Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Lymphatics and Immunity

FUNCTIONS OF THE LYMPHATIC AND IMMUNE SYSTEM– Fluid balance – returns fluid that has leaked from the

vascular system to the interstitial space back to the blood.– Defense- protects the body by removing foreign material

from lymph stream– Provides a site for immune surveillance– Fat absorption – absorbs fats and other substances from

the digestive tract

DISTRIBUTION AND STRUCTURE OF THE LYMPHATIC VESSELS

1.Lymphatic capillaries

2.Lymphatic collecting vessels

3.Lymphatic trunks

4.Ducts Right lymphatic duct Thoracic duct

• These two duct empty at the junction of the internal jugular vein and

subclavian vein on its own side of the body, thus back to the heart via

the superior vena cava.

Figure 14.2

Figure 14.1a

Figure 14.1b

• LYMPH TRANSPORT– The flow of the lymphatic fluid is slow, and maintained

by the compression of the lymphatic vessels by the following:

– Skeletal muscle contraction– Pressure changes in the thorax during respiration– Contraction of smooth muscle in the lymphatic

vessel wall– The backflow of lymph is prevented by the

presence of valves• Pathogens and cancer cells may spread through the body via

the lymphatic stream because of the nature of the lymphatic capillaries that are exceptionally permeable

LYMPHATIC ORGANS

Lymph node– Are round structures clustered along the lymphatic

vessels and serve as in-line mechanical filters of lymph.

– The lymph is transported towards the lymph node via the afferent lymphatic vessels

– Inside the lymph node, the lymph is filtered and antibodies are made by lymphocytes as a reaction to several particulate matters that were filtered.

– The filtered lymph with added antibodies is released through the efferent lymphatic vessels located on the convex surface.

Figure 14.4

Tonsils– These form a ring of lymphatic tissue around the

entrance of the pharynx, and is called the “Waldeyer’s Ring”

– The ring is made-up of the following tonsils:– Palatine tonsil- located on either side at the posterior end

of the oral cavity, largest and often infected.

– Pharyngeal tonsil (adenoids) – placed at the posterior wall of the nasopharynx.

– Lingual tonsil – to be found at the base of the tongue.

Figure 14.3

Spleen– The spleen is located in the left hypochondriac area.

– The spleen weighs about 150g in adults and forms the largest aggregation of lymphatic tissue in the body.

– Blood rich which is about the size of the fist, and largest of the lymphoid organ

– It is described as the “graveyard for aged and defective blood cells”

– It serves as the site for lymphocyte proliferation, immune surveillance, and response.

– There is about 30-40 ml blood are stored in the spleen.

– The spleen is easily ruptured in cases of traumatic injury (car accidents) and is commonly surgically removed to prevent continued hemorrhage.

Figure 14.5a

Figure 14.5b

Thymus gland•  It is to be found in the superior mediastinum.

• Prominent in newborns because of its significant function primarily during the early years of life for immunity.

• Continues to increase in size during childhood when it is most active, and the time where most antibodies are developing against several diseases.

• As one gets older, the growth of the thymus gland slows down and later atrophies.

• Functions as the site for the production and maturation of lymphocytes

Figure 14.6a

Figure 14.6b

Peyer’s Patches or the Gut-associated lymphoid tissue (GALT)– These are large isolated clusters of lymph nodules found

in the ileum.– The macrophages of the peyer’s patches are in ideal

position to capture and destroy bacteria, preventing them from traversing the intestinal wall.

– Peyer's patches are most evident in the ileum

Figure 14.7

IMMUNITY

• DEFINITION– This is a state of having enough biological defenses to

shun infection, disease, or other unwanted biological invasion.

– It is the ability of an organism to resist illness by identifying and destroying foreign substances or organisms.

TYPES OF IMMUNE RESPONSE

• Non-specific responses or Innate Immunity– It is a generalized defense against all foreign invaders to

hinder the infiltration and spread of disease.– This prevents entry of microorganisms into tissues, or

once they have gained entry, eliminates them prior to the occurrence of disease.

– Present from birth, and acts on many organisms without any specificity.

– This type of immune response does not become more efficient on succeeding exposure to the same organisms.

• This type of immunity is accomplished by the following factors:

– Mechanical Barriers• The skin and mucous membrane

• Body secretions (e.g. tears, saliva, and urine)

– Chemical mediators• These may be molecules on the cell’s surface that directly kill

microorganisms and also hinders their entry into the cell.

– Lysozymes

– Complement

– Interferons

– Cells• White blood cells – leaves the blood, and enter the affected

tissue when chemical mediators are released from the damaged tissues and microorganisms

• Phagocytic cells – Neutrophils – typically the first group of cells to proceed at the

infected tissue from the blood. After phagocytosis, neutrophils die and become part of the pus.

– Macrophages – prior to leaving the blood, these cells are called monocytes. Upon entering the specific tissue, these cells enlarge are given specific names. (e.g. langerhan’s cell of the skin; Kupffer cells of the liver; microglia of the central

– Cells of inflammation• Basophils and mast cells – as a reaction to foreign organisms

or matter, these cells release chemicals such as histamine and leukotrienes that produce an inflammatory response.

• Eosinophils – release enzymes that break down chemicals released by basophils and mast cells, consequently reducing the inflammatory response.

– Natural killer cells- a type of lymphocyte that recognizes tumor cells or virus-infected cells in general. These cells release chemicals that damage cell membranes and eventually the affected cells lyse.

• Non-specific Inflammatory Response– The response begins with damage to tissues or

microorganisms that cause the release or activation of chemical mediators such as prostaglandins, leukotrienes, complement, kinins, and histamine.

– These chemical mediators generate a number of effects, namely:

– Vasodilation which leads to an increase in blood circulation in the affected area.

– Increased vascular permeability

– Chemotactic attraction of phagocytic cells

• The inflammatory response maybe localized or systemic.– Local inflammation is limited to a specific area of the

body with the following symptoms:• Calor or heat• Rubor or redness• Dolor or pain• Tumor or swelling• Functio laesa or loss of function

Figure 14.8

– Systemic inflammation on the other hand is by and largely distributed throughout the body with three additional features, aside from those present in local inflammation. 

• Enhance red bone marrow production of neutrophils for phagocytosis.

• Cells release pyrogens that stimulate fever production. High body temperature inhibits microbial multiplication, and enhances body repair.

• Increased vascular permeability in severe systemic inflammation causes a very low blood volume leading to shock and death.

Specific responses or Acquired Adaptive immunity– Unlike innate immunity, adaptive immunity is also

highly specific to the pathogen. – One’s immune system recognizes and develops a

memory with increasing effectiveness to successive exposures to the same microorganism or antigen.

– The adaptive immune system can remember preceding infections.

– This exhibits specificity that following recovery from certain infections, the person who was infected will never again develop infection with that same organism.

Antigens and antibodies– Antigens are foreign proteins that enter our body via an

open wound or mucosa, through the digestive system, or through the urinary, and reproductive system.

– 2 types of antigen– Foreign antigens

– Self-antigens

– Autoimmune disease results when self antigens stimulate unwanted destruction of normal tissue. Ex. Rheumatoid arthritis

• Immunity may result from the production of antibodies specific to a given antigen.

• Antibodies or immunoglobulins are Y- shaped molecules consisting of four polypeptide chains.– Variable regions – These are ends of each arm of the

antibody that combines with the antigen.

– Constant regions – The rest of the body which can activate compliments, bind to other immune system cells, such as macrophages, basophils or mast cells.

Figure 14.12

Table Art 14.2

Table 14.2

Figure 14.13

The adaptive immune response to antigens may categorically divided into

1. Humoral immunity or antibody-mediated immunity

• Involves the B lymphocytes that give rise to antibodies.

• Main concern is protection against extracellular antigens.

2. Cell-mediated immunity– The responsible cells for this adaptive immune response are the T

lymphocytes from the thymus gland.

– Mainly against microorganisms that live inside the cells of the body such as intracellular viruses and bacteria, tumors, and also responsible for graft rejection

Figure 14.10

Humoral immunity or antibody-mediated immunity

Figure 14.11

Figure 14.13a

Figure 14.13b

Figure 14.13c

Figure 14.13d

Figure 14.13e

Figure 14.15

Cell-mediated immunity

Figure 14.16

Figure 14.17

TYPES OF MATURE LYMPHOCYTES1. T- Cells or T lymphocytes

– These are lymphocytes that have migrated to the thymus gland to proliferate.

– Specific T- cell subpopulations are:

• Helper T-cell or cooperator cell – These cells chemically or directly stimulate the development of other T-cells and some B-cells that have become bound to antigens.

• Cytotoxic T cells or Killer cells – These directly attack and lyse cancer cells, infected cells, as well as foreign human cells.

• Suppressor T-cells – These terminate normal immune responses by releasing suppressor factors that reduce the activity of helper T-cells and B –cells.

2. B- cells or B- lymphocytes – B- cells remain in the bone marrow and develop before

moving into the circulatory and lymph systems.– Provides humoral immune response when challenged by

antigens which eventually leads to production of antibodies

• Roles of B-cells in immune response:• Primary immune response

– This results from the first exposure of a B cell to an antigen.

– The antigen binds to the receptors of B-cells causing differentiation of B-cells into memory cell, and antibodies.

– Usually lasts for 3-14 days where symptoms of the disease are very apparent till the production of enough antibodies that coincides with the disappearance of symptoms.

• Secondary immune response – Happens when the immune system is exposed once more to the

same antigen.

– This provides better immunity than the primary response because in the presence of memory cells the production of antibodies occurs in less time, and more antibodies are produced.

– Therefore, the antigen is quickly destroyed, and no symptoms develop.

Figure 14.14

ACTIVE AND PASSIVE HUMORAL IMMUNITY

– Active immunity results when B cells encounter antigens, and as a result antibodies are produced against them.

• Natural active – an outcome from a bacterial and viral infection. The body is actively producing antibodies as a result of the infection.

• Artificial active – occurs when we receive vaccines of dead or attenuated (weakened) antigen.

– Passive immunity results when preformed antibodies are introduced in the body

• Natural passive – conferred on a fetus when the mother’s antibodies cross the placenta into the fetal circulation.

• Artificial passive- happens when a person receives an infusion of immune serum such as gamma globulins

Figure 14.18