THE VEINS convey the blood from the capillaries of the different parts of the body to the heart. They consist of two distinct sets of vessels, the pulmonary and systemic.
The Portal Vein, an appendage to the systemic venous system, is confined to the abdominal cavity, and returns the venous blood from the spleen and the viscera of digestion to the liver. This vessel ramifies in the substance of the liver and there breaks up into a minute network of capillary-like vessels, from which the blood is conveyed by the hepatic veins to the inferior vena cava.
The veins commence by minute plexuses which receive the blood from the capillaries. The branches arising from these plexuses unite together into trunks, and these, in their passage toward the heart, constantly increase in size as they receive tributaries, or join other veins. The veins are larger and altogether more numerous than the arteries; hence, the entire capacity of the venous system is much greater than that of the arterial; the capacity of the pulmonary veins, however, only slightly exceeds that of the pulmonary arteries. The veins are cylindrical like the arteries; their walls, however, are thin and they collapse when the vessels are empty, and the uniformity of their surfaces is interrupted at intervals by slight constrictions, which indicate the existence of valves in their interior. They communicate very freely with one another, especially in certain regions of the body; and these communications exist between the larger trunks as well as between the smaller branches. Thus, between the venous sinuses of the cranium, and between the veins of the neck, where obstruction would be attended with imminent danger to the cerebral venous system, large and frequent anastomoses are found. The same free communication exists between the veins throughout the whole extent of the vertebral canal, and between the veins composing the various venous plexuses in the abdomen and pelvis, e. g., the spermatic, uterine, vesical, and pudendal.
The Superficial Veins (cutaneous veins) are found between the layers of the superficial fascia immediately beneath the skin; they return the blood from these structures, and communicate with the deep veins by perforating the deep fascia.
The Deep Veins accompany the arteries, and are usually enclosed in the same sheaths with those vessels. With the smaller arteries—as the radial, unlar, brachial, tibial, peroneal—they exist generally in pairs, one lying on each side of the vessel, and are called venæ comitantes. The larger arteries—such as the axillary, subclavian, popliteal, and femoral—have usually only one accompanying vein. In certain organs of the body, however, the deep veins do not accompany the arteries; for instance, the veins in the skull and vertebral canal, the hepatic veins in the liver, and the larger veins returning blood from the bones.
Venous Sinuses are found only in the interior of the skull, and consist of canals formed by a separation of the two layers of the dura mater; their outer coat consists of fibrous tissue, their inner of an endothelial layer continuous with the lining membrane of the veins.
The United States Medical Licensing Examination (USMLE) is a three-step examination for medical licensure in the United States. The Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners (NBME) sponsors USMLE.
The Three Steps of the USMLE
Step 1 tests the important concepts of basic sciences basic to the practice of medicine. It also places special emphasis on principles and mechanisms underlying health, disease, and modes of therapy. Step 1 ensures mastery of the sciences that provide a foundation for the safe and competent practice of medicine. It also tests the scientific principles required for maintenance of competence through lifelong learning.
Step 2 CK tests the medical knowledge, skills, and understanding of clinical science essential for the provision of patient care under supervision. It also includes emphasis on health promotion and disease prevention. Step 2 CK ensures that due attention is devoted to principles of clinical sciences and basic patient-centered skills.
Step 2 CS tests your capacity to practice and provide good medical service in real-life situations. It also tests your communication skills.
Step 3 tests your medical knowledge and understanding of biomedical and clinical science essential for the unsupervised practice of medicine. Step 3 provides a final assessment of physicians assuming independent responsibility for delivering general medical care.
