The Lymphatic System and
Immunity:
I.
The Lymphatic
System
a.
Lymph – fluid in
the tissue spaces that carries protein molecules and other substances back to
the blood.
b.
Lymphatic Vessels
– permit only one-way movement of lymph
i.
Lymphatic
capillaries – tiny dead-end tubes distributed throughout the tissue spaces
1.
Microscopic in
size
2.
Walls are sheets
consisting of one cell layer of simple squamous
epithelium
3.
Poor “fit”
between adjacent cells results in porous walls
4.
Also called
“lacteals” when found in the intestinal walls – used for lipid transport
ii.
Right lymphatic
duct – drains lymph from the right upper extremity and the right side of the
head, neck, and upper extremity
iii.
Thoracic duct
1.
The largest
lymphatic vessel
2.
Has an enlarged
pouch along its course called cisterna chili
3.
drains lymph from
about three-fourths of the body
c.
Lymphedema – swelling of the tissues caused by blockage of lymph
vessels
i.
Lymphangitis – inflammation of lymph vessels; may progress to
septicemia (blood poisoning)
ii.
Elephantiasis –
severe lymphedema of the limbs caused by parasitic
infection of lymph vessels (tiny worms)
d.
Lymph nodes
i.
Their function is
to filter lymph
ii.
Located in
clusters along the pathway of lymphatic vessels
iii.
Functions include
defense and white blood cell formation
iv.
Flow of
lymph: into the lymph node via several
afferent lymph vessels and drained from node via a single efferent lymph vessel
e.
Lymphoma –
malignant tumor of the lymph nodes
i.
Two Types –
Hodgkin’s disease and non-Hodgkin’s Lymphoma
f.
Thymus
i.
Lymphoid tissue
organ located in mediastinum
ii.
Total weight is
just over an ounce
iii.
Plays a vital and
central role in immunity
iv.
Produces “Killer
T-Cells”; also known as T-Lymphocytes
v.
Secrets a hormone
called thymosin
vi.
Over time,
lymphoid tissue is largely replaced by fat in a process called involution
g.
Tonsils
i.
Composed of three
masses of lymphoid tissue around the oropharynx and nasopharynx
1.
Palatine tonsils
are located on either side of the oropharynx
2.
Adenoids are
located in the posterior nasopharynx
3.
Lingual tonsils
are located along the tongue on the floor of the oral cavity
ii.
Tonsils may
become subject to chronic infection and swelling
iii.
Enlargement of
the adenoids may impair breathing.
iv.
Routine removal
of the tonsils and adenoids is controversial.
h.
Spleen
i.
Largest lymphoid
organ in the body
ii.
Located in the
upper left quadrant of the abdomen
iii.
Often injured by
trauma to the abdomen
iv.
Surgical removal
is called a splenectomy
v.
Functions
included phagocytosis of bacteria and old red blood
cells; acts as a blood reservoir.
vi.
Splenomegaly – enlargement of the spleen.
II.
The Immune System
a.
Protects the body
from pathological bacteria, foreign tissue cells, and cancer
b.
Made up of
specialized cells and molecules
c.
Non-Specific
Immunity
i.
The Skin acts as
a mechanical barrier to bacteria and other harmful agents
ii.
Tears and Mucus –
wash eyes and trap and kill bacteria
iii.
Inflammation
attracts immune cells to site of injury; increases local blood flow, increases
vascular permeability; promotes movement of WBC’s to
site of injury or infection.
d.
Specific Immunity
– ability of the body to recognize, respond to, and
remember harmful substances or bacteria.
e.
Inherited or
Inborn Immunity – inherited immunity to certain diseases from birth
f.
Acquired Immunity
i.
Natural Immunity
– exposure to causative agent is not deliberate
1.
Active – active
disease produces immunity
2.
Passive –
immunity passes from mother to fetus through placenta or from mother to child
through breast milk.
ii.
Artificial
Immunity – exposure to causative agent is deliberate
1.
Active –
Vaccination results in immunity
2.
Passive –
protective material developed in another individual’s immune system and given
to previously non-immune individual.
III.
Immune System
Molecules
a.
Antibodies
i.
Protein compounds
with specific combining sites
ii.
Combining sites
attach antibodies to specific antigens (foreign proteins), forming an
antigen-antibody complex – called humoral or
antibody-mediated immunity
iii.
Antigen-Antibody complexs may:
1.
Neutralize toxins
2.
Clump or
agglutinate enemy cells
3.
Promote phagocytosis
b.
Complement
Proteins
i.
Group of proteins
normally present in blood in inactive state
ii.
Complement
Fixation:
1.
Important
mechanism of action for antibodies
2.
Causes cell lysis by permitting entry of water through a defect created
in the plasma membrane
IV.
Immune System
Cells
a.
Phagocytes –
ingest and destroy foreign cells or other harmful substances via phagocytosis
i.
Neutrophils
ii.
Monocytes
iii.
Macrophages
1.
Kupfer cells (liver)
2.
Dust Cells
(lungs)
iv.
Lymphocytes
1.
Most numerous of
immune system cells
2.
Development of B
cells – primitive stem cells migrate from bone marrow and go through two stages
of development:
a.
First stage –
stem cells develop into immature B cells; takes place in the liver and bone
marrow before birth and in the bone marrow only in adults; immature B cells are
small lymphocytes with antibody molecules (which they have synthesized) in
their plasma membranes; migrate chiefly to the lymph nodes.
b.
Second stage –
immature B cell develops into activated B cell; initiated by immature B cell’s
contact with antigens which bind to its surface antibodies; activated B cell,
by dividing repeatedly, forms two clones of cells – plasma cells and memory
cells – plasma cells secrete antibodies into blood; memory cells are stored in
the lymph nodes; if subsequent exposure to the antigen that activated the B
cells occurs, memory cells became plasma cells and secrete antibodies.
3.
Function of B
cells – indirectly, B cells produce humoral immunity;
activated B cells develop into plasma cells; plasma cells secrete antibodies
into the blood; circulating antibodies produce humoral
immunity.
4.
Development of T
cells – stem cells from bone marrow migrate to thymus gland.
a.
Stage 1 – stem
cells develop into T cells; occurs in thymus during few months before and after
birth; T cells migrate chiefly to lymph nodes.
b.
Stage 2 – T cells
develop into sensitized T cells; occurs when, and if, antigen bings to T cell’s surface proteins
5.
Function of T
cells – produce cell mediated immunity; kill invading cells by releasing a
substance that poisons cells and also by releasing chemicals that attract and
activate macrophages to kill cells by phagocytosis.
V.
Hypersensitivity
of the Immune System
a.
Inappropriate or
excessive immune response
b.
Allergy –
hypersensitivity to harmless environmental allergens
i.
Immediate
allergic responses usually involve humoral immunity
ii.
Delayed allergic
responses usually involve cell-mediated immunity
c.
Autoimmunity –
inappropriate, excessive responses to self-antigens
i.
Causes autoimmune
diseases
ii.
Example: Systemic Lupus Erythematosus
(SLE) – chronic inflammatory disease caused by numerous antibodies attacking a
variety of tissues
d.
Isoimmunity – excessive reaction to antigens from another human
i.
May occur between
mother and fetus during pregnancy
ii.
May occur in
tissue transplants causing rejection syndrome
VI.
Immune System
deficiency
a.
Congenital immune
deficiency or immunodeficiency (rare)
i.
Results from
improper lymphocyte development before birth
ii.
Severe combined
immune deficiency (SCID) – caused by disruption of stem cell development
b.
Acquired Immune
Deficiency
i.
Develops after
birth
ii.
Acquired
Immunodeficiency Sydrome (AIDS) – is caused by HIV
infection of T cells.