Inflammation is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and molecular mediators. The function of inflammation is to eliminate the initial cause of cell injury, clear out necrotic cells and tissues damaged from the original insult and the inflammatory process, and to initiate tissue repair.

Inflammation can be classified as either acute or chronic. 

Acute inflammation is the initial response of the body to harmful stimuli. A series of biochemical events propagates and matures the inflammatory response, involving the local vascular system, the immune system, and various cells within the injured tissue. Acute inflammation is typically self-limiting, and after the offending agent is eliminated the tissue returns to the homeostatic state (the property of a system within the body of a living organism in which a variable, such as the concentration of a substance in solution, is actively regulated to remain very nearly constant). 

Prolonged inflammation, known as chronic inflammation, leads to a progressive shift in the type of cells present at the site of inflammation, such as mononuclear cells, and is characterized by simultaneous destruction and healing of the tissue from the inflammatory process. Although chronic inflammation may follow acute inflammation, sometimes it likely begins insidiously as a low-grade, smoldering response with no manifestation of the cardinal signs of inflammation such as (Dolor (pain), Calor (heat), Rubor (redness) and Tumor (swelling)). However, even low-grade inflammation may impair tissue function (Functio laesa). The continuous progression of tissue injury and repair promotes tissue remodeling (e.g., extensive fibrosis) that may eventually cause irreversible tissue dysfunction.

Inflammation is a generic response, and therefore it is considered as a mechanism of innate immunity, as compared to adaptive immunity, which is specific for each pathogen. Too little inflammation could lead to progressive tissue destruction by the harmful stimulus (e.g. bacteria) and compromise the survival of the organism. In contrast, chronic inflammation may lead to a host of diseases, such as hay fever, periodontitis (a set of inflammatory diseases affecting the tissues surrounding the teeth), atherosclerosis, rheumatoid arthritis (a long-term autoimmune disorder that primarily affects joints), and even cancer (e.g., gallbladder carcinoma). Inflammation is therefore normally closely regulated by the body.

Polycystic ovary syndrome (PCOS)

Chronic inflammation is associated with reproductive system. Disease called polycystic ovary syndrome (PCOS) is a set of symptoms due to elevated androgens (male hormones) in women. Signs and symptoms of PCOS include irregular or no menstrual periods, heavy periods, excess body and facial hair, acne, pelvic pain, difficulty getting pregnant, and patches of thick, darker, velvety skin. Polycystic ovary syndrome (PCOS) is a common endocrine disorder in women of reproductive age group. 

Obesity, mainly visceral adiposity, is prevalent in patients with PCOS. Obesity is associated with a state of chronic systemic inflammation manifested by increased serum levels of inflammatory cytokines (a broad and loose category of small proteins) as well as alterations in peripheral blood lymfocyte (white blood cells) frequencies and function. These changes are present not only at the tissue level but also in adipose, liver, and other tissue beds. This inflammatory process could be the underlying cause of obesity-related comorbidities, including atherosclerosis, diabetes and steatohepatosis (a type of fatty liver disease, characterized by inflammation of the liver with concurrent fat accumulation in liver).

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Polycystic ovary syndrome ―sourced from Wikipedia licensed under CC BY-SA 3.0
Inflammation ―sourced from Wikipedia licensed under CC BY- SA 3.0
Macrophages in age-related chronic inflammatory diseases ―by Oishi and Manabe licensed under CC BY 4.0
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