The Lymphatic SystemThe Lymphatic System

Chapter 43, Campbell, 6Chapter 43, Campbell, 6thth edition edition Nancy G. Morris Nancy G. Morris

Volunteer State Community CollegeVolunteer 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)1) ErythrocytesErythrocytes – RBC’s

2)2) LeukocytesLeukocytes -WBC’s

3)3) PlateletsPlatelets - 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 cellsstem cells give rise to all three blood cells

• stem cells form early in the embryo & are renewed by mitosis

• found in red bone marrowred 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. Smoking2. Lack of exercise3. Diet high in animal fat

All lifestyle choices correlate directly

with an increased risk of cardiovascular

disease.

Lymphatic system:

1)1) returns fluid from returns fluid from interstitial spaces to the interstitial spaces to the circulatory system circulatory system

2) includes satellite organs important to defense

3) filter lymph by removing and phagocytosizing pathogens

Vocabulary:

• LymphLymph – the fluid part (similar in composition to the

interstitial fluid)

• Lymph vesselsLymph vessels – transport lymph– have valves to prevent backflow

of fluid– depend on movement of skeletal

muscles to squeeze lymph along

Vocabulary:Vocabulary:

• Lymph nodesLymph nodes– specialized lymphatic tissue – filter the lymph & attack

viruses & bacteria• Lymph capillariesLymph 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 NeutrophilPhagocytic Neutrophil

PhagocytPhagocytosis by a osis by a macrophamacrophagege

Second line of defense: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:Second line of defense:• Figure 43.4 (p. 842)

• The Human Lymphatic System

• Returns fluids from the interstitial fluid to the circulatory system– Adenoids - Right lymphatic duct– Tonsils - Thoracic duct– Lymph nodes - Peyer’s patches– Thymus– Spleen– Appendix

The human lymphatic system:

Second Line of Defense: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: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: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 How specific immunity arises: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 How specific immunity arisesarises

• 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 antibody-generator.

How specific immunity How specific immunity arises: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 Antigens elicit 2 responses: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 43.6Clonal Selection : Figure 43.6

Cell proliferation

clone of plasma cells

Clone of memory cells

Antigens

Clonal Clonal SelectioSelectionn

Secondary Immune Secondary Immune Response: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.

IImmunological mmunological MMemoryemory

Immune Response: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 ImmunityHumoral Immunity

Immune Response: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: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 AIDS – immunodeficiency disease caused by a virus. Figure 43.19

Budding HIV Budding HIV

HIV on HIV on LymphocLymphocyteyte

HIV Infections StagesHIV Infections Stages

Cytotaxic CellCytotaxic Cell

Cytotaxic Cytotaxic CellCell