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The Lymphatic System
Chapter 43, Campbell, 6th edition
Nancy G. Morris
Volunteer State Community College
The fluid compartment includes:
• plasma of the blood
• interstitial fluid of the tissues
• lymph of lymphatic system
Plasma:
• 90% water
• contains electrolytes – inorganic salts (dissolved
ions) that maintain osmotic balance & buffer
blood (electrolyte balance maintained by
kidneys)
• contains plasma proteins –
– immunoglobulins – transport lipids through the blood
– fibrinogens – blood clotting
– serum – plasma – clotting factors
• transports nutrients, metabolic wastes, respiratory
gases, hormones
Cellular elements include:
1) Erythrocytes – RBC’s
2) Leukocytes -WBC’s
3) Platelets - thrombocytes
Erythrocytes – RBC’s
• biconcave discs that transport oxygen
• mm3 of human blood contains 5-6 million RBC’s
• in mammals, RBC’s lack nuclei & mitochondria;
they generate ATP exclusively by anaerobic
metabolism (Who knew?)
• contain hemoglobin, an iron containing protein
that irreversibly binds oxygen; about 250 million
molecules per erythrocyte
Leukocytes
• white blood cells function in defense
and immunity
• 5,000-10,000 per mm3 of blood
• 5 types of leukocytes:
– lymphocytes (specialized during infection
produce body’s immune response)
–
–
–
–
basophils
eosinophils
neutrophils
monocytes
SEM:
specialized
lymphocytes
attacking a
cancer cell
Platelets or thrombocytes:
•
•
•
•
fragments of cells 2-3 µm in diameter
originate in bone marrow
lack nuclei
function in blood clotting
Replacement of cellular elements:
• cells must be replaced as they wear out
•
average RBC lives 3-4 months before being
destroyed by phagocytic cells in the liver &
spleen
• components are usually recycled
• pluripotent stem cells give rise to all three
blood cells
• stem cells form early in the embryo & are
renewed by mitosis
• found in red bone marrow, especially ribs,
vertebrae, breastbone, pelvis
Blood clotting:
• a clot forms when platelets clump together
to form a temporary plug
• platelets release clotting factors that initiate
a cascade reaction which prothrombin is
converted to thrombin
•
thrombin converts inactive water -soluble
fibrinogen to active insoluble fibrin
•
anticlotting factors prevent spontaneous
clotting in healthy tissues
Circulatory Diseases:
• Hemophilia – an inherited defect in any
step involved in clot formation
• Thrombus – spontaneous clot form
• Cardiovascular disease – leading cause of
death in US (50% of all deaths)
• Heart attack – death of the cardiac muscle
• Embolus – moving clot
• Atherosclerosis ( Figure 42.16)
Circulatory Health:
1. Smoking
2. Lack of exercise
3. Diet high in animal fat
All lifestyle choices correlate directly
with an increased risk of cardiovascular
disease.
Lymphatic system:
1) returns fluid from interstitial
spaces to the circulatory
system
2) includes satellite organs
important to defense
3) filter lymph by removing and
phagocytosizing pathogens
Vocabulary:
• Lymph
– the fluid part
(similar in composition to the interstitial fluid)
• Lymph vessels
– transport lymph
– have valves to prevent backflow of fluid
– depend on movement of skeletal muscles to
squeeze lymph along
Vocabulary:
• Lymph nodes
– specialized lymphatic tissue
– filter the lymph & attack viruses
& bacteria
• Lymph capillaries
– penetrate the small intestine villi,
absorb fats, & transport from
digestive to circulatory system
The human lymphatic system:
An overview of the body’s defenses:
First line of defense:
• Skin
– Unbroken skin is a barrier against bacteria & viruses
– Secretions from sweat & sebaceous glands produce a
pH of 3 to 5
– Bacterial colonization inhibited by washing action
of sweat, tears,
saliva & mucous
– Secretions contain antimicrobial proteins: lysozyme
– an enzyme which digests bacterial cell walls
• Mucous membranes
First line of defense:
• Mucous membranes
– Secrete mucus – a viscous fluid which traps
microbes and others particles
– Line the digestive, respiratory, and
genitourinary tracts
First-line
respiratory
defenses:
ciliated
epithelial cells
and mucus
producing cells
of the
respiratory
system
Second line of defense:
• Phagocytosis -- the body’s internal
mechanism of nonspecific defense
– Neutrophils
– Constitute about 60-70% of all leukocytes
– Average life span only a few days
– Upon injury, chemicals released by the
invading microbes attract neutrophils to the
site. This is chemotaxis.
Phagocytic Neutrophil
Phagocytosis
by a
macrophage
Second line of defense:
• Monocytes - 5% of all leukocytes
– Migrate into tissues developing into macrophages
(“big eaters”)
– Extend long pseudopodia that can attach to
polysaccharides on the microbe’s surface, engulf
microbe, and lysosomes digest
– Some bacteria have capsules to which macrophages
can not attach
– Other are resistant to lysosomal destruction
Second line of defense:
• Figure 43.4 (p. 842)
• The Human Lymphatic System
• Returns fluids from the interstitial fluid to the
circulatory system
–
–
–
–
–
–
Adenoids
Tonsils
Lymph nodes
Thymus
Spleen
Appendix
- Right lymphatic duct
- Thoracic duct
- Peyer’s patches
The human lymphatic system:
Second Line of Defense:
• Eosinophils
• 1.5 % of all leukocytes
• Defense against larger parasitic invaders such as
blood flukes, Schistosoma mansoni
• These cells position themselves against the parasite
wall & discharge destructive enzymes
Natural Killer (NK) cells
• Nonspecific defense
• Do not attack the microorganism directly
but destroy virus-infected body cells &
abnormal cells that could form tumors
• Not phagocytic
• Attach the cell membrane causing lysis
The Inflammatory Response
• Figure 43.5
• Upon injury, blood flow to the injury
increases
• This is responsible for the characteristic
redness & heat of inflammation
• The filled capillaries leak fluid into
neighboring tissues causing edema
(swelling)
Inflammatory Response:
• Initiated by chemical signals
• Some arise from the invading
organism itself
• Others, such as histamine (produced
by basophils), are released by cells
of the body in response to tissue
injury
1) Release of histamine or prostaglandins
2) Increased permeability; leaking; attraction of
phagocytes and lymphocytes
3) Clot formation
4) Phagocytes consume pathogens & debris
Nonspecific Defense:
• Figure 43.1
• 1st line: skin, mucous membranes, & their
secretions
• 2nd line: phagocytic leukocytes,
antimicrobial proteins, &
inflammatory response
• These are nonspecific because they do not
distinguish among specific pathogens.
Antimicrobial Proteins:
• Lysozyme – enzyme in tears, saliva
• Complement system – a set of 20 serum
proteins which carry out a cascade of
steps leading to the lysis of microbes
• Interferon – secreted by virus infected
cells, spread to adjacent non-infected
cells and prevent their infection
How specific immunity arises:
• Lymphocytes
– Provide specificity
– Provide diversity
• Because lymphocytes recognize & respond to
specific microbes and foreign molecules, they
are said to display specificity.
• A foreign molecule that elicits a specific
response by a lymphocyte is an antigen.
How specific immunity arises
• Vertebrates have two cells
specialized in different types of
antigens and they carry out
different defensive actions.
• B lymphocytes (mature in bone
marrow)
• T lymphocytes (mature in thymus)
How specific immunity arises
• Antigens can elicit a response by activating
B lymphocytes to secrete proteins called
antibodies.
• Antigens have a quaternary structure for
which a specific complimentary antibody is
synthesized.
• Antigen is a contraction of antibodygenerator.
How specific immunity arises:
• B cells have specific antigen receptors on the plasma
membrane (membrane antibodies or
immunoglobulins). Antigens can be agglutinated
by the receptors on the surface or by free antibodies
that have synthesized & secreted by B cells.
• T cell receptors are just as specific but are never
secreted.
• A single B or T lymphocyte bears about 100,000
antigen receptors, all with exactly the same
specificity.
Specific receptors of lymphocytes
Antigens elicit 2 responses:
• Immune response
• Immunological memory
• Each antigen, by binding to specific
receptors, selectively activates a tiny
fraction of cells from the body’s diverse
pool of lymphocytes; this relatively small
number of selected cells gives rise to clones
of thousands of cells, all specific for and
dedicated to eliminating that antigen.
• This is clonal selection.
Primary Immune Response:
• proliferation and differentiation of
lymphocytes that occurs the first time the
body is exposed to an antigen
• requires 10 – 17 days from initial exposure
to antigen for lymphocytes to response
with maximum force
• During this period, plasma cells are cloned
which produce antibodies against the
invading antigens.
Clonal Selection : Figure 43.6
Antigens
Cell proliferation
clone of plasma cells
Clone of memory cells
Clonal
Selection
Secondary Immune Response:
• occurs if and when an individual is
exposed a second time to the same
antigen
• the response is faster (only 2 – 7 days),
stronger, & prolonged.
• Figure 43.7
• Memory cells are poised to proliferate &
differentiate rapidly.
Immunological Memory
Immune Response:
• Humoral Immunity
• Involves B cell activation and results from
the production of antibodies that circulate
in the blood plasma & lymph. (Fluids were
long ago called “humors.”)
• Defend against free bacteria, toxins, and
viruses in body fluid.
• DEFEND AGAINST EXTRACELLULAR
PATHOGENS
B Lymphocyte
Humoral Immunity
Immune Response:
• Cell-mediated immunity
• Active against bacteria & viruses within
infected body cells and against fungi,
protozoa, & parasitic worms
• Crucial in transplanted tissue & cancer cells –
both of which are identified as “nonself.”
• DEFEND AGAINST INTRACELLULAR
PATHOGENS
Overview of Immune Responses
• Figure 43.10
• Figure 43.16
Immunity:
• Can be achieved either naturally or artificially
• Active immunity –occurs when the immune system
responds to a foreign antigen acquired either by
natural infection or artificially by immunization.
• Passive immunity occurs when antibodies are
transferred from one individual to another (mother
to fetus; mother to breastfeeding child; artificially
when antibodies produced by one organism
transferred to another organism
• Immune system’s capacity to distinguish
self from nonself limits blood transfusion
and tissue transplant
• Abnormal immune function can lead to
disease (allergy, rheumatoid arthritis,
insulin-dependent diabetes)
• AIDS – immunodeficiency disease caused
by a virus. Figure 43.19
Budding HIV
HIV on
Lymphocyte
HIV Infections Stages
Cytotaxic Cell
Cytotaxic Cell