They Lymphatic System & Body Defenses Human Anatomy & Physiology Unit 6

Lymphatic Vessels The function of lymphatic vessels is to pick up the excess tissue fluid (called lymph = clear water) and return it to the blood stream These vessels form a one-way system and only flow towards the heart Lymph capillaries spider web through the body tissues to collected leaked fluid

Lymphatic Vessels Like veins, lymphatic vessels have valves to prevent the fluid from flowing backwards While, blood stays relatively free of bacteria, viruses and cancer – they can easily enter the lymphatic vessels This creates a problem because bacteria, viruses and cancer can then easily travel to other parts of the body To solve this lymph nodes are throughout the body to “examine” and cleanse (if needed) by the immune system

Lymph Nodes They work along with the immune system to protect the body As the lymph is transported to the heart it makes several stops through lymph nodes to be “checked” before it reaches the heart A collection of lymphocytes are located in lymph nodes to respond if a foreign substance is detected This is why most of us will get swollen glands during an active infection

Lymph Nodes Most lymph nodes are kidney shaped and less than one inch long There are two regions of lymph nodes in the body the right lymphatic duct and the thoracic duct The neck and head drain into the right duct and the rest of the body goes through the thoracic duct (within these regions are thousands of lymph nodes)

Other Lymphoid Organs Spleen – helps to filter the blood and destroy worn- out red blood cells to they can be reabsorbed by the liver The thymus gland – functions at peak performance during youth; produces thymosin a hormone to create certain lymphocytes to heighten their protective roles Tonsils – their job is to trap foreign pathogens before they enter the body

Body Defenses Every second of everyday hostile bacteria, viruses and fungi are trying to invade our system There are two approaches to body defenses: nonspecific and specific defense system

Nonspecific Defense System This system responds immediately to ALL foreign substances First line of defense is the skin, mucous membranes and secretions of the skin The second line is phagocytic cells, antimicrobial proteins and an inflammatory response

Nonspecific Body Defenses Examples of Surface Membrane Barriers: Skin is a physical barrier Mucous membranes line all body cavities to act as a physical barrier Vaginal secretions of adult females are very acidic The stomach produces HCl to kill pathogens Saliva can kill some pathogens Tiny hairs in the nasal cavity trap inhaled

Nonspecific Body Defenses Examples of Cells and Chemical Defenses: A fever will help increase the rate at which defense cells work Phagocytes will engulf a foreign particle Natural killer cells will target any foreign particle and attack the cell's membrane (the cell will then shortly disintegrate) Inflammatory response will trigger redness, heat, swelling and pain The redness and heat is caused by the increase of blood to the site, the swelling and pain is caused by the body’s attempt to prevent movement and promote healing

Specific Defense System This is commonly called the immune system The most important immune cells are they lymphocytes and macrophages A proper working immune system will protect the body from bacteria, viruses, transplanted organ or blood and even our own cells that have turned against us

Specific Body Defenses The two main types of immune cells are B- cells and t-cells Within the B-cell family and T-cell family there are several types and each have their own job Memory B-cells Memory T-cells Helper T-cells Plasma cells Suppressor T-cell

Specific Body Defenses Active immunity can occur two ways naturally or artificially through immunizations The immune system has the ability to “remember” some diseases Passive immunity occurs when the protection is “borrowed” For example, a mother to fetus or through breast milk (the immune system does not “remember” using passive immunity)

Disorders of Immunity Allergies The body fights off a perceived threat that would otherwise be harmless (basically, the immune system overreacts) Allergies are rarely fatal; however, when the reaction enters the blood stream it circulates rapidly through the body This is call anaphylactic shock and can be fatal

Disorders of Immunity Immunodeficiency (both congenital and acquired) Basically, there is little to no immune response Severe combined immunodeficiency disease (SCID) – congenital Acquired immune deficiency syndrome (AIDS)

Disorders of Immunity Autoimmune Diseases Multiple sclerosis (MS) Myasthenia gravis Graves’ disease Type 1 diabetes mellitus Systemic lupus erythematosus (commonly called lupus) Rheumatoid arthritis