D’YOUVILLE COLLEGE
BIOLOGY 108/508 - HUMAN ANATOMY & PHYSIOLOGY II
LECTURE # 13
BLOOD III
IMMUNE RESPONSES/BLOOD GROUPS
5.
Lymphatic System and Lymphoid Tissue:
a. Organization:
• lymphatic capillaries (fig. 20 - 1) drain all tissue regions of body;
facilitate balanced fluid uptake and protein uptake from tissues
• larger lymphatics (are like venules - possess one-way valves in
dependent areas) drain lymphatic capillaries & lead to regional lymph node
• Regional Lymph Nodes: screen & detoxify lymph; reservoirs of
macrophages, lymphocytes (fig. 20 - 4)
• lymphatic trunks, e.g. thoracic duct, return lymph to bloodstream (fig.
20 - 2)
• Spleen: also stores lymphocytes & macrophages in areas known as
'white pulp' (figs. 20 - 5 & 20 - 6)
• Thymus: site of maturation of class of lymphocytes (T lymphocytes)
(figs. 20 - 5 & 20 - 7)
• other lymphoid organs include tonsils, appendix, and deposits in
walls of digestive tract (Peyer's patches) (figs. 20 - 8 & 20 - 9)
b. Functions:
• Lymphatic drainage: excess fluid & protein removed from tissue fluid
• Fat absorption: (from small intestine via lacteals)
• Filtering and Defense: lymph nodes, lymph nodules
c. Sites of Regional Lymph Nodes:
• inguinal, pelvic, abdominal, thoracic, axillary, cervical
6.
Lymphocytes and Immune Responses:
• specific immunity (response tailored to offending agent)
a. Types of Lymphocyte:
i. B-lymphocytes: deliver antibody-mediated immunity (AMI)
ii. T-lymphocytes: several subtypes (helpers, cytotoxic); deliver cellmediated immunity (CMI)
b. Antigens: large molecules, e.g. proteins; many binding sites (determinants)
(fig. 21 - 7); usually presented
c. Antibody-mediated Immunity (AMI):
• Antibody Structure: Y-shaped unit (monomer); antigen-binding sites;
additional binding functions (fig. 21 - 14)
• Immune Complexes: antibodies bind antigens with several possible
consequences: 1) precipitation or agglutination; 2) neutralization; 3) opsonization
4) complement fixation: complement system (group of plasma proteins)
binds to immune complex; activation of several factors, (e.g. chemotaxins,
Bio 108/508
lec. 13 - p. 2
vasoactive substances, opsonins, lysins), resulting in inflammation, phagocytosis,
leukocytosis, destruction of offending agent (fig. 21 - 6)
Bio 108/508
lec. 13 - p. 3
d. Cell-mediated Immunity (CMI):
• T-lymphocytes mature in thymus
- when activated by antigen binding (presented by dendritic cell - fig. 21
- 10), produce interleukins (mitogens, migration inhibitors, transfer factor,
chemotaxins, lysins)
- interleukins of helper T cells (CD4 receptors) stimulate other immune
system cells
- products of cytotoxic T cells (CD8 receptors) destroy antigens or cells
bearing antigens (e.g. virus-infected cells) (fig. 21 - 16)
e. Sensitization:
• initial exposure to antigen generates weak, slowly developing response;
(ineffective if initial dosage is strong!)
• subsequent exposures generate strong, rapid responses that may
dispatch potentially lethal antigen doses (fig. 21 - 12)
• clonal selection theory: explanation of sensitization (figs. 21 - 11 & 21 16):
i. antigen (usually processed by macrophages or dendritic cells)
attempts binding with various lymphocytes; unsuccessful until “good fit” with
receptor
ii. antigen binding stimulates lymphocyte to undergo mitosis,
proliferating a large population of identical cells (same antigen receptor); called a
“clone”
iii. clone believed to contain both active and dormant (memory) cells;
memory cells may populate lymphoid depots around body increasing likelihood of
successful response to another encounter with same antigen (sensitization)
iv. effector cells:
• B-cells: those that secrete antibodies, are known as plasma cells
• T-cells: secrete cytokines (interleukins) when they bind an antigen
(cytotoxic cells)
f. Vaccination: practice of clinically inducing sensitization to a particular
antigen, thus, guaranteeing a vigorous immune response (immunization)