The respiratory system of insects is a complex network of tubes called a tracheal system that delivers oxygencontaining air to every cell of the body The respiratory system of insects that consists of tracheae and their branches in a complicated form is known as ID: 1014122
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1. Tracheal respiration cock roach
2. The respiratory system of insects is a complex network of tubes, called a tracheal system that delivers oxygen-containing air to every cell of the body. The respiratory system of insects that consists of tracheae and their branches in a complicated form is known as tracheal system. All insects are aerobic organismsThe respiratory system is responsible for delivering sufficient oxygen to all cells of the body and for removing carbon dioxide (CO2) that is produced as a waste product of cellular respiration.
3. ComponentsThe tracheal system of insect consists of following components:(1) Spiracle(2) Tracheae(3) Tracheole cell(4) Tracheole(5) Air sacs
4. SpiraclesThese are the external openings of the tracheal system. They are lateral in position, usually on the pleura and there is never more than one pair of spiracles on a segment. Often the spiracle is bordered by an annular sclerite called peritreme.The spiracles are opened and closed by valves regulated by sphincter or spiracular muscles.Spiracles bears minute bristles in the inner margin. They prevent the entry of dust particles into tracheal system.
5. Contd…In cockroach they are 10 pairs in number.2 pairs are present in thoracic region and 8 pairs in the abdominal region.The arrangement of spiracles in cockroach is holopneustic arrangement. Spiracles leads into small chamber called atrium
6. TYPES OF SPIRACLES A. Simple or non- Atriate: An opening with no lip closure or filter chamber. B. Atriate with lip closure:Slit like apparatus with two movable valves/lips. C. Atriate with filter-apparatus:Atrium is lined with tiny hairs.
7. Types of tracheal respiratory systemKeilin (1944) classified respiratory system of insects on the basis of the number and distribution of the functional spiracle as mention below:I. Polyneustic Respiratory System: In this case there are at least 8 pairs of functional spiracles. (i) Holopneustic: Spiracles 10 pairs with 1 mesothoracic, 1 metathoracic and 8 abdominal. Found in bibinoid larvae.(ii) Perineustic: Spiracles 9 pairs with 1 mesothoracic and 8 abdominal. Found in cecidomyid larvae.(iii) Hemineustic: Spiracles 8 pairs with 1 mesothoracic and 7 abdominal. Found in mycetophilid larvae.
8. Types Contd…..II. Oligoneustic Respiratory System: In this case there are 1 or 2 pairs of functional spiracles.(i) Amphipneustic: Spiracles 2 pairs with 1 mesothoracic and 1 post-abdominal. Found in psychodid larvae(ii) Metapneustic: With 1 pair of post-abdominal spiracle. Found in culicid larvae.(iii) Propneustic: With 1 pair of mesothoracic spiracle. Found in dipterous larvae.III. Apneustic Respiratory System: In this case there are no functional spiracles i.e., the tracheal system does not open to the outside. Found in chironomid larvae.
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10. HolopneusticMetapneusticApneusticOPENCLOSEDCockroachMosquito larvaeMosquito larvaeMay fly larvaeDragon fly
11. Tracheae The tracheae are the larger tubes of the tracheal system, running inwards from the spiracles and usually breaking up into finer branches. These are formed by the invaginations of the ectoderm.The wall of tracheae consists of three layers, viz., outer epidermal layer basement membrane, middle layer epithelium and the inner cuticular layer intima.Intima produces spiral thickenings or chitinous rings at regular intervals called Taenidia.
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13. Contd.The thoracic spiracles lead into several horizontal trachea, where as each abdominal spiracle leads into atria. From each abdonimal spiracle 3 tracheal tubes arise.All these tracheal tubes of one side open into three separate longitudinal tracheal trunks.They are lateral, dorsal and ventral longitudinal trunks. The three pairs of longitudinal tracheal trunks of both the sides are interconnected by many commissural tracheae.
14. TracheoblastThe ultimate branches of tracheae end in polygonal cells called trcheoblasts.These are derived from the epidermal cells lining the trachea.These cells form tracheoles.
15. TracheolesThe fine branches of trachea are called tracheoles. The tracheole cell is the terminal structure of the tracheal tube ending close to the tissues.Taenidia are absent in tracheolesTracheoles arc internally lined by a protein called trachein.In a resting insect when respiratory activity is not high, the tracheoles are filled, not with air but with a tissue fluid of cells in which oxygen dissolves.
16. Air sacsThe absence of taenidia in certain parts of the tracheal system allows the formation of collapsible air sacs, balloon-like structures that may store a reserve of air.In dry terrestrial environments, this temporary air supply allows an insect to conserve water by closing its spiracles during periods of high evaporative stress.
17. Air Sacs
18. Tergo-sternal musclesIn cockroach the muscles which help in respiration are called Tergo-sternal muscles.They are attached between tergal and sternal plates. Relaxation of tergosternal muscles helps in inspiration and contraction of tergosternal muscles helps in expiration.
19. Mechanism of respiration In cockroach respiration includes two phases (i) Inspiration and (ii) ExpirationInspirationIn take of atmospheric air or O2 into the tracheal system is called as inspiration. Inspiration is a passive process in cockraoch. Whenever tergosternal muscles relax, the space present in the body cavity increases and pressure decreases. Thoracic spiracles are kept open and the abdominal spiracles are kept closed. Later, that air is carried towards tracheoles and diffuses into tissues through tracheolar fluid.Due to metabolism CO2 produced in tissues.
20. ExpirationElimination of CO2 is known as expiration. Whenever tergosternal muscles contract, the space present in body cavity decreases and pressure increases. Thoracic spiracles are closed and abdominal spiracles are kept open. In cockroach major amount of CO2 is sent out by diffusion method through cuticle. In cockroach respiratory movements are controlled and coordinated by nervous system.Expiration is a active process.
21. Cockroach, Grasshoppers and Beetles exhibit the phenomenon of discontinuous ventilation (oxygen (O2) uptake and carbon dioxide (CO2) release from the whole insect follow a cyclical pattern characterized by periods of little to no release of CO2 to the external environment).In this, exchange of gases is interrupted by extended periods during which spiracles arc closed. Opening and closing of spiracles is influenced by CO2 tension in hacmolymph and oxygen tension in the tracheae.In cockroach the first thoracic and first abdominal spiracles remain open all the time, but the second thoracic and last seven abdominal spiracles open during inspiration and close during expiration.
22. Other functions of tracheal systemApart from respiration the tracheal system has a number of other functions as-(i) The whole system lowers the specific gravity of the insect. (ii) In aquatic insects it also gives some degree of bouncy and in the larvae of Chaoborus (Diptera) the tracheae form hydrostatic organs enabling the bouncy to be adjusted. (iii) Air sacs allow for the growth of organs within the body without any marked changes in the body form.(iv) Air sacs also permit changes in gut volume as a result of feeding. (v) In some noctids (Lepidoptera) tracheae form a reflecting tapetum beneath the eye.(vi) Expansion of the tracheal system may assist in inflation of the insect after a moult.(vii) Some insects, such as Aeschna (Odonata), have an extensive development of air sacs round the pterothoracic musculature which probably serve an insulating function, helping to maintain the temperature of the flight muscles.(viii) An important general function of tracheae and tracheoblasts is in acting as connective tissue, binding other organs together.(ix) The tracheal system may be involved in defense mechanisms. In cockroache Diploptera quinones which probably have a defensive function can be forcibly expelled from the second abdominal spiracle.
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