History and Importance of Phagocytosis
- Phagocytosis was first described by Albert von Kölliker in 1849.
- Ernst Haeckel provided the first direct evidence of phagocytosis by immune cells in 1862.
- William Osler noted phagocytosis in 1876.
- Élie Metchnikoff studied and named phagocytosis in 1880 and 1883.
- Phagocytosis played a significant role in establishing immunology as a scientific field.
- Phagocytosis is a key mechanism in the innate immune defense.
- It is one of the first responses to infection and can initiate an adaptive immune response.
- Professional phagocytes, such as neutrophils, macrophages, and dendritic cells, specialize in phagocytosis.
- Phagocytosis is present in both vertebrates and invertebrates.
- Most cells have the ability to perform phagocytosis.
- Phagocytosis helps eliminate harmful substances from the body.
- Phagocytosis is essential for defense against pathogens.
- Phagocytosis is involved in maintaining tissue homeostasis and clearing cellular debris.
- Phagocytosis activates the immune response.
- Phagocytosis has implications in various diseases and disorders.

Phagocytic Cells and Receptors
- Neutrophils, macrophages, monocytes, dendritic cells, osteoclasts, and eosinophils are professional phagocytes.
- Neutrophils patrol the bloodstream and quickly migrate to infected tissues.
- Neutrophils efficiently kill pathogens through intracellular killing and the release of microbicidal molecules.
- Macrophages form a resting barrier in tissues and continue phagocytosis by forming new lysosomes.
- Dendritic cells break down pathogens for antigen presentation to the adaptive immune system.
- Phagocytosis receptors can be divided into opsonic receptors and non-opsonic receptors.
- Opsonic receptors depend on opsonins, such as IgG antibodies or complement proteins.
- Non-opsonic receptors include lectin-type receptors, scavenger receptors, and Dectin receptor.
- Pattern recognition receptors (PRRs) can provide a second signal for phagocytosis through attachment to pathogen-associated molecular patterns (PAMPs).
- Receptors like Fcγ receptors, complement receptors, and mannose receptors play a role in initiating phagocytosis.

Phagosome and Degradation
- The actin-myosin contractile system facilitates the engulfment of material during phagocytosis.
- The phagosome is the organelle formed by phagocytosis.
- Phagosomes fuse with lysosomes to form phagolysosomes for degradation.
- Degradation can be oxygen-dependent or oxygen-independent.
- Oxygen-dependent degradation involves the production of reactive oxygen species.
- Oxygen-independent degradation involves the release of granules containing enzymes and antimicrobial peptides.

Phagocytosis in Protists and Mixotrophy
- Phagocytosis is used for feeding in many protists.
- Phagotrophic nutrition provides nourishment for protists.
- Protists like amoeba can phagocytose red blood cells.
- Ciliates also engage in phagocytosis in a specialised groove called the cytostome.
- Mixotrophy can involve both phagotrophic and phototrophic nutrition.
- Some protists exhibit mixotrophic behavior.
- Phagocytosis plays a role in obtaining nutrients during mixotrophy.
- Mixotrophic organisms combine phagocytosis and photosynthesis.
- Phagocytosis enhances the nutritional capabilities of mixotrophs.

Related Concepts and Processes
- Active transport is related to phagocytosis.
- Antigen presentation is another process involving immune cells.
- Phagocytosis is distinct from pinocytosis, a process of fluid uptake.
- Emperipolesis is a phenomenon where one cell engulfs another.
- Endosymbionts in protists can also be involved in phagocytosis.

Note: The content has been organised into 5 comprehensive groups based on the similarity of concepts and their relationships.