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The blood vessels are the part of the circulatory system, and microcirculation, that transports blood throughout the human body.[1] There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and the tissues; and the veins, which carry blood from the capillaries back toward the heart. The word vascular, meaning relating to the blood vessels, is derived from the Latin
Latin
vas, meaning vessel. A few structures (such as cartilage and the lens of the eye) do not contain blood vessels and are labeled.

Contents

1 Structure

1.1 Types

2 Function

2.1 Vessel size 2.2 Blood
Blood
flow

3 Disease 4 References

Structure[edit] The arteries and veins have three layers. The middle layer is thicker in the arteries than it is in the veins:

The inner layer, Tunica intima, is the thinnest layer. It is a single layer of flat cells (simple squamous epithelium) glued by a polysaccharide intercellular matrix, surrounded by a thin layer of subendothelial connective tissue interlaced with a number of circularly arranged elastic bands called the internal elastic lamina. The middle layer Tunica media
Tunica media
is the thickest layer in arteries. It consists of circularly arranged elastic fiber, connective tissue, polysaccharide substances, the second and third layer are separated by another thick elastic band called external elastic lamina. The tunica media may (especially in arteries) be rich in vascular smooth muscle, which controls the caliber of the vessel. Veins don't have the external elastic lamina, but only an internal one. The outer layer is Tunica adventitia
Tunica adventitia
and the thickest layer in veins. It is entirely made of connective tissue. It also contains nerves that supply the vessel as well as nutrient capillaries (vasa vasorum) in the larger blood vessels.

Capillaries consist of little more than a layer of endothelium and occasional connective tissue. When blood vessels connect to form a region of diffuse vascular supply it is called an anastomosis. Anastomoses provide critical alternative routes for blood to flow in case of blockages. There is a layer of muscle surrounding the arteries and the veins which help contract and expand the vessels. This creates enough pressure for blood to be pumped around the body. Blood
Blood
vessels are part of the circulatory system, together with the heart and the blood. Types[edit]

Blood
Blood
vessel with an erythrocyte (red blood cell, E) within its lumen, endothelial cells forming its tunica intima (inner layer), and pericytes forming its tunica adventitia (outer layer)

There are various kinds of blood vessels:

Arteries Elastic arteries Distributing arteries Arterioles Capillaries (the smallest blood vessels) Venules Veins

Large collecting vessels, such as the subclavian vein, the jugular vein, the renal vein and the iliac vein. Venae cavae
Venae cavae
(the two largest veins, carry blood into the heart).

They are roughly grouped as "arterial" and "venous", determined by whether the blood in it is flowing away from (arterial) or toward (venous) the heart. The term "arterial blood" is nevertheless used to indicate blood high in oxygen, although the pulmonary artery carries "venous blood" and blood flowing in the pulmonary vein is rich in oxygen. This is because they are carrying the blood to and from the lungs, respectively, to be oxygenated.

Function[edit] See also: Circulatory system Blood
Blood
vessels function to transport blood. In general, arteries and arterioles transport oxygenated blood from the lungs to the body and its organs, and veins and venules transport deoxygenated blood from the body to the lungs. Blood
Blood
vessels also circulate blood throughout the circulatory system Oxygen
Oxygen
(bound to hemoglobin in red blood cells) is the most critical nutrient carried by the blood. In all arteries apart from the pulmonary artery, hemoglobin is highly saturated (95–100%) with oxygen. In all veins apart from the pulmonary vein, the saturation of hemoglobin is about 75%.[citation needed] (The values are reversed in the pulmonary circulation.) In addition to carrying oxygen, blood also carries hormones, waste products and nutrients for cells of the body. Blood
Blood
vessels do not actively engage in the transport of blood (they have no appreciable peristalsis). Blood
Blood
is propelled through arteries and arterioles through pressure generated by the heartbeat.[citation needed] Permeability of the endothelium is pivotal in the release of nutrients to the tissue. It is also increased in inflammation in response to histamine, prostaglandins and interleukins, which leads to most of the symptoms of inflammation (swelling, redness, warmth and pain). Vessel size[edit]

Constricted blood vessel.

Arteries—and veins to a degree—can regulate their inner diameter by contraction of the muscular layer. This changes the blood flow to downstream organs, and is determined by the autonomic nervous system. Vasodilation and vasoconstriction are also used antagonistically as methods of thermoregulation. Vasoconstriction
Vasoconstriction
is the constriction of blood vessels (narrowing, becoming smaller in cross-sectional area) by contracting the vascular smooth muscle in the vessel walls. It is regulated by vasoconstrictors (agents that cause vasoconstriction). These include paracrine factors (e.g. prostaglandins), a number of hormones (e.g. vasopressin and angiotensin) and neurotransmitters (e.g. epinephrine) from the nervous system. Vasodilation is a similar process mediated by antagonistically acting mediators. The most prominent vasodilator is nitric oxide (termed endothelium-derived relaxing factor for this reason). Blood
Blood
flow[edit] Main article: Vascular resistance The blood pressure in blood vessels is traditionally expressed in millimetres of mercury (1 mmHg = 133 Pa). In the arterial system, this is usually around 120 mmHg systolic (high pressure wave due to contraction of the heart) and 80 mmHg diastolic (low pressure wave). In contrast, pressures in the venous system are constant and rarely exceed 10 mmHg. Vascular resistance occurs where the vessels away from the heart oppose the flow of blood. Resistance is an accumulation of three different factors: blood viscosity, blood vessel length, and vessel radius.[2] Blood
Blood
viscosity is the thickness of the blood and its resistance to flow as a result of the different components of the blood. Blood
Blood
is 92% water by weight and the rest of blood is composed of protein, nutrients, electrolytes, wastes, and dissolved gases. Depending on the health of an individual, the blood viscosity can vary (i.e. anemia causing relatively lower concentrations of protein, high blood pressure an increase in dissolved salts or lipids, etc.).[2] Vessel length is the total length of the vessel measured as the distance away from the heart. As the total length of the vessel increases, the total resistance as a result of friction will increase.[2] Vessel radius also affects the total resistance as a result of contact with the vessel wall. As the radius of the wall gets smaller, the proportion of the blood making contact with the wall will increase. The greater amount of contact with the wall will increase the total resistance against the blood flow.[3] Disease[edit] Main article: Vascular disease Blood
Blood
vessels play a huge role in virtually every medical condition. Cancer, for example, cannot progress unless the tumor causes angiogenesis (formation of new blood vessels) to supply the malignant cells' metabolic demand. Atherosclerosis, the formation of lipid lumps (atheromas) in the blood vessel wall, is the most common cardiovascular disease, the main cause of death in the Western world.[4] Blood
Blood
vessel permeability is increased in inflammation. Damage, due to trauma or spontaneously, may lead to hemorrhage due to mechanical damage to the vessel endothelium. In contrast, occlusion of the blood vessel by atherosclerotic plaque, by an embolised blood clot or a foreign body leads to downstream ischemia (insufficient blood supply) and possibly necrosis. Vessel occlusion tends to be a positive feedback system; an occluded vessel creates eddies in the normally laminar flow or plug flow blood currents. These eddies create abnormal fluid velocity gradients which push blood elements such as cholesterol or chylomicron bodies to the endothelium. These deposit onto the arterial walls which are already partially occluded and build upon the blockage.[5] Vasculitis
Vasculitis
is inflammation of the vessel wall, due to autoimmune disease or infection. References[edit]

^ " Blood
Blood
Vessels – Heart
Heart
and Blood
Blood
Vessel Disorders – Merck Manuals Consumer Version". Merck Manuals Consumer Version. Retrieved 2016-12-22.  ^ a b c Anatomy Physiology: The Unity of Form and Function, Saladin, McGraw Hill, 2012 ^ "Factors that Affect Blood
Blood
Pressure" (PDF). Retrieved 6 Dec 2014.  ^ "Nerves and blood vessels". 420evaluationsonline. Retrieved 2 August 2016.  ^ Multiphase Flow and Fluidization, Gidaspow et al., Academic Press, 1992

v t e

Arteries and veins

Vessels

Arteries

Nutrient artery Arteriole

Metarteriole

Elastic artery

Capillaries

Types

Continuous Fenestrated Sinusoidal

Precapillary sphincter Precapillary resistance

Veins

Vena comitans Superficial vein Deep vein Emissary veins Venous plexus Venule

Lymph

Lymphatic vessel Lymph Lymph
Lymph
capillary

Circulatory system

Systemic

Left heart → Aorta
Aorta
→ Arteries → Arterioles → Capillaries → Venules → Veins → Vena cava → (Right heart)

Pulmonary

Right heart → Pulmonary
Pulmonary
arteries → Lungs → Pulmonary vein
Pulmonary vein
→ Left heart

Microanatomy

Microvessel Microcirculation Tunica intima

Endothelium Internal elastic lamina

Tunica media Tunica externa Vasa vasorum Vasa nervorum Vascular nerves Rete mirabile Circulatory anastomosis

Arteries in the human body

v t e

Arteries of the head and neck

CC

EC

sup. thyroid

superior laryngeal sternocleidomastoid branch infrahyoid branch cricothyroid branch glandular branches

asc. pharyngeal

posterior meningeal pharyngeal branches inferior tympanic

lingual

suprahyoid dorsal lingual deep lingual sublingual

facial

cervical branches (ascending palatine, tonsillar, submental, glandular) facial branches (inferior labial superior labial / nasal septum lateral nasal angular)

occipital

sternocleidomastoid meningeal occipital auricular descending

post. auricular

stylomastoid stapedial auricular occipital Parotid

sup. temporal

transverse facial middle temporal (zygomatico-orbital) anterior auricular frontal parietal

maxillary

1st part / mandibular

anterior tympanic deep auricular middle meningeal (superior tympanic, petrosal) accessory meningeal inferior alveolar

2nd part / pterygoid

to muscles of mastication (deep temporal, pterygoid, masseteric) buccal

3rd part / pterygopalatine

posterior superior alveolar infraorbital (anterior superior alveolar) descending palatine (greater palatine, lesser palatine) artery of the pterygoid canal sphenopalatine (posterior septal branches, posterior lateral nasal) pharyngeal

IC

cervical

carotid sinus

petrous

Vidian caroticotympanic

cavernous/ ophthalmic

orbital group:anterior ethmoidal posterior ethmoidal lacrimal (lateral palpebral) medial palpebral terminal (supraorbital, supratrochlear, dorsal nasal)

ocular group: central retinal

ciliary (short posterior, long posterior, anterior) Circulus arteriosus major hypophysial (superior, inferior)

brain

Circle of Willis ACA (anterior communicating, Recurrent artery of Heubner, Orbitofrontal artery) MCA (anterolateral central, Prefrontal artery, Superior terminal branch, Inferior terminal branch, Anterior temporal branch) posterior communicating anterior choroidal

SC

vertebral artery

meningeal spinal (posterior, anterior) basilar: pontine labyrinthine cerebellar (AICA, SCA, PICA) cerebral (PCA)

thyrocervical trunk

inferior thyroid

inferior laryngeal tracheal esophageal ascending cervical pharyngeal glandular branches

transverse cervical

superficial branch deep branch / dorsal scapular

scapular anastomosis

suprascapular

acromial branch scapular anastomosis

costocervical trunk

deep cervical Supreme Intercostal artery

v t e

Arteries of the torso and chest

Lungs

Pulmonary
Pulmonary
artery

Right Left (Ligamentum arteriosum)

Heart

Coronary circulation Right coronary:

SA nodal AV nodal Atrial Right marginal Posterior interventricular

Left coronary:

Anterior interventricular Left circumflex (Left marginal)

Aorta

Sections

Ascending aorta Aortic arch Descending aorta Thoracic aorta Abdominal aorta Aortic body

Aortic arch

Brachiocephalic

Thyreoidea ima Right subclavian Right common carotid

Left common carotid

External carotid Internal carotid

Carotid body Carotid sinus Carotid bifurcation

Left subclavian

Internal thoracic: Anterior intercostal Thymic Pericardiacophrenic Perforating branches terminal (Musculophrenic, superior epigastric) Costocervical trunk: Highest intercostal (Posterior intercostal 1–2) Deep cervical

Descending aorta

visceral: Bronchial Esophageal Mediastinal

parietal: Posterior intercostal 3–11 Subcostal Superior phrenic

v t e

Arteries of the abdomen and pelvis

Abdominal aorta

Celiac

Left gastric

Esophageal branches

Common hepatic

Proper hepatic

cystic

Right gastric Gastroduodenal

right gastroepiploic superior pancreaticoduodenal supraduodenal

Splenic

Pancreatic branches

greater dorsal

Short gastrics Left gastroepiploic

Superior mesenteric

Inferior pancreaticoduodenal Intestinal

jejunal ileal arcades vasa recta

Ileocolic

colic anterior cecal posterior cecal ileal branch appendicular

Right colic Middle colic

Marginal

Suprarenal

Middle suprarenal

Renal

Inferior suprarenal Ureteral

Gonadal

Testicular artery Ovarian artery

Lumbar

Lumbar arteries

Inferior mesenteric

Left colic

Marginal

Sigmoid Superior rectal

Common iliac

Internal iliac

Posterior surface

Iliolumbar

Lumbar branch Iliac branch

Anterior surface

Superior vesical artery

Umbilical artery

Medial umbilical ligament

to ductus deferens

Obturator

Anterior branch

Pubic branch

Posterior branch

Acetabular branch Cruciate anastomosis

Corona mortis

Middle rectal

Vaginal branch ♀ / Prostatic branch ♂

Uterine ♀

Arcuate Vaginal branches Ovarian branches Tubal branches Spiral

Vaginal ♀ / Inferior vesical ♂

Inferior gluteal

Accompanying of sciatic nerve Cruciate anastomosis

Internal pudendal

Inferior rectal Perineal

posterior scrotal posterior labial

Bulb of penis/vestibule Urethral Deep artery of the penis

helicine

Deep artery of clitoris Dorsal of the penis Dorsal of the clitoris

External iliac

Inferior epigastric

Corona mortis

Deep circumflex iliac Femoral

see arteries of lower limbs

Median sacral

Coccygeal glomus

v t e

Arteries of the human arm

Axillary

Shoulder (before teres minor)

1st part

Superior thoracic artery

2nd part

Thoracoacromial artery

pectoral branch acromial branch clavicular branch deltoid branch

Lateral thoracic artery

3rd part

Subscapular artery

scapular anastomosis circumflex scapular artery thoracodorsal artery

anterior humeral circumflex artery posterior humeral circumflex artery

Brachial

Forearm (before cubital fossa)

profunda brachii

radial collateral medial collateral

ulnar collateral

superior inferior

Radial artery

forearm

radial recurrent

wrist/carpus

Dorsal carpal branch

dorsal carpal arch

Palmar carpal branch

deep palmar arch

hand

Superficial palmar branch

princeps pollicis radialis indicis artery superficial palmar arch

Median artery

median artery

Ulnar artery

forearm

ulnar recurrent

anterior posterior

common interosseous

anterior posterior

interosseous recurrent

wrist/carpus

Dorsal carpal branch

dorsal carpal arch

Palmar carpal branch

superficial palmar arch

Arterial Arches

Dorsal carpal arch

dorsal metacarpal dorsal digital

Palmar carpal arch

superficial palmar arch

common palmar digital

proper palmar digital deep palmar arch

palmar metacarpal

v t e

Arteries of the human leg

Inferior epigastric

cremasteric ♂ / round ligament ♀

Deep circumflex iliac

no major branches

Femoral

In femoral canal

superficial epigastric superficial circumflex iliac superficial external pudendal deep external pudendal

(anterior scrotal ♂

Descending genicular

saphenous branch articular branches

Profunda femoris

medial circumflex femoral

ascending descending

superficial deep acetabular

lateral circumflex femoral

descending transverse ascending

perforating Cruciate anastomosis Trochanteric anastomosis

Popliteal

Genicular

superior genicular (medial, lateral) middle genicular inferior genicular (medial, lateral)

Sural

no major branches

Anterior tibial

tibial recurrent

posterior

anterior) anterior malleolar

medial lateral

dorsalis pedis: tarsal (medial, lateral)

Tibial-fibular (Tibial-peroneal) trunk

Posterior tibial

circumflex fibular medial plantar lateral plantar

fibular (peroneal)

Arches

arcuate

dorsal metatarsal first dorsal metatarsal

deep plantar dorsal digital arteries plantar arch

plantar metatarsal common plantar digital proper plantar digital

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