Acute Inflammation: Vascular and Cellular Events PDF

# **1. VASCULAR EVENTS** - Alteration in the microvasculature (arterioles, capillaries and venules) is the earliest response to tissue injury. - These alterations include: - A. Haemodynamic changes. - Changes in vascular permeability. # **A. Haemodynamic changes.** - The earliest features of...

# **1. VASCULAR EVENTS** - Alteration in the microvasculature (arterioles, capillaries and venules) is the earliest response to tissue injury. - These alterations include: - A. Haemodynamic changes. - Changes in vascular permeability. # **A. Haemodynamic changes.** - The earliest features of inflammatory response result from changes in the vascular flow and calibre of small blood vessels in the injured tissue. Such as - # **1. Vasoconstriction of arterioles** - Irrespective of the type of injury, immediate vascular response. - i.e. transient vasoconstriction of arterioles. - The blood flow may be re-established in 3-5 seconds. - With more severe injury, the vasoconstriction may last for about 5 minutes. # **2. Persistent progressive vasodilatation:** - Involves mainly the arterioles. - Affects other components of the microcirculation like venules and capillaries. - This change is obvious within half an hour of injury. - Vasodilatation results in increased blood volume. - "Responsible for redness and warmth at the site of acute inflammation." # **3. Local hydrostatic pressure:** - Progressive vasodilatation, in turn, may elevate the **Local hydrostatic pressure** resulting in transudation of fluid into the extracellular space. - "This is responsible for swelling at the local site of acute inflammation." # **4. Emigration:** - Stasis or slowing is followed by leucocytic margination (mainly neutrophils). - The leucocytes stick to the vascular endothelium briefly, and then move and migrate through the gaps between the endothelial cells into the extravascular space. # **B. Changes in vascular permeability.** - In and around the inflamed tissue, there is accumulation of oedema fluid in the interstitial compartment. - Which comes from blood plasma by its escape through the endothelial wall of peripheral vascular bed. - In the initial stage, the escape of fluid is due to vasodilatation and consequent elevation in hydrostatic pressure. - Increased vascular permeability of microvascular bed is explained on the basis of **Starling's hypothesis.** - "In normal circumstances, the fluid balance is maintained by two opposing sets of forces:" - **1. Forces that cause outward movement of fluid from microcirculation are intravascular hydrostatic pressure and colloid osmotic pressure of interstitial fluid.** - **2. Forces that cause inward movement of interstitial fluid into circulation are intravascular colloid osmotic pressure and hydrostatic pressure of interstitial fluid.** - However, in inflamed tissues, the endothelial lining of microvasculature becomes more leaky. - Consequently, intravascular colloid osmotic pressure decreases and osmotic pressure of the interstitial fluid increases. - Resulting in excessive outward flow of fluid into the interstitial compartment. - Which is exudative inflammatory oedema. *** # **ACUTE INFLAMMATION** A diagram of an acute inflammation process describes an inflammation pathway, beginning with vascular events, then separating into two branches. - The **vascular events** branch of the diagram includes: - **Arteriolar Changes** - Vasodilatation leads to hyperemia (redness). - **Venular Changes** - Increased Venular Permeability leads to swelling (oedema). - This leads to **Exudative Edema**. - The **cellular events** branch of the diagram includes: - **Neutrophilic influx in vessels** - **Margination** - **Rolling** - **Adhesion** - **Transmigration (Diapedesis)** - **Chemotaxis** - **Opsonophagocytic Destruction** *** A diagram depicting a section of inflamed tissue. The diagram includes: - A description of the process as **INFLAMMATION: VASCULAR EVENTS + LEUKOCYTE MIGRATION** - Red blood cells moving through the vessels. - White blood cells migrating through the gaps in the vessel walls to the outside of the vessel. - White blood cells moving toward a stimulus at the top of the diagram. # **2. CELLULAR EVENTS** - The cellular phase of inflammation consists of 2 processes: - I. Exudation of leucocytes. - II. Phagocytosis. # **I. Exudation of leucocytes.** - A diagram depicting a section of inflamed tissue. The diagram shows: - **A. Normal axial flow** of red and white blood cells in the vessel. - **B. Margination and pavementing** of white blood cells against the vessel's edge. - **C. Rolling and adhesion** of the white blood cells as they adhere to the vessel wall. - **D. Emigration and diapedesis** of white blood cells that have moved through the gaps between the endothelial cells on the vessel wall. - The most important feature of inflammatory response is escape of leucocytes from the lumen of microvasculature to the interstitial tissue. - "In acute inflammation, polymorphonuclear neutrophils (PMNs) comprise the first line of body defense. Followed later by monocytes and Macrophages." - The changes leading to migration of leucocytes are as follows: - **1. MARGINATION:** As a result of this redistribution, the neutrophils of the central column come close to the vessel wall; this is known as pavementing. - **2. ROLLING AND ADHESION:** - Peripherally marginated and pavemented neutrophils slowly roll over the endothelial cells lining the vessel wall (rolling phase). - This is followed by the transient bond between the leucocytes and endothelial cells becoming firmer (adhesion phase). - **3. EMIGRATION:** After sticking of neutrophils to endothelium, the former move along the endothelial surface till a suitable site between the endothelial cells is found where the neutrophils throw out cytoplasmic pseudopods. # **II. Phagocytosis.** - "Phagocytosis is defined as the process of engulfment of solid particulate material by the cells (cell-eating)." - The cells performing this function are called phagocytes. - There are 2 main types of phagocytic cells: - i. Polymorphonuclear neutrophils (PMNs): commonly called **Microphage**. - ii. Circulating monocytes: commonly called **Macrophage**. # **Steps of Phagocytosis** - The microbe undergoes the process of phagocytosis by polymorphs and macrophages involves the following 3 steps: - 1. Recognition and attachment - 2. Engulfment - 3. Killing and degradation - A diagram of 4 stages of phagocytosis shows: - **A. Opsonisation of the particle:** a microbe is attached by an IgG opsonin, a C3b opsonin, and a Lectin to the Fc receptor on the surface. - **B. Pseudopod engulfing the opsonised particle:** the microbe has been pulled into the cell while attached to the receptor. - **C. Incorporation within the cell (phagocytic vacuole) and degranulation:** the microbe is completely enclosed in the cell with pseudopods surrounding it. - **D. Phagolysosome formation after fusion of lysosome of the cell:** the microbe has been broken down within the phagolysosome. # **Thanks.**