The ulnar and radial arteries embody the two main arteries of the forearm. They both arise from bifurcation of the brachial artery in the crook of the arm. The ulnar artery travels along the ulna to the wrist and reaches the hand via the carpal tunnel, where it supplies oxygenated blood to the three “ulnar” fingers and the ulnar portion of the index finger, among others.
What is the ulnar artery?
In the crook of the elbow, the brachial artery (brachial artery) branches in a bifurcation into two forearm arteries, the ulnar artery (ulnar artery) and radial artery (radial artery). The ulnar artery, which runs along the ulna (ulnar bone) through the carpal tunnel in the wrist and into the hand, supplies oxygenated blood to certain areas of the forearm, the ulnar fingers, and a portion of the index finger. On its way from the crook of the elbow to the ulnar fingers, a total of five main branches branch off from the artery, supplying specific areas of the forearm. At the wrist, a branch of the ulnar artery forms anastomotic connections with a branch of the radial artery. This creates a back-up system between the ulnar and radial arteries. If a bottleneck develops in either artery or flow is completely blocked, the unblocked artery can help supply blood to some degree and serve as a virtual back-up.
Anatomy and structure
From the bifurcation of the brachial artery in the crook of the arm arise two continuing forearm arteries, the ulnar artery and the radial artery. In their course along the ulna and in the area of the wrist through the carpal tunnel, a total of five main branches branch off to supply the corresponding areas with oxygen-rich blood. In the region of the carpus, the ulnar artery forms the main supply network for the superficial palmar arch (arcus palmaris superficialis). The ulnar artery belongs to the type of muscular arteries that actively influence blood pressure regulation. In the middle of a total of three vessel walls, the tunica media, there are smooth muscle fibers as well as elastic and collagen fibers. The muscle fibers surround the media in a ring-like and partly oblique ring-like manner, similar to the coils of a stretched helical spring. The smooth muscle of the ulnar artery is vegetatively controlled by the sympathetic and parasympathetic nervous systems. Stress hormones and other neurotransmitters cause the smooth muscle fibers to contract, resulting in lumen reduction or vasoconstriction of the arteries in stressful situations and during vigorous exercise. This results in an increase in blood pressure. The parasympathetic nervous system can relieve the tension by inhibiting the stress hormones. In contrast to the muscular arteries, the large vessels close to the heart, such as the aorta, have only a passive influence on blood pressure because their media consists mainly of elastic fibers. The elastic fibers cause a strong volume expansion during the systolic tension phase of the ventricles, so that the blood pressure peaks are smoothed and the necessary (diastolic) residual pressure is maintained in the subsequent relaxation phase because the elastic walls of the large vessels contract again.
Function and Tasks
The primary function of the ulnar artery is to supply oxygenated blood to certain tissues of the elbow, forearm, and hand. The oxygenated blood comes from the pulmonary circulation and enters the aorta via the left atrium and ventricle. From the aorta branches the brachial artery, which in turn branches into the ulnar and radial arteries. The arterial side of the capillary system is supplied by arteries that branch off from the ulnar artery and are themselves usually subject to further branching. In addition to its primary supply function, the ulnar artery, together with other arteries of the muscular type, also participates in the active control of blood pressure. Arteries, whose vessel walls are largely composed of smooth muscle fibers, respond contractilely to certain neurotransmitters and stress hormones, so that the lumen of the vessels also constricts, causing an increase in blood pressure. The opposite effect occurs when the messenger substances and control hormones are recaptured by the parasympathetic nervous system. The influence on and control of blood pressure are largely vegetative, i.e. unconscious.Involvement in the control of blood pressure requires healthy, elastic vessel walls and intact sympathetic and parasympathetic hormonal control.
Diseases
Diseases or conditions that exclusively affect the ulnar artery are not known. However, the ulnar artery can be affected by dysfunction, as can all other arteries of the muscular type. Basically, locally occurring constrictions of the lumen of the artery can occur, so-called stenoses. Depending on their severity, they lead to a reduced supply to the downstream and branching arteries and thus to an undersupply of defined tissue parts. The most common reason for the formation of a stenosis is deposits, so-called plaques, in the vessel wall. The plaques can extend into the lumen and cause stenosis or even complete occlusion. In other cases, inflammatory reactions of the immune system can also lead to an accumulation of erythrocytes that develop into a thrombus and block the artery in the form of the thrombosis. If such a thrombus develops elsewhere in the body – for example, in the heart – it can be washed away with the bloodstream and accidentally become lodged in an artery whose cross-section is significantly smaller than that of the thrombus. In this case, an embolism is present. The effects of vascular occlusion by thrombosis or embolism are very similar. Only in extremely rare cases does the ulnar artery form an aneurysm, a bulging of the artery that usually results from injury to the vein. The lesion then forms the portal of entry for blood inflow between the internal and middle walls of the vessel.
