Lymphatic System

What is the Lymphatic system?

* Collection of cells and biochemicals that travel in lymphatic vessels
* Contains a network of vessels that assist in circulation fluids
* Closely associated with cardiovascular system

3 functions of the lymphatic system

1. transports excess interstitial fluid away from the interstitial spaces, and returns it to the bloodstream
2. absorbs lipids from digestive system and transport them to the blood stream (performed by lymphatic capillaries called Lacteals)
3. defends body against disease → allows humans to live in world with other organisms

What does the term, “Immune System,” mean?

many cells of the lymphatic system provide both defense against disease and permanent immunity against future infections

What is the lymphatic pathway?

Lymphatic capillaries → Afferent lymphatic vessels → Lymph node → Efferent lymphatic vessels → Lymphatic trunk → Collecting ducts → Subclavian vein in Thorax

How would you describe lymphatic capillaries?

* microscopic, closed ended tubes
* thin walled composed of simple squamous epithelium
* parallel blood capillaries throughout body
* when tissue (interstitial) fluid enters capillaries → now called lymph
* merge into lymphatic vessels

How would you describe lymphatic vessels?

* walls are similar to veins but thinner
* composed of 3 layers
* contains semilunar valves (one way flow of fluids)

What are lymphatic vessels composed of?

* 3 layers
* inner layer = an endothelial lining
* middle layer = smooth muscle and elastic fibers
* outer later = connective tissue

What happens when fluid accumulates in the tissues?

interstitial pressure increases, pushing the flaps inward, opening the gaps between cells, allowing fluid to flow in

What happens when pressure inside capillaries increase?

the endothelial cells are pressed outward, closing the gaps, preventing backflow

How would you describe lymphatic trunks?

* Drain lymph from lymphatic vessels
* Named for regions they serve
* Lumbar
* Intestinal
* Intercostal
* Bronchomediastinal
* Subclavin
* Jugular
* Drain into lymphatic collecting ducts

How would you describe lymphatic collecting ducts?

* Drain lymph from trunks
* 2 for entire lymphatic system:
* Thoracic duct
* Right lymphatic duct

What is the Thoracic duct?

* Longer and wider of the 2 ducts
* drains majority of body
* begins as sac called cisterna chyli, empties into left Subclavian vein

What is the Right lymphatic duct?

* Much smaller than Thoracic duct
* Begins in left thorax, empties into right Subclavian vein
* Drains upper left potion of body

What is lymph?

* Tissue fluid that has entered a lymphatic capillary


* Formation depends on tissue fluid formation

What is tissue fluid formation?

* Capillary blood pressure filters water and small molecules from the plasma into the tissue spaces

What is tissue fluid?

* Has about same composition as blood plasma
* contains water and dissolved nutrients, gases, and hormones
* Tissue fluid DOESN’T contain large plasma protein
* Tissue fluid = blood plasma - plasma proteins

Why does plasma proteins remain in the plasma?

To maintain osmotic pressure necessary to draw fluid bak into blood capillaries

How is a lymph formed?

* Filtration from the plasma normally exceeds reabsorption, leading to formation of tissue fluid
* this increases the tissue fluid hydrostatic pressure within interstitial spaces, forcing fluid into lymphatic capillaries, forming a lymph
* This process prevents accumulation of excess tissue fluid (edema)

What are examples of edema?

* women has axillary lymph nodes removed during breast cancer surgery, lymphatic drainage is obstructed form upper limb, resulting in edema
* on feet for long periods of time
* standing and hands down

What mechanisms encourage good lymph flow?

* Contraction of skeletal muscle → compresses lymphatic vessels, moving the lymph
* Respiratory process → creates low pressure in thorax and high pressure in abdomen during inspiration; sends lymph from abdomen to thorax
* Smooth muscle in the larger lymphatic vessels → contracts to aid in flow of lymph
* Valves in lymphatic vessels preven backflow

When is Lymphatic flow highest?

During physical exercise because contracting muscles, breathing harder, and drawing in more negative pressure

What is the roles of lymphatic capillaries during lymph formation?

* Absorption of dietary fats in small intestine and delivery to bloodstream
* Return of small proteins filtered by blood capillaries to bloodstream
* Collection of excess interstitial fluid
* Delivery of foreign particles to the lymph nodes
* Flap-like valves between cels of lymphatic capillaries allow easy entry of tissue fluid

What types of cells do lymphatic tissue contain?

* Lymphocytes
* Macrophages

What is Mucosa-associated lymphoid tissue (MALT)?

* Unencapsulated lymphatic tissue of the digestive, respiratory, urinary, and reproductive tracts
* Tonsils and appendix are composed of lymphatic nodules (compact masses of lymphatic tissue)
* Peyer’s patches are aggregates of lymphatic nodules found in ileum (distal part of small intestine)

What are lymphatic organs?

* Consist of encapsulated lymphatic tissue
* Lymph nodes, thymus, and spleen

What are lymph nodes?

* usually bean shaped
* located along lymphatic vessels
* Filters pathogens from lymph
* contains lymphocytes to attack viruses, bacteria, and parasitic cells
* contains macrophages to engulf and destroy foreign substances, damages cells, and cellular debris
* found in groups or chains along the paths of larger lymphatic vessels

What are major locations of lymph nodes?

* Cervical region
* Axillary region
* Supratrochlear region (superior to trochlear→ ulna)
* Inguinal region
* Pelvic cavity
* Abdominal cavity
* Thoracic cavity
* NOT found in central nervous system

What are the 2 primary functions of lymph nodes?

1. Filter potentially harmful particles form the lymph


1. Immune surveillance: Monitors body fluids via macrophages and lymphocytes

What do Lymphocytes do?

Attack various pathogens in lymph nodes

What do Macrophages do?

Engulf and digest foreign substances, damaged cells, debris

What is the thymus?

* Soft, bilobed gland
* In mediastinum
* Divided into lobules
* Contain lymphocytes derived from progenitor cells in red bone marrow
* Most cells are inactive → thymocytes
* Some cells mature into functional T lymphocytes (T Cells) → then leave thymus and provide immunity
* Large in infancy and early childhood → shrinks at puberty and small in an adult

What is Thymosins?

Hormones produced in thymus; stimulates T cell maturation

What happens to the thymus when you get older?

Tissue is replaced by adipose and other connective tissues

What is the spleen?

* Located in the upper left part of abdominal cavity
* Resembles large lymph node
* Contains venous sinuses filled with blood
* Filters blood, like lymph nodes filter lymph
* Break down worn-out red blood cells

What is the largest lymphatic organ?

The spleen

What 2 tissue types does the spleen contain?

* White pulp → Lymphocytes
* Red pulp → Red blood cells, lymphocytes, and macrophages

Where is the lymph nodes located?

In groups or chains along the paths of larger lymphatic vessels

Where is the thymus located?

In the mediastinum posterior to the upper portion of the body of the sternum

Where is the spleen located?

In the upper left potion of the abdominal cavity, inferior to the diaphragm and posterior and lateral to the stomach

What is the basic function of the Lymph nodes?

* Filter foreign particles and debris from lymph
* House lymphocytes that destroy foreign particles in lymph
* House macrophage that engulf and destroy foreign particles and cellular debris carried in lymph

What is the basic function of the Thymus?

* Houses lymphocytes; differentiates thymocytes into T lymphocytes

What is the basic function of the Spleen?

* Houses macrophages that remove foreign particles, damages red blood cells, and cellular debris from the blood
* Contains lymphocytes

Lymphatic system:

* Bodies defense against infection by pathogens
* disease-causing agents, such as bacteria, viruses, complex microorganisms like protozoa, and spores of multicellular organisms like fungi

What is Immunity?

Ability of body to prevent pathogen entry or destroy any pathogen that enter the body

What are the immune mechanisms?

1. Innate (nonspecific) defense:


1. General defense
2. Protect against many types of pathogens
2. Adaptive (specific) defense:


1. More specific and precise, targeting specific antigens
2. Carried out by lymphocytes (t cells and b cells) that recognize certain foreign molecules

Innate defenses: Species resistance

* Certain species are resistant to diseases that affect other species
* Certain species lack receptors, temperature, or chemical environment for a particular pathogen

Innate Defense: Mechanical barriers

* Skin and mucus membranes form mechanical barriers
* Prevent entrance of pathogens
* Considered the first line of defense

Examples of Innate Defense mechanical barriers

* As epidermis sloughs off, removes superficial bacteria
* Ciliated epithelium in respiratory tract traps and sweeps away pathogens
* Hair traps pathogens
* Tears, saliva, and urine wash away microorganisms

What is Inflammation?

* Produces local redness, swelling, head, and pain
* Process that walls off infection site and inhibits spread of infection

What is the redness in inflammation due to?

Due to vasodilations

What is the swelling in inflammation due to?

Increased capillary permeability and fluid entry into tissue spaces

What is the heat in inflammation due to?

Derived from blood arriving from deep areas of body

What is the pain in inflammation due to?

Due to stimulation of pain receptors

What happens to the cells that are lost during the inflammation process?

They are replaced by cell division

What results from white blood cells invading the region during inflammation?

Pus may form as white blood cells, bacterial cells, and cellular debris accumulate

What results from tissue fluids contains clotting factors seep into the areas during inflammation?

A clot containing threats of fibrin may form

What results from fibroblasts arriving during inflammation?

A connective tissue sac may form around the injured tissues

What results from phagocytes being active during inflammation?

Bacteria, dead cells, and other debris are removed

What results from cells dividing during inflammation?

Newly formed cells replace injured ones

Innate defenses: Chemical Barriors

1. Enzymes
2. Interferons
3. Defensins
4. Collectins
5. Complement

What does the chemical barrier “enzymes” do?

* In body fluids provide a chemical barrier to pathogens
* Degrade Messenger RNA
* Examples: Pepsin in gastric juice and lysozyme in tears destroy microorganisms

What does the chemical barrier “interferons” do?

* Block viral replication
* Act against growth of tumors
* Stimulate phagocytosis
* Apart of all cancer treatments
* Goes to other cells and tells about the virus so that they can prepare for it

What does the chemical barrier “defensins” do?

* Are peptides produced by neutrophils and other granulocytes; they cripple microbes, by making openings in cell membranes or walls

What does the chemical barrier “collectins” do?

* Are proteins that protect against many bacteria, yeast, and some viruses

What does the chemical barrier “Complement” do?

* a group of proteins in plasma and other body fluids that stimulates inflammation, attracts phagocytes, and enhances phagocytosis

What is the Innate Defenses natural killer cells?

* Small population of lymphocytes
* Very different from B cells and T cells that provide adaptive defenses
* Defend against viruses and cancer cells by secreting cytolytic substances called perforins that lyse cell membrane
* Enhance inflammation

What is the Innate Defenses Phagocytosis?

* Removes foreign particles from lymph
* phagocytes in the blood vessels and the tissues of the spleen, liver, or bone marrow remove particles from blood

What is chemotaxis?

Chemicals from damaged tissue attract these phagocytic cells to the injury

What do Monocytes do?

Leave the blood to become macrophages which can be free or fixed in tissues

What is the Mononuclear phagocytic system?

Consists of monocytes and macrophages of the body

What are the most active phagocytic cells?

Neutrophils and Monocytes (white blood cells)

Innate Defense: Fever

* Begins when a viral or bacterial infection stimulates lymphocytes to proliferate, producing cells that secrete a substance called interleukin-1 which raises thermoregulatory set point

What does elevated body temp indicate?

* Microbial growth; cause liver and spleen to take up iron, making it unavailable for bacteria and fungi to use in their normal metabolism
* High Temp also increases phagocytic activity

What is Interleukin-1 also called?

Endogenous pyrogen (fire maker from within)

What are 1st line of defense?

Mechanical barriers

What are the 2nd line of defense?

* Inflammation
* Chemical barriers
* Natural killer cells
* Phagocytosis
* Fever

Characteristics of adaptive (specific) defense

* third line of defense
* is resistance to particular pathogens or to their toxin or metabolic by-products → keeps pathogen out
* Antigens
* Carried out by lymphocytes and macrophages that can recognize specific antigens

What is an antigen?

Non-self molecules that can evoke an immune response; receptors on the surface of lymphocytes enable the cells to recognizes non-self antigens

What are the 2 types of adaptive defenses?

1. Cellular


1. Humoral

What is the cellular immune response?

Performed by immune cells (t cells)

What is the humoral immune response?

Performed by antibodies (formed by b cells)

What is the line of defenses against pathogen:

Pathogen begins to enter body → First line of defense (mechanical barrier, skin and mucous membranes) → pathogen enters body → 2nd (chemical barriers, natural killer cells, inflammation, phagocytosis, and fever) and 3rd (cellular and humoral immune response) line of defense

What does the Lymphatic system respond to in accordance with antigens?

Lymphatic system responses to non-self antigens, but not self antigens (under normal circumstances)

* Antibodies may be:
* Proteins
* Polysaccharides
* Glycoproteins
* Glycolipids

What are he most effective antigens?

Large and complex molecules

What are haptens?

Small molecules that are not antigenic by themselves, but when they combine with a large molecule in the body, they can evoke an immune response

Where are lymphocytes produced?

* Produced throughout life
* Starting during fetal development
* Red bone marrow releases unspecialized lymphocyte precursors into blood

Where do the Lymphocytes settle?

* Half of these settle in thymus, specialize, and are then released (become T cells)
* Other half differentiate in red bone marrow, and are then released (become B cells)

What are the 2 main types of lymphocytes

* T lymphocytes
* B lymphocytes

What do T lymphocytes do?

* Specialized in thymus
* After released from thymus, make up 70-80% of circulating lymphocytes
* Some settle in lymphatic organs (lymph nodes, thoracic duct, white pulp of spleen)

What do B lymphocytes do?

* After release from bone marrow, make up 20-30% of lymphocytes in blood
* Abundant in lymph nodes, spleen, bone marrow, intentional lining

What is the first step of the lymphocyte origin?

Stem cells in red bone marrow give rise to lymphocyte precursors

What is the second step of the lymphocyte origin?

Some lymphocyte precursors are processed in the thymus to become T cells

What is the third step of the lymphocyte origin?

Some lymphocytes precursors are processed within the bone marrow to become B cells

What is the fourth step of the lymphocyte origin?

Both T cells and B cells are transported through h the blood to lymphatic organs, such as the lymph nodes and spleen

Origin of undifferentiated cells

T cells = red bone marrow

B cells = red bone marrow

Site of differentiation

T cells = thymus

B cells = red bone marrow

Primary location of T cells

Lymphatic tissues, 70 to 80% of the circulating lymphocytes in blood

Primary location of B cells

Lymphatic tissues, 20 to 30% of the circulating lymphocytes in blood

Primary functions of T cells

Provide cellular immune response in which T cells interact directly with the antigens or antigen-bearing agents, to destroy them

Primary functions of B cells

Provide humoral immune response in which B cells interact indirectly, producing antibodies that destroy the antigens or antigen-bearing agents