lymphatic system

Lymphatic System

Network of organs and vein-like vessels that recover fluid, inspect it for disease agents, activate immune responses and return fluid back to the blood.

Where does the lymphatic system get the fluid?

Interstitial Space between cells. This is the fluid that wasn't reabsorbed by blood capillaries.

Lymphatic system has two uses:

1. Immunity
-Excess filtered fluid picks up foreign cells and chemicals from tissues. Passes through lymph nodes where immune cells are.

2. Lipid absorption
- Don't worry about this one as much

What is Lymph?

A clear, colorless fluid, similar to plasma but much less protein

What is the path of Lymph?

1. Interstitial Space
2. Lymphatic Capillaries
3. Lymphatic Vessels
4. Lymph Trunks
5. Collecting Ducts
6. Subclavian Veins

What are the three layers of Larger Lymphatic Vessels?

Tunica Interna: Endothelium

Tunica Media: Elastic Fibers, smooth muscle

Tunica Externa: Thin outer layer

What are the two collecting ducts?

Right Lymphatic Duct and the Thoracic Duct

Where does the Right lymphatic Duct receive from? Where does it empty?

Right arm, right side of head and right side of chest.

It empties in the Right Subclavian Vein

Where does the Thoracic Duct start? What is the name of the sac? Where does it receive from and empty?

The Thoracic Duct starts in the abdomen, and begins as a prominent sac called the cisterna chyli.

The Thoracic Duct receives from everywhere else in the body.

It empties into the Left Subclavian Vein.

Flow of Lymph

Lymph flows under similar forces to blood, at a much slower speed and pressure.

Lymph moves along RYTHMIC CONTRACTIONS of lymphatic vessels.

Others include skeletal muscle pump, arterial pulsation, thoracic pump.

Subclavian Veins and Lymph Return

The fast flowing blood in the Subclavian Veins draws the Lymph into it.

Lymphatic Cells include

Natural Killer Cells
T Lymphocytes
B Lymphocytes
Macrophages
Dendritic Cells
Reticular Cells

Describe Natural Killer cells

Large lymphocytes that attack and destroy practically anything foreign it encounters (bacteria, infected/cancerous host cells)

Where do T Lymphocytes mature?

Thymus

What do B lymphocytes produce and where do they mature?

They produce antibodies.
Mature in Bone marrow.

Describe Macrophages

Large, phagocytic cells that develop from Monocytes. Display antigenic fragments alerting immune system of presence of an enemy.

MACROPHAGES ARE APCs (Antigen-presenting cells)

Dendritic cells:

Branched, mobile APCs found in the epidermis, mucous membranes, and lymphatic organs; Alert immune system to pathogens that have breached their surface

Reticular cells

produce stroma that supports other cells in lymphoid organs

Lymphatic Tissue and Diffuse Lymphatic Tissue

Lymphoid (Lymphatic) Tissue
- Aggregations of lymphocytes in mucous membranes

Diffuse Lymphatic Tissue
- Lymphocytes are scattered
- Found in body passages that are open to exterior
- MALT (Mucosa-associated lymphatic tissue)

What are lymphatic nodules?

Dense masses of lymphocytes and macrophages that congregate in response to pathogens

This is a CONSTANT feature of lymph nodes, tonsils and appendix.

Lymphatic organs must have what?

They MUST have a connective tissue capsule

What are the primary lymphatic organs? What happens to T and B cells here?

Red bone marrow and Thymus

T and B cells become IMMUNOCOMPOTENT

What are the secondary lymphatic organs?

Lymph nodes, tonsils, and spleen

IMMUNOCOMPETENT cells populate these tissues.

Thymus' Fibrous capsule creates \______ on the surface?

Trabeculae (septa) that divide the gland into several lobes

Reticular epithelial cells seal off cortex from medulla forming \__________?

Blood-thymus barrier

Medulla and Cortex

Medulla in Thymus has contact with the blood.

Cortex houses non-immunocompetent T lymphocytes.

Lymphocytes can cross blood-thymus barrier once they become immunocompetent.

What is the concave structure called on a Lymph Node?

Hilum

Lymph Nodes

Bean-shaped filters that cluster along the lymphatic vessels of the body. They function as a cleanser of lymph as wells as a site of T and B cell activation. It is enclosed in a fibrous sac.

Several \________ lymphatic vessels lead into the node at the convex surface.

Afferent (access to node)

Lymph leaves the node through \_______ lymphatic vessels that leave at the hilum

Efferent (Exit)

Lymphadenitis/Lymphadenopathy

inflammation of the lymph glands/nodes

What is Metastatis?

-When cancer cells separate from a tumor, travel to other sites in the body, and establish new tumors.

- Lodge in nodes, multiply and destroy the lymph node.

Three main sets of tonsils:

1. Palatine tonsils
- Pair at posterior of oral cavity

2. Lingual tonsils
- Pair at root of tongue

3. Pharyngeal tonsil(adenoids)
- Single one at wall of nasopharynx

Spleen

the largest lymphatic organ in the body

Red pulp: Sinuses filled with RBC

White pulp: lymphocytes, macrophages surrounding small branches of splenic artery

Spleen Functions (Pulps)

GRAVEYARD
- White pulp monitors blood for foreign antigens, keeps monocytes at the ready

Three Lines of Defense

1. Skin and mucous membranes

2. Several nonspecific defense mechanisms (Leukocytes and macrophages, antimicrobial proteins, NK cells, inflammation and fever)

3. The Immune system (memory)

Specific and Adaptive Immunity

Body must develop separate immunity to each new pathogen present

External Barriers (Skin and Mucous Membranes)

SKIN
Microorganisms physically cannot enter the body
- Acid Mantle: Sweat and sebum that prevent growth
- Dermicidin, defensin, cathelicidins: Prevent bacterial growth

MUCOUS MEMBRANE
Tracts that are open to the exterior
- LYSOZYME: enxyme destroys bacterial cell walls

Five types of Neutrophils?

Neutrophils, Eosinophils, Basophils, Monocytes, Lymphocytes

What is a phagocyte?

A cell that engulfs foreign matter

How and what do neutrophils kill?

Neutrophils are Anti-Bacterial

They use phagocytosis and digestion, and can also degranulate to create a killing zone of chemicals

How and what do eosinophils kill?

Eosinophils guard against parasites and allergens

The "call over" basophils and mast cells, and they PHAGOCYTIZE antigen-antibody complexes.

They limit action of histamine (reduces inflammation)

What do basophils do? What do Mast cells do?

Secrete chemicals that aid mobility and attract other leukocytes. MAST CELLS SECRETE THE SAME.

- Leukotrienes - activates neutrophils and eosinophils

- Histamine - Vasodilator, increase blood flow

- Heparin - inhibits clots

What are the three types of lymphocytes listed by abundance?

1. T lymphocytes
2. B lymphocytes
3. Natural Killer cells (NK)

What is a macrophage?

A macrophage is a monocyte that leaves the blood and moves into the tissue.

2 Types:
- Wandering: Actively seek pathogens

- Fixed: Phagocytize when pathogens come to them
Microglia - Brain macrophages
Alveolar - Lung macrophages
Hepatic - Liver macrophages

Two types of Antimicrobial Proteins?

Interferons and Complement system

Interferons

Secreted by cells infected by viruses
- These alert surrounding cells to protect themselves
- These proteins bind to the surrounding cells receptors

Interferons can also activate NK cells and macrophages

Four Steps of Natural Killer Cells killing a cell/bacteria/cancer?

1. NK releases perforins, forming a hole in plasma membrane
2. Granzymes enter hole and degrade enemy cell enzymes
3. Enemy cell dies
4. Macrophage engulfs dead cell

What are fever and inflammation?

Fever - Abnormal elevation of body temperature
Inflammation - Local response to tissue injury

List the three general purposes of inflammation and the four cardinal signs:

PURPOSES:
1. Limits spread of pathogen
2. Removes debris from tissue
3. Initiates repair

CARDINAL SIGNS
1. Redness
2. Swelling
3. Heat
4. Pain

What is a chemotaxi?

Attraction to leukotriene and bradykinin to guide neutrohphils to the injury site

Tissue Cleanup and Repair

- Role of monocytes/macrophages
- Edema (compresses veins, limits venous drainage)
- Secretion of growth factors stimulate fibroblast growth

Two characteristics that distinguish immunity from nonspecific resistance?

Specificity: Immunity is for specific pathogen
Memory: Body reacts quickly when reexposed

Two types of Immunity:

Cellular (cell-mediated) immunity
- Lymphocytes directly attack other cells

Humoral (antibody-mediated) immunity
- Mediated by antibodies that don't directly destroy pathogen, but tag it for destruction

List the four ways someone can receive immunity:

1. Natural Active
- Production of one's antibodies as result from infection
2. Artificial Active
- Production of antibodies as result from vaccination
3. Natural Passive
- Antibodies passed from another person (mother --\> baby)
4. Artificial Passive
- Antibodies from injection of immune serum

What two ways someone can receive immunity are permanent? Temporary?

Natural Active and Artificial Active are PERMANENT
Natural Passive and Artificial Passive are TEMPORARY

What is an antigen? What is an epitope?

Antigen - any molecule that triggers an immune response

Epitopes - Region of an antigen that stim immune response

List the four types of T cells:

Cytotoxic (Tc)
Helper (Th)
Regulatory (T-regs)
Memory (Tm)

Three Stages of Life for T cells?

1. Born in Bone Marrow
2. Educated in thymus
3. Deployed to perform function

Two ways T cells can be killed if they recognize self antigens?

Clonal Deletion - T cell dies and gets phagocytized
Anergy - T cell is alive but unresponsive

B cells develop and mature in the:

The Bone

B cells also undergo clonal deletion and anergy

Do T cells require antigen presenting cells?

YES, T cells cannot recognize foreign antigens on their own

List the three types of APCs

B cells, Macrophages, and Dendritic cells

What does function of APCs depend on?

MAJOR HISTOCOMPATIBILITY COMPLEX PROTEINS
- Acts as a cell "identification tag" unique to each person
- THIS IS CALLED MHC-1

Antigen Processing

-APC encounters antigen
-Internalizes it by endocytosis
-Digests it into molecular fragments
-Displays relevant fragments (epitopes) in the grooves of the MHC protein
-Wandering T cells inspect APCs for displayed antigens
-If APC only displays a self-antigen, the T cell disregards it
-If APC displays a nonself-antigen, the T cell initiates an immune attack

Difference between MHC-I and MHC-II

MHC-I are constantly produced by nucleated cells
- If they are self-antigens, no T cell response
- If they are viral antigens, T cell response

MHC-II (human leukocyte antigens)
- Only occur on APCs and display foreign antigens ONLY

What T lymphocytes can respond to which MHC proteins?

Cytotoxic cells (Tc) can ONLY respond to MHC-I
Helper cells (Th) can ONLY respond to MHC-II

T-cell activation requires \________.

1. A MCH protein displaying an epitope it is programmed to target.

2. COSTIMULATION
- Basically a check method to make sure the T cell has the correct foreign cell (usually a protein binding)

What does successful costimulation cause?

CLONAL SELECTION (replication)
- The specific T cell will undergo mitosis, creating identical cells
- Some become EFFECTOR (actively attacking) cells and others become MEMORY cells

Cytotoxic T cell Attack

Once Tc cells find a foreign antigen in a MHC-I PROTEIN, it "docks" to the cell and destroys it. (Perforins and Granzymes)

3 effects of interleukins secreted by T cells when it recognizes the antigen -MHCP complex (Foreign!!!!!!)

1. Attract Neutrophils
2. Attract Macrophages and stimulate phagocytosis
3. Stimulate T and B cell mitosis

Memory

Occurs after primary response in cellular immunity
- Upon reexposure, the immune response is much faster

Humoral Immunity

B lymphocytes produce antibodies, which are HIGHLY SPECIFIC and bind to antigens to tag them for destruction.

3 stages of Humoral immunity:

1. Recognition
2. Attack
3. Memory

Recognition

Immunocompetent B cell has thousand of surface receptors
Activation begins when B cell takes in antigens by receptor-mediated endocytosis

B cell processes antigen and DISPLAYS THE EPITOPE ON ITS MHC-II PROTEIN

Humoral Response

1. Antigen recognition - Immunocompetent B cells exposed to antigens

2. Antigen Presentation - B cell digests antigen and displays epitope.

3. Clonal Selection - Interleukin stims B cell mitosis and division

4. Differentiation - Some of the cells become memory cells, most become PLASMA cells

5. Attack - Plasma cells and secrete antibodies

Antibody structure

Two HEAVY CHAINS, Two LIGHT CHAINS (half as long)

VARIABLE REGION in all four chains
- Gives Antibody its uniqueness

Antigen-binding site
- Attaches to the epitope of an antigen molecule

CONSTANT REGION
- Determines mechanism of antibody (unique to each person)

Actions of the Five Classes

1. Neutralizing Antigen
- Binding neutralizing toxins and prevents virus from attaching to host cells

2. Immobilizing Bacteria
- Cause Bacteria to lost mobility

3. Agglutinating and Precipitating Antigen
- Two antigen binding sites, causing agglutination
- Phagocytes ingest agglutinated microbes

4. Activating Complement
- Antigen - Antibody complexes activate complement proteins

5. Enhancing Phagocytosis
- Once antigens have bound to antibody, attracts phagocytes