INSECT DIGESTIVE & EXCRETORY SYSTEM LABORATORY

Alimentary Canals

• Tube which extends from anterior opening to the posterior anus.

• Gut is formed by a one cell, thick layer of epithelial cells on a non-cellular basement membrane.

• Consists of longitudinal and circular muscles.

• Shorter in Predator as compared to Herbivores.

Digestive Glands

•  These organs secrete digestive enzymes

•  Salivary glands & Gastric Cecae

Pharynx

 Food passageway located right after the mouth. By the cibarial muscles contraction, it creates a suction by enlarging its volume; sucking the food inwards and into the esophagus.

Esophagus

A simple tube that connects the pharynx to the crop. From the pharynx, food passes into the esophagus by means of peristalsis (rhythmic muscular contractions of the gut wall).

Crop

Food is stored here before being transmitted, in small quantities at a time, to the mid-gut.

Proventriculus

This organ contains tooth-like denticles that triturate and pulverize food particles.

Cardiac Sphincter

 aka “stomodeal valve”, a sphincter muscle located just behind the proventriculus, regulates the flow of food from the stomodeum to the mesenteron.

Gastric Caeca (hepatic caeca)

A series of stubby pointed tubes (finger-like) leading off from the stomach. These structures provide extra surface area for secretion of enzymes or absorption of water (and other substances) from the alimentary canal.

Ventriculus

It is the primary site for enzymatic digestion of food and absorption of nutrients. Digestive cells lining the walls of the ventriculus have microscopic projections (microvilli) that increase surface area for nutrient absorption.

Peritrophic Membrane

a semipermeable membrane secreted by a cluster of cells (the cardial epithelium) that lie just behind the stomodeal valve. Consists of chitin fibrils embedded in a protein-carbohydrate matrix. It protects the delicate digestive cells without inhibiting absorption of nutrient molecules.

cardial epithelium

a semipermeable membrane secreted by a cluster of cells (the _______ ________) that lie just behind the stomodeal valve.

Pyloric Sphincter

Sphincter muscle after the ventriculus. It regulates the flow of material from the mesenteron into the proctodaeum.

Malpighian Tubules

Located at the base of pyloric sphincter, these long, spaghetti-like structures extend throughout most of the abdominal cavity. Excretes nitrogenous wastes (principally NH4+) from the hemolymph. Other components include water with the usual inorganic salts, chlorides and phosphates of sodium, potassium, calcium, and magnesium, in solution. Inside MT, NH4+ is quickly converted to urea and then to uric acid by a series of chemical reactions. The uric acid, a semi-solid, accumulates inside each tubule and is eventually emptied into ileum as part of the fecal pellet.

Ileum

It is the anterior hindgut. It acts as a reservoir for most of the hindgut symbionts. Such as ciliates, flagellates and spirochaetes.

Colon

It is generally narrower middle portion of the hindgut located between ileum and rectum.

Rectum

 FF% of water and inorganic ions are actively absorbed by the rectum and this function is important in the regulation of osmotic pressure and ionic composition in the blood. In addition, amino acids can be absorbed in the rectum of the some locust species.

Anus

Serves as a terminal opening of insect alimentary canal, where frass and other waste product of digestion exits.

Salivary Glands

• Secretes saliva

• Paired structures

• Saliva consists of enzymes (amylase, sucrases, etc.)

Gastric Cecae

•  Finger-like projections

•  Two type of cells involved in the secretion of enzymes:

Holocrine: cells disintegrate or break down in the process of enzyme secretion.

Merocrine: enzyme secretion occurs w/o cell breakdown

Holocrine

cells disintegrate or break down in the process of enzyme secretion.

Merocrine

enzyme secretion occurs w/o cell breakdown

hyaluronidase

High ___________ in saliva of carnivorous insects attacks (digest mucopolysaccharides in connective tissues, also acts as spreading agents for other enzymes (proteases, once enzyme have acted on the food, they suck liquid).

anticoagulants

Blood suckers have ______________ and in the case of Glossina sp. (Tsetse fly), it is identified as Plasminogen activator. Once blood reaches crop, coagulation is rapid and thus it is ready for regular digestion.

Nutrition

is the nature or processing of materials from the environment by organisms for fuelling their energy needs, for augmenting their substance, and production of progeny

1. Rule of Sameness

2. Principle of Nutrient Proportionality

3. Principle of Cooperating Supplements

3 BASIC RULES OF INSECT NUTRITION:

Principle of Nutrient Proportionality

(quantitative differences), refer to the suitable balance of different nutrients needed for normal development (variation in food selecting capacity of the insect)

Principle of Cooperating Supplements

generally refer to the substitute sources of nutrients: microorganisms/symbionts that help or to substitutive substance of nutrients; variation in enzyme system present in insect groups; food reserves [newly hatched individuals with carry-over food reserves from the previous stage]

Fat body

is a group of loosely organized cells in the body cavity that also function in intermediate metabolism.

Uric acid

 is a semi-solid form and accumulates inside each MT, eventually emptied into the HG for elimination as fecal pellet.

 Uric acid

deposited in the cuticle as white crystals, producing patterns of white color.