Lymphatic and Immune System

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Lymphatic Vessels

• The lymphatic vessels are similar in structure and function to veins; movement of lymph is dependent upon skeletal muscle contraction, and internal valves prevent backflow.

• Lacteals collect fat molecules at intestinal villi and lymphatic capillaries collect excess tissue fluid at blood capillaries.

• Tissue fluid becomes lymph once it enters the lymphatic capillaries.

• Lymphatic capillaries merge to form larger lymphatic vessels that carry lymph to the subclavian veins.

• Edema is retention of fluids in the tissues due to a blockage of the flow of lymph.

Lymphatic system

Lymphoid Organs

• Lymphoid organs include the lymph nodes, tonsils, spleen, thymus gland, and the red bone marrow.

• Lymph nodes are located at certain points along lymphatic vessels and contain a cortex and a medulla.

• The cortex contains nodules where lymphocytes congregate when fighting off a pathogen.

• Macrophages are concentrated in the medulla where they work to cleanse the lymph.

• Tonsils are patches of lymphatic tissue in the pharynx; they are the first to encounter pathogens in the nose and mouth.

• Tonsils perform functions similar to those of the lymph nodes.

• The spleen cleanses blood of pathogens and their toxins.

• The thymus is located behind the sternum and is the site in which T lymphocytes mature.

• The thymus produces the hormone thymosin that appears to cause T lymphocytes to mature; thymosin may play other roles in immunity.

• The red bone marrow is the site where all types of blood cells are produced by stem cells.

• B lymphocytes mature in the red bone marrow.

The lymphoid organs

Barriers to Entry• Skin and mucous membranes lining the

respiratory, digestive and urinary tracts, oil glands in the skin, ciliated cells that sweep particles in mucus, and an acidic stomach all contribute to keeping pathogens from entering the body.

• Beneficial bacteria in the intestines and vagina also prevent pathogens from taking up residence.

Inflammatory Reaction

• The inflammatory reaction involves redness, heat, swelling, and pain.

• The release of histamine and kinins from damaged tissue cells and from mast cells causes redness and swelling.

• The swollen area and kinins stimulate free nerve endings, causing the sensation of pain.

• Macrophages migrate to the site of injury and can engulf pathogens and also release colony-stimulating factors that cause the bone marrow to release more white blood cells.

• Anti-inflammatory drugs combat chronic inflammation by acting against chemical mediators released by white blood cells.

• The presence of pus indicates the body is trying to overcome the infection.

Inflammatory reaction

Natural Killer Cells

• Natural killer cells kill virus-infected cells and tumor cells by cell-to-cell contact.

• They are large, granular lymphocytes with no specificity and no memory.

• Their number is not increased by prior exposure to that kind of cell.

Protective Proteins

• The complement system, or complement, refers to a number of plasma proteins that assist nonspecific immunity.

• A small amount of activated complement protein is needed to activate a cascade of other proteins.

• Complement is activated when pathogens enter the body.

• Complement amplifies the inflammatory reaction by attracting phagocytes and promoting phagocytosis.

• Some complement proteins join to form pores in the surface of bacteria and cause them to burst.

• Interferon is a protein produced by virus-infected cells that prepares non-infected cells for attack and interferes with viral replication; it is specific to species.

Action of the complement system against a bacterium

• Specific defenses require B lymphocytes (B cells) and T lymphocytes (T cells), which are both produced in the bone marrow; however, T cells mature in the thymus, while B cells mature in bone marrow.

• B cells give rise to antibodies that are shaped like antigen receptors and are capable of combining with and neutralizing antigens.

• T cells do not produce antibodies but instead attack foreign antigens directly.

B Cells and Antibody-Mediated Immunity

• A toxin is a chemical produced by certain bacteria that is poisonous.

• As a B cell encounters a bacterial cell or a toxin with a specific antigen in a lymph node or spleen, it is activated to divide.

• The resulting cells are plasma cells, mature B cells that mass-produce antibodies.

• Defense by B cells is thus called antibody-mediated immunity.

• According to the clonal selection theory, it is the antigen that selects which lymphocyte will undergo clonal expansion, mass producing lymphocytes bearing matching antigen receptors.

• Some members of the clone become memory B cells that remain in the body to divide and produce more lymphocytes able to secrete antibodies if the same antigen is encountered at a later date.

• When infection passes, plasma cells undergo apoptosis.

Clonal selection theory and B cells

Structure of IgG

• The most common type of antibody, the IgG antibody, is a Y-shaped molecule that has two binding sites for a specific antigen.

• Antigen-antibody complexes often mark the antigen for destruction by neutrophils or macrophages, or they may activate complement.

Structure of IgG

Other Types of Antibodies

• There are five types of antibodies:• IgG – the main type in circulation, binds to

pathogens, activates complement, and enhances phagocytosis

• IgM – the largest type in circulation, activates complement and clumps cells

• IgA – found in saliva and milk, prevents pathogens from attaching to epithelial cells in digestive and respiratory tracts

• IgD – on surface of immature B cells, its presence signifies the readiness of a B cell

• IgE – found as antigen receptor on basophils in blood and on mast cells in tissues, responsible for immediate allergic response and protection against certain parasitic worms.

• The different classes of antibodies vary in structure.

T Cells and Cell-Mediated Immunity

• T cells mature in the thymus. • Like B cells, each T cell bears a specific

receptor, however, for a T cell to recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC).

• When a viral or cancer cell antigen is presented, the antigen is first linked to a major histocompatibility complex (MHC) protein.

• Human MHC proteins are called HLA (human lymphocyte-associated) antigens; HLA antigens are self proteins that identify tissues as belonging to the body (the basis of tissue transplant rejection).

• Once a T cell’s antigen receptor matches up to its specific antigen presented to it by a macrophage (the APC), the T cell becomes activated and secretes cytokines and undergoes clonal expansion.

Clonal selection theory and T cells

Types of T Cells• Cytotoxic T cells kill infected cells that bear

a foreign antigen on contact using perforin molecules; cytotoxic T cells provide cell-mediated immunity.

• Helper T cells stimulate other immune cells and produce cytokines.

• Some T cells are memory T cells that will jump-start an immune reaction upon re-infection.

Cell-mediated immunity

Active Immunity• A person naturally develops active

immunity after infection.

• Immunization involves the use of vaccines, substances that contain an antigen to which the immune system responds.

• Vaccines are available to induce long-lived active immunity in a well person.

• After exposure to a vaccine, which is a non-virulent disease agent, antibodies are produced.

• With a booster shot or second exposure, the antibody titer rises to a much higher level.

• Active immunity is long-lived because there are memory B cells and memory T cells that will respond to lower doses of antigen in the body.

Active immunity due to immunizations

Passive Immunity• Passive immunity occurs when an

individual is given prepared antibodies. • For example, a newborn has antibodies

that passed from its mother through the placenta.

• Breast-feeding passes antibodies from mother to child.

• However, passive immunity is short-lived since the antibodies were not produced by the person’s own B cells.

Passive immunity

Cytokines and Immunity

• Cytokines are signaling molecules produced by T lymphocytes, monocytes, and other cells.

• Both interferon and interleukins are cytokines used to improve a person’s own T cell performance in fighting cancer.

• Interleukins show promise in the treatment of chronic infectious diseases.

Monoclonal Antibodies

• All plasma cells derived from the same B cell secrete an identical antibody.

• B lymphocytes can therefore be exposed to a particular antigen and will produce monoclonal antibodies to the specific antigen.

• Activated B lymphocytes are fused with myeloma cells and these hybridomas produce only one type of antibody.

Production of monoclonal antibodies

Allergies

• Allergies are hypersensitivities to substances such as pollen or animal dander that are normally not harmful.

• Weak antigens such as these are called allergens.

• The response itself can cause some degree of tissue damage.

Immediate Allergic Response• An immediate allergic response can occur

within seconds after contacting an antigen.• Anaphylactic shock is a severe reaction

characterized by a sudden life-threatening drop in blood pressure.

• Immediate allergic responses are caused by IgE antibodies attaching to mast cells and basophils; these cells then release histamine which causes the symptoms of allergies, some of which are severe.

Delayed Allergic Response

• Delayed allergic responses are started by memory T cells at the site of the allergen.

• The response is regulated by cytokines secreted by T cells and macrophages.

• Examples of delayed allergic responses include the skin test for tuberculosis and contact dermatitis from poison ivy, jewelry, and other possible irritants.

Blood-Type Reactions• Illness and death sometimes resulted from

the first attempts at blood transfusions.• It was later discovered that only certain

types of blood are compatible because red blood cell membranes carry proteins or sugar residues that are antigenic to recipients.

• The ABO blood system represents a series of antigens on red blood cells that denote blood type.

ABO System• The ABO blood typing system is based on

the presence of two antigens on the surface of red blood cells; antigen A and antigen B.

• Blood types include A, B, or AB, or type O, which has no antigens.

• In the plasma there are two possible naturally-occurring antibodies: anti-A and anti-B.

• If the corresponding antigen and antibody are put together, clumping, or agglutination, occurs; in this way the blood type of the individual may be determined.

Blood typing

Rh System• The Rh factor is also a blood type; a

person with this antigen on their red blood cells is Rh positive (Rh+); those without it are Rh negative (Rh-).

• Rh factor is important during pregnancy because an Rh- mother may form antibodies to the Rh antigen during the pregnancy or at the birth of a child who is Rh+.

• These antibodies can cross the placenta to destroy the red blood cells of any subsequent Rh+ child, causing hemolytic disease of the newborn.

• A Rho-Gam injection uses anti-Rh antibodies to attack Rh+ cells before they can stimulate the mother to produce her own antibodies.

Hemolytic disease of the newborn

Tissue Rejection

• Tissue rejection occurs when cytotoxic T cells bring about the destruction of foreign tissue in the body.

• A close match between donor and recipient can reduce rejection.

• Immunosuppressive drugs act by inhibiting the response of T cells to cytokines, but can result in kidney damage.

Autoimmune Diseases• Autoimmune disease occurs when

cytotoxic T cells or antibodies mistakenly attack the body’s own cells as if they bear foreign antigens.

• Autoimmune diseases include: myasthenia gravis, multiple sclerosis, systemic lupus erythematosus, and rheumatoid arthritis.

• It has been suggested that type I diabetes and heart damage after rheumatic fever are autoimmune diseases.

• Immunity consists of nonspecific and specific defenses to protect against disease.

• Nonspecific defenses consist of barriers to entry, the inflammatory reaction, natural killer cells, and protective proteins.

• Specific defenses involve two types of lymphocytes: B lymphocytes and T lymphocytes.

• Medically induced immunity involves use of vaccines to achieve long-lasting immunity and use of antibodies to provide temporary immunity.

• While immunity protects us, it is also responsible for undesirable effects, such as allergies, autoimmune diseases, and tissue rejection.

Ex 23: Arthropods!

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Evolutionary tree

Arthropods• Arthropods are the most varied and

numerous of animals.

• The success of arthropods is largely attributable to a flexible exoskeleton, jointed appendages, and specialization of body regions.

• Three body regions – head, thorax, and abdomen – with specialized appendages in each region, and a well-developed nervous system characterize this group.

Arthropod diversity

Crustaceans• Crustaceans are largely marine and have

a head that bears compound eyes, two pair of antennae, and specialized mouth parts.

• Five pairs of walking legs include a first pair of pinching claws.

• In the crayfish, head and thorax are fused into a cephalothorax which is covered on the top and sides by carapace.

• The abdominal segments have swimmerets.

• The crayfish has an open circulatory system in which the heart pumps blood into a hemocoel consisting of sinuses where the hemolymph flows about the organs.

• Respiration takes place by gills under the hard carapace, and there is a ventral solid nerve cord.

• Sexes are separate in the crayfish.

Male crayfish, Cambarus

Insects• The head of an insect usually bears a pair

of antennae, compound eyes, and simple eyes.

• The thorax bears three pairs of legs and up to two pairs of wings, and the abdomen contains most of the internal organs.

• The insect exoskeleton is lighter and contains less chitin than that of many other arthropods.

Insect diversity

• Grasshoppers are examples of insects adapted to a terrestrial life; they respire by tracheae and have wings that allow them to evade enemies; the third pair of legs is suitable for jumping.

• There is a tympanum for the reception of sound waves and a male penis for passing sperm to the female without desiccation.

• Malpighian tubules function in excretion in grasshopper.

• Grasshoppers undergo gradual metamorphosis from nymph to adult.

• Butterflies undergo complete metamorphosis, changing from larva to pupa to adult.

Female grasshopper

Arachnids

• The arachnids include terrestrial spiders, scorpions, ticks, and mites.

• The cephalothorax bears six pairs of appendages: the chelicerae and the pedipalps, and four pairs of walking legs.

• Scorpions are the oldest terrestrial arthropods.

• Ticks and mites are parasitic.

• Spiders are well-adapted to life on land and have Malphigian tubules – they secrete uric acid, helping to conserve water.

• Spiders spin silk used in various ways. • Where spiders spin webs, the type of web

is a feature that demonstrates the evolutionary relationship among spiders.

Arachnid diversity

Lab Ex 24: Echinodermata

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Evolutionary tree

Echinoderms

• Echinoderms and chordates are deuterostomes.

• In deuterostomes, the second embryonic opening becomes the mouth and a coelom forms by outpocketing of the primitive gut making these animals enterocoelomates.

• A dipleurula larva is found among some.

Characteristics of Echinoderms

• Echinoderms are a diverse group of marine animals; there are no terrestrial echinoderms.

• They have an endoskeleton consisting of spine-bearing, calcium-rich plates.

• Echinoderms are often radially symmetrical, although the larva is a free-swimming filter feeder with bilateral symmetry.

• Echinoderm Diversity• Echinoderms include:

• Sea lilies (class Crinoidea)

• Sea cucumbers (class Holothuroidea)

• Brittle stars (class Ophiuroidea)

• Sea urchins and sand dollars (class Echinoidea)

• Sea stars (class Asteroidea)

Echinoderm diversity

• Sea Stars• Sea stars are an example of echinoderms

and possess tiny skin gills, a central nerve ring with branches, and a water vascular system for locomotion.

• Water enters this system through the sieve plate, passes into a ring canal, then into ampullae, and into tube feet; expansion and contraction of tube feet move the sea star along.

• Each of the five arms contains branches from the nervous, digestive, and reproductive systems.

• When a sea star eats a bivalve, it everts its cardiac stomach into the bivalve and secretes enzymes; partially digested food is taken into the sea star.

• Echinoderms do not have a respiratory, circulatory, or excretory system.

• The water vascular system carries out these functions.

• Sea stars reproduce both sexually, and asexually by fragmentation.

Sea star anatomy and behavior