22 Questions
What is the main function of the Malpighian tubules in insects?
Excretion and osmoregulation
What is the purpose of the peritoneal coat and muscle fibers surrounding the Malpighian tubules?
To provide structural support and aid in peristalsis.
What is the relationship between the Malpighian tubules and the alimentary canal in insects?
The Malpighian tubules act in association with the rectum or ileum of the alimentary canal.
How many Malpighian tubules are present in different insects?
60 in cockroaches
What is the relationship between the primary urine produced by the Malpighian tubules and the haemolymph (insect blood)?
The primary urine is isosmotic to the haemolymph but ionically dissimilar.
What is the primary function of the excretory system in insects?
To remove waste products of metabolism, especially nitrogenous compounds
Which of the following is NOT considered a major excretory organ in insects?
Tracheal system
What is the primary function of the Malpighian tubules in the insect excretory system?
To regulate the salt, water, and nitrogenous waste excretion
What is the function of the nephrocytes (pericardial cells) in the insect excretory system?
To sieve the haemolymph for products that they metabolize
What is the role of the fat bodies in the insect excretory system?
To store and excrete excess nutrients and waste products
Which of the following is NOT considered an excretory organ in insects?
Tracheal system
Which of the following describes the excretion process in terrestrial insects?
Conserve water and excrete concentrated or dry wastes
What is the primary function of osmoregulation in insects?
Maintain favorable osmotic pressure and ionic concentration in body fluids
Which ions do both terrestrial and aquatic insects need to conserve?
Sodium (Na+), potassium (K+), and chloride (Cl-)
What is the role of chloride cells in the insect excretory system?
Absorb inorganic ions from dilute solutions
In freshwater insects, what is regulated in response to the loss of ions to the surrounding water?
Hemolymph composition
What is the major anion found in the isosmotic filtrate in malpighian tubules?
Cl-
What generates an osmotic pressure gradient in malpighian tubules for the passive flow of water?
Active transport of K+
What type of excretion is seen in terrestrial insects such as coleoptera and lepidoptera larvae?
Uricotely
In aquatic insects, what is the excretory product that requires more water for waste removal?
Ammonia
What holds the distal ends of the malpighian tubules in contact with the rectal wall?
Perinephric membrane
Which accessory function is NOT associated with malpighian tubules?
Saliva production in adult coleoptera
Study Notes
Excretory System of Insects
- The excretory system in insects is responsible for removing waste products of metabolism, particularly nitrogenous compounds, and maintaining salt-water balance and physiological homeostasis.
Malpighian Tubules
- Malpighian tubules are the main organ of excretion and osmoregulation in insects.
- They are thin, blind-ending tubules that originate near the junction of the mid and hindgut.
- Each tubule is covered with a peritoneal coat and supplied with muscle fibers that aid in peristalsis.
- The distal secretory region and proximal absorptive region of the tubules work together to produce a filtrate (primary urine) that is isosmotic but ionically dissimilar to the haemolymph.
Functions of Malpighian Tubules
- Remove nitrogenous wastes
- Regulate salt, water, and ion balance
- Produce a filtrate (primary urine) that is isosmotic but ionically dissimilar to the haemolymph
- Accessory functions include spittle secretion in spittle bugs and light production in Bolitophila
Other Excretory Organs
- Nephrocytes: cells that sieve the haemolymph for products they metabolize
- Fat bodies: loose or compact aggregations of cells that store and excrete waste products
- Oenocytes: specialized cells with many functions, including excretion
- Integument: outer covering of the insect body that aids in excretion
- Tracheal system: insect gas exchange system that also aids in excretion
- Rectum: posterior part of the hindgut that modifies urine to maintain fluid and ionic homeostasis
Excretion and Osmoregulation
- In aquatic insects, haemolymph composition is regulated in response to ion loss to the surrounding water.
- Special cells called Chloride cells in the hindgut absorb inorganic ions from dilute solutions.
- Active transport of ions generates an osmotic pressure gradient for the passive flow of water.
Nitrogenous Excretion
- Terrestrial insects excrete waste products as uric acid or urates (uricotelism), which requires less water for waste removal.
- Aquatic insects excrete ammonia, which requires more water for waste removal (ammonotelism).
- Cryptonephry is a specialized structure in some insects that aids in efficient dehydration of faeces or ionic regulation.
Learn about the excretory system in insects, focusing on the removal of waste products and maintenance of salt-water balance. Explore the functions and structures of excretory organs such as Malpighian tubules, nephrocytes, and more.
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