Insect Excretory System

Entomology

1. Kingdom of Saudi Arabia Al Imam Mohammad Ibn Saud Islamic University College of Science Department of Biology Entomology 353 Bio T. Amani Alsharidah 1441 – 2019

2. Lecture 11 Insect Excretory System

3. Introduction The excretion: The removal from the body of waste products of metabolism, especially nitrogenous compounds. It differs from defecation In that excretory wastes have been metabolized in cells of the body. The Defecation: Simply passing of waste directly from the mouth to the anus. Insect feces, either in liquid form or packaged in pellets and known as frass , contain both undigested food and metabolic excretions .

4. Aquatic insect Eliminate dilute wastes from their anus directly into water. in aquatic insects, lost ion into the water by diffusion. Terrestrial insect Must conserve water . This requires efficient waste disposal in a concentrated or even dry. both terrestrial and aquatic insects must conserve ions , such as sodium (Na+), potassium (K+), and chloride (Cl−), that may be limiting in their food. So the Production of insect urine or frass . therefore results from two intimately related processes: excretion and osmoregulation. Osmoregulation is the maintenance of a favorable body fluid composition (osmotic and ionic homeostasis)

5. The Excretory System The system responsible for excretion and osmoregulation is referred to loosely as the excretory system. Its activities are performed largely by the Malpighian tubules and hindgut. In freshwater insects, hemolymph composition must be regulated in response to constant loss of salts (as ions) to the surrounding water , and ionic regulation involves both the typical excretory system and special cells , called chloride cells . Chloride cells usually are associated with hind gut which are capable of absorbing inorganic ions from very dilute solutions.

6. The Malpighian tubules and rectum The main organs of excretion and osmoregulation in insects are the Malpighian tubules acting in concert with the rectum and/or ileum. Malpighian tubules are o utgrowths of the alimentary canal and consist of long thin tubules formed of a single layer of cells surrounding a blind-ending lumen. They range in number from as few as two in most scale insects ( coccoids ) to over 200 in large locusts. Generally they are free, waving around in the hemolymph, where they filter out solutes. Insect Malpighian tubules are considered to belong to the hindgut and be ectodermal in origin. Their position marks the junction of the midgut and the cuticle-lined hindgut .

7. The Malpighian tubules and rectum excretory process ( nitrogen excretion) The anterior hindgut is called the ileum , the generally narrower middle portion is the colon , and the expanded posterior section is the rectum . In many terrestrial insects the rectum is the only site of water and solute resorption from the excreta. Insects ingest nitrogen, particularly certain amino acids far in excess of requirements ,Most insects excrete nitrogenous metabolic wastes at some or all stages of their life, although some nitrogen is stored in the fat body or as proteins in the hemolymph in some insects. Many aquatic insects excrete large amounts of ammonia. Terrestrial insects wastes generally consist of uric acid combination with urea, pteridines, certain amino acids, and/or relatives of uric acid, such as hypoxanthine, allantoin, and allantoic acid . Amongst these waste compounds, ammonia is relatively toxic and usually must be excreted as a dilute solution

8. Cont. Urea is less toxic but more soluble, requiring much water for its elimination . Uric acid are non-toxic and, having low solubility in water. (at least in acidic conditions) , can be excreted essentially dry , without causing osmotic problems. Waste dilution can be achieved easily by aquatic insects , but water conservation is essential for terrestrial insects and uric acid excretion (uricotelism) is highly advantageous .

9. The Malpighian tubules and rectum

10. The Malpighian tubules and the hind gut The Malpighian tubules produce a filtrate ( th primary urine) which is isosmotic but ionically dissimilar to the hemolymph. And then the hindgut , especially the rectum, selectively reabsorbs water and certain solutes but eliminates others. Excretory process