Anatomy Terms Starting With V
Anatomy Glossary: V
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Vein
/ VAYN / · Latin vena, blood vessel
Vein is a blood vessel that carries blood toward the heart, characterized by thin, compliant walls, one-way endothelial valves, and a large collective volume that makes the venous system the primary capacitance reservoir of the circulatory system.
Venous walls contain the same three tunics as arteries but with far less smooth muscle and elastic tissue, allowing veins to distend and hold up to 60 percent of total blood volume at low pressure. Endothelial folds form cup-shaped valves that permit flow only toward the heart, and these valves are most numerous in the veins of the lower limbs, where blood must ascend against gravity. Two accessory mechanisms reinforce venous return: skeletal muscle contractions compress adjacent veins and push blood centrally, while the drop in intrathoracic pressure during inhalation draws venous blood toward the right atrium.
Varicose veins develop when venous valves fail and blood pools in superficial leg veins, distending them into tortuous, visible cords; the great saphenous vein, the longest vein in the body at roughly 45 centimeters, is the vessel most commonly affected and is also harvested by surgeons for coronary artery bypass grafting.
Circulatory System Fun Facts →Veins always carry oxygen-poor blood. Pulmonary veins carry oxygen-rich blood from the lungs to the left atrium, making oxygenation status an unreliable criterion for distinguishing veins from arteries.
Respiratory System Fun Facts →In the giraffe (Giraffa camelopardalis), the jugular veins contain a series of closely spaced valves that prevent blood from rushing back into the brain when the animal lowers its head to drink, a passive mechanism that protects against sudden intracranial pressure surges.
Muscular System Facts →Ventricle
/ VEN-trih-kul / · Latin ventriculus, small belly
Ventricle is one of the two lower chambers of the heart, with the right ventricle pumping deoxygenated blood to the lungs and the left ventricle pumping oxygenated blood to the body.
The right ventricle pumps deoxygenated blood to the lungs at low pressure, while the left ventricle drives oxygenated blood into the systemic circulation at much higher pressure. To sustain that greater workload, the left ventricular wall is approximately three times thicker than the right. Chronic pressure or volume overload can trigger ventricular hypertrophy, a maladaptive thickening of the wall that impairs filling and raises arrhythmia risk.
Each ventricle is separated from its corresponding atrium above by an atrioventricular valve, the tricuspid on the right and the mitral on the left, which prevent backflow during contraction.
The brain also contains structures called ventricles, four interconnected cavities that produce and circulate cerebrospinal fluid. These cerebral ventricles share only the name with the cardiac chambers and have no pumping function.
Ventricles are only found in the heart. The brain also contains ventricles, which are fluid-filled cavities that produce and circulate cerebrospinal fluid throughout the central nervous system.
In the domestic dog (Canis lupus familiaris), dilated cardiomyopathy preferentially weakens the left ventricle, reducing its ability to generate the pressure needed to perfuse the systemic circulation. Large breeds such as the Doberman Pinscher are disproportionately affected, and the resulting drop in cardiac output leads to exercise intolerance and fluid accumulation in the lungs.
Circulatory System Fun Facts →Venule
/ VEN-yool / · Latin venula, small vein
Venule is the smallest type of vein, receiving blood from capillary beds and collecting it into progressively larger veins, and is a major site of leukocyte extravasation into inflamed tissues.
Post-capillary venules consist of a single endothelial layer surrounded by a thin connective tissue coat; their endothelial cells respond to inflammatory mediators such as histamine and bradykinin by contracting and opening intercellular gaps, dramatically increasing vascular permeability. Through those gaps, plasma proteins and leukocytes exit into inflamed tissues, producing the swelling and immune-cell recruitment characteristic of acute inflammation. Collecting venules and muscular venules progressively acquire smooth muscle and additional connective tissue as they merge into larger veins.
At 10 to 50 micrometers in diameter, post-capillary venules are also the primary site where rolling and adhesion of neutrophils to the vessel wall begins, a step that precedes their migration into tissue.
In the 1960s, Guido Majno and George Palade used electron microscopy to document the intercellular gaps that open in venular endothelium during histamine exposure, providing the first ultrastructural evidence for the mechanism of inflammatory edema.
Circulatory System Fun Facts →Venules are simply tiny veins with no specialized function. Post-capillary venules are the primary site in the circulation where leukocytes adhere to the vessel wall and migrate into surrounding tissue during an immune response.
In the cremaster muscle preparation of the laboratory mouse (Mus musculus), researchers can observe individual venules through intravital microscopy and watch neutrophils roll along the endothelium, slow down, and squeeze through the vessel wall within minutes of an inflammatory stimulus. This preparation has been used to map the molecular adhesion cascade that governs leukocyte recruitment.
How To Become A Dermatologist? →Vertebral Column
/ VER-teh-brul KOL-um / · Latin vertebra, joint; columna, column
Vertebral column is the segmented bony axis of the body, formed by a series of vertebrae separated by intervertebral discs, that supports the trunk, transmits body weight to the pelvis, and encloses the spinal cord within its vertebral canal.
Adjacent vertebrae are separated by fibrocartilaginous intervertebral discs that absorb compressive shock and permit a range of motion; facet joints between vertebral arches guide movement direction and provide additional stability. Four spinal curvatures, cervical lordosis, thoracic kyphosis, lumbar lordosis, and sacral kyphosis, distribute body weight along the column’s length and developed with the evolution of bipedal posture in hominins. Degenerative disc disease and facet arthropathy are the leading causes of back pain worldwide, affecting an estimated 80% of people at some point in their lives.
Unlike the rigid thoracic region, the cervical and lumbar segments are more mobile and consequently more vulnerable to herniation and instability.
The number of cervical vertebrae is seven in nearly all mammals, from the long-necked giraffe (Giraffa camelopardalis) to the nearly neckless manatee (Trichechus manatus), a conservation of vertebral count that has persisted across roughly 200 million years of mammalian evolution.
Fun Facts About the Skeletal System →The spine is a single long bone. It is a column of 33 individual vertebrae connected by intervertebral discs, facet joints, and ligaments, with the sacral and coccygeal segments fusing into single bones only during adulthood.
In the cheetah (Acinonyx jubatus), an exceptionally flexible vertebral column with a highly mobile lumbar region acts like a spring during a full-speed gallop, extending and compressing with each stride to increase step length. This spinal flexibility contributes significantly to the cheetah's top speed of approximately 112 kilometers per hour.
Villus
/ VIL-us / · Latin villus, shaggy hair (singular of villi)
Villus is a finger-like projection of the small intestinal mucosa, covered by absorptive epithelial cells and containing a central lymphatic vessel called a lacteal and a network of blood capillaries, that greatly increases the surface area available for nutrient absorption.
Each villus stands 0.5 to 1.5 mm tall and is covered by enterocytes bearing dense apical microvilli that amplify the absorptive surface area by an additional 30-fold. Dietary fats packaged as chylomicrons enter the central lacteal and travel through the lymphatic system, while glucose, amino acids, and short-chain fatty acids pass directly into capillary blood for transport to the liver via the portal vein. Crypt stem cells at the base of each villus continuously replace the entire epithelial lining every 3 to 5 days, making the intestinal epithelium one of the most rapidly renewing tissues in the body.
Celiac disease, triggered by an immune response to dietary gluten, causes villus atrophy that can reduce absorptive surface area dramatically and lead to widespread nutrient deficiencies.
In the roundworm Caenorhabditis elegans, the intestinal cells bear apical microvilli but the gut tube lacks villi entirely, illustrating that microvilli and villi are structurally distinct features that evolved independently of one another.
Circulatory System Fun Facts →Villi are simply folds or wrinkles in the intestinal wall. Each villus is a distinct, living projection with its own epithelial cell layer, blood capillaries, and lacteal, making it a functional absorptive unit rather than a passive surface fold.
Fun Facts About Digestive System →In the domestic cat (Felis catus), intestinal villi are notably longer and more densely packed in the jejunum than in the ileum, reflecting the region where most protein and fat digestion is completed. Cats with inflammatory bowel disease show measurable villus blunting in biopsy samples, which correlates with weight loss and poor coat condition.