seminiferous tubule

Examples of seminiferous tubule in the following topics:

• Male Reproductive Anatomy

  • Coiled in each testis are seminiferous tubules that produce sperm.
  • Sperm develop in the seminiferous tubules that are coiled inside the testes .
  • The walls of the seminiferous tubules are composed of the developing sperm cells, with the least-developed sperm at the periphery of the tubule and the fully-developed sperm in the lumen.
  • Other cells mixed in the wall of the tubules are the interstitial cells of Leydig; these cells produce high levels of testosterone once the male reaches adolescence.
  • Sperm are produced in the seminiferous tubules, mature in the epididymis, and then are forced out into the vas deferens and out of the body through the urethra during ejaculation.

• Gametogenesis (Spermatogenesis and Oogenesis)

  • Spermatogenesis occurs in the wall of the seminiferous tubules , with stem cells at the periphery of the tube and the spermatozoa at the lumen of the tube.
  • Immediately under the capsule of the tubule are diploid, undifferentiated cells.
  • When it reaches the lumen of the tubule and grows a flagellum (or "tail"), it is called a sperm cell.

• 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.
  • The system of malpighian tubules consists of branching tubules, which increase their surface area, near the hemolymph (a mixture of blood and interstitial fluid that is found in insects, other arthropods, and most mollusks) and fat tissues.
  • Malpighian tubules work cooperatively with specialized glands in the wall of the rectum .
  • Explain how insects use malpighian tubules to excrete wastes and maintain osmotic balance

• 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.

• 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.

• Skeletal Muscle Fibers

  • The sarcolemma of myocytes contains numerous invaginations (pits) termed transverse tubules which are usually perpendicular to the length of the myocyte.
  • Transverse tubules play an important role in supplying the myocyte with Ca+ ions which are key for muscle contraction.
  • Each myofibril is surrounded by the sarcoplasmic reticulum which is closely associated with the transverse tubules.
  • The sarcoplasmic reticulum acts as a sink of Ca+ ions, which are released upon signalling from the transverse tubules.

• Kidney Function and Physiology

  • Second, the renal tubules collect the filtrate.
  • Tubular reabsorption occurs in the PCT part of the renal tubule.
  • Because Na+ is actively transported out of the tubule, water follows to even out the osmotic pressure.
  • It tends to absorb water from the renal tubule and concentrate the filtrate.
  • Additional solutes and wastes are secreted into the kidney tubules during tubular secretion, which is the opposite process to tubular reabsorption.

• The Endoplasmic Reticulum

  • The endoplasmic reticulum (ER) is a series of interconnected membranous sacs and tubules that collectively modifies proteins and synthesizes lipids.
  • The hollow portion of the ER tubules is called the lumen or cisternal space.

• Hormonal Regulation of the Excretory System

  • As ADH (which is also known as vasopressin) causes direct water reabsorption from the kidney tubules, salts and wastes are concentrated in what will eventually be excreted as urine.
  • ADH travels in the bloodstream to the kidneys where it changes the kidneys to become more permeable to water by temporarily inserting water channels, aquaporins, into the kidney tubules.
  • Water moves out of the kidney tubules through the aquaporins, reducing urine volume.
  • In contrast to ADH, which promotes the reabsorption of water to maintain proper water balance, aldosterone maintains proper water balance by enhancing Na+ reabsorption and K+ secretion from extracellular fluid of the cells in kidney tubules.