Veins are blood vessels that carry blood toward the heart. Most veins carry deoxygenated blood from the tissues back to the heart. In contrast to veins, arteries carry blood away from the heart. Veins are less muscular than arteries and are closer to the skin. There are valves in most veins to prevent backflow. Veins are present throughout the body as tubes. Veins are classified in a number of ways, including superficial vs. deep, pulmonary vs. systemic, large vs. small. Superficial veins are those closer to the surface of the body, have no corresponding arteries. Deep veins have corresponding arteries. Perforator veins drain from the superficial to the deep veins; these are referred to in the lower limbs and feet. Communicating veins are veins. Pulmonary veins are a set of veins. Systemic veins deliver deoxygenated blood to the heart. Most veins are equipped with valves to prevent blood flowing in the reverse direction. Veins are translucent, so the color a vein appears from an organism's exterior is determined in large part by the color of venous blood, dark red as a result of its low oxygen content.
Veins appear blue because the subcutaneous fat absorbs low-frequency light, permitting only the energetic blue wavelengths to penetrate through to the dark vein and reflect back to the viewer. The colour of a vein can be affected by the characteristics of a person's skin, how much oxygen is being carried in the blood, how big and deep the vessels are; when a vein is drained of blood and removed from an organism, it appears grey-white. The largest veins in the human body are the venae cavae; these are two large veins which enter the right atrium of the heart from below. The superior vena cava carries blood from the arms and head to the right atrium of the heart, while the inferior vena cava carries blood from the legs and abdomen to the heart; the inferior vena cava is retroperitoneal and runs to the right and parallel to the abdominal aorta along the spine. Large veins feed into these two veins, smaller veins into these. Together this forms the venous system. Whilst the main veins hold a constant position, the position of veins person to person can display quite a lot of variation.
The pulmonary veins carry oxygenated blood from the lungs to the heart. The superior and inferior venae cavae carry deoxygenated blood from the upper and lower systemic circulations, respectively; the portal venous system is a series of venules that directly connect two capillary beds. Examples of such systems include hypophyseal portal system; the peripheral veins carry blood from feet. Microscopically, veins have a thick outer layer made of connective tissue, called the tunica externa or tunica adventitia. During procedures requiring venous access such as venipuncture, one may notice a subtle "pop" as the needle penetrates this layer; the middle layer of bands of smooth muscle are called tunica media and are, in general, much thinner than those of arteries, as veins do not function in a contractile manner and are not subject to the high pressures of systole, as arteries are. The interior is lined with endothelial cells called tunica intima; the precise location of veins varies much more from person to person than that of arteries.
Veins serve to return blood from organs to the heart. Veins are called "capacitance vessels" because most of the blood volume is contained within veins. In systemic circulation oxygenated blood is pumped by the left ventricle through the arteries to the muscles and organs of the body, where its nutrients and gases are exchanged at capillaries. After taking up cellular waste and carbon dioxide in capillaries, blood is channeled through vessels that converge with one another to form venules, which continue to converge and form the larger veins; the de-oxygenated blood is taken by veins to the right atrium of the heart, which transfers the blood to the right ventricle, where it is pumped through the pulmonary arteries to the lungs. In pulmonary circulation the pulmonary veins return oxygenated blood from the lungs to the left atrium, which empties into the left ventricle, completing the cycle of blood circulation; the return of blood to the heart is assisted by the action of the muscle pump, by the thoracic pump action of breathing during respiration.
Standing or sitting for a prolonged period of time can cause low venous return from venous pooling shock. Fainting can occur but baroreceptors within the aortic sinuses initiate a baroreflex such that angiotensin II and norepinephrine stimulate vasoconstriction and heart rate increases to return blood flow. Neurogenic and hypovolaemic shock can cause fainting. In these cases, the smooth muscles surrounding the veins become slack and the veins fill with the majority of the blood in the body, keeping blood away from the brain and causing unconsciousness. Jet pilots wear pressurized suits to help maintain their venous blood pressure; the arteries are perceived as carrying oxygenated blood to the tissues, while veins carry deoxygenated blood back to the heart. This is true of the systemic circulation, by far the larger of the two circuits of blood in the body, which transports oxygen from the heart to the tissues of the body. However, in pulmonary circulation, the arteries carry deoxygenated blood from the heart to the lungs, veins return blood from the lungs to the heart.
The difference between veins a
In anatomy the apical foramen is the opening at the apex of the root of a tooth, through which the nerve and blood vessels that supply the dental pulp pass. Thus it represents the junction of the periodontal tissue; the average size of the orifice is 0.3 to 0.4 mm in diameter. There can be two or more foramina separated by cementum only. If more than one foramen is present on each root, the largest one is designated as the apical foramen and the rest are considered accessory foramina, it is a point of interest in endodontics, as it is considered necessary to chemomechanically debride the pulp space to remove all necrotic tissue and minimise bacterial load in the pulp space. Ideally this debridement would terminate at the apical foramen. In reality determining the exact position of the apical foramen is problematic, requiring radiography and/or use of an electronic apex locator to produce a refined estimate. A tooth may have multiple small accessory canals in the root apex area forming an apical delta which can complicate the endodontic problem.
An apical constriction is present. In immature teeth the root is not formed leading to an open apex; this is seen in some pathological teeth. This article incorporates text in the public domain from the 20th edition of Gray's Anatomy Color Atlas and Textbook of Oral Anatomy and Embryology by B. K. Berkovitz, G. R. Holland, B. J. Moxham. Hardcover, Mosby, ISBN 0-8151-0697-1
The skull is a bony structure that forms the head in vertebrates. It provides a protective cavity for the brain; the skull is composed of two parts: the mandible. In the human, these two parts are the neurocranium and the viscerocranium or facial skeleton that includes the mandible as its largest bone; the skull forms the anterior most portion of the skeleton and is a product of cephalisation—housing the brain, several sensory structures such as the eyes, ears and mouth. In humans these sensory structures are part of the facial skeleton. Functions of the skull include protection of the brain, fixing the distance between the eyes to allow stereoscopic vision, fixing the position of the ears to enable sound localisation of the direction and distance of sounds. In some animals such as horned ungulates, the skull has a defensive function by providing the mount for the horns; the English word "skull" is derived from Old Norse "skulle", while the Latin word cranium comes from the Greek root κρανίον.
The skull is made up of a number of fused flat bones, contains many foramina, fossae and several cavities or sinuses. In zoology there are openings in the skull called fenestrae. For details and the constituent bones, see Neurocranium and Facial skeleton The human skull is the bony structure that forms the head in the human skeleton, it forms a cavity for the brain. Like the skulls of other vertebrates, it protects the brain from injury; the skull consists of two parts, of different embryological origin—the neurocranium and the facial skeleton. The neurocranium forms the protective cranial cavity that surrounds and houses the brain and brainstem; the upper areas of the cranial bones form the calvaria. The membranous viscerocranium includes the mandible; the facial skeleton is formed by the bones supporting the face Except for the mandible, all of the bones of the skull are joined together by sutures—synarthrodial joints formed by bony ossification, with Sharpey's fibres permitting some flexibility.
Sometimes there can be extra bone pieces within the suture known as sutural bones. Most these are found in the course of the lambdoid suture; the human skull is considered to consist of twenty-two bones—eight cranial bones and fourteen facial skeleton bones. In the neurocranium these are the occipital bone, two temporal bones, two parietal bones, the sphenoid and frontal bones; the bones of the facial skeleton are the vomer, two inferior nasal conchae, two nasal bones, two maxilla, the mandible, two palatine bones, two zygomatic bones, two lacrimal bones. Some sources count the maxilla as having two bones; some of these bones—the occipital, frontal, in the neurocranium, the nasal and vomer, in the facial skeleton are flat bones. The skull contains sinuses, air-filled cavities known as paranasal sinuses, numerous foramina; the sinuses are lined with respiratory epithelium. Their known functions are the lessening of the weight of the skull, the aiding of resonance to the voice and the warming and moistening of the air drawn into the nasal cavity.
The foramina are openings in the skull. The largest of these is the foramen magnum that allows the passage of the spinal cord as well as nerves and blood vessels; the many processes of the skull include the zygomatic processes. The skull is a complex structure; the skull roof bones, comprising the bones of the facial skeleton and the sides and roof of the neurocranium, are dermal bones formed by intramembranous ossification, though the temporal bones are formed by endochondral ossification. The endocranium, the bones supporting the brain are formed by endochondral ossification, thus frontal and parietal bones are purely membranous. The geometry of the skull base and its fossae, the anterior and posterior cranial fossae changes rapidly; the anterior cranial fossa changes during the first trimester of pregnancy and skull defects can develop during this time. At birth, the human skull is made up of 44 separate bony elements. During development, many of these bony elements fuse together into solid bone.
The bones of the roof of the skull are separated by regions of dense connective tissue called fontanelles. There are six fontanelles: one anterior, one posterior, two sphenoid, two mastoid. At birth these regions are fibrous and moveable, necessary for birth and growth; this growth can put a large amount of tension on the "obstetrical hinge", where the squamous and lateral parts of the occipital bone meet. A possible complication of this tension is rupture of the great cerebral vein; as growth and ossification progress, the connective tissue of the fontanelles is invaded and replaced by bone creating sutures. The five sutures are the two squamous sutures, one coronal, one lambdoid, one sagittal suture; the posterior fontanelle closes by eight weeks, but the anterior fontanel can remain open up to eighteen months. The anterior fontanelle is located at the junction of the parietal bones. Careful observation will show that you can count a baby's heart
Anatomy is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science which deals with the structural organization of living things, it is an old science. Anatomy is inherently tied to developmental biology, comparative anatomy, evolutionary biology, phylogeny, as these are the processes by which anatomy is generated over immediate and long timescales. Anatomy and physiology, which study the structure and function of organisms and their parts, make a natural pair of related disciplines, they are studied together. Human anatomy is one of the essential basic sciences; the discipline of anatomy is divided into microscopic anatomy. Macroscopic anatomy, or gross anatomy, is the examination of an animal's body parts using unaided eyesight. Gross anatomy includes the branch of superficial anatomy. Microscopic anatomy involves the use of optical instruments in the study of the tissues of various structures, known as histology, in the study of cells.
The history of anatomy is characterized by a progressive understanding of the functions of the organs and structures of the human body. Methods have improved advancing from the examination of animals by dissection of carcasses and cadavers to 20th century medical imaging techniques including X-ray and magnetic resonance imaging. Derived from the Greek ἀνατομή anatomē "dissection", anatomy is the scientific study of the structure of organisms including their systems and tissues, it includes the appearance and position of the various parts, the materials from which they are composed, their locations and their relationships with other parts. Anatomy is quite distinct from physiology and biochemistry, which deal with the functions of those parts and the chemical processes involved. For example, an anatomist is concerned with the shape, position, blood supply and innervation of an organ such as the liver; the discipline of anatomy can be subdivided into a number of branches including gross or macroscopic anatomy and microscopic anatomy.
Gross anatomy is the study of structures large enough to be seen with the naked eye, includes superficial anatomy or surface anatomy, the study by sight of the external body features. Microscopic anatomy is the study of structures on a microscopic scale, along with histology, embryology. Anatomy can be studied using both invasive and non-invasive methods with the goal of obtaining information about the structure and organization of organs and systems. Methods used include dissection, in which a body is opened and its organs studied, endoscopy, in which a video camera-equipped instrument is inserted through a small incision in the body wall and used to explore the internal organs and other structures. Angiography using X-rays or magnetic resonance angiography are methods to visualize blood vessels; the term "anatomy" is taken to refer to human anatomy. However the same structures and tissues are found throughout the rest of the animal kingdom and the term includes the anatomy of other animals.
The term zootomy is sometimes used to refer to non-human animals. The structure and tissues of plants are of a dissimilar nature and they are studied in plant anatomy; the kingdom Animalia contains multicellular organisms that are motile. Most animals have bodies differentiated into separate tissues and these animals are known as eumetazoans, they have an internal digestive chamber, with two openings. Metazoans do not include the sponges. Unlike plant cells, animal cells have neither chloroplasts. Vacuoles, when present, are much smaller than those in the plant cell; the body tissues are composed of numerous types of cell, including those found in muscles and skin. Each has a cell membrane formed of phospholipids, cytoplasm and a nucleus. All of the different cells of an animal are derived from the embryonic germ layers; those simpler invertebrates which are formed from two germ layers of ectoderm and endoderm are called diploblastic and the more developed animals whose structures and organs are formed from three germ layers are called triploblastic.
All of a triploblastic animal's tissues and organs are derived from the three germ layers of the embryo, the ectoderm and endoderm. Animal tissues can be grouped into four basic types: connective, epithelial and nervous tissue. Connective tissues are fibrous and made up of cells scattered among inorganic material called the extracellular matrix. Connective tissue holds them in place; the main types are loose connective tissue, adipose tissue, fibrous connective tissue and bone. The extracellular matrix contains proteins, the chief and most abundant of, collagen. Collagen plays a major part in maintaining tissues; the matrix can be modified to form a skeleton to protect the body. An exoskeleton is a thickened, rigid cuticle, stiffened by mineralization, as in crustaceans or by the cross-linkin
The obturator foramen is the large opening created by the ischium and pubis bones of the pelvis through which nerves and blood vessels pass. It is bounded by a thin, uneven margin, to which a strong membrane is attached, presents, superiorly, a deep groove, the obturator groove, which runs from the pelvis obliquely medialward and downward; this groove is converted into the obturator canal by a ligamentous band, a specialized part of the obturator membrane, attached to two tubercles: one, the posterior obturator tubercle, on the medial border of the ischium, just in front of the acetabular notch the other, the anterior obturator tubercle, on the obturator crest of the superior ramus of the pubis Reflecting the overall sex differences between male and female pelvises, the obturator foramina are oval in the male and wider and more triangular in the female. Additionally, unilateral pelvis hypoplasia can cause differences in size between the obturator foramina, there are rare reports of individual pelvises featuring a double obturator foramen in one of the hip bones.
Through the canal the obturator artery, obturator vein and obturator nerve pass out of the pelvis. Obturator internus muscle Obturator externus muscle This article incorporates text in the public domain from page 237 of the 20th edition of Gray's Anatomy Anatomy photo:17:st-0205 at the SUNY Downstate Medical Center - "Major Joints of the Lower Extremity: hip and sacrum" Atlas image: male_urethrogram at the University of Michigan Health System - "Pelvis & Perineum: Male Urethrogram" Photo at vc.cc.tx.us
Greater sciatic foramen
The greater sciatic foramen is an opening in the posterior human pelvis. It is formed by the sacrospinous ligaments; the piriformis muscle occupies most of its volume. The greater sciatic foramen is wider in women than in men, it is bounded as follows: anterolaterally by the greater sciatic notch of the ilium posteromedially by the sacrotuberous ligament inferiorly by the sacrospinous ligament and the ischial spine superiorly by the anterior sacroiliac ligament The piriformis, which exits the pelvis through the foramen, occupies most of its volume. The following structures exit the pelvis through the greater sciatic foramen: The foramen contains: 7 nerves: Sciatic Nerve: Superior Gluteal Nerve: Inferior Gluteal Nerve: Pudendal Nerve: Posterior Femoral Cutaneous Nerve Nerve to Quadratus Femoris Nerve to Obturator Internus 3 Vessel Sets: Superior Gluteal Artery & Vein Inferior Gluteal Artery & vein Internal Pudendal Artery & vein 1 Muscle: Piriformis Lesser sciatic foramen This article incorporates text in the public domain from page 309 of the 20th edition of Gray's Anatomy Anatomy photo:41:os-0109 at the SUNY Downstate Medical Center Greater_sciatic_foramen at the Duke University Health System's Orthopedics program glutealregion at The Anatomy Lesson by Wesley Norman
In a typical vertebra, the vertebral foramen is the foramen formed by the anterior segment, the posterior part, the vertebral arch. The vertebral foramen begins at cervical vertebra #1 and continues inferior to lumbar vertebra #5; the vertebral foramen houses its meninges. This large tunnel running up and down inside all of the vertebrae contains the spinal cord and is called the spinal canal, not the vertebral foramen. Atlas #Vertebral foramen This article incorporates text in the public domain from the 20th edition of Gray's Anatomy Anatomy figure: 02:01-06 at Human Anatomy Online, SUNY Downstate Medical Center - "Superior and lateral views of typical vertebrae" Vertebral foramen - BlueLink Anatomy - University of Michigan Medical School Atlas image: back_bone16 at the University of Michigan Health System - "Typical Lumbar Vertebra, Superior View.