Medical Physiology Guyton- Cerebral Blood Flow; The Cerebral Spinal Fluid; And Brain Metabolism

Front 1

What is the effect of total cessation of blood flow to the brain?

Back 1

Unconciousness in 5 to 10 seconds.

Front 2

What is the normal rate of cerebral blood flow?

Back 2

55-65 ml/100 grams brain tissue /minute

750-900 ml/min

15% of resting cardiac output

Front 3

What controls cerebral blood flow?

Back 3

The metabolism of the cerebral tissue mediated through CO2, O2, and H+ concentrations. H+ concentration may be affected by lactic acid, pyruvic acid, and other acidic metabolites.

Front 4

How much does C02 increase cerebral blood flow?

Back 4

Arterial pCO2 has a large and linear effect on oxygen demand over the range of 20-100 mm Hg. At pCO2 20 demand is 50% of normal. At pCO2 100 demand is 200% of normal.

Front 5

How does CO2 increase cerebral blood flow?

Back 5

By combining with water in the body fluids to form Carbonic acid which disassociates to form hydrogen ions which vasodialate the cerebral vessels.

Front 6

Why is [H+] control cerebral blood flow?

Back 6

increased [H+] depresses neuronal activity. increased blood flow flushes acids, and acid precursors out of the brain.

Front 7

How does P02 regulate cerebral blood flow?

Back 7

When the PO2 of the cerebral tissue falls below 30 mm Hg vessels in the brain immediately vasodialate.

Front 8

Why does P02 regulate cerebral blood flow?

Back 8

Normal brain oxygen consumption is constant at 3.5 ml/100 g/minute. But consumption increases marketedly in actively firing regions. Normal tissue P02 is 35-45 mm Hg. Below 30 mm Hg brain function is deranged, below 20 mm Hg coma can result.

Front 9

What is the effect of blood pressure on cerebral blood flow?

Back 9

Mean artial pressure between 60 and 140 mm Hg causes almost no change in cerebral blood flow. For hypertensive patients the regulatory range may extend to 180-200 mm Hg. Above the upper limit of regulation stretching and rupture of vessels results in edema or hemorrhage. Below the regulatory limit cerebral blood flow is compromised.

Front 10

How does the sympathetic nervous system regulate blood flow?

Back 10

When arterial pressure spikes acutely as in the case of exercise, the sympathetic nervous system constricts large and intermediate sized arteries in the brain preventing cerebral stroke.

Front 11

How does blood flow to gey matter differ from blood flow to white matter?

Back 11

Capplieries, rate of flow, and metabolism are about 4 times greater in grey matter than in white matter. Grey matter is where the neuronal cell bodies lie.

Front 12

What protects brain capillaries from hemorrhage?

Back 12

projections from surrounding glial cells called "glial feet" coat cerebral capillaries. Glial feet prevent over stretching during high pressure also the small arterioles leading to the capillareis remain constricted preventing transmission of high blood pressure to the capillaries. The small arterioles leading to brain capillaries are greatly thickened in hypertensive patients. Breakdown of these systems leads to edema then coma then death.

Front 13

What is the life time prevalance of stroke?

Back 13

10% of the elderly have a stroke due to blockage of blood flow. Although almost all elderly people have blockage to some extent.

Front 14

How are strokes caused?

Back 14

Most strokes are caused by arteriosclerotic plaques in one or more of the feeder arteries to the brain. The plaques activate blood clotting mechanisms which form a clot and block blood flow in the artery leading to acute loss of function.

In 25% of people high blood pressure leads the one of the blood vessels to burst, hemorrhage ensues, compressing local tissue. Subsequently the blood clots leading to blockage.

Front 15

What is the neurological effect of blockage in the left middle cerebral arteries?

Back 15

demention due to lost function in Wiernicke's speeck comprehension area, and motor aphasia due to loss of Broca's area for word formation. Right side spastic paralysis due to loss of function in the neural motor control areas.

Front 16

What are the symptoms of blockage of the posterior cerebral artery?

Back 16

loss of vision in both eyes on the same half of the retina as the lesion. If the stroke involves both the hindbrain and the mid-brain it can block nerve conduction between the brain and spinal cord leading to incapacitating sensory and motor abnormalities.

Front 17

How much cerebral spinal fluid does a human have and where is it located?

Back 17

150 ml. It is found in the ventricles of the brain, the cisterns on the outside of the brain and the subarachnoid space around the brain and the spinal cord.

Front 18

What is the function of the cerebral spinal fluid?

Back 18

The cerebral spinal fluid allows the brain to float, and allows the brain to move simultaneously with the skull during minor acceleration preventing brain contortion.

Front 19

What causes a countrecoup brain injury?

Back 19

When skull is struck the brain compresses the fluid on the struck side, when the brain stops accelerating it is pulled to the countrecoup side by a temporary vacuum created in the cerebralspinal fluid during the strike. (propensity for countrecoup injury should depend on the mass of the brain, and be less common in pediatrics)

Front 20

What is the rate of cerebral spinal fluid formation?

Back 20

cerebral spinal fluid is formed at the rate of 500 ml/ day. 3-4 times the total volume of CSF in the system.

Front 21

Where is cerebral spinal fluid formed?

Back 21

over 66% comes from the choroid plexus in the four ventricles, but mostly from the 2 lateral ventricles.

A small amount comes from the ependymal surfaces of the ventricles and the arachnoidal membrane.

A small amount from the perivascular spaces surrounding the blood vessels entering the brain.

Front 22

What is the composition of the CSF?

Back 22

osmotic pressure equal to plasma. Sodium concentration equal to plasma. Chloride 15% greater than plasma. Potassium 40% less. Glucose 30% less.

Front 23

What is the normal CSF pressure?

Back 23

5-15 mm Hg

Front 24

What causes brain edema?

Back 24

Increased capillary pressure, or damamage to the calillary wall that makes it leaky.

Increased pressure decreases local blood flow, causing ischemia. This causes artiolar dialation increasing capillary pressure. Ischemia causes increased permeability of the capillaries. It also turns on sodium pumps in neuronal tissue cells leading them to swell.

Front 25

What are the treatments for brain edema?

Back 25

Intravenous infusion of a highly concentrated osmotic solution, Lateral ventricular puncture to relieve intracerebral.

Front 26

What is the relative metabolic rate of brain tissue?

Back 26

The brains consumes 7.5 times the average metabolism in non-nervous system cells. Or 15% of total metabolism. During excessive activity the consumption can increase 100-150%.

Front 27

Why does unconsciousness ensue if the brain is deprived of oxygen for 5-10 seconds?

Back 27

The brain has a high metabolic rate, with low oxygen and low glycogen reserves (2 min).

Front 28

How is glucose delivered into neurons?

Back 28

Independently of insulin. This prevents loss of mental function in diabetics.

Front 29

what are the consequences of low blood sugar?

Back 29

mental imbalances, psychotic disturbances, coma, death.