The other circulatory system

Chapter 14 – The Lymphatic System and Immunity

SummaryLymphatic system

FluidVesselsNodes and NodulesOrgans

Immune systemNonspecificSpecificCellsMechanisms

Lymphatic SystemFunction – responsible for returning tissue

fluid to the blood and for protecting the body against foreign material.

Lymph is a specialized fluid which is formed in the tissue spaces = interstitial fluid. Contains excess fluid and protein molecules that cannot enter or return through the capillary walls.

Lymphatic SystemLymphatic vessels

Lymph capillaries – blind ended vessels that are very permeable; collect tissue fluids and proteins in the tissues.

Lymphatic SystemVessels cont’d

Lymph venules then veins collect fluid from the capillaries.

Ducts – large vessels that drain the lymph into the blood in veins (subclavian) in the neck area.Right lymphatic duct

Thoracic duct

Lymphatic SystemVessels

Cisterna chyli – enlarged pouch-like structure formed by the union of the lower body lymphatic vessels. Lower portion of the thoracic duct in the abdomen; serves as a storage area for lymph that is moving toward its point of entry into the venous system.

Lymphatic SystemFluid is moving under low pressure and

against gravity – How?Smooth muscle in the walls of the larger

vessels contracts and moves fluid upward.Skeletal muscle pumpPressures in thoracic cavity

Lymphatic SystemLymph Nodes

Clusters of small encapsulated masses of lymphatic tissue located at strategic spots in the lymph system. They may be the size of a pin head or a lima bean.

Lymph enters the node through afferent vessels (usually more than one) and leaves through a single efferent vessel.

Lymphatic SystemLymph Nodes

Serve to filter and trap bacteria, cancer cells and other foreign material picked up by the lymphatic vessels. Fixed macrophages in the nodes phagocytize (eat) these particles.

Fixed plasma cells produce antibodies in response to foreign material and these antibodies then circulate in the blood stream.

**Also produce lymphocytes and monocytes.

Lymphatic SystemLymph Nodes

Significant groups: cervical, axillary and inguinal.

Clinical significance:

Lymphatic SystemLymph Nodules

Smaller masses of lymphatic tissue (not encapsulated) found just beneath the epithelium of all mucous membranes. Mucous membranes are located at

openings to the environment – respiratory, digestive, urinary and reproductive systems. Why is this a good spot for lymph tissue?

Lymphatic SystemSpecial Lymph Nodules

Peyer’s patches located in the small intestine.

Tonsils – located in the pharynx form a protective ring under the mucous membranes in the mouth and back of throat.Palatine – Pharyngeal – Lingual –

Lymphatic SystemOrgans

Thymus – located inferiorly to the thyroid gland in the mediastinum. Produces T-lymphocytes (T-cells) and secretes thymosin and other hormones that stimulate their development.The thymus is critical to immunity in the

fetus and infant.The thymus shrinks with age but is still

active.

Lymphatic SystemSpleen

Largest lymphoid organ in the body located in the upper left quadrant of the abdomen, lateral to the stomach, just below the diaphragm.

Functions:

Lymphatic SystemSpleen

Functions:Fixed macrophages, reticuloendothelial cells,

phagocytize pathogens in the blood. Also phagocytize and destroy old RBCs producing bilirubin.

Stores about 1 pint of blood – hemorrhageSplenectomy?

Liver and red bone marrow will compensate to remove old RBC’s and lymph nodes and nodules will produce lymphocytes and monocytes, etc.

Immune SystemImmunity – the body’s ability to destroy

pathogens or other foreign material and prevent further cases of certain infectious diseases.

Types of Immunity:

ImmunityNon-specific (innate) immunity -

maintained by mechanisms that attack any abnormal substance that threatens the body; general protection. Barriers: Skin, mucous membranes (and

mucus), cilia.Lysozymes in tears and saliva.SQ and areolar connective tissue WBC

phagocytize bacteria.

Immune SystemSpecific immunity

Includes protective mechanisms that confer very specific protection against certain types of invading materials.

Involves “memory” – when the body is attacked the first time a disease develops; the next time no disease signs/symptoms develop; i.e. the body is immune.

Immune SystemSpecific Immunity - Inherited

Genetic, inborn immunity is the result of our genetic make-up, i.e. we do not get distemper and dogs don’t get measles (species immunity).

This type does not involve antibodies and the efficiency does not increase with subsequent exposures.

Immune SystemSpecific Immunity - Acquired

Natural – exposure to the causative agent is not deliberate. Active –

Passive –

Immune SystemSpecific Immunity – Acquired

Artificial – exposure to the causative agent is deliberate.Active - injection of the agent (vaccine) results in

production of your own antibodies and memory cells.

Passive – injection of protective material (antibodies) that was developed by another individual’s immune system (gamma globulins or immune globulins).

Immune System - CellsPhagocytes – neutrophils, monocytes and

macrophages, derived from bone marrow, carry out ingestion and digestion of foreign cells or particles.Monocytes develop into macrophages.Macrophages – some wander and some are

fixed; example Kupffer’s cells in the spaces between liver cells.

Immune System - CellsLymphocytes – most numerous cells of the

immune system; responsible for antibody productionT-cells – produced in the bone marrow and

thymus of the embryo. They mature in the thymus and migrate to the spleen, lymph nodes and nodules.

Immune System - CellsLymphocytes

B-cells – produced in the bone marrowWhen activated by an antigen, they become plasma

cells that produce antibodies.They also can become memory cells that remain in

reserve until a stimulus by the same antigen is repeated and then produce antibodies.

Immune System CellsLymphocytes

Natural Killer Cells (Killer T-cells) – smaller in number but can attack many types of pathogens and tumor cells. Formed from activated T-cells. Mechanism : disrupt cell membranes of foreign cells.

Immune System - CellsReview Definitions:

Antigen – chemical markers that identify cells. Each cells has its own set of markers.

Antibodies (immune or gamma globulins)Proteins produced by plasma cells in response to

foreign antigens; each one is specific for a certain antigen.

Mechanism: When bound to an antigen they cause agglutination (clumping) of the material.

Also the mechanism for allergic responses.

Mechanisms of ImmunityRecognition of an antigen as foreign –

accomplished by macrophages and helper T-cells.

Foreign antigen is phagocytized by a macrophage.

Macrophage presents antigen material on its cell membrane.

Helper T-cell is exposed to this part of the macrophage membrane and becomes sensitized.

Mechanisms of ImmunityOnce an antigen has been recognized, the

activated helper T cells initiate one or both immune mechanisms.Cell Mediated ImmunityHumoral Immunity

Mechanisms of ImmunityCell- mediated Immunity – no antibody

producedT-cells activated by foreign material form

memory T-cells and killer (cytotoxic) T-cells.Memory cells will remember the specific

antigen and become active if it enters body again.

Killer T-cells chemically destroy foreign antigens (disrupt cell membranes).

Mechanisms of ImmunityCell-mediated immunity

T-cells cont’dKiller T-cells also produce cytokines –

chemicals that attract macrophages to an area to promote phagocytosis.

Suppressor T-cells stop the immune response once the antigen has been destroyed.

Mechanisms of ImmunityHumoral Immunity – involves production of

antibodies.Recognition of foreign antigen by

macrophages and activation of helper T-cells.Sensitized helper T-cell presents antigen to

B-cells B-cells activate the memory B cells and

plasma cells. The plasma cells then produce antibodies.

Mechanisms of ImmunityHumoral Immunity

Antibodies bind to antigens forming an antigen-antibody complex.Complex is labeled for phagocytosis by

macrophages = opsonization.Complement fixation – complement binds

to complex and is destroyed by lysis.

Immune SystemOYO Read:

Aids, p 332Interferon, p 328 (Chemical defenses)Vaccines, pp 335 and 337