In case of injury, platelets, together with the coagulation cascade, form the first line of defense by forming a blood clot. Thus, hemostasis and host defense were intertwined in evolution. For example, in the Atlantic horseshoe crab (living fossil estimated to be over 400 million years old), the only blood cell type, the amebocyte, facilitates both the hemostatic function and the encapsulation and phagocytosis of pathogens by means of exocytosis of intracellular granules containing bactericidal defense molecules. Blood clotting supports the immune function by trapping the pathogenic bacteria within.Although thrombosis, blood coagulation in intact blood vessels, is usually viewed as a pathological immune response, leading to obturation of lumen of blood vessel and subsequent hypoxic tissue damage, in some cases, directed thrombosis, called immunothrombosis, can locally control the spread of the infection. The thrombosis is directed in concordance of platelets, neutrophils and monocytes. The process is initiated either by immune cells by activating their pattern recognition receptors (PRRs), or by platelet-bacterial binding. Platelets can bind to bacteria either directly through thrombocytic PRRs and bacterial surface proteins, or via plasma proteins that bind both to platelets and bacteria. Monocytes respond to bacterial pathogen-associated molecular patterns (PAMPs), or damage-associated molecular patterns (DAMPs) by activating the extrinsic pathway of coagulation. Neutrophils facilitate the blood coagulation by NETosis. In turn, the platelets facilitate neutrophils NETosis. NETs bind tissue factor, binding the coagulation centres to the location of infection. They also activate the intrinsic coagulation pathway by providing its negatively charged surface to the factor XII.
Pallor is a pale color of the skin that can be caused by illness, emotional shock or stress, stimulant use, or anemia, and is the result of a reduced amount of oxyhaemoglobin and may also be visible as pallor of the conjunctivae of the eyes on physical examination. Pallor is more evident on the face and palms. It can develop suddenly or gradually, depending on the cause. It is not usually clinically significant unless it is accompanied by a general pallor (pale lips, tongue, palms, mouth and other regions with mucous membranes). It is distinguished from similar presentations such as hypopigmentation (lack or loss of skin pigment) or simply a fair complexion. Causes
migraine attack or headache
excess estradiol and/or estrone
osteoporosis
emotional response, due to fear, embarrassment, grief, rage
anorexia
anemia, due to blood loss, poor nutrition, or underlying disease such as sickle cell anemia
iron deficiency
vitamin B12 deficiency
shock, a medical emergency caused by illness or injury
acute compartment syndrome
frostbite
common cold
cancer
hypoglycaemia
bradycardia
panic attack
medications
ketorolac
amphetamines
ethanol
cannabis
lead poisoning
motion sickness
heart disease
Peripheral vascular disease
hypothyroidism
hypopituitarism
scurvy
tuberculosis
sleep deprivation
pheochromocytoma
squeamishness
visceral larva migrans
Orthostatic hypotension
methyldopa
loss of appetite
Space adaptation syndrome
fibromyalgia
Buergers disease
Hypovolemia

References


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