Arteries

Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Each of these types of arteries contain 3 primary layers: the tunica intima, tunica media, and tunica adventitia. In particular, the tunica media contains smooth muscle cells (allowing for vasoconstriction), and in the larger vessels, a significant amount of elastin (allowing these vessels to stretch and recoil in response to changes in pressure during systole and diastole).

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

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Overview

Definition

Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body.

General characteristics

All arteries have the following characteristics:

  • Thicker walls with smaller lumens than veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins 
  • Appear round on histology
  • Are resistance vessels: 
    • Create most of the resistance in the circulation
    • High-pressure system
    • Can regulate vascular resistance and blood flow velocity by contracting or relaxing the smooth muscle within their walls 
  • Vessels for the transport of flowing blood: The blood passes through arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the smallest (the arterioles) before entering the capillary beds.

Layers of the Vessel Wall

All arteries have the same basic structure and are made up of three primary layers: the tunica intima, tunica media, and tunica adventitia (also known as tunica externa).

Structure of an artery wall

Structure of an artery wall

Image: “Structure of an artery wall” by Phil Schatz. License: CC BY 4.0
Cross section of artery and vein

Cross section of artery and vein

Image: “Types of Arteries and Arterioles” by Phil Schatz. License: CC BY 4.0, edited by Lecturio.

Tunica intima

  • Made up of:
    • A single layer of endothelial cells (simple, squamous epithelial cells)
    • Small amounts of fibrous connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue
  • Functions:
    • Acts as a selectively permeable barrier
    • Secretes vasoactive substances
    • Provides a smooth lining to the blood vessel, preventing aggregation of platelets Platelets Platelets are small cell fragments involved in hemostasis. Thrombopoiesis takes place primarily in the bone marrow through a series of cell differentiation and is influenced by several cytokines. Platelets are formed after fragmentation of the megakaryocyte cytoplasm. Platelets and/or RBCs when intact
  • Endothelium appears wavy owing to constriction of the smooth muscle.
  • Vascularized by direct diffusion from the lumen
  • In capillaries Capillaries Capillaries are the primary structures in the circulatory system that allow the exchange of gas, nutrients, and other materials between the blood and the extracellular fluid (ECF). Capillaries are the smallest of the blood vessels. Because a capillary diameter is so small, only 1 RBC may pass through at a time. Capillaries: This is the only layer present in the vessel wall.
  • In larger vessels: There is an internal elastic membrane separating the tunica intima from the tunica media.

Tunica media

  • Made up of: 
    • Smooth muscle
    • Elastic fibers (e.g., elastin)
    • Collagen
  • Functions:
    • Smooth muscle allows the vessels to adjust blood flow through vasoconstriction and vasodilation.
    • Elastin in larger vessels allows for the vessel to recoil.
    • Collagen provides strength and structure.
  • Usually the thickest layer (can vary in size)
  • In larger vessels: There is an external elastic membrane separating the tunica media from the tunica adventitia.

Tunica adventitia

  • Also called the tunica externa
  • Made up of connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue
    • Collagenous and elastic fibers
    • Merges with connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue surrounding neighboring vessels, nerves, and organs
  • Functions:
    • Strengthens the vessel wall
    • Anchors the vessel
  • Innervated by tiny nerves known as nervi vasorum
  • Vascularized by tiny vessels known as vasa vasorum

Types of Arteries

There are 3 primary types of arteries, based on their overall size, function, and composition (known as segmental differentiation). The arteries generally exist on a continuum, with gradual changes in vessel morphology moving down the arterial tree.

The 3 primary types of arteries are:

  • Large elastic arteries (also known as conducting arteries)
  • Medium muscular arteries (also known as distributing arteries)
  • Small arteries and arterioles
Types of arteries and arterioles

3 primary types of arteries

Image: “Types of Arteries and Arterioles” by Phil Schatz. License: CC BY 4.0
Intraluminal pressures of different vessels

Intraluminal pressures of different vessels

Image by Lecturio.

Large/elastic arteries

This group includes the largest arteries in the body; all large/elastic arteries are close to the heart. The aorta is the largest artery in the body.

Large/elastic arteries include: 

  • Aorta
  • Pulmonary trunk and arteries
  • Brachiocephalic trunk
  • Common carotid arteries
  • Subclavian arteries
  • Common iliac arteries

Characteristics:

  • Large lumens
  • Tunica intima includes a subendothelial layer containing additional smooth muscle.
  • Many elastic fiber networks within the media
    • Elastic fibers have fenestrations: 
      • Small gaps, or “windows,” within the elastic fibers
      • Allow the diffusion of nutrients throughout the wall
    • Elastic fibers are the dominant tissue type within the aorta tunica media.
    • Allow these vessels to recoil
  • Recoil: Vessels can stretch and return to their original shape after receiving the stroke volume of blood ejected by the left ventricle during systole.
  • Effects of stretching and recoil on blood pressure:
    • Minimizes changes in blood pressure downstream during systole
    • Maintains blood pressure during diastole
  • Windkessel function:
    • During systole, the vessel walls stretch, enabling blood that is ejected during systole to be momentarily “stored.”
    • During diastole, the vessel walls recoil, and this “retracting force” moves the stored blood forward to the periphery.

Medium muscular arteries

  • Primary role: distribution of blood to the organs
  • Also known as distributing arteries
  • Tunica media has a predominance of smooth muscle:
    • Average 25–40 layers of smooth muscle (approximately ¾ of the wall thickness) 
    • Significant ability to vasoconstrict and vasodilate, resulting in significant ability to regulate blood flow
  • These arteries are more distant from the heart than large arteries.
  • Most “named” blood vessels, which are not large are medium muscular arteries (e.g., brachial, femoral, and splenic arteries).

Small arteries and arterioles

  • These vessels are usually not named.
  • Most of these vessels can be observed only under magnification.
  • Also known as resistance vessels
  • Relatively little elastic tissue
  • The tunica media is thick in proportion to its lumen relative to other arteries.
  • Small arteries: 
    • Have up to 25 layers of smooth muscle
    • Small arteries narrow toward the capillary network and become arterioles.
  • Arterioles:
    • Last vessels prior to entering the capillary beds
    • Primary point at which the body controls relative blood flow to the capillary beds of various organs 
    • Only 1–3 layers of smooth muscle
  • Metarterioles:
    • Short vessels linking arterioles and capillaries Capillaries Capillaries are the primary structures in the circulatory system that allow the exchange of gas, nutrients, and other materials between the blood and the extracellular fluid (ECF). Capillaries are the smallest of the blood vessels. Because a capillary diameter is so small, only 1 RBC may pass through at a time. Capillaries
    • Have precapillary sphincters: individual smooth muscle cells encircling the entrance to a capillary, regulating blood flow to the capillary beds

Clinical Relevance

Vasculitides Vasculitides Vasculitides are a group of conditions characterized by vasculitis, ischemia, and damage to the organs supplied by the affected vessels. The affected arteries are of different sizes and locations and vary by the type of vasculitis. Vasculitides

Vasculitides Vasculitides Vasculitides are a group of conditions characterized by vasculitis, ischemia, and damage to the organs supplied by the affected vessels. The affected arteries are of different sizes and locations and vary by the type of vasculitis. Vasculitides are a group of autoimmune conditions characterized by immune-mediated blood vessel inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation and wall damage. Loss of vessel integrity can lead to bleeding, as well as to downstream ischemia and necrosis. These processes can be primary or secondary, and they tend to affect only vessels of a specific type or in a specific location.

Table: Classification of vasculitides
Category of vasculitis Examples of conditions in each category
Large-vessel vasculitis
  • Takayasu arteritis
  • Giant cell arteritis Giant Cell Arteritis Giant cell arteritis (GCA), also known as temporal arteritis, is a type of large-vessel vasculitis that predominantly affects the aorta and its major branches, with a predilection for the branches of the carotid (including the temporal artery). Giant cell arteritis is defined by inflammatory leukocytes in the vessel walls leading to reactive damage, ischemia, and necrosis. Giant Cell Arteritis
Medium-vessel vasculitis
  • Polyarteritis nodosa
  • Kawasaki disease Kawasaki disease Kawasaki disease (KD), also known as mucocutaneous lymph node syndrome or infantile polyarteritis, is a medium-sized necrotizing febrile vasculitis that affects children < 5 years of age. Multiple systems are involved but the most serious is the predilection of the coronary arteries. Kawasaki Disease
  • Thromboangiitis obliterans Thromboangiitis Obliterans Thromboangiitis obliterans (TAO), also known as Buerger’s disease, is a rare condition causing inflammatory thrombosis of the small- to medium-sized arteries and veins of the upper and lower extremities. Thromboangiitis Obliterans (Buerger’s Disease) ( Buerger’s disease Buerger’s Disease Thromboangiitis obliterans (TAO), also known as Buerger’s disease, is a rare condition causing inflammatory thrombosis of the small- to medium-sized arteries and veins of the upper and lower extremities. Thromboangiitis Obliterans (Buerger’s Disease))
Small-vessel vasculitis
  • ANCA-associated vasculitis:
    • Microscopic polyangiitis
    • Granulomatosis with polyangiitis Granulomatosis with Polyangiitis Granulomatosis with polyangiitis (GPA) is a rare autoimmune disease of unknown etiology. It leads to a necrotizing granulomatous inflammation of small and medium-sized blood vessels of the nose, sinuses, throat, lungs, and kidneys. Granulomatosis with Polyangiitis
    • Eosinophilic granulomatosis with polyangiitis (Churg–Strauss syndrome)
  • Immune-complex vasculitis:
    • Anti–glomerular basement membrane disease ( Goodpasture syndrome Goodpasture Syndrome Goodpasture syndrome, also known as anti-glomerular basement membrane (GBM) disease, is an autoimmune disease characterized by circulating antibodies directed against glomerular and alveolar basement membranes. Affected individuals present with symptoms of rapidly progressive glomerulonephritis and alveolar hemorrhage. Goodpasture Syndrome)
    • Cryoglobulinemic vasculitis
    • IgA vasculitis (IgAV) (Henoch–Schönlein purpura)
Variable Variable Variables represent information about something that can change. The design of the measurement scales, or of the methods for obtaining information, will determine the data gathered and the characteristics of that data. As a result, a variable can be qualitative or quantitative, and may be further classified into subgroups. Types of Variables-vessel vasculitis
  • Behçet syndrome
  • Cogan syndrome
Single-organ vasculitis
  • Primary CNS vasculitis
  • Cutaneous leukocytoclastic angiitis
  • Isolated aortitis

Diseases involving abnormalities of the arterial walls (structure and/or function)

  • Hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension: elevated blood pressure, defined as > 130 mm Hg systolic or > 80 mm Hg diastolic: Hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension can result from either an increase in cardiac output or from systemic vascular resistance. Vascular resistance is largely determined by the relative constriction and/or dilation of the arterial walls. Hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension is a risk factor for many secondary diseases, such as stroke, congestive heart failure Congestive heart failure Congestive heart failure refers to the inability of the heart to supply the body with normal cardiac output to meet metabolic needs. Echocardiography can confirm the diagnosis and give information about the ejection fraction. Congestive Heart Failure, myocardial infarction Myocardial infarction MI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms. Myocardial Infarction, and chronic kidney disease Chronic Kidney Disease Chronic kidney disease (CKD) is kidney impairment that lasts for ≥ 3 months, implying that it is irreversible. Hypertension and diabetes are the most common causes; however, there are a multitude of other etiologies. In the early to moderate stages, CKD is usually asymptomatic and is primarily diagnosed by laboratory abnormalities. Chronic Kidney Disease
  • Atherosclerosis Atherosclerosis Atherosclerosis is a common form of arterial disease in which lipid deposition forms a plaque in the blood vessel walls. Atherosclerosis is an incurable disease, for which there are clearly defined risk factors that often can be reduced through a change in lifestyle and behavior of the patient. Atherosclerosis: common form of arterial disease in which lipid deposition forms a plaque within large, medium, and small blood vessels throughout the body: Endothelial injury triggers deposition of lipids, release of inflammatory molecules, smooth muscle hyperplasia, and the increased formation of connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue in the region, ultimately giving rise to the atherosclerotic plaques. These plaques lead to narrowing of the vessel lumen, loss of elasticity, and reduced or obstructed blood flow. Ruptured plaques can become embolic, leading to acute end-organ damage.
  • Arteriosclerosis: condition involving hardening of the vessels and loss of their intrinsic elasticity: Arteriosclerosis is most commonly associated with hypertension and diabetes mellitus Diabetes mellitus Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia and dysfunction of the regulation of glucose metabolism by insulin. Type 1 DM is diagnosed mostly in children and young adults as the result of autoimmune destruction of β cells in the pancreas and the resulting lack of insulin. Type 2 DM has a significant association with obesity and is characterized by insulin resistance. Diabetes Mellitus
  • Aortic aneurysm Aneurysm An aneurysm is a bulging, weakened area of a blood vessel that causes an abnormal widening of its diameter > 1.5 times the size of the native vessel. Aneurysms occur more often in arteries than in veins and are at risk of dissection and rupture, which can be life-threatening. Extremity and Visceral Aneurysms: abnormal dilation in the aorta resulting from a thinning and/or weakening of the aortic wall, causing it to bulge out: Aortic aneurysms may occur in the thoracic cavity ( thoracic aortic aneurysms Thoracic Aortic Aneurysms Thoracic aortic aneurysm (TAA) is the abnormal dilation of a segment of the thoracic aorta, usually the ascending aorta. Most TAAs are due to degenerative aortic disorders, commonly in patients > 65 years of age. Most TAAs are asymptomatic (incidentally found in imaging) but could present with symptoms from its effects on surrounding structures. Thoracic Aortic Aneurysms that affect primarily the ascending aorta) or in the abdominal cavity ( abdominal aortic aneurysms Abdominal aortic aneurysms An aortic aneurysm is the abnormal dilation of a segment of the aorta. Abdominal aortic aneurysm is the most common aortic aneurysm, occurring frequently in the infrarenal area. Most aneurysms are asymptomatic, but can cause compression of surrounding structures or rupture, which is a life-threatening emergency. Abdominal Aortic Aneurysms). Rupture of an aortic aneurysm Aneurysm An aneurysm is a bulging, weakened area of a blood vessel that causes an abnormal widening of its diameter > 1.5 times the size of the native vessel. Aneurysms occur more often in arteries than in veins and are at risk of dissection and rupture, which can be life-threatening. Extremity and Visceral Aneurysms is a life-threatening emergency.

References

  1. Taylor, A.M., Bordoni, B. (2021). Histology, blood vascular system. In StatPearls. Retrieved April 26, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK553217/ 
  2. Saladin, K.S., Miller, L. (2004). Anatomy and Physiology, 3rd ed., pp. 749–751). 
  3. Moore, K.L., Dalley, A.F. (2006). Clinically Oriented Anatomy, 5th ed., pp. 39–41).

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