Midterm Short Answers

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  1. In what way is bone part of a homeostatic system?
    • makes blood cells
    • maintains calcium levels when the drop--bones release it when it is needed for muscle contraction. Still need calcium in diet to replenish supply
    • structural support for organs
  2. Describe the function of hydrochloric acid (HCl) and pepsin in the stomach. How does the stomach protect itself from these substances?
    • HCl activates pepcinogen into pepsin
    • Pepsin aids in the chemical digestion of proteins by breaking peptide bonds
    • HCl kills bacteria
    • HCl denatures proteins, unfolding them so that the pepsin can access peptide bonds
    • Cells of the stomach lining produce mucus that protect themselves from HCl
  3. Describe how the pacemaker, the sinoatrial node, coordinates the contractions of the heart.
    • The pacemaker initiates the impulse that travels along nervous type cells to make the atria contract to push blood into the ventricles
    • The impulses are also sent to the AV node
  4. Explain how a blood clot forms and how it helps prevent bleeding.
    Injured cells in the wall of the vessel release a chemical that sets in motion a series of reactions that convert fibrinogen into fibrin, which forms a network to collect RBCs and platelets, sealing off the wound
  5. Smoking irritates the trachea and bronchi, causing mucus to build up and paralyzing the cilia. How do these changes affect the lung?
    The cilia's function of "sweeping the air" of bacteria, toxins, and other particles is impaired, making it easier for bacteria to infiltrate the lungs. This increases the smoker's likelihood of developing lung infections.
  6. How does urination differ between newborns and adults? Explain what is meant by this statement: In older children and adults, urination is a reflex with a conscious override.
    • Children are unable to control their external sphincter, while adults can
    • Chilren therefore cannot control when they urinate
    • "Quote" references this difference
    • Both adults and young children cannot control internal sphincter, which opens on reflex
    • Adults can counteract the opening by consciously controlling the external
  7. Draw a typical synapse, label the parts, and explain how a nerve impulse is transmitted from one nerve cell to another.
    • Diagram on book p. 176, fig 10-6
    • Arrival of the impulse stimulates the release of neurotransmitters from vesicles in axon terminals
    • Neurotransmitter diffuses across synaptic cleft, binds to postsynaptic membrane
    • Elicits another action potential that travels down the dendrite to the cell body
  8. Define the term adaptation. What advantages does it confer? Can you think of any disadvantages?
    • Adaptation is when sensory receptors stop generating impulses even though a stimulus is still present
    • Advantage-reduces pain or discomfort
    • Disadvantage-adaptation in muscle stretch receptors could be dangerous and lead to injury
  9. What is an autoimmune disease? Explain the reasons it forms.
    • AI diseas- when the immune system attacks the body's own cells
    • Normal body proteins can be modified by environmental polutants, viruses, or genetic mutations sp that they are no longer recognizable by the body as self
    • Normal body proteins usually isolated from the immune system enter the bloodstream and evoke an immune response
    • Exposure to antigens that are nearly identical to body proteins
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Midterm Short Answers
Key to the short answers for the human biology midterm
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