Circulatory and Respiratory Systems - NCLEX-PN

Platelets are small cell fragments that play an important role in hemostasis, or clot formation. Once activated, platelets release clotting factors that recruit more platelets till a clot is formed and bleeding stops.

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.

The S2 heart sound (sometimes referred to as the "dub" in "lub-dub") occurs in diastole, during the closing of the aortic and pulmonary valves. When pressure within the aorta and pulmonary arteries exceeds pressure within the heart, the cups of the valves fill with blood and snap shut, causing the "dub" sound.

The contraction rate for the heart is set by the cells of the sinoatrial node, also known as the pacemaker cells of the heart. These cells have membranes that are especially permeable to ions, and are able to depolarize on their own at a rate of 70-100 beats per minute. All the other areas listed do have their own spontaneous contractility, but their rates are slower than that of the sinoatrial node. Thus, the sinoatrial node is the pacemaker in a healthy heart.

The diaphragm is a thin sheet of muscle that separates the thoracic cavity from the abdominal cavity. At rest, it is drawn upward into a dome-like shape under the lungs. When the diaphragm contracts, the dome flattens out, which increases the size of the thoracic cavity. The negative pressure allows the lungs to expand and fill with air, causing an increase in total lung volume (inhalation).

The only sinuses that can be assessed on physical exam are the frontal and maxillary sinuses. The sphenoid and ethmoid sinuses are too deep in the skull to be assessed via physical examination.

The small flap of cartilage that covers the windpipe to prevent aspiration during swallowing is the epiglottis. It is located at the base of the tongue and attached to the entrance of the larynx.

The lumen of the trachea is maintained by the tracheal cartilages, a set of approximately 20 separate c-shaped rings of hyaline cartilage. The non-continuous cartilage allows for greater flexibility during inspiration and expiration.

The epithelium of the trachea is made up of pseudostratified columnar cells with cilia and goblet cells.

The esophagus is directly posterior to the trachea, and the cervical spine is posterior to the esophagus. The thyroid gland is anterior to the trachea. The pharynx is superior to both the trachea and the esophagus.

The trachea bifurcates into the left and right primary bronchi. This occurs at a location called the carina, which is at the level of T4-T5.

AB positive is a universal recipient, meaning a patient with AB positive type blood can receive a blood transfusion using any type of blood.

The average lifespan of a red blood cell is 4 months, after which it is phagocytosed by macrophages the spleen, liver, or lymph nodes. White blood cells, on the other hand, live for only about 3-4 days.

The casting of new red blood cells is stimulated by the hormone erythropoietin (EPO), released from the kidneys. Recall that all blood cells are made in the bone marrow. This hormone may increase as much as 1000 fold in times of oxidative stress.

Thyroxine is T4, the most biologically active form of thyroid hormone. Vasopressin, or anti-diuretic hormone, is part of the body's fluid-balance system. Luteinizng hormone is a hormone of the reproductive tract: in females it triggers ovulation, while in males it stimulates Leydig cells to produce testosterone.

Erythropoietin is produced by the peritubular interstitial cells of the kidney. These cells are very sensitive to tissue oxygen pressure. When oxygen demand increases, erythropoietin is released, stimulating the casting (hematopoiesis) of new red blood cells in bone marrow.

Supraoptic and paraventricular cells of the hypothalamus are the site of vasopressin (antidiuretic hormone) production. Lactotroph cells in the pituitary gland are responsible for the production of prolactin. Zona fasciculata cells of the adrenal glands produce cortisol.

Each heme group in hemoglobin encloses a single iron atom in the center of a protoporphyrin, a tetrapyrrol composed of four pyrrole rings linked together by four methyl groups, two vinyl groups, a methane bridge, and two propinoic acid side chains.

Neutrophils are the most common type of white blood cell, making up 55-70% of the total white blood cell population in the average blood sample.