Non-specific defenses - internal

Phagocytes

Specialised white blood cells that engulf and digest microorganisms and cell debris, eliminates many pathogens before infection takes hold

Phagocytic cells

Monocytes, macrophages, neutrophils, dendritic cells

Monocytes

Leave bloodstream, enter infected/inflamed tissues and differentiate into macrophages

Macrophages

Large phagocytic cells which either move around and seek out microbes/dying cells, or lie in wait

Neutrophils

Granulocytes (leucocyte with granules in cytoplasm and lobular nucleus), most abundant leucocyte, first cell to move into infected/inflamed tissue and phagocytise pathogen, short lifespan (dead neutrophils = pus)

Dendritic cells

Have projections from cytoplasm, phagocytises microbes/dead cells and have the ability to detect, engulf and process foreign particles, can present antigens to T-cells and B-cells

Lymphatic system

Composed of network of lymph capillaries joined to lymph vessels and lymph nodes, located along length of some lymph vessels.

Function - collect some fluid that escapes from blood capillaries and returns it to circulatory system, internal defense against pathogens

Functioning of lymphatic system

Lymph entering lymph nodes contain cell debris, foreign particles and microorganisms. Lymph nodes contain lymphoid tissue, where larger particles (bacteria) trapped in meshwork of fibres as lymph flows through nodes - bacteria is destroyed by macrophages via phagocytosis

When infections occur

Formation of B and T lymophocytes increases and lymph nodes can become swollen/sore

Inflammatory response

response to any damage to the tissues

Inflammatory response purpose

Reduce the spread of any pathogens, destroy and prevent the entry of additional pathogens.

Remove damaged tissue and cell debris

Repair damaged tissues

Four signs of inflammation

redness, swelling, heat, pain

Steps of inflammatory response 1

Mechanical damage/local chemical changes cause specified leucocytes (mast cells) to be activated by complement proteins - release of histamine, heparin etc. into tissue fluid

Steps of inflammatory response 2

Histamine increases blood flow through the area through vasodilation, making capillary walls more permeable. More fluid moves through capillary walls into the tissue, increased blood flow -> heat and redness. Escape of fluid from the blood -> swelling

Steps of inflammatory response 3

Heparin release from mast cells prevents clotting in immediate area of injury. A clot of the fluid forms around the damaged area, which slows the spread of the pathogen into healthy tissues.

Steps of inflammatory response 4

Complement system proteins and some chemicals released by the mast cells attract phagocytes, particularly neutrophils, which actively consume microorganisms and debris by phagocytosis

Steps of inflammatory response 5

The abnormal conditions in the tissue stimulate pain receptors, person feels pain in inflamed area

Steps of inflammatory response 6

Phagocytes, filled with bacteria, debris and dead cells, begin to die - the dead phagocytes and tissue fluid form a yellow liquid called pus

Steps of inflammatory response 7

New cells are produced by mitosis, and repair of damaged tissue takes place

Fever

high body temperature inhibits growth of some bacteria/viruses that are heat sensitive

Heat speeds rate of chemical reactions, helps body cells repair themselves during disease quickly

Fever functioning

Elevation of body temperature via hypothalamus resets set point to a higher temperature, causes person to feel cold -> homeostatic mechanisms like vasoconstriction/shivering etc. occur, causes body temp to rise

Pyrogens

Substance released by white blood cells, act directly on hypothalamus to regulate temperature