25 Pts) Conceptual Questions 1. Foundations (5 pts) a. Use science and engineeri

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25 Pts) Conceptual Questions 1. Foundations (5 pts) a. Use science and engineering. a diagram (that looks like a pyramid) to describe the foundation (and/or basis) of materials 2. Wound Healing and Biocompatibility (20 pts) a. Briefly describe how the coagulation process and cell injury help to initiate the inflammatory response b. Describe the FOUR steps associated with the leukocyte extravasation process (plus the resting stage). Label the diagram and briefly describe the primary mechanism or molecules involved ine step. 0

Explanation / Answer

2) (b) leucocyte extravasion- commonly called diapedesis, is the movement of leucocytes out of the circulatory system and towards the site of tissue damage or infection. This process forms part of innate immune response, involving the recruitment of non- specific leucocytes. Monocytes also use this process in absence of infection or tissue damage during their development into macrophages.

Leucocyte extravasion occurs mainly in post-op Larry venules where haemodynamic shear forces are minimised. This process can be described in several steps basically

Chemoattraction

Rolling adhesion

Tight adhesion

Endothelial transmigration.

1)chemoattraction- upon recognition of and activation by pathogens, resident macrophages in the affected tissue release cytokines which cause endothelial cells of blood vessels near the site of infection to express cellular adhesion molecules, including selections. Circulating leucocytes are localised towards the site of injury or infection due to presence of chemokines.

2) rolling adhesion - carbohydate ligands on the circulating leucocytes bind to selection molecules on the inner wall of the vessel with marginal affinity. This causes the leucocyte to slow down and begin rolling along the inner surface of vessel wall. During this rolling motion, transitory bonds are formed and broken between selectins and their ligands.

3) tight adhesion- at the same time, chemokines released by macrophages activate the rolling leucocytes and cause surface integrin molecules to switch from the default low-fat state to high affinity state.

4) transmigration- the cytoskeletons of leucocytes are recognised in such a way that leucocytes are spread out over the endothelial cells. In this form, leucocytes extend pseudopodia and pass through gap between endothelial cells.

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