Anatomy Terms Starting With J
Anatomy Glossary: J
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Jejunum
/ jeh-JOO-num / · Latin jejunus, empty or fasting ? believed to be empty after death
Jejunum jejunum is the middle section of the small intestine, connecting the duodenum to the ileum, and is the primary site where digested nutrients including amino acids, sugars, and fatty acids are absorbed into the bloodstream.
Spanning roughly 2.5 meters in a living adult, the jejunum has a thicker wall and a wider lumen than the ileum, and its inner surface is densely covered with circular folds called plicae circulares, finger-like villi, and microvilli that collectively increase absorptive surface area by about 600-fold. The rich blood supply delivered through branches of the superior mesenteric artery supports the high metabolic demand of active nutrient transport. Contractions of the circular and longitudinal smooth muscle layers mix chyme with digestive secretions and propel contents toward the ileum through coordinated peristaltic waves.
The jejunum lacks the dense lymphoid patches and vitamin B12 absorption specializations found in the ileum, distinguishing it functionally despite their structural similarity.
Surgeons can remove a large portion of the jejunum and the remaining small intestine can adapt over months by increasing villus height and crypt depth, a process called intestinal adaptation. This compensatory response allows some patients who have lost significant lengths of bowel to eventually absorb enough nutrients to survive without permanent intravenous feeding.
How To Become A Gastroenterologist? →The stomach is where most nutrient absorption occurs. The stomach mainly breaks food down mechanically and chemically; the real absorption of amino acids, glucose, and fats happens primarily in the jejunum.
In ruminants such as cattle, the jejunum is proportionally longer than in humans, reflecting a diet heavy in plant fiber that requires extended contact time for enzymatic digestion and microbial fermentation products to be absorbed across the intestinal wall.
Joint
/ JOYNT / · Old French joindre, to join
Joint joint is the anatomical site where two or more bones are connected, classified by structure as fibrous, cartilaginous, or synovial, and by the range of motion they permit.
Joints are classified structurally into fibrous joints with no joint cavity and collagen fibers connecting bones directly, cartilaginous joints with hyaline or fibrocartilage bridging bones, and synovial joints containing a fluid-filled joint cavity enclosed by a fibrous capsule. Functionally, synarthroses such as skull sutures are immovable, amphiarthroses like intervertebral discs are slightly movable, and diarthroses including hinge joints at the elbow, ball-and-socket joints at the hip and shoulder, and gliding joints in the wrist allow multiaxial movement. Synovial joints contain articular cartilage covering bone ends, synovial fluid secreted by the synovial membrane that reduces friction, ligaments reinforcing the capsule, and in some joints, articular discs or menisci that improve load distribution.
Movements at joints include flexion, extension, abduction, adduction, rotation, and circumduction depending on the joint structure and articulating bones.
Some joints move freely, while others move little or not at all. The sutures between skull bones are joints even though they normally do not move like knees or elbows.
Fun Facts About the Skeletal System →Every joint is a hinge. Ball-and-socket, pivot, gliding, saddle, and immovable joints all exist in the skeleton.
The shoulder joint of a gibbon allows a large range of motion for swinging through trees. Its mobility comes with a greater need for muscle control.
Types of Gibbons →Jugular Vein
/ JUG-yoo-ler VAYN / · Latin jugulum, collarbone or throat; Latin vena, vein
Jugular Vein jugular veins are a pair of large veins in the neck that drain deoxygenated blood from the brain, face, and neck back to the heart via the superior vena cava.
There are two main jugular veins on each side of the neck: the internal jugular vein, which runs alongside the carotid artery and drains blood from the brain and deep face structures, and the external jugular vein, which is more superficial and drains the scalp and outer face. The internal jugular vein is larger and clinically more important, commonly used for central venous catheter placement, blood pressure monitoring, and intravenous access in critical care. Jugular venous pressure, assessed by observing the pulsation visible in the neck, provides a bedside estimate of central venous pressure and right heart function.
The jugular veins empty into the subclavian veins and then into the superior vena cava before reaching the right atrium.
The term jugular comes from the Latin jugulum, meaning throat or collarbone, and has given rise to the phrase go for the jugular because the vein lies close to the surface of the neck and is vulnerable. Clinicians routinely inspect jugular venous distension in patients to rapidly assess fluid overload or right-sided heart failure at the bedside.
The jugular vein and the carotid artery are the same vessel. The carotid artery carries oxygenated blood up to the brain, while the jugular vein carries deoxygenated blood back down from it , they run alongside each other but are distinct structures with opposite functions.
During a cetacean dive, the jugular veins and other large central veins act as blood reservoirs. Blood shifts away from the peripheral circulation toward the thorax and brain, helping marine mammals tolerate the pressure changes and oxygen limitations of deep dives.