1. CHAPTER 24 The Immune System
Modules 24.3 – 24.9

2. The lymphatic system is a network of lymphatic vessels and organs
24.3 The lymphatic system becomes a crucial battleground during infection
The lymphatic system is a network of lymphatic vessels and organs
It returns tissue fluid to the circulatory system
It fights infections

3. LYMPHATIC VESSEL
Adenoid
Tonsil
VALVE
Right lymphatic duct, entering vein
Tissue cells
Lymph nodes
Interstitial fluid
Blood capillary
Thoracic duct, entering vein
Thoracic duct
Thymus
Appendix
LYMPHATIC CAPILLARY
Spleen
Masses of lymphocytes and
macrophages
Bone marrow
Lymphatic vessels
Figure 23.3

4. It will return it as lymph to the blood
This lymphatic vessel is taking up fluid from tissue spaces in the skin
It will return it as lymph to the blood
Lymph contains less oxygen and fewer nutrients than interstitial fluid
LYMPHATIC VESSEL
VALVE
Tissue cells
Interstitial fluid
Blood capillary
LYMPHATIC CAPILLARY
Figure 23.3B

5. Lymph nodes are key sites for fighting infection
They are packed with lymphocytes and macrophages
Masses of lymphocytes and
macrophages
Outer capsule of lymph node
Macrophages
Lymphocytes
Figure 23.3C, D

6. 24.4 The immune response counters specific invaders
SPECIFIC IMMUNITY
24.4 The immune response counters specific invaders
Our immune systems responds to foreign molecules called antigens
Infection or vaccination triggers active immunity
The immune system reacts to antigens and “remembers” an invader
We can temporarily acquire passive immunity

7. 24.5 Lymphocytes mount a dual defense
Two kinds of lymphocytes carry out the immune response
B cells secrete antibodies that attack antigens
T cells attack cells infected with pathogens
BONE MARROW
Stem cell
THYMUS
Via blood
Immature lymphocytes
Antigen receptors
T cell
B cell
CELL- MEDIATED IMMUNITY
HUMORAL IMMUNITY
Via blood
Lymph nodes, spleen, and other lymphatic organs
Final maturation of B and T cells in lymphatic organ
OTHER PARTS OF THE LYMPHATIC SYSTEM
Figure 24.5

8. 24.6 Antigens have specific regions where antibodies bind to them
Antigenic determinants are the molecules to which antibodies bind
Antibody A molecules
Antigen- binding sites
Antigenic determinants
Antigen
Antibody B molecule
Figure 24.6

9. 24.7 Clonal selection musters defensive forces against specific antigens
When an antigen enters the body, it activates only lymphocytes with complementary receptors
B and T cells multiply into clones of specialized effector cells that defend against the triggering antigen
This is called clonal selection

10. Antigen molecules
Variety of B cells in a lymph node
Antigen receptor (antibody on cell surface)
Cell growth
division, and
differentiation
Clone of many effector cells secreting antibodies
Endoplasmic reticulum
Antibody molecules
Figure 24.7

11. 24.8 The initial immune response results in a type of “memory”
In the primary immune response, clonal selection produces memory cells
These cells may confer lifelong immunity
Figure 24.8A

12. When memory cells are activated by subsequent exposure to an antigen, they mount a more rapid and massive secondary immune response
Unstimulated lymphocyte
First exposure to antigen
FIRST CLONE
Memory cells
Second exposure to antigen
Effector cells
SECOND CLONE
More memory cells
New effector cells
Figure 24.8B

13. 24.9 Overview: B cells are the main warriors of humoral immunity
Triggered by a specific antigen, a B cell differentiates into an effector cell
The effector cell is called a plasma cell
The plasma cell secretes antibodies

14. PRIMARY RESPONSE
(initial encounter
with antigen)
Antigen
Antigen receptor on a B cell
Antigen binding
to a B cell
Cell growth,
division, and
differentiation
Clone of cells
Memory B cell
Plasma cell
Antibody
molecules
Later
exposure
to same
antigen
SECONDARY RESPONSE
(can be years later)
Cell growth,
division, and further
differentiation
Larger clone
of cells
Plasma cell
Memory B cell
Antibody
molecules
Figure 24.9