Lymphatic & Immune System

Lymph: Definition (1) Lymph is excess tissue fluid contained in lymphatic vessels Consists of (mostly) water and plasma proteins that have leaked out of the capillaries

Semi-independent parts of the lymphatic system (1) 1.Meandering network of lymphatic vessels 2.Lymphoid tissues and organs scattered throughout the body

Functions of the lymphatic system (2) 1.Lymphatic vessels return interstitial fluid and leaked plasma proteins back to the blood 2.Lymphatic capillaries (lacteals) absorb fats/fat soluble vitamins at intestinal villi and transport to the blood 3.The lymphatic system helps defend the body against disease

Lymphatic vessels: 3 types (3) 1.Blind-ended capillaries 2.Lymphatic collecting vessels 3.Trunks and ducts

Blind-ended Capillaries Specially adapted: 1.Highly permeable 2.One-way valves (similar to veins) so lymph only flows towards the heart 3.Valves resist interstitial pressure to remain open 4.Can absorb cell debris, pathogens, cancer cells

Collecting Vessels Similar to veins but have thinner walls and more internal valves Lots of branching networks Anastomose = dividing/branching Anastomose = dividing/branching Travel with the superficial veins in skin Deep vessels travel with arteries Vasa vasorum (vessels of the vessels) supply nutrients to cells

Collecting Vessels Capillaries consist of a single layer of cells and are the only blood vessels that can exchange materials with the interstitial fluid Cells will die if they are not within 1 or 2 cell widths of a capillary The lymphatic system removes excess fluid

Trunks & Ducts Capillaries join to form vessels that merge in the thoracic cavity before entering one of two ducts: Thoracic duct & right lymphatic duct Trunks are formed by joining of the largest collecting ducts and are classified by the regions served Paired lumbar, subclavian, jugular, intestinal Paired lumbar, subclavian, jugular, intestinal

Trunks & Ducts cont’d Lymph is delivered into one of the two large trunks (ducts) 1.Right lymphatic duct 1. Drains right upper arm, the right side of the head and thorax 2.Thoracic duct 1. Drains the rest of the body

Lymph Transportation (4) Every region of the body has extensive lymphatic vessels Structural walls are similar to veins (but are thinner) and contain valves Movement is dependent on muscular contraction (skeletal) – when muscles contract lymph is squeezed past a valve that closes and prevents backwash

Chief lymphatic cells & function (5) T cells and B cells protect the body against antigens T for thymus origin T for thymus origin B for bone origin (red marrow) B for bone origin (red marrow) T lymphocytes (T cells) mature in the thymus (along trachea atop heart) and are “tested” if they react against “self” they die, if they have potential to attack foreign cells they leave the thymus

T cells cont’d Responsible for cell-mediated immunity Depends on actions of several types of T cells Depends on actions of several types of T cells Antibodies are not produced, instead they directly attack foreign cells that carry antigens Antibodies are not produced, instead they directly attack foreign cells that carry antigens Other T cells release proteins to coordinate other actions of the immune response: T cells, B cells and macrophages Other T cells release proteins to coordinate other actions of the immune response: T cells, B cells and macrophages Protects against parasites, bacteria, fungi, cancerous cells – anything “foreign” Protects against parasites, bacteria, fungi, cancerous cells – anything “foreign”

Chief lymphatic cells & function (5) cont’d B lymphocytes (B cells) are responsible for antibody-mediated immunity B cells produce antibodies – proteins that bind with and neutralize specific antigens B cells produce antibodies – proteins that bind with and neutralize specific antigens Growing within the bone marrow B cells develop unique surface receptors that allow them to recognize specific antigens Protects against viruses, bacteria and foreign molecules soluble in blood and lymph Protects against viruses, bacteria and foreign molecules soluble in blood and lymph

Lymph nodes (11) Round bean-shaped structures found at certain points along lymphatic vessels A fibrous capsule divided into nodules containing sinuses (open spaces) filled with macrophages and lymphocytes. Two distinct regions: cortex & medulla As lymph passes through the sinuses in the nodules it is cleansed of infectious organisms and debris

Lymph node

Lymph nodes (11) cont’d Nodules are mainly in the lymph nodes but can also be single or in groups (aggregations) Aggregations are found near the body surface in inguinal (groin), axillary (armpits) and cervical (neck) regions

Function of Lymph Nodes (12) 2 basic functions 1.Filtration – macrophages destroy microorganisms and debris 2.Immune system activation – monitor for antigens and mount attack against them!

Tuberculosis and leukemia can cause the spleen to enlarge

Spleen and its functions (14) Upper left abdominal cavity just beneath the diaphragm (fist-sized) Similar structure to a lymph node: outer connective tissue divides it into sinus- containing lobules BUT in the spleen sinuses are filled with blood NOT lymph Blood reservoir if needed in times of low pressure or extra oxygen is required Blood reservoir if needed in times of low pressure or extra oxygen is required

Spleen and its functions (14) cont’d Spleen lobules contain red pulp and white pulp Red pulp – rbc, lymphocytes and macrophages White pulp – contains only lymphocytes and macrophages Fxns: purify blood that passes through spleen = quality control (removal of damaged rbc and invaders)

Spleen’s 2 main functions (14) Quality control of circulating rbc by removing old damaged ones – cleansed blood stored in red pulp Helps fight infection – white pulp – primarily lymphocytes

Other spleen functions (14) Stores breakdown products of RBCs for later reuse Spleen macrophages salvage and store iron for later use by bone marrow Spleen macrophages salvage and store iron for later use by bone marrow Stores blood platelets

Important! Spleen cleanses the blood Lymph nodes cleanse the lymph Together they keep circulating body fluids relatively free of damaged cells and microorganisms

Thymus and its function (15) Located in lower neck behind sternum, just above the heart Bilobed organ that secretes 2 hormones: 1.Thymosin 2.Thymopoietin These cause certain lymphocytes to mature and become active in body defense

Thymus cont’d (15) Size and activity level vary with age: 1.Largest and most active during childhood 2.Stops growing during adolescence and slowly starts to shrink 3.May disappear entirely in old age – replaced by fibrous fatty tissue

Tonsils and their function (16) Masses of lymphatic tissue near the entrance to the throat Gather and filter microorganisms that enter the throat through air and food Familiar back of throat largest & most often infected = tonsilitis Adenoids (pharyngeal tonsils) lie at the back of the nasal passages – usually shrink by 5 years old & gone by puberty

Enlarged tonsils

Adenoids cont’d Can enlarge and obstruct air passages – causing mouth breathing and nasal voice & snoring Sometimes removed