Lymphatic System Lymphatic System

Lecture #2Lecture #2

Lymph nodesLymph nodes

Round bean-shaped structures found Round bean-shaped structures found at certain points along lymphatic at certain points along lymphatic vesselsvessels

A fibrous capsule divided into nodules A fibrous capsule divided into nodules containing sinuses (open spaces) filled containing sinuses (open spaces) filled with macrophages and lymphocytes.with macrophages and lymphocytes.

Two distinct regions: cortex & medullaTwo distinct regions: cortex & medulla As lymph passes through the sinuses As lymph passes through the sinuses

in the nodules it is cleansed of in the nodules it is cleansed of infectious organisms and debrisinfectious organisms and debris

Lymph nodeLymph node

Function of Lymph NodesFunction of Lymph Nodes

2 basic functions2 basic functions

1.1. Filtration – macrophages destroy Filtration – macrophages destroy microorganisms and debrismicroorganisms and debris

2.2. Immune system activation – Immune system activation – monitor for antigens and mount monitor for antigens and mount attack against them!attack against them!

Thymus and its functionThymus and its function

Located in lower neck behind sternum, Located in lower neck behind sternum, just above the heartjust above the heart

Bilobed organ that secretes 2 Bilobed organ that secretes 2 hormones:hormones:

1.1. Thymosin Thymosin

2.2. ThymopoietinThymopoietin

These cause certain lymphocytes to These cause certain lymphocytes to mature and become active in body mature and become active in body defensedefense

Thymus cont’d Thymus cont’d

Size and activity level vary with Size and activity level vary with age:age:

1.1. Largest and most active during Largest and most active during childhoodchildhood

2.2. Stops growing during adolescence Stops growing during adolescence and slowly starts to shrinkand slowly starts to shrink

3.3. May disappear entirely in old age – May disappear entirely in old age – replaced by fibrous fatty tissuereplaced by fibrous fatty tissue

Spleen and its functionsSpleen and its functions

Upper left abdominal cavity just Upper left abdominal cavity just beneath the diaphragm (fist-sized)beneath the diaphragm (fist-sized)

Similar structure to a lymph node: Similar structure to a lymph node: outer connective tissue divides it into outer connective tissue divides it into sinus-containing lobules BUT in the sinus-containing lobules BUT in the spleen sinuses are filled with blood spleen sinuses are filled with blood NOT lymphNOT lymph– Blood reservoir if needed in times of low Blood reservoir if needed in times of low

pressure or extra oxygen is requiredpressure or extra oxygen is required

Spleen and its functions Spleen and its functions cont’dcont’d

Spleen lobules contain red pulp and Spleen lobules contain red pulp and white pulpwhite pulp

Red pulp – rbc, lymphocytes and Red pulp – rbc, lymphocytes and macrophagesmacrophages

White pulp – contains only White pulp – contains only lymphocytes and macrophageslymphocytes and macrophages

Fxns: purify blood that passes Fxns: purify blood that passes through spleenthrough spleen

Spleen’s 2 main functionsSpleen’s 2 main functions

Quality control of circulating rbc by Quality control of circulating rbc by removing old damaged ones – removing old damaged ones – cleansed blood stored in red pulpcleansed blood stored in red pulp

Helps fight infection – white pulp – Helps fight infection – white pulp – primarily lymphocytesprimarily lymphocytes

Other spleen functionsOther spleen functions

Stores breakdown products of RBCs Stores breakdown products of RBCs for later reusefor later reuse

– Spleen macrophages salvage and store Spleen macrophages salvage and store iron for later use by bone marrowiron for later use by bone marrow

Stores blood plateletsStores blood platelets

Remember This!Remember This!

Spleen cleanses the bloodSpleen cleanses the blood Lymph nodes cleanse the lymphLymph nodes cleanse the lymph Together they keep circulating body Together they keep circulating body

fluids relatively free of damaged cells fluids relatively free of damaged cells and microorganismsand microorganisms

Red Bone MarrowRed Bone Marrow

Origin of all blood cells red & whiteOrigin of all blood cells red & white– Present in skull, sternum, ribs clavicle, Present in skull, sternum, ribs clavicle,

pelvis & spinal column & ends of femur pelvis & spinal column & ends of femur & humerus& humerus

White bc function in immunityWhite bc function in immunity 5 types – 13.4 on page 2555 types – 13.4 on page 255

Chief lymphatic cells & Chief lymphatic cells & functionfunction

T cells and B cells protect the body T cells and B cells protect the body against antigensagainst antigens– T for thymus originT for thymus origin– B for bone origin (red marrow)B for bone origin (red marrow)

T lymphocytes (T cells) mature in the T lymphocytes (T cells) mature in the thymus (along trachea atop heart) thymus (along trachea atop heart) and are “tested” if they react against and are “tested” if they react against “self” they die, if they have potential “self” they die, if they have potential to attack foreign cells they leave the to attack foreign cells they leave the thymusthymus

T cells cont’dT cells cont’d

Responsible for cell-mediated immunityResponsible for cell-mediated immunity– Depends on actions of several types of T cellsDepends on actions of several types of T cells– Antibodies are not produced, instead they Antibodies are not produced, instead they

directly attack foreign cells that carry directly attack foreign cells that carry antigensantigens

– Other T cells release proteins to coordinate Other T cells release proteins to coordinate other actions of the immune response: T cells, other actions of the immune response: T cells, B cells and macrophagesB cells and macrophages

– Protects against parasites, bacteria, fungi, Protects against parasites, bacteria, fungi, cancerous cells – anything “foreign”cancerous cells – anything “foreign”

Chief lymphatic cells & Chief lymphatic cells & function cont’dfunction cont’d

B lymphocytes (B cells) are responsible for B lymphocytes (B cells) are responsible for antibody-mediated immunityantibody-mediated immunity– B cells produce antibodies – proteins that bind B cells produce antibodies – proteins that bind

with and neutralize specific antigenswith and neutralize specific antigens Growing within the bone marrow B cells Growing within the bone marrow B cells

develop unique surface receptors that develop unique surface receptors that allow them to recognize specific antigensallow them to recognize specific antigens– Protects against viruses, bacteria and foreign Protects against viruses, bacteria and foreign

molecules soluble in blood and lymphmolecules soluble in blood and lymph