what is the first cell to migrate to an injured area
Leukocyte extravasation
title: Cell migration text: Cell migration Cell migration is a central process in the development and maintenance of multicellular organisms. Tissue formation during embryonic development, wound healing and immune responses all require the orchestrated movement of cells in particular directions to specific locations. Cells often migrate in response to specific external signals, including chemical signals and mechanical signals. Errors during this process have serious consequences, including intellectual disability, vascular disease, tumor formation and metastasis. An understanding of the mechanism by which cells migrate may lead to the development of novel therapeutic strategies for controlling, for example, invasive tumour cells. Due to the highly viscous title: Wound healing text: During migration, integrins on the pseudopod attach to the ECM, and the actin filaments in the projection pull the cell along. The interaction with molecules in the ECM through integrins further promotes the formation of actin filaments, lamellipodia, and filopodia. Epithelial cells climb over one another in order to migrate. This growing sheet of epithelial cells is often called the epithelial tongue. The first cells to attach to the basement membrane form the stratum basale. These basal cells continue to migrate across the wound bed, and epithelial cells above them slide along as well. The more quickly this migration occurs, title: Inflammation text: particularly neutrophils, are critically involved in the initiation and maintenance of inflammation. These cells must be able to move to the site of injury from their usual location in the blood, therefore mechanisms exist to recruit and direct leukocytes to the appropriate place. The process of leukocyte movement from the blood to the tissues through the blood vessels is known as "extravasation", and can be broadly divided up into a number of steps: Extravasated neutrophils in the cellular phase come into contact with microbes at the inflamed tissue. Phagocytes express cell-surface endocytic pattern recognition receptors (PRRs) that have affinity and title: Wound healing text: meet in the middle, at which point contact inhibition causes them to stop migrating. When they have finished migrating, the keratinocytes secrete the proteins that form the new basement membrane. Cells reverse the morphological changes they underwent in order to begin migrating; they reestablish desmosomes and hemidesmosomes and become anchored once again to the basement membrane. Basal cells begin to divide and differentiate in the same manner as they do in normal skin to reestablish the strata found in reepithelialized skin. Contraction is a key phase of wound healing with repair. If contraction continues for too long, it can lead title: Wound healing text: granulation tissue, and restore the epithelial layer. Subdivisions of the cellular phase are: [1] Macrophages and inflammatory components (within 1–2 days), [2] Epithelial-mesenchymal interaction: re-epithelialization (phenotype change within hours, migration begins on day 1 or 2), [3] Fibroblasts and myofibroblasts: progressive alignment, collagen production, and matrix contraction (between day 4 and day 14), [4] Endothelial cells and angiogenesis (begins on day 4), [5] Dermal matrix: elements of fabrication (begins on day 4, lasting 2 weeks) and alteration/remodeling (begins after week 2, lasting weeks to months—depending on wound size). Just before the inflammatory phase is initiated, the clotting cascade occurs in