General Biology - NCLEX-PN

Diapedesis, also known as leukocyte extravasation, is the process by which white blood cells move into and out of blood vessels. This process includes four stages: chemoattraction, rolling adhesion, tight adhesion, and endothelial transmigration. This process is integral in the delivery of white blood cells to sites of infection and in their return into the blood stream to mobilize and facilitate the excretion of waste.

Neutrophils, eosinophils, and basophils are all granulocytes, meaning they contain visible granules within their cytoplasms. These granules contains acids and antimicrobial enzymes, and are released at the site of infection. Monocytes and lymphocytes are agranulocytes, meaning they do not contain granules in their cytoplasm but rather destroy foreign proteins by other means, such as phagocytosis and cytotoxicity.

Platelets are derived from megakaryocytes, cells produced in bone marrow, kidney, liver, and spleen, with large, lobed nuclei. Platelets are formed within the cell and then released into plasma. Erythrocytes (mature red blood cells), plasma cells (a type of B cell) and progranulocytes (precursors to neutrophils, basophils, and eosinophils) take no part in the creation of platelets, which are fragments of cells, not whole cells.

Selenium is essential for conversion of T4 to T3. Deiodinase enzymes, which remove iodine from T4 during conversion into T3, are selenium dependent. Tyrosine and iodine are both required for synthesis of T4, and iron is the cofactor for conversion of phenylalanine into tyrosine.

Calcitonin is produced by the parafollicular (c cells) of the thyroid as a response to elevated blood calcium levels. Calcitonin reduces plasma calcium by inhibiting osteoclast activity and stimulating osteoblasts to deposit more bone. Parathyroid hormone has the opposite effect - it acts to increase calcium levels when serum calcium decreases. While they may ultimately affect serum calcium levels, thyroid hormone and cortisol are not directly involved in calcium homeostasis.

The nutrients specifically required for thyroid hormone production are tyrosine, iodine, and selenium, in addition to zinc and several B vitamins. While magnesium, manganese, and methionine are all essential for metabolism and overall hormone production, they are not direct substrates or cofactors in the production of thyroid hormone.

Tyrosine and iodine are both precursors for synthesis of T4. Selenium is essential for conversion of T4 to T3, and iron is the cofactor for conversion of phenylalanine into tyrosine.

The pineal gland is responsible for regulating melatonin. It is not known at this time to secrete any other hormone. Melatonin is thought to play a critical role in the regulation of the circadian rhythm. Cortisol is secreted by the adrenal cortex and is involved in regulating the stress response. Vitamin D become activated in three steps. First, ultraviolet light in the skin begins the process, then the process continues in the liver, and is completed in the kidney. The active form of vitamin D increases calcium absorption in the gut, decreases calcium loss in urine, and increases calcium mobilization from bone. Vasopressin is also known as antidiuretic hormone, and functions in water retention. Leptin is a hormone secreted by adipose tissue that tells the body that it is full, and not hungry.

Leptin is secreted by adipose cells, and acts on the arcuate nucleus of the lateral hypothalamus to promote the synthesis of alpha-MSH (alpha-melanocyte-stimulating hormone), which is a hunger suppressant. It also binds to receptors for neuropeptide Y (NPY), a powerful hunger promoter, in the arcuate nucleus.

None of the other hormones listed, while all involved in nutrient and blood sugar metabolism, directly trigger feeling of satiety.

Leptin, the hormone responsible for feelings of satiety, goes down during times of fasting, with high testosterone, during sleep deprivation, and during periods of prolonged exercise or physical training.

Insulin has many physiological effects on metabolism. It increases uptake of glucose and various ions, especially potassium, from the blood. It promotes glycogen and protein synthesis, and encourages storage of fats. Conversely, insulin inhibits lipolysis, gluconeogenesis, ketogenesis, and proteolysis.

IgA, primarily in its secretory form (sIgA), is the most abundant immunoglobulin in the lining of the gastrointestinal tract and in the mucus membranes of the respiratory tract. It is also present in the urogenital tract, in tears, in saliva, and in breast milk. All of the other immunoglobulins may be present in mucus membranes, depending on the presence of active infection or allergy, but none is as abundant in secretions as IgA. IgE is primarily involved in binding allergens and inducing the allergic response via release of histamine. IgM is expressed on the surface of B cells and is the first immunoglobulin to fight pathogens at the site of infection/injury. IgG are the most abundant antibody throughout the body and play the largest role in fighting pathogens. IgG can cross the placenta and thus confer passive immunity to the fetus.

The presence of CMV IgM would suggest an active cytomegalovirus infection, as IgM is the immunoglobulin released during the initial, active infection with a pathogen. The presence of IgG would suggest a past infection, where IgG specific to the virus would be present as part of adaptive immunity (ready to respond to the virus should the host ever be re-exposed). IgE is not formed when an individual contracts CMV, as IgE is produced in response to allergens rather than pathogens (except parasites). The function of IgD is thought to be related to the allergic response by regulating basophils and mast cells.

The only immunoglobulin that has been shown to be able to cross the placenta is IgG. This is important in that it confers short term immunity to the fetus that continues into the first few months of the infant's life. Note that it is common to give Rh-negative anti-Rh IgG injections at about 28 weeks gestation; a booster may also be given at about 34 weeks gestation.

Insulin is produced by beta cells of the pancreatic islets. Insulin's action is to decrease blood glucose, facilitating its uptake into cells. Alpha cells produce glucagon, which has the opposite effect as insulin. Delta cells produce somatostatin, which inhibits many digestive processes. and gamma cells produce pancreatic polypeptide, which regulate pancreatic secretion.

The costal cartilage of the ribcage is joined to the sternum, which is made up of three bony structures: the most superior is the manubrium, which articulates not just with the costal cartilage of the first rib but also with the clavicles. The body of the sternum is inferior to the manubrium, and articulates with the second through fifth ribs. The xiphoid process is a small protuberance just below the body of the sternum, at the point where the bottom of the ribcage meets the sternum. It is an attachment point for several muscles, including the diaphragm, the rectus abdominis, and the transverse abdominis. This is a common location for referred pain from gallbladder disease, GERD, or pain due to musculoskeletal injury or irritation.

The bony ridge of the brow is formed by the superciliary processes (superciliary means super, or above, cilia, the lens of the eye). The orbit refers to the bony socket in which the eye sits. The glabella is the small depression between the eyebrows where the two superciliary arches meet. The coronoid process is part of the mandible, or jawbone, and unrelated to the brow.

The nasal cavity is formed by the following bones: the maxilla, the vomer, the nasal bone, the palatine bones, the lacrimal bone, and the ethmoid bone. It is also formed by the nasal conchae and the septal cartilage. The sphenoid forms part of the orbit and multiple sinuses but does not form any art of the nasal cavity directly.

The foramen that forms the ear canal is called the external auditory meatus. This travels through the temporal bone and joins the inner ear to the outer ear. The internal auditory meatus passes through the temporal bone between the posterior cranial fossa and the inner ear, and is the track through which the vestibulocochlear nerve, the facial nerve, and the labyrinthine artery travel from the inner ear toward the CNS. The foramen ovale and foramen rotundum are both openings in the sphenoid bones and have to connection to the ear.