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Cerebral circulation

September 01, 2023

Cerebral circulation is the movement of blood through a network of cerebral arteries and veins supplying the brain. The rate of cerebral blood flow in an adult human is typically 750 milliliters per minute, or about 15% of cardiac output. Arteries deliver oxygenated blood, glucose and other nutrients to the brain. Veins carry "used or spent" blood back to the heart, to remove carbon dioxide, lactic acid, and other metabolic products. The neurovascular unit regulates cerebral blood flow so that activated neurons can be supplied with energy in the right amount and at the right time.[1] Because the brain would quickly suffer damage from any stoppage in blood supply, the cerebral circulatory system has safeguards including autoregulation of the blood vessels. The failure of these safeguards may result in a stroke. The volume of blood in circulation is called the cerebral blood flow. Sudden intense accelerations change the gravitational forces perceived by bodies and can severely impair cerebral circulation and normal functions to the point of becoming serious life-threatening conditions.

Cerebral circulation
Areas of the brain are supplied by different arteries. The major systems are divided into an anterior circulation (the anterior cerebral artery and middle cerebral artery) and a posterior circulation
Schematic of veins and venous spaces that drain deoxygenated blood from the brain
Identifiers
MeSHD002560
Anatomical terminology
[edit on Wikidata]

The following description is based on idealized human cerebral circulation. The pattern of circulation and its nomenclature vary between organisms.

Anatomy Edit

 
Cerebrovascular System

Blood supply Edit

 
 
Cortical areas and their arterial blood supply

Blood supply to the brain is normally divided into anterior and posterior segments, relating to the different arteries that supply the brain. The two main pairs of arteries are the Internal carotid arteries (supply the anterior brain) and vertebral arteries (supplying the brainstem and posterior brain).[2]. The anterior and posterior cerebral circulations are interconnected via bilateral posterior communicating arteries. They are part of the Circle of Willis, which provides backup circulation to the brain. In case one of the supply arteries is occluded, the Circle of Willis provides interconnections between the anterior and the posterior cerebral circulation along the floor of the cerebral vault, providing blood to tissues that would otherwise become ischemic.[3]

Anterior cerebral circulation Edit

 
The ophthalmic artery and its branches.

The anterior cerebral circulation is the blood supply to the anterior portion of the brain including eyes. It is supplied by the following arteries:

Posterior cerebral circulation Edit

 
The anterior and posterior circulations meet at the Circle of Willis, pictured here, which rests at the top of the brainstem. Inferior view.

The posterior cerebral circulation is the blood supply to the posterior portion of the brain, including the occipital lobes, cerebellum and brainstem. It is supplied by the following arteries:

Venous drainage Edit

The venous drainage of the cerebrum can be separated into two subdivisions: superficial and deep.

The superficial system

The superficial system is composed of dural venous sinuses, sinuses (channels) within the dura mater. The dural sinuses are therefore located on the surface of the cerebrum. The most prominent of these sinuses is the superior sagittal sinus which is located in the sagittal plane under the midline of the cerebral vault, posteriorly and inferiorly to the confluence of sinuses, where the superficial drainage joins with the sinus that primarily drains the deep venous system. From here, two transverse sinuses bifurcate and travel laterally and inferiorly in an S-shaped curve that forms the sigmoid sinuses which go on to form the two jugular veins. In the neck, the jugular veins parallel the upward course of the carotid arteries and drain blood into the superior vena cava. The veins puncture the relevant dural sinus, piercing the arachnoid and dura mater as bridging veins that drain their contents into the sinus.[5]

The deep venous system

The deep venous system is primarily composed of traditional veins inside the deep structures of the brain, which join behind the midbrain to form the great cerebral vein (vein of Galen). This vein merges with the inferior sagittal sinus to form the straight sinus which then joins the superficial venous system mentioned above at the confluence of sinuses.

Physiology Edit

 
Dural venous sinuses bordered by hard meninges (shown in blue) direct blood outflow from cerebral veins to the internal jugular vein at the base of skull

Cerebral blood flow (CBF) is the blood supply to the brain in a given period of time.[6] In an adult, CBF is typically 750 millilitres per minute or 15% of the cardiac output. This equates to an average perfusion of 50 to 54 millilitres of blood per 100 grams of brain tissue per minute.[7][8][9] CBF is tightly regulated to meet the brain's metabolic demands.[7][10] Too much blood (a clinical condition of a normal homeostatic response of hyperemia)[1] can raise intracranial pressure (ICP), which can compress and damage delicate brain tissue. Too little blood flow (ischemia) results if blood flow to the brain is below 18 to 20 ml per 100 g per minute, and tissue death occurs if flow dips below 8 to 10 ml per 100 g per minute. In brain tissue, a biochemical cascade known as the ischemic cascade is triggered when the tissue becomes ischemic, potentially resulting in damage to and the death of brain cells. Medical professionals must take steps to maintain proper CBF in patients who have conditions like shock, stroke, cerebral edema, and traumatic brain injury.

Cerebral blood flow is determined by a number of factors, such as viscosity of blood, how dilated blood vessels are, and the net pressure of the flow of blood into the brain, known as cerebral perfusion pressure, which is determined by the body's blood pressure. Cerebral perfusion pressure (CPP) is defined as the mean arterial pressure (MAP) minus the intracranial pressure (ICP). In normal individuals, it should be above 50 mm Hg. Intracranial pressure should not be above 15 mm Hg (ICP of 20 mm Hg is considered as intracranial hypertension). [11] Cerebral blood vessels are able to change the flow of blood through them by altering their diameters in a process called cerebral autoregulation; they constrict when systemic blood pressure is raised and dilate when it is lowered.[12] Arterioles also constrict and dilate in response to different chemical concentrations. For example, they dilate in response to higher levels of carbon dioxide in the blood and constrict in response to lower levels of carbon dioxide.[12]

For example, assuming a person with an arterial partial pressure of carbon dioxide (PaCO2) of 40 mmHg (normal range of 38–42 mmHg)[13] and a CBF of 50 ml per 100g per min. If the PaCO2 dips to 30 mmHg, this represents a 10 mmHg decrease from the initial value of PaCO2. Consequently, the CBF decreases by 1ml per 100g per min for each 1mmHg decrease in PaCO2, resulting in a new CBF of 40ml per 100g of brain tissue per minute. In fact, for each 1 mmHg increase or decrease in PaCO2, between the range of 20–60 mmHg, there is a corresponding CBF change in the same direction of approximately 1–2 ml/100g/min, or 2–5% of the CBF value.[14] This is why small alterations in respiration pattern can cause significant changes in global CBF, specially through PaCO2 variations.[14]

CBF is equal to the cerebral perfusion pressure (CPP) divided by the cerebrovascular resistance (CVR):[15]

CBF = CPP / CVR

Control of CBF is considered in terms of the factors affecting CPP and the factors affecting CVR. CVR is controlled by four major mechanisms:

  1. Metabolic control (or 'metabolic autoregulation')
  2. Pressure autoregulation
  3. Chemical control (by arterial pCO2 and pO2)
  4. Neural control

Role of intracranial pressure Edit

Increased intracranial pressure (ICP) causes decreased blood perfusion of brain cells by mainly two mechanisms:

Cerebral perfusion pressure Edit

Main article: Cerebral perfusion pressure

Cerebral perfusion pressure is the net pressure gradient causing cerebral blood flow to the brain (brain perfusion). It must be maintained within narrow limits; too little pressure could cause brain tissue to become ischemic (having inadequate blood flow), and too much could raise intracranial pressure.

Imaging Edit

Arterial spin labeling (ASL), phase contrast magnetic resonance imaging (PC-MRI), and positron emission tomography (PET) are neuroimaging techniques that can be used to measure CBF. ASL and PET can also be used to measure regional CBF (rCBF) within a specific brain region. rCBF at one location can be measured over time by thermal diffusion[16]

References Edit

  1. ^ a b Muoio, V; Persson, PB; Sendeski, MM (April 2014). "The neurovascular unit - concept review". Acta Physiologica. 210 (4): 790–8. doi:10.1111/apha.12250. PMID 24629161. S2CID 25274791.
  2. ^ Cipolla, Marilyn J. (2009). "Anatomy and Ultrastructure". National Center for Biotechnology Information, U.S. National Library of Medicine. Morgan & Claypool Life Sciences. Retrieved June 22, 2021.
  3. ^ Chandra, Ankush; Li, William A; Stone, Christopher R; Geng, Xiaokun; Ding, Yuchuan (2017-07-17). "The cerebral circulation and cerebrovascular disease I: Anatomy". Brain Circulation. 3 (2): 45–56. doi:10.4103/bc.bc_10_17. PMC 6126264. PMID 30276305.
  4. ^ "Carotid Arterial System". The Lecturio Medical Concept Library. Retrieved 2021-06-22.
  5. ^ Hufnagle, John J.; Tadi, Prasanna (2022). "Neuroanatomy, Brain Veins". StatPearls. StatPearls Publishing. Retrieved 28 February 2023.
  6. ^ Tolias C and Sgouros S. 2006. "Initial Evaluation and Management of CNS Injury."[full citation needed] March 2, 2007, at the Wayback Machine Emedicine.com. Accessed January 4, 2007.
  7. ^ a b Orlando Regional Healthcare, Education and Development. 2004. "Overview of Adult Traumatic Brain Injuries." February 27, 2008, at the Wayback Machine Accessed 2008-01-16.
  8. ^ Shepherd S. 2004. "Head Trauma." Emedicine.com. Shepherd S. 2004. "Head Trauma." Emedicine.com. Accessed January 4, 2007.
  9. ^ Walters, FJM. 1998. "Intracranial Pressure and Cerebral Blood Flow." May 14, 2011, at the Wayback Machine Physiology. Issue 8, Article 4. Accessed January 4, 2007.
  10. ^ Singh J and Stock A. 2006. "Head Trauma." Emedicine.com. Accessed January 4, 2007.
  11. ^ Heinrich Mattle & Marco Mumenthaler with Ethan Taub (2016-12-14). Fundamentals of Neurology. Thieme. p. 129. ISBN 978-3-13-136452-4.
  12. ^ a b Kandel E.R., Schwartz, J.H., Jessell, T.M. 2000. Principles of Neural Science, 4th ed., McGraw-Hill, New York. p.1305
  13. ^ Hadjiliadis D, Zieve D, Ogilvie I. Blood Gases. Medline Plus. 06/06/2015.
  14. ^ a b Giardino ND, Friedman SD, Dager SR. Anxiety, respiration, and cerebral blood flow: implications for functional brain imaging. Compr Psychiatry 2007;48:103–112. Accessed 6/6/2015.
  15. ^ AnaesthesiaUK. 2007. Cerebral Blood Flow (CBF) September 18, 2010, at the Wayback Machine. Accessed 2007-10-16.
  16. ^ P. Vajkoczy, H. Roth, P. Horn, T. Lucke, C. Thome, U. Hubner, G. T. Martin, C. Zappletal, E. Klar, L. Schilling, and P. Schmiedek, “Continuous monitoring of regional cerebral blood flow: experimental and clinical validation of a novel thermal diffusion microprobe,” J. Neurosurg., vol. 93, no. 2, pp. 265–274, Aug. 2000. [1]

External links Edit

  • Computer Model of the Cerebral Circulation for Training and Education

September 01, 2023
cerebral, circulation, movement, blood, through, network, cerebral, arteries, veins, supplying, brain, rate, cerebral, blood, flow, adult, human, typically, milliliters, minute, about, cardiac, output, arteries, deliver, oxygenated, blood, glucose, other, nutr. Cerebral circulation is the movement of blood through a network of cerebral arteries and veins supplying the brain The rate of cerebral blood flow in an adult human is typically 750 milliliters per minute or about 15 of cardiac output Arteries deliver oxygenated blood glucose and other nutrients to the brain Veins carry used or spent blood back to the heart to remove carbon dioxide lactic acid and other metabolic products The neurovascular unit regulates cerebral blood flow so that activated neurons can be supplied with energy in the right amount and at the right time 1 Because the brain would quickly suffer damage from any stoppage in blood supply the cerebral circulatory system has safeguards including autoregulation of the blood vessels The failure of these safeguards may result in a stroke The volume of blood in circulation is called the cerebral blood flow Sudden intense accelerations change the gravitational forces perceived by bodies and can severely impair cerebral circulation and normal functions to the point of becoming serious life threatening conditions Cerebral circulationAreas of the brain are supplied by different arteries The major systems are divided into an anterior circulation the anterior cerebral artery and middle cerebral artery and a posterior circulationSchematic of veins and venous spaces that drain deoxygenated blood from the brainIdentifiersMeSHD002560Anatomical terminology edit on Wikidata The following description is based on idealized human cerebral circulation The pattern of circulation and its nomenclature vary between organisms Contents 1 Anatomy 1 1 Blood supply 1 1 1 Anterior cerebral circulation 1 1 2 Posterior cerebral circulation 1 2 Venous drainage 2 Physiology 2 1 Role of intracranial pressure 2 2 Cerebral perfusion pressure 2 3 Imaging 3 References 4 External linksAnatomy Edit Cerebrovascular SystemBlood supply Edit Cortical areas and their arterial blood supply Blood supply to the brain is normally divided into anterior and posterior segments relating to the different arteries that supply the brain The two main pairs of arteries are the Internal carotid arteries supply the anterior brain and vertebral arteries supplying the brainstem and posterior brain 2 The anterior and posterior cerebral circulations are interconnected via bilateral posterior communicating arteries They are part of the Circle of Willis which provides backup circulation to the brain In case one of the supply arteries is occluded the Circle of Willis provides interconnections between the anterior and the posterior cerebral circulation along the floor of the cerebral vault providing blood to tissues that would otherwise become ischemic 3 Anterior cerebral circulation Edit The ophthalmic artery and its branches The anterior cerebral circulation is the blood supply to the anterior portion of the brain including eyes It is supplied by the following arteries Internal carotid arteries These large arteries are the medial branches of the common carotid arteries which enter the skull as opposed to the external carotid branches which supply the facial tissues the internal carotid artery branches into the anterior cerebral artery and continues to form the middle cerebral artery 4 Anterior cerebral artery ACA Anterior communicating artery Connects both anterior cerebral arteries within and along the floor of the cerebral vault Middle cerebral artery MCA Posterior cerebral circulation Edit The anterior and posterior circulations meet at the Circle of Willis pictured here which rests at the top of the brainstem Inferior view The posterior cerebral circulation is the blood supply to the posterior portion of the brain including the occipital lobes cerebellum and brainstem It is supplied by the following arteries Vertebral arteries These smaller arteries branch from the subclavian arteries which primarily supply the shoulders lateral chest and arms Within the cranium the two vertebral arteries fuse into the basilar artery Posterior inferior cerebellar artery PICA Basilar artery Supplies the midbrain cerebellum and usually branches into the posterior cerebral artery Anterior inferior cerebellar artery AICA Pontine branches Superior cerebellar artery SCA Posterior cerebral artery PCA Posterior communicating arteryVenous drainage Edit The venous drainage of the cerebrum can be separated into two subdivisions superficial and deep The superficial systemThe superficial system is composed of dural venous sinuses sinuses channels within the dura mater The dural sinuses are therefore located on the surface of the cerebrum The most prominent of these sinuses is the superior sagittal sinus which is located in the sagittal plane under the midline of the cerebral vault posteriorly and inferiorly to the confluence of sinuses where the superficial drainage joins with the sinus that primarily drains the deep venous system From here two transverse sinuses bifurcate and travel laterally and inferiorly in an S shaped curve that forms the sigmoid sinuses which go on to form the two jugular veins In the neck the jugular veins parallel the upward course of the carotid arteries and drain blood into the superior vena cava The veins puncture the relevant dural sinus piercing the arachnoid and dura mater as bridging veins that drain their contents into the sinus 5 The deep venous systemThe deep venous system is primarily composed of traditional veins inside the deep structures of the brain which join behind the midbrain to form the great cerebral vein vein of Galen This vein merges with the inferior sagittal sinus to form the straight sinus which then joins the superficial venous system mentioned above at the confluence of sinuses Physiology Edit Dural venous sinuses bordered by hard meninges shown in blue direct blood outflow from cerebral veins to the internal jugular vein at the base of skullCerebral blood flow CBF is the blood supply to the brain in a given period of time 6 In an adult CBF is typically 750 millilitres per minute or 15 of the cardiac output This equates to an average perfusion of 50 to 54 millilitres of blood per 100 grams of brain tissue per minute 7 8 9 CBF is tightly regulated to meet the brain s metabolic demands 7 10 Too much blood a clinical condition of a normal homeostatic response of hyperemia 1 can raise intracranial pressure ICP which can compress and damage delicate brain tissue Too little blood flow ischemia results if blood flow to the brain is below 18 to 20 ml per 100 g per minute and tissue death occurs if flow dips below 8 to 10 ml per 100 g per minute In brain tissue a biochemical cascade known as the ischemic cascade is triggered when the tissue becomes ischemic potentially resulting in damage to and the death of brain cells Medical professionals must take steps to maintain proper CBF in patients who have conditions like shock stroke cerebral edema and traumatic brain injury Cerebral blood flow is determined by a number of factors such as viscosity of blood how dilated blood vessels are and the net pressure of the flow of blood into the brain known as cerebral perfusion pressure which is determined by the body s blood pressure Cerebral perfusion pressure CPP is defined as the mean arterial pressure MAP minus the intracranial pressure ICP In normal individuals it should be above 50 mm Hg Intracranial pressure should not be above 15 mm Hg ICP of 20 mm Hg is considered as intracranial hypertension 11 Cerebral blood vessels are able to change the flow of blood through them by altering their diameters in a process called cerebral autoregulation they constrict when systemic blood pressure is raised and dilate when it is lowered 12 Arterioles also constrict and dilate in response to different chemical concentrations For example they dilate in response to higher levels of carbon dioxide in the blood and constrict in response to lower levels of carbon dioxide 12 For example assuming a person with an arterial partial pressure of carbon dioxide PaCO2 of 40 mmHg normal range of 38 42 mmHg 13 and a CBF of 50 ml per 100g per min If the PaCO2 dips to 30 mmHg this represents a 10 mmHg decrease from the initial value of PaCO2 Consequently the CBF decreases by 1ml per 100g per min for each 1mmHg decrease in PaCO2 resulting in a new CBF of 40ml per 100g of brain tissue per minute In fact for each 1 mmHg increase or decrease in PaCO2 between the range of 20 60 mmHg there is a corresponding CBF change in the same direction of approximately 1 2 ml 100g min or 2 5 of the CBF value 14 This is why small alterations in respiration pattern can cause significant changes in global CBF specially through PaCO2 variations 14 CBF is equal to the cerebral perfusion pressure CPP divided by the cerebrovascular resistance CVR 15 CBF CPP CVRControl of CBF is considered in terms of the factors affecting CPP and the factors affecting CVR CVR is controlled by four major mechanisms Metabolic control or metabolic autoregulation Pressure autoregulation Chemical control by arterial pCO2 and pO2 Neural controlRole of intracranial pressure Edit Increased intracranial pressure ICP causes decreased blood perfusion of brain cells by mainly two mechanisms Increased ICP constitutes an increased interstitial hydrostatic pressure that in turn causes a decreased driving force for capillary filtration from intracerebral blood vessels Increased ICP compresses cerebral arteries causing increased cerebrovascular resistance CVR Cerebral perfusion pressure Edit Main article Cerebral perfusion pressure Cerebral perfusion pressure is the net pressure gradient causing cerebral blood flow to the brain brain perfusion It must be maintained within narrow limits too little pressure could cause brain tissue to become ischemic having inadequate blood flow and too much could raise intracranial pressure Imaging Edit Arterial spin labeling ASL phase contrast magnetic resonance imaging PC MRI and positron emission tomography PET are neuroimaging techniques that can be used to measure CBF ASL and PET can also be used to measure regional CBF rCBF within a specific brain region rCBF at one location can be measured over time by thermal diffusion 16 References Edit a b Muoio V Persson PB Sendeski MM April 2014 The neurovascular unit concept review Acta Physiologica 210 4 790 8 doi 10 1111 apha 12250 PMID 24629161 S2CID 25274791 Cipolla Marilyn J 2009 Anatomy and Ultrastructure National Center for Biotechnology Information U S National Library of Medicine Morgan amp Claypool Life Sciences Retrieved June 22 2021 Chandra Ankush Li William A Stone Christopher R Geng Xiaokun Ding Yuchuan 2017 07 17 The cerebral circulation and cerebrovascular disease I Anatomy Brain Circulation 3 2 45 56 doi 10 4103 bc bc 10 17 PMC 6126264 PMID 30276305 Carotid Arterial System The Lecturio Medical Concept Library Retrieved 2021 06 22 Hufnagle John J Tadi Prasanna 2022 Neuroanatomy Brain Veins StatPearls StatPearls Publishing Retrieved 28 February 2023 Tolias C and Sgouros S 2006 Initial Evaluation and Management of CNS Injury full citation needed Archived March 2 2007 at the Wayback Machine Emedicine com Accessed January 4 2007 a b Orlando Regional Healthcare Education and Development 2004 Overview of Adult Traumatic Brain Injuries Archived February 27 2008 at the Wayback Machine Accessed 2008 01 16 Shepherd S 2004 Head Trauma Emedicine com Shepherd S 2004 Head Trauma Emedicine com Accessed January 4 2007 Walters FJM 1998 Intracranial Pressure and Cerebral Blood Flow Archived May 14 2011 at the Wayback Machine Physiology Issue 8 Article 4 Accessed January 4 2007 Singh J and Stock A 2006 Head Trauma Emedicine com Accessed January 4 2007 Heinrich Mattle amp Marco Mumenthaler with Ethan Taub 2016 12 14 Fundamentals of Neurology Thieme p 129 ISBN 978 3 13 136452 4 a b Kandel E R Schwartz J H Jessell T M 2000 Principles of Neural Science 4th ed McGraw Hill New York p 1305 Hadjiliadis D Zieve D Ogilvie I Blood Gases Medline Plus 06 06 2015 a b Giardino ND Friedman SD Dager SR Anxiety respiration and cerebral blood flow implications for functional brain imaging Compr Psychiatry 2007 48 103 112 Accessed 6 6 2015 AnaesthesiaUK 2007 Cerebral Blood Flow CBF Archived September 18 2010 at the Wayback Machine Accessed 2007 10 16 P Vajkoczy H Roth P Horn T Lucke C Thome U Hubner G T Martin C Zappletal E Klar L Schilling and P Schmiedek Continuous monitoring of regional cerebral blood flow experimental and clinical validation of a novel thermal diffusion microprobe J Neurosurg vol 93 no 2 pp 265 274 Aug 2000 1 External links EditComputer Model of the Cerebral Circulation for Training and Education Retrieved from https en wikipedia org w index php title Cerebral circulation amp oldid 1171541041, wikipedia, wiki, book, books, library,

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