Problem Set #3

Biology 235

Human Physiology

Fall 2001

Dr. Brundage

 

Each Problem is worth the indicated amount (25 points total). Answers should be short, but complete. Usually several sentences are required to answer each question thoroughly. When using diagrams, be sure to draw clearly and label completely. Answers maybe typed or neatly hand written (legible please!!) A problem answer key will be handed out prior to the exam and the problem set will be returned to you with your exam.

Questions?? E-mail: rbrundage@wvu.edu or phone 293 - 5201 ext. 2517

 

1. As you know the adaptive immune system has "memory" which assists in combating repeated exposures to disease causing agents such as viruses. In the space below briefly describe how immunological memory is generated by B cells. In addition explain how the immune response differs between the first exposure to a virus and a later encounter with that same virus. (6 points)

The generation of immunological memory by B cells begins with their exposure to antigen. An antigen is any substance that is recognized by the immune system. Typically antigens are proteins, but they can also be lipids and synthetic chemicals. The population of B cells in the body consists of cells which can each make one specific type of antibody. Cells that make an antibody that can recognize the foreign antigen are activated by exposure to antigen. The activated cell begins to divide producing identical cells that make the specific antibody. This process is referred to as "clonal selection" since the reproducing cells represent a clonal population formed by the division of a unique antibody producing founder cell. The majority of the cells in the clonal population begin to secrete antibodies to fight off the viral infection. A small number of the cells are set aside as memory cells during the clonal selection process. These memory cells persist in the body long after the initial viral infection has been cleared. Upon secondary exposure to the same virus the memory cells are activated and immediately begin producing the required antibody. The response to the infection is more rapid the second time it is encountered due to the presence of the memory cells made during the first infection.

 

 

2. In the space below list the types of cells which make up the mature vertebrate (human) immune system. For each cell type provide a short description of its function in the immune response.

(7 points)

Eosinophils: Fight of parasitic infections and are involved in allergic responses

Basophils: Release histamine and are involved in allergic responses

Neutrophils: Phagocytic cells which are found in the circulation

Macrophages: Phagocytic cells which reside in the bodies tissues. Much larger than neutrophils. Formed through maturation (development) of monocytes

B Cells: Produce antibodies which are specific for specific antigens

Cytotoxic T Cells: Destroy cells harboring viruses and part of the immuno-surveillance system which detects and destroys cancer cells. Detection of foreign material occurs through interaction with MHC (class I) which is expressed on the surface of all cells. MHC presents processed foreign antigens for detection by cytotoxic T cells.

Helper T Cells: Enhance the development of antigen stimulated B cells by secreting factors which influence cell replication. Also enhance the activity of cytotoxic and suppressor T cells. Activation occurs through interactions with MHC (class II) which is expressed only on cells of the immune system (such as macrophages).

Supressor T Cells: Suppress the activity of B cells and cytotoxic T Cells. Important in blocking inappropriate immune responses (self vs non-self descrimination)

 

 

 

 

 

3. Using a graph explain how the conditions in an active tissue such as skeletal muscle, alter the oxygen binding properties of hemoglobin such that additional oxygen is released. In addition to your graph list the changes that are found in tissues with increased metabolism and how these factors alter the properties of hemoglobin. (6 points)

See figure 13-30. The dotted curve above shows how the oxygen binding properties of hemoglobin change in a metabolically active tissue, like skeletal muscle. In these tissues Hb has a lower capacity for oxygen binding and the result is that more oxygen is released into these metabolically active tissues. The products of metabolism which influence Hb include acidic pH, Carbon dioxide, and increased temperature all of which decrease the binding of oxygen to HB.

 

 

 

4. As you know breathing is an active process, requiring energy. You also now know that some aspects of the ventilation cycle are passive. Answer the following questions I) Which parts of the normal respiratory cycle are active and which parts are passive? II) What are the changes that occur during exercise? III) What are the main muscles of respiration and how do they participate in the process? IV) What is responsible for the passive part of the process? (include the properties of the thoracic compartment and of the lung itself)

(6 points)

I) Normally inspiration is an active process and expiration is passive.

II) During exercise expiration becomes an active process as well. The result is a greater emptying of the lungs and an increase in the tidal volume. During exercise the accessory muscles of inspiration are also used to fill lungs to a greater extent.

III. The main muscles of respiration are:

Inspiratory Muscles:

Diaphragm: Generates negative pressure in the thoracic cavity

External Intercostal Muscles: Elevate the ribs to increase the volume of the thoracic cavity.

Neck Muscles: Elevate the sternum further increasing the thoracic volume. These muscles are accessory muscles which are normally only used during exercise to increase the lung capacity.

Expiratory Muscles:

Abdominal Muscles: Contraction forces diaphragm further into thoracic cavity emptying lungs more completely.

Internal Intercostal Muscles: Lower the ribs decreasing the thoracic cavity volume further.

IV. The factors responsible for the passive process of expiration during normal breathing include: The relaxation of the diaphragm and the external intercostal muscles which both passively decrease the thoracic cavity volume and the surface tension on the alveoli themselves. During expiration the alveoli shrink in volume due to the internal force of surface tension which causes the alveoli to decrease in diameter in the absence of external force provided by the inspiratory mechanism.