5.3 Regulation of Blood Flow

Question 1

Cerebral blood flow is regulated by two autoregulatory mechanisms (affecting total cerebral blood flow and localised blood flow):
• Autoregulation (affecting total cerebral blood flow): between mean arterial blood pressures of ________________ mmHg
• Local autoregulation (relating activity or local requirements to local flow): local oxygen delivery to brain tissue is related to the needs of that tissue
• Occurs via neural control and chemical control

Answer 1

60 – 160;

Question 2

Neural control of blood flow consists of sympathetic nerve stimulation, parasympathetic stimulation, central cortical neurones, and dopaminergic neurones:

• Sympathetic: Stimulation to ______________ to produce vasoconstriction:
  • Only operates with high arterial blood pressure → produces further increase in peripheral BP but decreases BP in the brain
• Parasympathetic: _________ stimulation to produce slight vasodilation
• Central cortical neurones: Release of a variety of vasoconstrictor neurotransmitters (e.g. catecholamines)
• Dopaminergic neurones: Produces localised vasoconstriction related to increased brain activity:
  • Dopaminergic neurones innervate _____________________
  • Pericytes are brain macrophages with diverse activities (e.g. immune function, transport properties, contractile) → participates in the diversion of cerebral blood flow to other areas of higher activity
  • Dopamine results in contraction of pericytes via _______________________

Answer 2

main cerebral arteries;

Facial nerve (CN VII);

penetrating arterioles and pericytes around capillaries;

aminergic and serotoninergic receptors

Question 3

Peripheral nerve fibres innervate the _____________ on the surface:
• Arterioles penetrate down into the brain tissue to form main central capillaries (wide networks) within the brain
• Pericytes surround the capillaries and are innervated by dopaminergic and other neurones

Answer 3

superficial pial arteries

Question 4

An arterial pCO2 of ________ corresponds to a normal cerebral blood flow of 1, and as pCO2 increases, cerebral blood flow increases due to cerebral artery vasodilation:
• Blood-brain barrier is made up of __________________ (H+ cannot cross; CO2 produced in the peripheral tissues/general circulation can cross)
• CO2 combines with H2O in smooth muscle cells lining the blood vessels (by carbonic anhydrase) → produces H+ and HCO3- (generated within blood-brain barrier)
• Any metabolically active neural tissue produces CO2 and H+, which causes vasodilation in the blood-brain barrier
• H+ causes decreased available free Ca2+ within the smooth muscle cells → CO2 indirectly causes vasodilation via H+

Answer 4

40mmHg;

endothelial cells with tight junctions between them;

Question 5

Cerebral blood flow is increased by dilatation of arterioles induced by nitric oxide synthesis:
• NO synthase converts arginine to ____________ with the release of NO, which stimulates __________ to convert GTP to cGMP
• cGMP decreases the ___________ to cause vasodilation
• cGMP is then broken down by _______________ (Viagra works by blocking the action of the phosphodiesterase → allows cGMP to accumulate)

Answer 5

citrulline;

guanylyl cyclase;

intracellular concentration of Ca2+;

phosphodiesterase

Question 6

The brain tissue is surrounded by ____________, and the intracerebral ventricular system contains __________________:
• Most of the brain is separated from blood by the blood-brain barrier (circumventricular organs lie outside the barrier)

Answer 6

extracellular fluid (ECF);

cerebrospinal fluid (CSF)

Question 7

Cerebrospinal fluid (CSF) is produced by the \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_, which are networks of capillaries surrounded by ependymal cells:
• \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ have tight junctions between them, making it selective in what substances are able to pass through

The passage of CSF through the interventricular system is as follows:
• Lateral ventricles (mainly) → ________________ → 3rd ventricle → ____________ → 4th ventricle → medial aperture (_______________) and lateral apertures (______________) → _____________
• Choroid plexuses are found in all the ventricles (mainly lateral ventricles)

Answer 7

choroid plexuses;

Ependymal cells;

interventricular foramen of Monro;

cerebral aqueduct;

foramen of Magendie;

foramina of Luschka;

subarachnoid space

Question 8

Which of the following [CSF] > [plasma]

Answer 8

Mg2+, Cl-, [H+]

Question 9

how is water transported in the brain?

Answer 9

Aquaporin (AQP1 and AQP4) channels

Question 10

how is glucose transported in the brain?

Answer 10

GLUT-1 proteins/transporters

Question 11

how is amino acids transported in the brain?

Answer 11

3 different transporters (1 for acidic, 1 for basic, 1 for neutral)

Question 12

Some areas of the brain (circumventricular organs) have fenestrated capillaries and thus lie outside the blood-brain barrier:
• Able to respond to changes within blood in the general circulation (e.g. ________, ____________ act as osmoreceptor sites → respond to osmolality changes in blood)
• Includes the SFO, OVLT, and median eminence region of hypothalamus

Answer 12

subfornical organ (SFO) and organosum vasculosum of lamina terminalis (OVLT)