Structure and function of blood vessels
Blood vessels (vessel: from the lower Latin vascellum, meaning small vase, blood, from the Latin sanguineus) are organs of the blood circulation. William Harvey, an English doctor of the 16th and 17th centuries, is known for this work and discoveries on the functioning of the blood circulation. Let’s have a look at the structure and function of blood vessels.
The blood vessels form a closed circuit through which the blood flows. This circuit is divided into a large body circulation and a small pulmonary circulation. These vessels consist of a wall with three tunics:
- The inner coat, or intima, composed of a cellular layer of endothelium and lining the inner surface of the vessels;
- The middle tunic, or media, constituting the intermediate layer and composed of muscular and elastic fibers;
- The outer coat, or adventitious, constituting the outer layer and composed of collagen fibers and fibrous tissue.
The blood vessels are divided into different groups:
The arteries constitute the vessels where the blood, rich in oxygen, leaves the heart to reach the various structures of the body, except for the pulmonary and placental circulation. There are different types of arteries, depending on their structure.
- The arteries of elastic type, of large caliber, have a thick wall and consist of many elastic fibers. They are mainly located near the heart, such as the aorta or the pulmonary artery.
- The muscle-type arteries have a smaller caliber, and their wall contains many smooth muscle fibers.
- The arterioles are located at the end of the arterial network, between the arteries and the capillaries. They are generally localized in an organ and do not contain an external coat.
The veins are the vessels where the blood, poor in oxygen, leaves the periphery to reach the heart, except for the pulmonary and placental circulation. From the capillaries, small veins, recover oxygen-poor blood and join the veins. The latter has a thinner wall than the arteries. Their wall has less elastic and muscular fibers but has a thicker outer coat. The veins have the particularity of being able to contain more blood than the arteries. To facilitate the venous return, the veins of the lower limbs have valves. They are sometimes visible under the skin: one can, for example, note their presence on the hand, wrists, or even the fold of the arm. On the other hand, it is impossible to perceive blood circulation because the blood pressure is rather low. In section, a
- vein presents a thin and flaccid, the wall which is not made, like that of the arteries, to resist a strong pressure. In addition, the veins can branch out into smaller vessels: the venules.
Forming a branched network, the capillaries are very thin vessels, with a diameter ranging from 5 to 15 micrometers. They make the transition between arterioles and venules. They allow both the distribution of oxygenated blood and nutrients; and both recovery of carbon dioxide and metabolic waste.
The blood vessels are innervated by sympathetic nerve fibers to regulate their diameter.
The direction of blood circulation
The role of an artery
The accidental section of the thigh artery or the carotid artery of the neck causes hemorrhage. This clearly shows that the blood circulates there under strong pressure; this allows it to go up in the arteries, from the heart to the irrigated organ. Thus the arteries supply the organs with blood enriched with oxygen and nutrients (in glucose, for example).
The role of a vein
The accidental section of a vein causes a hemorrhage, which results in a continuous and not jerky jet. This shows that, in a vein, blood circulates under rather reduced pressure, from the organ to the heart. Thus the veins bring back to the heart blood depleted in oxygen and enriched in carbon dioxide coming from an organ.
Functions of blood vessels
Distribution / Disposal
Blood vessels allow both the distribution of nutrients and the recovery of metabolic waste.
The blood vessels form a closed circuit. Nutrient-rich blood flows from the left ventricle of the heart through the aorta. It successively travels the arteries, arterioles, capillaries, venules, and veins. At the capillary level, nutrients and waste are exchanged. The blood lacking in nutrients then joins the right atrium of the heart through the two cava veins before enriching itself with nutrients and resuming its path in the body.
Pathologies linked to blood vessels.
Blood pressure problems. Excessive pressure of blood against the artery walls can lead to high blood pressure and can increase the risk of vascular disease too.
This pathology corresponds to a blood clot's formation at the level of a blood vessel.
Stroke, or stroke, manifests itself by the obstruction of a cerebral blood vessel, in particular by the formation of blood clots or by the rupture of a vessel.
Also called venous thrombosis, this pathology corresponds to the formation of a blood clot, or thrombus, in the veins. These clots can move and go up towards the inferior vena cava. This pathology can lead to various conditions such as venous insufficiency, which is to say a dysfunction of the venous network.
They include pathologies such as myocardial infarction or angina pectoris. If these diseases occur, the blood vessels are often affected and can, in particular, cause an insufficient supply of oxygen.
Depending on the pathology diagnosed, certain drugs may be prescribed, such as anticoagulants, anti-aggregates, or anti-ischemic.
Used in strokes, this treatment involves breaking up thrombus, or blood clots, using medication.
Depending on the pathology diagnosed and its evolution, surgical intervention may be necessary.
First, a clinical examination is carried out to identify and assess the pain perceived by the patient.
Medical imaging exams:
Examinations by radiography, CT, MRI, coronary angiography, CT angiography, or even arteriography can be used to confirm or deepen the diagnosis.
- Doppler ultrasound. This specific ultrasound allows you to observe blood flow.
Author: Vicki Lezama