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NE Exam 2 > Cerebral Vasculature & Brain Homeostasis > Flashcards

Cerebral Vasculature & Brain Homeostasis Flashcards

1
Q

This flows through the ventricles and around the brain and spinal cord.

A

Cerebrospinal Fluid (CSF)

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2
Q

At any given moment, there is _______ of CSF. This amount can go up with hydrocephalus or other abnormalities.

A

150 ml

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3
Q

CSF is not recirculated in the body, so we make _______ per day.

A

550 ml

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4
Q

There are 4 ventricles in the brain, which are…

A

2 Lateral Ventricles
Third Ventricle
Fourth Ventricle

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5
Q

This ventricle is located over the Medulla, and under the Cerebellum.

A

Fourth Ventricle

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6
Q

This connects the Lateral Ventricles to the Third Ventricle.

A

Intraventricular Foramen

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7
Q

This connects the 3rd and 4th ventricles.

A

Cerebral Aqueduct

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8
Q

This connects the 4th ventricle to the Cisterna Magna.

A

Median Aperture

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9
Q

This connects the 4th ventricle to the Arachnoid space.

A

Lateral Apertures

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10
Q

Most of the CSF (50-70 percent) is made by the specialized tissue of the…

A

Choroid Plexus

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11
Q

The Choroid Plexus has a lot of folds for what purpose?

A

To increase surface area

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12
Q

The remaining CSF is made by what (other than Choroid Plexus)?

A

Tissue that lines the ventricles and blood vessels

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13
Q

What are the two steps of CSF formation?

A

1) Passive filtration of serum

2) Modification of ion composition

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14
Q

Step 1 of CSF formation, passive filtration of serum, is dependent on two pressures which are…

A

Hydrostatic Pressure

Oncotic Pressure

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15
Q

Describe the two types of Hydrostatic Pressure for CSF.

A

– In the capillary and pushes fluid out, this pressure is large (same as blood pressure).

– Surrounding the capillary and pushes fluid into it, this pressure is small (called Tissue Hydrostatic Pressure).

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16
Q

Describe the two types of Oncotic Pressure for CSF.

A

– Inside the capillary, pulls the fluid into the capillary.

– Surrounding the capillary, pulls the fluid out of the capillary.

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17
Q

Why does Oncotic Pressure not have much effect?

A

Because the tissue Oncotic Pressure and the capillary Oncotic Pressure are equal and opposite and cancel each other out.

***This makes Hydrostatic Pressure (blood pressure) win, which pushes fluid out of capillary.

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18
Q

Briefly explain how step 1 of formation of CSF works.

A

Step 1: Passive filtration of serum

– Dependent on two pressures, which are hydrostatic and oncotic. The oncotic pressures cancel each other out, and the hydrostatic pressure in the capillary (blood pressure) is greater than the tissue hydrostatic pressure. This means fluid moves from the blood vessels into the ventricles.

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19
Q

Step 2 of CSF formation is the modification of ion composition. What ion concentrations are controlled by channels on epithelial cells?

A

HCO3 (bicarbonate)
Cl
K

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20
Q

For step 2 of CSF formation, this is what allows water to cross the barrier.

A

Aquaporin 1

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21
Q

T/F. Production of CSF is constant over a wide range of intracranial pressures.

A

True

***Remember, this isn’t always a good thing. The CSF does not have an “off” switch so it will continue to make CSF even if it already has too much and it’s within the appropriate intracranial pressure range.

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22
Q

What is in nearly equal concentrations between the blood plasma and the CSF?

A

Na+

HCO3

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23
Q

What is in greater concentration in the CSF, but less in the blood plasma?

A

Mg++
Cl-
CO2

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24
Q

What is in lesser concentrations in the CSF, but greater in the blood plasma?

A

K+
Ca++
Protein
Glucose

***Calcium can be very toxic to cells, and protein acts as a buffer for H+ ions. This is why the pH is different in the CSF and the plasma.

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25
Q

CSF flows through the ventricular system. The flow is one way and the CSF is reabsorbed by the _________ ________ at the end.

A

Arachnoid Villi

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26
Q

In the absorption of CSF by the Arachnoid Villi, the endothelium of the ______ _____ and the membrane on the villi have fused. This allows for the bulk flow of CSF into the ______ ______ (which is the primary method of absorption). Pinocytosis (cell drinking) has also been documented.

A

Venous Sinus

Venous Sinus

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27
Q

The absorption of CSF is proportional to what?

A

Intracranial pressure

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28
Q

At intracranial pressures below _______ CSF, there is no absorption. Normal pressure is _______ CSF.

A

68 mm

112 mm

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29
Q

T/F. Increased pressure causes damage to neurons.

A

True

***Remember neurons HATE pressure, which is why your hand/foot falls asleep when you put pressure or lay on it for too long!

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30
Q

From the arachnoid villi, the CSF enters the venous sinuses by…

A

Bulk flow

31
Q

What is the main role of CSF?

A

Protect the brain

32
Q

T/F. The brain could still survive without CSF.

A

False. The weight of the brain in air is 1400 g, but with CSF it’s 50 g. Normal head movements alone could kill the brain without CSF.

33
Q

Capillaries in the brain have two components that limit exchange, which are…

A
  • Tight junctions between endothelial cells
  • Glial end feet that come in close contact with blood vessels

***These make up Blood Brain Barrier!!!

34
Q

Some substances can cross the BBB via passive diffusion. These substances are…

A

Water (via Aquaporin-4)
CO2
O2
Free steroid hormones (most are protein bound)

35
Q

What is the major energy source for neurons?

A

Glucose

***Remember, this does NOT cross the BBB readily, has to use transporter.

36
Q

This is the transporter used for Glucose to pass the BBB. It is NOT insulin-dependent, so it works all the time.

A

Glut1

37
Q

There are two types of Glut1 transporters in the brain, ______ on capillaries and _______ on astroglia.

A

55k

45k

38
Q

Neurons use _______ transporters to move glucose in.

A

Glut3

39
Q

The BBB can move certain ions from the CSF to the blood in the same direction all at the same time via a transporter. These ions are…

A

Na+
K+
2 Cl-

40
Q

Expression of the transporter that moves Na+/K+/2 Cl- into the blood from CSF controlled by the release of _________ and ________ from endothelial cells of the blood vessels. This seems to be related to the concentration of ______ in the CSF.

A

Endothelin 1
Endothelin 3
K+

41
Q

It can be hard to get certain drugs across the BBB, but some do make it across and are then moved back to the blood via __________. This binds to a wide variety of substances (not typical of most transporters).

A

P-glycoprotein

***P stands for Pump

42
Q

What is the purpose of the BBB?

A

To protect the chemical composition of the CSF from blood-borne agents.

43
Q

The BBB maintains _________ composition, particularly related to K+ and maintenance of Vm (membrane potential), as well as protection from _______.

A

Electrolyte

Toxins

44
Q

There are four regions in the brain that require exposure to blood-borne substances to function. However, the normal function of the BBB would prevent them from doing their job, so we “handicap” the BBB. In these regions, the capillaries do not have the _________ _________ between endothelial cells.

A

Tight junctions

45
Q

There are several places in the brain where we want the brain exposed to the blood. The _________ ________ are neural tissue that is “outside” or not as well protected by the BBB as other neural tissue. There are four regions that fall in this category.

A

Circumventricular organs

46
Q

What are the 4 areas that the BBB does not protect?

A

1) Posterior Pituitary
2) Area Postrema
3) Organum vasculosum of the lamina terminalis (OVLT)
4) Subfornical organ

47
Q

This area not protected by the BBB is modified neural tissue that releases hormones into the blood. Also called the Neurohypophysis.

A

Posterior Pituitary

48
Q

This area not protected by the BBB is responsible for vomiting, but is independent of the gag reflex.

A

Area Postrema

49
Q

These areas that are not protected by the BBB are both involved in control of body water, thirst, and blood volume control.

A

OVLT

Subfornical organ

50
Q

What is the consequence of these four locations that aren’t protected by the BBB?

A

These areas can be exposed to toxins that the rest of the brain is protected from.

51
Q

How many ml/min of blood is required for cerebral circulation?

A

750 ml/min (14 percent of blood pumped from heart every minute)

52
Q

The 2 _______ ______ arteries and the _______ artery join to form the Circle of Willis. Despite appearance, there is little mixing of blood from the different sources. This means if there is disruption of one of the inputs, it produces localized (discrete) areas of ________.

A

Internal Carotid
Basilar
Ischemia

53
Q

What neurotransmitters provide cerebral sympathetic innervation?

A 
Norepinephrine 
Neuropeptide Y (NPY)
54
Q

The receptors for cerebral sympathetic innervation are ___________. This leads to _________ when systemic cardiac output/blood pressure increases.

A

Alpha-adrenergics

Constriction

55
Q

What neurotransmitters provide cerebral parasympathetic innervation?

A

ACh
Vasoactive intestinal polypeptide (VIP)
PHM-27 (derived from pre-pro-VIP)

56
Q

The neurotransmitters responsible for cerebral parasympathetic innervation cause (CONSTRICTION/DILATION) of the blood vessels.

A

Dilation

57
Q

T/F. There is sensory innervation of the distal blood vessels.

A

True

58
Q

What are the neurotransmitters responsible for cerebral sensory innervation (in distal blood vessels)?

A

Substance P
Neurokinin A
CGRP

59
Q

The neurotransmitters responsible for cerebral sensory innervation cause (CONSTRICTION/DILATION) of the blood vessels. They are released because sensory nerves sense decreased CSF and torsion (released at the site of torsion).

A

Dilation

60
Q

The sensory fibers render the blood vessels of the brain extremely sensitive to torsion/manipulation, which leads to…

A

Pain

61
Q

In the presence of the reduced CSF volume, the brain is effectively heavier and simple motion can cause pain because of the ‘torsion’ of the blood vessels. The activation of those afferents (causing pain) will also cause __________ and increase blood flow to the brain.

A

Vasodilation

***This doesn’t necessarily mean the brain will go back to normal, just increases the volume back to somewhat normal.

62
Q

Cerebral blood flow is under local control, _______ consumption dictates where in the brain the blood will go.

A

Oxygen

63
Q

We use the changes in brain metabolism/blood flow to infer activity in a variety of circumstances. For example, in a (NORMAL/DEPRESSED) brain there is blood flow to the frontal cortex but in a (NORMAL/DEPRESSED) brain there is no blood flow to the frontal cortex.

A

Normal

Depressed

64
Q

Cerebral blood flow is strongly __________. It is held constant over a wide range of systemic (mean arterial) blood pressures.

A

Autoregulated

65
Q

What is the range of mean arterial pressure in which the cerebral circulation has autoregulation under normal conditions?

A

60 mmHg – 140 mmHg

66
Q

Why is it bad if the mean arterial pressure goes over 140 mmHg?

A

Because that means this person has very high blood pressure, and tight junctions in the BBB are very sensitive to pressure. High blood pressure can damage them.

67
Q

What can severe hypertension cause to be damaged?

A

BBB

68
Q

In the event of high blood pressure that could damage the BBB, sympathetic stimulation occurs. Why is this important?

A

Sympathetics in the brain will vasoconstrict the vasculature. Although this will increase the systemic vasculature resistance, it protects the capillaries in the brain and the BBB from damage.

***Remember, the tight junctions of the BBB are being damaged because of the high BP. So the sympathetics increase resistance to help protect the BBB.

69
Q

Cerebral blood flow is influenced by intracranial pressure. As intracranial pressure goes up, _______ outflow is obstructed, leading to reduced ________ flow to the brain.

A

Venous

Arterial

70
Q

When there is increased intracranial pressure blocking the venous outflow, leading to reduced arterial flow to the brain then this activates the cardiovascular control centers in the _________ and increases systemic BP. Sometimes drastically. This is trying to force blood into the brain and we are not worried about protecting the capillaries. Your brain is not receiving blood and this is NOT GOOD (obvi).

A

Medulla

71
Q

What might increase the intracranial pressure?

A

Hydrocephalus
Cerebral Edema
Intracranial Bleeding

72
Q

What does it mean if the intracranial pressure suddenly starts dropping?

A

Could be a good thing if it was surgically performed to try to release pressure, but it can also be bad. At some point the brain can’t take the pressure anymore and it will begin to die. This causes the pressure to begin to drop.

73
Q

T/F. If blood flow to the brain is compromised, the brain will drive systemic blood pressure up to force blood into the brain. The consequence of this is that systemic blood pressure can be driven to very high levels in order to perfuse the brain.

A

True

NE Exam 2 (24 decks)

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