Singh 2: Blood Supply, BBB, Ventricles Flashcards
A significant amount of total cardiac output goes to ____________
Blood supply to the brain is ______ so that blood gets where it is needed
A significant amount of total cardiac output goes to support the high O2 requirements (due to high metabolism) of the brain
Blood supply to the brain is regulated so that blood gets where it is needed
The brain is well protected by the ____ & ______
__________ drain the brain
The brain is well protected by the skull and the meninges
Dural venous sinuses drain the brain
The Blood Brain Barrier:
- Blocks _______
- _______ & _______ deliver key nutrients
The Blood Brain Barrier:
- Blocks many large molecules
- Astrocytes and specific transporters deliver key nutrients
The ________ are sites of CSF production and flow
The ventricles are sites of CSF production and flow
CSF and intersitial fluid in the brain parenchyma are continous
The brain presents unique challenges for blood delivery in humans:
- __________ O2 requirement
- ____ of body’s oxygen
- Pumping against ____
- Escased in bone: ______
The brain presents unique challenges for blood delivery in humans:
- Highest oxygen requirement of any tissue…more oxygen than any other organ
- roughly 25% of body’s ozygen, or 15-20 % of total cardiac output goes to the brain
- Pumping against gravity (need to have a good pump to create adequate perfusion)
- Encased in bone: pressure issues
What are the directions in the CNS?
Dorsal and ventral (up and down)
Rostral (anterior)
Caudal (posterior)
What is the important function of the Circle of Willis?
What makes up the circle of willis
The circle of willis is an anastomic connection
It provides collateral circulation
This reduces the impact of a blockade in an artery on one side of the brain by giving alternative pathways for blood to get to the same place
Circle of willis:
The internal carotid artery becomes the anterior and middle cerebral arteries.
The ventricular artery becomes the basilar artery which becomes the posterior cerebral arteries.
The internal carotid artery branches into becoming the ______ and ______, which bathe the _____ and _____ parts of the brain respectively
The internal carotid artery branches into the anterior artery (which bathes the anterior and medial structures of the brain) and the middle cerebral artery (which bathes the lateral surfaces of the brain)
The vertebral artery becomes the ______ which becomes the _______ which bathes the _____ part of the brain
The vertebral arteries come together to form the basilar artery that runs on the ventral aspect of the brainstem, it then biforcates into two posterior arteries, which bathe the back or caudal parts of the brain
Cerebral arteries have specific domains:
The Anterior Cerebral Artery supplies the ____ and ____ structures
Disruption causes disruption of _____ and _______ in ______, as well as impaired _______
Anterior Cerebral Artery: (this is a branch from the internal carotid artery)
The anterior cerebral artery supplies the anterior and medial structures of the brain
Disruption causes disruption of somatosensory and motor function of lower limbs, and impaired social behavior
Cerebral arteries have specific domains:
Posterior cerebral artery supples the ____, _____, and _____
Disruption causes what?
POSTERIOR CEREBRAL ARTERY:
remember, the posterial cerebral artery comes from:
vertebral artery–> basilar artery–> posterior cerebral
The posterior cerebral artery supplies the posterior and medial structures and the temporal lobe
Disruption causes visual field disturbances and other impairments that can include memory disturbances
If you had an infarction/disruption of blood flow associated with the anterior cerebral artery what kind of symptoms would you see?
Disruption to anterior cerebral artery:
LOWER extremity issues (motor cortex is in the more medial part)
If you had a disruption of blood flow within your middle cerebral artery… what are the concenquences
Messed up middle cerebral artery: more lateral, so it will impact your upper extremities
Middle Cerebral Artery:
Disruption causes what?
Middle cerebral artery:
largest cerebral artery, supplies lateral surfaces and part of the temporal lobe
Most commonly occluded in an ischemic stroke
Disruption on left causes aphasia, paralysis of right face and arm
This is because the middle cerebral artery bathes more lateral aspects of the brain (head) causing language defecits
Define the term “lenticulostriate arteries”
Lenticulostriate arteries are branches of the middle cerebral artery
They are also called “end arteries”
Disruption causes contralateral weakness of limbs
Give the equation for Cerebral Perfusion Pressure
Cerebral Perfusion Pressure =
Mean Arterial Pressure - Intracranial Pressure
CPP = MAP - Intracranial Pressure
Cerebral Perfusion Pressure:
CPP is maintained between _____ and _____ mmHg
Increases in intracranial pressure can ______ cerebral blood flow
Cerebral Perfusion Pressure:
CPP is maintained between 60 mmHg and 150 mmHg (below 60 is the syncope/fainting zone, and above 150 is where the blood vessels are damaged or rupture)
Increases in intracranial pressure can DECREASE cerebral blood flow (eqn: CPP = MAP - Intracranial P)
- also this makes sense because an increase in intracranial pressure will press down on cerebral arteries and decrease blood flow
Cerebral Perfusion Pressure:
Cerebral blood flow is regulated by ___ and ____
Explain myogenic control
Explain pericytes
Explain metabolic (increase in CO2 vs decrease in CO2)
Cerebral blood flow is regulated by muscles and metabolism
Myogenic: smooth muscle surrounding arterioles dilate or constric to decrease or increase pressure respectively
Pericytes: cells that regulate blood flow LOCALLY
Metabolic: increased CO2 dilates arterioles, decreased CO2 constricts arterioles
Explain the graphs related to autoregulation of cerebral blood flow as a function of arterial pressure
Explain normal autoregulation vs shifted autoregulation
What things can cause the tolerance curve to the right?
Look at graphs in image below
Normally, CPP is maintained between 60 and 150 mmHg under “normal autoregulation”
That tolerance curve can shift tp the right with sympathetic activation (like running) or with prolonged hypertension
Explain Pericytes and what kind of control they have over cerebral blood flow
Pericytes regulate LOCAL blood flow
Under normal circumstances, pericytes constrict capillaries (so their default is to constrict capillaries)
In response to neural activity, they will dilate capillaries to allow more blood flow
HOWEVER, in instances of ischemia, the pericytes will get compromised and will default to constriction, creating even MORE of a problem
STROKE:
Explain the difference between anoxia and hypoxia
Anoxia: no oxygen
Hypoxia: insufficient oxygen
Explain Ischemic Strokes,
What percentage of all strokes do they take up?
What are they caused by?
Symptoms?
Explain penumbra vs lacuna
Ischemic Strokes: 80-85% of all strokes
Occlusion, resulting in O2 deprivation
Embolism blocks vessek: bloot clot, cholesterol plaque, fat or air
Symptoms depend on region of occlusion, and symptoms assist in prediction of location of stroke (which can determine severity)
Penumbra-shadow; damage surrounding infart area caused by release of NTs from necrotic (dying tissue)
Lacuna develops: lake - glia filled hole where neurons once were
Hemorrhagic Stroke:
How common are they?
What are they caused by
Hemorrhagic Stroke: 15-20% of all strokes
Bleeding of the vessels
Rupture or aneursym
Cerebral Venous System:
Superficial veins:
Drain blood from ______
Collect into the _______
Cerebral venous system:
Superficial veins
- drain blood from corticol and associated white matter
- These collect into the superior sagital sinus
Cerebral Venous System:
Deep veins:
- Drain blood from “deep” parts of the brain to include the ____ and _____ regions
- The deep veins collect into the ______, the ______, and the _____
- These all converge into the _______, leading eventually to the ____
-Eventually drain into the ______ vein
DEEP VEINS:
- Drain blood from deep parts of the brain to include the diencephalic (aka thalamus, hypothalamus), and basal ganglia regions
- The deep veins collect into the vein of Galen (aka the great cerebral vein), the inferior sagittal sinus and the internal cerebral vein
- These then converge into the straight sinus, leading eventully to the confluence of sinuses
- Eventually drain into the jugular vein
There are two venous systems in the brain:
1.
2.
Draw how the following relate to each other:
superior sagital sinus
Inferior sagital sinus
Great vein of Galen
Straight Sinus
Internal Jugular Vein
There are two venous systems in the brain: superficial veins and deep veins
Look at picture attached to see where they all lie
Protective coverings of the brain: the meninges
Explain the dura, arachnoid, and pia mater
Explain the two layers within the dura mater as well
Dura: two layers, periosteal (closer to skull) and meningeal (closer to brain)
Throughout most of the skull, these layers are together, but at places where the venous blood collects and drains, the periosteal and meningeal layers seperate to form “sinuses”
Arachnoid: Filmy, spider web-like
Pia: tightly adhered, covered in CSF
Explain where the following sinuses are using a MIDSAGITTAL view of the brain:
Superior Sagittal Sinus
Straight Sinus
Explain what the following terms mean:
Supratentorial fossa
Infratentorial fossa
Supratentorial fossa: above the tentorium cerebelli; all of forebrain
Infratentorial fossa: all of hindbrain (below the tetorium cerebelli)
The Dural sinuses drain the brain
Explain a coronal view of the Superior Sagital Sinus, the Straight Sinus, and the tranverse sinuses
Drainage for Venous Blood:
Dural sinuses are _________
- can see _______ where sinuses are located
- confluence of sinuses is where _______
- Venous blood and ________ collect into dural sinuses which eventially drain into the __
Drainage for Venous Blood:
Dural sinuses are spaces between the periosteal and meningeal layers of the dura
- Can see indentations in cranium where sinuses are located
- Confluence of sinuses, where superior saggital sinus, straight sinus, and transverse sinus meet
- Venous blood and some CSF collect into dural sinuses which eventually drain via internal jugular vein
Interstitual fluid is drained through venules and then into _______ through _______ running between pia and dura
Rupture of those bridging veins during head trauma causes _______
Interstitial fluid is drained through venules and then into dural sinuses through bridging veins running between pia and dura
Rupture of those bridging veins during head trauma causes subdural hematoma
The Blood Brain Barrier (BBB)
- The BBB is a selective barrier that encompasses ___________
- Function is
- ___________ have “leaky BBB”
The Blood Brain Barrier:
- Selective barrier that encompasses most of the brain
- Function is to tightly regulate passage of certain molecules and ions between the blood and the CNS
- Circumventricular organs have “leaky” BBB
What parts of the brain have a LEAKY blood brain barrier?
Circumventricular organs have a leaky BBB
What is the Blood Brain Barrier Comprised of?
The BBB is comprised of:
- Endothelial cells that are tightly connected by tight junctions
- Astrocytic end feet
- Pericytes
- vascular smooth muscle cells
The Circumventricular Organ:
- _______ region of the brain with fenestrated capillaries
- comprised of what?
- Area capable of actively __________
Circumventricular Organ: found in the ventral hypothalamic area of the brain
- Ventro-medial region of the brain with fenestrated capillaries
- comprised of organum vasculosum of the lamina terminalis, subfornical organ, median eminence, and area postrema
- Area capable of actively sampling blood constituents : relevance to the fever response, the response to volume/blood loss
Explain an example of the functional role of “blood sampling” by areas that have a leaky blood brain barrier
An example of a functional role of “blood sampling” by areas that have a leaky blood brain barrier:
Decrease in blood pressure due to a decrease in blood volume:
The kidneys will release Renin-> turns into Ang II-> SFO—> goes tot eh paraventricular nucleus (magnocellular division)
The brain then decides its time to conserve water:
- releases ADH/AVP which acts on the kidneys to restore blood volume
- stimulates thirst
What cannot cross the blood brain barrier?
Things that cannot cross the BBB:
- No cells: bacteria, parasites, fungi, WBCs, RBCs, platletes, proteins, any molecule that is strongly hydrophillic
- NO antibodies
- No large molecules, including pharmaceuticals
What can passively cross the blood brain barrier?
What is actively transported across the BBB?
What can passively cross the Blood Brain Barrier:
- gases
- freely permeable to water
- caffeine, ethanol
- small amphiphillic structures
What is actively transported across the BBB: glucose, AA’s, channels allow specific ions to cross
Intersititual fluid: is the extracellular fluid bathing brain _______, and it composed of…..
Intersititual fluid is the extracellular fluid bathing the brain parenchyma, and is composed of arterial blood that has been filtered by the BBB; exchanges freely with cerebrospinal fluid
If blood isn’t in direct contact with neurons what is?
CSF is in direct contact with neurons
Name the three functions of CSF:
1.
2.
3.
Functions of CSF:
- cushion/protect the brain and spinal cord from trauma
- Supply nutrients to the nervous system
- Facilitate the removal of “waste” products consequent to cerebral metabolism
CSF:
- Consists of _____, ____ fluid with low ____
- Derived from the _____
CSF:
Consists of clear, watery fluid with low protein, few cells
Derived from the choroid epithelium
Choroid Plexus:
- What is it made of?
Where is it found?
Choroid plexus:
- Specialized cuboidal epithelium + capillaries in the pia matter
- Found in lateral ventricles, 3rd ventricle, and 4th ventricle
Direction of flow of CSF:
CSF flows from the ______ through the _______
It also leaves via
How much CSF is produced per day?
Direction of flow of CSF:
CSF flows from choroid plexus through the ventricles of the brain and spinal chord in a caudal direction, filling the ventricular system
CSF also leaves the venticles via foramina (holes) to bathe the outer surface of the CNS
About half a liter of CSF is produced in a day
Explain how CSF is drained
CSF and interstitial fluid are drained into dural sinuses via arachnoid villi (small) or granulations (larger) for CSF and venules for insterstitial fluid
In addition, CSF can be drained via cranial nerve routes, especially by draining through the bribiform plate, where olfactory nerves penetrate the skull, and exit via the nose
