1. Chapter 43 Notes
The Body’s Defenses

2. Nonspecific Defenses Against Infection
The skin and mucous membranes provide first-line barriers to infection
-skin prevents the entry of pathogens
- mucous membranes line digestive and respiratory tracts
- the skin also secretes acids and chemicals
- lysozyme: digests the cell wall

3. Nonspecific Defenses Against Infection
Phagocytic cells, inflammation, and antimicrobial proteins function early in infection
Mechanisms depend mainly on phagocytosis: the ingestion of invading organisms by certain types of white cells

4. Nonspecific Defenses Against Infection
- neutrophils: make up 60-70% of WBC; engulf and destroy invaders
- monocytes: more effective; develop into macrophages (“big eaters”); will fuse with a lysosome that will release hydrolytic enzymes
- natural killer (NK) cells: destroy virus-infected body cells

5. Nonspecific Defenses Against Infection

6. Nonspecific Defenses Against Infection

7. Nonspecific Defenses Against Infection
Damage to tissue triggers a localized inflammatory response
- cells release histamine causing dilation of vessels
- increased blood supply, due to dilation, causes redness and warmth
- blood flow also brings large numbers of phagocytes to the infected area

8. Nonspecific Defenses Against Infection

9. How Specific Immunity Arises
Lymphocytes provide the specificity and diversity of the immune system
Two main types: B lymphocytes (B cells) and T lymphocytes (T cells)
- recognize and respond to particular microbes and foreign molecules (antigen)

10. How Specific Immunity Arises
- B cells secrete proteins (antibodies) to fight antigens
- T and B cells can distinguish among antigens
- each antigen has a particular molecular shape and stimulates certain B cells to secrete antibodies that interact with it

11. How Specific Immunity Arises
- T and B cells recognize specific antigens by plasma membrane-bound antigen receptors

12. How Specific Immunity Arises
Antigens interact with specific lymphocytes, inducing immune responses and immunological memory
- clonal selection: the cloning of lymphocytes into plasma cells (short-lived) and memory cells (long-lived)

13. How Specific Immunity Arises

14. How Specific Immunity Arises
Primary immune response: the first time the body is exposed to an antigen
- takes 10 to 17 days for effective response to an antigen
Secondary immune response: when the individual is exposed to the same antigen at a later date
- takes 2 to 7 days

15. How Specific Immunity Arises

16. How Specific Immunity Arises
Lymphocytes originate from stem cells of the bone marrow
- develop into T cells if the continue their development in the Thymus
- develop into B cells if they finish development in the bone marrow

17. How Specific Immunity Arises

18. How Specific Immunity Arises
The immune system exhibits the feature of self-tolerance
- major histocompatibility complex (MHC) are a series of glycoproteins that mark the body as “self”
- MHC provides a biological fingerprint; found in studying skin graft rejection and acceptance

19. How Specific Immunity Arises
There are two main types of T cells: cytoxic T cells (TC) and helper T cells (TH)
Cytoxic T cells have antigen receptors that bind to protein fragments displayed by class I MHC molecules
Helper T cells have receptors that bind to peptides displayed by class II MHC

20. How Specific Immunity Arises

21. Immune Responses
In response to antigens, the immune system can mount a humoral response or a cell-mediated response
Humoral immunity: involves B cell activation and results from the production of antibodies that circulate in the blood plasma and lymph to attack free antigens

22. Immune Responses - B cells form Plasma cells
- plasma cells secrete antibodies for an antigen
- B cells also give rise to B memory cells
- become activated during the second infection

23. Immune Responses
Cell-mediated immunity: T cells are active against viruses and bacteria that have infected cells; also is crucial in the body’s response against transplanted tissues and cancerous cells
- activated T cells become TH or TC; TH activate B cells that produce antibodies, TC destroy infected body cells

24. Immune Responses