglion (unpaired)**: located on the anterior wall of the esophagus and innervates the pharynx and muscles associated with swallowing **Recurrent nerve**: located along the anterio-dorsal surface of the foregut and connects the frontal ganglion with a hypocerebral ganglion **Hypocerebral ganglion**: innervates the heart, corpora cardiaca, and portions of the foregut **Gastric nerves**: arise from the hypocerebral ganglion and run posteriorly to ingluvial ganglia (paired) in the abdomen that innervate the hind gut **REPRODUCTION SYSTEM** Reproductive organs of insects similar in structure and function to those of vertebrates: a male's testes produce sperm and a female's ovaries produce eggs (ova) Most (but not all) insect species are bisexual and biparental ---one egg from a female and one sperm from a male fuse (syngamy) to produce a diploid zygote. **Parthenogenesis**: a form of asexual reproduction in which new individuals develop from an unfertilized egg (virgin birth) **EXTERNAL FERTILIZATION** Aquatic insects: sperm could simply swim from the male's body to the female's body where fertilization could occur Terrestrial Insects: males leave spermatophores ("packages" of sperm encapsulated within a water-tight lipoprotein shell secreted by the male's accessory glands) on the ground where they may be found and picked up by a passing female **INTERNAL FERTILIZATION** males deposit their sperm inside a female's body during an act of copulation **MALE REPRODUCTIVE SYSTEM** - - - - - **ACCESSORY GLANDS:** secretory organs that connect to the male reproductive system **Two major functions:** - - **FEMALE REPRODUCTIVE SYSTEM** - **Ovarioles**: subdivisions of ovaries where the eggs are actually produced - **Lateral oviducts:** join to form a common oviduct, which opens into a genital chamber called the **bursa copulatrix** **Female accessory glands (one or more pairs)**: supply lubricants for the reproductive system and secrete a protein-rich egg shell (chorion) that surrounds the entire egg. **Spermatheca**: a pouch-like chamber reserved for storage of sperm **Spermathecal gland**: produces enzymes (for digesting the protein coat of the spermatophore) and nutrients (for sustaining the sperm while they are in storage)