Tuesday, March 27, 2012

The Lymphatic System



Components

1) Lymph ; protein containing fluid

2) Organs
 i) Lymphatic vessels
 ii) Primary Lymphoid Organs ; development of cells ; bone marrow, thymus
 iii) Secondary Lymphoid Organs ; housing of cells ; lymphoid nodes, spleen

3) Cells
 i) Granulocytes : Eosinophils, Basophils, Neutrophils and most cells
 ii) Agranulocytes : Monocytes, Macrophages, B & T Lymphocytes, Natural killer cells

Functions

1) Maintenance of blood volume n the cardiovascular system.
2) Transport of fat and fat soluble material from digestive system.
3) Filtration of foreign material to defend against infection.
4) Defending the body from various pathogens and parasites.

There are 3 lines of defenses

FIRST LINE OF DEFENSE - PHYSICAL AND CHEMICAL BARRIERS

1) Skin
  - dead, dry and keratinized; so inhospitable

2) Other
  - lysozyme and antibody secretion ; tears, saliva
  - secretions to trap microorganisms ; earwax, mucus
  - acidic ; stomach, vagina
  - elimination mechanisms ; vomiting, urination, defecation
  - resident bacteria secreting antibiotics

SECOND LINE OF DEFENSE - NON SPECIFIC/INNATE IMMUNE MECHANISM

1) Phagocytosis
 - Pinocytosis ; via none specific
 - Receptor-mediated endocytosis ; via specific receptors

2) Interferon ; Induce virus resistance in neighboring cells

3) Compliment (C<sup>'</sup>) System ; complex series of proteins perform 3 vital functions
  - cell activation
  - cytolysis
  - opsonization

THIRD LINE OF DEFENSE - SPECIFIC/ADAPTIVE IMMUNE MECHANISM

-primarily in vertebrates
-a lag phase before the response
-antigen specificity
-identify a huge number of antigens due to B n T cell diversity
-immunological memory
-distinguish between self and none-self

1) B lymphocytes
- BCR binds with molecule and undergo proliferation
- differentiate into
         - effector/plasma cells ; secrete antibodies into blood
         - memory cells

2) T<sub>H</sub> -  Helper T Cells
- carry CD4
- TCR bind with molecule and proliferate and secrete hormones
- promote
  a) phagocytes
  b) induced formation of T<sub>c</sub>
  c) stimulate B cells to form antibodies

3) T<sub>c</sub> - Cytotoxic  T Cells
- carry CD4
- recognize foreign peptide on nucleated cells.
- kill infected host cells
- release proteins (perforin, granzyme ) which forms a pore in target cell and cause cell lysis