Chapter 22: The Lymphatic System and Immunity … · Copyright 2009, John Wiley & Sons, Inc. Antibody actions Neutralizing antigen Immobilizing bacteria Agglutinating and precipitating

Copyright 2009, John Wiley & Sons, Inc.

Chapter 22: The Lymphatic

System and Immunity


Immunity or Resistance

Ability to ward off damage or disease through our

defenses

2 types of immunity

Innate or nonspecific immunity – present at birth

No specific recognition of invaders, no memory

component

1st and 2nd line of defenses

Adaptive or specific immunity

Specific recognition of invaders with a memory

component


Lymphatic system structure and function

Consists of lymph, lymphatic vessels,

structures and organs containing lymphatic

tissue, red bone marrow

Functions of the lymphatic system

1. Drain excess interstitial fluid

2. Transport dietary lipid

3. Carry our immune responses


Components of the Lymphatic System


Lymphatic vessels and lymph circulation

Vessels begin as lymphatic capillaries

Closed at one end

Unite to form large lymphatic vessels

Resemble veins in structure but thinner

walls and more valves

Passes through lymph nodes

Encapsulated organs with masses and B

and T cells


Lymphatic capillaries

Slightly large diameter that blood capillaries

Unique one-way structure

Permits interstitial fluid to flow in but not out

Anchoring filaments pull openings wider when

interstitial fluid accumulates

Small intestine has lacteal for dietary lipid

uptake

Chyle is lymph with lipids


Lymphatic Capillaries


Lymph trunks and ducts

Vessels unite to form lymph trunks

Principal trunks are the lumbar, intestinal,

bronchomediastinal, subclavian and jugular

Passes from lymph trunks into 2 main

channels (thoracic and right lymphatic ducts)

before draining into venous blood


Routes for drainage of lymph


Formation and flow of lymph

More fluid filters out of blood capillaries than

returns to them by reabsorption

Excess filtered fluid – about 3L/day – drains into

lymphatic vessels and become lymph

Important function of lymphatic vessels to return

lost plasma proteins to blood stream

Contain valves

Same 2 “pumps” aiding venous return also used

Skeletal muscle pump – milking action

Respiratory pump – pressure changes during breathing


Relationship of the Lymphatic System to

the Cardiovascular System


Lymphatic tissues and organs

2 groups based on function

1. Primary lymphatic organs

Sites where stem cells divide and become

immunocompetent

Red bone marrow and thymus

2. Secondary lymphatic organs

Sites where most immune response occurs

Lymph nodes, spleen, lymphatic nodules


Thymus and Medulla

Thymus Outer cortex composed of large number of T cells

Immature T cells migrate here from red bone marrow where they proliferate and begin to mature

Dendritic cells derived from monocytes assist in T cell maturation

Specialized epithelial cells help educate T cells through positive selection – only about 25% survive

Macrophages clear out dead and dying cells

Medulla

More mature T cells migrate here from cortex

More epithelial cells, dendritic cells and macrophages

Thymus shrinks with age from 70g in infants to 3g in old age


Thymus


Lymph nodes

Located along lymphatic vessels

Scattered throughout body

Stroma – supporting connective tissue

Capsule, trabeculae, reticular fibers and fibroblasts

Parenchyma – functional part

Outer cortex – aggregates of B cells called lymphatic nodules (follicles) – site of plasma cell and memory B cell formation

Inner cortex – mainly T cells and dendritic cells

Medulla – B cells, antibody producing plasma cells from cortex, and macrophages


Structure of a Lymph Node


Lymph

Lymph flows through a node in 1 direction only Enters through afferent lymphatic vessels

Directs lymph inward

Lymph enters sinuses (irregular channels)

Into medulla

Medullary sinuses drain into efferent lymphatic vessels

Conveys lymph, antibodies and activated T cells out of the node

Lymph nodes function as a filter Foreign substances trapped

Destroyed by macrophages or immune response of lymphocytes


Spleen

Largest single mass of lymphatic tissue in the body

Stroma – capsule, trabeculae, reticular fibers, and fibroblasts

Parenchyma

White pulp – lymphatic tissue (lymphocytes and macrophages)

B cells and T cells carry out immune function

Red pulp


Red Pulp

Red pulp – blood-filled venous sinuses and

splenic (Bilroth’s) cords – red blood cells,

macrophages, lymphocytes, plasma cells, and

granulocytes

Macrophages remove ruptured, worn out or

defective blood cells

Storage of up to 1/3 of body’s platelet supply

Production of blood cells during fetal life


Structure of the Spleen


Lymphatic nodules

Not surrounded by a capsule

Scattered throughout lamina propria of

mucous membranes lining GI, urinary,

reproductive tract

Mucosa-associated lymphatic tissue (MALT)

of respiratory tract

Most small and solitary

Some larger – tonsils, Peyer’s patches,

appendix


Innate immunity

First line of defenses: Skin and mucous membranes

Provide both physical and chemical barriers

Physical barriers Epidermis – closely packed, keratinized cells

Periodic shedding

Mucous membranes

Mucus traps microbes and foreign substances

Nose hairs trap and filter

Cilia of upper respiratory tract propel trapped particles up and out


Innate Immunity

Fluids Lacrimal apparatus of eye

Washing action of tears

Lysozyme breaks down bacterial cell walls – also present in saliva, perspiration, nasal secretions, and tissue fluids

Saliva washes mouth

Urine cleanses urinary system

Vaginal secretions, defecation and vomiting

Chemicals Sebaceous (oil) glands secrete sebum – protective film,

acid

Perspiration, gastric juice, vaginal secretions – all acidic


Internal Defenses

Natural Killer (NK) cells Lymphocyte but not a B or T cell

Ability to kill wide variety of infected body cells and certain tumor cells

Attack any body cell displaying abnormal or unusual plasma membrane proteins

Can release perforin (makes perforations) or granzymes (induce apoptosis)

Phagocytes Neutrophils and macrophages (from monocytes)

Migrate to infected area

5 steps in phagocytosis


Inflammation

Nonspecific, defensive response of body to tissue

damage

4 signs and symptoms – redness, pain, heat and

swelling

Attempt to dispose of microbes, prevent spread,

and prepare site for tissue repair

3 basic stages

Vasodilation and increased blood vessel permeability

Emigration

Tissue repair


Vasodilation and increased permeability of

blood vessels

Increased diameter of arterioles allows more blood flow through area bringing supplies and

removing debris

Increased permeability means substances

normally retained in the blood are permitted to

pass out – antibodies and clotting factors

Histamine, kinins, prostaglandins (PGs),

leukotrienes (LTs), complement


Inflammation


Emigration of phagocytes

Depends on chemotaxis

Neutrophils predominate in early stages but

die off quickly

Monocytes transform into macrophages

More potent than neutrophils

Pus – pocket of dead phagocytes and

damaged tissue


Adaptive immunity

Ability of the body to defend itself against

specific invading agents

Antigens (Ags) – substances recognized as

foreign and provoking an immune response

Distinguished from innate immunity by

Specificity

Memory


Maturation of T cells and B cells

Both develop from pluripotent stem cells

originating in red bone marrow

B cells complete their development in red bone marrow

T cells develop from pre-T cells that migrate from red

bone marrow to the thymus

Helper T cells (CD4 T cells) and cytotoxic T cells (CD8 T

cells)

Immunocompetence – ability to carry out adaptive

immune response

Have antigen receptors to identify specific antigen


2 types of adaptive immunity

Cell-mediated

Cytotoxic T cells directly attack invading antigens

Particularly effective against intracellular pathogens, some

cancer cells and foreign tissue transplants

Antibody-mediated

B cells transform into plasma cells making antibodies (Abs) or

immunoglobulins

Works against extracellular pathogens in fluids outside cells

Helper T cells aid in both types

2 types of immunity work together


Antigens

Antigens have 2 characteristics

Immunogenicity – ability to provoke immune response

Reactivity – ability of antigen to react specifically with antibodies it provoked

Entire microbes may act as antigen

Typically, just certain small parts of large antigen molecule triggers response (epitope or antigenic determinant)


Pathways of antigen processing

B cells can recognize and bind to antigens

T cells must be presented with processed

antigens

Antigenic proteins are broken down into peptide

fragments and associated with MHC molecules

Antigen presentation – antigen-MHC complex

inserted into plasma membrane

Pathway depends on whether antigen is outside or

inside body cells


Antibodies (Ab)

Can combine specifically with epitope of the antigen that

triggered its production

Belong to group of glycoproteins called globulins

Ab are immunoglobulins (Igs)

4 polypeptide chains – 2 heavy (H) chains, 2 light (L)

chains

Hinge region – antibody can be T shape or Y shape

Variable (V) region at tips of each H and L chain

2 antigen-binding sites - bivalent

Constant (C) region – remainder of H and L chain

Same in each 5 classes – determines type of reaction


Antibody actions

Neutralizing antigen

Immobilizing bacteria

Agglutinating and precipitating antigen

Enhancing phagocytosis

Activating complement

Defensive system of over 30 proteins

Destroy microbes by causing phagocytosis, cytolysis, and

inflammation

Acts in a cascade – one reaction triggers another

3 different pathways ass activate C3

C3 then begins cascade that brings about phagocytosis,

cytolysis, and inflammation

Documents

Chapter 22: The Lymphatic System and Immunity … · Copyright 2009, John Wiley & Sons, Inc. Antibody actions Neutralizing antigen Immobilizing bacteria Agglutinating and precipitating