Blood vessel
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Overview
The blood vessels are part of the cardiovascular system and function to transport blood throughout the body. The most important types, arteries and veins, carry blood away from or towards the heart, respectively.
Anatomy
All blood vessels have the same basic structure. The inner lining is the endothelium and is surrounded by subendothelial connective tissue. Around this there is a layer of vascular smooth muscle, which is highly developed in arteries. Finally, there is a further layer of connective tissue known as the adventitia, which contains nerves that supply the muscular layer, as well as nutrient capillaries 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 (pl. anastomoses). Anastomoses provide critical alternative routes for blood to flow in case of blockages.
Laid end to end, the blood vessels in an average human body will stretch approximately 62,000 miles--2.5 times around the earth.
Types
There are various kinds of blood vessels:
- Arteries
- Aorta (the largest artery, carries blood out of the heart)
- Branches of the aorta, such as the carotid artery, the subclavian artery, the celiac trunk, the mesenteric arteries, the renal artery and the iliac artery.
- 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 (the 2 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.
Physiology
Blood vessels do not actively engage in the transport of blood (they have no appreciable peristalsis), but 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.
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 hemoglobin is desaturated at about 70%. (The values are reversed in the pulmonary circulation.)
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.
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).
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 and warmth).
Role in disease
Blood vessels play a 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 prime cause of cardiovascular disease, the main cause of death in the Western world.
Blood vessel permeability is increased in inflammation. Damage, due to trauma or spontaneously, may lead to haemorrhage. In contrast, occlusion of the blood vessel (e.g. by a ruptured atherosclerotic plaque, by an embolised blood clot or a foreign body) leads to downstream ischemia (insufficient blood supply) and necrosis (tissue breakdown).
Vasculitis is inflammation of the vessel wall, due to autoimmune disease or infection.
External Links
See also
Arteries of torso - abdomen | |||||||
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| AA: Anterior |
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| AA: Posterior | visceral: middle suprarenal – renal (inferior suprarenal) – testicular/ovarianparietal: inferior phrenic (superior suprarenal) – lumbar – median sacral terminal: common iliac (IIA, EIA) | ||||||
| IIA: Anterior |
(superior vesical,
to ductus deferens) –
inferior vesical –
middle rectal –
uterine
(azygos of the vagina) –
vaginal –
obturator
(anterior branch,
posterior branch) –
internal pudendal
(inferior rectal,
perineal,
artery of the urethral bulb,
urethral,
deep artery of the penis,
dorsal artery of the penis) –
inferior gluteal
(accompanying of ischiadic nerve,
crucial anastomosis)
| ||||||
| IIA: Posterior | |||||||
| EIA | |||||||
List of arteries of upper limbs | |
|---|---|
| Axillary | scapular anastomosis - 1st part superior thoracic - 2nd part thoracoacromial (deltoid branch) - lateral thoracic - 3rd part subscapular (circumflex scapular, thoracodorsal) - anterior humeral circumflex - posterior humeral circumflex |
| Brachial | profunda brachii (radial collateral, medial collateral) - ulnar collateral artery (superior, inferior) |
| Radial | forearm: radial recurrent
wrist/carpus: dorsal carpal branch - palmar carpal branch hand: superficial palmar branch - princeps pollicis (radial of index finger) |
| Ulnar | forearm: ulnar recurrent (anterior, posterior) - common interosseous (anterior, posterior, recurrent)
wrist/carpus: dorsal carpal branch - palmar carpal branch hand: deep palmar branch |
| Arches | dorsal carpal arch: dorsal metacarpal (dorsal digital)
superficial palmar arch: common palmar digital (proper palmar digital) deep palmar arch: palmar metacarpal |
List of arteries of lower limbs | |
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| EI: Femoral | superficial epigastric - superficial iliac circumflex
external pudendal: superficial - deep (anterior scrotal) profunda femoris: lateral circumflex femoral (descending, transverse, ascending) - medial circumflex femoral (ascending, superficial, deep, acetabular) - perforating descending genicular (saphenous branch, articular branches) |
| Popliteal | sural genicular: superior genicular (medial, lateral) - middle genicular - inferior genicular (medial, lateral) |
| Anterior tibial | tibial recurrent (posterior, anterior)
anterior malleolar (medial, lateral) dorsalis pedis: tarsal (medial, lateral) |
| Posterior tibial | circumflex fibular - fibular medial plantar - lateral plantar |
| 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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Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
