Singh 2: Blood Supply, BBB, Ventricles

Question 1

A significant amount of total cardiac output goes to ____________

Blood supply to the brain is ______ so that blood gets where it is needed

Answer 1

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

Question 2

The brain is well protected by the ____ & ______

__________ drain the brain

Answer 2

The brain is well protected by the skull and the meninges

Dural venous sinuses drain the brain

Question 3

The Blood Brain Barrier:

• Blocks _______
• _______ & _______ deliver key nutrients

Answer 3

The Blood Brain Barrier:

• Blocks many large molecules
• Astrocytes and specific transporters deliver key nutrients

Question 4

The ________ are sites of CSF production and flow

Answer 4

The ventricles are sites of CSF production and flow

CSF and intersitial fluid in the brain parenchyma are continous

Question 5

The brain presents unique challenges for blood delivery in humans:

• __________ O2 requirement
• ____ of body’s oxygen
• Pumping against ____
• Escased in bone: ______

Answer 5

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

Question 6

What are the directions in the CNS?

Answer 6

Dorsal and ventral (up and down)

Rostral (anterior)

Caudal (posterior)

Question 7

What is the important function of the Circle of Willis?

What makes up the circle of willis

Answer 7

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.

Question 8

The internal carotid artery branches into becoming the ______ and ______, which bathe the _____ and _____ parts of the brain respectively

Answer 8

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)

Question 9

The vertebral artery becomes the ______ which becomes the _______ which bathes the _____ part of the brain

Answer 9

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

Question 10

Cerebral arteries have specific domains:

The Anterior Cerebral Artery supplies the ____ and ____ structures

Disruption causes disruption of _____ and _______ in ______, as well as impaired _______

Answer 10

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

Question 11

Cerebral arteries have specific domains:

Posterior cerebral artery supples the ____, _____, and _____

Disruption causes what?

Answer 11

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

Question 12

If you had an infarction/disruption of blood flow associated with the anterior cerebral artery what kind of symptoms would you see?

Answer 12

Disruption to anterior cerebral artery:

LOWER extremity issues (motor cortex is in the more medial part)

Question 13

If you had a disruption of blood flow within your middle cerebral artery… what are the concenquences

Answer 13

Messed up middle cerebral artery: more lateral, so it will impact your upper extremities

Question 14

Middle Cerebral Artery:

Disruption causes what?

Answer 14

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

Question 15

Define the term “lenticulostriate arteries”

Answer 15

Lenticulostriate arteries are branches of the middle cerebral artery

They are also called “end arteries”

Disruption causes contralateral weakness of limbs

Question 16

Give the equation for Cerebral Perfusion Pressure

Answer 16

Cerebral Perfusion Pressure =

Mean Arterial Pressure - Intracranial Pressure

CPP = MAP - Intracranial Pressure

Question 17

Cerebral Perfusion Pressure:

CPP is maintained between _____ and _____ mmHg

Increases in intracranial pressure can ______ cerebral blood flow

Answer 17

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

Question 18

Cerebral Perfusion Pressure:
Cerebral blood flow is regulated by ___ and ____

Explain myogenic control

Explain pericytes

Explain metabolic (increase in CO2 vs decrease in CO2)

Answer 18

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

Question 19

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?

Answer 19

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

Question 20

Explain Pericytes and what kind of control they have over cerebral blood flow

Answer 20

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

Question 21

STROKE:
Explain the difference between anoxia and hypoxia

Answer 21

Anoxia: no oxygen

Hypoxia: insufficient oxygen

Question 22

Explain Ischemic Strokes,

What percentage of all strokes do they take up?

What are they caused by?

Symptoms?

Explain penumbra vs lacuna

Answer 22

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

Question 23

Hemorrhagic Stroke:

How common are they?
What are they caused by

Answer 23

Hemorrhagic Stroke: 15-20% of all strokes

Bleeding of the vessels

Rupture or aneursym

Question 24

Cerebral Venous System:

Superficial veins:

Drain blood from ______

Collect into the _______

Answer 24

Cerebral venous system:

Superficial veins

• drain blood from corticol and associated white matter
• These collect into the superior sagital sinus

Question 25

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

Answer 25

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

Question 26

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

Answer 26

There are two venous systems in the brain: superficial veins and deep veins Look at picture attached to see where they all lie

Question 27

Protective coverings of the brain: the meninges Explain the dura, arachnoid, and pia mater Explain the two layers within the dura mater as well

Answer 27

**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

Question 28

Explain where the following sinuses are using a MIDSAGITTAL view of the brain: Superior Sagittal Sinus Straight Sinus

Answer 28

Question 29

Explain what the following terms mean: Supratentorial fossa Infratentorial fossa

Answer 29

Supratentorial fossa: above the tentorium cerebelli; all of forebrain Infratentorial fossa: all of hindbrain (below the tetorium cerebelli)

Question 30

The Dural sinuses drain the brain Explain a coronal view of the Superior Sagital Sinus, the Straight Sinus, and the tranverse sinuses

Answer 30

Question 31

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 \_\_

Answer 31

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

Question 32

Interstitual fluid is drained through venules and then into _______ through _______ running between pia and dura Rupture of those bridging veins during head trauma causes \_\_\_\_\_\_\_

Answer 32

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

Question 33

The Blood Brain Barrier (BBB) - The BBB is a selective barrier that encompasses \_\_\_\_\_\_\_\_\_\_\_ * Function is * ___________ have "leaky BBB"

Answer 33

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

Question 34

What parts of the brain have a LEAKY blood brain barrier?

Answer 34

Circumventricular organs have a leaky BBB

Question 35

What is the Blood Brain Barrier Comprised of?

Answer 35

The BBB is comprised of: - Endothelial cells that are tightly connected by tight junctions - Astrocytic end feet - Pericytes - vascular smooth muscle cells

Question 36

The Circumventricular Organ: - _______ region of the brain with fenestrated capillaries - comprised of what? - Area capable of actively \_\_\_\_\_\_\_\_\_\_

Answer 36

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

Question 37

Explain an example of the functional role of "blood sampling" by areas that have a leaky blood brain barrier

Answer 37

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

Question 38

What cannot cross the blood brain barrier?

Answer 38

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

Question 39

What can passively cross the blood brain barrier? What is actively transported across the BBB?

Answer 39

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

Question 40

Intersititual fluid: is the extracellular fluid bathing brain \_\_\_\_\_\_\_, and it composed of.....

Answer 40

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

Question 41

If blood isn't in direct contact with neurons what is?

Answer 41

CSF is in direct contact with neurons

Question 42

Name the three functions of CSF: 1. 2. 3.

Answer 42

Functions of CSF: 1. cushion/protect the brain and spinal cord from trauma 2. Supply nutrients to the nervous system 3. Facilitate the removal of "waste" products consequent to cerebral metabolism

Question 43

CSF: - Consists of \_\_\_\_\_, ____ fluid with low \_\_\_\_ - Derived from the \_\_\_\_\_

Answer 43

CSF: Consists of clear, watery fluid with low protein, few cells Derived from the choroid epithelium

Question 44

Choroid Plexus: - What is it made of? Where is it found?

Answer 44

Choroid plexus: - Specialized cuboidal epithelium + capillaries in the pia matter - Found in lateral ventricles, 3rd ventricle, and 4th ventricle

Question 45

Direction of flow of CSF: CSF flows from the ______ through the \_\_\_\_\_\_\_ It also leaves via How much CSF is produced per day?

Answer 45

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

Question 46

Explain how CSF is drained

Answer 46

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