{"id":6538,"date":"2026-06-03T13:29:10","date_gmt":"2026-06-03T17:29:10","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/?post_type=chapter&#038;p=6538"},"modified":"2026-06-10T23:32:34","modified_gmt":"2026-06-11T03:32:34","slug":"the-inflammatory-response","status":"web-only","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/chapter\/the-inflammatory-response\/","title":{"raw":"Section 4:\u00a0 The Inflammatory Response","rendered":"Section 4:\u00a0 The Inflammatory Response"},"content":{"raw":"<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\"><strong>Inflammation<\/strong> is a protective response triggered by any type of cellular damage or irritation - cuts, burns, infections, sprains, ischemia, chemicals, foreign objects, extreme heat or cold.\u00a0 It facilitates removal of harmful agents, limits damage, and sets the stage for healing.<\/span><\/p>\r\n\r\n<h3><span style=\"color: #1f5c99\"><strong>How Inflammatory Is Initiated<\/strong><\/span><\/h3>\r\n<p style=\"text-align: justify\">When cells are damaged they release <strong>contents (ADP, K<sup>+<\/sup>, proteins, enzymes)<\/strong> and <strong>cytokines<\/strong> that activate <strong>macrophages<\/strong> and <strong>mast cells<\/strong>.\u00a0 Macrophages phagocytose debris and pathogens and release chemokines to recruit other WBCs.\u00a0 Mast cells <strong>degranulate,<\/strong> releasing <strong>histamine, bradykinin,<\/strong> and <strong>prostaglandin,<\/strong> which cause:<\/p>\r\n\r\n<ul>\r\n \t<li style=\"text-align: justify\"><strong>Vasodilation:<\/strong>\u00a0 local blood vessels dilate, increasing blood flow to the area.<\/li>\r\n \t<li style=\"text-align: justify\"><strong>Increased capillary permeability:<\/strong>\u00a0 plasma fluid <strong>(exudate)<\/strong> leaks from capillaries into the damaged tissue bed.<\/li>\r\n \t<li style=\"text-align: justify\"><strong>WBC diapedesis:<\/strong>\u00a0 endothelial cells of the blood vessel walls express adhesion molecules facilitating rolling, adhesion, and transmigration of WBCs into tissue.<\/li>\r\n<\/ul>\r\n<p style=\"text-align: justify\">The leaked <strong>exudate<\/strong> contains <strong>fibrinogen, complement proteins<\/strong>, <strong>C-reactive proteins<\/strong>, and <strong>platelets.<\/strong>\u00a0 Fibrin mesh and clots help contain the damaged area.\u00a0 Chemokines recruit neutrophils, monocytes, macrophages, dendritic cells, eosinophils, and basophils.\u00a0 WBCs also secrete <strong>growth factors<\/strong> to stimulate tissue repair once the area is cleared.<\/p>\r\n\r\n<h3><span style=\"color: #1f5c99\"><strong>Two Phases of Inflammation<\/strong><\/span><\/h3>\r\n<table class=\"grid landscape\" style=\"border-collapse: collapse;width: 100%\" border=\"0\">\r\n<tbody>\r\n<tr>\r\n<td style=\"width: 16.7954%\"><span style=\"color: #032c80\"><strong>Vascular <span style=\"color: #032c80\">phase<\/span><\/strong><\/span><\/td>\r\n<td style=\"width: 83.2046%\">Vasodilation and increased capillary permeability occur within local blood vessels.<\/td>\r\n<\/tr>\r\n<tr>\r\n<td class=\"shaded\" style=\"width: 16.7954%\"><span style=\"color: #032c80\"><strong>Cellular phase<\/strong><\/span><\/td>\r\n<td class=\"shaded\" style=\"width: 83.2046%\">Emigration (diapedesis\/transmigration) of WBCs from blood into the tissue bed occurs.<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<h3><span style=\"color: #1f5c99\"><b>The Five Signs of Inflammation<\/b><\/span><\/h3>\r\n<table class=\"grid landscape\" style=\"border-collapse: collapse;width: 100%;height: 75px\" border=\"0\">\r\n<tbody>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 14.7362%;height: 15px\"><span style=\"color: #032c80\"><strong>Redness<\/strong><\/span><\/td>\r\n<td style=\"width: 85.2638%;height: 15px\"><strong>Hyperemia<\/strong> (increased blood flow) to the area due to <strong>vasodilation.<\/strong><\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td class=\"shaded\" style=\"width: 14.7362%;height: 15px\"><span style=\"color: #032c80\"><strong>Warmth<\/strong><\/span><\/td>\r\n<td class=\"shaded\" style=\"width: 85.2638%;height: 15px\">Blood (37\u00b0C) is slightly warmer than surface tissues; increased <strong>perfusion<\/strong> warms the area.<\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 14.7362%;height: 15px\"><span style=\"color: #032c80\"><strong>Swelling<\/strong><\/span><\/td>\r\n<td style=\"width: 85.2638%;height: 15px\"><strong>Exudate<\/strong> accumulates in interstitial spaces due to <strong>increased capillary permeability<\/strong>.\r\n\r\nWhen substantial this is called <strong>edema.<\/strong><\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td class=\"shaded\" style=\"width: 14.7362%;height: 15px\"><span style=\"color: #032c80\"><strong>Pain<\/strong><\/span><\/td>\r\n<td class=\"shaded\" style=\"width: 85.2638%;height: 15px\"><strong>Nociceptors<\/strong> (pain sensory receptors) are stimulated by <strong>prostaglandins, bradykinin, leukotriene,<\/strong> <strong>leaked blood<\/strong>, <strong>extracellular ATP<\/strong>, and <strong>exudate pressure.<\/strong>\r\n\r\nHistamine activates a nociceptor subtype producing <strong>itching.<\/strong><\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 14.7362%;height: 15px\"><span style=\"color: #032c80\"><strong>Loss of Function (sometimes)<\/strong><\/span><\/td>\r\n<td style=\"width: 85.2638%;height: 15px\">Swelling or pain impedes joint or muscle movement.\r\n\r\nExudate in lung alveoli or interstitial spaces impairs gas exchange.\r\n\r\nSwelling in the esophagus impairs swallowing.<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n[caption id=\"attachment_6794\" align=\"alignnone\" width=\"300\"]<a href=\"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-content\/uploads\/sites\/1961\/2026\/06\/Mast-Cells-Inflammation.png\"><img class=\"size-medium wp-image-6794\" src=\"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-content\/uploads\/sites\/1961\/2026\/06\/Mast-Cells-Inflammation-300x127.png\" alt=\"(a) Mast cells detect injury to nearby cells and release histamine, initiating an inflammatory response. (b) Histamine increases blood flow to the wound site, and increased vascular permeability allows fluid, proteins, phagocytes, and other immune cells to enter infected tissue. These events result in the swelling and reddening of the injured site, and the increased blood flow to the injured site causes it to feel warm. Inflammation is also associated with pain due to these events stimulating nerve pain receptors in the tissue.\" width=\"300\" height=\"127\" \/><\/a> (a) Mast cells detect injury to nearby cells and release histamine, initiating an inflammatory response. (b) Histamine increases blood flow to the wound site, and increased vascular permeability allows fluid, proteins, phagocytes, and other immune cells to enter infected tissue. These events result in the swelling and reddening of the injured site, and the increased blood flow to the injured site causes it to feel warm. Inflammation is also associated with pain due to these events stimulating nerve pain receptors in the tissue.[\/caption]\r\n\r\n&nbsp;\r\n<div class=\"textbox textbox--key-takeaways\"><header class=\"textbox__header\">\r\n<p class=\"textbox__title\"><strong>Vasoactive Compounds in Inflammation<\/strong><\/p>\r\n\r\n<\/header>\r\n<div class=\"textbox__content\">\r\n<p style=\"text-align: justify\">Several key <strong>pro-inflammatory<\/strong>\u00a0<strong>mediators<\/strong> are classified as <strong>vasoactive<\/strong> compounds (they all change blood vessel diameter):<\/p>\r\n\r\n<ul style=\"text-align: justify\">\r\n \t<li><strong>Histamine:<\/strong>\u00a0 Nitrogenous compound released by mast cells, basophils, and platelets.<\/li>\r\n \t<li><strong>Bradykinin:<\/strong> Peptide activated by enzymatic cleavage of its kininogen precursor.<\/li>\r\n \t<li><strong>Prostaglandin:<\/strong> Lipid mediator released by mast cells, basophils, macrophages, and activated platelets.<\/li>\r\n \t<li><strong>Leukotrienes:<\/strong>\u00a0 Lipid mediators produced by mast cells, basophils, neutrophils, monocytes, and eosinophils.\u00a0 A potent <strong>bronchoconstrictor<\/strong> in asthma; also a vasodilator increasing capillary permeability.<\/li>\r\n<\/ul>\r\n<p style=\"text-align: justify\">All four compounds induce <strong>vasodilation,<\/strong> <strong>increase capillary permeability<\/strong>, cause <strong>bronchoconstriction,<\/strong> stimulate <strong>mucus<\/strong> production and trigger <strong>WBC chemotaxis<\/strong>.<\/p>\r\n<p style=\"text-align: justify\">Bradykinin, prostaglandin, and leukotriene also stimulate <strong>nociceptors,<\/strong> contributing to the <strong>pain<\/strong> of inflammation.\u00a0 Histamine stimulates <strong>itch<\/strong> (pruritus) especially during allergic reactions.<\/p>\r\n<p style=\"text-align: justify\"><strong>Side note:\u00a0<\/strong> Interestingly, itch and pain do share overlapping neuronal pathways and sharp pressure can temporarily override the itch sensation.\u00a0 However, the withdrawal neural reflex arc for pain differs from the scratching reflex for itch (which can damage the skin).<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<h3><span style=\"color: #1f5c99\"><b>Four Types of Exudate<\/b><\/span><\/h3>\r\n<table class=\"grid landscape\" style=\"border-collapse: collapse;width: 100%;height: 60px\" border=\"0\">\r\n<tbody>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 14.7362%;height: 15px\"><span style=\"color: #032c80\"><strong>Serous<\/strong><\/span><\/td>\r\n<td style=\"width: 85.2638%;height: 15px\">Watery, containing some proteins and WBCs.\u00a0 Found in unruptured burn blisters.<\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td class=\"shaded\" style=\"width: 14.7362%;height: 15px\"><span style=\"color: #032c80\"><strong>Fibrinous<\/strong><\/span><\/td>\r\n<td class=\"shaded\" style=\"width: 85.2638%;height: 15px\">Thick, sticky, contains <strong>fibrin;<\/strong> associate with severe injuries and infections.\r\n\r\nLinked to increased scar tissue formation.<\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 14.7362%;height: 15px\"><span style=\"color: #032c80\"><strong>Purulent<\/strong><\/span><\/td>\r\n<td style=\"width: 85.2638%;height: 15px\">Thick, yellow-green; contains WBCs and microorganisms.\r\n\r\nSeen in bacterially-infected abscesses and acne.\r\n\r\nContains <strong>pus<\/strong> - a protein-rich fluid of dead cells and debris.<\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td class=\"shaded\" style=\"width: 14.7362%;height: 15px\"><span style=\"color: #032c80\"><strong>Hemorrhagic<\/strong><\/span><\/td>\r\n<td class=\"shaded\" style=\"width: 85.2638%;height: 15px\">Contains blood from damaged blood vessels.<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n[caption id=\"attachment_2360\" align=\"alignnone\" width=\"300\"]<a href=\"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-content\/uploads\/sites\/1961\/2024\/09\/Swollen_eye_with_conjunctivitis.jpg\" target=\"_blank\" rel=\"noopener\"><img class=\"wp-image-2360 size-medium\" src=\"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-content\/uploads\/sites\/1961\/2024\/09\/Swollen_eye_with_conjunctivitis-300x194.jpg\" alt=\"A swollen, pus-filled eye with conjunctivitis. Purulent exudate discharge, thick, milky or yellowing pus, is a mixture of dead cells, bacteria, and white blood cells. \" width=\"300\" height=\"194\" \/><\/a> A swollen, pus-filled eye with conjunctivitis. Purulent exudate discharge, thick, milky or yellowing pus, is a mixture of dead cells, bacteria, and white blood cells.[\/caption]\r\n<h3><span style=\"color: #1f5c99\"><strong>Systemic Effects of Inflammation<\/strong><\/span><\/h3>\r\n<p style=\"text-align: justify\">Pro-inflammatory cytokines circulate the whole body, causing systemic effects; mild fever, <strong>malaise, fatigue, headache,<\/strong> <strong>loss of appetite<\/strong>, and - particularly in the elderly - decreased mental function.<\/p>\r\n\r\n<div class=\"textbox textbox--key-takeaways\"><header class=\"textbox__header\">\r\n<p class=\"textbox__title\"><strong>When Inflammation Goes Wrong:\u00a0 Too Little or Too Much<\/strong><\/p>\r\n\r\n<\/header>\r\n<div class=\"textbox__content\">\r\n<p style=\"text-align: justify\"><strong>Too little inflammation:<\/strong>\u00a0 In <strong>immunosuppressive<\/strong> diseases, insufficient inflammation allows prolonged tissue damage, infection, and potentially permanent tissue loss.<\/p>\r\n<p style=\"text-align: justify\"><strong>Too much inflammation:<\/strong>\u00a0 Chronic conditions such as atherosclerosis, diabetes, osteoarthritis, autoimmune diseases, allergies, and asthma drive prolonged inflammatory responses.\u00a0 Excessive WBC activity leads to cycles of tissue destruction and healing, causing progressive damage.<\/p>\r\n<p style=\"text-align: justify\"><strong>Systemic Inflammatory Response Syndrome (SIRS):<\/strong>\u00a0 A potentially fatal condition caused by a \"cytokine storm\", a massive pro-inflammatory cytokine release.\u00a0 Results in <strong>systemic vasodilation <\/strong>and <strong>increased capillary permeability<\/strong>\u00a0\u2192 <strong>hypotension<\/strong>\u00a0and <strong>circulatory shock<\/strong>.\u00a0 Most frequently caused by <strong>sepsis<\/strong> (dysregulated immune response to infection).<\/p>\r\n<p style=\"text-align: justify\"><strong>Fever of Unknown Origin (FUO):<\/strong>\u00a0 Thought to be caused by inflammatory responses to undetectable cellular damage - from infections, trauma, cancer, heart attacks, blood clots, inflammatory diseases, or drug reactions.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<h3><\/h3>","rendered":"<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\"><strong>Inflammation<\/strong> is a protective response triggered by any type of cellular damage or irritation &#8211; cuts, burns, infections, sprains, ischemia, chemicals, foreign objects, extreme heat or cold.\u00a0 It facilitates removal of harmful agents, limits damage, and sets the stage for healing.<\/span><\/p>\n<h3><span style=\"color: #1f5c99\"><strong>How Inflammatory Is Initiated<\/strong><\/span><\/h3>\n<p style=\"text-align: justify\">When cells are damaged they release <strong>contents (ADP, K<sup>+<\/sup>, proteins, enzymes)<\/strong> and <strong>cytokines<\/strong> that activate <strong>macrophages<\/strong> and <strong>mast cells<\/strong>.\u00a0 Macrophages phagocytose debris and pathogens and release chemokines to recruit other WBCs.\u00a0 Mast cells <strong>degranulate,<\/strong> releasing <strong>histamine, bradykinin,<\/strong> and <strong>prostaglandin,<\/strong> which cause:<\/p>\n<ul>\n<li style=\"text-align: justify\"><strong>Vasodilation:<\/strong>\u00a0 local blood vessels dilate, increasing blood flow to the area.<\/li>\n<li style=\"text-align: justify\"><strong>Increased capillary permeability:<\/strong>\u00a0 plasma fluid <strong>(exudate)<\/strong> leaks from capillaries into the damaged tissue bed.<\/li>\n<li style=\"text-align: justify\"><strong>WBC diapedesis:<\/strong>\u00a0 endothelial cells of the blood vessel walls express adhesion molecules facilitating rolling, adhesion, and transmigration of WBCs into tissue.<\/li>\n<\/ul>\n<p style=\"text-align: justify\">The leaked <strong>exudate<\/strong> contains <strong>fibrinogen, complement proteins<\/strong>, <strong>C-reactive proteins<\/strong>, and <strong>platelets.<\/strong>\u00a0 Fibrin mesh and clots help contain the damaged area.\u00a0 Chemokines recruit neutrophils, monocytes, macrophages, dendritic cells, eosinophils, and basophils.\u00a0 WBCs also secrete <strong>growth factors<\/strong> to stimulate tissue repair once the area is cleared.<\/p>\n<h3><span style=\"color: #1f5c99\"><strong>Two Phases of Inflammation<\/strong><\/span><\/h3>\n<table class=\"grid landscape\" style=\"border-collapse: collapse;width: 100%\">\n<tbody>\n<tr>\n<td style=\"width: 16.7954%\"><span style=\"color: #032c80\"><strong>Vascular <span style=\"color: #032c80\">phase<\/span><\/strong><\/span><\/td>\n<td style=\"width: 83.2046%\">Vasodilation and increased capillary permeability occur within local blood vessels.<\/td>\n<\/tr>\n<tr>\n<td class=\"shaded\" style=\"width: 16.7954%\"><span style=\"color: #032c80\"><strong>Cellular phase<\/strong><\/span><\/td>\n<td class=\"shaded\" style=\"width: 83.2046%\">Emigration (diapedesis\/transmigration) of WBCs from blood into the tissue bed occurs.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h3><span style=\"color: #1f5c99\"><b>The Five Signs of Inflammation<\/b><\/span><\/h3>\n<table class=\"grid landscape\" style=\"border-collapse: collapse;width: 100%;height: 75px\">\n<tbody>\n<tr style=\"height: 15px\">\n<td style=\"width: 14.7362%;height: 15px\"><span style=\"color: #032c80\"><strong>Redness<\/strong><\/span><\/td>\n<td style=\"width: 85.2638%;height: 15px\"><strong>Hyperemia<\/strong> (increased blood flow) to the area due to <strong>vasodilation.<\/strong><\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td class=\"shaded\" style=\"width: 14.7362%;height: 15px\"><span style=\"color: #032c80\"><strong>Warmth<\/strong><\/span><\/td>\n<td class=\"shaded\" style=\"width: 85.2638%;height: 15px\">Blood (37\u00b0C) is slightly warmer than surface tissues; increased <strong>perfusion<\/strong> warms the area.<\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td style=\"width: 14.7362%;height: 15px\"><span style=\"color: #032c80\"><strong>Swelling<\/strong><\/span><\/td>\n<td style=\"width: 85.2638%;height: 15px\"><strong>Exudate<\/strong> accumulates in interstitial spaces due to <strong>increased capillary permeability<\/strong>.<\/p>\n<p>When substantial this is called <strong>edema.<\/strong><\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td class=\"shaded\" style=\"width: 14.7362%;height: 15px\"><span style=\"color: #032c80\"><strong>Pain<\/strong><\/span><\/td>\n<td class=\"shaded\" style=\"width: 85.2638%;height: 15px\"><strong>Nociceptors<\/strong> (pain sensory receptors) are stimulated by <strong>prostaglandins, bradykinin, leukotriene,<\/strong> <strong>leaked blood<\/strong>, <strong>extracellular ATP<\/strong>, and <strong>exudate pressure.<\/strong><\/p>\n<p>Histamine activates a nociceptor subtype producing <strong>itching.<\/strong><\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td style=\"width: 14.7362%;height: 15px\"><span style=\"color: #032c80\"><strong>Loss of Function (sometimes)<\/strong><\/span><\/td>\n<td style=\"width: 85.2638%;height: 15px\">Swelling or pain impedes joint or muscle movement.<\/p>\n<p>Exudate in lung alveoli or interstitial spaces impairs gas exchange.<\/p>\n<p>Swelling in the esophagus impairs swallowing.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<figure id=\"attachment_6794\" aria-describedby=\"caption-attachment-6794\" style=\"width: 300px\" class=\"wp-caption alignnone\"><a href=\"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-content\/uploads\/sites\/1961\/2026\/06\/Mast-Cells-Inflammation.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-medium wp-image-6794\" src=\"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-content\/uploads\/sites\/1961\/2026\/06\/Mast-Cells-Inflammation-300x127.png\" alt=\"(a) Mast cells detect injury to nearby cells and release histamine, initiating an inflammatory response. (b) Histamine increases blood flow to the wound site, and increased vascular permeability allows fluid, proteins, phagocytes, and other immune cells to enter infected tissue. These events result in the swelling and reddening of the injured site, and the increased blood flow to the injured site causes it to feel warm. Inflammation is also associated with pain due to these events stimulating nerve pain receptors in the tissue.\" width=\"300\" height=\"127\" srcset=\"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-content\/uploads\/sites\/1961\/2026\/06\/Mast-Cells-Inflammation-300x127.png 300w, https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-content\/uploads\/sites\/1961\/2026\/06\/Mast-Cells-Inflammation-1024x434.png 1024w, https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-content\/uploads\/sites\/1961\/2026\/06\/Mast-Cells-Inflammation-768x326.png 768w, https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-content\/uploads\/sites\/1961\/2026\/06\/Mast-Cells-Inflammation-1536x651.png 1536w, https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-content\/uploads\/sites\/1961\/2026\/06\/Mast-Cells-Inflammation-65x28.png 65w, https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-content\/uploads\/sites\/1961\/2026\/06\/Mast-Cells-Inflammation-225x95.png 225w, https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-content\/uploads\/sites\/1961\/2026\/06\/Mast-Cells-Inflammation-350x148.png 350w, https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-content\/uploads\/sites\/1961\/2026\/06\/Mast-Cells-Inflammation.png 1840w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-6794\" class=\"wp-caption-text\">(a) Mast cells detect injury to nearby cells and release histamine, initiating an inflammatory response. (b) Histamine increases blood flow to the wound site, and increased vascular permeability allows fluid, proteins, phagocytes, and other immune cells to enter infected tissue. These events result in the swelling and reddening of the injured site, and the increased blood flow to the injured site causes it to feel warm. Inflammation is also associated with pain due to these events stimulating nerve pain receptors in the tissue.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<div class=\"textbox textbox--key-takeaways\">\n<header class=\"textbox__header\">\n<p class=\"textbox__title\"><strong>Vasoactive Compounds in Inflammation<\/strong><\/p>\n<\/header>\n<div class=\"textbox__content\">\n<p style=\"text-align: justify\">Several key <strong>pro-inflammatory<\/strong>\u00a0<strong>mediators<\/strong> are classified as <strong>vasoactive<\/strong> compounds (they all change blood vessel diameter):<\/p>\n<ul style=\"text-align: justify\">\n<li><strong>Histamine:<\/strong>\u00a0 Nitrogenous compound released by mast cells, basophils, and platelets.<\/li>\n<li><strong>Bradykinin:<\/strong> Peptide activated by enzymatic cleavage of its kininogen precursor.<\/li>\n<li><strong>Prostaglandin:<\/strong> Lipid mediator released by mast cells, basophils, macrophages, and activated platelets.<\/li>\n<li><strong>Leukotrienes:<\/strong>\u00a0 Lipid mediators produced by mast cells, basophils, neutrophils, monocytes, and eosinophils.\u00a0 A potent <strong>bronchoconstrictor<\/strong> in asthma; also a vasodilator increasing capillary permeability.<\/li>\n<\/ul>\n<p style=\"text-align: justify\">All four compounds induce <strong>vasodilation,<\/strong> <strong>increase capillary permeability<\/strong>, cause <strong>bronchoconstriction,<\/strong> stimulate <strong>mucus<\/strong> production and trigger <strong>WBC chemotaxis<\/strong>.<\/p>\n<p style=\"text-align: justify\">Bradykinin, prostaglandin, and leukotriene also stimulate <strong>nociceptors,<\/strong> contributing to the <strong>pain<\/strong> of inflammation.\u00a0 Histamine stimulates <strong>itch<\/strong> (pruritus) especially during allergic reactions.<\/p>\n<p style=\"text-align: justify\"><strong>Side note:\u00a0<\/strong> Interestingly, itch and pain do share overlapping neuronal pathways and sharp pressure can temporarily override the itch sensation.\u00a0 However, the withdrawal neural reflex arc for pain differs from the scratching reflex for itch (which can damage the skin).<\/p>\n<\/div>\n<\/div>\n<h3><span style=\"color: #1f5c99\"><b>Four Types of Exudate<\/b><\/span><\/h3>\n<table class=\"grid landscape\" style=\"border-collapse: collapse;width: 100%;height: 60px\">\n<tbody>\n<tr style=\"height: 15px\">\n<td style=\"width: 14.7362%;height: 15px\"><span style=\"color: #032c80\"><strong>Serous<\/strong><\/span><\/td>\n<td style=\"width: 85.2638%;height: 15px\">Watery, containing some proteins and WBCs.\u00a0 Found in unruptured burn blisters.<\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td class=\"shaded\" style=\"width: 14.7362%;height: 15px\"><span style=\"color: #032c80\"><strong>Fibrinous<\/strong><\/span><\/td>\n<td class=\"shaded\" style=\"width: 85.2638%;height: 15px\">Thick, sticky, contains <strong>fibrin;<\/strong> associate with severe injuries and infections.<\/p>\n<p>Linked to increased scar tissue formation.<\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td style=\"width: 14.7362%;height: 15px\"><span style=\"color: #032c80\"><strong>Purulent<\/strong><\/span><\/td>\n<td style=\"width: 85.2638%;height: 15px\">Thick, yellow-green; contains WBCs and microorganisms.<\/p>\n<p>Seen in bacterially-infected abscesses and acne.<\/p>\n<p>Contains <strong>pus<\/strong> &#8211; a protein-rich fluid of dead cells and debris.<\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td class=\"shaded\" style=\"width: 14.7362%;height: 15px\"><span style=\"color: #032c80\"><strong>Hemorrhagic<\/strong><\/span><\/td>\n<td class=\"shaded\" style=\"width: 85.2638%;height: 15px\">Contains blood from damaged blood vessels.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<figure id=\"attachment_2360\" aria-describedby=\"caption-attachment-2360\" style=\"width: 300px\" class=\"wp-caption alignnone\"><a href=\"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-content\/uploads\/sites\/1961\/2024\/09\/Swollen_eye_with_conjunctivitis.jpg\" target=\"_blank\" rel=\"noopener\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-2360 size-medium\" src=\"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-content\/uploads\/sites\/1961\/2024\/09\/Swollen_eye_with_conjunctivitis-300x194.jpg\" alt=\"A swollen, pus-filled eye with conjunctivitis. Purulent exudate discharge, thick, milky or yellowing pus, is a mixture of dead cells, bacteria, and white blood cells.\" width=\"300\" height=\"194\" srcset=\"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-content\/uploads\/sites\/1961\/2024\/09\/Swollen_eye_with_conjunctivitis-300x194.jpg 300w, https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-content\/uploads\/sites\/1961\/2024\/09\/Swollen_eye_with_conjunctivitis-1024x661.jpg 1024w, https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-content\/uploads\/sites\/1961\/2024\/09\/Swollen_eye_with_conjunctivitis-768x496.jpg 768w, https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-content\/uploads\/sites\/1961\/2024\/09\/Swollen_eye_with_conjunctivitis-65x42.jpg 65w, https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-content\/uploads\/sites\/1961\/2024\/09\/Swollen_eye_with_conjunctivitis-225x145.jpg 225w, https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-content\/uploads\/sites\/1961\/2024\/09\/Swollen_eye_with_conjunctivitis-350x226.jpg 350w, https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-content\/uploads\/sites\/1961\/2024\/09\/Swollen_eye_with_conjunctivitis.jpg 1407w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-2360\" class=\"wp-caption-text\">A swollen, pus-filled eye with conjunctivitis. Purulent exudate discharge, thick, milky or yellowing pus, is a mixture of dead cells, bacteria, and white blood cells.<\/figcaption><\/figure>\n<h3><span style=\"color: #1f5c99\"><strong>Systemic Effects of Inflammation<\/strong><\/span><\/h3>\n<p style=\"text-align: justify\">Pro-inflammatory cytokines circulate the whole body, causing systemic effects; mild fever, <strong>malaise, fatigue, headache,<\/strong> <strong>loss of appetite<\/strong>, and &#8211; particularly in the elderly &#8211; decreased mental function.<\/p>\n<div class=\"textbox textbox--key-takeaways\">\n<header class=\"textbox__header\">\n<p class=\"textbox__title\"><strong>When Inflammation Goes Wrong:\u00a0 Too Little or Too Much<\/strong><\/p>\n<\/header>\n<div class=\"textbox__content\">\n<p style=\"text-align: justify\"><strong>Too little inflammation:<\/strong>\u00a0 In <strong>immunosuppressive<\/strong> diseases, insufficient inflammation allows prolonged tissue damage, infection, and potentially permanent tissue loss.<\/p>\n<p style=\"text-align: justify\"><strong>Too much inflammation:<\/strong>\u00a0 Chronic conditions such as atherosclerosis, diabetes, osteoarthritis, autoimmune diseases, allergies, and asthma drive prolonged inflammatory responses.\u00a0 Excessive WBC activity leads to cycles of tissue destruction and healing, causing progressive damage.<\/p>\n<p style=\"text-align: justify\"><strong>Systemic Inflammatory Response Syndrome (SIRS):<\/strong>\u00a0 A potentially fatal condition caused by a &#8220;cytokine storm&#8221;, a massive pro-inflammatory cytokine release.\u00a0 Results in <strong>systemic vasodilation <\/strong>and <strong>increased capillary permeability<\/strong>\u00a0\u2192 <strong>hypotension<\/strong>\u00a0and <strong>circulatory shock<\/strong>.\u00a0 Most frequently caused by <strong>sepsis<\/strong> (dysregulated immune response to infection).<\/p>\n<p style=\"text-align: justify\"><strong>Fever of Unknown Origin (FUO):<\/strong>\u00a0 Thought to be caused by inflammatory responses to undetectable cellular damage &#8211; from infections, trauma, cancer, heart attacks, blood clots, inflammatory diseases, or drug reactions.<\/p>\n<\/div>\n<\/div>\n<h3><\/h3>\n<div class=\"media-attributions clear\" prefix:cc=\"http:\/\/creativecommons.org\/ns#\" prefix:dc=\"http:\/\/purl.org\/dc\/terms\/\"><h2>Media Attributions<\/h2><ul><li about=\"https:\/\/openstax.org\/books\/microbiology\/pages\/17-5-inflammation-and-fever\"><a rel=\"cc:attributionURL\" href=\"https:\/\/openstax.org\/books\/microbiology\/pages\/17-5-inflammation-and-fever\" property=\"dc:title\">Mast Cells Inflammation<\/a>  &copy;  Nina Parker, Mark Schneegurt, Anh-Hue Thi Tu, Philip Lister, Brian M. Forster    is licensed under a  <a rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by-nc-sa\/4.0\/\">CC BY-NC-SA (Attribution NonCommercial ShareAlike)<\/a> license<\/li><li about=\"https:\/\/commons.wikimedia.org\/wiki\/File:Swollen_eye_with_conjunctivitis.jpg\"><a rel=\"cc:attributionURL\" href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Swollen_eye_with_conjunctivitis.jpg\" property=\"dc:title\">Private: Swollen_eye_with_conjunctivitis<\/a>  &copy;  Tanalai, Wikipedia Commons    is licensed under a  <a rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY (Attribution)<\/a> license<\/li><\/ul><\/div>","protected":false},"author":1370,"menu_order":5,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":["zoe-soon"],"pb_section_license":"cc-by-nc-sa"},"chapter-type":[],"contributor":[60],"license":[57],"class_list":["post-6538","chapter","type-chapter","status-web-only","hentry","contributor-zoe-soon","license-cc-by-nc-sa"],"part":25,"_links":{"self":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters\/6538","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/users\/1370"}],"version-history":[{"count":14,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters\/6538\/revisions"}],"predecessor-version":[{"id":6798,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters\/6538\/revisions\/6798"}],"part":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/parts\/25"}],"metadata":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters\/6538\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/media?parent=6538"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapter-type?post=6538"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/contributor?post=6538"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/license?post=6538"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}