The Lymphatic and Immune System

Objectives

describe the composition of lymph

what are the major structures composing the lymphatic system and explain their relation to the immune and cardiovascular system

what is an antigen and a self antigen?

compare and contrast the development of B and T cells

Lymphatic System

works along side the cardiovascular system and the immune system

consists of two semi-independent systems: the lymphatic vessels and lymphoid tissues, and organs throughout the body

the vessels transport fluids that have escaped from the blood vascular system back to the blood

organs house the phagocytic cells and lymphocytes which are essential in body defense and disease resistance

https://www.youtube.com/watch?v=cCPyWFK0IKs

Lymphatic Vesselsalso called lymphatics

creates a one way system toward the heart picking up fluids along with plasma proteins to maintain sufficient blood volume in the cardiovascular system

accumulated fluid in the tissues produces edema

impairs tissue cells from making exchanges with interstitial fluid and the blood

extra fluid consisting primarily of water and some dissolved proteins (lymph)

Duct Systemlymph is transported from the lymphatic vessels and returned to the venous system through large ducts

right lymphatic duct: drains lymph from the right arm, the right side of the head and thorax

thoracic duct: receives lymph from the rest of the body

both ducts empty into the subclavian vein on their own side of the body

Lymph Nodesproteins, debris, bacteria, and viruses are normally prevented from entering blood capillaries

they do however, enter the lymphatic capillaries easily

especially in inflamed areas

the lymphatic vessels can transport these particles throughout the body

to prevent that, there are lymph nodes that clean the debris and examine it with cells from the immune system

Lymph Nodesclosely related to the immune system

help protect the body by removing bacteria and tumor cells from the lymphatic stream by producing lymphocytes (type of white blood cell)

lymphocytes function in the immune response

thousands of lymph nodes located along the track toward the heart

within the lymph nodes are macrophages which engulf and destroy bacteria, viruses and other foreign substances

swelling of lymph nodes during active infection is a result of the trapping function of the nodes

Node Structurevary in shape and size, most are kidney shaped and 2.5 cm long

each node is surrounded by a fibrous capsule which trabecular extend inward from, dividing the node into smaller compartments

lymphocytes arise from red bone marrow then migrate to the lymphatic organs

the outer part of the node is called the cortex and contains collections of lymphocytes called follicles

follicles have dark staining centers called germinal centers which enlarge when certain lymphocytes (B cells) are creating plasma cells (release antibodies)

the remainder of the cortical cells are lymphocytes in transit (T cells) which surveil the blood, lymph nodes and lymphatic stream

Node Structurecentral medulla of the lymph node houses phagocytic macrophages

lymph enters the convex side of a lymph node through afferent lymphatic vessels and flows through a number of sinuses and exits the lymph node at the indented region (hilus) via efferent lymphatic vessels

there are more afferent vessels than efferent making the flow of lymph very slow allowing time for lymphocytes and macrophages to perform protective functions

generally, lymph flows through several nodes before its “cleaning” process if complete

Lymphoid Organsincludes bits of lymphatic tissue scattered in epithelial and connective tissues

spleen: filters bacteria, viruses, and other debris from the blood; destroys worn out red blood cells and returns some of the by products to the liver (iron), produces lymphocytes in adults

thymus gland: produces hormones that function in programming of certain lymphocytes, enabling them to carry out their role in the body

tonsils: trap and remove bacteria or foreign pathogens entering the throat (mucosa-associated lymphatic tissue, MALT)

Peyer’s patches: resemble tonsils but are located in the wall of the small intestine, capture and destroy bacteria before they make their way through the intestinal wall (MALT)

Body Defensestwo types of body defenses

non-specific defense mechanisms

specific defense mechanisms (immune system)

Immune Systemworks against particular foreign substances

considered to be a functional system (not an organ system) because the structures are a variety of molecules and immune cells

inhabit lymphatic tissues and circulate in body fluids

immune cells: lymphocytes and macrophages

https://www.youtube.com/watch?v=zQGOcOUBi6s

Immune Systemworks both directly via cell attack and indirectly by releasing mobilizing chemicals and antibody molecules

must first encounter a foreign substance (antigen) before it can protect against it whereas the nonspecific defenses are always prepared to defend the body

the response of the system is called the “immune response”

Immune System

three important aspects of the immune response:

antigen specific: recognizes and acts against particular pathogens and foreign substances

systemic: immunity is not restricted to the initial infection site

has memory: recognizes and mounts even stronger attacks on previously encountered pathogens

Immune Systemtwo types of immunity

Hymoral immunity (antibody mediated immunity) provided when antibodies are present in the body’s fluids

cellular immunity (cell mediated immunity) where the protective factor is living cells (lymphocytes)

Antigens

any substance capable of exciting our immune system and provoking an immune response

usually large, complex molecules not normally present in the body

Self Antigensour cells have their own variety of protein molecules (self-antigens)

the immune system recognizes these as being part of the self and they do not trigger a response

explains why tissues (transplants) can be rejected

Immune Cellslymphocytes: originate in red bone marrow and where they mature determines the type of cell they become

T cells are lymphocytes that migrate to the thymus and mature in 2-3 days

B cells are lymphocytes that mature in the bone marrow, little is known about their maturation process

macrophages: arise in the bone marrow, act as antigen presenters because they present fragments of the antigens to be recognized by T cells

Vaccinesartificially acquired immunity

can be dead pathogens or an injection of immune serum

two benefits of vaccines:

we are spared the signs and symptoms of the disease that would otherwise occur

the weakened antigens are able to stimulate the body’s immunological memory

vaccines have virtually wiped out diseases like pneumonia, smallpox, polio, tetanus, diphtheria, measles and others

however, some of these diseases are becoming more prevalent because individuals are choosing not to vaccinate their children

Films

Bill Nye Saves the World: Do Some Shots, Save the World - available on Netflix

Explained: Pandemics - available on Netflix