Chapter 21: Lymphatic and Immune Systems

Lymphatic system?

Vessels that go through body tissues and organs that produce immune cells

Lymphatic system has three major functions?

Fluid recovery

Immunity

Lipid absorption

Fluid recovery?

Fluid is continually filtered out and reabsorb by the capillaries

The remaining water, and about half of plasma proteins, will enter the lymphatic system and will be returned to the → bloodstream

Immunity?

Excess filtered fluid contains foreign cells and chemicals from the tissues

Passes through lymph nodes where immune cells look for foreign matter (microbes or cancer)

Activates an immune response when foreign material is detected

Lipid absorption?

Lacteals in small intestine absorb dietary lipids that cannot be absorbed by the blood capillaries

Lymph?

The excess fluid removed from between tissue cells

Lymphatic vessels?

Transport the lymph

Lymphatic tissues?

Are made up of clusters of lymphocytes and macrophages (both immune cells) that populate many organs

Lymphatic organs?

Defense (immune) cells are concentrated in these organs

Separated from surrounding organs by connective tissue capsules

Lymph is a what?

Is a clear, colorless fluid, like plasma, but with less protein

Originates as extracellular fluid drawn into lymphatic capillaries

Chemical composition varies in different places (in intestines, after lymph nodes)

Lymphatic flow begins with?

Lymphatic capillaries (terminal lymphatics)

Go through nearly every tissue of the body

Absent from cartilage, cornea, bone, and bone marrow

Capillary wall consists of endothelial cells that overlapping each other

Closed at one end (blind-ended)

Cells are attached to surrounding tissue by protein → filaments

Gaps between cells are large enough to allow bacteria and cells to enter a lymphatic capillary

Endothelium creates valve-like flaps open when interstitial fluid pressure is high, and close when it is low

Collecting vessels?

Are formed by the merging of lymphatic → capillaries

Travel along arteries and veins

Contain valves to prevent the backward flow of lymph

Empty into lymph nodes in certain parts of the body

Foreign material (antigens) are removed from lymph in lymph nodes

Another collecting vessel comes off of a lymph node

Lymphatic trunks?

Are formed by the merging of collecting vessels

There are six trunks that are named based on the major regions that they empty

Collecting ducts?

Are formed by the merging of lymphatic → trunks

Right lymphatic duct

Thoracic duct

Right lymphatic duct?

Receives lymph from right arm, right side of head and thorax; empties into right subclavian vein

Thoracic duct?

Larger and longer

Begins as a prominent sac in abdomen called the cisterna chyli

Receives lymph from below diaphragm, left arm, left side of head, neck, thorax, and the remaining body structures empties into left subclavian vein

Diffuse lymphatic tissue?

Simplest form

Lymphocytes are scattered

Widespread in the body passages open to the exterior

Respiratory, digestive, urinary, and reproductive tracts

Mucosa-associated lymphatic tissue (MALT)

Lymphatic nodules (follicles)?

Dense masses of lymphocytes and macrophages that congregate in response to pathogens

Feature of lymph nodes, tonsils, and appendix

Aggregated lymphoid nodules: dense clusters in the ileum, the distal portion of the small intestine

They form clusters called Peyer patches or aggregate lymphoid nodules

Lymphatic (lymphoid) organs?

Have connective tissue capsule that separates lymphatic tissue from neighboring tissues

Red bone marrow and thymus?

Sites where T and B cells become immunocompetent (mature): able to recognize and respond to antigens

Red bone marrow?

Is involved in hemopoiesis (blood formation) and → immunity

B and T lymphocytes are both produced in the red bone marrow, but only B cells stay and mature in red bone marrow

Thymus?

Member of the endocrine, lymphatic, and immune systems

Houses developing T lymphocytes (except B cells)

Secretes hormones regulating their → activity

Degenerates with age

Lymph nodes?

Most numerous lymphatic organs

Serve two functions

Cleanse the lymph

Act as a site of T and B cell → activation

Several afferent lymphatic vessels lead into the node along its convex surface

Lymph leaves the node through one to three efferent lymphatic vessels that leave the hilum

Tonsils?

Patches of lymphatic tissue located at the entrance to the pharynx (throat)

Guard against ingested or inhaled pathogens

Have deep pits: tonsillar crypts lined with lymphatic nodules

Palatine tonsils?

Pair at posterior part of the oral cavity

Most often infected (tonsillitis)

Lingual tonsils?

Pair at the root of tongue

Pharyngeal tonsil (adenoids)?

Single tonsil on wall of the → nasopharynx

Spleen?

The body’s largest lymphatic organ

Red pulp?

Sinuses filled with → erythrocytes

White pulp?

Contains lymphocytes and macrophages surrounding small branches of splenic artery

Spleen functions?

Healthy red blood cells (RBCs) come and go, the spleen can hold about a cup of blood

For old, fragile RBCs are removed in the spleen by macrophages

The spleen is the site of blood cell production in a fetus (and very anemic adults)

White pulp monitors blood for foreign antigens and keeps an army of monocytes for release when needed

Stabilizes blood volume through plasma transfers to lymphatic system

Innate defenses?

Guard equally against a broad range of pathogens

They lack capacity to remember pathogens

Three kinds of innate defenses:

• Protective proteins

• Protective cells

• Protective processes

Local, nonspecific, lacks memory

First line of defense?

Skin and mucous membranes

Skin?

Makes it mechanically difficult for microorganisms to enter the body

Toughness comes from the protein → keratin

Too dry and nutrient-poor for microbial growth

Mucous membranes?

Digestive, respiratory, urinary, and reproductive tracts are open to the exterior and protected by mucous membranes

Mucus physically traps microbes

Second line of defense?

Several innate defense mechanisms

Come into play when the first line of defense fails and pathogens get in

Leukocytes and macrophages, antimicrobial proteins, natural killer cells, inflammation, and fever

Act as a sensory (warning) system to infections

Proteins that ____ microbial reproduction and provide short-term, innate immunity to pathogenic bacteria and viruses

Inhibit

Two families of antimicrobial proteins?

Interferons

Complement system

Interferons?

Secreted by cells infected by → viruses

No benefit to the cell that secretes them

Alert neighboring cells and protects/prevents them from becoming infected

Complement system?

A group of 30 or more proteins

Circulate in the blood in an inactive form

Activated by the presence of a pathogen

Activated complement brings about four methods of pathogen destruction?

Inflammation

Immune clearance

Phagocytosis

Cytolysis

Natural killer (NK) cells?

Continually patrol body looking for pathogens and diseased host cells

NK cells attack and destroy bacteria, transplanted cells, cells infected with viruses, and cancer cells

Recognize enemy cell, bind to it, and destroy it

Macrophages?

Large, phagocytic cells of connective tissue • Develop from → monocytes

Phagocytize tissue debris, dead neutrophils, bacteria, and other foreign matter

Lymphatic cells process what?

Process foreign matter and display antigenic fragments to certain T cells alerting immune system to the presence of the → "enemy"

Antigen-presenting cells (APCs)

B-cells, macrophages, and Dendritic cells

Dendritic cells?

Branched, mobile APCs found in epidermis, mucous membranes, and lymphatic organs

Alert the immune system to pathogens that have breached the body surface

Fever?

An abnormal elevation of body temperature

Results from trauma, infections, drug reactions, brain tumors, and other causes

Fever in moderation, does more good than harm?

Promotes interferon activity

Elevates metabolic rate and accelerates tissue repair

Inhibits reproduction of bacteria and viruses

Inflammation?

Local defensive response to tissue injury, including trauma and infection

What are the purposes of inflammation?

Limits spread of pathogens, then destroys them

Removes debris from damaged tissue

Initiates tissue → repair

What are the four cardinal signs of inflammation?

Redness, swelling, heat, and pain

Adaptive immunity?

Body must develop separate immunity to each pathogen

Body adapts to a pathogen and fights it off more easily upon future exposure (memory)

Systemic effect?

Throughout the body

Distinguish immunity from innate immunity

Specificity?

Immunity directed against a particular pathogen

Distinguish immunity from innate immunity

Memory?

When re-exposed to the same pathogen, the body reacts so quickly that there is no noticeable illness

Distinguish immunity from innate immunity

Third line of defense?

Is adaptive immunity

Defeats a pathogen, and leaves the body with a “memory” of it so it can defeat it faster in the future

Antigen?

Any molecule that triggers an immune response

Complex molecules with structures unique to the individual

Can be proteins, polysaccharides, glycoproteins, or glycolipids

Characteristics enable body to distinguish “self” molecules from foreign ones

T lymphocytes (T cells)?

Mature in thymus, perform cell mediated immunity

B lymphocytes (B cells)?

Mature in the bone marrow, active into plasma cells that produce → antibodies

Cellular (cell-mediated) immunity?

T lymphocytes directly attack and destroy foreign cells or diseased host cells

Rids the body of pathogens that are inside human cells, where they are inaccessible to antibodies

Kills cells that harbor them

Cytotoxic T (TC) cells?

Killer T cells

“Effectors” of cellular immunity; carry out attack on enemy cells

Helper T (TH) cells?

Help promote TC cell and B cell action and innate immunity

Regulatory T (TR) cells?

T-regs

Inhibit multiplication and cytokine secretion by other T cells, limit the immune response

Memory T (TM) cells?

Descend from T cells

Responsible for memory in cellular immunity

Humoral (antibody-mediated) immunity?

Mediated by antibodies (produced by B lymphocytes) that do not directly destroy a pathogen but tag it for destruction

Many antibodies are dissolved in body fluids (“humors”)

Can only work against the extracellular stages of infections by microorganisms

Immunoglobulin (Ig) - antibody?

A defensive gamma globulin found in blood plasma, tissue fluids, body secretions, and some leukocyte membranes