chromaffin cells

Examples of chromaffin cells in the following topics:

• Adrenal Medulla

  • Chromaffin cells are the neuroendocrine cells found in the medulla; they are modified post-synaptic sympathetic neurons that receive sympathetic input.
  • When stimulated, chromaffin cells secrete adrenaline and noradrenaline along with enkephalin and enkephalin-containing peptides into the bloodstream.

• Postganglionic Neurons

  • The two exceptions mentioned above are the postganglionic neurons of sweat glands and the chromaffin cells of the adrenal medulla.
  • The chromaffin cells of the adrenal medulla are analogous to post-ganglionic neurons—the adrenal medulla develops in tandem with the sympathetic nervous system and acts as a modified sympathetic ganglion.
  • Within this endocrine gland, the pre-ganglionic neurons create synapses with chromaffin cells and stimulate the chromaffin cells to release norepinephrine and epinephrine directly into the blood.
  • The postsynaptic cell then goes on to innervate the targeted end effector (i.e., gland, smooth muscle, etc.).
  • The pelvic splanchnic efferent preganglionic nerve cell bodies reside in the lateral gray horn of the spinal cord at the S2–S4 spinal levels.

• Development of the Urinary System

  • The adrenal medulla forms from neural crest cells that migrate into the fetal cortex and differentiate into chromaffin cells.

• Preganglionic Neurons

  • The preganglionic, or first neuron will begin at the outflow and will cross a synapse at the postganglionic, or second neuron's cell body.
  • The sympathetic division (thoracolumbar outflow) consists of cell bodies in the lateral horn of the spinal cord (intermediolateral cell columns) from T1 to L2.
  • These cell bodies are GVE (general visceral efferent) neurons and are the preganglionic neurons.
  • The chromaffin cells of the adrenal medulla.
  • This is the one exception to the two-neuron pathway rule: they create a synapse directly onto the target cell bodies.

• Specific T-Cell Roles

  • T helper cells assist the maturation of B cells and memory B cells while activating cytotoxic T cells and macrophages.
  • Differentiation into helper T cell subtypes occurs during clonal selection following T cell activation of naive T cells.
  • Cytotoxic T cells (TC cells, or CTLs) destroy virus-infected cells and tumor cells, and cause much of the damage in in transplant rejection and autoimmune diseases.
  • Memory T cells comprise two subtypes: central memory T cells (TCM cells) and effector memory T cells (TEM cells), which have different properties and release different cytokines.
  • Regulatory T cells (Treg cells), also known as suppressor T cells, are crucial for the maintenance of immunological tolerance.

• Natural Killer Cells

  • The role of NK cells is similar to that of cytotoxic T cells in the adaptive immune response.
  • NK cells provide rapid responses to virus-infected cells and respond to tumor formation by destroying abnormal and infected cells.
  • NK cells use wo cytolytic granule-mediated apoptosis to destroy abnormal and infected cells.
  • Virus-infected cells destroyed by cell lysis release their replicated virus particles into the body, which infects other cells.
  • Cells that are osponized with antibodies are easier for NK cells to detect and destroy.

• Lymphoid Cells

  • The three major types of lymphocyte are T cells, B cells, and natural killer cells.
  • If cancer cells evade NK cell detection for long enough, however, they can grow into tumors that are more resistant to NK cell activity.
  • T cells are involved in cell-mediated immunity whereas B cells are primarily responsible for humoral immunity.
  • There are two types of T cells involved in adaptive, cell-mediated immunity.
  • Following activation, B cells and T cells leave a lasting legacy of the antigens they have encountered in the form of memory cells.

• Maturation of T Cells

  • T cells belong to a group of white blood cells known as lymphocytes and play a central role in the cell-mediated branch of the adaptive immune system.
  • They are distinguished from other lymphocytes, such as B cells and natural killer cells (NK cells), by the presence of a T cell receptor (TCR) on the cell surface.
  • T cells can be either helper T cells or cytoxic T cells based on whether they express CD4 (helper) or CD8 (cytotoxic) glycoprotein.
  • A T cell is then signaled by the thymus to become a CD4+ cell by reducing expression of its CD8 cell surface receptors.
  • The remaining cells exit the thymus as mature naive T cells.

• Maturation of B Cells

  • B cells are lymphocytes that play a large role in the humoral immune response (as opposed to the cell-mediated immune response, which is governed by T cells) .
  • Once a B cell encounters its cognate antigen and receives an additional signal from a T helper cell, it can further differentiate into either plasma B cells or memory B cells.
  • B cells exist as clones.
  • A single B cell or a clone of cells with shared specificity, upon encountering its specific antigen, divides to produce many B cells.
  • B cells that encounter antigen for the first time are known as naive B cells.

• Lymphocytes

  • Subtype 2 helper T cells present antigens to B cells.
  • Suppressor T cells (T-reg cells) retain some of their ability to bind to self-cells.
  • Then mature helper T cells bind their antigen to naive B cells through BCRs.
  • Plasma cell and long-lived B cells that are the main source of antibodies.
  • Memory B cells are dormant B cells with the same BCR as the B cell from which they differentiated.