What is Thyroid Gland? Thyroid Gland Definition The thyroid gland is an endocrine gland that occurs in the neck and is essential for iodine metabolism and secretion of thyroid hormones. The gland is small and highly vascular, like most endocrine glands. It occurs in the neck between the 5th, 6th, and 7th cervical vertebrae. The development of the gland and …
Exocrine Glands Definition Exocrine glands are the glands with ducts that allow the cells to secrete their products into those ducts so that they can be released onto the surface of the target cells or organs. The cells of the exocrine glands are linked to the covering epithelium by narrow tubular ducts that carry the secretions to their target sites. …
What is Pituitary Gland? Definition of Pituitary Gland The pituitary gland is an endocrine gland that works to maintain cellular homeostasis in the body by the release of different hormones. The pituitary gland is also called the master gland as it regulates the working and secretion of other endocrine glands. Even though the pituitary gland is the most important endocrine …
What is Endocrine System? Definition of Endocrine System An endocrine system is a group of ductless glands where the secretory cells diffuse the hormones directly into the bloodstream. The glands of the endocrine system are termed endocrine glands and are defined by the lack of ducts for the passage of their secretions. The endocrine system is considered to work together …
What are Platelets (Thrombocytes)? Platelets (Thrombocytes) Definition Platelets or thrombocytes are anucleated cells derived from the megakaryocytic cells in the bone marrow that, besides being one of the key players in maintaining hemostasis, are involved in developing non-hemostatic immune functions. Platelets the second most abundant cells in the blood circulation, with the concentration ranging between 150-400 × 109 /L. The …
What are Monocytes? Definition of Monocytes Monocytes are cells of the immune system that represent immune effector cells with chemokine receptors and pathogen recognition receptors that circulate through blood or remain localized in lymphoid organs. These cells account for about 5% of the total circulating nucleated cells in human blood and have a half-life of three days. Monocytes are essential …
What are Basophils? Definition of Basophils Basophils are nonphagocytic granulocytes that are the least common leukocytes occurring in the blood circulation and are critical to the immune response against parasites. Basophils are similar to eosinophils in that these are produced in response to parasitic infections; however, in the absence of parasitic infections, basophils are involved in allergy symptoms. Even though …
What are Eosinophils? Definition of Eosinophils Eosinophils are motile phagocytic cells that play an important homeostatic role in providing defense against parasitic infections. Eosinophils are bone marrow-derived granulocytes that remain in the bloodstream for a shorter period of time and mostly reside in tissues. The functions of eosinophils are multifaceted, including antigen presentation, the release of peptides, lipids, and cytokine …
What are Mast Cells? Definition of Mast Cells Mast cells are cells of the immune system of the hematopoietic lineage that remain widely distributed in vascularized tissues throughout the body. Mast cells, unlike other immune cells, do not remain in the blood but remain localized in mucosal and epithelial tissues throughout the body. These are among the first cells to …
What are Dendritic Cells? Definition of Dendritic cells Dendritic cells are key antigen-presenting cells of the immune system that inform other effector immune cells to fight against invasive pathogens. These are also called professional antigen-presenting cells as these present antigens or parts of antigen to the receptors on different immune cells in order to elicit an immune response against them. …
What are Macrophages? Macrophages Definition Macrophages are mononuclear cells functioning as professional phagocytes in order to remove dying, dead or harmful pathogens. Macrophages are a type of white blood cell of the immune system where they engulf and digest particles that are detected as antigens by other blood cells. These are larger phagocytic cells that occur in essentially all types …
What are Natural Killer (NK) Cells? Definition of NK Cells Natural killer (NK) cells are a group of innate lymphocyte cells with cytolytic activity against virus-infected cells and physiologically stressed cells like tumor cells. Initially, NK cells were described as larger granular lymphocytes with cytotoxic activity against tumor cells. However, these have since been recognized as a separated lineage of …
What is Bordetella pertussis? Bordetella pertussis is a pathogenic Gram-negative aerobic bacterium that is the causative agent of the disease pertussis or whooping cough. B. pertussis is the type species of Bordetella that consists of minute mesophilic coccobacillus that facilitates the colonization of animal tissues. B. pertussis is one of the eight species belonging to the genus Bordetella and one …