Final answer:
The release of neutrophils from the bone marrow is influenced by stress hormones, chemokines, and colony-stimulating factors (CSFs) that trigger their production and mobilization into the bloodstream, and chemotactic agents that guide them to sites of infection or inflammation.
Step-by-step explanation:
The release of neutrophils from the bone marrow is influenced by several factors, most notably stress response, certain hormones and cytokines. These include neutrophil-eliciting chemokines like interleukins, colony-stimulating factors (CSFs), leukotrienes, and hormonal factors such as epinephrine (EPI) and corticosterone. During a stress response, epinephrine and norepinephrine increase leukocyte numbers, mobilizing immune cells such as neutrophils, monocytes, and lymphocytes.
Additionally, certain colony-stimulating factors, or CSFs, act as autocrine or paracrine factors and specifically encourage the production and release of various white blood cells, including neutrophils, by stimulating the differentiation of myeloblasts in the bone marrow. For instance, granulocyte colony-stimulating factor (G-CSF) specifically triggers differentiation into neutrophils. During episodes of infection or inflammation, leukotrienes attract neutrophils to the infection site through chemotaxis, and cytokines released by macrophages encourage further recruitment of phagocytes like neutrophils.
Figure 42.5 illustrates how after an injury, mast cells secrete histamines, leading to the dilation of capillaries and allowing neutrophils and other immune cells to exit the bloodstream and move to affected tissues. Concurrently, thrombopoietin, another set of colony-stimulating factors, and interleukins contribute to the proliferation and differentiation of formed elements such as leukocytes that can respond to chemical signals from pathogens and injured cells.