Prolonged exposure of receptor to their ligand will cause
- Deactivation
- Degeneration
- Desensitisation
- Receptor dysfunction
In response to prolonged exposure to their ligands, most receptors become unresponsive; that is, they undergo desensitization. This can be of two types: homologous desensitization, with loss of responsiveness only to the particular ligand and maintained responsiveness of the cell to other ligands; and heterologous desensitization, in which the cell becomes unresponsive to other ligands as well.
During an air raid, a bomb strikes a large office building composed of concrete blocks. Several civilians are killed immediately. By which of the following mechanisms did the victims most likely die from this event?
- Asphyxiation
- Blunt force trauma
- Cardiopulmonary arrest
- Extensive burns
- Myocardial infarction
Asphyxiation = Though there can be dust and debris from a blast, there is no lack of oxygen and no significant amount of toxic gases.
Blunt force trauma = ‘Precision bombing’ is an oxymoron which, when combined with a chronic inability of most politicians to think things through, leads to disasters. Blast injuries, like many physical force injuries, produce extensive contusions with multiple organ injuries.
Cardiopulmonary arrest = Of course, this defines death but says nothing about causation.
Extensive burns = Blasts such as this one are designed to produce injury at a distance.
Myocardial infarction = Though it may be acceptible in the media to say that someone ‘died of fright’ this rarely happens. Underlying diseases, however, may put survivors at risk.
Major defense mechanisms of the respiratory system include which of the following ?
- Phagocytic activity of type II pneumocytes
- Specific cell killing by type I pneumocytes
- Mucociliary action for tracheobronchial clearance
- The pores of Kohn
- Phagocytic activity by Clara cells
Mucociliary action is critical in protecting the respiratory system, which is exposed to constant assault from the environment. To protect the distal portions of the lung, which under normal conditions are considered a sterile environment, extensive defense mechanisms have evolved. Nasal clearance of material occurs through sneezing, whereas other material located posteriorly may be swept into the nasopharynx. The mucociliary action within the trachea and bronchi is often called the mucociliary, or tracheobronchial, escalator. At the distal end of the system, the alveolar macrophages phagocytose foreign material and secrete and respond to an array of cytokines. The type II pneumocytes resorb as well as secrete surfactant and surfactant associated proteins that have some antiviral and antibacterial function.
In the bronchi, there is extensive associated lymphoid tissue (BALT), which is analogous to the mucosa-associated lymphoid tissue (MALT) of the gut and the skin-associated lymphoid tissue (SALT). There are B and T cell areas throughout the BALT. The B cells are precursors of plasma cells and synthesize immunoglobulins such as IgA associated with the bronchial secretion. Helper T cells recognize foreign antigen in association with class II major histocompatibility complex (MHC) molecules. Cytotoxic T cells recognize fragments of antigen (specifically viral fragments) on the surface of viral-infected cells in association with class I MHC. Antigen-presenting cells (i.e., alveolar macrophages) also function in a similar fashion to those found elsewhere in the body; they present antigen to helper T cells in conjunction with class II MHC
A 2-month-old infant is found to have a horseshoe kidney. Which structure prevents this abnormal kidney from occupying its appropriate position?
- Aorta
- Celiac trunk
- Inferior mesenteric artery
- Inferior vena cava
- Superior mesenteric artery
A horseshoe kidney forms when the inferior poles of two kidneys fuse during development. As the kidneys rise from the pelvis, they encounter the inferior mesenteric artery and cannot rise to the normal level in the abdomen. These patients are typically asymptomatic if they have no other abnormalities.