malpighian tubule

Examples of malpighian tubule in the following topics:

• Malpighian Tubules of Insects

  • Malpighian tubules remove wastes from insects by producing urine and solid nitrogenous waste, which are then excreted from the body.
  • Malpighian tubules line the gut of some species of arthropods, such as bees.
  • Malpighian tubules work cooperatively with specialized glands in the wall of the rectum .
  • Malpighian tubules of insects and other terrestrial arthropods remove nitrogenous wastes and other solutes from the hemolymph.
  • Explain how insects use malpighian tubules to excrete wastes and maintain osmotic balance

• Phylum Arthropoda

  • Crustaceans possess green glands while insects use Malpighian tubules, which work in conjunction with the hindgut to reabsorb water while ridding the body of nitrogenous waste.

• Testes Ducts

  • Seminiferous tubules are located in the testes, and is where meiosis occurs and the gametes (spermatozoa) are created.
  • The seminiferous tubules are formed from primitive sex cords from the gonadal ridge.
  • The epithelium of the tubule consists of Sertoli cells, which are tall, columnar type cells that line the tubule.
  • There are two types of seminiferous tubules: 1) convoluted, located toward the lateral side, and 2) straight, as the tubule comes medially to form ducts that will exit the testis.
  • Diagram of cross-section of testes: 1: Testicular septa 2: Convoluted seminiferous tubules 3: Testicular lobules 4: Straight seminiferous tubules 5: Efferent ductules 6: Rete testis.

• Flame Cells of Planaria and Nephridia of Worms

  • Their excretory system consists of two tubules connected to a highly-branched duct system that leads to pores located all along the sides of the body.
  • The cells in the tubules are called flame cells (or protonephridia) because they have a cluster of cilia that looks like a flickering flame when viewed under the microscope .
  • They are similar to flame cells in that they have tubules with cilia and function like a kidney to remove wastes, but they often open to the exterior of the organism.
  • The ciliated tubules filter fluid from the body cavity and carry waste, including excess ions, through openings called nephrostomes.
  • In the excretory system of the (a) planaria, cilia of flame cells propel waste through a tubule formed by a tube cell.

• Nephron: The Functional Unit of the Kidney

  • A nephron consists of three parts: a renal corpuscle, a renal tubule, and the associated capillary network, which originates from the cortical radiate arteries.
  • The renal tubule is a long, convoluted structure that emerges from the glomerulus.
  • The first part is called the proximal convoluted tubule (PCT), due to its proximity to the glomerulus.
  • The third part of the renal tubule is called the distal convoluted tubule (DCT); this part is also restricted to the renal cortex.
  • The glomerulus and convoluted tubules of the nephron are located in the cortex of the kidney, while the collecting ducts are located in the pyramids of the kidney's medulla.

• Nephron, Parts, and Histology

  • It transfers fluid from the proximal to the distal tubule.
  • The distal convoluted tubule and collecting duct is the final site of reabsorption in the nephron.
  • However, anti-diuretic hormone (secreted from pituitary gland as a part of homeostasis) will act on the distal convoluted tubule to increase the permeability of the tubule to water, increasing water reabsorption.
  • The collecting duct is similar in function to the distal convoluted tubule and generally responds the same way to the same hormone stimuli.
  • The osmolarity of fluid through the distal tubule and collecting duct is highly variable depending on hormone stimulus.

• Tubular Reabsorption

  • The filtrate entering the proximal convoluted tubule is 300 mOsm/L, which is the same osmolarity as normal plasma osmolarity.
  • In the proximal convoluted tubules, all the glucose in the filtrate is reabsorbed, along with an equal concentration of ions and water (through cotransport), so that the filtrate is still 300 mOsm/L as it leaves the tubule.
  • In the ascending loop of henle, which is permeable to ions, but not water, osmolarity falls to 100-200 mOsm/L. finally in the distal convoluted tubule and collecting duct, a variable amount of ions and water are reabsorbed depending on hormonal stimulus.
  • The final osmolarity of urine is therefore dependent on whether or not the final collecting tubules and ducts are permeable to water or not, which is regulated by homeostasis.

• Glucosuria

  • The proximal tubule can only reabsorb a limited amount of glucose.
  • When the blood glucose level exceeds about 160 – 180 mg/dl, the proximal tubule becomes overwhelmed and begins to excrete glucose in the urine.
  • However, in those with renal glycosuria, glucose is abnormally elevated in the urine due to improper functioning of the renal tubules, which are the primary components of the nephrons that act as the filtering units of the kidneys.

• Other Hormonal Controls for Osmoregulation

  • This, in turn, stimulates the renal tubules to reabsorb more sodium.
  • Almost all of the sodium in the blood is reclaimed by the renal tubules under the influence of aldosterone.
  • By contrast, absence of aldosterone means that no sodium is reabsorbed in the renal tubules; all of it is excreted in the urine.
  • ANP also prevents sodium reabsorption by the renal tubules, decreasing water reabsorption (thus acting as a diuretic) and lowering blood pressure.

• Testes

  • Under a tough membranous shell, the tunica albuginea contains very fine coiled tubes called seminiferous tubules.
  • The tubules are lined with a layer of cells (germ cells) that develop into sperm cells (also known as spermatozoa or male gametes) from puberty into old age.
  • The developing sperm travels through the seminiferous tubules to the rete testis located in the mediastinum testis, to the efferent ducts, and then to the epididymis where newly-created sperm cells mature.
  • Leydig cells, localized between seminiferous tubules, produce and secrete testosterone and other androgens important for sexual development and puberty, including secondary sexual characteristics such as facial hair and sexual behavior.