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LYMPHATIC SYSTEM. Chapter 14. The lymphatic system is part of the circulatory system. Two key roles in the body: Carries fluid from the extracellular environment into the bloodstream, and thereby helps to maintain fluid balance.

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Lymphatic system

LYMPHATIC SYSTEM

Chapter 14



Specialized organs of lymphatic system
Specialized organs of Lymphatic System

  • Lymph nodes, the spleen, the thymus, the tonsils, and Peyer’s patches


The lymphatic network
The Lymphatic Network

  • Interstitial fluid is formed when plasma from the bloodstream is pushed through capillary walls.

  • This watery fluid serves as a transport medium for gases, nutrients, and other molecules that travel between cells and the blood.


  • Most of the interstitial fluid (about 90%) diffuses back into capillaries for the return trip to the heart, but some of it does not.

  • How is the remaining interstitial fluid returned?

    • The accumulation of interestitial fluid in the extra cellular space generates a pressure gradient, which creates enough force to literally push the remaining interestitial fluid into the lymphatic network.



Lymphatic capillaries
Lymphatic Capillaries returns it to the bloodstream in a one-way flow that moves slowly toward the heart.

  • Tiny vessels are found between cells and among capillary beds of nearly all tissues and organs in the body.

  • Areas where they are not found include the brain and spinal cord, bone tissue, and epidermis.


Lymphatic vessels
Lymphatic Vessels returns it to the bloodstream in a one-way flow that moves slowly toward the heart.

  • Their structure resembles veins, as their walls consists of the same three layers of tissue with the inner endothelium forming one-way valves.

  • The valves of lymphatic vessels help prevent the backflow of lymph.

  • As lymphatic vessels extend toward the heart, they gradually increase in size and merge to form the larger lymphatic trunks and collecting ducts.



Lymphatic trunks and collecting ducts
Lymphatic Trunks and Collecting Ducts returns it to the bloodstream in a one-way flow that moves slowly toward the heart.

  • Lymphatic trunks are formed from the merging of numerous lymphatic vessels.

  • They extend a short distance toward the heart until they converge to form one of the two collecting ducts in the lymphatic network: the thoracic duct or the right lymphatic duct.


  • The returns it to the bloodstream in a one-way flow that moves slowly toward the heart.thoracic duct is the main collecting vessel for the lymphatic network.

  • It drains lymph from the left side of the head, neck, and thorax; the left upper limb; and the entire body below the diaphragm.

  • It originates in the lower abdomen as an expanded vessel (cysterna chyli) and travels upward against the back wall to the upper chest.


  • The returns it to the bloodstream in a one-way flow that moves slowly toward the heart.thoracic duct empties lymph into the bloodstream where it unites with the left subclavian vein.

  • The right lymphatic duct drains lymph from the right side of the head, neck, and thorax and the right upper limb.

  • It extends a short distance in the neck to empty lymph into the right subclavian vein, with which it unites.


Movement of lymph
Movement of lymph returns it to the bloodstream in a one-way flow that moves slowly toward the heart.

  • Lymph is propelled through the lymphatic network by pressure gradients.

  • Gradients are established by a number of factors, including the accumulation of protein in the interstitial fluid, skeletal muscle contraction, and breathing movements.


Lymph formation
Lymph Formation returns it to the bloodstream in a one-way flow that moves slowly toward the heart.

  • Interstitial fluid is formed by the movement of blood plasma out of blood capillaries.

  • It is composed of water and dissolved substances, but it lacks larger substances such as cells and large proteins.

  • The concentration of small proteins in the remaining interstitial fluid tends to rise, causing the osmotic pressure of the fluid to rise as well.



Flow of lymph
Flow of lymph concentrations rise; in this case, the proteins are the solutes.

  • As lymph begins to accumulate in the blind-ended capillaries, the pressure in these tiny tubes rises.

  • This provides the force to move the lymph into the larger lymphatic vessels, where the pressure is lower.


Other lymphatic organs
Other Lymphatic Organs concentrations rise; in this case, the proteins are the solutes.

  • Lymphatic organs other than the vessels consist mostly of packed lymphocytes that perform defensive functions.

  • Lymphoid Tissue contains collections of lymphocytes, a type of white blood cell.

  • Lymphocytes play a role in mounting a defensive immune response to foreign materials such as pathogenic microorganisms.


Lymph nodes
Lymph Nodes concentrations rise; in this case, the proteins are the solutes.

  • Lymph nodes are small, oval masses of lymphoid tissue located along the lymphatic pathways.

  • There are hundreds of nodes in the body: nodes are usually found in clusters or chains in the neck, armpit, groin, and deep within the abdominal cavity.


Lymph node structure
Lymph Node Structure concentrations rise; in this case, the proteins are the solutes.

  • Most are shaped like a kidney bean and are less than 2.5 cm in length.

  • A lymph node is a receiving and sending station for lymph.

  • Along its convex margin it receives incoming lymph by way of lymphatic vessels that merge with it.


  • These vessels are called concentrations rise; in this case, the proteins are the solutes.afferent lymphatic vessels.

  • At its concave margin, known as the hilus, the node sends lymph on its way toward the heart by way of efferent lymphatic vessels.


  • The internal structure consists of two portions: concentrations rise; in this case, the proteins are the solutes.

    • An outer area, called the cortex, and an inner part, known as the medulla.

    • The cortex consists of many lymph nodules, where lymphocytes and macrophages are located.

    • It is also the site of lymphocyte maturation.


  • In the concentrations rise; in this case, the proteins are the solutes.medulla, the lymphocytes are arranged in strands called medullary cords.


Lymph node function
Lymph Node Function concentrations rise; in this case, the proteins are the solutes.

  • Microorganisms and other foreign particles carried by the lymph are filtered and removed. (bacteria, toxins released by bacteria, and viruses)

  • These are inactivated by large numbers of lymphocytes that are packed within the lymph nodes.



Spleen
Spleen cell debris.

  • Largest of the lymphatic organs.

  • It is enveloped by a fibrous capsule whose protein fibers divide it internally into compartments, many of which contain lymphocytes and macrophages.

  • The spleen also contains venous sinuses that are normally filled with large numbers of red blood cells.

  • These areas are referred to as red pulp.


The regions of the spleen that contain white blood cells are called the white pulp.

The spleen functions as a large filter for removing foreign particles,old and defective red blood cells, and platelets from the bloodstream.

These functions are accomplished by the lymphocytes and macrophages Within the white pulp.



Thymus gland
Thymus Gland large volume of blood that can be called upon during emergency situations involving blood loss

  • The Thymus Gland also plays a role in the Endocrine System.

  • In infants, it is a large, bilobed gland located in the thoracic cavity, where it lies behind the sternum.

  • In adults it is very much reduced in size and function.


  • During infancy, the large volume of blood that can be called upon during emergency situations involving blood lossthymus cells promote the maturity of lymphocytes into T lymphocytes (T cells) and releases them into the bloodstream.

  • T cells play an important role in the immune response.

  • In adolescence, the thymus gland begins to atrophy, and by adult age it has been replaced by fibrous and fatty tissue.


Tonsils
Tonsils large volume of blood that can be called upon during emergency situations involving blood loss

  • Located in the mouth and throat, where they lie partially embedded within the mucous membrane.

  • They are named according to their location:

    • Palatine tonsils—on the back end of the palate (2)

    • Pharyngeal tonsils—lie against the wall of the upper throat (2)


  • Lingual tonsils large volume of blood that can be called upon during emergency situations involving blood loss---at the base of the tongue (2)

  • These cells gather and engulf disease-causing microorganisms in the mouth and throat regions.

  • During an infection, the palatine tonsils in particular may enlarge because of the proliferation of bacteria and white blood cells.

  • Consequently, you have a sore throat!



Peyer s patches
Peyer’s Patches tonsils by way of a procedure called

  • Isolated clusters of lymphoid tissue in the wall of the small intestine near its distal end.

  • They contain lymphocytes and macrophages in large numbers.

  • They identify microorganisms and other foreign particles that reside in the intestine.



The defense mechanisms of the body
The Defense Mechanisms of the Body movement of bacteria across the intestinal wall and into the abdominal cavity.

  • All self cells contain a similar distribution of membrane receptors which can be read by white blood cells as “code” and which differs from the distribution of membrane receptors found in nonself cells.

  • The specific distribution of membrane receptors is determined by a group of genes in the chromosomes of all self cells, called major histocompatibility complex (MHC).



  • Specific defense mechanisms employs:: this keys into the particular type of pathogen or toxin that is infecting the body.

  • Once the invaders have been identified, they may be inactivated by a variety of defensive mechanisms.

  • The selective production of special proteins, called antibodies, is one way of inactivating the invaders.



Nonspecific mechanisms
Nonspecific Mechanisms as the

  • There are many defense mechanisms that are nonspecific.

  • The most important include physical barriers, Phagocytosis, natural killer cells, proteins, and inflammation.


Physical barriers
Physical Barriers as the

  • Most important barrier is the skin.

  • Mucous membranes provide a second important physical barrier.

  • Mucous membranes also produce chemicals that help in the defensive strategy.

  • An invasion by a pathogen that successfully penetrates the body’s physical barriers is called an infection.


Phagocytosis
Phagocytosis as the

  • Phagocytosis is the ingestion and destruction of particles by specialized cells.

  • Once collected, the particle is digested by vacuoles inside the cell.

  • A cell that performs this function is called a phagocyte.


  • Phagocytosis is a type of as the nonspecific defense because the white blood cells performing this function do not distinguish between different types of foreign cells.

  • Phagocytosis is performed by most white blood cells.


  • The most active in this defensive activity are as the monocytesand neutrophils,which squeeze through blood vessel walls to reach sites of infection and inflammation.

  • Monocytes give rise to their more mature form, known as macrophages, which often become attached to the walls of lymphatic vessels and other lymphatic organs.


  • Macrophages may also wander freely throughout the circulatory system, or they may fix themselves to the walls of blood vessels, the liver, and the lungs.

  • Attached macrophages constitute an important part of the body’s defense network, known as mononuclear phagocytic system.


Natural killer cells
Natural Killer Cells circulatory system, or they may fix themselves to the walls of blood vessels, the liver, and the lungs.

  • Natural killer cells are a type of white blood cell that kills invading foreign cells nonspecifically by a method other than phagocytosis.

  • Natural killer cells are unique in that they kill cancer cells and virus-infected cells by puncturing a hole in their plasma membrane (called cell lysis).



Proteins
Proteins of

  • Certain groups of proteins play a role in nonspecific defense.

  • One group called complement; it includes more than 20 types of plasma proteins that are normally in an inactive state.

  • COMPLEMENT becomes activated by the onset of an infection.




Inflammation
Inflammation by viruses.

  • Inflammation is a response to body stress, or disruption of homeostasis, which often follows an infection or physical injury.

  • It is a nonspecific mechanism because it may occur in any tissue of the body.

  • The inflammatory responses are initiated when a damaged cell releases substances into the bloodstream.


  • These substances include by viruses.histamine and serotonin.

  • They produce two main responses by local tissue:

    • Vasodilation of blood vessels

    • Increased permeability of blood vessels




Specific mechanisms the immune response
Specific mechanisms: The Immune Response known as

  • The immune response relies upon the ability of lymphocytesto recognize specific antigens.

  • The defense mechanisms that are specific constitute the immune response of the body, or immunity.


  • Two types of immune responses: known as

    • Cell-mediated immunity—cells provide the main defensive strategy;

    • Humoral immunity---utilizes antibodies as the main weapon against invaders.


Components of immunity
Components of Immunity known as

  • ANTIGENS—substances that provoke an immune response when they enter the body.

  • They are recognized by white blood cells as foreign.

  • Antigens include toxic molecules released by microorganisms, or the whole microorganisms themselves.


Antibodies
Antibodies known as

  • An antibody is a protein molecule that is produced in response to a specific antigen.

  • It binds to the antigen to form an antigen-antibody complex, which inactivates the toxic effects of the antigen.

  • Antibodies belong to a family of proteins known as immunoglobulins (Ig).


  • There are five classes of known as Ig:

    • IgG--- found in the blood, lymph, intestines

    • IgA---in tears, salvia, mucus, milk, blood, and lymph

    • IgM and IgD---in blood and lymph, and attached to surfaces of B cells

    • IgE---attached to surfaces of basophil cells, mast cells, and B cells.


Lymphocytes
Lymphocytes known as

  • The most important type of white blood cell in immunity is the lymphocyte.

  • Lymphocytes originate from the red bone marrow before birth.

  • Soon after their production, about half of them migrate to the thymus gland.

  • Once within the tissues of the thymus gland, these cells mature into a form of lymphocyte called T cells.

  • The rest migrate to the spleen or Peyer’s patches, where they mature into B cells.


  • Soon after this maturation process, T cells and B cells leave their site of development and migrate to lymphoid tissue.

  • Here they become “programmed” to recognize self cells and distinguish them from nonself cells.

  • Once a lymphocyte has developed this ability, it is called immunocompetent.



  • Killer T cells properties that enable it to react against the particular antigen. are specialized in destroying virus-infected cells, cancer cells, and foreign cells.

  • They bind to these cells once they are recognized and release toxic chemicals called lymphotoxins.

  • Killer T cellsare also calledcytolytic T cells.


  • Helper T cells properties that enable it to react against the particular antigen.---when they identify an antigen, they release proteins into the bloodstream that signal other cells to attack the invader.

  • These proteins, called lymphokines, stimulate killer T cells to grow and divide,attract neutrophils and monocytes to the site of intrusion, and enhance the ability of macrophages to ingest and destroy nonself cells.



  • Memory T cells body.----provide the immune response with a “memory” of the specific antigen that caused the initial sensitization.

  • B Cells---account for about 20% of the lymphocyte population in a normal blood sample.

  • In B cells, most of the descendents of the sensitized cell become plasma cells.


  • Plasma cells body. swing into action to synthesize vast amounts of antibodies at an incredible rate (2000 antibody molecules per second).

  • The plasma cells are the only cells of the body that produce antibodies.

  • Memory B cells---found mainly in the bone marrow. They provide a “memory bank” of sensitized cells that can respond to the same antigen when it is encountered again.


Cell mediated immunity
Cell-Mediated Immunity body.

  • Provided by the various types of T cells.

  • Initiated when a macrophage identifies an antigen, phagocytizes it, and processes it.

  • Processed antigen is expressed on the macrophage plasma membrane.

  • Macrophage then presents the antigen to a T cell, resulting in T cell sensitization.

  • The sensitized T cell then proliferates into various T-cell lines (killer, helper, suppressor, and memory).


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