Insects tegument, digestive system, respiratory system of insects.

1. CONTENTS
Tentorium
Digestive system
Respiratory system and types
of respiration

2. TENTORIUM

3. Tentorium
 The body wall in insects becomes inpushed or
invaginated to form rigid process called apodemes.
 The framework of these apodemes is called
endoskeleton.
The endoskeleton of head is called
tentorium.
 The tentorium is named from its resemblance with a
tent which is tightened by four ropes.

4. Tentorium

5. Functions of Tentorium
Afford a basis for the attachment of cephalic
muscles.
Provide rigidity to the head.
Support to the brain and fore intestine.
Strengthen the points of articulation of certain
mouthparts.

6.  It consists of four openings:
o An upper
o Two lateral
o A lower one
Tentorium

7. Alaforamen
Through which pass the
alimentary canal.
Neuraforamen
Through which pass
nervous system
The tentorium is X-shaped and consists:
A central body
Two anterior arms
Two posterior arms
Two dorsal arms

8. Corpotentorium
The central body is a large triangular plate called corpotentorium
Pretentorium
 Two anterior arms are broadened at their anterior ends and are the
ingrowths from the anterior tentorial pits.
Metatentorium
 Two posterior arms are broader at their posterior ends and are the
invaginations from the posterior tentorial pits.
Supratentorium
 Two dorsal arms are the outgrowth from the bases of the anterior arms.
 They are sclerotised threads slightly broadened at their tips.

9. DIGESTIVE
SYSTEM

10. Digestive System
Insects feed on a wide range of organic materials.
Almost 75% of all species of insects are
phytophagous.
Insects may be:
Carnivorous
Entomophagous
Wood borers
Wool feeders or saprophytic,
Parasitic on other animals or insect species.

11. There are structural modifications in the
digestive system.
If the food ingested in a liquid form, it may be:
Plant sap
Nectar
Blood
Sap suckers possess a filter chamber
Solid feeders have well developed gizzard.

12. start cutting here
stop cutting here
Alimentary Canal
 A long, muscular and an enclosed tube that extends from the
mouth to the anus.
 insert the tip of scissor under the top surface of the abdomen.
 Cut straight up the middle of the abdomen up to the head.

13. . Alimentary Canal

14.  The alimentary canal in insects is divided in to three regions:
Foregut (stomodaeum)
food is stored, filtered and partially digested.
Midgut (mesenteron or stomach or ventriculus)
primary site for digestion and aborption of food.
Hindgut (proctodaeum)
some abosorption and feces formation occur
Alimentary Canal / Digestive gut
Foregut Midgut Hindgut

15. Structure of Alimentary Canal

16. oStarts from mouth cavity to gizzard
or proventriculus.
oThe mouth cavity: labrum as upper
lip, labium as lower lip with
mandibles and maxillae laterally
and hypopharynx at the centre.
oAt the base of the hypopharynx,
salivary glands open into the mouth
cavity.
Foregut

17. Salivary glands
The glands are grape-like clusters
called acinus.
Involved in the secretion of salivary
juices into the salivary ducts.
The secretion of the glands contain:
amylases,
lipases,
proteases etc.

18. Foregut is divided into:
Pharynx
region between the mouth and oesophagus.
Oesophagus
 it is a narrow part, food get transported from pharynx
into the crop.
Crop
 It is a sac like structure which is a dilated and store food material.
Gizzard
 It is a small constricted part modified in to a teeth like denticles that
grind the food material.
 The junction of foregut and midgut is provided with a cardiac
(oesophageal) valve.
Structure of Foregut

19.  A short, cylindrical and straight tube.
 Its anterior end arise six large,
elongated sacs, the gastric caeca
which consists of a longer anterior lobe
and shorter posterior lobe.
 The posterior lobes are filled with food
whereas the anterior lobes have
secretary function.
 The posterior end of the mid-gut is
marked by the presence of malpighian
tubules.
 At the junction of mid-gut and hindgut is
a pyloric valve.
Structure of Mid-gut

20. The midgut has a very thin and delicate layer called
peritrophic membrane secreted by the epithelial
cells.
 The peritrophic membrane protects the tender epithelial
cells / secretary cells of the midgut from friction by hard
food particles.
 It forms a coat over the food particles.
Midgut (Peritorphic membrane)

21.  Hindgut is divided into 3 regions;
Ileum (small intestine) is a thick and straight tube.
Colon (large intestine) is a short narrow tube which dilates
posteriorly to merge into the rectum.
 Rectum: wider tube provided with six bands of longitudinal muscles
alternating. These are involved in reabsorption of water and salts
from the faecal matter.
 The rectum ends into an anal opening.
Hindgut

22.  Digestion take place in following 5 steps:
Ingestion
Transportation
Digestion
Absorption
Egestion
Process of Digestion

23. 1. Ingestion
 Food is partially digested in the oral cavity with the help of
salivary enzymes.
2. Transportation
 The food material entered in to the oesophagus is
transported in to the crop by muscular activity.
 From the crop, food enters in to the gizzard where it is still
broken in to very minute particles with the help of denticles
or the cuticular teeth.
Digestion take place in 5 steps

24. 3. Digestion
From gizzard food passes in to the midgut where
actually digestion starts.
The epithelial cells produce enzymes i.e.
Proteases which break proteins in to aminoacids,
Carbohydrases breaking carbohydrates in to mono &
disaccharides,
Lipases breaking lipids in to fatty acids and glycerol.

25. 4. Absorption
 Midgut epithelial cells absorb the nutrients from the
digested food and pass on the faecal matter and
undigested food material in to the hindgut.
5. Egestion:
 The waste food material is discharged through the anus due to
the action of the anal muscles.

26. RESPIRATORY
SYSTEM

27. Respiratory system
 In insects, exchange of gases takes place through
tubular structures, called trachea.
 They are distributed throughout the body collectively
forming tracheal system.
 These trachea open outside on the body wall through
small openings called spiracles.
 The tracheal system with functional spiracles is called
the open tracheal system and with non-functional
spiracles is called closed tracheal system.

28. Spiracles
 The spiracles are the external openings through which air
enters and leaves the body.
 They consists of a small ring like sclerite at opening
called ‘peritreme’ leading to a cavity known as atrium’.

29.  Ak-grasshopper has 10 pairs of spiracles:
 2- thoracic (one between the prothorax and
mesothorax and the other between the meso and
metathorax).
 8- abdominal (one on each side of the first eight
abdominal segmens).
Spiracles in grasshopper

30. Trachea
 Trachea are fine elastic tubular structures.
 The cuticular lining appear as a spiral thickening throughout
the length of trachea tube.
 Spiral thickenings are known as ‘taenidia’ which support to
the trachea from being
collapsed when no air.

31. Tracheoles
 The trachea divide into very fine branches known as
tracheoles which are about 0.1-1 µm in diameter.
 Tracheoles form a network over the visceral organs including
the alimentary canal as well as the gonads (ovaries, tests) and
penetrate into the tissues of organs and supply oxygen to the
tissues.

32. Tracheal trunks
The trachea coming from spiracles through out the
body join with those of neighbouring spiracles
forming ‘longitudinal trunks’.
Dorsal trunk
 Supply oxygen to proximal part of body and heart
Lateral trunks
Spread tracheoles to alimentary canal, legs, wings.
Ventral trunk
Supply oxygen to the central nervous system.

33. Tracheal trunks (Video Resp. B)

35. Types of respiration

36. Respiration in Terrestrial Insects
e.g. Grasshopper, Crickets etc.

38. a) Extraction of Oxygen by gills
Spiracles are closed and non-functional.
Molecular oxygen in water extracted by thin-walled gills.
Tracheal gills
These are outgrowth of trachea which are thread like and richly supplied
with trachea and tracheoles.
Presesnt on the sides or end of abdomen.
e.g. nymph of mayflies, stonefly, dragonfly, damselfly
Spiracular gills
Spiracles are closed and non-functional.
These are outgrowth of spiracles that directly open into the trachea.
Blood gills
Filled with blood and finger like.
e.g. some larvae of true flies
Respiration in aquatic Insects

39. Extraction of Oxygen by gills
Mayfly nymph
Stonefly nymph

40. Damselfly and Dragonfly

41. Diffusion of oxygen through body wall
 It is also called cutaneous respiration.
 Tracheal system closed.
e.g. 1st instar larvae of Chironomus (Diptera)

42. Utilization of oxygen of aquatic plants
 Some insects with open tracheal system get oxygen from
submerged vegetation.
 Capture air bubbles from the surface of plants with hydrofuge
hairs on different parts of the body.
 These insects live in the bottom mud and have spiracles at
the tip of abdomen.
e.g. coleoptera, Diptera

43. Utilization of atmospheric oxygen
 Spiracles are open
 Maintain a semi-permanent connection with the air through a
long respiratory tube (Siphon).
 Exchange of gases in tracheal system occur through frequent
visits to surface of water.
Hover fly
Water scorpion
Mosquito larave
Diving beetle
Aquatic bugs
Aquatic beetles

44. i. Hover fly
 Spiracle on the tip of a long telescopic siphon at the end of abdomen.
 At respiration siphon extended, breaking water surfaces, reaches water
surface to get oxygen.
 When siphon retract peristgmatic glands prevent water entry into
spiracle.

45. Water scorpion & Mosquito larvae
 Respiratory tubes present at the end of abdomen carry
spiracles at their bases.
 Spiracles are surrounded with:
Dense group of hydrofuge hairs (water scorpion)
Provided with valves (Mosquito larvae)

46. Diving beetle
 Take air- bubbles beneath their elytra when visit water surface

47. Plastron respiration
 The plastron is a special type of air store in the form of a thin
film held by a system of hydrofuge hairs or scales.
 If there is adequate oxygen dissolved in water, the plastron
can act as a permanent physical gill.
e.g. aquatic bugs and beetles

48. Respiration in endoparasitic insects
 Like aquatic insects they extract oxygen from the blood of host or
make contact with atmosphere.
 Cutaneous respiration
e.g. Brachonid, Ichneumonid
 Through caudal filaments
e.g. Brachonid parasite
 Atmospheric oxygen
e.g Chalcid larvae

49. Respiration in endoparasitic insects
Brachonid wasp
Ichneumonid Chalcid

50. THANKS