Innate immunity is present before any exposure to pathogens and is effective from the time of birth Acquired immunity

Chapter 43 Name_______________________________ Date

1. 
   What is the difference between innate and acquired immunity?
   

Innate immunity is present before any exposure to pathogens and is effective from the time of birth

Acquired immunity, or adaptive immunity, develops after exposure to agents such as microbes, toxins, or other foreign substances

2. 
   What are some barrier defenses? Describe them.
   

Barrier defenses include the skin and mucous membranes of the respiratory, urinary, and reproductive tracts

Mucus traps and allows for the removal of microbes

Many body fluids including saliva, mucus, and tears are hostile to microbes

The low pH of skin and the digestive system prevents growth of microbes

3. 
   What is the difference between invertebrate and vertebrate immune systems?
   

Invertebrates - In insects, an exoskeleton made of chitin forms the first barrier to pathogens

• 
  The digestive system is protected by low pH and lysozyme, an enzyme that digests microbial cell walls
  
• 
  Hemocytes circulate within hemolymph and carry out phagocytosis, the ingestion and digestion of foreign substances including bacteria
  

Vertebrates -

• 
  Innate defenses include barrier defenses, phagocytosis, antimicrobial peptides
  
• 
  Additional defenses are unique to vertebrates: the inflammatory response and natural killer cells
  
• 
  White blood cells (leukocytes) engulf pathogens in the body
  
• 
  Groups of pathogens are recognized by TLR, Toll-like receptors
  

4. 
   Complete the following table that summarizes the functions of the cells and chemicals of the innate defense mechanisms.
   

Cells or Compounds	Functions
Neutrophils	engulf and destroy microbes
Macrophages	are part of the lymphatic system and are found throughout the body
Eosinophils	discharge destructive enzymes
Dendritic cells	stimulate development of acquired immunity
Natural Killer Cells	All cells in the body (except red blood cells) have a class 1 MHC protein on their surface Cancerous or infected cells no longer express this protein; natural killer (NK) cells attack these damaged cells
Mast Cells	Following an injury, mast cells release histamine, which promotes changes in blood vessels
Histamine	Following an injury, mast cells release histamine, which promotes changes in blood vessels
Interferons	proteins provide innate defense against viruses and help activate macrophages
Complement system	About 30 proteins make up the complement system, which causes lysis of invading cells and helps trigger inflammation
Lysozyme	an enzyme that digests microbial cell walls

5. 
   What is an epitope?
   

All antigen receptors on a single lymphocyte recognize the same epitope, or antigenic determinant, on an antigen

6. 
   Describe the differences between the antigens that B cell receptors and antibodies recognize and the antigens that T cell receptors on cytotoxic T cells and helper T cells recognize.
   

B Cells

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  bind to specific, intact antigens
  
• 
  The B cell receptor consists of two identical heavy chains and two identical light chains
  
• 
  The tips of the chains form a constant (C) region, and each chain contains a variable (V) region, so named because its amino acid sequence varies extensively from one B cell to another
  
• 
  Secreted antibodies, or immunoglobulins, are structurally similar to B cell receptors but lack transmembrane regions that anchor receptors in the plasma membrane
  

T Cells

• 
  Each T cell receptor consists of two different polypeptide chains
  
• 
  The tips of the chain form a variable (V) region; the rest is a constant (C) region
  
• 
  T cells can bind to an antigen that is free or on the surface of a pathogen
  
• 
  T cells bind to antigen fragments presented on a host cell
  
• 
  These antigen fragments are bound to cell-surface proteins called MHC molecules
  

7. 
   Answer the following questions concerning the three major stages in the development of lymphocytes.
   

1. 
   How is the great diversity of B and T cells produced?
   

Differences in the variable region account for specificity of antigen receptors

The immunoglobulin (Ig) gene encodes one chain of the B cell receptor

Many different chains can be produced from the same Ig chain gene by rearrangement of the DNA

Rearranged DNA is transcribed and translated and the antigen receptor formed

2. 
   What prevents B and t cells from reacting against the body’s own molecules?
   

Antigen receptors are generated by random rearrangement of DNA

As lymphocytes mature in bone marrow or the thymus, they are tested for self-reactivity

Lymphocytes with receptors specific for the body’s own molecules are destroyed by apoptosis, or rendered nonfunctional

3. 
   Describe clonal selection.
   

In the body there are few lymphocytes with antigen receptors for any particular epitope

The binding of a mature lymphocyte to an antigen induces the lymphocyte to divide rapidly

This proliferation of lymphocytes is called clonal selection

Two types of clones are produced: short-lived activated effector cells and long-lived memory cells

8. 
   What surface molecule of a helper T cell facilitates the interaction with a class II MHC molecule of an antigen-presenting cell and the helper T cell?
   

CD4

MHC molecules are so named because they are encoded by a family of genes called the major histocompatibility complex

• 
  Class I MHC molecules are found on almost all nucleated cells of the body
  
  • 
    They display peptide antigens to cytotoxic T cells
    
• 
  Class II MHC molecules are located mainly on dendritic cells, macrophages, and B cells
  
• 
  Dendritic cells, macrophages, and B cells are antigen-presenting cells that display antigens to cytotoxic T cells and helper T cells
  

• 
  A surface protein called CD4 binds the class II MHC molecule
  
• 
  This binding keeps the helper T cell joined to the antigen-presenting cell while activation occurs
  

9. 
   What surface molecule on a cytotoxic T cell assists in the interaction with a
   

class I MHC molecule displayed on infected cells?

CD8

• 
  Cytotoxic T cells are the effector cells in cell-mediated immune response
  
• 
  Cytotoxic T cells make CD8, a surface protein that greatly enhances interaction between a target cell and a cytotoxic T cell
  

10. 
    What does an activated helper T cell release?
    

Activated helper T cells secrete cytokines that stimulate other lymphocytes

11. 
    What does a cytotoxic T cell attached to an infected body cell release?
    

Binding to a class I MHC complex on an infected cell activates a cytotoxic T cell and makes it an active killer

The activated cytotoxic T cell secretes proteins that destroy the infected target cell

12. 
    List three ways in which antibodies mediate the disposal of antigens.
    
    1. 
       viral neutralization- occurs when a pathogen can no longer infect a host because it is bound to an antibody
       
    2. 
       opsonization -occurs when antibodies bound to antigens increase phagocytosis
       
    3. 
       activation of complement system and pore formation- Antibodies together with proteins of the complement system generate a membrane attack complex and cell lysis
       

13. 
    Why is AIDS such a deadly disease? Why has it proved so difficult to prevent and cure this disease (AIDS)?
    

Human immunodeficiency virus (HIV) infects helper T cells

The loss of helper T cells impairs both the humoral and cell-mediated immune responses and leads to AIDS

HIV eludes the immune system because of antigenic variation and an ability to remain latent while integrated into host DNA

• 
  People with AIDS are highly susceptible to opportunistic infections and cancers that take advantage of an immune system in collapse
  
• 
  The spread of HIV is a worldwide problem
  
• 
  The best approach for slowing this spread is education about practices that transmit the virus
  

14. 
    What is the difference between passive and active immunity? Provide an example of each.
    

Active immunity develops naturally in response to an infection. It can also develop following immunization, also called vaccination

Passive immunity provides immediate, short-term protection

It is conferred naturally when IgG crosses the placenta from mother to fetus or when IgA passes from mother to infant in breast milk

It can be conferred artificially by injecting antibodies into a nonimmune person

15. 
    Briefly describe the exaggerated, self-direct, and diminished immune responses.
    

1. 
   Allergies - Allergies are exaggerated (hypersensitive) responses to antigens called allergens
   

• 
  In localized allergies such as hay fever, IgE antibodies produced after first exposure to an allergen attach to receptors on mast cells. The next time the allergen enters the body, it binds to mast cell–associated IgE molecules
  
• 
  Mast cells release histamine and other mediators that cause vascular changes leading to typical allergy symptoms
  
• 
  An acute allergic response can lead to anaphylactic shock, a life-threatening reaction that can occur within seconds of allergen exposure
  

2. 
   Autoimmune diseases - In individuals with autoimmune diseases, the immune system loses tolerance for self and turns against certain molecules of the body
   

Autoimmune diseases include systemic lupus erythematosus, rheumatoid arthritis, insulin-dependent diabetes mellitus, and multiple sclerosis

3. 
   Immunodeficiency diseases - Inborn immunodeficiency results from hereditary or developmental defects that prevent proper functioning of innate, humoral, and/or cell-mediated defenses
   

Acquired immunodeficiency results from exposure to chemical and biological agents

Acquired immunodeficiency syndrome (AIDS) is caused by a virus

4. 
   Cancer - The frequency of certain cancers increases when the immune response is impaired
   

Two suggested explanations are

Immune system normally suppresses cancerous cells

Increased inflammation increases the risk of cancer

Chapter 45

1. 
   What are hormones?
   

Animal hormones are chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body

2. 
   Which two systems coordinate communication throughout the body? Describe them
   
   1. 
      The endocrine system secretes hormones that coordinate slower but longer-acting responses including reproduction, development, energy metabolism, growth, and behavior
      
   2. 
      The nervous system conveys high-speed electrical signals along specialized cells called neurons; these signals regulate other cells
      

3. 
   Complete the chart below.
   

Chemical Signal	Function	Example
Hormone	Endocrine signals (hormones) are secreted into extracellular fluids and travel via the bloodstream. mediate responses to environmental stimuli and regulate growth, development, and reproduction
Local regulator	chemical signals that travel over short distances by diffusion Local regulators help regulate blood pressure, nervous system function, and reproduction
Neurotransmitter	At synapses, neurons often secrete chemical signals called neurotransmitters that diffuse a short distance to bind to receptors on the target cell Neurotransmitters play a role in sensation, memory, cognition, and movement
Neurohormone	Neurohormones are a class of hormones that originate from neurons in the brain and diffuse through the bloodstream
Pheromones	Pheromones are chemical signals that are released from the body and used to communicate with other individuals in the species Pheromones mark trails to food sources, warn of predators, and attract potential mates

4. 
   List and describe the two types of local regulators below.
   
   1. 
      Paracrine signals act on cells near the secreting cell
      
   2. 
      Autocrine signals act on the secreting cell itself
      

5. 
   What are the 3 major classes of molecules that function as hormones in vertebrates:
   
   1. 
      Polypeptides (proteins and peptides)
      
   2. 
      Amines derived from amino acids
      
   3. 
      Steroid hormones
      

6. 
   What is the difference between lipid-soluble hormones and water-soluble hormones? What is the benefit of each?
   

Lipid-soluble hormones (steroid hormones) pass easily through cell membranes, while water-soluble hormones (polypeptides and amines) do not

The solubility of a hormone correlates with the location of receptors inside or on the surface of target cells

7. 
   Briefly describe the pathway of lipid-soluble hormones (for example the pathway of steroids and thyroid hormones).
   

Water-soluble hormones are secreted by exocytosis, travel freely in the bloodstream, and bind to cell-surface receptors

Lipid-soluble hormones diffuse across cell membranes, travel in the bloodstream bound to transport proteins, and diffuse through the membrane of target cells

8. 
   Explain the difference between negative and positive feedback in the control of hormonal pathways.
   

• 
  A negative feedback loop inhibits a response by reducing the initial stimulus
  
• 
  Negative feedback regulates many hormonal pathways involved in homeostasis
  
• 
  A positive feedback loop stimulates a response by reducing the initial stimulus