Cells (Immunity) - Phagocytosis Flashcards
What is the difference between phagocytes and lymphocytes?
Phagocytes ingest and destroy the pathogen by a process called phagocytosis before it can cause harm. Lymphocytes are involved in immune responses.
What is phagocytosis?
When large particles, such as some types of bacteria, are engulfed and internalised by cells in the vesicles formed from the cell-surface membrane.
What are phagocytes?
In the blood, the types of white blood cells that carry out phagocytosis are known as phagocytes. They provide an important defence against the pathogens that manage to enter the body. Some phagocytes travel in the blood but can move out of blood vessels into other tissues.
Describe the steps in phagocytosis.
- Chemical products of pathogens or dead, damaged and abnormal cells act as attractants, causing phagocytes to move towards the pathogen (e.g. a bacterium) along a concentration gradient.
- Phagocytes have several receptors on their cell-surface membrane that recognises the foreign marker on the pathogen’s outer membrane called the antigen. Small non-specific protein molecules called opsonins then attach to the antigen. The phagocyte can then bind to the opsonins attached to the pathogen antigen - allowing the phagocyte to get closer to the pathogen.
- The phagocytes form pseudopods that eventually engulf the pathogen to form a vesicle, known as a phagosome.
- Lysosomes move towards the vesicle and fuse with it.
- Proteolytic enzymes such as lysozymes are present within the lysosome. These lysozymes destroy ingested bacteria by hydrolysis of their cell walls, leaving a residual body.
- The soluble, digestive products from the breakdown of the pathogen are absorbed into the cytoplasm of the phagocyte.
- Indigestible and residual material is removed by exocytosis.
- There are a few special cells like macrophages that do not completely destroy the pathogen and instead save the pathogen antigen.
- These cells put the pathogen antigen on a special protein complex. This is then moved to the cell surface membrane so other immune cells (a B-lymphocyte or T-lymphocyte) can recognise the pathogen antigen. Macrophages and other special cells which do this are called antigen presenting cells.
Where are white blood cells produced?
White blood cells are continually produced from stem cells in bone marrow. They are stored in bone marrow and released into the blood to engulf and digest foreign bodies.
What are the two types of phagocytes?
- neutrophils
- macrophages (or monocytes, depending on the stage of their life that they’re in)
How do monocytes become macrophages?
Monocytes are present in the blood when they enter the tissues they become macrophages.
What is the difference in function between neutrophils and macrophages?
When any pathogen infects a tissue, neutrophils arrive first and each neutrophil can engulf 5-20 pathogenic cells. Neutrophils die quickly after a few days whereas macrophages are long lived cells. When neutrophils die, the macrophages then arrive at the infected tissue and each macrophage can engulf 100 pathogenic cells.
What is inflammation?
Histamine triggers dilation of blood vessels and permeability of capillary walls. Phagocytes, macrophages and natural killer cells that fight infection are attracted to the site of infection. (chemotaxis)
What is chemotaxis?
The movement of a motile cell or organism, or part of one, in a direction corresponding to a gradient of increasing or decreasing concentration of a particular substance.
What are the specialisations of phagocytes?
- Phagocytes are specialised to carry out each step in phagocytosis.
- Phagocytes have well developed cytoskeletons to help them change shape to engulf the pathogen and move lysosomes around.
- They have many mitochondria to release energy required for cell movement.
- They also contain lots of ribosomes to synthesis the lysosome enzymes.
- Phagocytes have a lobed nucleus to help them squeeze through narrow gaps between cells in the tissues.
What is the function of lysosomes?
When the pathogen is engulfed, it is sealed into a phagosome (a vacuole) inside the cytoplasm. Phagocytes have many organelles called lysosomes that contain proteolytic enzymes. A lysosome fuses with the phagosome and releases the proteolytic enzymes into the phagosome. The enzymes break down/hydrolyse the pathogen.
What is agglutination?
Agglutination ‘clumps’ the pathogens together. The pathogens are engulfed by phagocytes via phagocytosis. The pathogens are destroyed.
How are pathogens found?
1.
- Antibodies can recognise and bind to pathogens.
- They act as a chemical beacon which attracts phagocytes to the pathogen.
2.
- Chemicals attract pathogens.
- The phagocyte releases chemicals, attracting pathogens to the site.
Both chemical and antibody processes are examples of chemotaxis.
