HS 130 Anatomy & Physiology IIUnit 3 Seminar

Chapter 13The Lymphatic System

And Immunity

•Questions, Problems, Concerns

The Lymphatic System

• Functions of the lymphatic system Allows exchange of substances, such as

excess fluid and protein molecules, that cannot occur in the capillary beds

Filters out harmful substances from the lymph before returning it to the blood

Acts as sewer system of the body

What is the role of lymph nodes in the spread of cancer?

What role do tonsils play in preventing the spread of infection to the lower respiratory tract?

Lymph—fluid in the tissue spaces that carries protein molecules and other substances back to the blood

Lymphatic vessels—permit only one-way movement of lymph Lymphatic capillaries—tiny blind-ended tubes distributed in

tissue spaces Microscopic in size Sheets consisting of one cell layer of simple squamous

epithelium Poor “fit” between adjacent cells results in porous walls Called lacteals in the intestinal wall (fat transportation from

food to bloodstream) Right lymphatic duct

Drains lymph from the right upper extremity and right side of head, neck, and upper torso

Thoracic duct Largest lymphatic vessel Has an enlarged pouch along its course, called cisterna

chyli Drains lymph from about three-fourths of the body

The Lymphatic System

What happens to fluid from blood plasma that is not reabsorbed by blood vessels?

Which lymphatic duct drains most of the body?

What is the function of the cisterna chyli?

What are lacteals?

Lymph nodesFilter lymphLocated in clusters along the pathway

of lymphatic vesselsFunctions include defense and WBC

formationFlow of lymph: to node via several afferent lymph

vessels drained from node by a single

efferent lymph vessel

The Lymphatic System

What is this diagram showing?

• Thymus: Lymphoid tissue organ located in mediastinum Total weight of 35 to 40 g (a little more

than an ounce) Plays a vital and central role in immunity Produces T lymphocytes, or T cells Secretes hormones called thymosins In adults, lymphoid tissue is largely

replaced by fat and connective tissue in the process called involution

The Lymphatic System

What would you expect the course of therapy to be if a baby were born without a thymus gland?

• Tonsils Composed of three masses of lymphoid

tissue around the openings of the mouth and throat Palatine tonsils (“the tonsils”) Pharyngeal tonsils (adenoids) Lingual tonsils

Subject to chronic infection Enlargement of pharyngeal tonsils may

impair breathing

The Lymphatic System

Why would you try to avoid removal of the tonsils if at all possible?

• Spleen Largest lymphoid organ

in body Located in upper left

quadrant of abdomen Often injured by trauma

to abdomen Surgical removal called splenectomy Functions include

phagocytosis of bacteria and old RBCs

acts as a blood reservoir

The Lymphatic System

Often after the surgical removal of a breast, lymph nodes, and lymphatic vessels — especially those in the upper arm — swelling occurs. What is the physiological reason that swelling takes place?  

Some surgical treatments for breast cancer involve removal of lymph nodes in the axillary region. Why might this have a therapeutic effect in some cases?

Diseases of the lymphatic system:LymphangitisLymphedemaElephantiasisLymphomaTonsillitisSplenomegaly

• Functions of the immune system Protects the body from pathologic bacteria,

foreign tissue cells, and cancerous cells Made up of specialized cells and molecules

The Immune System

• Nonspecific immunity Skin: Mechanical barrier to bacteria and

other harmful agents Tears and mucus: Wash eyes and trap

and kill bacteria Inflammation

Attracts immune cells to site of injury, increases local blood flow, increases vascular permeability

Promotes movement of WBCs to site of injury or infection

The Immune System

• Inflammatory Response Inflammation is a generalized response to an

invader, such as bacteria that are causing tissue damage

This triggers release of factors from immune cells The presence of immune factors attracts WBCs Factors also cause increased blood flow (site

becomes warm and reddened) and increased vascular permeability (site swells with associated discomfort)

These immune factor-mediated changes help phagocytic WBCs reach the site and enter the affected tissue

The Immune System

Specific immunity Also called adaptive immunity because of the

ability of the body to recognize, respond to, and remember harmful substances or bacteria

Types of specific immunityNatural immunity—exposure to causative

agent is not deliberateActive—active disease produces immunityPassive—immunity passes from mother to

fetus through placenta or from mother to child through mother’s milk

Artificial immunity—exposure to causative agent is deliberateActive—vaccination results in immunityPassive—protective material developed in

another individual’s immune system and given to previously nonimmune individual

The Immune System

• Antibodies: Protein compounds with specific combining sites Combining sites attach antibodies to specific

antigens, forming an antigen–antibody complex Inactivation of foreign protein in this way

is called humoral or antibody-mediated immunity

Antigen–antibody complexes have various modes of action Neutralize toxins Clump or agglutinate enemy cells Promote phagocytosis

The Immune System Molecules

• Complement Proteins Group of at least 14 proteins normally present

in blood in an inactive state Complement fixation

Important mechanism of action for antibodies

Causes cell lysis by permitting entry of water through a defect created in the plasma membrane

• Phagocytes: Ingest and destroy foreign cells or other harmful substances via phagocytosis Types

Neutrophils Monocytes Macrophages

o Kupffer’s cellso Dust cells

The Immune System Molecules

Where do phagocytes and lymphocytes originate?

• Lymphocytes Most numerous of immune system cells Development of B cells

Primitive stem cells migrate from bone marrow and go through two stages of development

The Immune System Molecules

• Development of B Cells Stage 1

Stem cells develop into immature B cellsoImmature B cells are small lymphocytes; each synthesizes highly specific antibody molecules in their plasma membranes

Migrate via the bloodstream chiefly to lymph nodes

Become seed cells in the lymph nodes Undergo mitosis to make clones of

themselves containing their specific antibody

The Immune System Molecules

• Development of B Cells Stage 2

Immature B cell develops into activated B cell if it comes in contact with its specific antigen

B cell is activated by antigens binding to its surface antibodies

Activated B cell divides repeatedly, forming two clones of cells:

o Plasma cells o Memory cells

Slide 31

• Function of B Cells Humoral immunity

Activated B cells develop into plasma cells

Plasma cells secrete antibodies into the blood

Circulating antibodies produce humoral immunity

• Development of T Cells Stage 1

Stem cells from bone marrow migrate to thymus gland

Stem cells develop into T cells several months before and after birth

T cells have protein molecules on their cytoplasmic membrane shaped to bind to only one kind of antigen

T cells migrate from thymus chiefly to lymph nodes, liver, and spleen

Stage 2 Occurs only if a specific antigen binds to T

cells’ surface proteins T cells develop into sensitized T cells

• Functions of T Cells Provide cell-mediated immunity Kill invading cells directly by releasing

a substance that poisons cells Release chemicals that attract and

activate macrophages to kill cells by phagocytosis

What happens when T-cell function is impaired?

• Humoral immunity Immunity conferred by the action of

antibodies Activated B cells plasma cells and

memory cells • Cell-mediated immunity

Immunity conferred by the action of cells Sensitized T cells Kill invading cells directly by releasing

lymphotoxin or releasing lymphokines that attract and activate macrophages to kill cells by phagocytosis

Humoral vs Cell-mediated Immunity

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